Tetrapod footprints from the uppermost level of the Permian Ikakern Formation (Argana Basin, Western...

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Tetrapod footprints from the uppermost level of the Permian IkakernFormation (Argana Basin, Western High Atlas, Morocco)

Sebastian Voigt a,*, Abdelkbir Hminna b, Hafid Saber b, Jörg W. Schneider a, Hendrik Klein c

a Geological Institute, TU Bergakademie Freiberg, B.-v.-Cotta-Str. 2, 09596 Freiberg, Germanyb Department of Geology, Chouaïb Doukkali University, B.P. 20, 24000 El Jadida, Moroccoc Rübezahlstrasse 1, 92318 Neumarkt, Germany

a r t i c l e i n f o

Article history:Received 3 August 2009Received in revised form 23 November 2009Accepted 1 December 2009Available online 5 December 2009

Keywords:HyloidichnusPachypesVertebrate tracksIchnofaunaBasal sauropsidsLate Palaeozoic

a b s t r a c t

Tetrapod footprints from the Permian Ikakern Formation of the Argana Basin have long been known butnever studied in detail. Here we present the first comprehensive description of recently discovered tracksand trackways that come from near the uppermost layers of an up to 1800 m thick red-bed sequence.Assigned to Hyloidichnus Gilmore, 1927 and Pachypes Leonardi et al., 1975, these ichnofossils suggest aMiddle to Late Permian age of the track-bearing strata. Potential trackmakers are medium to large-sizedmoradisaurine captorhinids and pareiasaurs. This strongly parallels the bodyfossil record inasmuch as theonly known skeletal remains of terrestrial tetrapods from the study area belong to both of these groups.Based on this twofold evidence, captorhinids and Pareiasauria have to be considered as abundant faunalelements of the ancient floodplain environment that is represented by the upper part of the IkakernFormation. As one of only a few places in the world with closely associated body and ichnofossils of LatePalaeozoic age, the Argana Basin has a high potential for allowing the reconstruction of terrestrial ecosys-tems during the early stages of the break-up of central Pangaea and just before Mesozoic diapsid reptilesgained ascendancy. Further research on this stimulating topic will significantly contribute to theunderstanding of still poorly known Middle and Late Permian tetrapod ichnofaunas.

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1. Introduction

Tetrapod footprints are among the most common fossils in LatePalaeozoic continental deposits (Haubold, 1971; Gand, 1988; Lucasand Heckert, 1995; Buta et al., 2005; Voigt, 2005). Despite theirgreat abundance, our knowledge of Palaeozoic vertebrate ichno-faunas remains a patchwork because the vast majority of findingscome from a narrow stratigraphic interval of the Late Carbonifer-ous to Early Permian (Haubold, 2000; Voigt, 2005; Gand andDurand, 2006; Lucas and Hunt, 2006). A significant lack of dataconcerns tetrapod ichnofaunas from non-aeolian continentaldeposits of Middle to Late Permian age (Lucas, 2004), which areknown only by a few tracks from geographically and stratigraphi-cally distant occurrences in Southern France (Gand et al., 2000), theItalian Alps (Conti et al., 1977), central Germany (Müller, 1959),South Africa (de Klerk, 2002), and Eastern European Russia (Gubinet al., 2003; Surkov et al., 2007). The Middle to Late Permian is animportant period in the evolution of terrestrial vertebrate ecosys-tems due to the ascendance and radiation of therapsids, large

parareptiles, and neodiapsids (Sidor et al., 2005; Kemp, 2006; Mod-esto et al., 2007). The cause and temporal course of this probablydramatic change from ‘pelycosaurian’ - to therapsid-dominatedfaunas, however, is not yet understood in detail.

Here we present the first occurrence of tetrapod footprints fromnear the uppermost level of the Permian Ikakern Formation in theArgana Basin of central Morocco. The ichnofossil findings areimportant because: (1) they represent an additional locality of lit-tle known post-Early Permian Palaeozoic footprint assemblages,(2) they extend the record of such assemblages to Northern Africa,and (3) they virtually co-occur with vertebrate remains ofcandidate trackmakers. Considering these facts, the study areaplays a key role for the understanding of the evolution of LatePalaeozoic terrestrial tetrapod communities.

