Fossil bird study, and paleoecological and paleoenvironmental consequences: Example from the Saint-Gérand-le-Puy deposits (lower miocene, Allier, France)

Palaeogeography, Palaeoclimatology, Palaeoecology, 73 (1989): 295 309

Elsevier Science Publishers B.V., Amsterdam

295

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FOSSIL BIRD STUDY, AND PALEOECOLOGICAL AND PALEOENVIRONMENTAL CONSEQUENCES: EXAMPLE FROM THE SAINT-GI RAND-LE-PUY DEPOSITS (LOWER MIOCENE, ALLIER, FRANCE) JACQUES CHENEVAL Centre des Sciences de la Terre, Universitd Claude Bernard-Lyon 1, 27 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex (France)

(Received August 29, 1988; revised and accepted April 13, 1989)

Abstract Cheneval, J., 1989. Fossil bird study, and paleoecological and paleoenvironmental consequences: example from the Saint-G~rand-le-Puy deposits (Lower Miocene, Allier, France). Palaeogeogr., Palaeoclimatol., Palaeoecol., 73: 295 309. Study of the aquatic avifauna from the Agenian deposits of the Saint-G~rand-le-Puy area (Allier Department, France) proves that paleornithology is not only a systematical and evolutionary science, but also that it can provide interesting data, sometimes unsuspected from the study of other animal groups, on paleoecological,paleoenvironmental and paleoclimatologicalconditions. Thus, the comparison of the ecological adaptations of such fossil species from this area with those of their nearest living relatives provides new information about the paleoenvironment, such as climatic and physico-chemical conditions, water depth, predation relationships and migration.

Introduction P a l e o r n i t h o l o g y w a s f o u n d e d by t h e F r e n c h a u t h o r M i l n e - E d w a r d s (1867-71) w h o des c r i b e d some F r e n c h T e r t i a r y a n d Q u a t e r n a r y a v i f a u n a s , e s p e c i a l l y t h e M i o c e n e s p e c i e s from t h e S a i n t - G ~ r a n d - l e - P u y d e p o s i t s ( M a s s i f Central, Allier Department, France). F r o m t h e b e g i n n i n g of p a l e o r n i t h o l o g y , v e r y few s c i e n t i s t s t o o k i n t e r e s t in t h e s t u d y of fossil birds. H o w e v e r , a b o u t 40 y e a r s ago, a n u m b e r of a u t h o r s from v a r i o u s p a r t s of t h e w o r l d t o o k up s u c h s t u d i e s a n d t h e s y s t e m a t i c s a n d e v o l u t i o n of b i r d s g r a d u a l l y b e c a m e b e t t e r known. B u t t h e s t u d y of fossil b i r d s in t h e d e p o s i t s a n d t h e p a l e o e c o l o g i c a l or p a l e o e n v i r o n m e n t a l d a t a , to w h i c h t h i s s t u d y c a n c o n t r i b u t e , a r e 0031-0182/89/$03.50

often neglected by specialists concerned with other groups of animals. However, the ecological adaptations to some particular ways of life find expression, maybe more so than in other animal groups, in osteological characteristics of birds. These adaptations are well known for modern birds and can be used to interpret fossil species. So, by the study of the osteological adaptations, and by comparison with the ecological behavior of the most closely related modern species, the ecology of the fossil birds can often be specified. In a studied deposit, the ecological data, as a whole, enable one to determine the paleoenvironmental conditions. Even if the distribution of flightless birds on the southern continents seems to be the most interesting point about them, most birds can

(!~ 1989 Elsevier Science Publishers B.V.

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fly and they migrate if the climatic conditions are not appropriate; they are probably the animals which can cover a long distance most rapidly. Each bird species lives under quite specific climatic conditions and can quickly move if these become inappropriate. Owing to this fact, we can consider, certainly with a greater probability than for other animal groups, that each fossil species lived under similar climatic conditions to its living relatives. So, a comparison with the current distribution maps for the most closely related modern species can provide accurate data about the past climatic conditions. And all the data provided by the entire avifauna of a deposit can often enable the paleoclimatology to be specified. Thus, in addition to our knowledge of the systematics and evolution of birds, paleornithology can provide some data that sometimes remained unsuspected in the study of other animal groups, in other areas such as paleoecology, paleoenvironment and paleoclimatology. This can be proved by an example I have been working on for some years: the avifauna from the Saint-G~rand-le-Puy deposits. Deposits of the Saint-G~rand-le-Puy area

