Middle Triassic (Ladinian) amphibian tracks from the Lower Keuper succession of southern Germany: Implications for temnospondyl locomotion and track preservation

https://doi.org/10.1016/j.palaeo.2020.109625Get rights and content

Highlights

  • The lowermost Triassic unambiguous temnospondyl tracks are recovered from Vellberg.

  • Capitosaur stereospondyls are the most probable trackmakers.

  • Only tetradactyl manus tracks: forelimbs prevailing over hindlimbs in locomotion

  • Locomotion of temnospondyls similar to present-day swimming crocodiles

  • Low probability of amphibian track preservation: environment and mode of locomotion

Abstract

Triassic temnospondyl amphibian tracks are relatively rare, in contrast with the body fossil record. Herein we report temnospondyl tracks from the base of the Anthrakonitbank carbonate bed, within the upper Middle Triassic Lower Keuper succession (Erfurt Formation) in the Vellberg Fossil-Lagerstätte of southern Germany. The sedimentary succession comprises restricted marine deposits, and the track-bearing layer includes microbial mats covering thin bone-beds. The ichnological material includes >20 footprints, four of which are arranged in a trackway, and all footprints comprise manus impressions with no pes preserved. The combination of characters, such as tetradactyl clawless manus impressions, relative digit length and angulation, and trackway with low pace angulation, are different from any known tetrapod ichnotaxon. While the scarcity of material precludes a confident ichnotaxonomy, comparison with the autopodia in the body fossil record suggests capitosaur stereospondyls as the most probable trackmakers. Ichnological and sedimentological features indicate that the trackmakers displayed a walking-swimming locomotion, with a sprawling posture, only touching the substrate with the forelimbs, as seen in present-day swimming crocodiles. The Vellberg tetrapod tracks reported here contribute to our knowledge of the Triassic ichnological record, as well as the life style and habitats of temnospondyls.

Introduction

Tetrapod tracks are abundant fossil components of Triassic terrestrial and coastal deposits worldwide (Klein and Lucas, 2010a). Such ichnofossils are useful for the reconstruction of past ecosystems, as they provide direct evidence of the habitat of the potential trackmakers (Melchor, 2015). In this regard, tetrapod ichnofaunas are often considered a reflection of the tetrapod faunas themselves. However, this is not the case in the Triassic temnospondyl amphibian record because a direct correlation between skeletal and footprint data is problematic. The bone record shows that temnospondyls were common in Triassic ecosystems, where they acquired gigantic sizes (Schoch, 1999) and occupied a wide range of (often aquatic) environments (Schoch and Milner, 2000; Warren, 2000; Fortuny et al., 2016). By contrast, temnospondyl tracks are extremely scarce within the Triassic fossil record (Klein and Lucas, 2010a, Klein and Lucas, 2010b; Marsicano et al., 2014). Until recently, the Triassic ichnogenus Capitosauroides was attributed to amphibian trackmakers (e.g., Haubold, 1971a, Haubold, 1971b). However, the revisions of Capitosauroides by Marchetti et al., 2019a, Marchetti et al., 2019b now suggest therapsids as potential trackmakers. Other evidences of Triassic amphibian tracks rely on sparse and sometimes poorly preserved ichnites that deserve further analyses (Peabody, 1948; Klein and Lucas, 2010b; Marsicano et al., 2014). So far, only one ichnotaxon from the Upper Triassic of Lesotho has been unambiguously attributed to a temnospondyl producer (Marsicano et al., 2014). Therefore, perhaps due to a preservational and/or environmental bias, the osteological fossil richness of temnospondyl amphibians is not reflected in the ichnological record.

Herein we report tetrapod ichnites recovered from the Middle Triassic Lower Keuper succession of the Vellberg Fossil-Lagerstätte, southern Germany. The shape of the tracks, which consist in tetradactyl manus impressions, suggests temnospondyl amphibians as the most likely trackmakers. These ichnofossils widen the palaeontological record of the already rich Middle Triassic Lower Keuper of Germany (Schoch and Seegis, 2016). The different modes of impression and preservation of the ichnites reveal palaeoenvironmental and palaeoecological affinities of the potential trackmakers, and shed light on the notable bias between osteological and ichnological remains of temnospondyls. Furthermore, these ichnites widen the picture of the Triassic tetrapod track record worldwide, as they represent the earliest unambiguous evidence of temnospondyl tracks from the Triassic.

Section snippets

Geological setting

During Middle Triassic time, the Central European Basin formed a vast but shallow depression with a very subdued relief, which was readily and frequently affected even by minor sea level changes (Beutler et al., 1999). After the regression of the Muschelkalk epicontinental sea (mostly represented by carbonate deposits), the Lower Keuper was deposited in a deltaic setting (Nitsch, 2015). In the study area, which is located in the southern sub-basin, lakes and lagoons of various sizes alternated

Material and methods

The track-bearing surface was found in spring of 2019 during palaeontological prospecting at the Eschenau Quarry (Vellberg municipality, Baden-Württemberg, Germany) (Fig. 1). Footprints were discovered in the lowermost layer of a fallen block from the lower half of the Anthrakonitbank bed (block dimensions: ~90 cm each side, ~35–40 cm thick) (Figs. 1B, 2B). The layer was manually detached from the fallen block. It is composed of fragmented but well-connected pieces and preserves the footprints

