Eodromaeus
From Greek eos (dawn) + dromeus (runner): 'dawn runner', reflecting its status as one of the earliest known theropods.
Eodromaeus is an extinct genus of probable basal theropod dinosaurs from the Late Triassic of Argentina. Like many other of the earliest-known dinosaurs, it hails from the Carnian-age (~230 Ma) Ischigualasto Formation, within the Ischigualasto-Villa Unión Basin of northwestern Argentina. Upon its discovery, it was argued to be one of the oldest true theropods, supplanting its contemporary Eoraptor, which was reinterpreted as a basal sauropodomorph.
Under dispute
Eodromaeus murphi is recovered as sister to Neotheropoda by most analyses (Martínez and colleagues, 2011; Novas and colleagues, 2021) but variously as a basalmost theropod, just outside Theropoda, or ancestral to both theropods and sauropodomorphs by others.
Diagnosis
- No more than 11 maxillary teeth with caniniform crowns more than three times the basal mesiodistal width near the anterior end of the tooth row
- Fine serrations (~nine per millimeter) on mesial and distal margins of maxillary teeth, with ventrally convex maxillary alveolar margin
- Very shallow jugal suborbital ramus
- Centrale in carpus positioned between the radiale and distal carpal 1; large distal carpal 5 overlapping distal carpal 4 with a posteroventral heel
- Pubic apron with sinuous lateral margin and pubic foot with squared posterior margin
Species
Eodromaeus murphi Martínez et al., 2011
Type species
Named for Jim Murphy, an Earthwatch volunteer who helped discover the first fossils near the Ischigualasto Formation of Argentina.
- Holotype
- PVSJ 560 , División de Paleontología de Vertebrados del Museo de Ciencias Naturales y Universidad Nacional de San Juan
- Material
- Articulated skeleton lacking scapulocoracoids, most of the right forelimb, some cervical and dorsal ribs, gastralia, four anterior caudal vertebrae, and most chevrons; adult based on fused neurocentral sutures
- Horizon
- Valle de la Luna Member, Ischigualasto Formation, Carnian, Late Triassic , 237.0–227.3 million years ago
- Locality
- Valle de la Luna, San Juan, Argentina The holotype lies about 200 m above the base of the formation, in the Valle de la Luna Member, with two referred specimens in the underlying La Peña and Cancha de Bochas members (Martínez and colleagues, 2011). Martínez and colleagues (2012) list the species' occurrence as the Cancha de Bochas Member, but their own member thicknesses put the base of the Valle de la Luna Member near 180 m, below the holotype.
References
-
Martínez, R. N.; Sereno, P. C.; Alcober, O. A.; Colombi, C. E.; Renne, P. R.; Montañez, I. P.; Currie, B. S. (2011). A Basal Dinosaur from the Dawn of the Dinosaur Era in Southwestern Pangaea. Science 331(6014): 206-210. American Association for the Advancement of Science (AAAS). doi:10.1126/science.1198467
Gives the holotype's type locality and coordinates in the Valle de la Luna Member of the Ischigualasto Formation.
martínez2011a -
Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Theropods. Princeton University Press.
Source of the hip height estimate.
jones2026c -
Novas, F. E.; Agnolín, F. L.; Ezcurra, M. D.; Müller, R. T.; Martinelli, A. G.; Langer, M. C. (2021). Review of the fossil record of early dinosaurs from South America, and its phylogenetic implications. Journal of South American Earth Sciences 110: 103341. doi:10.1016/j.jsames.2021.103341
Recovered Eodromaeus as sister to Neotheropoda in their early dinosaur review
novas2021a -
Martínez, R. N.; Apaldetti, C.; Alcober, O. A.; Colombi, C. E.; Sereno, P. C.; Fernandez, E.; Santi Malnis, P.; Correa, G. A.; Abelín, D. (2012). Vertebrate succession in the Ischigualasto Formation. Journal of Vertebrate Paleontology 32(sup1): 10-30. doi:10.1080/02724634.2013.818546
Lists the Eodromaeus occurrence as the Cancha de Bochas Member, at odds with the holotype's horizon; gives the member thicknesses of the formation.
martínez2012b