Chronological account Geoffroy-Saint-Hilaire was the first author to mention the discovery of vertebrate fossil remains in the Miocene deposits of the SaintG~rand-le-Puy area. Croizet (1833) and Domnando (1833) made preliminary studies of these remains. Up to now, there have been numerous geological and paleontological studies of these deposits. The most recent complete geological studies are those of Donsimoni (1975) and Donsimoni and Giot (1977). A more recent study was also made of one of the deposits (Bucher et al., 1985).

Geological description The Agenian terrains of the Saint-G~rand-lePuy area are situated in the "Limagne bour-

bonnaise", a subsidence basin in the center of the Massif Central where the river Allier flows. The history of Limagne is connected with the formation of the chain of the Alps. The subsidence of this basin started in the Eocene and, during Chattian and Agenian times, lacustrine depressions were disseminated over the area, more or less independently from one another. These expanses of water were the origin of limestone deposits whose appearance and structure differ widely. Later on, the lakes dried up and, up to the present, the Limagne has been under the influence of river erosion. The quarries of the Saint-G~rand-le-Puy area were first exploited for lime and more recently for cement. Most quarries were filled in at the end of exploitation, but some are still being exploited and others are still visible. All these quarries are situated on the civil parish lands of Saint-G~rand-le-Puy, Montaigu-le-Blin and Bouc~ (Fig.l). In a wider sense, the name ~'Saint-G~rand-le-Puy" is also sometimes used to include deposits from Bransat, Chavroches, Langy and Saulcet. In these quarries, various shapes of algal concretions may be seen, from the smallest (oolites, pisoliths, ~'pebbles") to the largest (spheroid and columnar constructions) coalescence of which sometimes gives rise to a reef limestone more than 20 meters thick; it provides an abundant fossil fauna.

Faunal arrangement The fauna from the Saint-G~rand-le-Puy deposits is very diverse and particularly abundant. Remains of mammals (marsupial, insectivores, bats, rodents, "rabbits", carnivores, ungulates), birds (especially aquatic species such as loon, cormorants, pelican, heron, marabou, flamingos, tree ducks, swan, crane, rail, shorebirds, gulls), reptiles (testudos, lizards, snakes, crocodile) and batrachians (toad, triton) have been found in thousands (for a complete bibliography, see Cheneval, 1983a). During the greater part of the exploitation of the quarries, the remains of vertebrates were found by quarrymen who gave (or sold!) them

297

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to research workers. This explains why such remains are scattered in collections all over the world. The most important French collections are those of the Museum national d'Histoire naturelle of Paris and the D6partement des Sciences de la Terre of Lyon University. As far as paleornithology is concerned, the Saint-G6rand-le-Puy deposits are almost the only deposits in France where bird remains are so abundant. The peculiar feature of these deposits is the great abundance of aquatic birds; there is no European equivalent and they can only be compared to the deposits from Canyon Creek (Wyoming) where thousands of bones of the flamingo-like bird Presbyornis have been found. The avifauna from the Saint-G~rand-le-Puy deposits was first studied by Milne-Edwards (1867-71). Since this study, there has been no

general systematic revision, but some species have been restudied (Lambrecht, 1933; Gaillard, 1939; Storer, 1956; Brodkorb, 1970; Cracraft, 1973; Collins, 1976; Harrison and Walker, 1976; Olson, 1981). When I started the general revision of this avifauna, owing to the great abundance of remains, I limited myself, first of all, to the study of the aquatic avifauna (Cheneval, 1983a, 1983b, 1983c, 1984a, 1984b).

