On a moderately diverse continental ichnofauna from the Permian Ikakern Formation (Argana Basin, Western High Atlas, Morocco)

Journal of African Earth Sciences 68 (2012) 15–23

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On a moderately diverse continental ichnofauna from the Permian Ikakern Formation (Argana Basin, Western High Atlas, Morocco) Abdelkbir Hminna a, Sebastian Voigt b, Hafid Saber a,⇑, Jörg W. Schneider b, Driss Hmich a a b

Department of Geology, Chouaïb Doukkali University, B.P. 20, 24000 El Jadida, Morocco Geological Institute, TU Bergakademie Freiberg, B.-v.-Cotta-Str. 2, 09596 Freiberg, Germany

a r t i c l e

i n f o

Article history: Received 26 November 2011 Received in revised form 24 March 2012 Accepted 28 March 2012 Available online 6 April 2012 Keywords: Trace fossils Scoyenia ichnofacies Palaeoecology Red beds Late Palaeozoic NW Africa

a b s t r a c t The Permian Ikakern Formation of the Argana Basin yielded important tetrapod skeletal remains but is still poorly known for any other kind of fossils. Here we present a moderately diverse assemblage of invertebrate and vertebrate traces from red beds in the upper part of the formation (Tourbihine Member, T2) near Timezgadiouine. Recorded ichnotaxa include Spongeliomorpha carlsbergi (Bromley and Asgaard, 1979), Striatichnium natalis Walter, 1982, Amphisauropus Haubold, 1970, Hyloidichnus Gilmore, 1927, Erpetopus Moodie, 1929, and Dromopus Marsh, 1894. The traces occur in laminated muddy siltstone and fine-grained sandstone that we interpret as slack-water deposits in an episodically high energy fluvial setting. Including arthropod burrows, arthropod grazing traces and tetrapod footprints, the ichnofossil assemblage corresponds to the Scoyenia ichnofacies. The described trace fossils provide evidence for various invertebrates and vertebrates hitherto unknown from the body fossil record of the study area. By extending the stratigraphic and geographic range of some of the recorded ichnotaxa, our finds strongly emphasise the importance of the Argana Basin for the reconstruction and understanding of Late Palaeozoic terrestrial ecosystems. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction The Permian Ikakern Formation of the Argana Basin (Western High Atlas, Morocco) is famous for its locally abundant and diverse vertebrate body fossil remains (e.g., Dutuit, 1976, 1988; Jalil and Dutuit, 1996; Jalil and Janvier, 2005; Steyer and Jalil, 2009). By comparison, other kind of fossils such as plants and traces are poorly known or basically unknown from this unit. For the first time, tetrapod tracks were mentioned from the upper part of the Ikakern Formation (T2 Member) by Jones (1975) and Brown (1980). Based on photographs, Donald Baird pers. comm. in Jones, 1975 assigned these finds to Rhynchosauroides Maidwell, 1911. More than three decades later, Hmich et al. (2006) reported tracks of Synaptichnium Nopcsa, 1923 on a loose block that the authors first assigned to the T2 Member. Reinvestigation of the locality and the discovery of nearby in situ tracks, however, revealed provenance of these ichnofossils from Early Triassic beds of the overlaying Timezgadiouine Formation (T3, Tanamert Member; Klein et al., 2010). During joint fieldwork of the authors in the Argana Basin in 2008 and 2009, several new sites with trace fossils have been ⇑ Corresponding author. Tel.: +212 6 76 87 70 09; fax: +212 5 23 34 21 87. E-mail addresses: [email protected] (A. Hminna), [email protected] (S. Voigt), hafi[email protected] (H. Saber), [email protected] (J.W. Schneider), [email protected] (D. Hmich). 1464-343X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jafrearsci.2012.03.011

found in the Permian Ikakern Formation (Hminna et al., 2009; Voigt et al., 2009, 2010) and the Triassic Timizgadiouine Formation (Klein et al., 2009, 2010, 2011; Voigt et al., 2011). The present paper is focused on a moderately diverse ichnofossil assemblage from the upper part of the Ikakern Formation near Timezgadiouine including five ichnotaxa that are new for the Argana Basin or even the African continent. Our main purpose is to call attention to trace fossils in the study area and to demonstrate their importance for palaeoenvironmental reconstruction.

