Astrapotheria
| Astrapotheria Temporal range: Late Paleocene–Late Miocene |
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| Reconstruction of Astrapotherium in natural habitat | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Subclass: | Theria |
| Infraclass: | Eutheria |
| Superorder: | †Meridiungulata |
| Order: |
†Astrapotheria Lydekker 1894 |
| Families | |
†Astrapotheriidae
†Eoastrapostylopidae
†Trigonostylopidae
Astrapotheria is an extinct order of South American and Antarctic hoofed mammals that existed from the Late Paleocene (Itaboraian SALMA) to the Middle Miocene (Laventan SALMA), 59 to 12 million years ago. Astrapotheres were large and rhinoceros-like animals and are certainly one of the most bizarre orders of mammals with an enigmatic evolutionary history.
The history of this order is enigmatic, but it may taxonomically belong to Meridiungulata (along with Notoungulata, Litopterna and Pyrotheria). In turn, Meridungulata is believed to belong to the extant superorder Laurasiatheria. However, some scientists regard the astrapotheres (and sometimes the Meridiungulata all together) to be members of the clade Atlantogenata. An example of this order is Astrapotherium magnum. When alive, Astrapotherium might have resembled a mastodon, but was only three meters (ten feet) long.
Their lophodont molars and tusk-like canines became extremely large and ever-growing in later astrapotheres. The upper molars lack an ectocingulum and are dominated by well-developed ectoloph and protoloph. Additional lophs formed in some derived taxa. They had lower molars with two cross-lophs, including a high protocristid, and eventually became almost selenodont. As a result, their dentition is similar to notoungulates, but it seems to have evolved independently. The cheek teeth are similar to rhinocerotoids, including similar microstructure, which indicate they had the same function.
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