Quantitative composition of the aquatic avifauna from Saint-G6rand-le-Puy The abundance of remains differs for each species of birds. So, it seems of great interest to determine the relative frequency of each species. I therefore calculated the rates for each species relative to: (a) the sum of remains studied,

298

(b) the sum of long bones, which are most easily determined and are the most significant remains, providing evidence of paleoecological adaptations and (c) the calculated minimal number of individuals (Table I). These are only partial results because I studied only remains from the collections of the Paris Museum, the Lyon Museum and the Lyon University. However, in view of the abundance of the material, these results can be considered as representative. The most numerous aquatic species were the flamingo-like birds of the Palaelodidae family (almost 50% of the aquatic avifauna) and the tree-ducks of the fossil genus Dendrochen (almost 34% of the aquatic avifauna); these two families of birds thus representing more than 80% of the aquatic avifauna. All the other birds were distinctly more rare; among them, the most numerous were the ibis Plegadis paganus (more than 5%), and the marabou-like bird GraUavis edwardsi (a little less than 4%). As stated above, there are not only remains

of aquatic birds in the Saint-G6rand-le-Puy deposits, but also of land birds. With respect to the number of species, the aquatic birds represented about a third of the whole avifauna; however, with regard to the number of remains seen in the collections, I think that these represented about three quarters of the entire avifauna. So, the paleoecological and paleoenvironmental data we can deduce from them will be very meaningful. Paleoenvironmental

background

Climatic conditions For the greater part, aquatic bird species from the Saint-G6rand-le-Puy deposits belong to, or are closely related to, modern genera living in tropical regions. This is a primary indication, but the study of fossil birds enables the climatic conditions to be better specified. Accordingly, I tried to locate the geographic regions where modern birds closely related to the fossil species can be found; the climatic

TABLE I Q u a n t i t a t i v e composition of the aquatic a v i f a u n a of the Saint-G6rand-le-Puy deposits

Colymboides minutus (loon) Plotornis arvernensis (albatross) Phalacrocorax littoralis (cormorant) Nectornis miocaenus (anhinga-like cormorant) Empheresula arvernensis (gannett) Miopelecanus gracilis (pelican) Proardeola walkeri (heron) Grallavis edwardsi (marabou) Plegadis paganus (ibis) Palaelodus ambiguus (flamingo-like bird) P. gracilipes P. crassipes Megapaloelodus goliath Phoenicopterus croizeti (flamingo) Dendrochen blanchardi (tree-duck) D. consobrina D. natator Cygnopterus alphonsi Total

Entire r e m a i n s

Long bones

Individuals

n

n

n

207 2 7 157 3 122 3 865 772 8333 690 320 63 88 4889 42 49 11 16623

% 1.25 0.01 0.04 0.94 0.02 0.73 0.02 5.20 4.64 50.13 4.15 1.93 0.38 0.53 29.41 0.25 0.30 0.07 100

207 2 7 151 1 113 3 687 762 7230 689 320 63 84 4569 42 49 11 14990

% 1.38 0.01 0.05 1.01 0.007 0.75 0.02 4.58 5.08 48.23 4.60 2.14 0.42 0.56 30.48 0.28 0.33 0.07 100

%

36 1 2 20 1 20 1 43 61 477 55 32 13 14 374 11 8 3 1172

3.07 O.O9 0.17 1.71 0.09 1.71 0.09 3.67 5.20 40.70 4.69 2.73 1.11 1.19 31.91 0.94 0.68 0.25 100

299

conditions for these regions would be approxim a t e l y the same as those for the Saint-G6randle-Puy area d u r i n g the time of the deposits. W h e n we c o m p a r e the c u r r e n t d i s t r i b u t i o n maps for the m o d e r n g e n e r a Phalacrocorax and Anhinga (Fig.2), Pelecanus (Fig.3), Ardeola (Fig.4), Ephippiorhynchus and Leptoptilos (Fig.5), Plegadis (Fig.6), P h o e n i c o p t e r i d a e (Fig.7) and D e n d r o c y g n i n a e (Fig.8), we can recognise five g e o g r a p h i c regions which all these birds s h a r e (Fig.9): Y u c a t a n peninsula, in M e x i c o N o r t h e r n parts of Colombia and Venezuela Coast of W e s t e r n Africa, from Senegal to Liberia S o u t h e r n Africa, from Congo w e s t w a r d to E t h i o p i a e a s t w a r d and to T r a n s v a a l P r o v i n c e of S o u t h Africa s o u t h w a r d S o u t h e r n part of P a k i s t a n and n o r t h - w e s t e r n part of India N e i t h e r the albatross Plotornis arvernensis

