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Late Carboniferous-Early Permian Tetrapod Ichnofauna from the Khenifra Basin, Central Morocco
Geobios 44 (2011) 399–407
Original article
Late Carboniferous-Early Permian Tetrapod Ichnofauna from the Khenifra Basin, Central Morocco§ La palichnofaune de vertébrés tétrapodes du Carbonifère supérieur-Permien inferieur du Bassin de Khenifra, Maroc central Sebastian Voigt a,*, Hafid Saber b, Jörg W. Schneider a, Driss Hmich b, Abdelkbir Hminna b a
Geological Institute, TU Bergakademie Freiberg, B.-v.-Cotta-Str. 2, 09596 Freiberg, Germany b Department of Geology, Chouaïb Doukkali University, B.P. 20, 24000 El Jadida, Morocco Received 5 January 2010; accepted 30 November 2010 Available online 29 April 2011
Abstract In terms of cumulative thickness and areal extent, the Khenifra Basin is one of the most important outcrops of Late Palaeozoic red-beds in central Morocco. Macro- and microfloral remains near the centre of the 1800 m-thick succession of interbedded conglomerates, sandstones, and mudstones are considered to be of middle to late Early Permian age. Here we give the first comprehensive analysis of the vertebrate ichnofossil record from the study area, based on 17 specimens of isolated footprints and incomplete step cycles collected at three localities that are lithostratigraphically equivalent to the plant-bearing horizons. The tetrapod ichnofauna comprises tracks of the plexus Batrachichnus Woodworth – Limnopus Marsh, Ichniotherium sphaerodactylum (Pabst), Dimetropus Romer and Price, and Dromopus Marsh which can be referred to temnospondyl, diadectomorph, synapsid (‘‘pelycosaurian’’) and early sauropsid trackmakers. This clearly Euramerican footprint assemblage, including the first occurrences of Ichniotherium and Dimetropus from outside Europe and North America, indicates a Late Carboniferous to Early Permian age of the fossiliferous strata. Judging from the relatively diverse ichnofauna and flora, the Khenifra Basin must have represented a wellestablished terrestrial ecosystem during that period. Its habitat could be specially important for the understanding of the phylogeny and dispersal of early tetrapods, inasmuch as we are able to report on an extremely rare type of diadectomorph footprint hitherto known only from the Early Permian of central Germany. # 2011 Elsevier Masson SAS. All rights reserved. Keywords: Vertebrate tracks; Early tetrapods; Biostratigraphy; Biogeography; Late Palaeozoic; NW Africa
Résumé Du point de vu de l’épaisseur des sédiments et de leur extension géographique, le bassin de Khénifra est l’un des plus importants affleurements de terrains rouges du paléozoïque supérieur dans le Maroc central. Les restes de macro- et microflores provenant du milieu de la série, d’environ 1800 m d’épaisseur, formée essentiellement de niveaux interstratifiés de conglomérats, de grès et d’argiles ont donné un âge permien inférieur moyen à tardif. Nous présentons dans ce travail une première analyse des ichnofossiles de vertébrés de la zone d’étude, basée sur 17 spécimens de traces isolées, recueillis dans trois localités lithostratigraphiquement équivalentes aux niveaux où ont été découverts les paléoflores. Les ichnofaunes des tétrapodes comprennent des empreintes de pas de plexus Batrachichnus Woodworth – Limnopus Marsh, Ichniotherium sphaerodactylum (Pabst), Dimetropus Romer et Price et Dromopus Marsh qui peuvent être attribuées à des temnospondyles, diadectomorphes, synapsides (« pelycosauriens ») et sauropsides primitifs. Cet assemblage de traces de pattes est clairement euraméricain, incluant les premières occurrences d’Ichniotherium et Dimetropus hors d’Europe et d’Amérique du Nord et indiquant un âge Carbonifère supérieur à Permien inférieur pour ces couches fossilifères du bassin de Khénifra. D’après ces ichnofaunes et paléoflores relativement diverses, le basin de Khénifra a du représenter un écosystème terrestre bien établi au cours de cette période. Son habitat pourrait être d’une importance particulière pour
§
Corresponding editor: Davide Olivero. * Corresponding author. E-mail address: [email protected] (S. Voigt).
0016-6995/$ – see front matter # 2011 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.geobios.2010.11.008
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la compréhension de la phylogénie et la dispersion des premiers tétrapodes, d’autant plus qu’un type extrêmement rare d’empreinte de pas de diadectomorphe, jusqu’ici connu seulement dans le Permien inférieur d’Allemagne centrale y est observé. # 2011 Elsevier Masson SAS. Tous droits réservés. Mots clés : Traces de pattes de vertébrés ; Premiers tétrapodes ; Biostratigraphie ; Biogéographie ; Paléozoïque supérieur ; Afrique nord-occidentale
1. Introduction Permo-Carboniferous rocks of central Morocco are preserved in a number of small, isolated basins that originated as NNE-SSW oriented, graben-like structures during the late phase of the Hercynian orogeny (El Wartiti et al., 1990; Saber et al., 1995; Saber and El Wartiti, 1996; Ben Abbou et al., 2001; Fig. 1(A)). The predominantly red-coloured volcano-sedimentary successions are especially interesting in terms of palaeobiogeography, because the study area obviously appears to be one of the main corridors for the exchange of Late Palaeozoic biota from Laurussian (North-America, Europe, European Russia) and Gondwanan (South-America, Africa, India, Antarctica) continental realms (Broutin et al., 1998; Sidor et al., 2005; Hmich et al., 2006). The special palaeogeographic position, together with generally wellexposed strata, preordains this part of NW Africa a premier area in which to study the evolution of terrestrial ecosystems during Late Carboniferous and Permian times. Insufficient knowledge of the stratigraphic range and regional correlation of individual successions, however, still limits comparative analyses. Depositional age constraints based on palynomorphs and macrofloral remains have been proposed for some of the relevant strata (Broutin et al., 1998); additional biostratigraphic data are scarce, insofar as a significant faunistic fossil record
[(Fig._ 1)TD$FIG]
exists only for the Argana and Souss basins (e.g., Dutuit, 1988; Jalil and Dutuit, 1996; Jalil and Janvier, 2005; Hmich et al., 2005; Steyer and Jalil, 2009; Voigt et al., 2010), and to a much lesser degree for some of the smaller occurrences of PermoCarboniferous red-beds from the Moroccan Meseta (El Wartiti, 1990; Hmich et al., 2006). We present here the first comprehensive overview of recently discovered tetrapod footprints from the Khenifra Basin that not only extends the knowledge of faunal biota in the study area, but also exemplifies the region’s potential for an improved understanding of more global aspects of tetrapod phylogeny, biogeography, stratigraphy, and palaeoecology. 2. Material and methods Institutional abbreviations: CDUE: Department of Earth Science, Chouaïb Doukkali University El Jadida, Morocco; GUF: Institut für Geowissenschaften, Goethe-Universität, Frankfurt am Main, Germany; MNB: Museum für Naturkunde Berlin, Germany; MNG: Museum der Natur Gotha, Germany; VF: tetrapod footprint collection of S. Voigt, stored at the Museum der Natur Gotha, Germany. This analysis is based on 17 specimens of tetrapod footprints preserved in reddish-brown mudstone to finegrained sandstone collected in the study area from CDUE
Fig. 1. Geological framework of the Khenifra Basin. A. The study area as one of the main outcrops of Permo-Carboniferous red-beds in the central Moroccan Meseta. B. Simplified geological map and columnar section of the Late Palaeozoic strata of the Khenifra Basin showing the position of the tetrapod footprint localities: 1, Dahra hill, CDUE locality 14; 2, Ifri Ou Châou hill, clay pit dump, CDUE locality 15; 3, Ifri Ou Châou hill, western slope, CDUE locality 16; 4, Tarhat hill, CDUE locality 17. For detailed locality data, see Table 1. Geological map and columnar section adapted from Broutin et al. (1998).
