Evolution of early-middle miocene rodent faunas in relation to long-term palaeoenvironmental changes

Palaeogeography, Palaeoclimatology, Palaeoecology,93 (1992): 227-253 Elsevier Science Publishers B.V., Amsterdam

227

Evolution of Early-Middle Miocene rodent faunas in relation to long-term palaeoenvironmental changes A l b e r t J. v a n d e r M e u l e n a a n d R e m m e r t

Daams b

a Institute of Earth Sciences, University of Utrecht, Budapestlaan 4, 3508 TA Utrecht, The Netherlands Museo Nacional de Ciencias Naturales, Josk Gutikrrez Abascal 2, E 28006, Madrid, Spain (Received July 2, 1991; revised and accepted December 5, 1992)

ABSTRACT Van der Meulen, A.J. and Daams, R., 1992. Evolution of Early-Middle Miocene rodent faunas in relation to long-term palaeoenvironmental changes. Palaeogeogr., Palaeoclimatol., Palaeoecol., 93: 227-253. Cluster and principal components analyses have been applied to the composite sequence of 59 rodent assemblages from Ramblian to Lower Vallesian deposits in the Daroca Calamocha area in the Calatayud-Teruel Basin (North Central Spain). The studied record is thought to represent the interval from the late Aquitanian to the end of the Serravallian (i.e. Early to Middle Miocene, from ca. 22-10.5 Ma ago). The quantitative results are interpreted by using individual rodent taxa as environmental indicators, and by extrapolating the predominant adaptive strategies of recent taxonomic groups, which also seem to form natural groups on a demographic scheme (French et al., 1975). A general warming trend starts in the Ramblian (Early Miocene) and continues into the Middle Aragonian (early Middle Miocene). The cooling in the Middle to Late Aragonian boundary interval is correlated to the middle Miocene cooling phase. Another cooling occurred around the Aragonian-Vallesian boundary (late Middle Miocene). We relate a major increase of aridity in the beginning of the Middle Aragonian (ca. 16.5 Ma) to the spread of low biomass vegetation due to intensification of the subtropical belt (Wolfe, 1985). A notable feature around the Early-Middle Aragonian boundary, indicating a major shift of climatic belts, is the reversal of the relationship between our relative temperature and humidity curves: before the reversal we find a positive correlation, after it a negative correlation. Arol2nd the Middle to Late Aragonian boundary humidity increased again, and a further increase of humidity is indicated by the earliest Vallesian faunas. Our data suggest that the nature of favoured adaptive strategy amongst rodents is related, in the end, to the degree of climatic humidity.

Introduction The m a r i n e r e c o r d has s h o w n t h a t i m p o r t a n t climatic changes t o o k place d u r i n g the Miocene. As Vincent a n d Berger (1985, p.456) p u t it, " t h e o c e a n - a t m o s p h e r e system c h a n g e d p e r m a n e n t l y t o w a r d a c o l d e r s t a t e " between 15 a n d 13 millions years ago. O n land, w o o d l a n d s r e p l a c e d forests in s o u t h w e s t e r n N o r t h A m e r i c a a n d the M e d i t e r r a nean, a n d A n t a r c t i c a was d e f o r e s t e d a n d for the first time c o m p l e t e l y glaciated (Wolfe, 1985; R o b i n , 1989). I m p o r t a n t changes are k n o w n to have o c c u r r e d

Correspondence to: A. van der Meulen, Institute of Earth Sciences. University of Utrecht, Budapestlaan 4, 3508 TA Utrecht, The Netherlands. 0031-0182/92/$05.00

in the E a r l y a n d M i d d l e M i o c e n e m a m m a l fauna o f E u r o p e : the i m m i g r a t i o n o f Anchitherium t h r o u g h a t e m p o r a r y Bering l a n d b r i d g e c o n n e c t i o n ( R a m b l i a n , Z o n e A, a c c o r d i n g to the terrestrial s t r a t i g r a p h i c a l subdivision o f Spain), the beginning o f the A f r i c a n - E u r a s i a n N e o g e n e faunal exchange (e.g. the entry o f the first m a s t o d o n t s in E u r o p e in Z o n e B, E a r l y A r a g o n i a n ) , the dispersal o f the Hispanotherium f a u n a s in Spain, P o r t u g a l a n d F r a n c e ( E a r l y - M i d d l e A r a g o n i a n ) , a n d the Vallesian i m m i g r a t i o n o f Hipparion ( Z o n e H) are events t h a t have been extensively dealt with in the literature (e.g. A n t u n e s , 1979; B e r n o r et al., 1988; F a h l b u s c h , 1989; G i n s b u r g , 1990; R6gl a n d Steininger, 1983). A s to the r o d e n t fauna, Van de Weerd a n d

~) 1992 - - Elsevier Science Publishers B.V.

228

Daams (1978) recognized and discussed the Ramblian to Early Aragonian (Early Miocene) association dominated by Gliridae and Eomyidae, and the Middle Aragonian to Early Vallesian (Middle Miocene) association dominated by Cricetidae. Fahlbusch (1989) considers the immigration of the cricetids Democricetodon, Megacricetodon and others, leading to the replacement of the eomyidglirid fauna by the cricetid-glirid faunas in the Aragonian, as the most important change in the Early-Middle Miocene rodent fauna of Europe. The immigration of these Asian cricetids started at the beginning of the Aragonian, and seems to be contemporaneous with the immigration of the proboscideans. Some of the mentioned faunistic events are evidently related to sealevel changes or plate tectonics, but we will focus on those changes that can be related to the climatic changes that took place during the Early and Middle Miocene. On the one hand we will further develop palaeoecological interpretations on the basis of the compositions of rodent assemblages, on the other hand we will investigate the consequences of climatic changes on the rodent fauna. Whereas the mid-Miocene cooling step is now generally accepted, the effect of this permanent change in the evolution of the climate on the mammal fauna is not well known. In this paper we present the first results of a cluster and principal components analysis (PCA) applied to a succession of 59 Ramblian to Lower Vallesian (Lower-Middle Miocene) rodent assemblages from the Daroca-Calamocha area in the Basin of Teruel (Spain). The aim of these analyses is to achieve a more objective description and a better understanding of the temporal changes in the compositions of fossil rodent faunas, and thus improve our previous palaeoecological interpretations based on a semi-quantitative analysis of the faunal compositions (Daams and Van der Meulen, 1984). This quantitative study has been made possible through the exceptionally dense mammalian faunal record, brought together during ten years of intensive collecting in the area (see Daams and Freudenthai, 1988 for a recent synopsis of the Aragonian; Daams et al., 1987 for the Ramblian). The 59 localities have yielded over 30,000 first and second

A.J. VAN D E R M E U L E N A N D R. D A A M S

molars which constitute the database. Having such a wealth of faunistic data at our disposal it seemed the logical next step to apply multivariate analyses. For this purpose the first author developed a database management system to store and selectively retrieve faunal lists with the numbers of molars per taxon. The calibration of our continental succession to the marine time scale heavily relies upon literature data, Berggren et al. (1985) in particular, but we also use Langereis' reinterpretation (in Daams et al., in prep.) of the palaeomagnetic data from sections in the nearby Calatayud area of Dijksman (1977). Stratigraphy and correlations of the succession

The succession Our composite succession is based on rich rodent assemblages from different sections in the DarocaCalamocha area of the Calatayud-Teruel Basin. The type sections of the Aragonian and the Ramblian Stages, which yielded the majority of the assemblages, lie about 50 km apart. Daams and Freudenthal (1988) and Freudenthal and Daams (1988) summarize the lithostratigraphic and biostratigraphic evidence upon which the faunal sequence is based. During the field campaign of 1990 new assemblages (not included in this study) have been found which demonstrate that Zones D3, E, F and G1 are in superposition in the type section of the Aragonian. Previously, the succession of these zones was based on biostratigraphic evidence only (Freudenthal and Daams, 1988). Five assemblages not incorporated in the range chart in Daams and Freudenthal (1988) are included in the present study: Artesilla, Muela Alta, Moratilla 2, 3 and 4. Muela Alta, Moratilla 2 and 3 are placed in the new Zone DO (lower Middle Aragonian). The abbreviations of the locality names used in the figures, the faunal lists of the above mentioned localities and a short discussion of Zone DO are given in Appendix 1. The discovery of these new faunas in such a well researched area demonstrates the incompleteness of the record used previously, and warns us of further possible gaps in the succession used

229

E V O L U T I O N O F EARLY M I D D L E M I O C E N E R O D E N T F A U N A S

here. In fact, Freudenthal and Mein (1989) mention already another new locality, Nombrevilla 2, which will (partly) fill the obvious gap in documentation between the uppermost Aragonian of Solera and the Lower Vallesian of Nombrevilla 1. We also suspect the presence of a documentary gap in the Zone A/B boundary interval. In our sections we have not encountered faunas that are comparable to Ateca 1 and 3 in the, Calatayud area (De Bruijn, 1967) which we correlate to the top of Zone A.

Calibration of the spanish mammal succession to the GPTS of Berggren et al. (1985) We use the amended definition of the Aragonian stage by Daams et al. (1987), i.e. its lowermost recognized zone is Zone B. Thus, in contrast to the original definition by Daams et al. (1977), the beginning of the Aragonian is not marked by the entry of Anchitherium, which has only sporadically been found in Zone A in the Ramblian and Aragonian type areas, but by the entry of Democricetodon. The presence of this hamster in Artenay (France), generally considered to be the oldest European locality with Gomphotherium, indicates that the entry of Democricetodon in Spain is more or less contemporaneous with the entry of the mastodonts in Europe (Bulot, 1988; Mein, 1990). The boundary between Aragonian and Vallesian is marked by the entry of Hipparion, which is estimated to have occurred around 11.5 Ma in the Mediterranean area by Sen (1986, 1989) and ca. 11.0 11.5 Ma in Central Europe by Bernor et al. (1988). Recently Daams et al. (in prep.) discussed in detail the calibration of the Ramblian to Early Vallesian to the GPTS of Berggren et al. (1985) on occasion of a reinterpretation of the palaeomagnetic data of Dijksman (1977) from sections near Calatayud. This calibration, which is used here, differs from existing ones (R6gl and Steininger, 1983; Berggren et al., 1985; Steininger et al., 1990) but yields satisfactory correlations from an ecostratigraphical point of view. A discussion of the calibration is given in Appendix 2.

