Saturday, October 3, 2009

New Hominid Findings

Ardipithecus image source: BBC

Science has a set of new articles from a team of researchers that have studied one of the now oldest known hominids, Ardipithecus ramidus, dated to about 4.4 million years ago.

The skeletal remains indicate that "Ardi" walked upright but still had prehensile feet with opposable large toes enabling it to climb and nest in trees. Unlike later, grassland-dwelling hominins, Ardi "lived in a woodland, climbing among hackberry, fig, and palm trees and coexisting with monkeys, kudu antelopes, and peafowl" according to Ann Gibbons, author of the article Habitat For Humanity, available free online after registration.

This find indicates that key human features appeared in the hominids inhabiting woodlands. Consequently, we can no longer explain some of those features--such as bipedalism--as adaptations to a grassland habitat.

Regarding Ardi's diet, according to Gibbons,

"The team suggests that Ar. ramidus was 'more omnivorous' than chimpanzees, based on the size, shape, and enamel distribution of its teeth. It probably supplemented woodland plants such as fruits, nuts, and tubers with the occasional insects, small mammals, or bird eggs. Carbon-isotope studies of teeth from five individuals show that Ar. ramidus ate mostly woodland, rather than grassland, plants. Although Ar. ramidus probably ate figs and other fruit when ripe, it didn't consume as much fruit as chimpanzees do today."

To clarify, by "more omnivorous" they mean that Ardi ate more animal food so it would be more appropriate to say that Ardi ate more carnivorously than chimpanzees. Ardi's diet of animal foods, fruits, nuts, and tubers sounds a lot like many recent hunter-gatherer diets.

Ardi also lacks the large, honing canines present in chimpanzees, which according to C. O. Lovejoy (Reexamining Human Origins in Light of Ardipithecus ramidus) indicates that Ardi tribes most likely had reduced male-to-male conflict compared to apes. Based on this, Lovejoy also believes that Ardi probably "...combined three previously unseen behaviors associated with their ability to exploit both trees and the land surface: (i) regular food-carrying, (ii) pair-bonding, and (iii) reproductive crypsis (in which females did not advertise ovulation, unlike the case in chimpanzees)" and that that "Together, these behaviors would have substantially intensified male parental investment—a breakthrough adaptation with anatomical, behavioral, and physiological consequences for early hominids and for all of their descendants, including ourselves."

In Paleobiological Implications of the Ardipithecus ramidus Dentition Gen Suwa et al conclude that the Ardi data suggests that "fundamental reproductive and social behavioral changes probably occurred in hominids long before they had enlarged brains and began to use stone tools."

I have not read all the articles yet, but as I contemplated this woodland origin of hominids, I thought of the aurochs, the ancestor of modern cattle. Although we raise cattle on open grasslands today, the Extinction Website states that the aurochs "appears to have preferred swamps and swamp woods, like river valleys, river deltas, and different kind of bogs. Beside swamp woods the aurochs shall also have lived in less wet forests." I have understood that this provides one reason cattle so easily damage open ranges compared to bison, i.e. cattle are naturally adapted to woodlands, and are more natural browsers than grazers.

Aurochs and wolves image source: The Extinction Website

The aurochs' range included North Africa, and I don't know if it ever ranged in the area where archaeologists unearthed Ardi (Ethiopia). Nevertheless, my mind went to consider the possibility that the hominid relationships with cattle and wolves (dogs) began in woodlands, not grasslands. Ardi is a fascinating find.


Natural Athlete said...

Excuse me but Ardipithicus is not the oldest known human ancestor. That term is in fact misleading, in general as it is impossible to determine if any fossil primate is in the direct ancestral line to modern humans one can only safely say if it is or is not the earliest known hominin.

Even that is not the case that would appear to be Orrorin Tugensis depending on whether Sahelanthropus turns out to be a hominin. Ramidus is not even the old fossil species currently placed in the Ardipithicus genus that would be A. Kadaba.

The evidence of the purposed social characteristics of A. Ramidus is extremely thin and controversial.

What is very worthwhile of hype about this fossil is the completeness of the skeleton and what is says about locomotor adaptions. There has been a growing body of evidence casting doubt on the idea of the last common ancestor of chimps and humans as being a knuckle walker. Something more similar the vertical oriented climbing adaption of the gibbons seemed more likely this confirms that, though this species would not likely have been close to the suspensory acrobat that gibbons are.

Don said...

Natural Athlete,

Thanks for the comments, I made adjustments to my word choices to correct what you found misleading.

Richard Nikoley said...

Always very interesting, Don.

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