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Table 1 Specifications of Permo-Carboniferous tetrapod footprint localities in the Khenifra Basin and their fossil record. CDUE locality number
Coordinates
Tetrapod ichnotaxa, CDUE collection number
14: Dahra Hill
N 32˚58’17.51’’ W 005˚39’01.52’’
Dromopus (80–82); tetrapod footprints indet. (85–86)
15: Ifri Ou Châou hill, clay pit dump
N 32˚58’57.10’’ W 005˚38’50.20’’
Batrachichnus-Limnopus (71–72); Ichniotherium (74); Dimetropus (75–79); cf. Dromopus (no material collected)
16: Ifri Ou Châou hill, western slope
N 32˚58’56.62’’ W 005˚38’52.80’’
Batrachichnus-Limnopus (73); tetrapod footprints indet. (83–84, 87)
17: Tarhat hill
N 32˚59’21.00’’ W 005˚38’38.90’’
cf. Dromopus; tetrapod footprints indet. (no material collected)
localities 14–16 in 2001 through 2004 (Hmich et al., 2006; Fig. 1(B), Table 1). During the spring of 2009, while exploring for additional fossil sites in the Khenifra Basin, another footprint locality (CDUE locality 17; Fig. 1(B), Table 1) was discovered. Because all of the collected material represents isolated tracks or incomplete segments of a step cycle, prohibiting quantification of trackway parameters, our analysis is restricted to a comparison of ichnotaxonomically significant features of the imprint morphology. For that purpose, the best preserved tracks were photographed and outlined on transparency film. Based on the record of relevant features (e.g., shape, size, and relative position of pads; width and length of the imprint; length of the digits; value of the interdigital angles), the Moroccan specimens were compared with the huge data set that is available for contemporaneous Late Palaeozoic tetrapod footprints from Europe and North America (e.g., Haubold, 1971, 1984; Gand, 1987; Lucas and Heckert, 1995; Voigt, 2005; Voigt et al., 2007). 3. Geological setting All fossils described herein come from the approximately 7 17 km large, SSW-NNE trending Khenifra Basin, the easternmost of the Late Palaeozoic basins of central Morocco, situated about 160 km SE of Rabat at the western front of the Middle Atlas (Fig. 1). The Khenifra Basin refers to a succession of red-beds about 1800 m-thick that unconformably rests on Hercynian basement (= deformed Ordovician to Early Carboniferous marine schists, quartzites, sandstones, siltstones, and limestones; Termier, 1936). El Wartiti (1990) proposed a lithostratigraphic division of the Late Palaeozoic deposits into three members of similar thickness: The lower member consists of stacked, coarse-grain dominated, fining-upward cycles whose conglomerates, sandstones, and few mudstones were probably accumulated in an alluvial-fan to alluvial-plain environment with major gradient changes; The middle member is characterised by a volumetric dominance of red and grey mudstones representing deposition on an extended floodplain with minor ponds or small lakes; Above an erosional unconformity indicating activation of the basin relief, the upper member begins with fluvial conglomerates; towards the top, fine-grained sandstones and pedogenetically overprinted mudstones become increasingly frequent.
After red-bed deposition had ceased, first rhyolithicrhyodacitic, then dacitic-andesitic magma intruded the succession to form the Permian volcanites that outcrop in the middle section of the basin and along its north-western margin (Youbi and Cabanis, 1995; Fig. 1(B)). Fossils from the Late Palaeozoic sediments of the Khenifra Basin have been described by Broutin et al. (1998) and Hmich et al. (2006). Only conifer imprints preserved in fine-grained silty sandstones are known from the lower member. Fossil remains are most abundant and diverse in the middle member, including palynomorphs and plants (17 taxa each; see Broutin et al., 1998), conchostracans, isolated tetrapod bones, Scoyenia-like invertebrate burrows, and vertebrate ichnofossils (Hmich et al., 2006). Tetrapod footprints have been found on the north-western slope of the Dahra hill (CDUE locality 14; Fig. 1(B), Table 1), as well as on the northern and western slopes of the Ifri Ou Châou hill (CDUE localities 15 and 16; Fig. 1(B), Table 1). The footprint-bearing horizons seem to be situated in the thickest sequence of mudstones, near the base of the upper half of the middle member, and are probably laterally equivalent to the fossiliferous grey levels where Broutin et al. (1998) recovered micro- and macrofloral remains. Indeterminate vertebrate tracks discovered on the southern slope of the Tarhat hill during the 2009 field season are the only fossils recorded from the upper member (CDUE locality 17; Fig. 1(B), Table 1). 4. Systematic palaeoichnology Plexus Batrachichnus Woodworth, 1900 - Limnopus Marsh, 1894 Referred specimens and locality: CDUE 71–72 (Fig. 2(A, B, E, F)), two specimens with three large manus imprints preserved as convex hyporeliefs in fine-grained sandstone, from CDUE locality 15; CDUE 73 (Fig. 2(C, D)), print and counterprint with two consecutive sets of small manus-pes tracks preserved in coarse-grained siltstone, from CDUE locality 16. Description: Tracks of quadrupedal tetrapods with tetradactyl, plantigrade manus imprints ranging from 12–80 mm in length. Manus imprints 10–30% wider than long, with digits exhibiting a serial increase in length from I to III, IV about as long as II; longest digit about half the length of the imprint. All digits are straight with blunt and somewhat thickened proximal ends. The incompletely preserved step cycle of CDUE 73 (Fig. 2(C, D)) is showing a distinctly alternating arrangement of
[(Fig._ 2)TD$FIG] 402
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Fig. 2. Fossil footprints of the plexus Batrachichnus Woodworth, 1900 – Limnopus Marsh, 1894 from the Permo-Carboniferous of the Khenifra Basin (A–F) and the Early Permian of central Germany (G, H). All photographs show tracks preserved as convex hyporeliefs. Single tracks represent manus imprints; for coupled tracks, the manus is in front of the pes imprint. Material: A, B and E, CDUE 71; C, D, CDUE 73; F, CDUE 72; G, VF 4307–4314, Oberhof Formation, Thuringian Forest Basin; H, GUF 31–11, Bleichenbach Formation, Wetterau Basin. Scale bars in cm.
coupled manus-pes imprints. Accessories such as skin imprints or tail drag marks are not recorded. Remarks: Tetradactyly of the manus imprints is the main feature of Batrachichnus Woodworth, 1900 and Limnopus Marsh, 1894. Except for size range, tracks of these ichnotaxa are quite similar (Haubold, 1996). Voigt (2005) noted a slight difference with respect to the width-length ratio of the manus imprint and the relative length of the fourth digit. However, these traits most likely characterise end-members of a continuous morphological spectrum, questioning the status of the forms as separate ichnotaxa. For isolated imprints, such as the material under study, assignation to one of these two ichnotaxa must be uncertain, because the input of extramorphological factors on the imprint morphology (= variability due to sedimentary facies and animal behaviour) can not be assessed without comparing consecutive tracks from the same individual (Haubold, 1996). Potential trackmakers are small to medium-sized anamniote tetrapods, e.g. temnospondyls and microsaurs (Haubold, 1971,
1996, 2000). Small Batrachichnus-like tracks are especially common in mudstones deposited of wet floodplain palaeoenvironments, indicating that the trackmakers spent a significant part of their life in or near bodies of standing water (Voigt, 2005). Large imprints of the plexus Batrachichnus-Limnopus exceeding 50 mm in length are usually referred to eryopoid temnospondyls (Haubold, 1973, 1984, 2000; Fichter, 1983; Gand, 1987; Voigt, 2005). Ichniotherium sphaerodactylum (Pabst, 1895) Referred specimen and locality: CDUE-74, natural cast of an incompletely preserved pes imprint (Fig. 3(A, B)); finegrained silty sandstone from CDUE locality 15. Description: Pentadactyle, plantigrade imprint showing a deeply impressed, mediolaterally expanded, oval sole-pad and well-separated digits outlined faintly by cleavage relief. Digit II is the best preserved; it is broad and sturdy, and about 40 mm in length; its straight appearance with a distally rounded and
[(Fig._ 3)TD$FIG]
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Fig. 3. Tracks of Ichniotherium sphaerodactylum (Pabst, 1895) from the Permo-Carboniferous of the Khenifra Basin (A, B) and the Early Permian of central Germany (C). The Moroccan specimen shows an incompletely preserved pes imprint; the outline drawing was produced using the scaled morphology of the pes imprint of the German specimen shown in C. Both photographs represent tracks preserved as convex hyporeliefs. Material: A–B, CDUE 74; C, MB I.058.19, Tambach Formation, Thuringian Forest Basin. Scale bars = 5 cm.
