bird-like tracks from the imilchil formation (middle...

Bollettino della Società Paleontologica Italiana, 56 (2), 2017, 207-215. Modena

ISSN 0375-7633 doi:10.4435/BSPI.2017.19

Bird-like tracks from the Imilchil Formation(Middle Jurassic, Bajocian-Bathonian) of the Central High Atlas, Morocco,

in comparison with similar Mesozoic tridactylous ichnotaxa

Gerard D. Gierliński, Abdelouahed Lagnaoui, Hendrik klein, Hafid saber, Mostafa OukassOu &André Charrière

G.D. Gierliński, Państwowy Instytut Geologiczny - Państwowy Instytut Badawczy, ul. Rakowiecka 4, 00-975 Warszawa, Poland; Stowarzyszenie “Delta”, ul. Sandomierska 4, 27-400 Ostrowiec Św., Poland; Moab Giants, 112W.SR 313, Moab, UT 84532, USA; [email protected]

A. Lagnaoui, Laboratory of Geodynamic and Geomatic, Department of Geology, Faculty of Sciences, Chouaïb Doukkali University, B.P. 20, El Jadida, MA-24000 Morocco; Laboratory of Stratigraphy of Oil and Gas Bearing Reservoirs, Department of Paleontology and Stratigraphy, Institute of Geology and Petroleum Technologies, Kazan (Volga Region) Federal University, Kremlyovskaya str. 18, 420008 Kazan, Russia; [email protected]

H. Klein, Saurierwelt Paläontologisches Museum, Alte Richt 7, D-92318 Neumarkt, Germany; [email protected]. Saber, Laboratory of Geodynamic and Geomatic, Department of Geology, Faculty of Sciences, Chouaïb Doukkali University, B.P. 20, El Jadida,

MA-24000 Morocco; [email protected] M. Oukassou, Laboratory of Sedimentary Basins Dynamic and Geological Correlations, Department of Geology, Faculty of Sciences Ben M’sik, Hassan

II University of Casablanca, B.P. 7955, Sidi Othman, Casablanca, Morocco; [email protected]. Charrière, Toulouse III University, 13 Terrasses de la Figuière, F-30140 Anduze, France; [email protected]

KEYWORDS - Bird-like tracks, Middle Jurassic, Morocco, Trisauropodiscus, Carmelopodus, Ornithomimipodidae.

ABSTRACT - Small bird-like tracks have recently been discovered at three outcrops of the Imilchil Formation (Middle Jurassic, Bajocian-Bathonian) in the Central High Atlas of Morocco. The track-bearing strata are part of a marine-continental transitional succession, the studied surfaces being sandy marls and limestones of a brackish depositional environment. The footprints strongly resemble the ichnogenus Trisauropodiscus Ellenberger, 1970, from the Lower Elliot Formation (latest Triassic) of Lesotho, southern Africa and are assigned to Trisauropodiscus isp. These are functionally tridactyl, widely divaricated pes tracks with digit III being longest and a trace of the reverted digit I (hallux) being occasionally imprinted. In contrast to some former studies suggesting Trisauropodiscus as a junior synonym and extramorphological variation of the ornithischian ichnogenus Anomoepus, this ichnotaxon is considered here as a distinctive morphotype among similar theropod tracks found in Jurassic-Cretaceous ichnoassemblages. An amended diagnosis is proposed focusing on the features that are here discussed and considered as key characters of this ichnotaxon. An avian interpretation of the trackmaker is problematical, especially against the background of the stratigraphic range of Trisauropodiscus back to the Late Triassic. Presently, theropods with very bird-like feet are the more likely producers. Future analyses and comparison of Trisauropodiscus with pes skeletons of avian and non-avian theropods might enlighten this.

