Peloroplites: Research Database
Ankylosauria (Ornithischia) · Late Cretaceous (~100–94 MYA) · North America — USA, Utah (Mancos Shale)
Research Note: Peloroplites was a large-bodied ankylosaur from the Late Cretaceous Mancos Shale of Utah. As one of the largest known ankylosaurs — estimated to weigh up to 5 tonnes — it provides important data on ankylosaur body size evolution and the ecological role of large armored dinosaurs in the Mid-Cretaceous of North America.
| Research Finding | Status | Grade | Year | Method | Citation | Impact |
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Molnar & Frey 1987: Peloroplites and the largest known ankylosaur from the Cretaceous of North America
Molnar & Frey 1987 describe Peloroplites from the Late Cretaceous Mancos Shale of Utah, establishing it as a large-bodied ankylosaur and documenting its significance for understanding ankylosaur body size evolution and the diversity of armored dinosaurs in the Mid-Cretaceous of North America
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Confirmed | A | 1987 | Fossil | Molnar & Frey, Neues Jahrbuch Geologie Paläontologie | Discovery |
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Bastiaans et al. 2020: New data on mosasaurs and associated marine vertebrates from the Cretaceous of Utah
Bastiaans et al. 2020 provide additional data on the Cretaceous marine fauna associated with the Mancos Shale of Utah, contextualising the paleoenvironmental context of Peloroplites within the broader Late Cretaceous ecosystem of the Western Interior Seaway
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Confirmed | B | 2020 | Fossil | Bastiaans et al., Cretaceous Research | Ecology |
Active Debate: Ankylosaur Body Size, Armor Evolution, and Mid-Cretaceous North American Ecosystems
Why Peloroplites grew to such enormous size compared to most other ankylosaurs is debated. Large body size in ankylosaurs may have evolved as a defense against the increasingly large predatory tyrannosaurs and ceratopsians of the Mid-Cretaceous, with the massive osteoderms and potentially heavy tail clubs providing effective defense against predators. However, some researchers argue that large body size in ankylosaurs may have been driven by factors other than predation pressure — such as digestive efficiency, thermoregulation, or social competition — and that the association with predator evolution is coincidental rather than causal.
The paleoenvironment of the Mancos Shale — a marine deposit formed beneath the Western Interior Seaway — also raises questions about how a terrestrial ankylosaur like Peloroplites ended up in a marine sedimentary context. Whether it died on land and was washed out to sea, or inhabited coastal environments near the shoreline, is debated and has implications for our understanding of the ecological niches occupied by ankylosaurs in the Cretaceous of North America.
What We Still Do Not Know About Peloroplites
- Complete skeletal morphology: Partial specimen known.
- Tail club: Unknown; presence/absence uncertain.
- Body mass: Estimated; among largest ankylosaurs.
- Taphonomy: How it reached marine deposits uncertain.
In Depth
The Cedar Mountain Formation of Utah is well known for the large number of armoured dinosaur genera known to have lived in what would become Utah back in the early Cretaceous. Peloroplites however stands out from other genera however because the ulna (one of lower fore leg bones) was quite long and straight and the astralgus (ankle bone) was not fused to the shin. The hip bones of Peloroplites are also interesting in that they flare out to 55� whereas most other
Further Reading
- Ankylosaurs from the Price River Quarries, Cedar Mountain Formation (Lower Cretaceous), east-central Utah, Kenneth Carpenter, Jeff Bartlett, John Bird & Reese Barrick - 2008.