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n o r the g a n n e t Empheresula arvernensis are t a k e n into account; I t h i n k these fossil species, whose r e m a i n s are v e r y rare, were s t r a y m a r i n e birds carried into the a r e a by gusts of wind or storms (Cheneval, 1983a, 1984b). In o t h e r respects, some birds, whose c u r r e n t distribution is in more p a l e a r c t i c and n e a r c t i c areas, were also represented, such as a swan (Cygnopterus alphonsi) and a loon (Colymboides minutus). Remains of the swan are fairly rare, and this bird could h a v e been m i g r a t o r y (see below). The problem is a little different for the loon; m o d e r n species live more often in p a l e a r c t i c and n e a r c t i c t h a n in tropical areas, but, in m a n y aspects, remains of C. minutus look v e r y similar to grebes of the genus Tachybaptus; so the fossil species could h a v e had similar b e h a v i o r to Tachybaptus, m o d e r n species of which can be found in all the abovem e n t i o n e d g e o g r a p h i c regions, except the n o r t h e r n parts of Colombia and Venezuela.

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Fig.2. Present-day distribution of the modern cormorants, genus Phalacrocorax (dotted lines: northern and southern boundaries of the distributive area) and anhingas, genus Anhinga (hachures).

300

( Fig.3. Present-daydistribution of modern pelicans, genus Pelecanus(arrows: seasonal migrations). All the defined areas extend in the intertropical belt where there are different climatic regions (Koeppe and Long, 1958; Viers, 1968; Pagney, 1976) (Fig.9): -Wet and dry tropical (Aw) climate (or savanna climate): definitely dry season of variable length followed by a definite rainy season, wide mean annual range of temperature, intermediate to heavy precipitation. -Low-latitude steppe (Bsh) climate: long dry season and short rainy season, significant mean annual range of temperature, weak to intermediate precipitation. -Mesothermal, hot summer (Cfa) climate: hot summers and mild winters, very large mean annual range of temperature, heavy precipitation. -Mesothermal, hot summer, dry winter (Cwa) climate: hot summers with high relative humidity, very wide mean annual range of temperature, intermediate to heavy precipitation.

In brief, all the defined regions are characterized by an alternation of dry and rainy seasons. The mean annual temperature is about 21 ° with a significant mean annual excursion. The rainfall is often heavy (on average 1000-2000 mm). Thus, the Agenian climate of the Saint-G~rand-le-Puy area would have been of a tropical to intertropical nature. Fossil species of other groups seem to corroborate this conclusion. A crocodile, Diplocynodon rateli, has been described from this area; it would indicate a climate with a mean temperature of about 10° for the coldest month (Berg, 1965; Buffetaut and Corn~e, 1982) and this tallies with the climates described above. Mammal (Ginsburg, 1968) and Oligo-Miocene palynological studies (Gorin, 1975) also seem to support our conclusion: the Agenian would have been characterized by a warmer and drier climate than the Late Oligocene; this change would have coincided with 'tan emergence, or an emphasis, of a dry season" (Ginsburg, 1968).

301

Fig.4. Present-day distribution of modern herons, genus Ardeola (arrows: seasonal migrations). In fact, it seems that, during the Late Oligocene, the climate showed some dry seasons. This aridification of the climatic conditions also became apparent from the study of marine invertebrates from the Mediterranean Miocene (Demarcq, 1979) and the study of the fauna and flora from the Neogene of the Rhone valley (Demarcq et al., 1983).

Limnologic features Salinity of water The description of a flamingo, Phoenicopterus croizeti, in the avifauna from the SaintG~rand-le-Puy area seems to indicate that there were expanses of brackish water' because modern flamingos always occur on expanses of alkaline-water (Uys et al., 1963; Cramp et al., 1977; Brown et al., 1982). With the intention of checking this hypothesis, I searched for the probable biotopes of the fossil species by comparison with those of

the most closely related modern species. The following biotopes can be found: -Oceanic biotope: Plotornis arvernensis and Empheresula arvernensis. -Strictly brackish-water biotopes: Plegadis paganus, Phoenicopterus croizeti and more probably the Palaelodidae species [these strange flamingo-like birds were very different from the true flamingos, but it seems they had the same feeding behavior (Cheneval and Escuilli~, in press) and could be found in the same biotope], -Preferentially brackish-water biotopes: Phalacrocorax littoralis, Miopelecanus gracilis, Grallavis edwardsi and the Dendrocygninae species, -Ubiquitous in water-covered (fresh or brackish water) biotopes: Colymboides minutus, Nectornis miocaenus, Proardeola walkeri and Cygnopterus alphonsi. Thus, there were no species whose biotope was strictly in fresh water, whereas the species

