Extinct genus of mammals
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Piauhytherium is an extinct genus of herbivorous notoungulate mammal of the family Toxodontidae. It lived during the Late Pleistocene; fossils have been found in Brazil. The only known species is Piauhytherium capivarae.
Description.
This animal in general terms resembles a hippopotamus, with a big short snout, a massive body and a large head. The skull measured almost in length, which indicates that "Piauhytherium" could be as big as a modern black rhinoceros. With regard to its nearest relatives, such as "Toxodon", this animal's legs were shorter and thicker, in addition, certain differences in the denture distinguish it from other notoungulates of this period.
Classification.
"Piauhytherium capivarae" was described for the first time in 2013, based on a complete skull including a jaw and some postcranial bones found in Serra da Capivara in Piauí, in northeastern Brazil. This animal belonged to a group of notoungulates known as Toxodonta, which comprises numerous herbivores from the Cenozoic of South America, whose better-known representative is "Toxodon". (Some remains found in Brazil have been reassigned to "Piauhytherium".) "Piauhytherium" was very similar to "Toxodon", but is differentiated in some features of is leg bones and characteristics of the teeth.
The 2018 study that described "Falcontoxodon" found "Piauhytherium", along with "Mixotoxodon", "Gyrinodon" and "Falcontoxodon", to be in the same monophyletic clade within Toxodontinae. Below is a parsimony tree establishing the relationships between the genera of Toxodontidae, as proposed by Carrillo "et al", 2018. Some authors have suggested that "Piauhytherium" is a junior synonym of the previously named species "Trigodonops lopesi."
Paleobiology.
The limb bones, which are particularly short and massive, led the authors of the original scientific description to hypothesise that "P. capivarae" led a semiaquatic lifestyle, similar to that of modern hippopotamus. This hypothesis had already been previously proposed for other toxodontids (including "Toxodon"), but equally has been refuted by other studies. The discovery of "Piauhytherium" is remarkable since it increases the degree of diversity of the toxodontids in the final stages of their evolutionary history: in the Upper Pleistocene only "Toxodon", "Trigodonops" and "Mixotoxodon" were also known.
Paleoecology.
Large, mesoherbivorous mammals in the BIR were widespread and diverse, including the other toxodont "Toxodon platensis", the macraucheniid litoptern "Xenorhinotherium" and equids such as "Hippidion principale" and "Equus neogaeus." Toxodontids were large mixed feeders as well and lived in forested areas, while the equids were nearly entirely grazers. Xenarthran fossils are present in the area as well from several different families, like the giant megatheriid ground sloth "Eremotherium," the fellow scelidotheriid "Valgipes", the mylodontids "Glossotherium", "Ocnotherium", and "Mylodonopsis". Smaller ground sloths such as the megalonychids "Ahytherium" and "Australonyx" and the nothrotheriid "Nothrotherium" have also been found in the area. "Eremotherium" was a generalist, while "Nothrotherium" was a specialist for trees in low density forests, and "Valgipes" was an intermediate of the two that lived in arboreal savannahs. Glyptodonts and cingulates like the grazing glyptodonts "Glyptotherium" and "Panochthus" and the omnivorous pampatheres "Pampatherium" and "Holmesina" were present in the open grasslands. A proboscidean species has also been found in the BIR, "Notiomastodon platensis," which was also present and was a mixed grazer on the open grasslands. Carnivores included some of the largest known mammalian land carnivores, like the giant felid "Smilodon populator" and the bear "Arctotherium wingei." Several extant taxa are also known from the BIR, like guanacos, giant anteaters, collared peccaries, and striped hog-nosed skunks. Two crab-eating types of extant mammals are also known from the BIR, the crab-eating raccoon and the crab-eating fox, indicating that crabs were also present in the region. The environment of the BIR is unclear, as there were both several species that were grazers, but the precede of the arboreal fossil monkeys "Protopithecus" and "Caipora" in the area causes confusion over the area’s paleoenvironment. Most of Brazil was thought to have been covered in open tropical cerrado vegetation during the Late Pleistocene, but if "Protopithecus" and "Caipora" were arboreal, their presence suggests that the region may have supported a dense closed forest during the Late Pleistocene. It is possible that the region alternated between dry open savannah and closed wet forest throughout the climate change of the Late Pleistocene.
References.
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