expanded termination, resembles a drumstick in outline. A decrease in relief seems evident from digits I to V. The prominent sole-pad has a mediolateral extension of about 90 mm; the proximodistal extension does not exceed 45 mm. Width of the imprint is estimated to be 110–120 mm. Remark: Although CDUE 74 is a poorly preserved fragmentary track, there is no doubt that it represents a pes imprint of Ichniotherium sphaerodactylum, one of the most characteristic Late Palaeozoic ichnotaxa due to an extensive record from its German type locality (Voigt et al., 2007). The description of the Moroccan specimen, particularly the laterally expanded sole-pad, the drumstick like digits, and the mediolateral decrease of the digit’s relief, matches the features of I. sphaerodactylum in every respect (Fig. 3(C)). Four Ichniotherium ichnospecies can be differentiated based on anatomically controlled features of the imprint morphology and trackway pattern (Haubold and Sarjeant, 1973; Voigt et al., 2007; Voigt and Ganzelewski, 2010); the distinct mediolaterally expanded, ovalshaped sole-pad represented by this specimen is unique to I. sphaerodactylum (Voigt, 2005; Voigt et al., 2007). Ichniotherium tracks are consensually referred to diadectid trackmakers, based on the abundant record of Ichniotherium tracks and diadectid skeletal remains from the Early Permian Bromacker locality in central Germany (Berman et al., 1998,
2004; Haubold, 1998; Voigt and Haubold, 2000; Voigt et al., 2007). Diadectids are the most diverse clade of Late Carboniferous to Early Permian diadectomorphs (= limnoscelids, tseajaiids, and diadectids), which are generally considered to be the sister-taxon of amniotes (e.g., Reisz, 2007). Voigt et al. (2007) demonstrated that the tracks of I. sphaerodactylum from the Bromacker locality were most likely made by Orobates Berman et al., 2004. This well-established track-trackmaker relationship, however, cannot simply be transferred to the Moroccan specimen, because for most diadectomorphs – with exception of the diadectid genera Orobates and Diadectes Cope, 1878 – the appendicular skeleton is inadequately known. Without associated skeletal remains, as it is the case for the Khenifra ichnofossil, the occurrence of I. sphaerodactlyum suggests the former presence of Orobates or any other diadectomorph sharing ichnotaxonomically relevant features of its appendicular skeleton. Dimetropus isp. indet. Romer and Price, 1940 Referred specimens and locality: CDUE 75–79 (Fig. 4), natural casts of 11, mostly indistinct imprints preserved on five slabs of silty, fine-grained sandstone from CDUE locality 15 (Fig. 1; Table 1). Though all specimens were collected as loose blocks from the damp of the Ifri Ou Châou clay pit and do not fit
[(Fig._ 4)TD$FIG] 404
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Fig. 4. Tracks of Dimetropus Romer and Price, 1940 from the Permo-Carboniferous of the Khenifra Basin (A–D) and the Early Permian of central Germany (E). The isolated tracks of the Moroccan specimens do not permit clear differentiation between manus and pes imprints; the track couple of the German specimen exhibits manus (front) and pes (back) differing in the relative length of the fifth digit. All photographs show tracks preserved as convex hyporeliefs. Material: A, B, CDUE 75; C, D, CDUE 76; E, MNG 13490, Tambach Formation, Thuringian Forest Basin. Scale bars in cm.
together exactly, the uniform size of the imprints, as well as having tail drag and raindrop marks in common, suggest that these slabs represent segments of the same surface and trackway. Description: Trackway of a quadrupedal tetrapod having pentadactyle, plantigrade footprints with manus and pes imprints similar in shape and size. Imprints are about 140– 160 mm in length; more completely preserved tracks show a proximolaterally elongated heel, making these imprints significantly longer than wide. The sole of the imprint may cover almost half the length of the entire imprint. The rather straight, distally slightly thickened imprints of the digits exhibit a serial increase in length from I to IV; Vabout as long as II in presumed manus imprints and as long as III in pes imprints. Judging from slabs with incomplete step cycles, the trackway pattern can be characterised as a more or less alternating arrangement of imprints in which a manus imprint on one side of the trackway is nearly opposite a pes footprint on the other side. Tail drag marks (CDUE 77–79) ranges in width from 40–60 mm. Remarks: The elongated heel, as described for the referred footprints from the study area, is a unique characteristic of Dimetropus Romer and Price, 1940. Assignation is additionally
supported by the shape, orientation, and proportions of the digits, as well as by the presence of a distinct tail drag mark, which is a relatively common accessory in trackways of the ichnotaxon (Haubold, 1973; Gand, 1987; Voigt, 2005). A number of ichnospecies have been introduced for Dimetropus (e.g., Geinitz, 1863; Tilton, 1931; Haubold and Sarjeant, 1973; Gand and Haubold, 1984), but none of them is actually based on anatomically-controlled features of the imprint morphology and trackway pattern (Haubold, 1996, 2000; Voigt, 2005). Because a careful taxonomic revision of Dimetropus is pending, and since the Moroccan material is only fragmentary, we prefer an assignation by open nomenclature at the ichnospecies level. At the present state of knowledge, the ichnogenus Dimetropus subsumes tracks of a wide range of Late Carboniferous and Early Permian non-therapsid synapsids, including edaphosaurids, sphenacodontids, ophiacodontids, and caseids (Haubold, 2000; Voigt, 2005; Voigt and Ganzelewski, 2010). Dromopus isp. indet. Marsh, 1894 Referred specimens and locality: CDUE 80–82 (Fig. 5), three specimens with several incomplete imprints preserved as
[(Fig._ 5)TD$FIG]
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Fig. 5. Tracks of Dromopus Marsh, 1894 from the Permo-Carboniferous of the Khenifra Basin (A, B) and the Early Permian of central Germany (C). Both photographs are showing coupled tracks preserved as convex hyporeliefs with the manus in front of the pes imprint. The outline drawing results from complementary parts of print and counterprint. Material: A-B, CDUE 80; C, MNG 13436, Oberhof Formation, Thuringian Forest Basin. Scale bars in cm.
concave epireliefs (a counterprint only was collected for CDUE 80) on red-brown mudstone from CDUE locality 16 (Fig. 1; Table 1). Elephant skin structures on the track-bearing surfaces indicate deposition in shallow pools or near-shore lacustrine environments with microbial-mat coatings. Description: Based on the track couple of CDUE 80, these specimens represent footprints of a quadrupedal tetrapod. Preservation of manus and pes is restricted to the impressions of the middle digits, which serially increase in length from II to IV; digit imprints are long and slender, distinctly curved, with interdigital angles of 25–458. Imprint size varies between 40 and 50 mm, estimated from the digit length. Remarks: CDUE 80–82 show typical lacertoid imprints with strongly curved digits. In the context of the previously described ichnotaxa from the Khenifra Basin, this description only fits the characteristics of Dromopus Marsh, 1894, which is the most common vertebrate track of Permo-Carboniferous deposits in Europe and North America (Haubold, 1971; Gand, 1987; Haubold et al., 1995; Voigt, 2005). Differentiation of Dromopus at the ichnospecies level, based on the relative distance between digits III and V, is disputed (Gand, 1987; Haubold and Lucas, 2003). Because of their incomplete preservation, the Moroccan tracks do not contribute to a resolution of this question, and ichnospecific assignation is, therefore, consistently refrained. Potential trackmakers of Dromopus are representatives of the Late Carboniferous to Early Permian araeoscelids (Haubold, 2000; Voigt, 2005). However, lacertoid pes structures that fit the discussed morphotype are also exhibited by other groups of early sauropsids such as the bolosaurids (Berman et al., 2000). 5. Stratigraphical and biogeographical implications The Late Palaeozoic red-beds of the Khenifra Basin are generally considered to be of Early Permian age (El Wartiti, 1990; Broutin et al., 1998; Hmich et al., 2006). Because the sedimentary facies, the macrofloral content, and the bimodal
405
magmatism of the Khenifra Basin in some respect resembles other occurrences of Late Palaeozoic units in the northern Moroccan Meseta and south-western Spain, Broutin et al. (1998) supposed it was part of a single large basin that – based on all available palaeontological data – developed in this area during Kungurian times. The study area, however, seems to be stratigraphically opposed to this hypothesis in that it lacks records of typical late Early Permian Ginkophytes, but instead has a rather earliest Permian microflora (Broutin et al., 1998) – two indications that the fossiliferous strata of the Khenifra Basin could be slightly older than those of the adjacent Bou Achouch and Tiddas basins. The tetrapod ichnofauna described herein has significance for Late Carboniferous to Early Permian continental deposits recorded from various localities in Europe and North America (Haubold, 1971, 1973, 2000; Gand, 1987; Haubold et al., 1995; Voigt, 2005; Lucas, 2007). The earliest occurrence of unambiguous Batrachichnus-Limnopus tracks comes from the Westphalian D (Kasimovian) of Shropshire, Great Britain (Haubold and Sarjeant, 1973; Tucker and Smith, 2004); Ichniotherium and Dimetropus are even known from the Westphalian A (Moscovian) of Germany (Voigt and Ganzelewski, 2010), whereas Dromopus probably did not appear before the Stephanian (Gzhelian), as indicated by records from Kansas, Ohio and Germany (Marsh, 1894; Haubold, 1971, 1973; Patterson, 1971; Voigt, 2005). Consequently, tetrapod footprint evidence cannot exclude deposition in the Khenifra Basin starting as early as the latest Carboniferous. The minimum age of the most important track-bearing horizon from the study area (CDUE locality 15) is late Early Permian, inasmuch as Ichniotherium tracks are not known from younger strata, and diadectomorphs – their most probable trackmakers – became extinct during the Cisuralian (Berman and Henrici, 2003; Reisz, 2007). [Passing remark: A presently unpublished, large fragmentary blattodean forewing from CDUE locality 15, which resembles an unnamed opsiomylacrid species from Stephanian deposits of Kansas and central Germany (Müller, 1975; Schneider, 1983), rather supports an age near the Carboniferous-Permian boundary for the fossiliferous horizons.] The described assemblage of tetrapod footprints is a proxy for a relatively diverse vertebrate fauna that includes small to medium-sized temnospondyls, diadectomorphs, caseid to sphenacodontid synapsids, as well as early sauropsids (araeoscelid diapsids and/or bolosaurid parareptiles). Apart from an abundant and diverse micro- and macroflora (Broutin et al., 1998), the tetrapod ichnofauna is more evidence of a welldeveloped, complex ecosystem having been established in the Khenifra Basin during Late Carboniferous/Early Permian times. Both the sedimentary facies and the fossil biota suggest sufficient precipitation from, at least, seasonal rain to ensure persistence of habitats being favourable to diverse terrestrial life. This is an interesting fact, especially with respect to the evolutionary biogeography of diadectomorphs. Our work yields the first evidence of this important group of early tetrapods from Africa, and the first record of the ichnospecies Ichniotherium sphaerodactylum (Pabst, 1895) outside of its
[(Fig._ 6)TD$FIG] 406
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Fig. 6. The global record of tracks assigned to Ichniotherium Pohlig, 1892 shown on the Late Carboniferous – Early Permian geography of central Pangaea. I. sphaerodactylum (Pabst, 1895) is known only from its central German type locality (Thuringian Forest) and the Khenifra Basin. Palaeogeographical map adapted from Roscher and Schneider (2006).