2. Material and methods This work is based on about 30 specimens with invertebrate and vertebrate trace fossils observed and partially collected in March 2008 and May 2009 during lithostratigraphic work in the stratotype area of the Ikakern Formation. The material has been found in place on undercut slopes and slip-off banks of a recent stream bed or, to a minor extent, by selective fossil digging. Latex moulds were produced, where collecting of the original specimens was impossible due to natural conditions. Laboratory work included photography and drawing of the fossils and, if necessary, the production of polished sections. All numbered fossils (originals and replicas) are housed in the collection of the Department of Earth Sciences, Chouaïb Doukkali University El Jadida, Morocco (CDUE). Locality data are on file at the same institution.

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3. Geologic setting The Argana Basin is located in the Western High Atlas of southcentral Morocco about 50 km northeast of Agadir and 125 km southwest of Marrakech (Fig. 1). Its mainly Permian–Triassic continental deposits represent the fill of a small half-graben as part of the much larger Essaouria-Agadir Basin (Medina, 1994, 1995; Tourani et al., 1997; Olson and Et-Touhami, 2008). The Argana Basin is limited to the north by the Ichemraren-Imi N’Tanout inverse fault and to the south by the El Menizla fault that coincides with the morphological boundary between the Western High Atlas mountains and the Souss plain (Medina et al., 2000). Along the eastern margin of the Argana Basin its Permian deposits rest with an angular unconformity on older Palaeozoic rocks of the High Atlas, whereas to the west Triassic deposits are conformably covered by continental to shallow marine Jurassic strata (Harding and Brown, 1974). The Permian and Triassic red beds of the Argana Basin crop out in a 20x70 km, NNE–SSW trending area between Ameskroud in the south and Imi N’Tanout in the north (Fig. 1; Tixeront, 1973; Brown, 1980; Medina et al., 2000; Tourani et al., 2000). Only the lower part of the 2500–5000 m thick succession is referred to the Permian Ikakern Formation subdivided into the basal Ait Driss Member (T1; 61500 m thick) and the overlying Tourbihine Member (T2; 200–1800 m thick) (Figs. 1 and 2). Basal sediments of the Ait Driss Member follow with a structural and erosional unconformity on Cambrian to Devonian metasediments or, locally, on Late Carboniferous (Stephanian) siliciclastics (Jones, 1975; Hmich et al., 2006). According to our own observations in the stratotype area of the Ikakern Formation near Ikakern (Fig. 1), Permian sediments of the Argana Basin start with structureless or poorly stratified pebble- to cobble-sized fanglomerates that form 2–5 m thick units separated by massive, reddish-brown, pebble-bearing mudstones (T1a). These two lithofacies types probably represent debris flows and mudflows on proximal to medial alluvial fans. Upsection, sediments become increasingly better sorted and the average grain

size decreases. Interbedding of 1–2 m thick fanglomeratic to clast-supported conglomerates and 0.2–0.5 m thick fine-grained sandy siltstones characterise the transition from the lower part (T1a) to the upper part (T1b) of the Ait Driss Member. The upper part is dominated by up to 2-m thick, horizontally-bedded conglomerates and intercalations of 1.0–2.5-m thick muddy, sandy or pebbly siltstones. Pure siltstones often exhibit bioturbation indicated by indeterminate subvertical tubes (3–5 mm in diameter) and rhizoconcretions of variable size. We interpret the sediments of the upper part of the Ait Driss Member (T1b) as distal alluvial fan deposits laid down by hyperconcentrated flows, mud-dominated debris flows, and mudflows. The Ait Driss Member (T1) grades vertically and laterally into alluvial plain deposits of the Tourbihine Member (T2). Those red beds are particularly well-exposed in the middle part of the Argana Basin. We studied the Tourbihine Member in more detail along the Irhzer River southeast of Timezgadiouine (Fig. 1) where the unit amounts to 220 m in total thickness. The predominantly light reddish-brown siliciclastics of the T2 Member are organised in one to several tens of metres thick, fining-upward cycles. These cycles usually start with matrix- to clast-supported, massive to largescale trough cross-bedded, amalgamated channels of fine-grained conglomerates that are overlain by channels of pebble-bearing, medium- to fine-grained sandstones. Intercalations of up to 1-m thick, small-scale ripple-bedded to even horizontally bedded, sandy siltstones may occur in the sandstones but they are rare and laterally not persistent. Stacked channels can often be laterally traced for tens to hundreds of metres, exhibiting a wide range of grain sizes and bed geometries. Distinct scour-and-fill structures are common with deep scours occasionally containing coarse, channel-lag deposits. The channel horizons may be interrupted by decimetres to several metres thick units of platy-bedded to massive, carbonate-cemented siltstones and mudstones that sometimes contain rhizoconcretions and carbonate nodules. We interpret the T2 Member as deposits of a braided alluvial plain with wide channels of moderate sinuosity between minor overbank fines.

