Uintaceras

Uintaceras
Temporal occurrence
Middle Eocene to Upper Eocene
46.3 to 41.1 million years
Locations
North America
Systematics
Higher mammals (Eutheria) Laurasiatheria Unpaired ungulate (Perissodactyla) Rhinocerotoidea Rhinoceros (Rhinocerotidae) Uintaceras
Scientific name
Uintaceras
Holbrook & Lucas , 1997

Uintaceras is an extinct genus of rhinos thatlivedin what is now North America during the Upper Eocene 42 to 46 million years ago. It is one of the earliest rhino representatives with a relatively small stature. Uintaceras alreadyshowedadaptations to the sluggish gait of the later rhinos. Finds are known so far only from two areas in the western part of the USA .

features

Uintaceras was a small to medium-sized representative of the rhinos . It was characterized by a musculoskeletal system that was not designed for fast running. The skull was about 36 cm long and was therefore relatively small, in addition it had a narrow shape with only slightly protruding cheekbones . The rostrum had against the posterior cranial area just a short design, was in favor but quite high. The occiput was not extended, but rather rectangular in shape, while the nasal bone was poorly developed and showed no attachment points for a horn, which is typical of very early rhinos. The interior of the nose was not very extensive and only reached as far as the first premolar , while the orbit was above the first and second molars . Atypical for today's rhinos, Uintaceras had a pronounced crest . The anterior teeth are not well known - some isolated incisors had a blade- like shape - the posterior comprised four premolars and three molars per jaw branch. The anterior molar teeth did not show any molarization and thus differed greatly from the posterior ones, which were characterized by clearly folded enamel . In their characteristics, the molars were also largely similar to those of other early unpaired ungulates and had characteristically low tooth crowns ( brachyodont ). The largest tooth in the dentition was the last molar with a length of about 3.3 cm.

The postcranial skeleton is largely known, but is mostly only very fragmented. Characteristic are the forelimbs, which show a long humerus compared to a shorter radius that only reached around 80% of the length of the humerus, which is typical of rhinos with their often clumsy gait. The closely related Indricotheriidae , however, had longer lower forelimbs and so descended from faster ancestors. In addition, in Uintaceras the radius was not fused with the ulna . The forefoot also typically had four rays ( metacarpus II to V) with a particularly pronounced third ray. The hind legs have also been handed down, with the thigh bone partially damaged. The shin and fibula were not fused together. The hind foot had three rays ( metatarsus II to IV).

Fossil finds

Finds of Uintaceras have so far been discovered at two locations in the western part of the USA . This includes a skull and much of the postcranial skeleton from the Uinta Basin in the US state of Utah . These finds also include the holotype (specimen number CM 12004). Other fossils include skull and mandible fragments. The second point of discovery is the Washakie Formation in Sweetwater County in Wyoming . Here fragmented skulls and upper and lower jaw remains came to light. All finds belong to the early Obereocene and are between 46 and 42 million years old (locally stratigraphically Uintum ).

Systematics

Internal systematics of the North American rhinos according to Prothero 2005   Rhinocerotidae    Uintaceras      Teletaceras      Penetrigonias      Trigonias      Amphicaenopus      Subhyracodon      Diceratherium      Skinneroceras      Menoceras      Floridaceras      Aphelops      Galushaceras      Peraceras      Teleoceras

Uintaceras is a genus of the family of rhinos . Within this he is one of the most primitive representatives and closely related to Teletaceras from the late Eocene of North America and Asia, another related genus is the North American Penetrigonias . All of these forms belong to the rhinoceros stem group, from which the later subfamilies such as Diceratheriinae , Aceratheriinae and Rhinoceratheriinae developed. The latter group includes the modern representatives of the rhinos still alive today.

The first fossils, two fragments of the lower jaw and the rest of an upper jaw from the Uinta basin, had already been described by OA Peterson in 1919 as Hyrachyus grande and thus placed among the most original representatives of the rhinocerotoid or tapiroid ; Horace Elmer Wood corrected the name in 1934 to H. grandis . In 1967 Leonard Radinsky referred the finds to Forstercooperia , the oldest member of the Indricotheriidae phylogenetically , relatives of the rhinos, which had produced Paraceratherium, the largest land mammal in the history of the earth. In addition, this would have been the only representative of this odd ungulate group on North American soil. New finds from Utah's Uinta Basin prompted Luke T. Holbrook and Spencer George Lucas to describe Uintaceras in 1997 as being among the original rhinos. The genus is monotypical and contains the only species U. radinskyi . The generic name Uintaceras refers on the one hand to the Uinta basin that has found its place, and the Greek word κέρας ( kéras "horn") continues to refer to the relationship with the rhinos. The species name radinskyi honors the paleontologist Leonard Radinsky and his services to the research of the odd ungulate in general and the Ceratomorpha in particular.

Individual evidence

1. ^ ^{A b c d} Luke T. Holbrook and Spencer George Lucas: A new genus of rhinocerotoid from the Eocene of Utah and the status of North American "Forstercooperia". Journal of Vertebrate Paleontology 17 (2), 1997, pp. 384-396
2. ^ ^{A b c} Donald R. Prothero: The evolution of North American rhinoceroses. Cambridge University Press, 2005, pp. 1-219
3. ↑ Kurt Heissig: The American genus Penetrigonias Tanner & Martin, 1976 (Mammalia: Rhinocerotidae) as a stem group elasmothere and ancestor of Menoceras Troxell, 1921. Zitteliana A 52, 2012, pp. 79-95
4. ^ OA Peterson: Report on the material discovered in the Upper Eocene of the Unita Basin by Earl Douglas in the years 1908-1909 and by OA Peterson in 1912. Annals of the Carnegie Museum 12, 1919, pp. 127-138
5. ^ Leonard B. Radinsky: A review of the Rhinocerotoid Family Hyracodontidae (Perissodactyla). Bulletin of the American Museum of Natural History 136 (1), 1967, pp. 1-47