type locality – the Bromacker quarry of the Early Permian Tambach Formation in the Thuringian Forest, central Germany (Haubold, 1998; Voigt and Haubold, 2000; Voigt, 2005). Ichniotherium from the Bromacker locality is represented by two different ichnospecies, I. cottae (Pohlig, 1885) and I. sphaerodactylum (Pabst, 1895), which can be referred to two different diadectid trackmakers: Diadectes Cope, 1878 and Orobates Berman et al., 2004 (Voigt et al., 2007). Although Orobates, as one of the most basal members of the diadectid clade, must have originated in the Carboniferous (Berman et al., 2004; Reisz, 2007), there is no evidence regarding this taxon, neither as skeletal remains nor as footprints, from any place in the world other than the Tambach Formation, which is about Sakmarian to Artinskian in age (Schneider and Werneburg, 2006). Tracks assigned to I. cottae are known from many Permo-Carboniferous units of Germany that are stratigraphically below the Tambach Formation, whereas Orobates is restricted to the youngest Early Permian deposits of the Thuringian Forest area, appearing there in deposits that were accumulated after significant changes of the basin configuration (Voigt, 2005). At that time, Orobates migrated into central Europe from an unknown area of distribution, which perhaps was situated outside of what today is Europe and North America. Even if we do not presently know the exact stratigraphic age of the Khenifra tetrapod ichnofauna, and cannot be sure that the Moroccan I. sphaerodactylum actually refers to Orobates, the occurrence of this ichnotaxon is the first valuable evidence of where to search for other populations of diadectomorphs with an Orobates-like anatomy of the appendicular skeleton (Fig. 6). 6. Conclusions Here we present the first comprehensive overview on the tetrapod ichnofauna of the Late Palaeozoic Khenifra Basin. From the middle section of the up to 1800 m-thick, red-bed succession of the study area, four main morphs of tetrapod
footprints have been recorded. With tracks of BatrachichnusLimnopus, Ichniotherium, Dimetropus, and Dromopus, which can be referred to temnospondyl, diadectomorph, early synapsid and sauropsid trackmakers, this record parallels a set of well-known Late Carboniferous to Early Permian footprint assemblages from Europe and North America. The occurrence of Ichniotherium supports a minimum age of Early Permian for the track-bearing horizons of the Khenifra Basin, which agrees with radiometric ages for the overlaying volcanites (Jebrak, 1982). With respect to the relatively high diversity of the described footprint assemblage, we state that the study area, at least temporarily, provided favourable conditions for complex terrestrial life during Permo-Carboniferous times. Wellestablished palaeoecosystems in this region might have played a pivotal role in the evolution of early tetrapods, as indicated by the first evidence for a rare type of diadectomorph outside of its central European type locality. Further exploration for both tetrapod ichno- and body fossils is strongly recommended in the Khenifra Basin, as well as in related localities in Africa and around the world. Acknowledgements This research was supported by a grant from the German Science Foundation (DFG SCHN 408/17-1). D. Hmich and A. Hminna participated in fieldwork through the financial support of the German Academic Exchange Service. We thank Marco Avanzini and Spencer G. Lucas for constructive reviews, and Robert Sproule of Plymouth, Massachusetts for linguistic assistance. References Ben Abbou, M., Soula, J.C., Brusset, S., Roddaz, M., N’Tarmouchant, A., Driouch, Y., Christophoul, F., Bouadbelli, M., Majesté-Menjoulas, C., Béziat, D., Déramond, J., 2001. Contrôle tectonique de la sédimentation dans le système de bassins d’avant-pays de la Meseta marocaine. Comptes Rendus de l’Académie des Sciences de Paris 332, 703–709. Berman, D.S., Henrici, A.C., 2003. Homology of the astragalus and structure and function of the tarsus of Diadectidae. Journal of Paleontology 77, 172–188. Berman, D.S., Henrici, A.C., Kissel, R.A., Sumida, S.S., Martens, T., 2004. A new diadectid (Diadectomorpha), Orobates pabsti, from the Early Permian of central Germany. Bulletin of Carnegie Museum 35, 1–36. Berman, D.S., Reisz, R.R., Scott, D., Henrici, A.C., Sumida, S.S., Martens, T., 2000. Early Permian bipedal reptile. Science 290, 969–972. Berman, D.S., Sumida, S.S., Martens, T., 1998. Diadectes (Diadectomorpha, Diadectidae) from the Early Permian of central Germany, with description of a new species. Annals of Carnegie Museum 67, 53–93. Broutin, J., Aassoumi, H., El Wartiti, M., Freytet, P., Kerp, H., Quesada, C., Toutin-Morin, N., 1998. The Permian Basins of Tiddas, Bou Achouch and Khenifra (central Morocco). Biostratigraphic and palaeophytogeographic implications. Mémoires du Muséum National d’Histoire Naturelle 179, 257–278. Cope, E., 1878. Descriptions of extinct Batrachia and Reptilia from the Permian formation of Texas. American Philosophical Society 17, 505–530. Dutuit, J.-M., 1988. Diplocaulus minimus n. sp. (Amphibia: Nectridea), Lépospondyle de la Formation d’Argana, dans l’Atlas marocain. Comptes Rendus de l’Académie des Sciences de Paris 307, 851–854.
