Eubrontes and associated ichnofauna of Early Jurassic theropods + Gorgonopus, new ichnogenus from Permian of Russia
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Ben Creisler
Feb 5, 2026, 2:09:40 PM (7 days ago) Feb 5
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Ben Creisler
A new paper not yet posted on the Geology of the Intermountain West website:
Free pdf:
Martin G. Lockley, James O. Farlow, Andrew R.C. Milner, and Jack Davidson (2026)
Eubrontes out west (and beyond)—distribution, morphology, ichnotaxonomy, and associated ichnofauna of footprints of large, Early Jurassic theropod trackmakers.
Geology of the Intermountain West 13: 1–51
doi: https://doi.org/10.31711/giw.v13.pp1-51
https://www.researchgate.net/publication/400360232_EUBRONTES_OUT_WEST_AND_BEYOND-DISTRIBUTION_MORPHOLOGY_ICHNOTAXONOMY_AND_ASSOCIATED_ICHNOFAUNA_OF_FOOTPRINTS_OF_LARGE_EARLY_JURASSIC_THEROPOD_TRACKMAKERS
The large theropod ichnogenus Eubrontes (footprint length >30 cm) has been reported from 168 sites in the Upper Triassic–Lower Jurassic Glen Canyon Group of the Western United States, mostly from Utah. At most sites, the associated ichnofauna and their possible producers include one or more of the following ichnogenera: Grallator (small theropods), Kayentapus (medium-sized to large theropods), Anomoepus (small ornithischians), Batrachopus (crocodyliforms), and more rarely, Otozoum (“prosauropod” sauropodomorphs), Moyenisauropus (large ornithischians), and Brasilichnium (mammaliaforms), and also other synapsid ichnomorphotypes requiring further study. These are collectively considered representative of a globally widespread Early Jurassic tetrapod footprint biochron. Although tridactyl in almost all cases, Eubrontes tracks occasionally show hallux (digit I) traces, inviting comparison with Gigandipus (possibly a variant of Eubrontes), which has been tentatively identified at a single site in the Western United States. The common attribution of the Late Triassic–Early Jurassic Eubrontes trackmaker to Dilophosaurus is plausible but not proven; we reject the hypothesis that the Eubrontes trackmaker was a “prosauropod.” The ‘eponymous’ track Dilophosauripus is also a likely subjective junior synonym of Eubrontes or Kayentapus. Previous studies of these latter two ichnogenera suggest that they are distinct and separable on morphometric grounds, although this has been contested. Glen Canyon Group theropod tracks, including those in the allometric Grallator-Anchisauripus-Eubrontes plexus, are variable, with smaller morphotypes being more elongate and more strongly mesaxonic than larger morphotypes. These three ichnogenera, but especially the end members, Grallator and Eubrontes, probably do not represent the same species of trackmaker. Thus, with Kayentapus also considered, the Glen Canyon Group track record suggests a diversity of theropod trackmakers, in a theropod-dominated ecosystem, in which non-theropodan trackmakers were generally minor elements, even if locally abundant. The Eubrontes morphotype has been reported from some pre- and post-Jurassic tracksites. We compare and contrast footprint proportions of Eubrontes with those of other ichnotaxa attributed to large theropods and consider possible osteological correlates of the digit III and “heel” region proportions. Most notably, the Late Triassic–Early Jurassic Eubrontes differs from the larger Middle-Late Jurassic Megalosauripus in having proportionally a longer digit III and less well-developed “heel” pad.
Martin G. Lockley, James O. Farlow, Andrew R.C. Milner, and Jack Davidson (2026)
Eubrontes out west (and beyond)—distribution, morphology, ichnotaxonomy, and associated ichnofauna of footprints of large, Early Jurassic theropod trackmakers.