2. Material and methods

This work is based on two isolated footprints collected frombedrock fragments and 23 imprints of three associated trackwaysdiscovered in-situ. The latter ones are preserved as natural castson the sub-face of fluvial red-beds, which are exposed along theundercut slope of a recent stream bed. Because collection of thein-situ tracks, being 3.5 m above the bottom floor, seemed to be

1464-343X/$ - see front matter � 2009 Elsevier Ltd. All rights reserved.doi:10.1016/j.jafrearsci.2009.12.003

* Corresponding author. Tel.: +49 3731 392038; fax: +49 3731 393599.E-mail addresses: [email protected] (S. Voigt), hminna_abdelkbir@

yahoo.fr (A. Hminna), [email protected] (H. Saber), [email protected] (J.W. Schneider), [email protected] (H. Klein).

Journal of African Earth Sciences 57 (2010) 470–478

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impossible without severe damage of the extended trackway sur-face, a boulder staircase was constructed to study the ichnofossilsin the field. To assess the variability of the trackways, they werephotographed both in overview and as individual imprints. Thetrackways were outlined on transparency film in order to recordmeasurements of 28 different parameters of imprint morphologyand trackway pattern (Appendix A). All of the measurements arewidely accepted as standard, procedural practice and have beenfully described in other such studies (e.g., Haubold, 1971; Leonardi,1987; Voigt and Haubold, 2000; Voigt et al., 2007). Latex mouldsand imprints in squares of orthopedic foam were produced of themost well-preserved tracks to get plaster and silicon casts forcomparative morphological studies.

2.1. Institutional abbreviation

All of the described fossil footprint material including originalspecimens, latex moulds, and artificial casts is housed in thecollection of the Department of Earth Science, Chouaïb DoukkaliUniversity El Jadida, Morocco (CDUE).

2.2. Ichnological abbreviations

A, distance between manus and pes; B, width of pace; C, appar-ent body length (gleno-acetabular distance); m, manus imprint;mb, width of manus imprint; ml, length of manus imprint; mI–mV, length of digit I–V of the manus imprint; P, length of pace; p,pes imprint; pb, width of pes imprint; pl, length of pes imprint;pI–pV, length of digit I–V of the pes imprint; S, length of stride;a, pace angulation; b, divarication of manus or pes from midline,plus = outward rotation, minus = inward rotation; c, interdigitalangle I–V; I–II–III–IV–V, first to fifth digit, numbered from medialto lateral side of imprint.

3. Geological setting

All fossils described herein come from the Argana Basinbetween Marrakech and Agadir in southern Morocco (Fig. 1). TheArgana Basin refers to an approximately 20 km wide and 70 km

long, NNE–SSW trending area of excellently exposed Permian–Triassic red-beds at the south-western edge of the High Atlasmountain range. The 2500–5000 m thick succession consists ofalluvial, fluvial, lacustrine, aeolian and playa deposits that accumu-lated in a continental rift basin during the initial opening phase ofthe central Atlantic (Manspeizer, 1988; Zühlke et al., 2004).

Tixeront (1973) proposed a subdivision of the succession ineight lithostratigraphical units (T1–T8), which Brown (1980)formally assigned to three formations (Fig. 1). These are from baseto top: the Ikakern Formation (T1–T2, 900–1800 m), the Timezga-diouine Formation (T3–T5; 1000–2000 m), and the BigoudineFormation (T6–T8; 300–1500 m). Each of these is separated fromolder strata by either an angular or erosional unconformity. Thebasal Ikakern Formation consists of alluvial fan conglomerates(T1) grading vertically and laterally into alluvial plain conglomer-ates, sandstones, and mudstones (T2). The Timezgadiouine Forma-tion is represented by braided river deposits (T3), playa mudstoneswith intercalations of sheetflood and ephemeral stream sandstones(T4), and alluvial plain sandstones and mudstones (T5). The upperBigoudine Formation starts with braided river conglomerates andaeolian sandstones (T6) that grade into increasingly fine-grainedpartially evaporitic playa red-beds (T7–T8). The Permo-Triassicsedimentary succession of the Argana Basin is concluded by upto 150 m thick tholeiitic basalts that unconformably overlieslightly deformed mudstones of the Bigoudine Formation.