RIASSUNTO - [Impronte bird-like dalla Formazione Imilchil (Giurassico Medio, Baiociano-Bathoniano) dell’Alto Atlante Centrale, Marocco] - Recentemente sono state scoperte alcune piccole impronte bird-like (simili a quelle di uccello) in tre affioramenti della Formazione di Imilchil (Giurassico Medio, Baiociano-Bathoniano) nell’Alto Atlante Centrale del Marocco. Gli strati con le impronte sono parte di una successione transizionale marina-continentale e le superfici studiate sono rappresentate da marne sabbiose e calcaree di un ambiente deposizionale salmastro. Le impronte assomigliano fortemente all’icnogenere Trisauropodiscus Ellenberger, 1970, dalla Lower Elliot Formation (Triassico Superiore) del Lesotho (Africa meridionale) e sono stati assegnati a Trisauropodiscus isp. Queste impronte sono funzionalmente tridattile, presentano un pes ampiamente divaricato, il dito III più lungo e la traccia del dito I (hallux) occasionalmente impressa.

In contrasto con alcuni studi precedenti, che suggeriscono Trisauropodiscus come junior synonym e variante extramorfologica dell’icnogenere ornitischio Anomoepus, questo ichnotaxon è considerato come un morfotipo distintivo fra simili tracce di teropodi giurassico-cretacei. Si propone una diagnosi emendata basata su caratteristiche ben conservate che si osservano sia nel materiale tipo dall’Africa meridionale che nel nuovo materiale. Un’interpretazione aviana del produttore è problematica, soprattutto sulla base del range stratigrafico (Triassico Superiore). Attualmente, i produttori più probabili sono teropodi con piedi simili a quelli degli uccelli. Questo scenario potrebbe essere ulteriormente chiarito da analisi future e dal confronto di Trisauropodiscus con resti scheletrici del pes di teropodi aviani e non.

INTRODUCTION

Footprints of birds or avian theropods are abundantly known from Cretaceous and Cenozoic deposits of North America, Europe and East Asia. In particular shorebirds have left their tracks on numerous surfaces variously co-occurring with those of non-avian theropods, ornithopods or pterosaurs (Lockley et al., 1992, 2006; Lockley, 1999; Lockley & Rainforth, 2002; Kim et al., 2012; McCrea et al., 2014; Xing et al., 2015). Bird-like footprints are known from the Jurassic but were poorly recognized in comparison with avian theropod body fossils, which include new finds from the Callovian-Oxfordian of China

(e.g., Godefroit et al., 2013) as well as the classic material of Archaeopteryx von Meyer, 1861, from the Tithonian Solnhofen Limestone of Germany. The stratigraphically oldest bird-like footprints are reported from deposits that are latest Triassic and Early Jurassic in age. They come from the Lower Elliot Formation of Lesotho, southern Africa (Ellenberger, 1970, 1972), the Newark Supergroup of Massachusetts and Virginia, USA (Hitchcock, 1858) and from the Przysucha Formation of Poland (Gierlinski, 1996). Younger records are known from the latest Jurassic-earliest Cretaceous Tuchengzi Formation of Liaoning Province, China (Lockley et al., 2006), an area famous for its discoveries of avian theropods. Ichnotaxonomically all

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these footprints were assigned to different ichnogenera and ichnospecies. Hitchcock (1858) introduced the ichnotaxon Plesiornis pilulatus for specimens from the Newark Supergroup while those from the Lower Eliott Formation were named Trisauropodiscus by Ellenberger (1970). For the footprints from Liaoning the new ichnotaxon Pullornipes aureus was erected by Lockley et al. (2006). Unnamed bird tracks were also reported from the Late Jurassic of Asturias, Spain (Pinuela et al., 2002). From Middle Jurassic deposits of Msemrir, Morocco, Belvedere et al. (2011) reported small tridactyl bird-like imprints similar to the footprints from Imilchil described here.

The latter material was found during two field trips to the Central High Atlas of Morocco, in September 2009 and October 2016. First finds came from the vicinity of Imilchil in 2009 and were mentioned by Gierliński et al.

(2009) as tracks similar to Carmelopodus Lockley, Hunt, Paquette, Bilbey & Hamblin (1998), an ichnogenus also recognized in Middle Jurassic strata of this region. In 2016, authors collected more material from the original site and also found similar bird-like footprints near Sountate, co-occurring with the invertebrate traces Selenichnites and Kouphichnium in the same stratigraphic unit (Lagnaoui et al., 2016) (Fig. 1).

