Gondwanatheria
| Gondwanatheria | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Mandible fragment of Sudamerica ameghinoi |
||||||||||||
| Temporal occurrence | ||||||||||||
| Upper Cretaceous to Eocene | ||||||||||||
| 100 to 40 million years | ||||||||||||
| Locations | ||||||||||||
|
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Gondwanatheria | ||||||||||||
| Mones , 1987 | ||||||||||||
The Gondwanatheria are a group of extinct mammals that lived from the Upper Cretaceous to the Eocene in the continents of the southern hemisphere (former continent Gondwana ). They are the least known group of extinct mammals to date.
features
For a long time the finds were limited to teeth and parts of the lower jaw. The molars are high crowned ( hypsodont ) and have transverse cusps. This building is reminiscent of that of the Multituberculata , a group of mammals living in the northern continents at the same time, which is why the earlier finds of Gondwanatheria were classified in this group. The jaw parts found show clear differences, however: the Gondwanatheria had four molars (Multituberculata only had two) and their premolars did not have the jagged cusps of that group. From the findings it can be concluded that the mammals were very small, mostly herbivorous.
The description of Vintana in November 2014 shed more light on the group's anatomy and system. An approximately 12.5 cm long, strongly domed skull by Vintana was found in northwestern Madagascar and dated to the Maastrichtian . During its lifetime the animal probably looked like a marmot , but with a calculated weight of about 9 kg it was two to three times as large; it was the largest previously known Cretaceous mammal in Gondwana. In the Cretaceous it was only surpassed by Repenomamus on the northern continent of Laurasia . The eyes are strikingly large with a diameter of around three centimeters, which suggests that Vintana was probably crepuscular. The sense of smell was also well developed, which can be deduced from the size of the nasal cavity and, above all, the structure of the interior of the skull, which suggests a large olfactory bulb . Like all Gondwanatheria of the Sudamericidae family, Vintana probably fed on roots, seeds and nuts, while the basal forms such as Ferugliotherium and Trapalcotherium , formerly part of the Ferugliotheriidae family, were omnivores.
Systematics
Because of the scarce finds, the relationship between the Gondwanatheria and other groups of mammals was controversial for a long time. A relationship to the Multituberculata was assumed early on and both groups were classified in the Allotheria taxon . Although the structure of the jaw speaks against this relationship, they are likely to have occupied similar ecological niches - small, herbivorous mammals - that were later taken over by the rodents . Other theories, which have largely been rejected today, saw the Gondwanatheria as relatives of the joint animals or the monotremes (which also occurred in South America in the Paleocene). Still other theories they viewed as an isolated side branch not closely related to any other group of mammals. In all the analyzes carried out during the investigation of Vintana , the Gondwanatheria belong to the Allotheria, which turn out to be Monophylum , and the clade with the Gondwanatheria is the sister group of the Multituberculata.
The following cladogram according to Krause et al. shows the position of the Gondwanatheria within the Allotheria and the relationship between the eight genera described so far:
| Allotheria |
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
Most of the Gondwanatheria finds, which were best preserved until the description by Vintana in November 2014, come from South America , more precisely from Patagonia , from where the genera Ferugliotherium and Gondwanatherium from the Upper Cretaceous and Sudamerica from the Paleocene are known. The genus Lavanify is known from Madagascar , further material was found in India ( Bharattherium ), Tanzania and the Antarctic . The Antarctic finds come from Seymour Island and are the youngest known at around 40 million years ago ( Eocene ); they suggest that the Gondwanatheria on this continent could have survived until it was iced over. Overall, these animals are likely to have occurred on all continents of the former Gondwana.
literature
- Thomas S. Kemp: The Origin & Evolution of Mammals . Oxford University Press, Oxford 2005, 331 pages, ISBN 0-19-850761-5 .
- David W. Krause, Simone Hoffmann, John R. Wible, E. Christopher Kirk, Julia A. Schultz, Wighart von Koenigswald, Joseph R. Groenke, James B. Rossie, Patrick M. O'Connor, Erik R. Seiffert, Elizabeth R. Dumont, Waymon L. Holloway, Raymond R. Rogers, Lydia J. Rahantarisoa, Addison D. Kemp, Haingoson Andriamialison. First cranial remains of a gondwanatherian mammal reveal remarkable mosaicism. Nature , 2014; DOI: 10.1038 / nature13922
Individual evidence
- ↑ Krause et al. (2014), page 5.
- ↑ David W. Krause, GVR Prasad, Wighart von Koenigswald, Ashok Sahni, Frederick E. Grinek (1997): Cosmopolitanism among Gondwanan Late Cretaceous mammals. Nature 390: 504-507.
- ↑ Guntupalli VR Prasad, Omkar Verma, Ashok Sahni, David W Krause, Ashu Khosla, Varun Parmar (2007): A new Late Cretaceous gondwanatherian mammal from central India. Proceedings of the Indian National Science Academy 73 (1): 17-24.
- ^ David W. Krause, Michael D. Gottfried, Patrick O'Connor, Eric M. Roberts (2003): A Cretaceous mammal from Tanzania. Acta Palaeontologica Polonica 48 (3): 321-330.
- ^ Francisco J. Goin, Marcelo A. Reguero, Rosendo Pascual, Wighart von Koenigswald, Michael O. Woodburne, Judd A. Case, Sergio A. Marenssi, Carolina Vieytes, Sergio F. Vizcaíno: First gondwanatherian mammal from Antarctica. Geological Society, London, Special Publications 2006, v. 258, p. 135-144. doi : 10.1144 / GSL.SP.2006.258.01.10
