Adrian P. Hunt

Tetrapod Ichnofacies: A New Paradigm

We recognize three fundamental terms in ichnology: (1) ichnoassemblage, which is an assemblage of ichnofossils conceptually equivalent to an assemblage of body fossils; (2) ichnocoenosis, which is a trace fossil assemblage produced by a biological community that can be characterized by morphological criteria; and (3) ichnofacies, which refers to recurrent ichnocoenoses that represent a significant portion of Phanerozoic time. There are two different kinds of ichnofacies, ethoichnofacies (mostly invertebrate ichnofacies) and biotaxonichnofacies (mostly tetrapod ichnofacies). Nonmarine invertebrate ichnologists now recognize five archetypal ichnofacies (Mermia, Skolithos, Scoyenia, Coprinisphaera, Psilonichnus) to which we add the Octopodichnus ichnofacies. We propose a coherent and consistent classification and nomenclature for tetrapod ichnofacies. We name five archetypal vertebrate ichnofacies for nonmarine environments: Chelichnus, Grallator, Brontopodus, Batrachichnus and Characichnos ichnofacies.

The fossil trackway Pteraichnus is pterosaurian, not crocodilian: Implications for the global distribution of pterosaur tracks

There has been much confusion regarding the fossil footprint record of pterosaurs, with both non‐pterosaurian tracks assigned to pterosaurs, and pterosaurian tracks assigned to non‐pterosaurian track‐makers such as crocodilians and turtles. Various authors have also debated whether pterosaurs were bipedal or quadrupedal, erect or semi‐erect, digitigrade or plantigrade, when progressing on land. Recent claims that Pteraichnus was made by a crocodilian effectively implied that there are no known pterosaurian tracks in the fossil record. We show here, on the basis of new material from the Jurassic Sundance and Summerville formations of Wyoming and Utah, and other Jurassic and Cretaceous sites in Europe and North America, that pterosaur tracks are now quite widely known and indicative of quadrupedal progression on land. The fossil trackway Pteraichnus is pterosaurian in origin as originally proposed by Stokes (1957), and not crocodilian as suggested by Padian and Olsen (1984). The animals responsible for maki...

Late Triassic dinosaursfrom the western United States

Western North America has one of the most extensive fossil records of Late Triassic dinosaurs. AllUpper Triassic strata are assigned to the Chinle Group which yields four successive, dinosaur-bearing faunas. Otischalkian (early Tuvalian) dinosaur specimens are fragmentary and indeterminate. Adamanian (late Tuvalian) dinosaurs include a herrerasaurid, Camposaurus arizonensis nov. gen. et sp., Caseosaurus crosbyensis nov. gen. et sp., Tecovasaurus murryi, a new ornithischian and an indeterminate prosauropod. Revueltian (early-middle Norian) dinosaurs include Chindesaurus bryansmalli, two new herrerasaurids, a prosauropod, Revueltosaurus callenderi, Technosaurus smalli, Lucianosaurus wildi, Protoavis texensis and the original syntypes of Coelophysis bauri. Apachean (Rhaetian) evidence for dinosaurs is principally ichnological (Grallator, Pseudotetrasauropus, Tetrasauropus), but at least three dinosaurs are known from osseous remains, including the neotype of Coelophysis bauri. Dinosaurs define three biogeographic provinces in the Late Triassic. In North America, dinosaurs are rare before the late Tuvalian (late Carnian) and appear to become increasingly numerous through the remainder of the Late Triassic.

Ceratopsid tracks and associated ichnofauna from the Laramie Formation (Upper Cretaceous: Maastrichtian) of Colorado

ABSTRACT The Laramie Formation (Upper Cretaceous: Maastrichtian) contains multiple trackbearing horizons exhibiting a diverse assemblage of ceratopsid, ornithopod and theropod tracks and trackways. The ceratopsid tracks are the first attributable to this family and we describe them as a new ichnotaxon, Ceratopsipes goldenensis, ichnogen. et ichnosp. nov. These tracks indicate that models of forelimb posture of ceratopsids that postulated a sprawling stance are incorrect. The ceratopsid-dom-inated ichnofauna reflects the body fossil record of the Laramie Formation. Theropod tracks indicate a diverse fauna including an ichnite that possibly represents Tyrannosaurus. A partial trackway represents the first reported champsosaur ichnites herein named Champsosaurichnus parfeti ichnogen. et ichnosp. nov. The ichnofauna also includes hadrosaur tracks and is useful in reconstructing the animal communities that inhabited the area.