We focus here on the ichnotaxonomic status of the studied material, leaving the problem of the affinity to distinct biological groups open for future debates. Prospective detailed analyses of bird-like footprints especially from the Lower and Middle Jurassic and comparison with known skeletal material might enlighten the dark ages of bird evolution and help to better discriminate between bird and non-avian theropod feet.

Fig. 1 - Location of described bird-like tracks from the Middle Jurassic of the Central High Atlas, Morocco. a) Map showing study area in Morocco. b) Geological map of the Imilchil region with position of tracks. c) Stratigraphic section showing Middle Jurassic succession near Imilchil with position of tracks and invertebrate body fossils.

209G.D. Gierliński - Bird-like tracks from the Imilchil Formation, Marocco

MATERIAL, METHODS AND SPECIMENS REPOSITORY

All ichnites, described herein, are preserved as natural casts and molds. Artificial casts to replicate specimens were produced by using Sculpey polymer clay (polyvinyl chloride). Photographs were taken strictly parallel to the surface by ultra low distortion Carl Zeiss lens, under controlled artificial low-key lighting diffused by an additional filter. All measurements are based on standard methods proposed by Haubold (1971) and Leonardi (1987). Track images with cropped matrix around footprints were made using few photos (taken with different lighting or virtually obtained from a single picture) as background layers and then hand shaped and drawn (usually combined with re-drawing of track replicas) using a graphic tablet, employing vector-based drawing software. This method combined few different techniques of illustrating the footprints in order to reduce subjectivity of interpretation.

Institutional abbreviations of specimens’ repositoryAC: Pratt Museum of Natural History, Amherst

College, Amherst, Massachusetts, USA;CDUE: Chouaïb Doukkali University, El Jadida, Morocco; CMN: Canadian Museum of Nature, Ottawa, Canada; CU-MWC: Joined collection of the University of

Colorado and the Museum of Western Colorado, Boulder and Grand Junction, Colorado, USA;

GNM: Georgian National Museum Tbilisi, Georgia; JuraPark: collection of Stowarzyszenie “Delta”,

Ostrowiec Św., Poland;LES: Laboratoire de Paléontologie, Institut de

Sciences de l’Evolution, University of Montpellier II, Montpellier, France;

Muz. PIG: Muzeum Geologiczne, Państwowy Instytut Geologiczny - Państwowy Instytut Badawczy, Warsaw, Poland;

UCM: University of Colorado Museum of Natural History, Denver, Colorado, USA.

GEOLOGICAL SETTING

The Imilchil region is situated in the heart of the Central High Atlas that was formed through inversion of former Triassic-Liassic rift basins during the Africa-Eurasia convergence, which consists of different anticlinal-synclinal structures (Frizon de Lamotte et al., 2008). The studied area lies in an elliptically-shaped basin of the Ait Ali Ou Ikko Syncline, trending toward ENE-WSW. The approximately 30 km long and 5-15 km wide syncline is bounded by two anticline ridges: the Msadrid-Ikko Ridge in the North and Amagmag Ridge in the South (Fig. 1b-c), slightly deformed during the Cenozoic and crosscut by several transverse faults. The post-Variscan sedimentation began with the deposition of thick Permian and Triassic clastics and evaporites producing the subsequent diapirism (Bouchouata et al., 1995; Ettaki et al., 2007; Michard et al., 2011; Saura et al., 2014). In the Imilchil area, the Jurassic marine succession overlies the widespread Central Atlantic Magmatic Province (CAMP) basalts (Youbi et al., 2003). Formerly, Studer (1987) subdivided

the Jurassic deposits near Imilchil into three formations that were later revised as five formations (Ibouh, 1995, 2004). The synthetic classification is from base to top: 1) Tassent Formation (= Agoudim 1; Toarcian-Aalenian), consisting of platform carbonates, marls and shales (> 600 m), overlying shallow water limestones (~ 300-400 m) of Hettangian-Sinemurian age; 2) Bab n’Ouayad Formation (= Agoudim 2; early Bajocian), dominated by reefal limestones or “Calcaire Corniche” and outcropping mostly along the ridge of the anticline (> 200 m); 3) Tislit Formation (= Agoudim 3, late Bajocian), consisting of shallow water limestones and marls (~ 600 m). These three formations constitute a marine sequence of about 2000 m thickness, upwardly followed by 4) brackish deposits of the marine-continental transitional Imilchil Formation (= Anemzi 1; late Bajocian-Bathonian; ~ 200 m) and topped by 5) continental red beds of the Isli Formation (= Anemzi 2; late Bathonian-?Callovian; ~ 250 m).