Fig. 1. Location and geological overview of the study area. (A and B) Position of the Argana Basin in Northwest Africa and Central Morocco. (C) Simplified geological map of the central part of the Argana Basin with position of the Irhzer River section and the studied trace fossil sites (CDUE localities 1–5) in the upper part of the Ikakern Formation(Tourbihine Member, T2). Map based on Tixeront (1974) and Jones (1975).

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Fig. 2. Simplified section of the Ikakern Formation in the central part of the Argana Basin showing distribution of tetrapod body- and ichnofossils. Lithostratigraphic subdivision and facies interpretation based on Tixeront (1973), Jones (1975), Brown (1980), Tourani et al. (2000), Hmich et al. (2006) and own observations.

Thin, shaly, even horizontally-bedded siltstones with oscillation ripples, current ripples or linguoid ripples most likely represent post-flooding slack-water deposits in abandoned channels. Pedogenetic overprinting of overbank fines (vertisols to immature calcisols) and mudcracks indicate semiarid climatic conditions. All trace fossils described in this paper come from the middle part of the Tourbihine Member southeast of Amsoul-ou-Guerram (CDUE localities 1–5; Fig. 1 and 2). A 4-m thick section at the right bank of the Irhzer River has been studied in detail (CDUE locality 1; Fig. 3). This section starts with pedogenetically-overprinted sandy siltstone (vertisol; bed 1) overlain by fluvial fine-grained sandstone (bed 2) with rounded clasts of reworked, pedogenetic carbonate nodules at the base. It is followed by thick, silty, fine-grained sandstone (bed 3). The horizontally laminated to micro-scale flaserbedded lowermost strata yielded several surfaces with shallow current ripples, raindrop impressions, microbially induced sedimentary structures, root traces, invertebrate traces, and tetrapod footprints. Bed 3 becomes massive at the top and is capped by fine-grained sandstone with dolomitic cement (bed 4). The pedogenetically overprinted siltstone (vertisol) of bed 5 is erosionally cut by stacked channels of pebbly sandstone to sandy conglomerate (bed 6). The upper part of the section is composed of thick, massive sandstone (bed 7), poorly stratified, granular to fine-pebble conglomerate (bed 8) and another pedogenetically overprinted sandy siltstone (vertisol; bed 9). Trace fossils have been found at four other localities close to the studied section: CDUE localities 2 and

Fig. 3. Detailed stratigraphic section of alluvial red beds in the middle part of the Ikakern Formation along the Irhzer River at CDUE locality 1.

4 are lateral equivalents to the described strata and CDUE localities 3 and 5 are laterally and vertically displaced a few metres below the section. It is remarkable that all trace fossils are related to fine-grained deposits within fluvial channels and not to overbank fines. Interpretation of the age of the Ikakern Formation has changed several times. Based on presumed remains of Voltzia heterophylla Brongniart, 1828 from Jebel Tafilalt, De Koning (1957) concluded a Triassic age. Jones (1975) and Brown (1980) supported this view due to finds of supposed rhynchosauroid tracks. The first vertebrate remains were also ascribed to the Triassic (Dutuit, 1976), but later redefined as Permian (Dutuit, 1988). Jalil (1996) and Jalil and Dutuit (1996) suggested a Kazanian (Middle Permian) age inferred from diplocaulid and captorhinid remains. The close relationship of pareiasaur skeletal remains from the Argana Basin to material from the Elgin locality in Scotland led finally to the assumption of a latest Permian age (Jalil and Janvier, 2005).