Material and methods

The data sets Our database consists of the ca. 30,000 first and second upper and lower molars from the 59 localities. Only three assemblages consist of less than hundred specimens. Recent taxonomic revisions are available for most of the representatives of the various rodent groups found in the area: Daams (1985) on the Glirinae (Gliridae); $6s6 (1987) on Eucricetodon and Melissiodon (Cricetidae); Alvarez Sierra (1987) on the Eomyidae; Cuenca Besc6s (1988) on the Sciuridae; Daams and Freudenthal (1988) on Megacricetodon (Cricetidae) and Freudenthal and Daams (1988) on Democricetodon, Fahlbuschia, Pseudofahlbuschia and Renzimys (Cricetidae); Daams (1989) on small assemblages of miscellaneous Gliridae; and Daams (1990) on Armantomys and Praearmantomys. Pseudodryomys and Mierodyromys are presently under study by Daams. The aim of our quantitative analyses of the Ramblian to Lower Vallesian rodent faunas from the Daroca-Calamocha area is the recognition of patterns in the complex database. The assemblages will be treated as objects characterized by several variables, which are the percentages of the taxa distinguished. A special feature of the raw database, obscuring possibly existing longterm patterns, is the little overlap of the ranges of the species due to the considerable faunal change in the studied time interval. The only way to increase the overlap is by an a priori grouping of the species. In order to loose the minimum amount of information, we have made two different groupings of the species before entering them as variables in the data set. The results from the quantitative analyses of the two data sets are treated as complementary. In the one grouping (data set A) we simply entered the numbers of first and second molars per genus. In the other (data set B) we lumped species of evolutionary lineages assuming that species of single lineages (not showing drastic changes in morphology and size) are ecologically more similar amongst each other than they are to other species of the same genus.

230

Data set A consists primarily of the genera, with the following exceptions. Cricetodon and Hispanomys have been lumped, as there is general agreement among specialists that the latter is a descendant of the former. Armantomys and Praearmantomys have been lumped, because they share remarkable dental specialisation, for which reason we have grouped them also in earlier studies (Daams and Van der Meulen, 1984). The extremely rare taxa Palaeoseiurus, Freudenthalia, Albanensia, Tamias, Bransatoglis, Cricetidae gen. et sp. indet. and Petauristinae indet, have been lumped in the REST group. The set contains 32 taxa. The criteria for the 34 taxonomic categories of data set B are to achieve maximal ranges and maximal numbers by lumping well established lineages of species (see below). When these criteria could not both be met we lumped the species of the genus. The very rare species are again placed in the rest group. The latter contains Heteroxerus cf. paulhiacensis, Aragoxerus ignis, Pseudodryomys sp., P. julii and Altomiramys daamsi in addition to the members of the rest group of data set A. The most drastic differences between the two sets of variables result from the differentiation of the Megacricetodon lineages, described by Daams and Freudenthal (1988). They discuss two alternative models of evolution in the Megacrieetodon primitivus-ibericus group: (a) there is a single lineage, or (b) there are two lineages: the small to medium sized Middle Aragonian M. primitivuscollongensis lineage and the large Late Aragonian to Early Vallesian M. crusafonti-iberieus lineage. The possibility of the latter model was suggested by an abrupt change of various dental features and the wide range in size of the Megacricetodon molars in Zone E, that could be explained by assuming the presence of a larger species (a new one or M. crusafonti) in addition to M. collongensis. The study of Megaericetodon from Zone DO (Berends, 1987) shows that the large species in this zone (Megacricetodon sp. A) may well be the ancestor of the larger Megacricetodon species in Zone E, and thus that the concept of two lineages is the more likely one. Figure 1 gives the biostratigraphical distribution of the taxa as they are used in counting entries and exits, and in data set B. The evolutionary

A.J. VAN D E R M E U L E N A N D R. D A A M S

stages that have been put in a single category are:

Megacricetodon primitivus-collongensis, Megacricetodon sp. A (from Zone DO)-erusafonti-ibericus, M. minor-debruijni (Daams and Freudenthal, 1988b), Fahlbuschia koenigswaldi-darocensis, F. freudenthali-crusafonti (Freudenthal and Daams, 1988), Cricetodon-Hispanomys, Muscardinus thaleri-hispanicus (Daams, 1985), Tempestia ovilishartenbergeri (Daams, 1989), Ligerimys antiquuspalomae, L. aft. magnus-magnus (Alvarez Sierra, 1987), Spermophilinus besanus-bredai and A tlantoxerus idubedensis-blacki (Cuenca Besc6s, 1988). In other cases genera contain several species because all or most of them occur very rarely (Eucricetodon, Democricetodon, Eumyarion). In some cases species with open names are lumped with similar species that do occur in the succession. Finally a few species groups have not yet been completely revised, such as Pseudodryomys simplicidens-robustus and the various species of Microdyromys. The differences between biostratigraphic units due to immigration or extinction of taxa are here losely called qualitative differences. To express the nature and magnitude of differences between zones we have counted the last occurrences (LO, excluding pseudo-extinctions), temporary last occurrences (TLO), first occurrences (FO) and re-entries (RE) of taxa per zone (Fig. 1). Under EV the LO + T L O of the previous zone have been added to the FO + R E of the next zone. As these events are counted irrespective of their occurrence within the zones, the EV values are a measure of faunal change taking place in the total interval of two successive zones, i.e. they are neither related to the boundary interval, nor to absolute time. In Fig. 2 numbers of species, the percentage of the dominant taxon per assemblage, and Shannon's equitability index are given. All values are valid for the discussed succession only. It should be remembered that not all species have as yet been determined. Nevertheless, the countings enable comparison of the changes in different biostratigraphical intervals and appear to be useful as such.

Methods We have used cluster techniques to find groups of taxa, and principal components analysis (PCA)

EVOLUTION OF EARLY MIDDLE MIOCENE RODENT FAUNAS

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Fig. 1. Stratigraphic ranges of the taxonomic categories used in data set B and in the counts (on the right) of qualitative events in the studied sequence in North Central Spain. The local Zones Z and A (Ramblian), B-G3 (Aragonian) and H-I (Vallesian) are after Freudenthal and Daams (1988) except for Zone DO which is defined in Appendix 1. Notable faunistic changes are the successive appearances of several Cricetidae starting in Zone B; the appearance of a new association of Gliridae starting in Zone D3; and the disappearance of Ligerimys (Eomyidae) at the end of Zone C. The values of EV (the sum of the LO and TLO of a zone and the FO and RE of the next one) are a measure of faunal change in the total interval of two successive zones. to get insight in the structure o f the matrix by reducing the multidimensional space defined by the variables and find a small n u m b e r o f meaningful linear combinations between them (Davis, 1973). In the cluster analysis correlation coefficients between the taxa have been used which have been corrected following the procedure proposed by D r o o g e r (1982). The correction is meant to reduce the effects o f the closed sum problem caused by the use o f percentages. The d e n d r o g r a m s have been constructed according to the unweighted pairg r o u p clustering method. We have applied R - m o d e principal c o m p o n e n t s analysis, i.e. the correlations between the taxa are our starting point. Labeling the scores for the assemblages with their stratigraphical position, curves have been drawn for the different c o m p o -

nents. The pattern o f each curve represents a certain aspect o f the compositional changes o f the rodent assemblages. The patterns and (the combination of) the most heavily weighted taxa, as indicated by the loadings, are interpreted in the light o f our working hypotheses.

Working hypotheses It is general practice in m a m m a l palaeontology to deduce past changes in humidity from changes in the proportions o f open country versus forest dwelling species in a succession o f faunal assemblages. To make this ecological distinction between fossil rodent species a variety o f means is used: (a) extrapolation o f habitat preferences o f extant relatives, (b) functional morphological inferences from

232

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molar patterns, and (c) repeated association of species with certain sedimentary environments. Examples of (a) are the aquatic habitat of beavers and the open country habitat of groundsquirrels, which form the great majority of the Sciuridae in our assemblages; of (a) and (b) the open country habitat of the Myomiminae (Armantomys, Praearmantomys, most Peridyromys species, Pseudodryomys and Myomimus) and the forest habitat of most other dormice (Gliridae); of (c) the forest habitat

of the extinct Eomyidae (Mayr, 1979; Van der Meulen and De Bruijn, 1982; Daams et al., 1988). Mammal species are rarely used as temperature proxies, mainly because of the homeothermic nature of the group. In a semi-quantitative study on Early to Middle Miocene faunas from Spain Daams and Van der Meulen (1983, 1984) introduced the ratio between the quantities of Peridyromys rnurinus and Microdyromys as a temperature signal, which was subsequently accepted by

EVOLUTION OF EARLY MIDDLE MIOCENE RODENT FAUNAS

Hugueney (1984), as our conclusions appeared to be consistent with her findings on Late Oligocene to Early Miocene faunas from France. Our assumption was based on the opposite frequency trends of the mentioned dormice, and the unrelatedness of these trends to fluctuations indicating changes in humidity. The higher temperature tolerance of Microdyromys was deduced from the evidence of northward migrations of Spanish Gliridae during the interval of expansion of Microdyromys at the cost of Peridyromys murinus (in the Early to Middle Aragonian). With the ongoing expansion of the European faunal database for the Tertiary and with the improvement of systematics and correlations, we expect N-S shifts in distributions to become increasingly useful to determine past temperature changes. The present study did not lead to changes in our previous assumptions. We will, however, introduce another one. We are looking for the characterization of the groups of taxa and of fossil assemblages which are yielded by the quantitative techniques. When one can characterize groups of taxa in terms of palaeoenvironment then their coming and going can be interpreted as responses to environmental and climatic changes without having to consider the many other, but largely unknown, limiting factors determining the presence/absence and population sizes of individual fossil species. A general biological distinction that can be related to environment is on type of adaptive strategy: r- and K-strategists. As will appear later, the cluster analysis shows for each of the data sets the presence of three main groups of taxa that differ not only in stratigraphic range, but also in the diversity within (sub)families. We will interpret the latter differences in terms of adaptive strategies of the different taxonomic groups following the results of French et al. (1975) on patterns of demography in recent small mammal populations. These authors found that "by and large, the groups set up on a taxonomic basis also form natural groups on a demographic scheme" (op. cir., p. 95), The three demographic categories into which most small mammals fall on the basis of life history data, are: (a) the murid and microtine type of groups, characterized by a combination of high repro-

