The Original Southern Ape

Australopithecus afarensis was in the news again recently after researchers reported the discovery of a second set of tracks at Laetoli, Tanzania. If you are not yet familiar with this famous Australopithecus site and its importance for understanding human evolution, I suggest you read this excellent post from the Cleveland Museum of Natural History. It tells you all you need to know about the tracks at Laetoli, Australopithecus afarensis, and one of the most famous fossils of all time, “Lucy.”

I mention this discovery not to highlight Australopithecus afarensis, but rather to highlight an extinct South American species: Notopithecus adapinus. Among placental mammals, these two species could hardly be more different from one another. Australopithecus afarensis was a relatively large, bipedal primate that lived in Africa between about 4 and 3 million years ago. Notopithecus was a small (< 1 kg), quadrupedal ungulate that roamed South America about 45 million years ago. About the only thing they have in common is the derivation of their name; Australopithecus and Notopithecus both mean “southern ape,” the former composed with a Latin prefix and the latter with a Greek one.

MACN 10787
Photograph (left) and reconstruction (right) of a skull of Notopithecus adapinus from Argentina (MACN 10787). The two appear slightly different because the specimen is somewhat crushed and was restored based on other specimens. Photo by D. Croft. Reuse permitted under CC BY-NC-SA 2.0. Reconstruction from Simpson (1967:fig. 21, reversed).

“Southern ape” is clearly an appropriate name for Lucy and her kin. After all, humans and our closest relatives are all apes, and Africa is a southern continent. But the name Notopithecus is only half appropriate for a notoungulate, the group to which Notopithecus belongs. South America is a southern continent, but notoungulates are certainly not apes, nor are they closely related to them. (No one really knows where notoungulates fit in the tree of life, but no one has proposed that they belong to Euarchontoglires, the supraordinal group that includes primates and our closest relatives.)

Florentino Ameghino’s illustrations of specimens of Notopithecus adapinus, including a left dentary (left) and a right maxilla (right), both in lateral view. Note the low-crowned teeth, deep lower jaw, and the lack of spaces among the teeth, features shared with many primates. From Ameghino (1897).

So why did Florentino Ameghino choose Notopithecus when he named his species in 1897?  Because he thought Notopithecus really was a primate – not an ape per se, but an ancient relative of them. Such a belief may seem too far-fetched to be true, and indeed no one that I am aware of other than Ameghino ever believed his proposition. However, it should be kept in mind that Ameghino mostly just had teeth and jaws of the animal to study, not a complete skeleton. Additionally, he did not think that Notopithecus and kin were closely related to modern apes. Rather, he believed they were ancestral to extinct primates known as adapids that inhabited much of the Northern Hemisphere more than 30 million years ago. It is for this reason that he chose the specific epithet adapinus.

Postcranial morphology of Notopithecus Ameghino, 1897 (Notoungul
Skeletal reconstruction of Notopithecus adapinus from Vera (2012:fig. 7). Much of the skeleton is reconstructed based on the early Miocene interathere Interatherium robustum (all of the bones with a dark outline), but no limb bones of Notopithecus had been identified prior to this study.

An important factor that contributed to Ameghino’s confusion is that he thought that Notopithecus was Cretaceous rather than Eocene in age and thus tens of millions of years older than it actually was. This overestimation of the age of many South American mammals lead to Ameghino’s belief that nearly all groups of mammals originated in South America, specifically in Argentina. Ironically, nearly the opposite is more likely true; no major groups of mammals are thought to have originated in South America, with the possible exception of Xenarthra, the group that includes armadillos, sloths, and anteaters. That being said, Xenarthra is one of the most intriguing groups of mammals around and a pretty cool group to have originated there.*

Ameghino is rightfully revered as the father of paleontology in Argentina, so it is unfortunate that the name Notopithecus will forever stand as a testament to one of his mistaken beliefs. Nevertheless, I prefer to remember the fact that Ameghino coined the name in 1897, nearly three decades before Raymond Dart named Australopithecus africanus (in 1925). Thus, although the name Notopithecus will never gain the wide recognition that Australopithecus enjoys today, it remains the original “Southern Ape.”

* Xenarthra actually includes into two major groups (orders), but it clearly constitutes a single evolutionary lineage (clade).

References Cited:

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