302

2

Fig.5. Present-day distribution of the modern tribe Leptoptilini (marabous, genera Ephippiorhynchus, Jabiru, and Leptoptilos). restricted to brackish water were the most numerous (more than 55%; see Table II). The species that can be found today in brackishwater areas were clearly in the majority (Table II), representing almost 95% of the aquatic avifauna. Therefore, the hypothesis that the Saint-G~rand-le-Puy area was covered with areas of brackish-water seems to be confirmed. Nevertheless, as some species were probably piscivorous (see below), the salinity must not have been excessive or it would have precluded the presence of fishes, as sometimes happens today in some East-African lakes (Beadle, 1932; Bartholomew and Pennycuick, 1973); in the same way, ~'a too-high salt concentration becomes harmful" for chicks, even of flamingos (Vareschi, 1978). Inversely, the water could not have been too fresh because life conditions for flamingos would then have been impossible. Today in

Africa, it happens t h a t flamingos leave lakes where the water becomes too fresh (for instance, after heavy rains). These more or less local migrations are explained by a deficiency in food availability: flamingos are mainly phytoplankton and zooplankton feeders and planktonic organisms seem to be very sensitive to changes in the salt concentration (Brown, 1958; Uys et al., 1963; Vareschi, 1978). As for the other aquatic species of the fauna, it seems that the crocodile Diplocynodon rateli could endure a certain salinity of the water (Buffetaut and Corn~e, 1982). Among mammals, Potamotherium valetoni could have had the same biotope as modern otters, which are ubiquitous (both in fresh and brackish-water areas); in other respects, it is astonishing that a beaver-like species, Steneofiber eseri, was present; modern beavers live strictly in freshwater biotopes, but it is possible that S. eseri was living in neighbouring small streams and

303

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Fig.6. Present-day distribution of modern ibis, genus Plegadis (arrows: seasonal migrations). that the carcasses were carried down to the lakes thereby. Among the gastropods, the aquatic species Hydrobia can also endure a certain salt concentration; the same is true for the aquatic insect larvae of Phryganea (Guillot 1979). In any case, the salinity of the water in the Saint-G~rand-le-Puy lakes cannot be explained by a marine invasion, or infiltration. The Aquitanian was a very regressive period in France; the coasts were almost the same as today, with only a transgression of the sea in the Bay of Biscay and Gascony Basin and one on the M e d i t e r r a n e a n coast from Carry-leRouet to Montpellier (Fig.l). Thus, the SaintG~rand-le-Puy area lay as far away from the coasts as it does today. We should therefore assume a system with an alternating salt concentration, doubtless in relation with the climatic conditions. At present, the same phenomenon appears in the lake district of East-Africa; during the dry season, the salinity

increases with evaporation, whereas it decreases during the rainy season (Beadle, 1932; Vareschi, 1978). This could have happened in the Saint-G~rand-le-Puy area where the climate certainly was characterized by alternately dry and rainy seasons.

Depth of water The presence of some birds adapted to diving may give an idea of the depth of water in the lakes of the Saint-G~rand-le-Puy area. The best diving bird was certainly the loonlike Colymboides minutus; modern loons can dive to a depth of 20 meters, but C. minutus seemed to have a behaviour more like modern grebes of the genus Tachybaptus (Cheneval, 1983a, 1984b) which dive to depths of only a few meters. Also, Palaelodidae birds were certainly better divers than swimmers (Cheneval, 1983c). These birds were taller than C. minutus; their height could be estimated as about one meter. Thus, the depth should have been adequate

304 TABLE II

TABLE III

Probable biotope of the aquatic birds of the Saint-G6randle-Puy deposits, based on the biotope of the nearest modern species: (1) oceanic biotope (2) strictly in brackish-water expanses (3) preferentially in brackish-water expanses (4) ubiquitous in water expanses (the percentages used here are founded on the minimal number of individuals; see Table I).