The tracksites with bird-like footprints presented in this paper are located at both flanks of the Ait Ali Ou Ikko Syncline, about 2 km northeast of Imilchil village and 500 m east of Sountate Village near the road R317 (Fig. 1b). The material comes from the middle and uppermost parts of the Imilchil Formation that mainly consist of alternating red and green sandy marls and sandy limestones laid down in a brackish depositional environment. Characteristic features of the track-bearing layers are lamination, mud-cracks, and diverse invertebrate ichnoassemblages, including the ichnogenus Selenichnites (Lagnaoui et al., 2016).

SYSTEMATIC PALEONTOLOGY

Theropoda Marsh, 1881Ichnofamily TrisaurOpOdiscidae Lockley, Yang,

Matsukawa, Fleming & Lim, 1992

Ichnogenus Trisauropodiscus Ellenberger, 1970Type ichnospecies Trisauropodiscus aviforma

Ellenberger, 1970(Fig. 3)

Emended diagnosis - Functionally tridactyl (with main digit group II-IV) footprints of small to medium-sized bipeds with occasional presence of a trace of the reversed semi functional hallux. Footprints mesaxonic, symmetrical with digit III being longest and lateral digits are subequal in length. Tracks lack metatarsophalangeal pads of digits II and IV, while that one of digit III is occasionally present, but not clearly separated from phalangeal portion of digit III. Digits are very narrow and widely divaricated (> 90°).

Included ichnotaxa - Trisauropodiscus aviforma, T. galliforma Ellenberger, 1970 and T. superaviforma Ellenberger, 1970.

Remarks - Trisauropodiscus is slightly different from other Triassic and Jurassic tracks of supposed avian origin. It differs from Plesiornis Hitchcock, 1858 by being larger and much wider with relatively shorter claws and is distinguished from Pullornipes Lockley, Matsukawa, Ohira, Li, Wright, White & Chen, 2006 by being more gracile in its morphology and showing more narrow digits.


However, contrary to Trisauropodiscus, the most important feature of Plesiornis and bird tracks is the well developed and separated metatarsophalangeal pad of digit III. The reversed hallux and swollen proximal pad of digit

III extends the main gripping surface axially from digit III to the hallux. This adaptation observed in modern flying birds enhances foot grasping ability and evolved probably parallel to wings’ development compensating for the deterioration of the forelimbs’ grasping functions (Gierliński & Sabath, 1998; Gierliński, 2000).

Trisauropodiscus does not exhibit a clearly separated proximal pad of digit III and the reversed hallux is not well visible or is absent. Thus, Trisauropodiscus is less bird-like than Plesiornis, Pullornipes and the Cenozoic avian ichnogenus Gruipeda Panin & Avram, 1962. The latter was considered as a junior synonym of Trisauropodiscus by Valais & Melchor (2008), which is not widely accepted (Abrahams et al., 2017).

On the other side, Trisauropodiscus was considered as the junior synonym of Anomoepus (e.g., Lockley & Harris, 2010), or as a separate ichnogenus, but close to Anomoepus (Abrahams et al., 2017). Recently described Trisauropodiscus-like footprints from the Early and Middle Jurassic of China are assigned directly to Anomoepus (Xing et al., 2016a, 2017), whereas Abrahams et al. (2017) argued to keep Trisauropodiscus as a separate ichnogenus from Anomoepus, but similar to the latter and of ornithischian origin as well (precisely of heterodontosaurid origin). In our opinion however, Trisauropodiscus does not exhibit any of the typical anomoepodid nor ornithischian foot patterns (see, discussion chapter).

