The Caveman’s Corner

So this is probably all you’re going to get of my promised great series on anthropoid origins. Basically, I ran out of confidence that I could handle the material intelligently and am now out of time. So, I only got about two pages in to the Adapoid Theory. Just so that work isn’t a total waste, I’ll share it with you here. It’s unfinished obviously.

Anthropoid Origins:

Up From the Adapoids

Gallia est omnes divisa in partes tres, and early anthropoids come from three places: Southeast Asia, China, and North Africa. This fossil roster stretching (tentatively) from the Early Eocene to the Middle Oligocene is our sole record of evidence as to the earliest beginnings of our anthropoid kind. The generally most famous and certainly longest studied fossils in the midst of all this grand geographic diversity come from a single, long-dead forest in Egypt known as the Fayum. These Fayum anthropoids form half the crux of the fossil argument for the theory of the adapoid origins of the anthropoids, and workers from the Fayum have formed much of its support. But the theory’s earliest history considerably predates the extensive exploitation of the Fayum in the 1970s and is ultimately dependant on long understood little Eocene primates known as adapoids.

The classic European adapoid is a lemur or loris-like prosimian, relatively large by Eocene primate standards, and generally a slow-moving, arboreal quadruped. Adapoid history in Europe went through two faunal stages. The first was a period of domination by a subfamily of the predominantly North American family Notharctidae known as the Cercomoniinae.

By the late Eocene the Cercomoniinae had begun rapidly losing ground to newcomers from Asia: the Adapidae. It is members of this family which gave the Adapoidae its name and established the lemurform stereotype. The two groups are quite different. Cercomoniines were generally much smaller, fed on fruits and insects, and had somewhat elongated ankle bones facilitating rapid leaping between vertical supports. They vaguely resembled in this aspect modern galagos. Also in common with galagos, many members of the Cercomoniinae were nocturnal, unheard of among the diurnal, browsing adapids.[1]

After the adapid onslaught, only the smallest cercomoniines ere able to prosper, by exploiting the insectivorous niches adapids were maladapted too. Appropriate to the beginnings of the Adapoid Theory in American paleontologists’ work with the North American Notharctidae, modern supporters cite the Cercomoniinae as the most plausible ancestors to the anthropoids of the Fayum.

The original argument and Phillip Gingrich’s resurrection of it in the 1970s are both anchored in features common between adapoids and anthropoids, especially North African fossil species. The group most specifically referred to is an enigmatic family discovered straddling the modern-day Straits of Aden in northeast Africa and the Arabian Peninsula, the Oligopithecidae. This family of early anthropoid lived from the late Eocene until into the Oligocene when they petered out.

As any paleontologist will tell you, the majority of the fossil record consists of jaws and teeth. And the majority of features cited by the Adapoid theory are dental. First it is worth pointing out the particularly primitive nature of adapoid dentition. Many adapoids retain all four premolars in the condition of generalized mammals. As other primates evolved more reduced snouts, they trimmed the number of these teeth to three and eventually two in Old World monkeys, apes, and humans, starting from the front. Thus in most other primates the first premolar is absent or reduced, and the second lower premolar is squeezed in the jaw until it is supported by a single root, while in the Adapoidae it has its primitive two.[1] The subsequent adapoid premolars are also lined up parallel to the jaw with no hint of the lateral slanting resorted to by less-muzzled primates to cram the teeth into their mouths.

But these primitive features don’t preclude a relationship with the Anthropoidae. If anything, they make it more likely, because they allow that dentally, Adapoids haven’t specialized terribly in some direction away from the anthropoids (although other features may suggest just that vis-à-vis living lemurs).

This entry was posted on Wednesday, August 13th, 2008 at 10:21 am and is filed under Primate Evolution, Uncategorized. 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.