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Recently described large tetrapod tracks of Hyloidichnus Gilmore, 1927 and Pachypes Leonardi et al., 1975 from the uppermost part of the Ikakern Formation conform with a Middle to Late Permian age of the footprint-bearing strata (Voigt et al., 2010). The Irhzer River section with CDUE localities 1–5 is located in the middle part of the Tourbihine Member (T2) and represents the lowermost fossiliferous horizon of the Ikakern Formation known to date (Fig. 2). Although there is no independent control on the chronostratigraphical position of the described beds, we consider its age largely equivalent to the fossil-bearing strata in the uppermost part of the Ikakern Formation near Irerhi (Dutuit, 1988; Jalil and Dutuit, 1996; Jalil and Janvier, 2005; Voigt et al., 2010) because the Tourbihine Member of the wider study area is of principally uniform sedimentary character. By adopting the most conservative view (Voigt et al., 2010), a Middle to Late Permian age is proposed for the trace fossils from the Irhzer River section. 4. Systematic palaeoichnology 4.1. Invertebrate traces 4.1.1. Spongeliomorpha carlsbergi (Bromley and Asgaard, 1979) (Fig. 4A–D) 4.1.1.1. Referred specimen. CDUE 3 (Fig. 4A–B), single slab from CDUE locality 3 with three, partially overcrossing burrows in convex epirelief. Numerous other specimens at CDUE localities 2 and 3 have been studied in place only (Fig. 4C–D). 4.1.1.2. Description. Networks of cylindrical, predominantly horizontal burrows with unlined, deeply scratched walls. All burrows are preserved as epichnial ridges with striate, convex traces on the outer surface. Burrow diameter ranges from 6 to 10 mm. Striae are oblique or transverse to the main axis of the burrow and measure up to 1 mm in relief. Burrows commonly intersect, but also exhibit T- and Y-bifurcation; individual burrow segments seem to be randomly arranged. Burrow fill is in most cases silty sandstone similar to the host rock excepting for its massive appearance and abundant micro-brecciated mud-pebbles.

4.1.1.3. Discussion. Cylindrical burrows with sharp transverse striations were first described as Steinichnus carlsbergi by Bromley and Asgaard (1979) from non-marine Triassic red beds of Greenland. Later, Steinichnus was repeatedly suggested to be a subjective synonym of Spongeliomorpha Saporta, 1887 (Ekdale et al., 1984; Bromley and Asgaard, 1991; Bromley, 1996), although others (Metz, 1993a, 1995; Hasiotis, 2002; Gillette et al., 2003), based on traces from non-marine strata of North-America, argued for retention of Steinichnus, because the continental traces could be different from the marine Spongeliomorpha by the lack of dichotomous branching, box-network system, vertical shafts, and large chambers. With respect to shape, size, ornamentation, and filling, the described traces from the Ikakern Formation are indistinguishable from Steinichnus carlsbergi Bromley and Asgaard, 1979 and Spongeliomorpha milfordensis Metz, 1993a. Recently, Melchor et al. (2009) not only suggested the ichnotaxonomic identity of these two forms by careful revision of the type material but also argued for the priority of the ichnogenus Spongeliomorpha. We agree with this view and assign the traces from the Argana Basin to S. carlsbergi (Bromley and Asgaard, 1979). Cylindrical burrows with sharp transverse striation from nonmarine deposits have been interpreted to reflect locomotion and deposit feeding behaviour of insects, particularly mud-loving beetles (Heteroceridae) and mole crickets (Gryllotalpidae), that lived in wet habitats of alluvial and marginal lacustrine environments (Bromley and Asgaard, 1979; Metz, 1993a, 1995; Hasiotis, 2002; Gillette et al., 2003; Melchor et al., 2009).

4.1.2. Striatichnium natalis Walter, 1982 (Fig. 4E–F) 4.1.2.1. Referred specimen. CDUE 2 (Fig. 4E–F), one slab with a single trace preserved in convex hyporelief from CDUE locality 2.

4.1.2.2. Description. Indistinct, faint trace fossil, about 80 mm long and 25–30 mm wide, consisting of up to 15 mm long, slightly curved, delicate striae. Individual striae are transverse to the long axis of the trace; the distance between adjacent striae is less than 0.5 mm. Striae of right and left side overlap in a 5–10 mm wide zone along the midline of the trace at constant angles of ca. 80°.

Fig. 4. Invertebrate trace fossils from the Ikakern Formation of the Irhzer River section: (A–D) Spongeliomorpha carlsbergi (Bromley and Asgaard, 1979) and (E–F) Striatichnium natalis Walter, 1982. Material: (A and C) CDUE 3, (B and D) field photographs of uncollected material, all specimens from CDUE locality 3, preserved in convex epirelief; (E–F) CDUE 2 from CDUE locality 2, in convex hyporelief. Scale bars equal 2 cm.