Trisauropodiscus corresponds quite well with the morphology of seemingly non-avian theropod tracks of Carmelopodus Lockley, Hunt, Paquette, Bilbey & Hamblin, 1998, which in turn are very similar to Cretaceous tracks assigned to the ichnofamily Ornithomimipodidae by Lockley et al. (2011).

Occurrence - Late Triassic to Middle Jurassic of southern and northwestern Africa, and southeastern Asia.

Trisauropodiscus isp. (Fig. 2)

Material - Collected specimens from Imilchil vicinity CDUE 700 and CDUE 701 (Fig. 2c-d); casted specimen from Imilchil vicinity Muz. PIG 1816.II.1 (Fig. 2a); uncollected and not casted specimen from Sountate vicinity located at N32°9’58.56” and W5°36’31.82” (Fig. 2b); uncollected and not casted specimen located at N32°7’19.72” and W5°32’50.54” (Fig. 2e).

Localities - Vicinity of Imilchil and Sountate, Moroccan High Atlas (Fig. 1).

Description - The small pes imprints are functionally tridactyl with the reversed and reduced hallux shallowly impressed. Their length, excluding the trace of the hallux, varies from 5.4 cm up to 7.3 cm and their width is 6 cm to 9.3 cm depending on the varying digit divarication. The length/width ratio can be calculated with 0.8-0.9 indicating imprints that are slightly wider than long. Digits II, III and IV are relatively long and narrow and continuously tapering distally. Digit III is about twice as long when compared to lateral digits II and IV. The latter are equal

Fig. 2 - Trisauropodiscus isp. from Imilchil Formation (Middle Jurassic) of Central High Atlas, Morocco. a) Casted specimen Muz PIG 1816.II.1 from the vicinity of Imilchil. b) Uncollected specimen from the vicinity of Imilchil, located at N32°9’58.56” and W5°36’31.82”. c) Collected specimen from Imilchil vicinity CDUE 700. d) Collected specimen from Imilchil vicinity CDUE 701. e) Uncollected specimen from the vicinity of Sountate, located at N32°7’19.72”, W5°32’50.54”. Figs c-e are reversed for comparison.


in length representing 44-61% of the length of digit III. Digit I (hallux) is about 22% up to 32% in length when compared to the length of digit III. The projection of digit III above the tips of the lateral digits is very high and amounts to 52-73% of the footprint length excluding the hallux trace. The total divarication (the angle measured between the long axes of digits II and IV) varies between 98° and 127°.

Remarks - The morphology is comparable to the

type material of Trisauropodiscus from the Lower Elliot Formation of Lesotho (Fig. 3) which comprises mesaxonic footprints, symmetrical with narrow and widely divaricated digits II-IV (> 90°) and characterized by lack of metatarsophalangeal pads of digits II and IV, very long digit III, digits II and IV of about half the length of digit III, occasional presence of a trace of the short and clearly reversed semi functional digit I.

Stratigraphy and age - Imilchil Formation, Middle Jurassic (Bajocian-Bathonian).

DISCUSSION

Morphologically similar footprints from the Middle Jurassic of Morocco have been described from the Msemrir region by Belvedere et al. (2011). They show widely divaricated, slender digits and a prominent middle toe strongly resembling the material from Imilchil. Belvedere et al. (2011) are uncertain about the presence of a hallux (digit I) trace questionably preserved in some imprints. Indeed these tracks from Msemrir seem to lack this feature. In this respect and by the absence of a metatarsophalangeal pad they are morphologically closer to the ichnogenus Carmelopodus (see below).

Described footprints from Imilchil strongly resemble the Late Triassic ichnogenus Trisauropodiscus. The latter was originally introduced by Ellenberger (1970) based on

material from the Lower Elliot Formation (latest Triassic) of Lesotho, southern Africa (Fig. 3). Ellenberger (1970, 1972) erected different ichnospecies such as T. aviforma, T. galliforma, T. superaviforma and several others, which seem to be junior synonyms of T. aviforma and T. galliforma. It was apparent that Trisauropodiscus is distinct from other tridactyl theropod tracks occurring in the same unit, mostly small to large grallatorid forms that were described by Ellenberger (1970, 1972, 1974) under various new names. However, the exact status and the affinity of Trisauropodiscus were questioned and widely discussed by several authors.