Probable feeding behavior of the aquatic birds of the SaintG~rand-le-Puy deposits, based on the feeding behavior of the closest present species: (1) fish-feeders (2) small vertebrates (small fishes, batrachians, reptiles) feeders (3) small invertebrates (insects, crustaceans, molluscs, worms) feeders (4) phytoplankton and zooplankton feeders (5) aquatic weeds feeders (the percentages used here are founded on the minimal number of individuals; see Table I)

Species

(1)

Colymboides minutus Plotornis arvernensis 0.09 Phalacrocorax littoralis Nectornis miocaenus Empheresula arvernensis 0.09 Miopelecanus gracilis Proardeola walkeri Grallavis edwardsi Plegadis paganus Palaelodus ambiguus P. gracilipes P. crassipes Megapaloelodus goliath Phoenicopterus croizeti Dendrochen blanchardi D. consobrina D. natator Cygnopterus alphonsi Total % of individuals

0.18

(2)

(3)

(4) 3.07

Species

(1)

(2)

(3)

(4)

(5)

0.17 1.71 1.71 0.09 3.67 5.20 40.70 4.69 2.73

1.11 1.19 31.91 0.94 0.68 0.25 55.62

39.08

5.12

Colymboides minutus Phalacrocorax littoralis 0.17 Nectornis miocaenus 1.71 Miopelecanus gracilis 1.71 Proardeola walkeri Grallavis edwardsi Plegadis paganus Palaelodus ambiguus P. gracilipes P. crassipes Megapaloelodus goliath Phoenicopterus croizeti Dendrochen blanchardi D. consobrina D. natator Cygnopterus alphonsi Total ~o of individuals

to permit these birds to dive. It seems to me t h a t the depth of water in the lakes of the Saint-G~rand-le-Puy area was about 5 to 10 meters. On the other hand, many aquatic birds lived in shallow water. It may be admitted, therefore, either th at the banks were gently sloping or t h at there were some shallow-water lakes for these birds.

Life conditions of the aquatic birds Feeding behavior The aquatic birds described had diverse feeding behaviors (Table III). P l a n k t o n and aquatic weed feeders were the most numerous (almost 85% of the aquatic avifauna). So, the aquatic flora should have been very abundant in the lakes.

3.59

3.07

0.09 3.67 5.20 40.70 4.69 2.73 1.11 1.19 31.91 0.94 0.68 0.25 3.76

8.27

50.42

33.78

Up to now, no fishes have been determined in the Saint-G~rand-le-Puy deposits, but a few vertebrae have been found. The presence of some fish-feeding birds (exclusively or occasionally; about 7%) seems to imply t hat the fish must have been abundant; it is thus surprising t hat fossil remains of fishes are not more numerous. Several birds should have had similar feeding behavior, but it seems they did not enter into competition with one another. For instance, the loon-like Colymboides minutus and the ibis Plegadis paganus must have eaten almost the same small invertebrates, but C. minutus must have fished in open water whereas P. paganus waded near the bank in shallow water. Among the fish-feeders, cormorants and anhingas are found today in the same areas, but

305

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Fig.7. Present-day distribution map of modern flamingos, genera

they fish during different periods of the day or they eat different species of fish (Brown et al., 1982); this could be true of the cormorant Phalacrocorax littoralis and the anhinga-like cormorant Nectornis miocaenus.

Predation As birds were very numerous over and around the lakes of the Saint-G~rand-le-Puy area, there must have been many predators on the aquatic birds. Among predatory birds, gulls sometimes hunt the chicks of flamingos (Uys et al., 1963) and gulls are known in the Saint-G~rand-lePuy deposits where three species have been referred to the modern genus Larus. Also, herons and ibises occasionally eat eggs and chicks of flamingos (Uys et al., 1963); it must have been the same on the banks of the lakes, where these birds could also find eggs and chicks of other breeding species.

Phoenicopterus,Phoeniconaias,and Phoenicoparrus. Among reptiles, the crocodile Diplocynodon rateli certainly preyed on some adult birds; modern crocodiles are occasional predators of birds like cormorants, anhingas, ducks and sometimes even pelicans (Pitman, 1957). Lizards and tortoises are also predators of birds (Pitman, 1957, 1958); it is possible that lizards of the genus Sauromorus and tortoises, specially the species of the genus Trionyx, may have eaten eggs and chicks. Among mammals, the small carnivores (mustelids, viverrids) must have been the main predators of birds, eating both eggs and chicks, but the larger carnivores could sometimes have caught some adult birds. Among all the material observed, I found some bones with a callosity of fracture, but these were very rare in such an environment with numerous predators; identical cases can scarcely be observed today (Didier, 1953).

