Middle Jurassic, Bajocian-Bathonian) of the Central High Atlas, Morocco, in Comparison with Similar Mesozoic Tridactylous Ichnotaxa
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TO L O N O G E I L C A A P I ' T A A T L E I I A Bollettino della Società Paleontologica Italiana, 56 (2), 2017, 207-215. Modena C N O A S S. P. I. 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] H. 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] A. 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 (e.g., Godefroit et al., 2013) as well as the classic material of Archaeopteryx von Meyer, 1861, from the Tithonian Footprints of birds or avian theropods are abundantly Solnhofen Limestone of Germany. The stratigraphically known from Cretaceous and Cenozoic deposits of North oldest bird-like footprints are reported from deposits that America, Europe and East Asia. In particular shorebirds are latest Triassic and Early Jurassic in age. They come have left their tracks on numerous surfaces variously co- from the Lower Elliot Formation of Lesotho, southern occurring with those of non-avian theropods, ornithopods Africa (Ellenberger, 1970, 1972), the Newark Supergroup or pterosaurs (Lockley et al., 1992, 2006; Lockley, 1999; of Massachusetts and Virginia, USA (Hitchcock, 1858) Lockley & Rainforth, 2002; Kim et al., 2012; McCrea and from the Przysucha Formation of Poland (Gierlinski, et al., 2014; Xing et al., 2015). Bird-like footprints are 1996). Younger records are known from the latest Jurassic- known from the Jurassic but were poorly recognized earliest Cretaceous Tuchengzi Formation of Liaoning in comparison with avian theropod body fossils, which Province, China (Lockley et al., 2006), an area famous for include new finds from the Callovian-Oxfordian of China its discoveries of avian theropods. Ichnotaxonomically all ISSN 0375-7633 doi:10.4435/BSPI.2017.19 208 Bollettino della Società Paleontologica Italiana, 56 (2), 2017 these footprints were assigned to different ichnogenera and (2009) as tracks similar to Carmelopodus Lockley, Hunt, ichnospecies. Hitchcock (1858) introduced the ichnotaxon Paquette, Bilbey & Hamblin (1998), an ichnogenus also Plesiornis pilulatus for specimens from the Newark recognized in Middle Jurassic strata of this region. In 2016, Supergroup while those from the Lower Eliott Formation authors collected more material from the original site and were named Trisauropodiscus by Ellenberger (1970). also found similar bird-like footprints near Sountate, co- For the footprints from Liaoning the new ichnotaxon occurring with the invertebrate traces Selenichnites and Pullornipes aureus was erected by Lockley et al. (2006). Kouphichnium in the same stratigraphic unit (Lagnaoui Unnamed bird tracks were also reported from the Late et al., 2016) (Fig. 1). Jurassic of Asturias, Spain (Pinuela et al., 2002). From We focus here on the ichnotaxonomic status of the Middle Jurassic deposits of Msemrir, Morocco, Belvedere studied material, leaving the problem of the affinity et al. (2011) reported small tridactyl bird-like imprints to distinct biological groups open for future debates. similar to the footprints from Imilchil described here. Prospective detailed analyses of bird-like footprints The latter material was found during two field trips to especially from the Lower and Middle Jurassic and the Central High Atlas of Morocco, in September 2009 comparison with known skeletal material might enlighten and October 2016. First finds came from the vicinity of the dark ages of bird evolution and help to better Imilchil in 2009 and were mentioned by Gierliński et al. 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. G.D. Gierliński - Bird-like tracks from the Imilchil Formation, Marocco 209 MATERIAL, METHODS AND the Jurassic deposits near Imilchil into three formations SPECIMENS REPOSITORY that were later revised as five formations (Ibouh, 1995, 2004). The synthetic classification is from base to top: 1) All ichnites, described herein, are preserved as Tassent Formation (= Agoudim 1; Toarcian-Aalenian), natural casts and molds. Artificial casts to replicate consisting of platform carbonates, marls and shales (> specimens were produced by using Sculpey polymer 600 m), overlying shallow water limestones (~ 300-400 clay (polyvinyl chloride). Photographs were taken m) of Hettangian-Sinemurian age; 2) Bab n’Ouayad strictly parallel to the surface by ultra low distortion Carl Formation (= Agoudim 2; early Bajocian), dominated by Zeiss lens, under