In contrast to the well-established lithostratigraphy, much lessis known about the stratigraphic age of the Argana red-beds. Basalconglomerates of the Ikakern Formation rest with an angularunconformity on Hercynian (Cambrian to Devonian) basementand, locally, on Late Carboniferous (Stephanian) clastics (Jones,1975; Hmich et al., 2006) constraining the maximum age to thePermo-Carboniferous. Vertebrate remains from the uppermostlevel of T2 suggest a Late Permian age for the top of the IkakernFormation (Dutuit, 1988; Jalil and Dutuit, 1996; Jalil and Janvier,2005). The Timezgadiouine and Bigoudine formations are datedas Late Triassic (Middle Carnian to earliest Norian) based onvertebrate remains and palynomorphs (Jali, 1999; Tourani et al.,2000). Recently recovered tetrapod footprints from the base ofthe Timezgadiouine Formation suggest, however, that deposition

Fig. 1. Location and geological overview of the study area. (A–B) Position of the Argana Basin in Northwest Africa and Central Morocco. C. Simplified geological map (afterTixeront, 1974) and generalized lithostratigraphic subdivision of the Late Palaeozoic to Early Mesozoic succession of the Argana-Timezgadiouine part of the Argana Basin. Thetetrapod footprint localities are indicated by asterisks (1-Hyloidichnus: CDUE localities 6 and 7; 2-Pachypes: CDUE locality 8).

S. Voigt et al. / Journal of African Earth Sciences 57 (2010) 470–478 471


of the Mesozoic part of the Argana red-beds had already startedduring the Early Triassic (Klein et al., 2009). Radiometric agedeterminations of tholeiitic basalts on top of the succession rangebetween 197.8 ± 0.7 and 201.7 ± 2.4 Ma (Hettangian to Rhaetian;Verati et al., 2007).

The fossil footprints discussed in this paper were recovered inthe upper part of the Ikakern Formation (Tourbihine Member,T2). Permian deposits of the Argana Basin have been much lessintensively studied than the overlying Mesozoic strata. The mostdetailed lithological descriptions of the Tourbihine Member weregiven by Tixeront (1973), Jones (1975), and Brown (1980). Remark-ably, these authors measured the maximum thickness of thesuccession very differently to 1800 m, 200 m, and 1000 m, respec-tively. According to Jones (1975) and Brown (1980), the TourbihineMember is characterised by a variety of clastic sedimentary rocksranging from conglomerates to mudstones, which are arranged incycles of 5–20 m thickness. Each cycle consists of thin lenticularto wedge shaped conglomerates or conglomeratic sandstonesgrading laterally and vertically into thick tabular sandstones,siltstones, and mudstones. Coarser units decrease in abundanceand thickness towards the top of the succession suggesting atendency of equiplanation of the local relief. Based on a carefuldescription of the lithology, geometry, and thickness of beds andassociated primary structures, Jones (1975) interpreted the red-beds of the Tourbihine Member as channel and floodplain depositsof low and high sinuosity meandering streams. In such deposi-tional environments the preservation of tetrapod tracks is usuallyconfined to fine-grained sand- and siltstones of shallow channelsand subaerially exposed deposits of the proximal floodplain (Voigt,2005). As already stated by Jones (1975), mudcrack casts are rare inthe Tourbihine Member probably indicating that overbank areaswere frequently water-saturated or shallowly inundated withwater. The footprints described in this paper are restricted tolow-energy fluvial sandstones (Fig. 2) suggesting that the likelyheavily built trackmakers preferred to walk on firm ground ofsandy streambeds rather than on muddy overbank deposits.

4. Systematic palaeoichnology

4.1. Hyloidichnus sp. indet. Gilmore, 1927 (Figs. 3 and 4, Appendix A)

Referred specimens and locality: (1) CDUE 50 to CDUE 52 (Figs. 3and 4A–C), lower surface of a WNW dipping stream bed with 23imprints preserved in situ; left bank of the Oued Issene about1.5 km south of Irerhi (CDUE locality 6; N30�49021.500W009�04050.000; Fig. 1C). Specimen numbers refer to the most well-pre-served footprints, which have been replicated by latex moulds.The naturally exposed trackway surface measures up to 2.8 m inlength (N–S) and less than 0.8 m in width (E–W) covering about1.5 m2. The tracks are preserved in convex hyporelief and belongto three separate trackways (Fig. 3): Trackway 1 consists of 13 im-prints leading south; trackway 2 with four manus-pes sets pointsto the northwest; and trackway 3, represented by only two shallowimprints of consecutive couples, refers to a trackmaker that walkedeastward. (2) CDUE 53 (Fig. 4D), incomplete isolated pes imprintpreserved in convex hyporelief on a fragment of reddish-brownfine-grained sandstone; right bank of the Oued Issene about1.5 km south of Irerhi (CDUE locality 7; N30�49026.800W009�040