Olsen & Galton (1984) suggested Trisauropodiscus as a junior synonym of Anomoepus Hitchcock, 1848. Lockley et al. (1992) defended Trisauropodiscus as a distinct ichnogenus erecting the ichnofamily Trisauropodiscidae and new ichnospecies Trisauropodiscus moabensis based on footprints from the Lower Jurassic of Utah (USA). Subsequently, Lockley & Rainforth (2002) again favored synonymy of Trisauropodiscus with Anomoepus and Trisauropodiscus moabensis was redescribed as Anomoepus by Lockley & Gierlinski (2006). However, in the meantime, Knoll (2004) argued against the synonymy of Trisauropodiscus with Anomoepus and later Valais & Melchor (2008) referred Trisauropodiscus to the Cenozoic avian ichnogenus Gruipeda Panin & Avram, 1962.

Presently, most authors consider Trisauropodiscus as the junior synonym of Anomoepus (e.g., Lockley & Harris, 2010), or distinct morphotype similar to Anomoepus (Abrahams et al., 2017). Originally Anomoepus was described from Early Jurassic deposits of the Newark Supergroup of eastern North America (Hitchcock, 1848; Olsen & Rainforth, 2003). The well-preserved type material shows footprints of a functionally tridactyl and facultative biped with moderately divaricated, relatively short and slightly cigar-shaped digits that are subequal in length. The pes of Anomoepus is asymmetrical because of the presence of a metatarsophalangeal pad in digit IV. This is similar to the pad configuration in the classic theropod ichnotaxon Grallator Hitchcock, 1858 and in most of no-avian dinosaur tracks. The relatively short digits being subequal in length, or with digit IV being longest when including the metatarsophalangeal pad impression, is the characteristic feature of all anomoepodid-like pes imprints that can be comprised in the Anomoepus-Moyenisauropus-Shenmuichnus plexus (Fig. 4), which combines morphologically similar tracks of basal ornithischians and basal thyreophorans.

Whatever the biological affinity of the Trisauropodiscus trackmaker might be, this ichnogenus comprises tracks of small bipeds with relatively long, elongate, widely divaricated digits, and with the pes being symmetrical - V or U shaped (Gierlinski, 2016; Abrahams et al., 2017). Similar to Grallator and all grallatorid tracks (Fig. 5), and contrary to Anomoepus and other Anomoepus-like footprints (Fig. 4), Trisauropodiscus shows a prominent, very long middle digit III and lateral digits II and IV of about half the length of the middle digit and nearly equal in their extension.

Looking at the osteological record and the skeletons of preserved theropod feet, such a long digit III is found among abelisauroid theropods. An exceptionally long digit III is seen in the abelisauroid Velocisaurus Bonaparte,

Fig. 3 - Type material of Trisauropodiscus aviforma Ellenberger, 1970 (type species of Trisauropodiscus) from the Lower Elliot Formation (Upper Triassic) of Lesotho. a) Casted specimen LES 47,2 of the holotype left in situ. b) Casted specimen LES 47,4 of the paratype left in situ.


1991 from the Upper Cretaceous of Argentina (Gierlinski et al., 2017). Grallatorid tracks that reflect that feature come from the mid-Cretaceous of Argentina (Fig. 5a) and very recently it has been also found by the authors in mid-Cretaceous deposits of Morocco (Fig. 5b). This distinguished type of theropod footprints was named Deferrariischnium by Calvo, 1991 (see also Calvo, 2007).