306

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Fig.8. Present-daydistribution of modern tree-ducks, genera Dendrocygna and Thalassornis.

Migration For some authors, the migrational instinct is connected with hard climatic conditions during the winter. In this opinion, seasonal migrations of birds would have appeared only from the Pleistocene (Miller, 1928). If we can explain the migration of the palearctic and nearctic birds in this way, this could not be applied to the tropical and sub-tropical birds which are also migratory. Of course, it is impossible to prove conclusively that the Miocene birds already had a migratory instinct. However, such behavior, which is deeply marked in some modern species, certainly appeared a long time ago. On the other hand, the climatic conditions in the Saint-G~rand-le-Puy area were certainly characterized by an alternation of dry and rainy seasons (see above); so, it is possible that Miocene birds were indeed migratory. By comparison with the behavior of the most closely related modern species, the Miocene

birds capable of migration could have been the pelican Miopelecanus gracilis (Fig.3), the heron Proardeola walkeri (Fig.4) and the ibis Plegadis paganus (Fig.6). Both the pelican and the ibis bred around the lakes of the Saint-G~randle-Puy area because some juvenile bones were found; they certainly lived and bred in the region during the dry season, and migrated southwards during the rainy season, as do modern species. The remains of the heron are too little known to determine whether it bred in the region or not, but it is highly probable that its behavior was the same as that of the pelican and the ibis. In other respects, the loon-like Colymboides minutus and the swan Cygnopterus alphonsi could also be migratory species, as are their modern close relatives, but it seems that these species did not breed in the Saint-GSrand-lePuy area as there are no juvenile bones. Thus, it is possible t h a t these birds bred further north and migrated for the rainy season to the studied

307

U

Bsh ~WO

Aw

fa

Fig.9. Map of the present-day distributions of the nearest living relatives of the fossil aquatic birds of the Saint-G6rand-lePuy deposits (from Fig.2 to 8) and climatic conditions (from Koeppe and Long, 1958): Aw: wet and dry tropical climate Bsh: low-latitude steppe climate Cfa: mesothermal, hot summer climate Cwa: mesothermal, hot summer, dry winter climate a r e a . T h i s c o u l d a l s o e x p l a i n t h e p r e s e n c e of these two r a t h e r p a l e a r c t i c and nearctic birds in a s u b - t r o p i c a l a v i f a u n a .

Conclusion T h e a q u a t i c a v i f a u n a of t h e S a i n t - G ~ r a n d - l e P u y d e p o s i t s is a good e x a m p l e p r o v i n g t h a t p a l e o r n i t h o l o g y c a n be of g r e a t s e r v i c e in t h e r e c o n s t r u c t i o n of p a s t c o n d i t i o n s of life. Of c o u r s e , t h e r e s u l t s of t h i s s t u d y a r e o n l y p a r t i a l b e c a u s e t h e a v i f a u n a of t h e s e d e p o s i t s is e x t r a o r d i n a r i l y r i c h a n d will s t i l l n e e d some y e a r s of w o r k b e f o r e b e i n g c o m p l e t e l y res t u d i e d . A l l t h e l a n d b i r d s n e e d to be s t u d i e d a n e w a n d t h i s w i l l be a n o p p o r t u n i t y to specify the paleoecological and paleoenvironmental c o n d i t i o n s on l a n d b e t t e r a n d also to i m p r o v e

t h e p r e s e n t d a t a , e s p e c i a l l y c o n c e r n i n g paleoclimatic conditions.

Acknowledgements I t h a n k Dr. C. M o u r e r - C h a u v i r ~ for a h e l p f u l r e a d i n g of t h e m a n u s c r i p t . T h i s p a p e r w o u l d n o t h a v e e x i s t e d w i t h o u t a d v i c e on t h e E n g l i s h by E l l e n C h e n e v a l a n d E l l e n F ~ v r i e r .

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