55.200; Fig. 1C).Horizon: Uppermost level of the Tourbihine Member (T2), Ika-

kern Formation, Late Permian.Description: Trackway of a quadrupedal tetrapod with pentadac-

tyl, semiplantigrade footprints. Manus and pes imprints are espe-cially distinct in relief and, therefore, also in completeness ofpreservation. Pes imprints usually exhibit only the first three

digits. In one case, a faint and questionable impression of the tipof digit IV is present (trackway 1; Fig. 3, 4A). The length of thepes imprints of trackway 1 can be estimated at 80 mm; there areno data available on their width because the fifth digit is not pre-served in any pedal track. Digits I–IV of the pes imprint exhibit aserial increase in length; digits are relatively long and slender withsomewhat thickened proximal end and rounded digit tip giving thewhole structure a barbell-shaped appearance. The sole of the pesimprint is shorter than the first digit showing a segmented convexproximal margin and a significantly lateral decrease in relief.

The manus imprints measure 64 mm in length on average andare about one fourth wider than long. Digits I–IV exhibit a serial in-crease in length, whereas digit V is about as long as I. The shape ofthe digits, digit tips, and palm is similar to the equivalent parts ofthe pes imprints. Therefore, manus and pes imprints mainly differin size and relief. Based on the relative proportions of the first threedigits, the pes imprints are 15–20% larger than the manus imprints.Additionally, the latter ones show a more evenly distributed relieffavouring the preservation of all five digits in contrast to the pesimprint.

The trackway pattern is characterised by an alternating arrange-ment of coupled manus-pes imprints (Fig. 3). Although the pesimprint is always positioned behind the manus imprint, at leastone set of trackway 1 shows marginal primary overstepping. Pes

Fig. 2. Simplified stratigraphic section of fluvial red-beds in the uppermost part ofthe Permian Ikakern Formation, Argana Basin, at CDUE locality 6 showing theposition of the Hyloidichnus in-situ tracks (see Fig. 3).

472 S. Voigt et al. / Journal of African Earth Sciences 57 (2010) 470–478


imprint slightly, manus imprint strongly inward-rotated withrespect to the trackway midline (Appendix A). While length ofstride, length of pace, and pace angulation consistently suggest thatthe width of pace of the pes imprints slightly exceeds those of themanus imprints, absolute measurements of this parameter (track-way parameter B; Appendix A) are contradictory; the sample sizeseems to be inadequate to confirm this character. The apparentbody length (gleno-acetabular distance) for the producers oftrackway 1 and 2 amounts to about 285 mm and 325 mm. Accesso-ries such as skin imprints or tail drag marks are not recorded.

Discussion: Based on the imprint morphology and trackwaypattern, the described tetrapod footprints are congruent withHyloidichnus Gilmore, 1927. This ichnogenus and the tetrapodfootprints from the Argana Basin share a number of features. Theseinclude the specific digit and imprint proportions, the short soleand palm of the imprints, the typical barbell-shaped digit impres-sions, the asymmetric relief of the pes imprints, and the trackwaypattern with strongly alternating manus-pes sets (Gilmore, 1927;Gand, 1988).

Hyloidichnus was introduced for a reptile trackway consisting ofless than 5 cm long pentadactyl tracks from the Early PermianHermit Formation of the Grand Canyon, USA (Gilmore, 1927;Haubold, 1971). Well-preserved large footprints from the late EarlyPermian Rabejac Formation of the Lodève Basin, southern France(Heyler and Lessertisseur, 1963; Gand, 1988), confirm that Hyloid-ichnus actually represents a valid ichnotaxon of Late Palaeozoictetrapod ichnofaunas (Haubold, 2000). However, Hyloidichnus issometimes hard to separate from the very similar morphotypeVaranopus Moodie, 1929 (Voigt, 2005). Both ichnotaxa differ