S. Voigt et al. / Geobios 44 (2011) 399–407 El Wartiti, M., 1990. Le Permien du Maroc mésétien: Étude géologique et implications paléogéographiques. Thèse d’État, Université Mohamed V, Rabat (unpublished). El Wartiti, M., Broutin, J., Freytet, P., Lahrhib, M., Toutin-Morin, N., 1990. Continental deposits in Permian Basins of the Mesetian Morocco, geodynamic history. Journal of African Earth Sciences 10, 361–368. Fichter, J., 1983. Tetrapodenfährten aus dem saarpfälzischen Rotliegenden (?Ober-Karbon - Unter-Perm; SW-Deutschland). 1. Die Fährten der Gattungen Saurichnites, Limnopus, Amphisauroides Protritonichnites, Gilmoreichnus, Hyloidichnus und Jacobiichnus. Mainzer geowissenschaftliche Mitteilungen 12, 9–121. Gand, G., 1987. Les traces de vertébrés tétrapodes du Permien français. Thèse de Doctorat d’État, Université de Bourgogne, Dijon (unpublished). Gand, G., Haubold, H., 1984. Traces de vertébrés tétrapodes du Permien du bassin de Saint-Affrique (Description, datation, comparaison avec celles du bassin de Lodève). Revue de Géologie Méditerranéenne 11, 321–348. Geinitz, H.B., 1863. Beiträge zur Kenntnis der organischen Überreste in der Dyas. Neues Jahrbuch für Mineralogie. Geologie und Paläontologie 1863, 385–398. Haubold, H., 1971. Ichnia Amphibiorum et Reptiliorum fossilium. Encyclopedia of Palaeoherpetology 18, 1–124. Haubold, H., 1973. Die Tetrapodenfährten aus dem Perm Europas. Freiberger Forschungshefte C285, 5–55. Haubold, H., 1984. Saurierfährten. Ziemsen-Verlag, Wittenberg. Haubold, H., 1996. Ichnotaxonomie und Klassifikation von Tetrapodenfährten aus dem Perm. Hallesches Jahrbuch für Geowissenschaften B 18, 23–88. Haubold, H., 1998. The Early Permian tetrapod ichnofauna of Tambach, the changing concepts in ichnotaxonomy. Hallesches Jahrbuch für Geowissenschaften B20, 1–16. Haubold, H., 2000. Tetrapodenfährten aus dem Perm – Kenntnisstand und Progress 2000. Hallesches Jahrbuch für Geowissenschaften B22, 1–16. Haubold, H., Hunt, A.P., Lucas, S.G., Lockley, M.G., 1995. Wolfcampian (Early Permian) vertebrate tracks from Arizona and New Mexico. New Mexico Museum of Natural History and Science Bulletin 6, 135–165. Haubold, H., Lucas, S.G., 2003. Tetrapod footprints of the Lower Permian Choza Formation at Castle Peak, Texas. Paläontologische Zeitschrift 77, 247–261. Haubold, H., Sarjeant, W.A.S., 1973. Tetrapodenfährten aus den Keele und Enville Groups (Permokarbon: Stefan und Autun) von Shropshire und South Staffordshire, Großbritannien. Zeitschrift für Geologische Wissenschaften 1, 895–933. Hmich, D., Schneider, J.W., Saber, H., El Wartiti, M., 2005. Spiloblattinidae (Insecta, Blattida) from the Carboniferous of Morocco, North Africa – implications for biostratigraphy. New Mexico Museum of Natural History and Science Bulletin 30, 111–114. Hmich, D., Schneider, J.W., Saber, H., Voigt, S., El Wartiti, M., 2006. New continental Carboniferous and Permian faunas of Morocco – implications for biostratigraphy, palaeobiogeography and palaeoclimate. Geological Society, London, Special Publications 265, 297–324. Jalil, N.E., Dutuit, J.M., 1996. Permian Captorhinid reptiles from the Argana Formation, Morocco. Palaeontology 39, 907–918. Jalil, N.-E., Janvier, P., 2005. Les pareiasaures (Amniota, Parareptilia) du Permien supérieur du Bassin d’Argana, Maroc. Geodiversitas 27, 35–132. Jebrak, M., 1982. Les districts à fluorine du Maroc central. Bulletin du BRGM 2, 211–221. Lucas, S.G., 2007. Tetrapod footprint biostratigraphy and biochronology. Ichnos 14, 5–38. Lucas, S.G., Heckert, A.B. (Eds.), 1995. Permian footprints and facies. New Mexico Museum of Natural History and Science Bulletin 6, 1–300. Marsh, O.C., 1894. Footprints of vertebrates in the Coal Measures of Kansas. American Journal of Science 48, 81–84. Müller, A.H., 1975. Zur Entomofauna des Permokarbon: 1. Mylacridae (Blattodea) aus dem Unterrotliegenden (Unterperm, Autun) von Thüringen. Zeitschrift für Geologische Wissenschaften 3, 621–641. Pabst, W., 1895. Thierfährten aus dem Rothliegenden von Friedrichroda, Tambach und Kabarz in Thüringen. Zeitschrift der Deutschen Geologischen Gesellschaft 47, 570–576.
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Original article
Late Carboniferous-Early Permian Tetrapod Ichnofauna from the Khenifra Basin, Central Morocco§ La palichnofaune de vertébrés tétrapodes du Carbonifère supérieur-Permien inferieur du Bassin de Khenifra, Maroc central Sebastian Voigt a,*, Hafid Saber b, Jörg W. Schneider a, Driss Hmich b, Abdelkbir Hminna b a
Geological Institute, TU Bergakademie Freiberg, B.-v.-Cotta-Str. 2, 09596 Freiberg, Germany b Department of Geology, Chouaïb Doukkali University, B.P. 20, 24000 El Jadida, Morocco Received 5 January 2010; accepted 30 November 2010 Available online 29 April 2011
Abstract In terms of cumulative thickness and areal extent, the Khenifra Basin is one of the most important outcrops of Late Palaeozoic red-beds in central Morocco. Macro- and microfloral remains near the centre of the 1800 m-thick succession of interbedded conglomerates, sandstones, and mudstones are considered to be of middle to late Early Permian age. Here we give the first comprehensive analysis of the vertebrate ichnofossil record from the study area, based on 17 specimens of isolated footprints and incomplete step cycles collected at three localities that are lithostratigraphically equivalent to the plant-bearing horizons. The tetrapod ichnofauna comprises tracks of the plexus Batrachichnus Woodworth – Limnopus Marsh, Ichniotherium sphaerodactylum (Pabst), Dimetropus Romer and Price, and Dromopus Marsh which can be referred to temnospondyl, diadectomorph, synapsid (‘‘pelycosaurian’’) and early sauropsid trackmakers. This clearly Euramerican footprint assemblage, including the first occurrences of Ichniotherium and Dimetropus from outside Europe and North America, indicates a Late Carboniferous to Early Permian age of the fossiliferous strata. Judging from the relatively diverse ichnofauna and flora, the Khenifra Basin must have represented a wellestablished terrestrial ecosystem during that period. Its habitat could be specially important for the understanding of the phylogeny and dispersal of early tetrapods, inasmuch as we are able to report on an extremely rare type of diadectomorph footprint hitherto known only from the Early Permian of central Germany. # 2011 Elsevier Masson SAS. All rights reserved. Keywords: Vertebrate tracks; Early tetrapods; Biostratigraphy; Biogeography; Late Palaeozoic; NW Africa
Résumé Du point de vu de l’épaisseur des sédiments et de leur extension géographique, le bassin de Khénifra est l’un des plus importants affleurements de terrains rouges du paléozoïque supérieur dans le Maroc central. Les restes de macro- et microflores provenant du milieu de la série, d’environ 1800 m d’épaisseur, formée essentiellement de niveaux interstratifiés de conglomérats, de grès et d’argiles ont donné un âge permien inférieur moyen à tardif. Nous présentons dans ce travail une première analyse des ichnofossiles de vertébrés de la zone d’étude, basée sur 17 spécimens de traces isolées, recueillis dans trois localités lithostratigraphiquement équivalentes aux niveaux où ont été découverts les paléoflores. Les ichnofaunes des tétrapodes comprennent des empreintes de pas de plexus Batrachichnus Woodworth – Limnopus Marsh, Ichniotherium sphaerodactylum (Pabst), Dimetropus Romer et Price et Dromopus Marsh qui peuvent être attribuées à des temnospondyles, diadectomorphes, synapsides (« pelycosauriens ») et sauropsides primitifs. Cet assemblage de traces de pattes est clairement euraméricain, incluant les premières occurrences d’Ichniotherium et Dimetropus hors d’Europe et d’Amérique du Nord et indiquant un âge Carbonifère supérieur à Permien inférieur pour ces couches fossilifères du bassin de Khénifra. D’après ces ichnofaunes et paléoflores relativement diverses, le basin de Khénifra a du représenter un écosystème terrestre bien établi au cours de cette période. Son habitat pourrait être d’une importance particulière pour
§
Corresponding editor: Davide Olivero. * Corresponding author. E-mail address: [email protected] (S. Voigt).
0016-6995/$ – see front matter # 2011 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.geobios.2010.11.008
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la compréhension de la phylogénie et la dispersion des premiers tétrapodes, d’autant plus qu’un type extrêmement rare d’empreinte de pas de diadectomorphe, jusqu’ici connu seulement dans le Permien inférieur d’Allemagne centrale y est observé. # 2011 Elsevier Masson SAS. Tous droits réservés. Mots clés : Traces de pattes de vertébrés ; Premiers tétrapodes ; Biostratigraphie ; Biogéographie ; Paléozoïque supérieur ; Afrique nord-occidentale
1. Introduction Permo-Carboniferous rocks of central Morocco are preserved in a number of small, isolated basins that originated as NNE-SSW oriented, graben-like structures during the late phase of the Hercynian orogeny (El Wartiti et al., 1990; Saber et al., 1995; Saber and El Wartiti, 1996; Ben Abbou et al., 2001; Fig. 1(A)). The predominantly red-coloured volcano-sedimentary successions are especially interesting in terms of palaeobiogeography, because the study area obviously appears to be one of the main corridors for the exchange of Late Palaeozoic biota from Laurussian (North-America, Europe, European Russia) and Gondwanan (South-America, Africa, India, Antarctica) continental realms (Broutin et al., 1998; Sidor et al., 2005; Hmich et al., 2006). The special palaeogeographic position, together with generally wellexposed strata, preordains this part of NW Africa a premier area in which to study the evolution of terrestrial ecosystems during Late Carboniferous and Permian times. Insufficient knowledge of the stratigraphic range and regional correlation of individual successions, however, still limits comparative analyses. Depositional age constraints based on palynomorphs and macrofloral remains have been proposed for some of the relevant strata (Broutin et al., 1998); additional biostratigraphic data are scarce, insofar as a significant faunistic fossil record
[(Fig._ 1)TD$FIG]
exists only for the Argana and Souss basins (e.g., Dutuit, 1988; Jalil and Dutuit, 1996; Jalil and Janvier, 2005; Hmich et al., 2005; Steyer and Jalil, 2009; Voigt et al., 2010), and to a much lesser degree for some of the smaller occurrences of PermoCarboniferous red-beds from the Moroccan Meseta (El Wartiti, 1990; Hmich et al., 2006). We present here the first comprehensive overview of recently discovered tetrapod footprints from the Khenifra Basin that not only extends the knowledge of faunal biota in the study area, but also exemplifies the region’s potential for an improved understanding of more global aspects of tetrapod phylogeny, biogeography, stratigraphy, and palaeoecology. 2. Material and methods Institutional abbreviations: CDUE: Department of Earth Science, Chouaïb Doukkali University El Jadida, Morocco; GUF: Institut für Geowissenschaften, Goethe-Universität, Frankfurt am Main, Germany; MNB: Museum für Naturkunde Berlin, Germany; MNG: Museum der Natur Gotha, Germany; VF: tetrapod footprint collection of S. Voigt, stored at the Museum der Natur Gotha, Germany. This analysis is based on 17 specimens of tetrapod footprints preserved in reddish-brown mudstone to finegrained sandstone collected in the study area from CDUE
Fig. 1. Geological framework of the Khenifra Basin. A. The study area as one of the main outcrops of Permo-Carboniferous red-beds in the central Moroccan Meseta. B. Simplified geological map and columnar section of the Late Palaeozoic strata of the Khenifra Basin showing the position of the tetrapod footprint localities: 1, Dahra hill, CDUE locality 14; 2, Ifri Ou Châou hill, clay pit dump, CDUE locality 15; 3, Ifri Ou Châou hill, western slope, CDUE locality 16; 4, Tarhat hill, CDUE locality 17. For detailed locality data, see Table 1. Geological map and columnar section adapted from Broutin et al. (1998).