A track of the giant theropod dinosaur Tyrannosaurus from close to the Cretaceous/Tertiary Boundary, northern New Mexico

The first unequivocal example of a large tyrannosaur track attributable to the species Tyrannosaurus rex is an 86 cm long tetradactyl pedal impression assigned to Tyrannosauripus pillmorei ichnogen. et ichnosp. nov. The ichnospecies Tyrannosauropus petersoni Haubold is a nomen dubium. The only other example of a possible track of Tyrannosaurus is from the Laramie Formation of Colorado.

A thin-shelled reptile from the Late Triassic of North America and the origin of the turtle shell

A new, thin-shelled fossil from the Upper Triassic (Revueltian: Norian) Chinle Group of New Mexico, Chinlechelys tenertesta, is one of the most primitive known unambiguous members of the turtle stem lineage. The thin-shelled nature of the new turtle combined with its likely terrestrial habitat preference hint at taphonomic filters that basal turtles had to overcome before entering the fossil record. Chinlechelys tenertesta possesses neck spines formed by multiple osteoderms, indicating that the earliest known turtles were covered with rows of dermal armour. More importantly, the primitive, vertically oriented dorsal ribs of the new turtle are only poorly associated with the overlying costal bones, indicating that these two structures are independent ossifications in basal turtles. These novel observations lend support to the hypothesis that the turtle shell was originally a complex composite in which dermal armour fused with the endoskeletal ribs and vertebrae of an ancestral lineage instead of forming de novo. The critical shell elements (i.e. costals and neurals) are thus not simple outgrowths of the bone of the endoskeletal elements as has been hypothesized from some embryological observations.

Ichnofaunas from the Triassic-Jurassic Boundary Sequences of the Gateway area, Western Colorado: Implications for Faunal Composition and Correlations with Other Areas

Large fossil footprint assemblages have been recovered from the Chinle Group and overlying Wingate Formation, of the Dolores Valley canyonlands near Gateway, Colorado. Current evidence suggests that all the Chinle and many of the lower Wingate Formation assemblages are Late Triassic in age, but that the upper Wingate ichnofaunas are probably Lower Jurassic. Evidence for mammal and non-mammalian synapsid-like tracks in the Chinle is equivocal, but evidence for synapsid tracks in the eolian Wingate is abundant and strongly suggestive of significant facies control (i.e., the synapsid-eolian facies association is similar to that found in older and younger eolian deposits). Currently a great imbalance exists between the lack of ichnotaxonomic names assigned to northern hemisphere Mesozoic mammal and mammal-like tracks and the plethora of names, some of dubious value, assigned to similar tracks from the southern hemisphere. The problems inherent in this imbalance are discussed in the context of the triple influences of faunal provincialism (including facies controls), provincial taxonomy, and uncertain biostratigraphic dating. Current evidence suggest that while small theropod tracks (i.e., Grallator) are abundant throughout the Colorado sequence, large theropod tracks (e.g., Eubrontes) do not occur below the Wingate-Kayenta transition zone, which may lie close to the Triassic-Jurassic boundary. Evidence of Brachychirotherium from the lower Wingate and the first reports of large Otozoum from higher in the section (probably from just below the Kayenta Formation) tend to confirm this inference, help differentiate Late Triassic from Liassic ichnofaunas, and facilitate regional and global correlations.