primarily in the relative length of the fifth digit of the pes imprint,which is about two-third of the length of the fourth digit in Varan-opus, but only two-fifth in Hyloidichnus (Gand, 1988; Voigt, 2005).Other differences concern the first occurrence date of each ichno-taxon in the fossil record and the maximum size of the imprints(Voigt et al., 2009). The most distinctive feature of the imprintmorphology, which is the relative length of the fifth digit of thepes imprint, is not applicable in the present case because of theincomplete preservation of the Argana footprints. Despite thisapparent problem, the assignment of the discussed footprints tothe ichnogenus Hyloidichnus seems still to be justified in consider-ation of the following three aspects: (1) Strongly inward-rotatedmanus imprints, as observed for the Moroccan footprints, areknown from the holotype of Hyloidichnus (Gilmore, 1927) aswell as from French specimens of the ichnogenus (Gand, 1988).These clearly differ from Varanopus, which exhibit only slightlyinward-rotated manual imprints (Voigt, 2005). (2) Varanopus andHyloidichnus seem to differ in the interdigital angle I–V of themanus imprints, which is obtuse-angled in the former (Voigt,2005) and acute-angled in the latter ichnogenus (Gilmore, 1927;Gand, 1988) and the footprints from the Argana Basin. (3) TheMoroccan tracks are about twice as large as the largest knownVaranopus pes imprints, which do not exceed 45 mm in length(Haubold, 1971; Gand, 1988; Haubold and Lucas, 2003; Van Allenet al., 2005; Voigt, 2005). The maximum imprint size can be usedhere as an auxiliary means of ichnotaxonomic assignment becausethis feature is most likely phylogenetically controlled (Voigt et al.,2009). According to the present state of knowledge, the footprintsfrom the Argana Basin should be assigned to Hyloidichnus sp. indet.

Fig. 3. Undercut slope on the left bank of the Oued Issene south of Irerhi, Argana Basin (CDUE locality 6, Fig. 1C). Fluvial red-beds from the uppermost part of the PermianIkakern Formation are exposed with in-situ tracks of Hyloidichnus seen. The track-bearing sub-face exhibits 23 imprints of three trackway segments.



Ichnospecific assignment is kept in open nomenclature inasmuchas the validity of different North American and European Hyloidich-nus ichnospecies has never been systematically investigated.

Osteological interpretation: Based on the overall similarity be-tween the digit proportions of tracks and autopods, Hyloidichnusand Varanopus have usually been referred to captorhinid trackmak-ers (Haubold, 1971, 1973, 2000; Fichter, 1983; Gand, 1988; Hau-bold and Lucas, 2003; Voigt, 2005; Gand and Durand, 2006;Voigt et al., 2009). The short sole and strongly mediolateral de-crease in relief as the most distinctive characteristics of Varanopusand Hyloidichnus pes imprints can be easily explained by particularfeatures of the captorhinid tarsus (Holmes, 2003; Voigt, 2005): (1)The presence of a mesotarsal joint between the calcaneum-astrag-alus-centrale complex and the distal tarsals as the most proximalhinge of the autopod implicates semiplantigrade pedal tracks forcaptorhinids. (2) As the most mobile part of the tarsus, the medialside between the centrale and first to third distal tarsals carried themaximum weight during locomotion, which is reflected by theasymmetric relief of the captorhinids pes tracks. Comparison ofthe captorhinid body to the ichnofossil record by various aspectsincluding morphology, phylogeny, stratigraphy, and biogeography,provides strong arguments for the assumption that Varanopusrepresents footprints of small to medium-sized early captorhinids,whereas Hyloidichnus can be referred to large derived captorhinidsof the Moradisaurinae clade (Voigt et al., 2009).

4.2. Pachypes sp. indet. Leonardi et al., 1975 (Fig. 5)

Referred specimen and locality: CDUE 54, slab of light reddish-brown fine-grained sandstone, 36 � 44 cm in size with natural castof a single left manus imprint; southeastern slope of a small valleynorth of Targante (CDUE locality 8; N30�49001.000W009�03049.100;Fig. 1C).

Horizon: Uppermost level of the Tourbihine Member (T2), Ika-kern Formation, Late Permian.