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4.1.2.3. Discussion. CDUE 2 fits well the diagnostic features of Striatichnium natalis Walter, 1982. The ichnotaxon has been introduced for bi-lateral traces from continental red beds of the Upper Hornburg Formation of the Saale Basin, central Germany, considered to be Middle to Late Permian in age (personal communication U. Gebhardt, Karlsruhe). All other occurrences of the ichnotaxon are from Early Permian red beds of the Thuringian Forest, Germany (Martens, 1982; Walter, 1983; Voigt, 2005). A comprehensive discussion of Striatichnium Walter, 1982 and its four accepted ichnospecies is given by Minter and Braddy (2009). Walter (1982) interpreted the type material of S. natalis as combined locomotion and feeding traces of aquatic insect larvae or annelids. 4.2. Vertebrate tracks 4.2.1. Amphisauropus isp. indet. Haubold, 1970 (Fig. 5) 4.2.1.1. Referred specimen. CDUE 1 (Fig. 5), print and counterprint of isolated manus-pes set from CDUE locality 1. 4.2.1.2. Description. Incomplete trackway of a quadrupedal tetrapod with pentadactyl, plantigrade tracks of different size. The larger, ca. 90 mm long track, regarded to be the pes imprint, is a little bit longer than wide. It exhibits a serial increase in digit length from I to IV; digit V is not preserved. Digit impressions are broad and straight with rounded tips. The sole is characterised by a convex proximal margin and measures about half of the length of the imprint. The smaller track, regarded to be the manus imprint, is one third shorter than the pes imprint and almost as long as wide. Digit lengths increase from I to IV; digit V is about as long as II. The interdigital angle I–V measures ca. 130°. Digit imprints are broad with rounded to partially acute tips. The distal parts of the middle digits are curved inward. The unstructured palm shows a slightly convex proximal margin and is about half of the imprint’s length. In comparison to the pes, the manus imprint seems to be strongly rotated inward. 4.2.1.3. Discussion. CDUE 1 shares most characters with Amphisauropus Haubold, 1970, in particular the relative size of the imprints and the shape and proportions of the digits. With respect to im-

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print size, digit proportions, and the divarication of the manus and pes from hypothetical trackway midline, there are also similarities to Hyloidichnus Gilmore, 1927 (Voigt et al., 2010). Hyloidichnus differs from Amphisauropus by slender digits and semiplantigrade imprints. Ichniotherium Pohlig, 1892 as another similar ichnotaxon (e.g., Voigt et al., 2007) can be excluded because of the unstructured sole of the supposed pes imprint of CDUE 1. Consequently, we attribute the described tracks to the ichnogenus Amphisauropus. Ichnospecific assignment is kept open because of the limited material as well as the imprint proportions and the large size of the tracks that differ from A. kablikae (Geinitz and Deichmüller, 1882), as the only valid species of the ichnogenus (see Voigt, 2005). Amphisauropus has been referred to seymouriid trackmakers (Fichter, 1979, 1983a; Haubold, 2000; Lucas et al., 2001; Voigt, 2005, 2007). Skeletal remains of Seymouriidae are known from Late Carboniferous to Late Permian deposits of North America, Europe, Russia, China, and Central Asia (Berman et al., 1997). 4.2.2. Hyloidichnus isp. indet. Gilmore, 1927 (Fig. 6) 4.2.2.1. Referred specimen. CDUE 4 (Fig. 6), single trackway consisting of four coupled manus-pes tracks preserved as convex hyporelief on the lower surface of reddish-brown fine-grained sandstone at CDUE locality 4. CDUE 4 refers to latex moulds of each manuspes set and part of the original specimen (second manus-pes set of the left side). 4.2.2.2. Description. Trackway of a quadrupedal tetrapod with pentadactyl semiplantigrade footprints up to 60 mm in length. Manus and pes imprints differ slightly in size and digit proportions. Both imprints are one fifth wider than long and the pes is one fifth longer than the manus. The relatively long and slender digits increase in size from I to IV; V is about as long as I in the manus imprint, but ranges in length between I and II in the pes imprint. Digit tips are acute and enlarged, curved inwards in digits I–IV, but parallel to the digit or outward rotated in V. Both imprints, manus and pes, exhibit a very short sole with a straight to concave proximal margin. The trackway pattern is characterised by an alternating arrangement of coupled manus-pes tracks with forward-directed pes imprints, and inward- rotated manus imprints.

Fig. 5. Amphisauropus isp. indet. Haubold, 1970 from the Ikakern Formation of the Irhzer River section (CDUE locality 1), represented by an isolated manus-pes couple. (A) Concave epirelief, (B) convex hyporelief, (C) outline drawing. Material: CDUE 1; scale bars equal 5 cm.

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Fig. 6. Hyloidichnus isp. indet. (Gilmore, 1927) from the Ikakern Formation of the Irhzer River section. (A and D) Trackway and outline drawing; (B) first manus-pes set of the left side; (C) first manus-pes set of the right side. Material: Field photographs, tracks preserved in convex hyporelief on undercut slope (CDUE locality 4). Scale bars equal 5 cm (A and D) and 2 cm (B and C).