Grallator-Dominated Fossil Footprint Assemblages and Associated Enigmatic Footprints from the Chinle Group (Upper Triassic), Gateway Area, Colorado

The upper part of the Chinle Group (Late Triassic) of the Gateway area in western Colorado is extraordinarily rich in fossil footprint assemblages. Dominant track types include small Grallator tracks, generally attributed to Coelophysis-like theropods, which often occur in high densities of 50 to 100 per m2. Other abundant ichnotaxa that are attributable to dinosaurs or dinosaur-like archosaurs include Pseudotetrasauropus and Tetrasauropus, attributed to prosauropods and sauropods, respectively. Several Pseudotetrasauropus-like tracks appear to be functionally didactyl and may indicate a new ichnotaxon that represents an animal that shows certain unusual features that are convergent with dromeosaurs and certain birds. Such convergence may reflect inherent growth programs as much as functional adaptations. Non-dinosaurian ichnotaxa include Brachychirotherium (probably of aetosaur affinity) and Rhynchosauroides, attributed to a sphenodontid/lizard-like form. Other ichnotaxa include probable therapsid (dicynodont) tracks labeled Pentasauropus sp., mammaloid (non-therian mammal and/or mammal-like reptile) tracks, and the trails of arthropods. Excellent preservation and high track densities mark the Gateway assemblages in a thin stratigraphic interval in the upper part of the Chinle Group (Rock Point Formation). The track assemblages are similar to those reported from the Chinle Group in other parts of the Colorado Plateau and Rocky Mountain region, extending over most of Colorado, Utah, northern Arizona and northern and eastern New Mexico. Some of the Chinle ichnotaxa (Grallator and Brachychirotherium) are found in the overlying Wingate Formation, indicating that it is also Late Triassic in age, at least in the lower part. However, overall the Chinle and Wingate assemblages are quite different, most notably in the rarity of mammaloid/mammal-like tracks in the Chinle Group.

Redescription of Redondasuchus reseri,, a Late Triassic aetosaur (Reptilia: Archosauria) from New Mexico (U.S.A.), and the biochronology and phylogeny of aetosaurs

Abstract The Late Triassic (Rhaetian) aetosaur Redondasuchus reseri from the Redonda Formation of eastern NewMexico, U.S.A. is distinguished from all other aetosaurs except Typothorax by its paramedian scutes with ventral keels, and from Typothorax by its paramedian scutes with discontinuous ventral keels. Redondasuchus can be further distinguished from other aetosaurs by its paramedian scutes in which the lateral third is flexed downward approximately 45°. It is the only Rhaetian aetosaur currently known from the United States and is an index taxon for the Apachean land-vertebrate faunachron. A cladistic analysis of the aetosaurs, utilizing both characters derived from armor and other skeletal information, indicates that two distinct grades of aetosaurs exist. There is a basal grade consisting of the paraphyletic assemblage of Aetosaurus and (Stagonolepis + Aetosauroides)), and an advanced grade consisting of the clade Neoaetosauroides + Redondasuchus + ((Longosuchus + Desmatosuchus) + (Paratypothorax + Typothorax))). Integration of the existing aetosaur biochronology with operating cladistic definitions of aetosaur taxa produces a useful biostratigraphy of Upper Triassic strata in the western United States.

A survey of fossil footprint sites at glen canyon national recreation area (western USA): A case study in documentation of trace fossil resources at a national preserve

Fossil footprints are very widespread in the Late Paleozoic and Mesozoic rocks of eastern Utah, but until recently have not been studied in detail. This is surprising in light of the fact that skeletal remains of fossils in this area are generally rare, whereas footprints are common and very informative about the distribution and behavior of ancient vertebrates. In this report we describe more than three dozen tracksites in the Glen Canyon National Recreation Area (GCNRA) and immediate vicinity, from eight formations (Cedar Mesa, Moenkopi, Chinle, Wingate, Kayenta, Navajo, Summerville, and Morrison) that range in age from Permian through Jurassic. Tracks in the Permian, cf. Anomalopus (or Chelichnus) and Stenichnus, represent at least two types of pre‐archosaurian reptiles, and reveal evidence of predator–prey interaction and digging activity. Footprints in the Moenkopi include a large number of swim traces attributable to amphibians, and horseshoe crabs. Footprints in the Chinle Group include the first e...