Description: Semiplantigrade, most probably pentadactyl,mesaxonic imprint of sub-elliptical outline; length of imprint170 mm, width of imprint 240 mm, length–width ratio 0.71. Thedeepest impressed digits I–IV are sturdy and short with sub-rounded tips; the questionable imprint of a fifth digit is less thanhalf as long and wide as the other digits. The relative length ofthe digit impressions seems to be as V� I < II–IV < III with digitsI–IV being almost sub-equal in size. All digit imprints slightly di-verge (ca. 15–25�). At least the distal parts of the digit imprintsIII and IV seem to be slightly turned inward.

Discussion: CDUE 54 fits well with the characteristics of themanus imprint of Pachypes Leonardi et al., 1975 following theemended diagnosis of the ichnogenus given by Valentini et al.(2009). Shared features include sturdy, short digits, the sub-equallength of digits II–IV, shorter external digits, the semiplantigrade,but well-developed imprint of the palm, and the length–width

Fig. 4. Hyloidichnus sp. Gilmore, 1927 from the Middle to Late Permian Ikakern Formation, Argana Basin, Morocco (A–D) in comparison to a co-ichnogeneric specimen fromthe late Early Permian Rabejac Formation, Lodève Basin, France (E). (A–C) Well-preserved imprints (manus-pes sets) of the in situ trackway surface at CDUE locality 6. D.Medial part of an isolated pes imprint from CDUE locality 7. E. Well-preserved manus-pes set with distinct imprint of the diagnostic fifth digit of the pes. F. Outline drawing ofa hypothetic manus-pes couple based on the Moroccan specimens. Material: A–C, field photographs (figured specimens correspond to latex moulds CDUE 50 to CDUE 52); D.CDUE 53; E, Musée Fleury, Lodève, France, specimen No. 239A. All photographs show natural casts of footprints; in all coupled imprints, the manus is in front of the pes. Scalebars equal 5 cm.



ratio of the imprint. Manus and pes imprints of Pachypes arewell-separated by the proportions and relative length of the digits.The digits of the pes imprint increase in length from II to IV and aremuch shorter than the sole. Digit III, being longest and measuringalmost half of the length of the imprint, clearly identifies CDUE 54as a manus imprint.

Among Palaeozoic tetrapod ichnotaxa, only Brontopus Heylerand Lessertisseur, 1963 and Sukhonopus Gubin et al., 2003 fromthe Middle Permian of Southern France (Heyler and Lessertisseur,1963; Gand, 1988; Gand et al., 2000) and the Late Permian ofRussia (Gubin et al., 2003), respectively, exhibit a set of featuressimilar to Pachypes. In their re-evaluation of the latter ichnogenera,Valentini et al. (2009) synonymised Sukhonopus with Pachypes, butconfirmed the ichnotaxonomic separation of Pachypes and Bronto-pus from the French type locality especially due to different digitand imprint proportions (see also Gand et al., 2000; Haubold,2000). Brontopus described by Surkov et al. (2007) from the LatePermian of Russia was also assigned to Pachypes by Valentiniet al. (2009). In our opinion, neither the French nor the Russianmaterial of these large Permian tetrapod footprints is sufficientlywell-preserved or abundant enough in order to record ichnotaxo-nomically relevant features. Such requirements are currently metonly by the track and trackway material of Pachypes from the typelocality in the Southern Alps (Valentini et al., 2009). The Arganaspecimen is the most well-preserved specimen of Pachypes outsideits type locality; continued collecting in the Moroccan Permianbasin is therefore warrented in order to further substantiate thediagnostic features of this general morphotype of Late Palaeozoictetrapod footprints. Due to the still incomplete record of thePachypes material from the Argana Basin, ichnospecific assignmentis kept in open nomenclature.

Osteological interpretation: Pachypes has been invariably referredto pareiasaurian trackmakers by all authors who did research onthat ichnogenus (Leonardi et al., 1975; Conti et al., 1977; Mietto,

1981; Haubold, 1984, 2000; Lockley and Meyer, 2000; Nicosiaet al., 2005). The most comprehensive and recent discussion onthe pareiasaurian affinity of Pachypes is given by Valentini et al.(2008, 2009). Based on those specimens that display evidence,the pedal phalangeal formula of Pareiasauria is 23343, that of themanus 23332 (Lee, 1997; Jalil and Janvier, 2005). The autopodsof other large-bodied Permian reptiles such as derived caseidsand some dicynodont therapsids differ from those of pareiasaursby their homopody, tapered to acute claws, and rather uniformlydeveloped digits (Reisz, 1986; Hopson, 1995). Heteropody, sturdydigits with rounded tips, and a remarkable reduction of theoutermost digit establish a unique set of characters that suggestsPareiasauria as the most likely producers of Pachypes footprints.