233

ductive rate and high turnover rate of individuals, and hence strong fluctuations in population densities, (b) the cricetine and Soricinae type of groups, characterized by moderate reproductive rates, medium survival rates and moderate population densities, and (c) a third category, including heteromyid, sciurid, Zapodidae and fossorial forms, characterized by low reproductive rate, high survival and rather low population densities. The first category thus includes r-strategists, the third K-strategists and the second intermediates. Although French et al. (1975) studied the data of a wide variety of rodents, they did not include Gliridae and Cricetinae (in the stricter sense of Carleton and Musser, 1984), which are of special interest to our Miocene rodents. From the life history (reproduction and longevity) data on these groups (Storch, 1978) it may safely be assumed that the Gliridae are K-strategists, and the Cricetinae r-strategists. Extrapolating these data for recent (sub)families we assume that the fossil members of the Sciuridae and the Gliridae followed the K-strategy, and the majority of those of the Cricetodontinae (which are connected to the origin of the Cricetinae) from our succession a more r-selection type of strategy. The Eomyidae have no living relatives, so we can only guess about their place in the r to K continuum. The following arguments suggest that the Eomyidae were more K-strategists than the cricetids. Firstly, most of the species concerned here

(Pseudotheridomys fejfari, Ligerimys.fahlbuschi, L. aft. magnus, L. magnus, L. freudenthali, L. ellipticus) have short ranges and restricted geographical distributions (Alvarez Sierra, 1987), indicating that they are specialists of some kind. The longest range is that of Ligerimys antiquus-palomae lineage, comprising small species of which a broader tolerance in comparison to their larger relatives may be expected. L. antiquus is widely distributed in Europe during the Early Miocene. Secondly, the species diversity of the eomyids is associated with great diversity of the glirids in the Ramblian to Early Aragonian. Thirdly, forest species (the forest-dwelling interpretation for Eomyidae is generally accepted amongst specialists) are more likely

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A.J. VAN DER MEULEN A N D R. DAAMS

to be K-strategists according to Fleming (1975, p. 296), although he adds that this hypothesis sorely needs testing.

Interpretation of the quantitative results Cluster analys&

Before reconstructing climatic events from the succession we will discuss the taxa clusters (Figs. 3 and 4) and the curves of the scores (Figs. 5 and 6) and the way we interpret them. Taxa clusters f r o m data set A

In order to simplify our data set as much as possible we use the clustering analysis to obtain the most compact grouping of the taxa. The dendrogram shown in Fig. 3a contains three main clusters which are negatively correlated to each other. In Table 1 the representatives of the clusters are ordered per family (below the family name the prevailing adaptive strategy is given). Our database has an inherent structure due to the stratigraphic distribution of the taxa. Co-

occurrence and co-absence of the taxa in the succession highly influence the correlations. Therefore, the clusters are primarily of a stratigraphic nature, comparable to Benda's (1971) "Pollenbilder", or Kretzoi's (1956) "faunal waves". On the other hand, since the associations at large were adapted to their environment, we may look for general biological differences between the clusters. We will, therefore, consider the composition of the clusters also in the light of the extrapolated adaptive strategies (see above). In view of the clustering method, taxa of our main clusters may be correlated to taxa of another main cluster, i.e. they have, as we will refer to it, out-group correlations. We have checked the correlation coefficient matrix in order to see which and how many significant out-group correlations (P >~ 0.05) are present. The relative number of outgroup correlations is a measure for the coherence of the clusters. We will argue that in spite of the six cases of out-group correlation the three main clusters of taxa are quite acceptable as units, but we note that the placing of Megacricetodon in cluster A2 is rather arbitrary.

TABLE 1 The composition according to family and adaptive strategy of the three main clusters in data set A shown in Fig. 3. Cluster AI

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Romys multlcrestatus

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Eomyops cotola~mcus

Muscordlnus

Democrlcetodon

Sperrnophilinus

Renzlrnys lacombo/

Fohlbuschio freud crusefonti

Eumyorion

Fohlbuschle koen-derocens/s

Pseudofohlbuschio Heteroxerus (af£) grivensis

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22

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34

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Fig. 3. Dendrograms based on the correlation coefficients between the taxa in data set A (genera) and data set B (lineages) to show the main clusters discussed in the text. The coarse, fine and middle hatching in the two dendrograms indicate clusters A2 and B2, A3 and B3, and AI and BI respectively.

19

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236

AJ. VAN DER MEULENAND R. DAAMS Zones Localities

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Fig. 4. Stratigraphic distributions of the three main clusters (Fig. 3) of data set A (left) and of data set B (right) which, in combination, give a condensed picture of the development of the rodent fauna during the Ramblian to Early Vallesian in the studied area. The Ramblian and Early Aragonian faunas dominated by Gliridae and Eomyidae (clusters AI and BI) are replaced by the Cricetidae dominated (clusters A2, A3, B2, B3) faunas in the Early to Middle Aragonian boundary interval. Clusters AI and BI and cluster B2 are assumed to indicate environments that favour K-strategy and r-strategy, respectively. Five successive faunal stages are recognized from the combination of the two distributional patterns and from the scores on the first principal component (Fig. 5): stage h Zone Z-B; stage 2: Zone C-D0; stage 3: Zone DO (top)-E; stage 4: Late Aragonian; stage 5: Early Vallesian.

The majority of the taxa of cluster A1 has high in-group correlations only. Exceptions are the REST group, which has significant correlations with Cricetulodon and Muscardinus of cluster A3, and Pseudotheridomys which is correlated with Heteroxerus of cluster A2. The case of the Rest group is explained by its content of both Ramblian and Upper Aragonian taxa. Pseudotheridomys is

only present in Bafion 11 and Moratilla 1, the two localities that contain the highest percentages of Heteroxerus in the Ramblian. The mutual correlation of Pseudotheridomys and Heteroxerus is for both genera the lowest they have. Cluster A1 is, therefore, remarkably coherent, and contains the most typical elements of the Ramblian and Lower Aragonian assemblages.

EVOLUTION OF EARLY-MIDDLE

237

MIOCENE RODENT FAUNAS T Data 1

Principal

Set

A 2" Principal

Component

10 i

0 J

10 20 I J

30 40 i I

3' Principal

Scores

Scores

3O 20 i i

Component

60 L

60 I

70 I

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L i g e r i m y s - 32 M e g a c r i c e t o d o n + 86 Per idy r o m y s - 27 P s e u d o d r y o f n v s - 19 (Pra ( , / A rman ton) ys- 16

L l g e f i m y s - 42 M e g a c r i c e t o d o n 32 P e H d y r o m y s - 18

F a h l b u s c h i a + 81 Microdyromys + 012

( P r a e / A r m a n t - 33 L i g e r l m y s + 76 P s e u d o d r y o m y s - 27 F a h l b u s c h i a + 38 Democficetodon 21 P e r i d y r o m y s - 20

Fig. 5. Curves based on the scores of the assemblages on the first three principal components for data set A. The percentages given at the lower part of the curves are the percentages of the total variance explained. The most strongly contributing taxa and their loadings are given for each component below the curves. The five faunal stages are indicated by different hatching on the curve of the first principal component and are repeated with numbers in the bar at the right and in Figs. 2 and 6. The curve of the first component is interpreted in terms of faunal history, of the second in terms of adaptive strategy (negative and positive scores indicating K- and r-strategy, respectively), while the third is assumed to be a temperature related response (lower and higher scores indicating lower and higher temperatures, respectively). Cluster A1 contains a majority o f K-strategists, since it is characterized by the preponderance o f glirid genera a c c o m p a n i e d by E o m y i d a e and Sciuridae; Melissiodon is a rare and aberrant cricetid (extrapolating the adaptive strategy o f living Cricetinae is highly speculative), and Eucricetodon is only abundant in Navarrete del Rio, the oldest assemblage o f our succession. The great diversity o f the Gliridae is even m o r e m a r k e d if one takes

into account that we lumped Praearmantomys and Armantomys, and that the single glirid genus in the R E S T group, Bransatoglis?, also can be reckoned a m o n g this cluster, since it only occurs in Ramblar 1 o f Z o n e Z. The diversity o f Sciuridae is also greater than appears from the listing, since we m a y safely add Palaeosciurus and Freudenthalia from the R E S T group. In c o m p a r i s o n to the other clusters the presence o f two E o m y i d a e genera is

238

A.J. VAN DER M E U L E N A N D R. DAAMS

Data Set B 1~ P r i n c i p a l C o m p o n e n t Scores S t a g e s ~ °nes Localities ~

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-210 ~0 ? I? 210 3? 410

50

60 70 80 90+1

Data Set B 2 ° Principal Component

Data Set B 3 ° Principal Component

Scores

Scores

-5o, .o, ~o, 2o, ,o, o, ,o, 2o, 3o, .o, so+, -2,0 ,o o ,,o 2? 3?.,~ so V+

i

::4:

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i,

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Muel, OIr 8 OIr 5 Varg,tA Arte. Vill 2A San R 2 SanR1 OIr 3 OIr. 2 OPr 1 Mor 1 Ban.1 1 Ban. 2 Ban, 5 Agreda LaDeh Ramb5 Ramb.7 Ramb.3B Ramb.4A Valh.3A Valh. 1 Ramb.l Nava.

