''Rooneyia viejaensis'' is a relatively small primate belonging to the extinct monotypic genus ''Rooneyia''. ''Rooneyia viejaensis'' is known from the North American Eocene of the

Sierra Vieja The Sierra Vieja is a small mountain range in the Trans-Pecos region of West Texas, 42 miles northwest of the city of Marfa in far western Jeff Davis County and northwestern Presidio County. The range extends 16 miles south, from just east of th ...

of West Texas; the species is only known from the type specimen (TMM 40688-7). The lack of additional fossils at this time makes it difficult to hypothesize where and how ''Rooneyia'' may have evolved. The minimal wear upon the molar teeth of the specimen has led to the assumption that the type specimen is that of a young adult. ''Rooneyia'' does not consistently fall within any one group of fossil or extant primates.

Taxonomy

''Rooneyia'' is often referred to as enigmatic and does not seem to be closely related to most of the

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

primates from the

Rocky Mountain The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...

Region. There is disagreement into which suborder ''Rooneyia'' should be placed. Debate exists as to whether ''Rooneyia'' is a stem tarsiiaform to be grouped with omomyoids (F.S. Szalay), is a stem haplorrhine (C. Ross), stem strepsirrhine (R.F. Kay), or a stem anthropoid (A.L. Rosenberger). Primates ''Rooneyia'' has been compared to include: ''Microcebus'', ''Galago'', ''Tetonius'', and ''Necrolemur''.

History of discovery

The sole ''Rooneyia'' specimen was found at the Duchesnean Rifle Range Hollow locality in the Chambers Tuff Formation in 1964 by John A. Wilson.

Morphology

The type specimen is relatively intact, missing only the

premaxillae The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

, post orbital bars, zygomatic arches, and portions of the neurocranium. The natural

endocast An endocast is the internal cast of a hollow object, often referring to the cranial vault in the study of brain development in humans and other organisms. Endocasts can be artificially made for examining the properties of a hollow, inaccessible sp ...

of the braincase is largely undistorted as well. While only the skull of ''Rooneyia'' has been recovered, much can be learned. ''Rooneyia viejaensis'' preserves a funnel-shaped orbital fossa deeply recessed below the forebrain; located posteriorly in the face near the craniofacial junction. ''Rooneyia''’s orbits are highly convergent and forward facing. The frontal bone is relatively large in size with a fused metopic suture that extends like a roof above the orbit. The exterior surface of the frontal lacks any indication of longitudinal ridge or sagittal canal. ''Rooneyia'' has a dorsoventrally and laterally extensive frontal process that forms a partial postorbital septum which implies the existence of a relatively large ascending processes of the zygomatic bone. Though the absence of the ascending process of the zygomatic makes it impossible to make an accurate reconstruction of the structure. ''Rooneyia'' is more primitive than some tarsiiaforms it has been compared to, which typically had relatively small orbits. While the tip of the snout is missing from the ''Rooneyia'' fossil, based on the premolar to molar layout, it can be inferred that the dental arcade was not bell-shaped ''Rooneyia'' retains primitive features in its nasal region, but has a relatively large brain and what some have interpreted to be the beginnings of a post orbital closure.

Paleobiology

''Rooneyia'' had a body mass of about 400g. The small orbit size suggests a possible diurnal activity pattern meaning they were relatively more active during the day. The morphology of the semicircular canals in Rooneyia’s inner ears suggests agile locomotor abilities similar to those of ''Shoshonius'' or ''Omomys''. The rounded cusps on ''Rooneyia''’s molars suggest a frugivorous diet.

References

External links