4.2.2.3. Discussion. CDUE 4 corresponds well with tracks of Hyloidichnus Gilmore, 1927 from the uppermost level of the Ikakern Formation south of Irerhi (Voigt et al., 2010). Hyloidichnus is most similar to Varanopus Moodie, 1929; both ichnotaxa differ only in the relative length of the fifth digit of the pes imprint (Voigt et al., 2009). Digit V is about 40% of the length of digit IV in Hyloidichnus, whereas it is more than 60% in Varanopus. Preservation of CDUE 4 does not allow reliable determination of this proportion, because digit V is preserved only in the first and last pes imprint as a faint impression of the digit tip. Nonetheless, the trackway pattern with inward-rotated manus imprints supports assignation to Hyloidichnus inasmuch as manus imprints are always forward directed in Varanopus (Voigt, 2005). Ichnospecific assignment is not possible due to the relatively poor preservation of the specimen. Tracks of Hyloidichnus and Varanopus are usually referred to captorhinids (Haubold, 1971; Fichter, 1983a,b; Gand, 1988; Haubold and Lucas, 2003; Voigt, 2005; Gand and Durand, 2006). More specifically, Voigt et al. (2009, 2010) argued for a track-trackmaker relationship of Hyloidichnus and moradisaurine captorhinids. 4.2.3. Erpetopus isp. indet. (Moodie, 1929) (Fig. 7) 4.2.3.1. Referred specimens. CDUE 357 to CDUE 360, four specimens with numerous tracks and indistinct trackways from CDUE locality 5, mainly preserved in convex hyporelief. 4.2.3.2. Description. Trackways of quadrupedal tetrapods with small pentadactyl plantigrade imprints. Pes imprints range from 4.0 to 7.5 mm in length and 5.0–6.0 mm in width. The slightly smaller manus imprints are between 3.5 and 6.8 mm long and 4.0–5.0 mm wide. Digits I to IV exhibit a serial increase in length; digit V of manus and pes imprint ranges in length between digits I and II. All digits exhibit distinct claw marks, which are curved inward in I and IV and outward or backward directed in V. The only known trackway shows an alternating arrangement of coupled manus-pes tracks with mainly forward-directed pes imprints and inward-rotated manus imprints. The stride length varies between 32 and 38 mm, the pace angulation between 60° and 70°. 4.2.3.3. Discussion. Imprint morphology and trackway pattern of the described tracks are most similar to Erpetopus (Moodie, 1929) from the late Early Permian Choza Formation, Texas (Haubold

and Lucas, 2001, 2003; Minter et al., 2007). Other occurrences of this ichnotaxon come from the late Early to Middle Permian of France and Italy (Haubold and Lucas, 2001, 2003; Gand and Durand, 2006; Santi, 2007). The validity of several Erpetopus ichnospecies is contradictorily assessed (Haubold and Lucas, 2001, 2003; Gand and Durand, 2006; Santi, 2007). Until careful revision of the ichnotaxon, we assign the Moroccan tracks to Erpetopus isp. indet. Erpetopus can be referred to small captorhinid trackmakers (Haubold, 2000; Haubold and Lucas, 2001, 2003). 4.2.4. Dromopus isp. indet. Marsh, 1894 (Fig. 8) 4.2.4.1. Referred specimens. CDUE 360, 366–369, five specimens with single and coupled manus-pes tracks preserved in concave epirelief and convex hyporelief from CDUE locality 5. Extremely poorly preserved material of the ichnotaxon from CDUE locality 2 has not been collected. 4.2.4.2. Description. Mainly digitigrade footprints of quadrupedal tetrapods with long and slender digits. All imprints are incompletely preserved commonly showing digits 2–3 (the middle digits) only. Very faint impressions of the digit tips of two short outer digits may be present in single isolated tracks. Middle digits increase in length from II to IV; IV significantly longer than III and moderately to strongly curved. The digit impressions usually exhibit an acute tip. Manus and pes imprints seem to be similar except for size. Estimated length of imprints ranges between 3 and 5 cm. 4.2.4.3. Discussion. Dromopus is the most common and most widespread Late Palaeozoic tetrapod ichnotaxon (Haubold, 1971, 1996, 2000; Gand, 1988; Lucas and Hunt, 2006; Voigt, 2005, 2007). The long, slender, often strongly curved digit imprints are easily recognisable and well represented in the material from the Ikakern Formation. Although more than a dozen ichnospecies of Dromopus are available from the literature, any separation based on anatomical characters has never been convincingly demonstrated (Gand, 1988; Haubold, 1996, 2000; Haubold and Lucas, 2003; Voigt, 2005). Incomplete tracks such as the described material does not contribute to this issue. Because of the rather poor preservation, we prefer to keep the specimens of the Ikakern Formation in open nomenclature at the ichnospecies level and assign them conservatively to Dromopus isp. indet. Dromopus is usually referred to liz-