>:': C'>

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Ligerimys-22 M e g a prim-coil-21 Pertdyromys_.l

Mega crus-tber+,92

6

Mega p r i m - c o l l - 6 4 Ligerimys+52 Fahl. koen -daroc-36 Peridyromys+ 36

Democr-27 Peridyromys-.19

Ligerimys+72 Fahl koen daroc + 46

Fig. 6. Curves based on the scores of the assemblages on the first three principal components for data set B (see Fig. 5 for further explanation). On the first principal component cluster B3 assemblages of Zone DO and the Late Aagonian are contrasted to all other assemblages. The second component reflects the replacement of the Ramblian to Early Aragonian assemblages, which are dominated by K-strategists (cluster BI) by the Middle Aragonian cluster B2 assemblages dominated by r-strategists. The third component is assumed to be a temperature-related response (lower and higher scores indicating lower and higher temperatures respectively). remarkable, the more so if one considers the Ramblian and Early Aragonian diversity o f Ligerimys at the species level. Cluster A2 is less coherent than cluster A I. In addition to Heteroxerus mentioned above, Megacricetodon and Microdyromys have significant correlations to members o f cluster A3. The correlation coefficient for Microdyromys and Democricetodon ( r = 0.33) is the second highest for both taxa. Megacricetodon is correlated to Cricetodon-His-

panomys and Muscardinus. The correlation coefficient with the former ( r = 0.34) is almost the same as with Heteroxerus ( r = 0.35). On the basis of this extremely small difference Megacricetodon has been placed in cluster A2 instead o f cluster A3. We will return to this later. As may be seen from the table with the correlation coefficients, the core o f cluster A2 is formed by the middle sized cricetids Fahlbuschia, Pseudofahlbuschia and Renzimys, ~vhich have only in-

239

E V O E U T I O N O F EARLY M I D D L E M I O C E N E R O D E N T F A U N A S

group correlations and are particularly characteristic of the Middle Aragonian. Megacricetodon is well represented in the Middle Aragonian and occurs abundantly in the Upper Aragonian. Cluster A2 can be characterized as an association of r-strategists on the basis of the diversity of the Cricetidae, the rarity of other families, and the low number of constituent taxa, which could possibly only be augmented by Cricetidae gen. et sp. indet, from Villafeliche 4A (Zone D2) placed in the REST group. Cluster A3 contains a core of taxa with very high mutual correlations: Spermophilinus, Eomy-

ops, Myoglis, Eliomys, Ramys, Tempestia, Myomimus and the Castoridae. We may safely add Cricetulodon (its out-group correlation is to the REST group) and the Cricetodon-Hispanomys group on the basis of their stratigraphic distribution. Cricetodon-Hispanomys has seven correlation coefficients (with other group members) which are higher than the one with Megacricetodon. Thus, cluster A3 contains characteristic genera of the Upper Aragonian and Lower Vallesian. Although a fairly large group, most taxa are not very abundant in the faunas. Exceptions are Hispanomys, Cricetulodon, Myomimus ~and Ramys which may be frequent in Eower Vallesian assemblages. Democricetodon and Spermophilinus, which have longer ranges than the other representatives, constitute a highly significantly correlated subgroup of cluster A3. The correlation between Spermophilinus and Eomyops (r-- 0.39) is higher than the one between Democricetodon and Microdyromys (r= 0.33). Thus the Democricetodon-Spermophilinus subgroup is linked to the main subgroup of cluster A3 through the Muscardinus-Eomyops subgroup. Muscardinus has high correlations with Cricetulodon, Cricetodon-Hispanomys and

myomimus. Cluster A3 is again dominated by Gliridae. As in cluster A1 an Eomyidae is present, but Eomyops shows no diversity at the species level unlike Ligerimys. The cluster consists predominantly of K-strategist taxa, but in contrast to cluster A1, the K-strategists of cluster A3 are rather rare and cricetids dominate the Upper Aragonian and, to a lesser degree, the Lower Vallesian assemblages

in numbers. Fair amounts of glirid molars are present in the Lower Vallesian.

Clusters from data set B The arbitrary inclusion of Megacricetodon in cluster A2 might be explained by the existence of the two lineages with different correlations, and this was one of the reasons to create data set B that starts primarily from the distinction of lineages. The dendrogram based on this data set (Fig. 3b) also shows three main clusters on the basis of the same criterion as used for the dendrogram based on data set A. In this run other taxa (Heteroxerus, (Prae)Armantomys, Pseudodryomys, Fahlbuschia) had been subdivided as well, but only the subgroups of Megacricetodon have changed position in the clusters in comparison to data set A. In the clusters based on data set B there are only four cases of out-group correlations (Table 2). Cluster B1 has the same composition as cluster Al, is again very coherent, and comprises mainly K-strategists. Only Pseudodryomys simplicidensrobustus has out-group correlations: with Pseudofahlbuschia (r = 0.36) and with Heteroxerus rubricati (r= 0.27) of cluster B2. These correlations result from the co-occurrence of the three taxa in Zone D2 in which all three peak. In cluster B2 the Megacricetodon primitivuscollongensis lineage is added to the core of taxa with only in-group correlations. On the other hand Pseudofahlbuschia and Heteroxerus rubricati have now an out-group correlation with Pseudodryomys simplicidens- robustus of cluster B1 and Heteroxerus grivensis and Microdyromys with members of cluster B3. The cluster is similar to A2 except for the loss of three Megacricetodon lineages. Because of this loss cluster B2 is a typical Middle Aragonian cluster, and consists mainly of r-strategists. The majority of the taxa of cluster B3 has ingroup correlations only. Spermophilinus and Demoericetodon which again form a subgroup, are correlated to Heteroxerus grivensis and Microdyromys of cluster B2, respectively. Cluster B3 is enriched in comparison to cluster A3 as it includes the large and small Megacricetodon species. Thus it contains all typical Late Aragonian to Early

240

A.J. VAN DER MEULEN AND R. DAAMS

TABLE 2 The composition according to family and adaptive strategy of the three main clusters in data set B shown in Fig. 3 Cluster B1

Cluster B2

Cluster B3

Fam. ad. strat.

Atlantoxerus

Heteroxerus rubricati Heteroxerus grivensis

Spermophilinus

Sciuridae

Ligerimys

K Eomyops

Eomyidae

K Peridyromys Praearmantomys Pseudodryomys ibericus P. simplicidens-robustus Armantomys Glirudinus

Microdyromys

Muscardinus Eliomys Ramys Tempestia Myomimus Myoglis

Gliridae K

Eucricetodon Melissiodon

M. prirn-collogensis Pseudofahlbuschia F. koenig-darocensis E freud-crusafonti Renzimys Eumyarion

Democricetodon Cricetodon- Hispanomys M. minor-debruijni M. sp A-ibericus Megacricetodon rafaeli Cricetulodon

Cricetidae

REST

Vallesian representatives. As to adaptive strategy cluster B3 is a mixed association.

Temporal quantitative distribution of the clusters If one accepts that both our a priori groupings of the taxa are valid, the quantitative distributions of the two sets of main groups (Figs. 4a, b) supplement each other, and together they give a condensed picture of the faunal development of the rodents during the Ramblian-Early Vallesian in the Daroca-Calamocha area. The quantitative patterns in Fig. 4a, b are the same for Zones Z E, except that in Fig. 4b the peak of cluster B3 in Zone DO is higher than that of cluster A3 due to the inclusion of Megacricetodon sp. A in cluster B3. The diminishing of clusters A1 and B1 in the Zone A-D0 interval constitutes a clear trend. The dominance of group A2 is very pronounced in the Middle and Upper Aragonian, that of cluster B2 is pronounced in the Middle Aragonian only. In the Middle Aragonian peaks of Megacricetodon primitivus, M. collongensis, Fahlbuschia and Pseudofahlbuschia succeed each other, while in the

r

Castoridae (K)

Upper Aragonian the dominance of cluster A2 is almost entirely due to M. collongensis-crusafonti, M. crusafonti and M. crusafonti-ibericus. As a result of the splitting of Megacricetodon a very sudden change caused by the expansion of cluster B3 is shown in Zone F in Fig. 4b, but on the other hand the faunal change around the AragonianVallesian boundary, appearing in Fig. 4a and also evident from the range charts, is now obscured. The abruptness of the change around the MiddleUpper Aragonian boundary is somewhat exaggerated due to the fact that it is impossible at the moment to adequately separate the larger Megacricetodon species in the rather poor material from the Las Planas 4 localities of Zone E. In Fig. 4b a significant increase of group B2 is shown in Zone G2 due to relatively high percentages of Fahlbuschia darocensis in Manchones 1 and Borjas. In Fig. 4a the significant increase of cluster A3 in the Upper Aragonian is caused by the assemblage of Las Planas 5K. We distinguish five successive stages in the history of the studied rodent fauna. These stages are

241

E V O L U T I O N O F E A RL Y M I D D L E M I O C E N E R O D E N T F A U N A S

also apparent in the curve of the scores on the first principal component for data set A (see below and Fig. 5). Stage 1, ranging from the Ramblian to the Early Aragonian (Zone Z-B), is characterized by the dominance of clusters A1 and B1 and comprises the typical Myomiminae and Eomyidae assemblages. The environments during the interval strongly favoured K-strategists. Stage 2, during the Early to Middle Aragonian boundary interval (Zone C-D0), is called transitional since we find a mixture of K- and r-strategists. In Zone C the first expansion of clusters A2 and B2 and in Zone DO the first expansion of clusters A3 and B3 take place. Stage 3, ranging from the later part of Zone DO to Zone E (Middle Aragonian), is characterized by the dominance of cluster B2 and comprises Fahlbuschia-Megacricetodon assemblages. The environments favoured r-strategy amongst the rodents. Stage 4, Late Aragonian, is characterized by the expansion of cluster B3. Most assemblages are dominated by the supposedly r-selected Megacricetodon, but there is a fairly diversified admixture of K-selected glirids. Stage 5, Early Vallesian, is characterized by the dominance of cluster A3, which is a predominantly K-selected group. However, in the assemblages the cricetids are numerically important. Apparently the environments supported both r-strategists and allowed an expansion of K-selected glirids. Our conclusion from the quantitative distributions of the clusters is that they indicate that stable environments during the Ramblian and Early Aragonian favoured K-strategists. Through intermediate stages the environments changed to unstable/ unpredictable ones in the Middle Aragonian which strongly favoured r-strategists. More stable conditions returned in the Late Aragonian. The environments during the Early Vallesian were again more stable, but less so than during the Ramblian-Early Aragonian.

Principal components analysis We have studied the first three components because each of the remaining ones explains only

a very small fraction of the total variation. By PCA one examines the interactions between the taxa and finds the most efficient linear combinations of them. High loading values (a group of positive and another one of negative values for each principal component) indicate the taxa whose proportions play an important role in explaining the variation in the data sets. These most heavily weighted taxa are given below the curves of Figs. 5 and 6. When the positively and negatively loading groups each represent a single cluster or a single demographic group, the principal component is interpreted in terms of faunal replacement or adaptive strategy. When one or both groups are not homogeneous in these aspects, we look for a plausible interpretation in terms of a palaeoclimatological factor. Labeling the scores with the stratigraphical position of the assemblages, curves have been drawn for the scores on the different components (Figs. 5 and 6). The pattern of each curve represents a certain aspect of the compositional changes of the rodent assemblages. The patterns are interpreted in the light of the meaning attributed to the combination of the most heavily weighted taxa.

Curves of the scores for data set A (Fig. 5) The first three components account for 78.4% of the variance in the data set. Most heavily weighted are the contributions of Megacricetodon, Fahlbuschia, Ligerimys, three Myomiminae (Peridyromys, Pseudodryomys and the ( Prae ) Armantomys group), and, on the third component only, Democricetodon. All other genera virtually play no role in these first three components. The first principal component, accounting for 52.8% of the total variance, represents the ratio between Megaericetodon on the one hand and Ligerimys and the three Myomiminae on the other. Megacricetodon, representative of cluster A2, is a typical Aragonian fauna-element (particularly abundant in the Upper Aragonian), while the other genera, the main representatives of cluster A1, are abundant in the Ramblian and Lower Aragonian. From Zone D3 onwards the first component essentially represents the proportion of Megacricetodon in the assemblages, because the genera with negative loadings have disappeared or are rare.

