Eogrus

By Ripley Cook

Etymology: Dawn Crane

First Described By: Wetmore, 1934

Classification: Dinosauromorpha, Dinosauriformes, Dracohors, Dinosauria, Saurischia, Eusaurischia, Theropoda, Neotheropoda, Averostra, Tetanurae, Orionides, Avetheropoda, Coelurosauria, Tyrannoraptora, Maniraptoromorpha, Maniraptoriformes, Maniraptora, Pennaraptora, Paraves, Eumaniraptora, Averaptora, Avialae, Euavialae, Avebrevicauda, Pygostaylia, Ornithothoraces, Euornithes, Ornithuromorpha, Ornithurae, Neornithes, Neognathae, Neoaves, Gruiformes, Grui, Gruoidea, Eogruidae

Referred Species: E. aeola, E. crudus, E. turnicus

Status: Extinct

Time and Place: Between 41 and 34 million years ago, from the Bartonian to the Priabonian of the Eocene in the Paleogene 

Eogrus is known from a variety of locations across Mongolia, Kazaskhstan, and China: The Ulan Shireh Formation, the Irdin Manha Formation, the Ergilin Dzo Formation, the Tunggur Formation, the Tsagan Khutel Formation, the Karabulak Formation, the Alag Tsav, and the Mergen Formation 

Physical Description: Eogrus was a very large, long-legged bird, adapted extensively for fast movement. Though related to modern cranes and trumpetetrs, they actually adapted legs similar to those of ostriches – built for running, they had strengthened toes to allow for faster movement over their environments, and long thin limbs for more distance to be covered with each stride. Though other members of this group were also flightless like Ostriches, Eogrus was an early enough member to have retained flight capabilities, though it probably would have been rather bad at it, since it was on the path to a flightless physiology. Little else is known about its body size, head morphology, or other characteristics, given all we have of it are leg and wing bones.

Diet: It is uncertain what Eogrus may have fed upon, given its lack of a skull; given they were probably closely related to cranes, it’s possible they ate similar things to cranes, but that seems unlikely since they lived in a much drier sort of environment. 

By Scott Reid

Behavior: Eogrus would have probably mainly relied on running to escape large predators, sprinting across its environment in order to escape predators. While they could have flown away if needed, they were probably in the process of not relying on it like their later relatives would with abandoning it completely. Eogrus also would have probably taken care of its young. It’s possible they would have lived in small family groups or pairs, but it seems unlikely that they would have lived in larger flocks given their similarity to Ostriches, which tend to not. Again, without more fossil evidence, the jury is out.

Ecosystem: In general, Eogrus lived in a very extensive floodplain environment, with arid portions and more muddy river areas as well. This was right as the climate was drying and getting colder, after the global rainforest of the earlier Eocene began to break down. Eogrus was a common fixture in many environments and would have interacted with a wide variety of transitional mammals and birds, much more than I would really have time to list here in any great detail. It would have had to compete with early horse-like animals and would have had to run away from carnivorous mammals convergent with cats. As for other dinosaurs, there were a variety of ducks, swans, and potentially things like Presbyornithid and Pelagornithids, pointing to the more wet environment Eogrus lived in than typical modern ostriches do – indicating its link to the Gruiforms, despite its cursorial adaptations and evolution along with the increasing arid nature of its environment. 

By José Carlos Cortés

Other: For a long time, the phylogenetic affinities of Eogrus and its relatives was a major question, with many claiming they were closely related to the superficially similar Ostriches. However, much of their anatomy is so similar to the cranes that they were placed there instead. Rather, the similarities between the Eogruids and the Ostriches are a classic example of Convergent Evolution.

Species Differences: The different species of Eogrus mainly differ based on where and when they lived.

~ By Meig Dickson

Sources under the Cut 

Carroll, R. L. 1988. Vertebrate Paleontology and Evolution 1-698

Clarke, J. A., M. A. Norell, D. Dashzeveg. 2005. New Avian Remains from the Eocene of Mongolia and the Phylogenetic Position of the Eogruidae (Aves, Gruoidea). American Museum Novitates 3494: 1 – 17.

Mayr, G. 2009. Paleogene Fossil Birds. Springer-Verlag Berlin Heidelberg.

Mayr, G. 2017. Avian Evolution: The Fossil Record of Birds and its Paleobiological Significance. Topics in Paleobiology, Wiley Blackwell. West Sussex.

Wetmore, A. 1934. Fossil Birds from Mongolia and China. American Museum Novitates 711: 1 – 16.

Wetmore, A. 1960. A classification for the birds of the world. Smithsonian Miscellaneous Collections 139(11):1-37