5. Faunistic and stratigraphic implications

The red-beds of the Permian Ikakern Formation of the ArganaBasin have yielded a few plants (De Koning, 1957), some inverte-brate and vertebrate ichnofossils (Jones, 1975; Hmich et al.,2006; Hminna et al., 2008), and a more diverse tetrapod faunaincluding remains of a diplocaulid lepospondyl (Dutuit, 1988;Germain, 2009), a small temnospondyl (Steyer and Jalil, 2009), atleast one pareiasaur reptile (Jalil and Janvier, 2005), and two capto-rhinid reptiles (Dutuit, 1976; Jalil and Dutuit, 1996). The latterones are represented by a multitooth-rowed maxilla of amedium-sized captorhinid (Acrodonta irerhi Dutuit, 1976) ofunclear systematic position and cranial and postcranial remainsof a medium- to large-sized moradisaurine captorhinid. It isremarkable that the only known truly terrestrial tetrapods of theIkakern Formation are pareiasaurian and captorhinids recoveredin the uppermost level of the Tourbihine Member (T2) (Jalil andDutuit, 1996; Jalil and Janvier, 2005). The tetrapod footprintsdescribed herein come from the same stratigraphic level andalmost the same place inasmuch as all vertebrate body - and

Fig. 5. Pachypes sp. Leonardi et al., 1975 from the Permian Ikakern Formation, Argana Basin. Natural cast of a left manus imprint under different lighting conditions (A–C) andas outline drawing (D). Material: CDUE 54. Specimen is equally scaled in all photographs and drawing.



ichnofossil localities are within an areal distance of less than 3 kmto Irerhi (Fig. 1C). Hyloidichnus and Pachypes, up to now the onlyknown footprints from the fossiliferous horizons of the upper partof the Ikakern Formation, are most likely referred to large morad-isaurine captorhinids and pareiasaurs representing one of only afew examples for the co-occurrence of highly related vertebratebody- and ichnofossils from the Palaeozoic period (Voigt et al.,2007). In addition to the skeletal remains, the trackway recordgives evidence that representatives of these two groups of reptileswere important elements of the terrestrial tetrapod fauna of thestudy area during the Late Palaeozoic. The Hyloidichnus trackwaysurface covered with more than 10 imprints per square metre,which were made by differently sized individuals walking invarious directions, emphasizes not only the relative abundance oflarge derived captorhinids at that time but also that the ancientfloodplain of the Ikakern Formation was at least part of the habit-ual range of these reptiles.

The stratigraphic age of the Ikakern Formation has been arguedsince the beginning of geological research in the Argana Basin be-cause of the scarcity of biostratigraphic index fossils and the lack ofradiometric data. De Koning (1957) mentioned the presence ofVoltzia heterophylla from the upper part of the succession and as-sumed a Triassic age. His macrofloral remains, however, have neverbeen published and are now lost (Jali, 1999). Duffaud et al. (1966)favored a Permian age for the succession, because it is enclosed be-tween two major unconformities with Late Carboniferous depositsbelow and Triassic strata above. Jones (1975) argued for a Triassicage based on the findings of Rhynchosauroides footprints in theupper part of the Ikakern Formation. Vertebrate remains of diplo-caulids and captorhinids finally constrained the age of the succes-sion to the Permian (Dutuit, 1988; Jalil and Dutuit, 1996). An evenmore precise minimum age of the strata is given by the remains ofa derived pareiasaur, Arganaceras vacanti, from the topmost level ofthe Ikakern Formation, which may be regarded as closely related toElginia mirabilis Newton, 1893 and an unnamed Kupferschieferpareiasaur from the latest Permian of Scotland and Germany,respectively (Jalil and Janvier, 2005). The occurrence of Hyloidich-nus and Pachypes footprints in equivalent strata partially confirmsthis assignment. Both ichnotaxa are elements of clearly Permiantetrapod ichnofaunas (Haubold, 2000). Hyloidichnus is best knownfrom the Hermit Formation of the Grand Canyon, USA, and the Rab-ejac Formation in the Lodève Basin of Southern France, both ofwhich are probably of late Early Permian age (Lucas and Hunt,2006; Gand and Durand, 2006; Schneider et al., 2006). Steyeret al. (2007) reported on possible Hyloidichnus trackways fromthe Moradi Formation of northern Niger extending the range ofthe ichnogenus up to the Late Permian (Sidor et al., 2005). Beforethis study, unambiguous material of Pachypes was restricted tothe type locality of the Late Permian Val Gardena Formation inNorthern Italy (Leonardi et al., 1975; Valentini et al., 2009). Pachy-

