7 The Campanian Crucible: A synthesis of vertebrate paleobiogeography and ecosystem dynamics in Laramidia (Posters)

Laramidia’s Campanian deposits reveal vertebrate diversification, geographic isolation, and provincialism, and its fossil record informs paleoecology and biogeography. This session synthesizes research on evolution, endemism, WIS dynamics, and underexplored geochronology across this Late Cretaceous landscape.

Monday, 18 May 2026
8:00 AM - 5:30 PM
Alvarado D/E

New Vertebrate Localities with Toothmarked Bone from the Iles Formation (Campanian), Mesaverde Group of Colorado: Implications for Faunal Diversity and Paleoecology

Paper number: 7-3
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Late Cretaceous-aged Mesaverde Group in northwestern Colorado has produced an increasing number of vertebrate fossils in recent years. Most localities and taxa, to date, have been discovered in the Campanian-Maastrichtian Williams Fork Formation, the uppermost unit of the group. The middle formation of the Mesaverde Group, the Iles Formation (Campanian; bracketed between the Sego Sandstone and Williams Fork Formation), has historically produced relatively few vertebrate fossils. Here, we report new localities in the Iles Formation near the northern end of the Douglas Creek Arch and just south of the Blue Mountain uplift. Among these sites, the most diverse so far is the T&M Castle locality. This site has produced a vertebrate assemblage sharing numerous taxa with the overlying Williams Fork Formation, as well as bite marks and feeding damage on bones that provide new insight into the ancient food web. T&M Castle preserves fragmentary bones and teeth of: Osteichthyes (Lepisosteidae, Paralbula sp., Melvius sp., Teleostei, and Acipenseridae?), Chondrichthyes (Myledaphus sp., Meristodonoides sp.), Amphibia, Testudinata (Adocus sp.), Crocodylia, theropods (Troodon sp., Dromaeosauridae, Tyrannosauridae), indeterminate ankylosaurian, ceratopsian, and hadrosaurid dinosaurs, as well as multituberculate mammals. A nearby site, Pebbles Precarious Perch, yielded shell fragments of the turtle Denazinemys sp. (also found in the Williams Fork Formation), broadening this species’ predominantly southern biogeographic range into the "boundary" zone between northern and southern provinces of Laramidian faunas.

 

Notably, some of the bones preserve tooth marks and other traces. When compared to similar-aged formations (i.e., Judith River and Williams Fork Formations), the feeding damage found on fossil bones in the Iles Formation is similar in morphology. Namely, tooth scores and gnaw marks point toward potential predators and scavenger taxa, such as small-bodied theropods, crocodilians, and/or mammals. These feeding traces, alongside the body fossils, add a novel, as yet unstudied, paleoecological dimension to the vertebrate community that once inhabited the Campanian of northwestern Colorado. This report also demonstrates that the Iles Formation preserves a taxonomically and trophically structured vertebrate assemblage comparable to other Campanian units in the Western Interior.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410554

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