However, in contrast to Deferrariischnium (as well as to Grallator and Anomoepus), Trisauropodiscus, has no metatarsophalangeal pad of the fourth digit. The proximal pad of Trisauropodiscus is located centrally below the middle toe, but not well separated from digit

III. Sometimes when no hallux is visible, Trisauropodiscus tracks are not much distinguishable from Carmelopodus ichnites. This is why Trisauropodiscus tracks from Imilchil were previously reported as Carmelopodus by Gierliński et al. (2009). On the other hand, Carmelopodus is consistent morphologically with tracks of the ichnofamily Ornithomimipodidae Lockley, Cart, Martin & Milner, 2011. Ornithomimipodidae comprises the ichnogenera Irenichnites Sternberg, 1932, Columbosauripus Sternberg, 1932, Magnoavipes Lee, 1997, Ornithomimipus Sternberg, 1926 and Xiangxipus Zeng, 1982. The latter ichnogenus Xiangxipus was referred recently to Ornithomimipodidae by Xing et al. (2016b). However, Xiangxipus is rather comparable to Saurexallopus Harris, 1997, as shown by Gierlinski & Lockley (2013) and that view was not disproved by Xing et al. (2016b), nor Saurexallopus was added to Ornithomimipodidae. So, here we consider the ornithomimipodid morphotype as Irenichnites-Columbosauripus-Magnoavipes-Ornithomimipus plexus of tridactylous ichnotaxa only, excluding similar tetradactyl forms like Xiangxipus and Saurexallopus.

Ornithomimipodid tracks are symmetrical with the middle digit III being longer than the lateral ones. Digits are widely divaricated and slender. More precisely, Lockley et al. (2011) listed ornithomimipodid diagnostic features as follows: 1) digit II separated from the rest of the footprint; 2) proximal pad connected to digit III and IV, centrally located and separated from the phalangeal portion of digit III. Carmelopodus does not share those features concerning the proximal pad because its characteristic is the lack of those pads. However, it shares some ornithomimipodid characteristics such as the widely divaricated slender digits with the prominent middle toe and digit II separated from the rest of the footprint, which is well visible in the holotype of Carmelopodus untermannorum Lockley, Hunt, Paquette, Bilbey & Hamblin, 1998 (specimen CU-MWC 184.12; Fig. 6a), in Carmelopodus tracks from the Middle Jurassic of Morocco (Fig. 6b) and in cf. Carmelopodus from the

Fig. 4 - Anomoepus-Moyenisauropus-Shenmuichnus plexus footprints for comparison. a) Collected specimen AC 48/1, Anomoepus scambus Hitchcock, 1848 from Turners Falls Formation (Lower Jurassic) of Massachusetts, USA. b) Collected specimen Muz. PIG 1560,II,28, Anomoepus pienkovskii Gielinski, 1991 from Przysucha Formation (Lower Jurassic) of Holy Cross Mts., Poland. c) Specimen Muz. PIG 1651.II.3, Moyenisauropus natator Ellenberger, 1974, from Zagaje Formation (Lower Jurassic) of Holy Cross Mts., Poland. d) Track C6, the holotype of Shenmuichnus youngteilhardorum Li, Lockley, Zhang, Hu, Matsukawa & Bai, 2012, from Fuxian Formation (Lower Jurassic) of Shaanxi Province, China.

Fig. 5 - Grallatorid footprints of probable abelisauroid affinity. a) Uncollected specimen of Deferrariischnium mapuchensis Calvo, 1991 (adapted from Calvo, 2007) from Rio Limay Fomation (mid-Cretaceous) of Patagonia, Argentina. b) Casted specimen JuraPark J525, Deferrariischnium isp. from Midelt Formation (mid-Cretaceous) of High Moulouya, Morocco. Images reversed for comparison.


Lower Cretaceous of Utah reported by Lockley et al., 2014 (Fig. 6c).

The Carmelopodus-Irenichnites-Columbosauripus-Magnoavipes-Ornithomimipus plexus (Fig. 6) seems to be more closely related to the Trisauropodiscus morphotype than the Anomoepus-Moyenisauropus-Shenmuichnus plexus (Fig. 4).

Carmelopodus and ornithomimipodid are similar, but this does mean that Carmelopodus should be referred to the ichnofamily Ornithomimipodidae. Both types of tracks, Carmelopodus and ornithomimipodid footprints, are rather produced by two different groups of derived theropods with similar foot morphologies. Carmelopodus footprints are supposed to be of alvarezsauroid origin (Niedźwiedzki et al., 2017) and Ornithomimipodidae are widely considered as ornithomimosaurid tracks (e.g. Lockley et al., 2011; Xing et al., 2016b). However, it is also noteworthy that some researchers suggest more complicate picture of Carmelopodus and ornithomimipodid affinities. Hunt-Foster supposed ornithomimosaurid affinity of Carmelopodus-like tracks from the Early Cretaceous Cedar Mountain Formation of Utah (Rebecca Hunt-Foster personal comm., 2017). On the other hand, ornithomimosaurid footprints (possibly Ornithomimipus misidentified as Magnoavipes) from the Late Cretaceous Cantwell Formation of Alaska are supposed of direct avian origin (see Fiorillo et al., 2011).