S. Voigt et al. / Geobios 44 (2011) 399–407
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Table 1 Specifications of Permo-Carboniferous tetrapod footprint localities in the Khenifra Basin and their fossil record. CDUE locality number
Coordinates
Tetrapod ichnotaxa, CDUE collection number
14: Dahra Hill
N 32˚58’17.51’’ W 005˚39’01.52’’
Dromopus (80–82); tetrapod footprints indet. (85–86)
15: Ifri Ou Châou hill, clay pit dump
N 32˚58’57.10’’ W 005˚38’50.20’’
Batrachichnus-Limnopus (71–72); Ichniotherium (74); Dimetropus (75–79); cf. Dromopus (no material collected)
16: Ifri Ou Châou hill, western slope
N 32˚58’56.62’’ W 005˚38’52.80’’
Batrachichnus-Limnopus (73); tetrapod footprints indet. (83–84, 87)
17: Tarhat hill
N 32˚59’21.00’’ W 005˚38’38.90’’
cf. Dromopus; tetrapod footprints indet. (no material collected)
localities 14–16 in 2001 through 2004 (Hmich et al., 2006; Fig. 1(B), Table 1). During the spring of 2009, while exploring for additional fossil sites in the Khenifra Basin, another footprint locality (CDUE locality 17; Fig. 1(B), Table 1) was discovered. Because all of the collected material represents isolated tracks or incomplete segments of a step cycle, prohibiting quantification of trackway parameters, our analysis is restricted to a comparison of ichnotaxonomically significant features of the imprint morphology. For that purpose, the best preserved tracks were photographed and outlined on transparency film. Based on the record of relevant features (e.g., shape, size, and relative position of pads; width and length of the imprint; length of the digits; value of the interdigital angles), the Moroccan specimens were compared with the huge data set that is available for contemporaneous Late Palaeozoic tetrapod footprints from Europe and North America (e.g., Haubold, 1971, 1984; Gand, 1987; Lucas and Heckert, 1995; Voigt, 2005; Voigt et al., 2007). 3. Geological setting All fossils described herein come from the approximately 7 17 km large, SSW-NNE trending Khenifra Basin, the easternmost of the Late Palaeozoic basins of central Morocco, situated about 160 km SE of Rabat at the western front of the Middle Atlas (Fig. 1). The Khenifra Basin refers to a succession of red-beds about 1800 m-thick that unconformably rests on Hercynian basement (= deformed Ordovician to Early Carboniferous marine schists, quartzites, sandstones, siltstones, and limestones; Termier, 1936). El Wartiti (1990) proposed a lithostratigraphic division of the Late Palaeozoic deposits into three members of similar thickness: The lower member consists of stacked, coarse-grain dominated, fining-upward cycles whose conglomerates, sandstones, and few mudstones were probably accumulated in an alluvial-fan to alluvial-plain environment with major gradient changes; The middle member is characterised by a volumetric dominance of red and grey mudstones representing deposition on an extended floodplain with minor ponds or small lakes; Above an erosional unconformity indicating activation of the basin relief, the upper member begins with fluvial conglomerates; towards the top, fine-grained sandstones and pedogenetically overprinted mudstones become increasingly frequent.
After red-bed deposition had ceased, first rhyolithicrhyodacitic, then dacitic-andesitic magma intruded the succession to form the Permian volcanites that outcrop in the middle section of the basin and along its north-western margin (Youbi and Cabanis, 1995; Fig. 1(B)). Fossils from the Late Palaeozoic sediments of the Khenifra Basin have been described by Broutin et al. (1998) and Hmich et al. (2006). Only conifer imprints preserved in fine-grained silty sandstones are known from the lower member. Fossil remains are most abundant and diverse in the middle member, including palynomorphs and plants (17 taxa each; see Broutin et al., 1998), conchostracans, isolated tetrapod bones, Scoyenia-like invertebrate burrows, and vertebrate ichnofossils (Hmich et al., 2006). Tetrapod footprints have been found on the north-western slope of the Dahra hill (CDUE locality 14; Fig. 1(B), Table 1), as well as on the northern and western slopes of the Ifri Ou Châou hill (CDUE localities 15 and 16; Fig. 1(B), Table 1). The footprint-bearing horizons seem to be situated in the thickest sequence of mudstones, near the base of the upper half of the middle member, and are probably laterally equivalent to the fossiliferous grey levels where Broutin et al. (1998) recovered micro- and macrofloral remains. Indeterminate vertebrate tracks discovered on the southern slope of the Tarhat hill during the 2009 field season are the only fossils recorded from the upper member (CDUE locality 17; Fig. 1(B), Table 1). 4. Systematic palaeoichnology Plexus Batrachichnus Woodworth, 1900 - Limnopus Marsh, 1894 Referred specimens and locality: CDUE 71–72 (Fig. 2(A, B, E, F)), two specimens with three large manus imprints preserved as convex hyporeliefs in fine-grained sandstone, from CDUE locality 15; CDUE 73 (Fig. 2(C, D)), print and counterprint with two consecutive sets of small manus-pes tracks preserved in coarse-grained siltstone, from CDUE locality 16. Description: Tracks of quadrupedal tetrapods with tetradactyl, plantigrade manus imprints ranging from 12–80 mm in length. Manus imprints 10–30% wider than long, with digits exhibiting a serial increase in length from I to III, IV about as long as II; longest digit about half the length of the imprint. All digits are straight with blunt and somewhat thickened proximal ends. The incompletely preserved step cycle of CDUE 73 (Fig. 2(C, D)) is showing a distinctly alternating arrangement of
[(Fig._ 2)TD$FIG] 402
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Fig. 2. Fossil footprints of the plexus Batrachichnus Woodworth, 1900 – Limnopus Marsh, 1894 from the Permo-Carboniferous of the Khenifra Basin (A–F) and the Early Permian of central Germany (G, H). All photographs show tracks preserved as convex hyporeliefs. Single tracks represent manus imprints; for coupled tracks, the manus is in front of the pes imprint. Material: A, B and E, CDUE 71; C, D, CDUE 73; F, CDUE 72; G, VF 4307–4314, Oberhof Formation, Thuringian Forest Basin; H, GUF 31–11, Bleichenbach Formation, Wetterau Basin. Scale bars in cm.
coupled manus-pes imprints. Accessories such as skin imprints or tail drag marks are not recorded. Remarks: Tetradactyly of the manus imprints is the main feature of Batrachichnus Woodworth, 1900 and Limnopus Marsh, 1894. Except for size range, tracks of these ichnotaxa are quite similar (Haubold, 1996). Voigt (2005) noted a slight difference with respect to the width-length ratio of the manus imprint and the relative length of the fourth digit. However, these traits most likely characterise end-members of a continuous morphological spectrum, questioning the status of the forms as separate ichnotaxa. For isolated imprints, such as the material under study, assignation to one of these two ichnotaxa must be uncertain, because the input of extramorphological factors on the imprint morphology (= variability due to sedimentary facies and animal behaviour) can not be assessed without comparing consecutive tracks from the same individual (Haubold, 1996). Potential trackmakers are small to medium-sized anamniote tetrapods, e.g. temnospondyls and microsaurs (Haubold, 1971,
1996, 2000). Small Batrachichnus-like tracks are especially common in mudstones deposited of wet floodplain palaeoenvironments, indicating that the trackmakers spent a significant part of their life in or near bodies of standing water (Voigt, 2005). Large imprints of the plexus Batrachichnus-Limnopus exceeding 50 mm in length are usually referred to eryopoid temnospondyls (Haubold, 1973, 1984, 2000; Fichter, 1983; Gand, 1987; Voigt, 2005). Ichniotherium sphaerodactylum (Pabst, 1895) Referred specimen and locality: CDUE-74, natural cast of an incompletely preserved pes imprint (Fig. 3(A, B)); finegrained silty sandstone from CDUE locality 15. Description: Pentadactyle, plantigrade imprint showing a deeply impressed, mediolaterally expanded, oval sole-pad and well-separated digits outlined faintly by cleavage relief. Digit II is the best preserved; it is broad and sturdy, and about 40 mm in length; its straight appearance with a distally rounded and
[(Fig._ 3)TD$FIG]
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403
Fig. 3. Tracks of Ichniotherium sphaerodactylum (Pabst, 1895) from the Permo-Carboniferous of the Khenifra Basin (A, B) and the Early Permian of central Germany (C). The Moroccan specimen shows an incompletely preserved pes imprint; the outline drawing was produced using the scaled morphology of the pes imprint of the German specimen shown in C. Both photographs represent tracks preserved as convex hyporeliefs. Material: A–B, CDUE 74; C, MB I.058.19, Tambach Formation, Thuringian Forest Basin. Scale bars = 5 cm.