242

A.J. VAN DER MEULEN AND R. DAAMS

There is a clear relationship between the ranges of the contributing taxa and their loadings (Table 3). The first principal component reflects, therefore, a stratigraphic succession, essentially corresponding to the combined cluster patterns of Fig. 4. The scores of the assemblages clearly group into five successive categories, which correspond to the five stages distinguished on the basis of the quantitative distribution of our main clusters. The second principal component, which accounts for 14.2% of the total variance, most heavily weights the contribution of Fahlbuschia, which has a positive loading of +0.81. Negative loadings are contributed by Ligerimys, Megacricetodon and Peridyromys. These three taxa form an inhomogeneous group as far as Megacricetodon does not belong to the same cluster and demographic category as the other two taxa. Furthermore, Megacricetodon contains various species which supposedly had different ecological preferences (Daams and Van der Meulen, 1984; Mein, 1984), and Ligerimys and Peridyromys are considered to be opposite proxies of humidity: Daams and Van der Meulen (1984) considered species of Ligerimys as forestdwellers and of Peridyromys as open country dwellers. In the mentioned paper we also argued that Peridyromys murinus (the main representative of the genus) and Microdyromys are opposite temperature proxies, but the contributions of these two taxa to the second principal component are weak. Considering the opposition of the two most strongly contributing taxa, Fahlbuschia and Ligerimys, one might choose for both an interpretation in terms of adaptive strategy and humidity. FahlTABLE 3 Table showing the relationship between the loadings and biostratigraphic ranges of the taxa contributing most to the first principalcomponentfor data set A Loading

Genus

Range

+ 0.86

Megacricetodon (Prae) Armantomys Pseudodryomys Peridyromys Ligerimys

C-I

- O. 16 - O. 19 - 0.27 - 0.32

Z-F,

G3

Z-D3 Z-D 1 Z-C

buschia species thrive in the Middle Aragonian, an interval we suppose to have been generally dry since forestdwellers are very rare (Daams and Van der Meulen, 1984). However, in the light of our remarks on the palaeoecology of the three negatively loading taxa we prefer the interpretation, that Fahlbuschia differs from both Megacricetodon as well as Ligerimys and Peridyromys in being more r-selected. Or, in other words, that Fahlbuschia is the most extreme r-strategist of cluster A2, i.e. of the whole data set. This assumption agrees with our interpretation of the clusters and is corroborated by the observation that the assemblages (except in Zone G2), in which Fahlbuschia is dominant or abundant, contain always less than the mean number of species. There is no such straightforward correlation between species numbers and Megacricetodon assemblages. Finally, we note that in Zone D2, in which Fahlbuschia is replaced by Pseudofahlbuschia, the K-selected Gliridae Pseudodryomys and Armantomys temporarily increase in numbers, but we find no increase of forestdwellers. The third principal component, which accounts for 11.5% of the total variance, weights the contributions of Ligerimys (cluster A1) and Fahlbuschia (cluster A2) with positive loadings, and the Myomiminae (cluster A1) and Democricetodon (cluster A3) with negative loadings. We find a mixture of representatives of all three different clusters contributing to this component. Following our previous interpretations Fahlbuschia and Ligerimys are opposites in adaptive strategy and in preference for humidity. Looking for a single factor represented by this linear combination we can only choose for temperature. Thus the positive peaks of the curve would represent the warmer, the zero o~ negative parts the cooler intervals. Since the positively contributing taxa (Fahlbuschia and Ligerimys) have very different ranges we do not interpret the peaks in the absolute sense that the highest positive score values would represent the warmest intervals.

Curves of the scores for data set B The first three components account for 73.2% of the variance in data set B. Most heavily weighted are the contributions of Megacricetodon sp.A-

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EVOLUTION OF EARLY-MIDDLE MIOCENE RODENT FAUNAS

ibericus, M. primitivus-collongensis, Fahlbuschia koenigswaldi-darocensis lineages, Ligerimys, Peridyromys and Democricetodon. The first component, accounting for 39% of the total variance, very heavily weights the contribution of the Megacricetodon ibericus lineage (loading is + 0.92) and less Ligerimys (-0.22), the M. primitivus-collongensis lineage (-0.21) and Peridyromys (-0.16). Thus the Zone DO and Upper Aragonian cluster B3 assemblages are contrasted to all other assemblages. The upper and lower boundaries of Zone DO, but in particular those of the Upper Aragonian, are now ranked as important intervals of compositional change. We have argued above that cluster B3 contains a mixture of r- and K-strategists as opposed to cluster B1 containing K-strategists and to cluster B2 containing predominantly r-strategists. The second component, accounting for 20% of the total variance, is a linear combination of cluster B1 and B2 representatives. There is an opposition of taxa with different stratigraphic ranges, but at the same time with the most strongly different adaptive strategies. As the Megacricetodon ihericus lineage does not contribute to the component, it are the Ramblian to Middle Aragonian assemblages which are now contrasted. The curve shows the replacement of the Eomyidae-Gliridae association by the Cricetidae association and at the same time the change from K- to r-selecting environments. Thus, this curve complements the one for the first principal component. Together they are taken to represent the changes of prevailing adaptive strategies in the studied interval. The curve showing the scores on the third component (accounting for 14.2% of the total variance) resembles very much the one for the third component of data set A. The main difference is for Zone D3 which is due to the splitting up of the Fahlbuschia lineages in data set B. Our interpretation of the two curves is the same. The splitting up of the lineages allows some refinement of the interpretations on Fahlbuschia. It appears from the results of the principal components analysis of data set B, that the representatives of the Fahlbuschia koenigswaldi-darocensis lineage are the most extreme r-strategists and the best high temperature indicators.

Palaeoenvironmental synthesis We will review the environmental and. climatic history of the Early to Middle Miocene following the five successive stages we distinguished above. In addition to the results from the cluster and principal components analyses we will use the qualitative data summarized in Figs. 1 and 2. In the course of our discussion we will explain the way we arrived at the relative temperature and humidity curves given in Fig. 7.

Ramblian-Early Aragonian (Zones Z B); ca. 22 17.5 Ma This interval is characterized by stable environments as is interpreted from the dominance of clusters A1 and B1. We presume that the most stable conditions reigned during Zone B, because of the prolonged sequence of equitable assemblages in this zone (Fig. 2). The main climatic changes that took place are the oscillations in humidity which are deduced from the temporal changes of the ratio's between forestdwellers (Eomyidae) and open country dwellers (Myomiminae). Thus, Zone A is thought to be definitely more humid than Zones Z and B (Daams and Van der Meulen, 1984). Agreda (Zone A) is the only locality with beavers in the lower part of the succession. The conditions during the later part of Zone Z and during Zone A provided habitats especially favourable to Eomyidae. In these intervals we not only find the highest numbers of Ligerimys, but also its largest, and supposedly most K-selected, species Ligerimys aft. magnus and L. magnus, in stead of the small sized representatives of the L. antiquuspalomae lineage. The latter occur in the assemblages with lower numbers of the genus (Alvarez Sierra, 1987). In our model the environments during intervals with abundant Eomyidae were relatively densely forested. The composition of Zone B assemblages suggests that in this interval the forest became more open. The resulting greater diversity of the vegetation (structural and otherwise) may have caused the increasing diversity of rodent species (Fig. 3). Our oldest fauna of Navarrete del Rio (Zone Z) is dominated by Eucricetodon. This cricetid disap-

244

A . J. V A N D E R M E U L E N

RELATIVE

IMZ;AT°.E I

&

HUMIDITY CURVE

CURVE

< dr ier

,

wetter

z

.J ,J

w

~ .-

14-

w

CO Z

15-

-Z 22

w 16-

~ 0

77-

-

°

~

18-

-<

20-

21-

if:

U3

22-

Z -z

23-

OF-"

Fig. 7. Relative temperature and humidity curves, and intervals of prevailing adaptive strategies based on quantitative and qualitative analyses of the sequence of 59 rodent assemblages from lower to middle Miocene continental deposits in the Daroca-Calamocha area of the Calatayud-Teruel Basin (North Central Spain). The correlations of the continental stages to the marine stages and to the time scale are discussed in Appendix 2. The lower parts of the relative temperature and humidity curves are positively correlated in contrast to the upper parts, indicating a shift of climatic belts in the late early Miocene, causing an increase of aridity in Spain, presumably as a result of intensification of the subtropical systems. The decrease of temperature around the Middle to Late Aragonian boundary interval is correlated to the middle Miocene cooling. Comparison of the two curves at the right indicates a relation between prevailing adaptive strategy amongst rodents and climatic humidity. pears at the beginning of the wet interval of Zone A. This indicates that Eucricetodon is a dry environment indicator (Daams and Freudenthal, 1990), and that the beginning of Zone Z was more arid than the remainder of the Zone. Previously we considered Zone B to be warmer than the preceding zones because of the increase

AND

R. D A A M S

of Microdyromys and decrease of Peridyromys murinus (Daams and Van der Meulen, 1984). On the basis of the third principal components we have concluded that Ligerimys species are also indicators of higher temperature. Therefore, the lower part of present temperature curve (Fig. 7) is based on the ratio between the proportion of Peridyromys and the combined proportions of Microdyromys and Ligerimys per assemblage. This new ratio does not change our interpretation that (part) of Zone Z was the coolest episode of the discussed interval; Zone A, however, is now considered as a warmer interval than Zone B. It is noted that the Zone Z - A interval shows the highest number of last occurrences, while during Zone B the maximal number of first occurrences is noted (Fig. 2). The number of qualitative events ( E V = 16) for the A - B zonal interval is in fact the highest in our succession. We relate the high number of last occurrences to the K-selected nature of the majority of the species concerned, and the resulting sensitivity to environmental changes. Amongst the 14 LO in the Zone Z-B interval are 3 Gliridae, 4 Eomyidae and 4 Sciuridae, three families which we placed in the K-selected category. All first occurrences are by species belonging to t h e same families, except for the cricetid Democrieetodon in Zone B.

