The Caveman’s Corner

This is Meet an Ancestor installment three: Leptadapis magnus. The subject here also dovetails nicely with the post I’m writing on the adapoid theory of anthropoid origins, though it was selected a while before the idea for the latter series came into my head.

L. magnus cranium

Why is it relevant? Because L. magnus is an adapoid, specifically a member of the European family of the Adapidae. And that gives me the opportunity to tell an interesting story.

The type specimine of the Adapidae, the Adapoidae, and indeed the first fossil primate ever discovered was Adapis parisiensis, described by no less than Georges Cuvier in 1822. It was unearthed in the Montmatre quarry south of Paris, which was the origin of its specific epithet (parisiensis).

A. parisiensis cranium

Cuvier didn’t recognize A. parisiensis as a primate however, and instead classified it in with an eclectic mix of elephants, hippos, and perissodactyls he called the “Pachyderms.” In a flight of mythological fancy, Cuvier imagined the fossil reminiscent of a sacred bull of Egyptian legend known as Apis. Thus, the generic name ad (toward)- apis.¹

At 1.3 to 4 kg, L. magnus is the largest of member of the family moving toward Egypt’s sacred bull. Think of adapoids as like lemurs. The were diurnal and arboreal with long snouts and bony bars behind their eyes. Advanced features that might link adapoids conclusively with modern lemurs are controversial, however, and L. magnus shows none of them.

Reconstruction of A. parisiensis. Scale this up a bit to get L. magnus.

Like the rest of the Adapoidae, L. magnus was a denizen of the second geological period of the Cenozoic, the Eocene (54-34 mya), and also lingered a bit into the early succeeding Oligocene Period. Leptadapis is the best known of the Adapid genera other than Adapis itself, and this is largely due to L. magnus. It occurs in abundance in the same south French deposits as Adapis at Quercy. The two are broadly similar as well. Both have high-crested cheek teeth ideal for eviscerating foliage and large attachment points for chewing muscles, the sagittal and nuchal crests, on the rears of their skulls. Those of Leptadapis are much larger, however, concomitant with its more muscular build.

As in Adapis, males are much larger than females, intimating a social organization of groups consisting of multiple females and males who would attempt to dominate each other for reproductive access. Other than its size and robusticity, Leptadapis is largely a more primitive genus than Adapis, lacking anything resembling a incisor-canine tooth-comb complex and with eyes placed further apart and toward the outer sides of the skull.

L. magnus was a large, slow-moving primate which was a member of an important prosimian radiation in the Eocene and early Oligocene. It demonstrates that the diversity of the group, both in adaptation and in derivation from the primitive pattern, at its height. Adapoids and their nocturnal counterparts the omomyoids ruled the primate world in the Eocene, so it makes sense that they would diversify into all manner of niches. This has implications to explain the rarity of early anthropoids in Europe and Asia. There my simply have been no room for them until a cooling climate forced the Eocene prosimians off their perch during the Oligocene.

¹ This story is related in Beard, page 35.

References

Beard, Chris. The Hunt for the Dawn Monkey. 2004. U of California Press.

Fleagle, John G. Primate Adaptation and Evolution. 2^nd ed. 1998. Academic Press.

Hartwig, Walter C. The Primate Fossil Record. 2002. Cambridge UP.

This entry was posted on Saturday, June 14th, 2008 at 8:26 pm and is filed under Meet an Ancestor. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.