expanded termination, resembles a drumstick in outline. A decrease in relief seems evident from digits I to V. The prominent sole-pad has a mediolateral extension of about 90 mm; the proximodistal extension does not exceed 45 mm. Width of the imprint is estimated to be 110–120 mm. Remark: Although CDUE 74 is a poorly preserved fragmentary track, there is no doubt that it represents a pes imprint of Ichniotherium sphaerodactylum, one of the most characteristic Late Palaeozoic ichnotaxa due to an extensive record from its German type locality (Voigt et al., 2007). The description of the Moroccan specimen, particularly the laterally expanded sole-pad, the drumstick like digits, and the mediolateral decrease of the digit’s relief, matches the features of I. sphaerodactylum in every respect (Fig. 3(C)). Four Ichniotherium ichnospecies can be differentiated based on anatomically controlled features of the imprint morphology and trackway pattern (Haubold and Sarjeant, 1973; Voigt et al., 2007; Voigt and Ganzelewski, 2010); the distinct mediolaterally expanded, ovalshaped sole-pad represented by this specimen is unique to I. sphaerodactylum (Voigt, 2005; Voigt et al., 2007). Ichniotherium tracks are consensually referred to diadectid trackmakers, based on the abundant record of Ichniotherium tracks and diadectid skeletal remains from the Early Permian Bromacker locality in central Germany (Berman et al., 1998,
2004; Haubold, 1998; Voigt and Haubold, 2000; Voigt et al., 2007). Diadectids are the most diverse clade of Late Carboniferous to Early Permian diadectomorphs (= limnoscelids, tseajaiids, and diadectids), which are generally considered to be the sister-taxon of amniotes (e.g., Reisz, 2007). Voigt et al. (2007) demonstrated that the tracks of I. sphaerodactylum from the Bromacker locality were most likely made by Orobates Berman et al., 2004. This well-established track-trackmaker relationship, however, cannot simply be transferred to the Moroccan specimen, because for most diadectomorphs – with exception of the diadectid genera Orobates and Diadectes Cope, 1878 – the appendicular skeleton is inadequately known. Without associated skeletal remains, as it is the case for the Khenifra ichnofossil, the occurrence of I. sphaerodactlyum suggests the former presence of Orobates or any other diadectomorph sharing ichnotaxonomically relevant features of its appendicular skeleton. Dimetropus isp. indet. Romer and Price, 1940 Referred specimens and locality: CDUE 75–79 (Fig. 4), natural casts of 11, mostly indistinct imprints preserved on five slabs of silty, fine-grained sandstone from CDUE locality 15 (Fig. 1; Table 1). Though all specimens were collected as loose blocks from the damp of the Ifri Ou Châou clay pit and do not fit
[(Fig._ 4)TD$FIG] 404
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Fig. 4. Tracks of Dimetropus Romer and Price, 1940 from the Permo-Carboniferous of the Khenifra Basin (A–D) and the Early Permian of central Germany (E). The isolated tracks of the Moroccan specimens do not permit clear differentiation between manus and pes imprints; the track couple of the German specimen exhibits manus (front) and pes (back) differing in the relative length of the fifth digit. All photographs show tracks preserved as convex hyporeliefs. Material: A, B, CDUE 75; C, D, CDUE 76; E, MNG 13490, Tambach Formation, Thuringian Forest Basin. Scale bars in cm.
together exactly, the uniform size of the imprints, as well as having tail drag and raindrop marks in common, suggest that these slabs represent segments of the same surface and trackway. Description: Trackway of a quadrupedal tetrapod having pentadactyle, plantigrade footprints with manus and pes imprints similar in shape and size. Imprints are about 140– 160 mm in length; more completely preserved tracks show a proximolaterally elongated heel, making these imprints significantly longer than wide. The sole of the imprint may cover almost half the length of the entire imprint. The rather straight, distally slightly thickened imprints of the digits exhibit a serial increase in length from I to IV; Vabout as long as II in presumed manus imprints and as long as III in pes imprints. Judging from slabs with incomplete step cycles, the trackway pattern can be characterised as a more or less alternating arrangement of imprints in which a manus imprint on one side of the trackway is nearly opposite a pes footprint on the other side. Tail drag marks (CDUE 77–79) ranges in width from 40–60 mm. Remarks: The elongated heel, as described for the referred footprints from the study area, is a unique characteristic of Dimetropus Romer and Price, 1940. Assignation is additionally
supported by the shape, orientation, and proportions of the digits, as well as by the presence of a distinct tail drag mark, which is a relatively common accessory in trackways of the ichnotaxon (Haubold, 1973; Gand, 1987; Voigt, 2005). A number of ichnospecies have been introduced for Dimetropus (e.g., Geinitz, 1863; Tilton, 1931; Haubold and Sarjeant, 1973; Gand and Haubold, 1984), but none of them is actually based on anatomically-controlled features of the imprint morphology and trackway pattern (Haubold, 1996, 2000; Voigt, 2005). Because a careful taxonomic revision of Dimetropus is pending, and since the Moroccan material is only fragmentary, we prefer an assignation by open nomenclature at the ichnospecies level. At the present state of knowledge, the ichnogenus Dimetropus subsumes tracks of a wide range of Late Carboniferous and Early Permian non-therapsid synapsids, including edaphosaurids, sphenacodontids, ophiacodontids, and caseids (Haubold, 2000; Voigt, 2005; Voigt and Ganzelewski, 2010). Dromopus isp. indet. Marsh, 1894 Referred specimens and locality: CDUE 80–82 (Fig. 5), three specimens with several incomplete imprints preserved as
[(Fig._ 5)TD$FIG]
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Fig. 5. Tracks of Dromopus Marsh, 1894 from the Permo-Carboniferous of the Khenifra Basin (A, B) and the Early Permian of central Germany (C). Both photographs are showing coupled tracks preserved as convex hyporeliefs with the manus in front of the pes imprint. The outline drawing results from complementary parts of print and counterprint. Material: A-B, CDUE 80; C, MNG 13436, Oberhof Formation, Thuringian Forest Basin. Scale bars in cm.
