Dromomeron

Description

It is known from partial remains, largely from the hindlimbs, which indicate an animal with an overall length of 1 m.

The brain of D. gregorii is characterised by a floccular lobe of the cerebellum that projects within the space of the semicircular canals, which are large relative to other archosauromorphs. The anterior canal is circularly shaped.

Classification

The bones of Dromomeron are most similar to those of the older pterosauromorph Lagerpeton,

Cladogram simplified after Kammerer, Nesbitt & Shubin (2012):

Discovery and species

Dromomeron romeri

The species name romeri honors influential 20th-century vertebrate paleontologist Alfred Sherwood Romer. These have been assigned to a second species, D. gregorii, named in 2009.

''Dromomeron gregorii''

D. gregorii, named for Joseph T. Gregory, is based on TMM 31100–1306, a right femur (thigh bone) from the Otis Chalk Quarry, Colorado City Formation, (Dockum Group), near Otis Chalk, Texas. Several other limb bones from the quarry, and a partial femur (thigh bone) from the Placerias Quarry of eastern Arizona have been assigned to this species. The rocks that D. gregorii is known from are older than those romeri has been found in. As with the Hayden Quarry, the Otis Chalk Quarry has at least one specimen of a herrerasaurid.

''Dromomeron gigas''

A third species, D. gigas, was described by Martínez et al. (2016) on the basis of fossils recovered from the Norian Quebrada del Barro Formation in northwestern Argentina.

Paleoecology

Also found at the Hayden Quarry are the remains of phytosaurs, aetosaurs, rauisuchians, and several types of dinosaurs and dinosaur relatives, including a Silesaurus-like animal, the herrerasaurid Chindesaurus, and the basal theropod Tawa. Finding the remains of four types of dinosaurs and dinosaur relatives (including Dromomeron itself) is noteworthy because it shows that dinosaurs did not immediately replace their dinosauromorph predecessors; that some of these groups, like the lagerpetonids, persisted (for longer than previously known) and diversified; and that dinosaurian replacement may have occurred at different times in different areas.

References

References

1. (2013). "Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and Their Kin". The Geological Society of London.
2. (2013). "A Rebuttal to Nesbitt's and Hone's "An external mandibular fenestra and other archosauriform characteristics in basal pterosaurs"". International Symposium on Pterosaurs.
3. (2017). "Are the dinosauromorph femora from the Upper Triassic of Hayden Quarry (New Mexico) three stages in a growth series of a single taxon?". Anais da Academia Brasileira de Ciências.
4. Irmis, Randall B.. (2007). "A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs". Science.
5. Nesbitt, Sterling J.. (2009). "Hindlimb osteology and distribution of basal dinosauromorphs from the Late Triassic of North America". Journal of Vertebrate Paleontology.
6. Estimate after the scale diagram at [https://web.archive.org/web/20160611105404/http://socrates.berkeley.edu/~irmisr/hayden/sciencefaq.html#pron the article's press fact sheet].
7. (4 October 2023). "Braincase and neuroanatomy of the lagerpetid Dromomeron gregorii (Archosauria, Pterosauromorpha) with comments on the early evolution of the braincase and associated soft tissues in Avemetatarsalia". [[The Anatomical Record]].
8. 10.1038/nature21700
9. (2012). "The First Silesaurid Dinosauriform from the Late Triassic of Morocco". Acta Palaeontologica Polonica.
10. (2016). "A Norian lagerpetid dinosauromorph from the Quebrada del Barro Formation, northwestern Argentina". Ameghiniana.