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Fig. 7. Erpetopus isp. indet. Moodie, 1929 from the Ikakern Formation of the Irhzer River section. (A and E) Trackway and outline drawing; (B) close-up of the first manus-pes set of the left side of this trackway, preserved in convex hyporelief; (C) isolated left manus imprint; (E) isolated single tracks. Material: (A, B and E) CDUE 357, (C) CDUE 358, (D) CDUE 360, all from CDUE locality 5 and preserved in convex hyporelief. Scale bars equal 1 cm (A, B, D and E) and 0.3 cm (C).

ard-like diapsid eureptiles and parareptiles, such as araeoscelids and bolosaurids (Haubold, 1971, 1996, 2000; Gand, 1988; Haubold and Lucas, 2003; Voigt, 2005; Gand and Durand, 2006).

5. Palaeoecological implications and site’s importance

Fig. 8. Dromopus isp. indet. (Marsh, 1894) from the Ikakern Formation of the Irhzer River section. Single and coupled tracks showing impressions of digits II to IV or III and IV, respectively. Material: (A and B) CDUE 368, (C and D) CDUE 369, both from CDUE locality 5, preserved in convex hyporelief. Scale bars equal 1 cm.

Our data, and the preliminary ichnological work by Voigt et al. (2010), give evidence that invertebrate and vertebrate traces are abundant and diverse fossils in Permian red beds of the Argana Basin. Traces of S. carlsbergi (Bromley and Asgaard, 1979) were hitherto only known from Late Triassic to Miocene continental deposits (Bromley and Asgaard, 1979; Metz, 1993a,b, 1996; Gillette et al., 2003; Melchor et al., 2007). The Moroccan specimens extend the range of the ichnotaxon to the Palaeozoic. With respect to environmentally and morphologically similar burrows recorded from the late Early Permian of Texas (Lucas et al., 2011), there are now strong arguments that insects, i.e. most likely early coleopterans, had adopted subsurface burrowing behaviour in episodically inundated freshwater settings well before the Mesozoic. The occurrence of Striatichnium natalis Walter, 1982, so far restricted to Permian red beds of Germany, provides the first indirect evidence for aquatic invertebrates, such as larval insects or annelids, from the Ikakern Formation. The tetrapod footprint record from the Permian of the Argana Basin now includes five different ichnotaxa: Amphisauropus Haubold, 1970, Pachypes Leonardi et al., 1975, Hyloidichnus Gilmore, 1927, Erpetopus Moodie, 1929, and Dromopus Marsh, 1894. Tracks of these morphotypes can be referred to anamniote reptiliomorph, parareptilian, and diapsid and non-diapsid eureptilian producers. With moradisaurine captorhinids (?Hyloidichnus) and pareiasaurs (?Pachypes) only two tetrapod ichnotaxa have potential equivalents in the skeletal record of the Ikakern Formation (Jalil and Dutuit, 1996; Jalil and Janvier, 2005; Voigt et al., 2010). It is remarkable, that neither the body fossil record nor the ichnofauna of the study area yields evidence for synapsids so far.

