The ankle of Lepidus.
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From Nesbitt and Ezcurra, 2015.
The ankle of Lepidus.

Paleo Profile: Lepidus praecisio

Name: Lepidus praecisio

Meaning: Together, the dinosaur’s genus and species names translate to “fascinating scrap”.

Age: Late Triassic, more than 223 million years ago.

Where in the world?: Near Big Spring, in northern Texas.

What sort of critter?: Lepidus was a theropod dinosaur, relatively closely-related to the well-known Coelophysis.

Size: Unknown, but comparable to other small theropods of the Late Triassic.

How much of the creature’s body is known?: An ankle joint, as well as a femur and a jaw bone that may have belonged to the same dinosaur.

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A maxilla – part of the upper jaw – that may have belonged to Lepidus. From Nesbitt and Ezcurra, 2015.

Claim to fame: 
The Late Triassic of North America was not very hospitable to dinosaurs. These dinosaurs were small, rare, and – so far as has been discovered – only represented the theropod branch of the dinosaur family tree. Still, as Sterling Nesbitt and Martín Ezcurra write in their description of Lepidus, a closer look at previously-known and unpublished fossils is yielding a few new dinosaurs from this slice of Mesozoic time.

Lepidus is one such dinosaur. The bones that represent the creature were discovered by a Works Progress Administration paleontology team in 1941 as part of a collection of fragments and isolated bones that have mostly gone unstudied until now.

Relatively little of Lepidus has been found. But, compared to other dinosaur fossils that are little more than a piece of limb bone, it’s one of the best specimens to come out from its particular place and time. Dinosaurs are rarely found in this part of the Triassic in Texas, and Lepidus establishes that a particular subset of the “beast footed” dinosaurs – the neotheropods – were present in the Triassic tropics of North America before 223 million years ago. They were part of a meek dinosaurian community that mixed the archaic and the novel – older forms that more closely resembled some of the earliest dinosaurs as well as derived animals that better fit the sleek and slender profile of celebrity species such as Coelophysis. These latter lineages would help launch the true Age of Dinosaurs after the end-Triassic mass extinction turned fate in their favor.


Nesbitt, S., Ezcurra, M. 2015. The early fossil record of dinosaurs in North America: A new neotheropod from the base of the Upper Triassic Dockum Group of Texas. Acta Palaeontologica Polonica. doi: 10.4202/app.00143.2014

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