Early-middle Aragonian boundary interval (zones C-DO)" ca. 17.5-16.5 Ma The species numbers remain above average indicating varied environments, but there are several indications for increasing instability of the environment during this interval which is transitional between the predominantly K-selected associations of the previous and the r-selected associations of the following interval. In the first place, the assemblages of Zones C and DO differ quite strongly from and amongst each other. In Zone C the first expansion of clusters A2 and B2 takes place, while in Zone DO there is a considerable expansion of clusters A3 and B3. The decreasing trend of clusters A1 and B1 starting in the uppermost part of Zone A continues. Within Zone C there are striking compositional differences between the assemblage of Artesilla and the other ones, while the assem-

245

EVOLUTION OF EARLY MIDDLE MIOCENE RODENT FAUNAS

blage of Moratilla 3 is fairly different from the other two Zone DO assemblages. In the second place, r-selected cricetid species increase in diversity in the interval: 4 species in Zone C, 6 in Zone DO as opposed to 1 in Zone B. We have expressed this in the r and K curve (Fig. 7) as an intermediate step. Finally, the equitability of the assemblages decreases (Fig. 3). In Zone C the highest number of temporary last occurrences is registrated (TLO = 4). All of them return in Zone D1 (see also below). This observation together with the fairly high number of qualitative events in Zones C - D 0 (EV= 11) points to the rather special, but poorly understood, conditions during Zone DO, a peak zone of Democricetodon of clusters A3 and B3. We explain the quantitative and qualitative differences between the assemblages in terms of changing climatic conditions. The fluctuations in the proportions of Ligerimys have been used for the humidity curve. Humidity in Zone C is thought to be less pronounced than during Zone A, because the expansion of Ligerimys is less extreme, and no large sized species of the genus and no beavers have been encountered. From the disappearance of Ligerimys (after a continuous presence in the area of some 5 Ma) and the great expansion of cluster A3 and B3 around the Zone C - D 0 boundary we infer a major expansion of open vegetation at the cost of forests in the area, due to an increase of aridity. According to our criteria the assemblage of Artesilla indicates lower temperatures than for Zone B and the later part of Zone C. The latter interval is considered warmer than Zone B, because Peridyromys murinus disappears (temporarily), Fahlbuschia appears, and Microdyromys and Ligerimys expand. We take the disappearance of Peridyromys murinus and the expansion of Microdyromys as indications that Zone C was also warmer than Zone A. From the curves of the scores on the third components it follows that the beginning of Zone DO was cooler than Zone C. From Zone C to the end of the Middle Aragonian the compositions are more variable than in the preceeding and following periods, and, if our correlations to the GPTS are correct, the compositional changes succeed each other rapidly. The faunistic

changes around the Early to Middle Aragonian boundary, resulting in the replacement of the K-selected rodent communities of the RamblianEarly Argonian by the r-selected ones of the Middle Aragonian, are the most drastic in the succession. The disappearance of the EomyidaeGliridae association is permanent. The main climatic changes, which according to our interpretations induced the immigration of the Cricetidae and the faunistic turnover, are increased aridity and instability.

The Middle Aragonian (Zones D1-E)," ca 16.5-14 Ma This interval is characterized by the poorly diversified, r-selected, cricetid assemblages of cluster B2 indicating unstable environments. In Zone D1 the numbers of species decrease, and they stay below average, except for two assemblages of Zone D2, which show the average number. Megacricetodon and Fahlbuschia are the most frequent taxa. Zone D2 assemblages are different from the others in being more equitable, and having relative high proportions of Myomiminae; in one assemblage Pseudodryomys is even the most frequent taxon. Apparently during Zone D2 the environment was relatively stable. Daams and Van der Meulen (1984) considered the Middle Aragonian as a dry and warm period because forestdwellers are extremely rare and Microdyromys is frequent. On the basis of the interpretation of the third principal components we now consider Fahlbuschia to be another high temperature proxy. Therefore, the present relative temperature curve, which is based on the proportions of Microdyromys plus Fahlbuschia, differs from the one published previously. We assume now that during Zone E a cooling took place, because of the decreasing proportions of Fahlbuschia. Another difference with the previous curve is the cooler episode during Zone D2, during which Fahlbuschia is replaced by Pseudofahlbuschia and there is a significant expansion of Pseudodrvomys and Armantomys of cluster A1 and Bl. We have no indication for an increase of humidity in Zone D2. Notable qualitative events are (a) the fairly high

246

number of last occurrences in D I (LO= 5), (b) the high number of first occurrences in Zone D3 (FO = 6), and (c) the high number of re-entries in Zone D1 and E (RE= 4). The re-entries at the beginning of Zone D1 are related to the temporary last occurrences of Zone C. We think that the earlier part of Zone D1 is somewhat wetter (relatively high percentage of Eumyarion and return of Peridyromys aft. jaegeri) and cooler (return of P. murinus) in comparison to the later part of Zone DO. A drastic increase in temperature and aridity (based on the proportion of Fahlbuschia plus Microdyromys and the almost total disappearance of forestdwellers) within Zone D1 is thought to be responsible for the last occurrences of several taxa in this zone. The maximum number of first occurrences in Zone D3 is caused by taxa which are characteristic of the Late Aragonian and Early Vallesian fauna of Spain. Muscardinus and Tempestia, which belong to clusters A3 and B3, and the Fahlbuschia freudenthali-crusafonti lineage return in the Upper Aragonian of the studied area, Renzimys is known from the Lower Vallesian of Molina de Aragon (Lacomba Andueza, 1985), and Peridyromys rex from the Upper Aragonian of the Duero Basin (L6pez Martinez et al., 1986). The appearance of Muscardinus and Peridyromys rex is interpreted to indicate a slight increase of humid conditions in comparison to the preceeding and following zones. This interpretation would explain the faunal similarities between Zone D3 and the Late Aragonian zones. Three of the four re-entries in Zone E are related to temporary last occurrences around the Zone D0-D1 boundary interval. Cluster B3, abundant in the lower part of Zone DO, expands again in Zone F. These events are related to the increase in temperature and aridity in the Zone D0-DI interval and the decrease of these factors in Zone E. The first occurrence of the glirid Paraglirulus in the top of Zone E is taken as evidence for expansion of forest, and, hence, increase of humidity. Since in Zone F Fahlbuschia and Microdyromys d.rop to very low percentages, we conclude that temperatures became lower than they had been before. In Zone DO and Zone E - F the large Megacricetodon sp. A-ibericus lineage and Fahl-

A.J. VAN DER MEULEN AND R. DAAMS

busch& koenigswaldi-darocensis show opposite trends. Apparently, the former species are less tolerant to high temperatures than the latter.

The Late Aragonian (zones F-G3); ca. 14-11.5 Ma We have characterized the Late Aragonian communities as r- plus K communities. The majority of the cluster A2 and B3 assemblages of the Upper Aragonian are dominated by a representative of the Megacricetodon sp. A-ibericus lineage. The Gliridae are fairly well diversified, but they are much less numerous as the Cricetidae. Amongst the (re)immigrating Gliridae are some typical forestdwellers (Myoglis, Muscardinus). Megacricetodon minor appearing in Zone G1 is also considered a forestdwelling species (Daams and Freudenthal, 1988). We take these immigrations as a signal of slightly increasing humidity. The equitability of the assemblages is the lowest of the studied record. The unequitability of the assemblages may partly be explained by the fact that the r-strategists yield a greater number of potential fossil teeth than the K-strategists. We have not found extreme values for any of the qualitative events in the Upper Aragonian. Only the last occurrences (LO =5) for Zone G3 may be noted. Amongst these is our high temperature indicator Fahlbuschia darocensis. The main change, the establishment of a new Gliridae association, proceeded rather gradually, i.e. was not concentrated at a certain interval. The return of the dominant large Megacricetodon took place in Zone E. Quantitatively the interval is confined between the great expansions of clusters B2 and A3. Two noticeable events within the interval are the expansions of clusters B2 in the lower and A3 in the upper part of Zone G2. These events are also expressed in a number of the curves of the scores. On the basis of the expansion of Fahlbuschia darocensis in the localities Manchones 1 and Borjas (basal Zone G2), we conclude that this interval was warmer and dryer than the remainder of the Late Aragonian, and more similar to Middle Aragonian conditions. The expansion of Eomyops and Muscardinus in Las Planas 5K indicates more

EVOLUTION OF EARLY MIDDLE MIOCENE RODENT FAUNAS

forested and more humid conditions than usual during the Late Aragonian. Probably it was also somewhat cooler because Fahlbuschia darocensis is absent as in the Early Vallesian. The aberrant compositions of the three mentioned G2 localities underline the different environment and climate during the major part of the Late Aragonian in comparison to the Middle Aragonian and the Early Vallesian.

Early Vallesian (zones H I); ca. 11.5-10.5 Ma Several important compositional changes take place around the Aragonian-Vallesian boundary: (a) the increase of the proportions of the Gliridae, (b) the increase of the small sized Megacricetodon at the cost of the large sized one, (c) the increase of the representatives of Cricetodon-Hispanomys. Also the equitability increases. Notable qualitative events are the disappearence of Fahlbuschia darocensis (high temperature indicator) and the return of the Castoridae (indicators of the permanent presence of water). Daams and Van der Meulen (1984) argued for the onset of a cooler and wetter interval around the Aragonian Vallesian boudary. The expansion of Myomimus dehmi, which is related to Peridyromys murinus (our cooler temperature proxy for the Ramblian and Early Aragonian), seems to fit well with the postulated cooling trend (Daams et al., 1988). Discussion

Daams and Van der Meulen (1984) and Daams et al. (1988) summarized the many similarities between their temperature and humidity curves and palaeoclimatic reconstructions based on other faunal and floral proxy evidence and oxygen isotope curves. As a result of the application of quantitative methods and the new palaeomagnetic calibration our present curves (Fig. 7) agree even better with those in the literature. The inferred ages of Armantes 7 (13.5 Ma) of Zone F and of Armantes 1 (extrapolated age of 15.5 Ma, Zone D2; see Appendix 2) bracket the cooling event based on the diminishing proportions of Fahlbuschia in Zone E, within the age interval of the

