Floridaceras
| Floridaceras | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Early to Middle Miocene | ||||||||||||
| 20 to 15.2 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Floridaceras | ||||||||||||
| Wood , 1964 | ||||||||||||
Floridaceras is a now extinct genus of rhinos and lived in the Lower and Middle Miocene 20 to 15 million years ago mainly in North America , but is also found in today's Panama . It belongs to the group of Aceratheriinae and wasone of the largest American rhino representativeswith a size that is comparable to today's black rhinoceros. Characteristics of the genus were the extremely long and slender legs and the missing horn.
features
Floridaceras was one of the largest representatives of the rhinoceros in North America and, with a weight of about 1 to 2 tons, reached about the size of today's black rhinoceros ( Diceros bicornis ). Characteristic were the long legs, which had not yet been cut like those of its relative Aceratherium . Another original feature is the four-pointed forefoot. As with all rhinos, the hind feet ended in three rays.
The skull has only survived in fragments , especially in the area of the rostrum . The occiput was very narrow and short. It is noteworthy that Floridaceras had a distinct crest on the parietal legs , which is typical of some very early rhinos but does not occur in today's rhinos. The nasal bone was rather weak and sloped slightly forward. There were no roughened surfaces on the surface, so that it can be assumed that the rhinoceros genus had no horns. The interior of the nose extended to the third premolar and was significantly less pronounced than in later aceratheriines.
The lower jaw reached a length of 55 cm, the body of the lower jaw had a sturdy structure and was up to 8.9 cm high. The dentition was slightly reduced and no longer had a canine , but the exact number of front teeth is not known. However, it has been proven that the lower jaw only had one incisor , the second (I2), which was shaped like a pointed cone . The posterior teeth, which consisted of four premolars and three molars per jaw branch, had a large, up to 10 cm long diastema . The molars generally had low ( brachyodonte ) crowns. The first two premolars were small and barely molarized, while the rear two were very similar to the molars. These were large and the last almost 6 cm long.
The postcranial skeleton is only partially known, the spine is largely unknown. One of the few known thoracic vertebrae had an unusually long spinous process measuring up to 26 cm . The long limbs were characteristic, with the humerus reaching 44 cm in length and the thigh bone 58 cm. The lower limbs, on the other hand, were significantly shorter, reaching 36 cm for the ulna and 33 cm for the tibia . The forefoot is not fully known, but had a long and functional fifth ray, so it was built up with four rays ( tetradactyl ) ( metacarpus II to V), another primeval feature. The hind foot had three rays ( metatarsus II to IV) typical of the rhinoceros , with the third metatarsal bone being up to 16.8 cm long.
Fossil finds
The majority of the finds are from North America , especially from the US state of Florida , and come here mainly from a quarry on the grounds of Thomas Farm in Gilchrist County . These finds include about 60 fossil remains of the skull and the skeleton; they are now in the Florida Museum of Natural History . Another partial skeleton was discovered in Dawes County , Nebraska , while only a few isolated finds are known from Oregon . The rhino genus is also represented in the Gaillard Cut local fauna in Panama with a few fragments of the mandible and long bone remains . All finds belong to the Lower and Middle Miocene . Overall, Floridaceras showed a wide distribution, but due to the rather sparse remains, it was a rare element of fauna at that time.
Paleobiology
The low-crowned molars suggest a preference for soft vegetable foods ( browsing ). Isotope studies on the teeth confirmed this assumption and show that bushes or small trees may have been used as food resources. Since hardly any variations in the isotope values of oxygen and carbon have been detected, the researchers assume that the food supply will hardly fluctuate over the year. The climate is therefore reconstructed as tropical- warm with only minor seasonal changes in temperature and precipitation. Further investigations concerned the palaeo-habitat in the southernmost distribution area. Here, some experts assumed that an archipelago was formed in the Middle Miocene in southern Central America, before North and South America were finally connected by a land bridge in the Pliocene . However, this cannot be confirmed on the basis of the mammalian fauna, since most of the large animal species, including Floridaceras , had a body size similar to that of their North American conspecifics and an island dwarfing apparently did not take place here.
Systematics
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Internal systematics of the North American rhinos according to Prothero 2005
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Floridaceras is a genus of the rhinoceros family . Within the rhinoceros it belongs to the subfamily Aceratheriinae , ancestral older representatives, which were characterized by the absence of horn formations on the nasal or frontal bone. The tetradactyle forefoot and the archaic structure of the molars relegate Floridaceras to a very early position within this subfamily, the closest related forms are Aceratherium from Europe or the also very large Aphelops from North America. With these it belongs together in the tribe of the Aceratheriini .
The genus Floridaceras is monotypical with the only species Floridaceras whitei . The generic name refers to the Florida region, while the Greek words α ( a “not”) and κέρας ( kéras “horn”) emphasize the absence of the horn. The American scientist Theodore E. White is honored with the species name whitei , who collected numerous fossil finds on the grounds of the Thomas Farm in Florida and thus contributed to the discovery of Floridaceras , whereby he also presented an assessment of the geological age of the finds in 1942. The genus was first described in 1964 by Horace Elmer Wood on the basis of the findings collected by White. The holotype is a damaged skull with preserved back molars (specimen number MCZ 4046).
Individual evidence
- ^ A b c d e Horace Elmer Wood: Rhinoceroses from the Thomas Farm miocene of Florida. Bulletin of the Museum of Comparative Zoology, Harvard University 130 (5), 1964, pp. 361-386.
- ^ A b c d Donald R. Prothero: The evolution of North American rhinoceroses. Cambridge University Press, 2005, pp. 1-219.
- ↑ Bruce J. MacFadden: North American Miocene land Mammals from Panama. Journal of Vertebrate Paleontology 26 (3), 2006, pp. 720-734.
- ↑ Bruce J. MacFadden and Pennilyn Higgins: Ancient ecology of 15-million-year-old browsing mammals within C3 plant communities from Panama. Oecologia 140, 2004, pp. 169-182.
- ↑ Michael Xavier Kirby and Bruce MacFadden: Was southern Central America an archipelago or a peninsula in the middle Miocene? A test using land-mammal body size. Palaeogeography, Palaeoclimatology, Palaeoecology 228, 2005, pp. 193-202.