Sedimentology of the track-bearing layer

The deposits below the track-bearing layer, corresponding to the Sandige Pflanzenschiefer, consist of greyish and laminated marly siltstones and fine-grained sandstones. The deposits overlying the track-bearing layer, the Anthrakonitbank unit, correspond to layered dolomites (Figs. 1B, 2). Layers of the Anthrakonitbank unit are evidenced as an alternation of greyish (in fresh fracture) micrite and medium- to coarse-grained deposits building up cyclic sequences (Fig. 2A, B). Such layering or

Temnospondyl amphibian tracks

Fig. 3, Fig. 4, Fig. 5, Fig. 6; Table 1

Palaeoenvironment, preservation and taphonomy

The sedimentological analyses of the track-bearing layer, together with the preservation state of the ichnites and the whole stratigraphic framework, from the Sandige Pflanzenschiefer to the Anthrakonitbank (Fig. 1B), allow to decipher the palaeoenvironmental setting and the taphonomic processes of the uncovered tetrapod footprints. The carbonate sandstone intervals with abundant quartz and bone fragments at the base of each cycle of the track-bearing layer (Fig. 2C, D, E, G) are interpreted as

Conclusions

Temnospondyl amphibian tracks are rare components of the Triassic fossil record. This forms a strong contrast to both the rich record of other tetrapod footprints and the relatively abundant temnospondyl bone remains of this period. Here we report an exceptional record of diagnostic amphibian tracks from the upper Middle Triassic (Ladinian) of Vellberg (southern Germany). They were recovered from the base of the Anthrakonitbank, within the Lower Keuper succession, being the first tetrapod

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We thank Norbert Adorf and Isabell Rosin (SMNS) for invaluable help during fieldwork, and for the preparation of the track-bearing layer. Christoph Wimmer-Pfeil (SMNS) is thanked for the skillful preparation of thin sections. We thank Erin Maxwell (SMNS) for fruitful discussions and logistics, and Michael Rasser (SMNS) to help in scanning the thin sections. We thank the Schumann Quarry owners for allowing access to the outcrops. We acknowledge the reviewers Lorenzo Marchetti and Hendrik Klein,

References (61)

  • H. Brunner

    Zur Stratigraphie des Unteren Keupers (Lettenkeuper, Trias) im nordwestlichen Baden-Württemberg

    Jb. Mitt. Oberrh. Geol. Ver., N.F.

    (1980)
  • H. Brunner et al.

    Standard profile des Unteren Keupers (Lettenkeuper, Trias) im nördlichen Baden-Württemberg

    Jb. Mitt. Oberrh. Geol. Ver., N.F.

    (1977)
  • S.L. Brusatte et al.

    Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic

    Proc. R. Soc. B

    (2011)
  • N. Carmona et al.

    The role of microbial mats in the preservation of bird footprints: a case study from the mesotidal Bahia Blanca estuary (Argentina)

  • M.T. Carrano et al.

    Taxon distributions and the tetrapod track record

    Paleobiology

    (2001)
  • J.C. Cisneros et al.

    Small footprints expand middle Permian amphibian diversity in the South African Karoo

    Palaios

    (2020)
  • P. Ellenberger

    Les niveaux paléontologiques de première apparition des mammifères primordiaux en Afrique du Sud et leur ichnologie. Établissement de zones stratigraphiques détaillées dans le Stormberg de Lesotho (Afrique du Sud) (Trias Supérieur a Jurassique)

  • P. Ellenberger

    Contribution à la classification des pistes de vertèbres du Trias: les types du Stormberg d’Afrique du Sud (II partie): le Stormberg Supérieur-I. Le biome de la zone B/1 ou niveau de Moyeni: ses biocénoses

    Palaeovertebrata Mémoire Extraordinaire

    (1974)
  • A. Etzold et al.

    Der Keuper in Baden-Württemberg

  • P.L. Falkingham

    Interpreting ecology and behavior from the vertebrate fossil track record

    J. Zool.

    (2014)
  • P.L. Falkingham et al.

    Fossil vertebrate tracks as paleopenetrometers: confounding effects of foot morphology

    Palaios

    (2010)
  • J.O. Farlow et al.

    Trackways of the American crocodile (Crocodylus acutus) in Northwestern Costa Rica: Implications for crocodylian ichnology

    Ichnos

    (2018)
  • J.O. Farlow et al.

    Footfall pattern of a bottom-walking crocodile (Crocodylus acutus)

    Palaios

    (2018)
  • J. Fortuny et al.

    Comparative 3D analyses of palaeoecology of giant early amphibians (Temnospondyli: Stereospondyli)

    Sci. Rep.

    (2016)
  • G. Gand

    Les traces de vertébrés tétrapodes du Permien français

    (1987)
  • H. Hagdorn et al.

    Wirbeltierlagerstätten im Lettenkeuper

  • H. Haubold

    Ichnia amphibiorum et reptiliorum fossilium

  • H. Haubold

    Die Tetrapodenfährten des Buntsandsteins in der Deutschen Demokratischen Republik und in Westdeutschland und ihre Äquivalente in der gesamten Trias. Paläontologische Abhandlungen, Abteilung A Paläozoologie

    (1971)
  • H. Hellrung

    Gerrothorax pustuloglomeratus, ein Temnospondyle (Amphibia) mit knöcherner Branchialkammer aus dem Unteren Keuper von Kupferzell (Süddeutschland). Stuttgarter Beitr

    Naturkunde

    (2003)
  • E.C.N. van Hoepen

    Stegocephalia of Senekal

    O.F.S. Ann. Transvaal Mus.

    (1915)
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