247

mid-Miocene cooling trend: e.g. between 15.5 and 12.5 Ma (Vincent and Berger, 1985), between 16 and 14 Ma (Wei and Kennet, 1986), between 14.6 and 13.2 Ma (corresponding to about 15-13.5 Ma of the time scale of Berggren et al., 1985; Kennett and Barker, 1990). Allowing for the inherent problems in ocean-continent correlations there is a particularly good resemblance between our temperature curve and the Early to Middle Miocene part of the oxygen isotope curve for site 563 in Miller and Fairbanks (1985, fig. l). They show a slight decrease of temperatures to a low in the early part of N5 followed by an increase in temperatures to the end of the zone. This interval may be compared to our Zones Z and A. After a cooler interval in N6 and N7 high but strongly variable temperatures are indicated for N8 to early Ni0. We arrived at a similar pattern in the Zone B-D3 interval. Then, at 14.7 Ma (N10) there is the rapid increase of the oxygen isotope values which is associated to the mid Miocene cooling. There are indications of two short warming events in the late Middle Miocene, one in the basal part of NI2 (?basal Zone G2), and the next one around the N14-N15 boundary (?beginning of the Late Vallesian), but otherwise the oxygen isotope values are high. Chamley et al. (1986) recognized a cooling step around 13.8 Ma and a following around 11 Ma in the Mediterranean Serravallian, which fit well with our temperature drops at the beginning and the end of the Late Aragonian. A cooler (and wetter) Early Vallesian scenario, in comparison to the Late Aragonian, is also supported by floral and faunal evidence from the Pannonian Basin (Bernor et al., 1988). There is good correspondance between our reconstructions from the Spanish rodent evidence and the reconstructions based on floral and large mammal evidence from the Tagus Basin near Lisbon in Portugal (Antunes and Pals, 1984; Antunes, 1984; Pais, 1986). In both areas a late Ramblian (Lisboa IVa division), warm and humid phase preceeds the entry of the Proboscidea in the Early Aragonian. The Portuguese flora from division Lisboa IVa most likely indicates a tropical climate (Pais, 1986; Van de Burgh, pets. comm.). The flora from Lisboa IVb (correlative to our Zone B)

248

indicates a cooler and drier climate in comparison to that during the deposition of the Lisboa IVa division. The opening of the forests may be due to the installation of a distinct dry season (Antunes and Pais, 1984). A remarkable feature of our relative temperature and humidity curves is the reversal of the relationship between them around the Early-Middle Aragonian boundary, i.e. in the late Early Miocene. During the Ramblian and Early Aragonian we find a positive correlation between temperature and humidity, in the remainder of the studied interval we find the opposite. The reversal did not show up in our previous curves (Daams and Van der Meulen, 1984; Daams et al., 1988), since we did not use then Ligerimys and Fahlbuschia for reconstructing the temperature curve. The following observations give additional support to our opinion that the reversal is not merely an artefact of our new interpretations. An increase in aridity is postulated on the basis of floral, large mammal and marine evidence from the final Burdigalian Lisboa division Va (our Zone C) with forested environment under warm and humid conditions, to division Vb (Zone D) with open landscapes and galery forests (Antunes and Pais, 1984; Antunes, 1984; Pais, 1986). According to Wolfe (1986) the origin and spread of low biomass vegetation (savanna, steppe and grasslands) starts in the Early to Middle Miocene (Wolfe, 1986). Olson (1986) refers to this development as the Neogene transformation, as, according to him, it implies a considerable reduction of the world's plant carbon mass (from 1550.109 in the Early Miocene to 800.109 metric tons C in midHolocene time). According to Sarnthein et al. (1982) a climatic deterioration in the late Early Miocene gave rise to widespread continental aridity evidenced by enhanced aeolomarine dust deposition off the Northwest African coast. It seems, therefore, that the deforestation at the beginning of the Middle Aragonian suggested by the change in our rodent faunas, is the expression of a large scale phenomenon. Our interpretation of prevailing high temperatures during the Middle Aragonian (Langhian) in the Western Mediterranean is corroborated by, for instance, the presence of mangrove forest along

A,J. VAN DER MEULEN AND R. DAAMS

the Western Mediterranean coast (Bessedik, 1984). R6gl and Steininger (1983) quote evidence from various marine groups and from isotope records indicating high temperatures during the Langhian in the Mediterranean and Paratethys areas. Therefore, we attribute the inversion of the relationship between the temperature and humidity curves to a major shift of climatic belts in the late Early Miocene. Such a shift fits the model of Wolfe (1985) explaining the development of savanna during the Early to Middle Miocene. According to him decreasing temperatures in polar, and increasing temperatures in equatorial areas during the Neogene led to an increased latitudinal temperature gradient, which intensified the subtropical high-pressure systems and the summer drought along the western sides of continents. The two step climatic change which we recognize in the Middle Miocene mammal record (an increase of aridity followed by decrease of temperature) may be related to Kennett's (1986; in Kennett and Barker, 1990) interpretation of the major positive 6180 shift in the Middle Miocene. He argues that the earliest phase of the shift (16-14.6 Ma) resulted from a cooling of high-latitude deep waters, while the later phase (14.6-13.2 Ma) resulted from formation of an extensive ice-sheet on East Antarctica. Finally, it appears from Fig. 7 that the schematic curve indicating prevailing adaptive strategy is correlated to the humidity curve rather than to the temperature curve. This may be expected in view of the endotherm nature of the small herbivores. Thus it is understandable that the major change in the rodent fauna preceeded the drop of temperature around 14 Ma during which planktonic assemblages much like modern ones originated (Vincent and Berger, 1985).

Acknowledgements We acknowledge the fruitful discussions with Drs. J.W. Zachariasse, B.J. van der Zwaan, J. van de Burgh (Utrecht) and M. Freudenthal (Leiden), and thank Drs. J.W. Zachariasse and B.J. van der Zwaan for their critically reading of the manuscript. We are indebted to Dr. A. Azzaroli (Florence, Italy) and an anonymous referee for their

EVOLUTION OF EARLY MIDDLE MIOCENE RODENT FAUNAS

constructive comments on an earlier version of this paper. J. van D a m (Utrecht) wrote the programs that link our dBase database and the PeA and CLUSTR (Davis, 1973) and BALANC (Drooger, 1982) programs, which are all written in mRTRAY. We thank J. Luteyn who made Figs. 1, 2, 4 7, and T. van Hinte, who made Fig. 3. Appendix 1 Artesilla is a very rich locality with large (amongst which

Deinotherium; J. Morales, Madrid, pers. comm.) and small m a m m a l s near Villafetiche (Daams, 1989). The rodents have been identified by the second author. The locality is stratigraphically intrapolated between Villafeliche 2A and Vargas IA, and placed in Zone C on the basis of the presence of Megacricetodon primitivus. However, the faunal composition is more like Zone B faunas, because of the scarcity of Ligerimys (L. florancei, thusfar only known from Zone B) and Microdyromys, and of the high proportion of Praearmantomys and other Myomiminae. Another peculiar feature of the faunal composition is the relatively high percentage (16%) of Heteroxerus rubricati. Artesilla seems, therefore, to represent a hitherto unknown faunal phase in the area. Berends (1987, unpublished report) describes the rodent species from Muela Alta, Moratilla 2, 3, 4 and 5 in the Calamocha area. One assemblage, Moratilla 5, is too poor to be included here. The new Moratilla localities (numbered in stratigraphical order) are situated in a vertical section above the published locality Moratilla 1 (Zone A) from which they are separated by a hiatus. Muela Alta lies a few hundred meters laterally of Moratilla 2 and may represent the same level. These two localities and Moratilla 3 contain a smaller and a larger Megacricetodon species, M. primitivus and Megacricetodon sp. A respectively. Hitherto the co-occurrence of two Megacricetodon species was only known from the Upper Aragonian and possibly in Zone E (Daams and Freudenthal, 1988). A special feature of the Muela Alia and Moratilla 2 assemblages is the dominance of a large Democricetodon hispanicus. The cooccurrencc of the two Megacricetodon species characterizes Zone DO. Zone DO has not been encountered in the Aragonian type section. We intrapolate Zone DO between zones C and DI on the basis of the following arguments: (a) the composition of the new faunas is too different from known ones to consider them lateral equivalents, (b) the presence of Pseudqfahlbuschia points to a position higher than Zone C, and (c) the presence of Megacricetodon primitivus and the diversity of the Sciuridae indicates that Zone DO assemblages are not younger than Zone DI. Moratilla 4 is dominated by Fahlbuschia koenigswaldi. For this reason, and because it contains 3% Pseudofahlbuschia, we have placed it high in Zone D1 (Tables AI and A2).

Appendix 2 The palaeomagnetic data of the Calatayud section from Dijksman (1977) have recently been reinterpreted by Langereis

249 TABLE AI List of the rodent species from the new localities. In the middle column the numbers of first and second, upper and lower molars are given. N:MIM2

%%

318 18 200 184 153 25 18 413 9 492 149

16.0 0.9 I 0.1 9.3 7.7 1.2 0.9 20.8 0.4 24.8 7.5

Artesilla

Heteroxerus rubricati Microc!vrorn)'s legidensis Peridyromys murinus Pseudodryomys ibericus Pseudodryomys simplicidens/robustus Pseudodrvomys julii A rmantomys sp. Praearmantomys crusalonti Ligerimys .[torancei Megacricetodon primitivus Democricetodon hispanicus Muela alta

Heteroxerus aft. grivensis Atlantoxerus blacki Spermophilinus bredai M icrodyromys monspeliensis Microdyromys koenigswaldi Microdyromys complicatus Pseudodrvomys simplicidens Pseudod~vomys ibericus Megacricetodon primitivus Megacricetodon sp. A Fahlbuschia koenigswaldi Pseudo[ahlbuschia sp. Democricetodon hispanicus

7

5.5

0

0.0

6

4.7

4 7

3. l 5.5

1 3

0.7 2.3

0

0.0

I 15 2 2 79

0.7 11.8 1.5 1.5 62.2

38 8 24 259 6

5.4 0.9 3.9 10.8 0.4

41 14

2.9 1.0

3 17 77 96 802

0.2 1.2 5.5 6.9 57.9

17

11.4

3 3 3 11

2.0 2.0 2.0 7.4

18 4

12.1 2.7

33 33

22.3 35.8

Moratilla 2

Heteroxerus aft. grivensis Atlantoxerus blacki Spermophilinus bredai Microclvromys monspeliensis Pseudodryomys ibericus Pseudodrvomys simplicidens Armantomys aragonensis Eumyarion sp. Megacricetodon primitivus Megacricetodon sp. A Fuhlbuschia koenigswaldi Democricetodon hispanicus Moratilla 3

Heteroxerus aft. grivensis Atlantoxerus blacki Spermophilinus bredai Microa{vromys koenigswaldi Pseudodryomys ibericus Pseudodryomys simplicidens Megacricetodon primitivus Megacricetodon sp. A Fahlbuschia koenigswaldi Pseudofahlbuschia jordensi Democricetodon hispanicus

2

1.3

I

0.6

250

A.J. VAN DER MEULENAND R. DAAMS

TABLE A1 (continued) N:M1M2

%%

Moratilla 4

Heteroxerus aft. grivensis Glirudinus modestus Microdyromys koenigswaldi Pseudodryomys simplicidens Megacricetodon primitivus Fahlbuschia koenigswaldi Pseudofahlbuschia sp.

