Ben Creisler
New papers:
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The importance of facies analyses when studying tetrapod ichnofossils.
In coastal settings, ichnoassociations are Rhynchosauroides-dominated.
Terrestrial settings ichnoassociations are non-Rhynchosauroides-dominated.
A database of Middle Triassic tetrapod footprint localities worldwide is presented.
Abstract
Tetrapod ichnology is a powerful tool to reconstruct the faunal composition of Middle Triassic ecosystems. However, reconstructions based on a single palaeoenvironment provide an incomplete and impoverished picture of the actual palaeodiversity. In this paper, we analyse Middle Triassic tetrapod ichnoassociations from the detrital Muschelkalk facies of the Catalan Basin of northeast Spain, ranging from terrestrial to coastal settings. We identified two main tetrapod ichnoassociations, preserved in two different palaeoenvironments, comprising the following ichnogenera and morphotypes: Procolophonichnium, Chelonipus, Rhynchosauroides, Rotodactylus, Chirotherium, Isochirotherium, Sphingopus, and indeterminate chirotheriids. We also statistically analyse a database of all known Middle Triassic tetrapod footprint localities worldwide; this database includes, for each track locality, the precise age, the palaeoenvironment and the presence/absence of ichnotaxa. Our results on the composition of ichnofauna within the palaeoenvironments of the Catalan Basin are integrated into this database. This approach allows us to revisit the palaeoenvironmental bias linked to the marine transgression that affected the Western Tethys region. Tetrapod ichnoassociations reveal the following palaeoenvironmental patterns: (1) in coastal settings, ichnoassociations are Rhynchosauroides-dominated and diversity is relatively low; (2) in terrestrial settings and those with less marine influences, ichnoassociations are non-Rhynchosauroides-dominated, usually characterised by more abundant chirotheriid tracks and, generally, a higher track diversity. The correlation between tetrapod ichnoassociations and sedimentary facies reveals how palaeoenvironmental constraints influenced faunal assemblages, especially those of the Middle Triassic of the Western Tethys region. Ichnoassociations allow the ecological response of tetrapod faunas to the environmental changes to be inferred for this critical time interval. Marine transgressions strongly influenced tetrapod ecosystems: environmental conditions were key for the faunal recovery in the aftermath of the end-Permian extinction, with the settlement of the so-called modern faunas and the rise of the dinosaur lineage.
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Free pdf:
Spencer G. Lucas, Larry F. Rinehart, Ben Chesebrough, Robert Chesebrough & Sam Chesebrough (2021)
A Late Jurassic crocodile from New Mexico.
In: Lucas, S. G., Hunt, A. P. & Lichtig, A. J., 2021, Fossil Record 7. New Mexico Museum of Natural History and Science Bulletin 82: 245-247
https://www.researchgate.net/publication/348000272_A_LATE_JURASSIC_CROCODILE_FROM_NEW_MEXICO New Mexico has a relatively sparse record of Jurassic fossil vertebrates because the Middle Jurassic stratigraphic units in the state consist of eolian and evaporitic facies and relatively little exploration has been undertaken of the more promising Upper Jurassic facies (Morrison Formation). Thus, the only Middle Jurassic vertebrates from New Mexico are "holostean" fish from the Callovian Luciano Mesa Member of the Todilto Formation, whereas the Morrison Formation vertebrate-fossil record is dominated by fragmentary remains of sauropod dinosaurs. We add to this sparse record the first Jurassic crocodile fossil from New Mexico. This fossil is from the Brushy Basin Member of the Morrison Formation at NMMNH (New Mexico Museum of Natural History) locality 12333 in the Ojito Wilderness Area of Sandoval County. One of us (Ben C.) discovered this fossil in 2018, and it consists of part of the postero-dorsal skull roof of a goniopholidid crocodile catalogued as NMMNH P-81149. This fossil includes much of the parietal, fragments of the squamosals and frontals, the medial margins of both supratemporal fenestrae and part of a natural endocast. We cannot distinguish this fossil from Eutretauranosuchus or Amphicotylus, but it is so incomplete that we only identify it as Goniopholididae. Scaled to a complete skull of Eutretauranosuchus, NMMNH P-81149 had a skull with a total length of 26 cm and a total body length of about 1 .5 m, which is a characteristic body size of an adult Morrison goniopholidid. This discovery of a Morrison Formation crocodile in New Mexico comes more than one century after the first discovery of dinosaur bones in the New Mexico Morrison. The discovery of the crocodile fossil, as well as the relatively recent discovery (early 2000s) of a Morrison turtle fossil in New Mexico, provide incentive to search further for relatively small, non-dinosaurian vertebrate fossils in the New Mexican Morrison Formation.