Geology of the Intermountain West 13: 1–51
doi: https://doi.org/10.31711/giw.v13.pp1-51
https://www.researchgate.net/publication/400360232_EUBRONTES_OUT_WEST_AND_BEYOND-DISTRIBUTION_MORPHOLOGY_ICHNOTAXONOMY_AND_ASSOCIATED_ICHNOFAUNA_OF_FOOTPRINTS_OF_LARGE_EARLY_JURASSIC_THEROPOD_TRACKMAKERS
The large theropod ichnogenus Eubrontes (footprint length >30 cm) has been reported from 168 sites in the Upper Triassic–Lower Jurassic Glen Canyon Group of the Western United States, mostly from Utah. At most sites, the associated ichnofauna and their possible producers include one or more of the following ichnogenera: Grallator (small theropods), Kayentapus (medium-sized to large theropods), Anomoepus (small ornithischians), Batrachopus (crocodyliforms), and more rarely, Otozoum (“prosauropod” sauropodomorphs), Moyenisauropus (large ornithischians), and Brasilichnium (mammaliaforms), and also other synapsid ichnomorphotypes requiring further study. These are collectively considered representative of a globally widespread Early Jurassic tetrapod footprint biochron. Although tridactyl in almost all cases, Eubrontes tracks occasionally show hallux (digit I) traces, inviting comparison with Gigandipus (possibly a variant of Eubrontes), which has been tentatively identified at a single site in the Western United States. The common attribution of the Late Triassic–Early Jurassic Eubrontes trackmaker to Dilophosaurus is plausible but not proven; we reject the hypothesis that the Eubrontes trackmaker was a “prosauropod.” The ‘eponymous’ track Dilophosauripus is also a likely subjective junior synonym of Eubrontes or Kayentapus. Previous studies of these latter two ichnogenera suggest that they are distinct and separable on morphometric grounds, although this has been contested. Glen Canyon Group theropod tracks, including those in the allometric Grallator-Anchisauripus-Eubrontes plexus, are variable, with smaller morphotypes being more elongate and more strongly mesaxonic than larger morphotypes. These three ichnogenera, but especially the end members, Grallator and Eubrontes, probably do not represent the same species of trackmaker. Thus, with Kayentapus also considered, the Glen Canyon Group track record suggests a diversity of theropod trackmakers, in a theropod-dominated ecosystem, in which non-theropodan trackmakers were generally minor elements, even if locally abundant. The Eubrontes morphotype has been reported from some pre- and post-Jurassic tracksites. We compare and contrast footprint proportions of Eubrontes with those of other ichnotaxa attributed to large theropods and consider possible osteological correlates of the digit III and “heel” region proportions. Most notably, the Late Triassic–Early Jurassic Eubrontes differs from the larger Middle-Late Jurassic Megalosauripus in having proportionally a longer digit III and less well-developed “heel” pad.
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Also, not yet mentioned:
Gorgonopus opokensis ichnogen. et ichnosp. nov.
S. V. Naugolnykh (2025) [2026]
Paleosols, Floristic Paleosuccession, and a New Genus of Fossil Tetrapod Traces from the Upper Permian of the North of European Russia
Paleontological Journal 59: 957–974
doi: https://doi.org/10.1134/S0031030125600544
https://link.springer.com/article/10.1134/S0031030125600544
This paper discusses the possible depositional settings of the Upper Permian beds (Severodvinian and Vyatkian stages), exposed in the basin of the Sukhona and Malaya Severnaya Dvina rivers. Carbonate paleosols and floristic paleosuccession that took place during the Late Permian epoch in this region are considered. A new ichnogenus and a new ichnospecies (Gorgonopus opokensis Naugolnykh Ichnogenus et Ichnospecies nov.) are described.
S. V. Naugolnykh (2025) [2026]
Paleosols, Floristic Paleosuccession, and a New Genus of Fossil Tetrapod Traces from the Upper Permian of the North of European Russia
Paleontological Journal 59: 957–974
doi: https://doi.org/10.1134/S0031030125600544
https://link.springer.com/article/10.1134/S0031030125600544
This paper discusses the possible depositional settings of the Upper Permian beds (Severodvinian and Vyatkian stages), exposed in the basin of the Sukhona and Malaya Severnaya Dvina rivers. Carbonate paleosols and floristic paleosuccession that took place during the Late Permian epoch in this region are considered. A new ichnogenus and a new ichnospecies (Gorgonopus opokensis Naugolnykh Ichnogenus et Ichnospecies nov.) are described.
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