pes is referred to pareiasaurian trackmakers, which are currentlyknown by skeletal remains from the Middle Permian Tapinoceph-alus Assemblage Zone of South Africa up to the Late Permian ElginSandstones of Scotland (Lee, 1997; Valentini et al., 2008), and re-stricts the age of the upper part of the Ikakern Formation bytetrapod footprints according to the present stage of knowledgeto the same time frame (Wordian/Capitanian – Changsingian,about 268–251 Ma; International Commission on Stratigraphy,2009).

6. Conclusions and perspective

The present paper is the first comprehensive description of tet-rapod footprints from the Permian Ikakern Formation of the Arg-ana Basin. Based on recently discovered tracks and trackways ofHyloidichnus Gilmore, 1927 and Pachypes Leonardi et al., 1975,we postulate the presence of a typical Late Palaeozoic vertebrateichnofauna for the uppermost part of the up to 1800 m thick red-bed sequence. Medium- to large-sized moradisaurine captorhinidsand pareiasaurs postulated as the most likely trackmakers stronglyparallels the bodyfossil record inasmuch as skeletal remains as-signed to these taxa represent the only terrestrial tetrapods thatare hitherto known from the study area. Without question, capto-rhinids and pareiasaurs were abundant faunal elements of the an-cient floodplain environment represented by the IkakernFormation. The Argana Basin, due to this special track-trackmakerassociation, acquires an important position in our understanding ofthe ontogeny, behaviour, biogeography, and ecology of Late Palae-ozoic basal eureptiles and derived parareptiles. With respect to fu-ture research in this area, there is not only much potential for thereconstruction of a highly interesting Middle to Late Permian ter-restrial ecosystem of central Pangea, but also a unique chance tosubstantiate principal morphs of the inadequately known tetrapodichnofaunas of that period.

Acknowledgements

We appreciate helpful comments on the manuscript by P.G.Eriksson as the managing editor and two anonymous reviewers.We are indebted to Allan J. Lerner, Albuquerque, for linguisticassistance. A. Hminna thanks the German Academic ExchangeService for financial support of fieldwork. This research is a contri-bution to the project on Late Palaeozoic and Early Mesozoic tetra-pod ichnofaunas of Morocco kindly supported by the GermanResearch Foundation (SCHN 408/17-1).

Appendix A

Trackway and imprint parameters of Hyloidichnus from CDUElocality 6 (in mm and degrees).

Trackway Sp Sm Pp Pm A Bp Bm C D E ap am bp bm

Trackway 1 417.0 396.5 290.7 286.0 87.5 183.0 191.0 285.5 129.0 �0.8 92.5 92.0 �8.3 �31.7Trackway 2 457.5 442.0 311.0 305.3 86.0 185.3 184.7 326.0 157.3 �0.5 98.5 102.0 �9.5 �28.8Mean 437.3 419.3 300.9 295.7 86.8 184.7 187.9 305.8 143.2 �0.7 95.5 97.0 �8.9 �30.3

Trackway pI pII pIII pIV pV mI mII mIII mIV mV pl pb ml mb cp cm

Trackway 1 27.5 40.3 51.0 – – 27.0 38.0 48.0 53.5 25.0 – – 65.0 82.0 – 75.0Trackway 2 36.0 41.0 52.0 – – 22.0 34.5 41.0 46.3 23.0 – – 63.0 77.8 – 76.5Mean 31.8 40.7 51.5 – – 24.5 36.3 44.5 49.9 24.0 – – 64.0 79.9 – 75.8



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