Oryctodromeus
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Oryctodromeus Temporal range: Late Cretaceous, Cenomanian |
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| Reconstructed skeleton, Museum of the Rockies | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Order: | †Ornithischia |
| Family: | †Thescelosauridae |
| Subfamily: | †Orodrominae |
| Genus: |
†Oryctodromeus Varricchio et al., 2007 |
| Type species | |
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†Oryctodromeus cubicularis Varricchio et al., 2007 |
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Oryctodromeus (meaning "digging runner") was a genus of small ornithopod dinosaur. Fossils are known from the middle Cretaceous Blackleaf Formation of southwestern Montana and the Wayan Formation of southeastern Idaho, USA, both of the Cenomanian stage, roughly 95 million years ago. A member of the small, presumably fast-running herbivorous family Thescelosauridae, Oryctodromeus is the first dinosaur published that shows evidence of burrowing behavior.
Oryctodromeus was originally described as lacking ossified tendons in the tail. However, specimens from the Wayan Formation demonstrate the presence of a thick tendon lattice in the dorsal, sacral, and caudal columns of some specimens; perhaps indicating more flexibility in ossified tendons than has previously been supposed. Adaptations in the jaws, forelimbs, and pelvis were described in the Blackleaf specimens that could have helped move and manipulate soil.
The authors pointed out that Oryctodromeus had only modest forelimb modifications in comparison to dedicated burrowing animals, like moles, echidnas, and wombats. Instead, it was comparable to, but somewhat more specialized for digging than animals that both run and burrow today, like aardwolves, cavies, hyenas, and rabbits. Because it was a biped, it could have a more modified forelimb without affecting its ability to run.
Oryctodromeus is based on specimens from the Blackleaf Formation: MOR 1636a, a partial skeleton of an adult individual including: the premaxillae (upper beak); part of the braincase; three neck, six back, seven hip, and twenty-three tail vertebrae; ribs; the shoulder girdle; an arm (minus the hand); both tibiae and an incomplete fibula; and a metatarsal. Two additional individuals, both juveniles about 55 to 65% the size of MOR 1636a, are represented by MOR 1636b. Numerous additional partial skeletons are known from the Wayan Formation.
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