CONCLUSIONS

Trisauropodiscus comprises tracks of small bipeds with the symmetrical pes, with widely divaricated digits, prominent middle toe and lateral digits shorter and

subequal in length. Similar to Grallator and all grallatorid tracks and contrary to Anomoepus and other Anomoepus-like footprints, Trisauropodiscus shows a prominent, very long middle digit III and lateral digits II and IV of about half the length of the middle digit and nearly equal in their extension.

Trisauropodiscus is morphologically different from Anomoepus-Shenmuichnus-Moyenisauropus plexus footprints. This ichnogenus represents a distinct morphotype most similar to the plexus comprising Carmelopodus, Irenichnites, Columbosauripus, Magnoavipes and Ornithomimipus.

We suggest Trisauropodiscus morphotype as a hypothetical predecessor of Carmelopodus and ornithomimipodid morphotypes.

ACKNOWLEDGEMENTS

This work is a contribution to the call for papers arising from the Fourth International Congress on Ichnology “Ichnia 2016 - Ichnology for the 21st century: (palaeo)biological traces towards sustainable development”, held in Idanha-a-Nova (Portugal), 6-9 May 2016.

We are grateful to Marco Balini, Lida Xing and Anthony R. Fiorillo for reviewing and improving the paper. The authors thank Tamara Beridze from Tbilisi State University and Rusudan Chagelishvili from Georgian National Museum for the permission to study track collection at the Georgian National Museum, help and guidance during the trip to Sataplia tracksite. Thanks are also due to Richard McCrea from the Peace Region Palaeontology Research Centre for the picture of Irenichnites holotype specimen. We like to thank Hassan Yamani for the assistance in the fieldtrip and Tomasz Singer for his valuable suggestions on Deferrariischnium affinity. The Faculty of Sciences of Chouaïb Doukkali University El Jadida kindly provided logistical support during fieldtrips.

Fig. 6 - Examples of Carmelopodus footprints (a-c) in comparison with track samples grouped in the Irenichnites-Columbosauripus-Magnoavipes-Ornithomimipus plexus (d-g). a) Casted specimen CU-MWC 184.12, the holotype of Carmelopodus untermannorum Lockley, Hunt, Paquette, Bilbey & Hamblin, 1998, from Carmel Formation (Middle Jurassic) of Utah, USA. b) Uncollected specimen located at N32°9’53.67” and W5°32’43.91”, Carmelopodus isp. from Isli Formation (Middle Jurassic) of Central High Atlas, Morocco. c) Casted specimen UCM 199.84, cf. Carmelopodus from the Cedar Mountain Formation (Lower Cretaceous) of Utah. d) Collected specimen CMN 8552, the holotype of Irenichnites gracilis Sternberg, 1932, from the Gething Formation (Lower Cretaceous) of British Columbia, Canada. e) Casted specimen GNM 11g-84, cf. Columbosauripus isp. (Satapliasaurus dsocenidzei Gabunija, 1951) from the Urgonian Limestone (Lower Cretaceous) of Georgia. f) Casted specimen UCM 207.105, Magnoavipes isp. from Dakota Group (mid-Cretaceous) of Colorado. g) Uncollected specimen reported by Nicosia et al. (2007), located at N 41°30’0.900” and E 013°02’52.98”, Ornithomimipus isp. from the Cenomanian (Upper Cretaceous) of Cava Petrianni, Italy. Track images (a-b, e-f) reversed for comparison.


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Manuscript received 23 December 2016Revised manuscript accepted 29 August 2017Published online 18 September 2017Guest Editors Andrea Baucon & Carlos Neto de Carvalho

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