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Recent progress on the palaeontology of the Ikakern Formation indicates the great potential of this unit for the reconstruction and understanding of Late Palaeozoic terrestrial ecosystems. All available data previous to this work suggest a Middle to Late Permian age of the formation’s upper part (Tourbihine Member, T2; Jalil and Dutuit, 1996; Jalil and Janvier, 2005; Voigt et al., 2010). If the latest Permian age of the beds (as proposed by the analysis of pareiasaurian remains; Jalil and Janvier, 2005) were to become confirmed, the Argana Basin will serve soon as a key reference for the evolutionary ecology of low latitude inland basins right before or even during the much debated end-Permian biotic crisis. Acknowledgements The support of the German Academic Exchange Survey (DAAD) is gratefully acknowledged by A. Hminna (PhD Sandwich Scholarship; A/07/80641) and H. Saber (study-visit grants for joint research work at the TU Bergakademie Freiberg). This work contributes to the project on late Palaeozoic and early Mesozoic tetrapod ichnofaunas of Morocco supported by the German Research Foundation (DFG SCHN 408/17-1). We thank S.G. Lucas and an anonymous reviewer as well as journal editor P.G. Eriksson for constructive comments on the manuscript. References Berman, D.S., Sumida, S.S., Lombard, R.E., 1997. Biogeography of primitive amniotes. In: Sumida, S.S., Martin, K.L.M. (Eds.), Amniote Origins: Completing the Transition to Land. Academic Press, Sand Diego, pp. 85–139. Bromley, R.G., 1996. Trace Fossils: Biology, Taphonomy, and Applications. Chapman and Hall, London, p. 361. Bromley, R.G., Asgaard, U., 1979. Triassic freshwater ichnocoenoses from Carlsberg Fjord, East Greenland. Palaeogeography, Palaeoclimatology, Palaeoecology 28, 39–80. Bromley, R.G., Asgaard, U., 1991. Ichnofacies: a mixture of taphofacies and biofacies. Lethaia 24, 153–163. Brown, R.H., 1980. Triassic rocks of Argana Valley, Southern Morocco and their regional structural implications. American Association of Petroleum Geologists Bulletin 64, 988–1003. De Koning, G., 1957. Géologie des Ida ou Zal (Maroc). Stratigraphie, pétrographie et tectonique de la partie Sud-Ouest du bloc occidental du Massif ancien du HautAtlas (Maroc). Leidse Geologische Mededelingen 23, 1–215. Dutuit, J.-M., 1976. Il est probable que les Rhynchocéphales sont représentés dans la faune du Trias marocain. Comptes Rendus de l’Académie des Sciences, Paris D283, 483–486. Dutuit, J.-M., 1988. Diplocaulus minimus n. sp. (Amphibia: Nectridea), Lépospondyle de la formation d’Argana dans l’Atlas occidental marocain. Comptes Rendus de l’Académie des Sciences, Paris D307, 851–854. Ekdale, A.A., Bromley, R.G., Pemberton, S.G., 1984. Ichnology: the use of trace fossils in sedimentology and stratigraphy. SEPM Short Course Notes 15, 1–317. Fichter, J., 1979. Aktuopaläontologische Studien zur Lokomotion rezenter Urodelen und Lacertilier sowie paläontologische Untersuchungen an Tetrapodenfährten des Rotliegenden (Unter-Perm) SW-Deutschlands. Unpublished PhD thesis, Johannes Gutenberg University Mainz, p. 425. Fichter, J., 1983a. Tetrapodenfährten aus dem saarpfälzischen Rotliegenden (OberKarbon – Unter-Perm; Südwest-Deutschland) I: Fährten der Gattungen Saurichnites, Limnopus, Amphisauroides, Protritonichnites, Gilmoreichnus, Hyloidichnus und Jacobiichnus. Mainzer Geowissenschaftliche Mitteilungen 12, 9–121. Fichter, J., 1983b. Tetrapodenfährten aus dem saarpfälzischen Rotliegenden (?OberKarbon – Unter-Perm; SW-Deutschland). Teil II: Die Fährten der Gattungen Foliipes, Varanopus, Ichniotherium, Dimetropus, Palmichnus, cf. Chelichnus, cf. Laoporus und Anhomoiichnum. Mainzer Naturwissenschaftliches Archiv 21, 125–186. Gand, G., 1988. Les traces de vertébrés tétrapodes du Permien francais. Thèse de Doctorat d’ Etat ès Sciences Naturelles, Université de Bourgogne, Edition Centre des Sciences de la Terre, Dijon, p. 341. Gand, G., Durand, M., 2006. Tetrapod footprint ichnoassociations from French Permian basins. Comparisons with other Euramerican ichnofaunas. Geological Society London, Special Publications 265, 157–177. Geinitz, H.B., Deichmüller, J.V., 1882. Die Saurier der unteren Dyas von Sachsen. Palaeontographica 29, 1–46. Gillette, L., Pemberton, S.G., Sarjeant, W.A.S., 2003. A Late Triassic invertebrate ichnofauna from Ghost Ranch, New Mexico. Ichnos 10, 141–151. Gilmore, G.W., 1927. Fossil footprints from the Grand Canyon II. Smithsonian Miscellaneous Collections 80, 1–78. Harding, A.G., Brown, R.H., 1974. Structural controls over thickness and facies distributions in a Late Triassic–Early Jurassic carbonate–sulfate-redbed

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