concave epireliefs (a counterprint only was collected for CDUE 80) on red-brown mudstone from CDUE locality 16 (Fig. 1; Table 1). Elephant skin structures on the track-bearing surfaces indicate deposition in shallow pools or near-shore lacustrine environments with microbial-mat coatings. Description: Based on the track couple of CDUE 80, these specimens represent footprints of a quadrupedal tetrapod. Preservation of manus and pes is restricted to the impressions of the middle digits, which serially increase in length from II to IV; digit imprints are long and slender, distinctly curved, with interdigital angles of 25–458. Imprint size varies between 40 and 50 mm, estimated from the digit length. Remarks: CDUE 80–82 show typical lacertoid imprints with strongly curved digits. In the context of the previously described ichnotaxa from the Khenifra Basin, this description only fits the characteristics of Dromopus Marsh, 1894, which is the most common vertebrate track of Permo-Carboniferous deposits in Europe and North America (Haubold, 1971; Gand, 1987; Haubold et al., 1995; Voigt, 2005). Differentiation of Dromopus at the ichnospecies level, based on the relative distance between digits III and V, is disputed (Gand, 1987; Haubold and Lucas, 2003). Because of their incomplete preservation, the Moroccan tracks do not contribute to a resolution of this question, and ichnospecific assignation is, therefore, consistently refrained. Potential trackmakers of Dromopus are representatives of the Late Carboniferous to Early Permian araeoscelids (Haubold, 2000; Voigt, 2005). However, lacertoid pes structures that fit the discussed morphotype are also exhibited by other groups of early sauropsids such as the bolosaurids (Berman et al., 2000). 5. Stratigraphical and biogeographical implications The Late Palaeozoic red-beds of the Khenifra Basin are generally considered to be of Early Permian age (El Wartiti, 1990; Broutin et al., 1998; Hmich et al., 2006). Because the sedimentary facies, the macrofloral content, and the bimodal
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magmatism of the Khenifra Basin in some respect resembles other occurrences of Late Palaeozoic units in the northern Moroccan Meseta and south-western Spain, Broutin et al. (1998) supposed it was part of a single large basin that – based on all available palaeontological data – developed in this area during Kungurian times. The study area, however, seems to be stratigraphically opposed to this hypothesis in that it lacks records of typical late Early Permian Ginkophytes, but instead has a rather earliest Permian microflora (Broutin et al., 1998) – two indications that the fossiliferous strata of the Khenifra Basin could be slightly older than those of the adjacent Bou Achouch and Tiddas basins. The tetrapod ichnofauna described herein has significance for Late Carboniferous to Early Permian continental deposits recorded from various localities in Europe and North America (Haubold, 1971, 1973, 2000; Gand, 1987; Haubold et al., 1995; Voigt, 2005; Lucas, 2007). The earliest occurrence of unambiguous Batrachichnus-Limnopus tracks comes from the Westphalian D (Kasimovian) of Shropshire, Great Britain (Haubold and Sarjeant, 1973; Tucker and Smith, 2004); Ichniotherium and Dimetropus are even known from the Westphalian A (Moscovian) of Germany (Voigt and Ganzelewski, 2010), whereas Dromopus probably did not appear before the Stephanian (Gzhelian), as indicated by records from Kansas, Ohio and Germany (Marsh, 1894; Haubold, 1971, 1973; Patterson, 1971; Voigt, 2005). Consequently, tetrapod footprint evidence cannot exclude deposition in the Khenifra Basin starting as early as the latest Carboniferous. The minimum age of the most important track-bearing horizon from the study area (CDUE locality 15) is late Early Permian, inasmuch as Ichniotherium tracks are not known from younger strata, and diadectomorphs – their most probable trackmakers – became extinct during the Cisuralian (Berman and Henrici, 2003; Reisz, 2007). [Passing remark: A presently unpublished, large fragmentary blattodean forewing from CDUE locality 15, which resembles an unnamed opsiomylacrid species from Stephanian deposits of Kansas and central Germany (Müller, 1975; Schneider, 1983), rather supports an age near the Carboniferous-Permian boundary for the fossiliferous horizons.] The described assemblage of tetrapod footprints is a proxy for a relatively diverse vertebrate fauna that includes small to medium-sized temnospondyls, diadectomorphs, caseid to sphenacodontid synapsids, as well as early sauropsids (araeoscelid diapsids and/or bolosaurid parareptiles). Apart from an abundant and diverse micro- and macroflora (Broutin et al., 1998), the tetrapod ichnofauna is more evidence of a welldeveloped, complex ecosystem having been established in the Khenifra Basin during Late Carboniferous/Early Permian times. Both the sedimentary facies and the fossil biota suggest sufficient precipitation from, at least, seasonal rain to ensure persistence of habitats being favourable to diverse terrestrial life. This is an interesting fact, especially with respect to the evolutionary biogeography of diadectomorphs. Our work yields the first evidence of this important group of early tetrapods from Africa, and the first record of the ichnospecies Ichniotherium sphaerodactylum (Pabst, 1895) outside of its
[(Fig._ 6)TD$FIG] 406
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Fig. 6. The global record of tracks assigned to Ichniotherium Pohlig, 1892 shown on the Late Carboniferous – Early Permian geography of central Pangaea. I. sphaerodactylum (Pabst, 1895) is known only from its central German type locality (Thuringian Forest) and the Khenifra Basin. Palaeogeographical map adapted from Roscher and Schneider (2006).
type locality – the Bromacker quarry of the Early Permian Tambach Formation in the Thuringian Forest, central Germany (Haubold, 1998; Voigt and Haubold, 2000; Voigt, 2005). Ichniotherium from the Bromacker locality is represented by two different ichnospecies, I. cottae (Pohlig, 1885) and I. sphaerodactylum (Pabst, 1895), which can be referred to two different diadectid trackmakers: Diadectes Cope, 1878 and Orobates Berman et al., 2004 (Voigt et al., 2007). Although Orobates, as one of the most basal members of the diadectid clade, must have originated in the Carboniferous (Berman et al., 2004; Reisz, 2007), there is no evidence regarding this taxon, neither as skeletal remains nor as footprints, from any place in the world other than the Tambach Formation, which is about Sakmarian to Artinskian in age (Schneider and Werneburg, 2006). Tracks assigned to I. cottae are known from many Permo-Carboniferous units of Germany that are stratigraphically below the Tambach Formation, whereas Orobates is restricted to the youngest Early Permian deposits of the Thuringian Forest area, appearing there in deposits that were accumulated after significant changes of the basin configuration (Voigt, 2005). At that time, Orobates migrated into central Europe from an unknown area of distribution, which perhaps was situated outside of what today is Europe and North America. Even if we do not presently know the exact stratigraphic age of the Khenifra tetrapod ichnofauna, and cannot be sure that the Moroccan I. sphaerodactylum actually refers to Orobates, the occurrence of this ichnotaxon is the first valuable evidence of where to search for other populations of diadectomorphs with an Orobates-like anatomy of the appendicular skeleton (Fig. 6). 6. Conclusions Here we present the first comprehensive overview on the tetrapod ichnofauna of the Late Palaeozoic Khenifra Basin. From the middle section of the up to 1800 m-thick, red-bed succession of the study area, four main morphs of tetrapod
footprints have been recorded. With tracks of BatrachichnusLimnopus, Ichniotherium, Dimetropus, and Dromopus, which can be referred to temnospondyl, diadectomorph, early synapsid and sauropsid trackmakers, this record parallels a set of well-known Late Carboniferous to Early Permian footprint assemblages from Europe and North America. The occurrence of Ichniotherium supports a minimum age of Early Permian for the track-bearing horizons of the Khenifra Basin, which agrees with radiometric ages for the overlaying volcanites (Jebrak, 1982). With respect to the relatively high diversity of the described footprint assemblage, we state that the study area, at least temporarily, provided favourable conditions for complex terrestrial life during Permo-Carboniferous times. Wellestablished palaeoecosystems in this region might have played a pivotal role in the evolution of early tetrapods, as indicated by the first evidence for a rare type of diadectomorph outside of its central European type locality. Further exploration for both tetrapod ichno- and body fossils is strongly recommended in the Khenifra Basin, as well as in related localities in Africa and around the world. Acknowledgements This research was supported by a grant from the German Science Foundation (DFG SCHN 408/17-1). D. Hmich and A. Hminna participated in fieldwork through the financial support of the German Academic Exchange Service. We thank Marco Avanzini and Spencer G. Lucas for constructive reviews, and Robert Sproule of Plymouth, Massachusetts for linguistic assistance. References Ben Abbou, M., Soula, J.C., Brusset, S., Roddaz, M., N’Tarmouchant, A., Driouch, Y., Christophoul, F., Bouadbelli, M., Majesté-Menjoulas, C., Béziat, D., Déramond, J., 2001. Contrôle tectonique de la sédimentation dans le système de bassins d’avant-pays de la Meseta marocaine. Comptes Rendus de l’Académie des Sciences de Paris 332, 703–709. Berman, D.S., Henrici, A.C., 2003. Homology of the astragalus and structure and function of the tarsus of Diadectidae. Journal of Paleontology 77, 172–188. Berman, D.S., Henrici, A.C., Kissel, R.A., Sumida, S.S., Martens, T., 2004. A new diadectid (Diadectomorpha), Orobates pabsti, from the Early Permian of central Germany. Bulletin of Carnegie Museum 35, 1–36. Berman, D.S., Reisz, R.R., Scott, D., Henrici, A.C., Sumida, S.S., Martens, T., 2000. Early Permian bipedal reptile. Science 290, 969–972. Berman, D.S., Sumida, S.S., Martens, T., 1998. Diadectes (Diadectomorpha, Diadectidae) from the Early Permian of central Germany, with description of a new species. Annals of Carnegie Museum 67, 53–93. Broutin, J., Aassoumi, H., El Wartiti, M., Freytet, P., Kerp, H., Quesada, C., Toutin-Morin, N., 1998. The Permian Basins of Tiddas, Bou Achouch and Khenifra (central Morocco). Biostratigraphic and palaeophytogeographic implications. Mémoires du Muséum National d’Histoire Naturelle 179, 257–278. Cope, E., 1878. Descriptions of extinct Batrachia and Reptilia from the Permian formation of Texas. American Philosophical Society 17, 505–530. Dutuit, J.-M., 1988. Diplocaulus minimus n. sp. (Amphibia: Nectridea), Lépospondyle de la Formation d’Argana, dans l’Atlas marocain. Comptes Rendus de l’Académie des Sciences de Paris 307, 851–854.
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