2 1 2

3.0 1.5 3.0

0

0.0

16 42 2

24.6 64.4 3.0

TABLE A2 Abbreviations of locality names used in the figures. Pedr. 2C Pedr. 2A Carr. 1 Nombr. 1 Sole. LPI. 5H Toril. Alco. 2B Viii. 9 LPI. 5K LPI. 5L Borjas Manch. 1 Valt. 1 LP1. 5B Valt. 2C Valt. 2B LPI. 4C LP1.4B LPI. 4A Valh. 4 Rega. 2 Valm. 3E Valm. 3D Viii. 4B Viii. 4A Valm. 3B Mor. 4 Cas. 3B Cas. IA

Pedregueras 2C Pedregueras 2A Carrilanga 1 Nombrevilla 1 Solera Las Planas 5H Toril Alcocer 2B Villafeliche 9 Las Planas 5K Las Planas 5L Borjas Manchones I Valalto 1 Las Planas 5B Valalto 2C Valalto 2B Las Planas 4C Las Planas 413 Las Planas 4A Valhondo 4 Regajo 2 Valdemoros 3E Valdemoros 3D Villafeliche 4B Villafeliche 4A Valdemoros 3B Moratilla 4 Caseton 2B Caseton IA

Valm. IA Valdemoros IA Olr. 9 Olmo Redondo 9 Mor. 3 Moratilla 3 Mor. 2 Moratilla 2 Muel. Muela Alta Olr. 8 Olmo Redondo 8 Otr. 5 Olmo Redondo 5 Varg. 1A Vargas 1A Arte. Artesilla Vill. 2A Villafeliche 2A SanR. 2 San Roque 2 SanR. 1 San Roque 1 Olr. 3 Olmo Redondo 3 Olr. 2 Olmo Redondo 2 Olr. I Olmo Redondo 1 Mor. 1 Moratilla 1 Ban. 11 Bafion I 1 Ban. 2 Bafion 2 Ban. 5 Bafion 5 Agreda Agreda LaDeh. Le Dehesa Ramb. 5 Rambler 5 Ramb. 7 Rambler 7 Ramb. 4B Rambler 4B Ramb. 4A Rambler 4A Valh. 3A Valhondo 3A Valh. 1 Valhondo 1 Ramb. 1 Ramblar I Nava. Navarrete del Rio

(Utrecht). The results and their far reaching implications for the correlation of Middle and Late Aragonian (late Orleanian and Astaracian) to the time scale will be discussed by Daams et al. (in prep.). Their main result, which we have used in our time scale of Fig. 7, is that Armantes 7 (Zone F-basal MN6, according to Daams and Freudenthal, 1988) can be correlated to the interval around the lower boundary of the normal polarity interval 5AB in Dijksman's Calatayud section. The age of this boundary is 13.46 Ma according to Berggren et al. (1985).

The top of the limestones containing Armantes I in the Ribota section has been correlated to a level some 18.5 m below the top (15.13 Ma) of the lower part of polarity interval 5B. As the mean sediment accumulation rate of the Calatayud section is 3.7 cm 10 -3 year the age of Armantes 1 may be estimated at about 15.6 Ma which is in the Langhian. The locality is placed in Zone D2 as it contains a fair amount of Pseudofahlbuschia jordensi (Freudenthal and Daams, 1988). Armantes 1 also contains Hispanotherium according to Antunes (1979) who correlates the so-called Hispanotherium faunas to the Langhian. This correlation is corroborated by the discovery of Hispanotherium in the Langhian Faluns of the Tourraine and Anjou (Loire Basin, France; Ginsburg, 1990). Our new data and the latter correlations agree well, but differ considerably from the calibrations by R6gl and Steininger (1983), Berggren et al. (1985) and Steininger et al. (1990). The reader is referred to Daams et al. (in prep.) for a detailed discussion. Other tie-points used for our age-model are the following: (1) Zone Z straddles the Aquitanian-Burdigalian boundary (21.8 Ma), between Ramblar I and Ramblar 4A in the type section of the Ramblian. Daams et al. (1987) correlate the oldest localities of the studied succession, Navarrete del Rio and Ramblar 1, with Laugnac, the reference locality of MN 2b. MN 2b is equivalent to part of the Aquitanian according to Hugueney and Ringeade (1990). Ramblar 4A has been correlated by Daams et al. (1987) with Estrepouy (MN 3), which in its turn is considered to be of Burdigalian age (e.g. Baudelot and Collier, 1978; Hugueney and Ringeade, 1990). Antunes and Mein (1986) correlate the Portuguese localities Universidade Catolica and Avenida do Uruguay with Zone Z and Estrepouy. The sediments yielding these Portuguese faunas are considered to be correlative to Blow's zone N5 (Burdigalian) according to Antunes et al. (1973). (2) The lower boundary of the Aragonian is tentatively put at ca. 18.5 Ma. As Zone B faunas contain Democricetodon, the first of the modern cricetids, it is placed in MN 4 by definition. Quinta do Narigfio has been placed in M N 3b on the presence of mastodonts, but, as mentioned above, the latest consensus is that the Proboscidea datum is at the beginning of M N 4 (Mein, 1989). Quinta do Narigao is underlain by marine sediments placed in Zone N7 of Blow (Late Burdigalian; e.g. Antunes et al., 1973; Antunes, 1979). Berggren et al. (1985, p. 231), however, correlate Quinta do Narigfio to "basal N.6?= 19.0 Ma", estimating Antunes' (loc. cit.) data "according to current standards". Steininger et al. (1990) date the arrival of the first Proboscidea within Zone NN3 (between 18.8 and 17.4 Ma in Berggren et al., 1985). (3) The end of the Early Aragonian is in the Late Burdigalian, around 17 Ma. Spanish Zone C faunas like Bufiol were usually placed in MN 4a (Mein, 1979). Quinta do Pombeiro and Quinta das Pedreiras were also placed in MN 4a and correlated to Zone C (Antunes, 1987). These faunas share the co-occurrence of Praearmantomys and Deinotherium with Artesilla. The sediments yielding the Portuguese faunas are correlated to the Late Burdigalian as they are intercalated in marine sediments placed in the lower part of Zone N8 of Blow (without Praeorbulina). Berggren et al. (1985) correlate Quinta do Pombeiro to basal

EVOLUTIONOF EARLY MIDDLEMIOCENERODENTFAUNAS N8 (with question mark) which has an estimated age of 16.8 Ma. In the Valles Penedes Zone C localities of the so-called Can Martivell phase are older than the Late Burdigalian transgression that is supposed to have started in N7 (Agusti et al., 1984a, b). (4) Zones Dl and D2, with Hispanotherium, and Zone D3 are correlative to the Langhian. In our time-scale the Langhian/Serravallian boundary coincides with the boundary between NN5 and NN6 (14.4 Ma, Berggren et al., 1985). The Lisboa Vb division containing faunas comparable to Zone D faunas is thought to correspond to the Langhian possibly starting at the Burdigalian-Langhian boundary interval (Antunes et al., 1973; 1987). The faunas are characterized by the presence of Hispanotherium. This rhinoceros genus has been encountered in Valdemoros IB and II in the Daroca area (Antunes, 1979). These localities (see Freudenthal, 1964, fig. 7) may now be placed in Zones Dl and D2 of the Middle Aragonian. Chelas 1 (a Lisboa Vb rodent fauna) comparable in age to Bufiol (Zone C) or slightly younger according to Aguilar (1981), fits better in Zone DI on the basis of the composition of this small assemblage. We correlate the younger faunul¢ of Chelas 2, which is still associated to the Lisboan Hispanotherium faunas, to Zone D2. The m l determined as Democricetodon or Fahlbuschia koenigswaldi closely resembles Pseudt~/'ahlbuschia jordensi, which is abundant in Zone D2 (Freudenthal, pers. comm.). Berggren et al. (1985) correlate Quinta da Farinheira to N9 (middle N9? = 15.2 Ma). From the stratigraphical information given by Antunes et al. (1973) and Aguilar (1981) it appears that the levels of Quinta da Farinheira, Chelas 1 and 2 are older than (supposedly the top of) N9 (15.2-15.0 Ma; FAD of Orbulina suturalis is 15.2 Ma) and younger than the lower part of N8 without Praeorbulina. This implies that the beginning of Zone Dl lies between 16.6 and 16.3 Ma (Berggren et al., 1985). Our estimated age for the D2 locality Armantes 1 is compatible with the stratigraphic constraints found in the Lisboa area (see above). The locality Amor (Portugal) has been considered to be somewhat younger than the Hispanotherium faunas of Lisboa Vb and has been assigned a late Langhian Age on the basis of second order correlations (Antunes and Mein, 1981). The co-occurrence of Cricetodon and Fahlbuschia freudenthali in this locality is not known in the Daroca-Calamocha area. The determination of Cricetodon ("cf. Cricetodon indet.") from Amor is uncertain, because only a fragment of a lower molar is available. In our area the co-occurrence of Fahlbuschia Jheudenthali and Renzimys lacombai characterizes Zone D3, while Cricetodon enters in Zone E. Antunes and Mein (1981) correlate Amor to Las Planas 4A (basal Zone E) partly on the presence of Cricetodon, but a correlation to Zone D3 cannot be excluded in our opinion. (5) Pov6a de Santar6m, thought to be time-equivalent with Manchones (Zone G2, MN6), has been correlated to the NI l NI2 interval (11.8-13.8 Ma). The only tie-point between marine and continental scales in the Lisboa area is Pov6a de Santar6m, which has been correlated to Manchones (Zone G2, MN6). The deposition of the sediments of this locality (Antunes and Mein, 1977) is supposed

251 to have occurred in the interval Nl0-N14, probably nearer to NI 1-Nl2, i.e. Serravallian. (6) Immigration of Hipparion in Europe is around 11.0-11.5 Ma. The presence of Hipparion and the extreme rareness of Muridae indicate an Early Vallesian age, respectively MN9, for Zones H and !. The date of l l.0 11.5 Ma (see above) indicates a late Serravallian for the entry of Hipparion, which is confirmed in the section of Kastellios Hill, where lower Tortonian marine sediments overly Upper Vallesian continental sediments (De Bruijn and Zachariasse, 1979).

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