James Valentine On Phyla

Consider the changing morphospace within the stem group of a phylum when it is traced back through successively earlier nodes from the ancestor of the crown group (the crown ancestor) to its last common ancestor with a sister phylum. The crown synapomorphies are lost immediately. Some stem-group branches may be quite diverse, and their derived features may be so morphologically striking that in Linnean classification these branches would rank as extinct classes or orders of the phylum, ranks they can not be assigned in cladistic classifications. Proceeding toward the last common ancestor with a sister phylum, the constellation of features continue to erode. Eventually the morphologies at the nodes on the main line toward the common ancestor become dominated by features that are plesiomorphic. Finally, unique features of the phylum can no longer be recognized, and by definition the phylum is no longer present.

The above quote occurs on page thirty-one of Valentine’s book On the Origin of Phyla. Earlier Valentine had said:

Stem-group taxa expand the morphological features and, usually, the morphological disparity of a phylum beyond that of a crown group, while at the same time they lack crown-group synapomorphies.

This has some interesting implications for primate and human evolution. To see how this plays out in primate evolution you should read this post by Hawks. I had just finished reading Valentine’s book when Berger announced Australopithecus sebida and Curnoe announced Homo gautengensis. Some anthropologists (Clarke, for example) have long thought there were more than several species of australopithecine in South Africa and the same can be said for early Homo. Although Valentine was referring specifically to phyla above, the basic ideas in the above quotes can be applied to any crown group and stem group(s) – collectively known as a total group. More on this later.

Begging for Articles

Can some kind soul send me copies of these two papers:

Haile-Selassie Y, Saylor BZ, Deino A, Alene M, Latimer BM. 2010. New hominid fossils from Woranso-Mille (Central Afar, Ethiopia) and taxonomy of early Australopithecus. Am J Phys Anthropol (in press)

Kimbel WH, Lockwood CA, Ward CV, Leakey MG, Rak Y, Johanson DC. 2006. Was Australopithecus anamensis ancestral to A. afarensis? A case of anagenesis in the hominin fossil record. J Hum Evol 51:134-152. doi:10.1016/j.jhevol.2006.02.003

These are the two papers Hawks discusses.

Update 1: These are the fossils I mentioned way back in 2005:

Portions recovered thus far include a complete tibia, parts of a femur, ribs, vertebrae, clavicle, pelvis, and a complete scapula of an adult whose sex and stature are yet to be determined, although it is already clear that the individual was larger than Lucy. In addition to this discovery, skeletal parts of other individuals were found in different localities in the area. These discoveries include isolated teeth, and elements from below the neck (arm bones, leg bones, phalanges).

However, the paper only describes teeth, a maxillary fragment, and a mandibular fragment.

Were Crocodiles Responsible For The Stones We Call Tools?

Bob O’H brings an interesting Correspondence item in Nature to our attention. An excerpt is below: Continue reading

Fallback Foods and The Diet of Australopithecines

Physorg.Com has an interesting report on new research by Nate Dominy on underground storage units:

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Laetoli Footprints To Have Museum Built Over Them

As I mentioned back in January the Laetoli footprint trackways are in some danger due to erosion from heavier than normal rainfall. According to Nature a solution has been chosen:

The world’s oldest human footprints are to have a museum built around them in a bid to protect them. The 3.7-million-year-old tracks in an ash bed in Laetoli, Tanzania, are threatened by erosion. A 15-member government committee approved the 5-year plan, which calls for US$25 million to be raised for the facility.

In Which I Disagree With Hawks

I have been somewhat busy and have just read the Richmond and Jungers paper on Orrorin tugenensis, along with some of what has been written in the blogosphere about it. Unfortunately, I have to disagree with one post on the subject – that of Hawks. In his post Hawks is trying to argue that there isn’t that much difference between the results of Richmond and Jungers and the position of Senut and Pickford:

The overall morphological pattern of this femur, with its long neck and broad shaft, is much like known australopithecine femora. But to go a bit further, their metric comparisons show BAR 1002’00 to be the most Homo-like of the early hominid femora they examined, and their phenetic cluster puts it basal to the other australopithecines. That’s pretty much exactly what Senut et al. have consistently said [emphasis mine - afarensis]. So I have a hard time understanding how those observations refute the idea that Orrorin has a more Homo-like femur than later australopithecines!


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Question For Creationists: What’s Up With Knuckle Walking?

Really, it seems like every time I turn around some creationist or another is trying to argue that Australopithecus afarensis is not a transitional fossil because there are some osteological indicators of knuckle walking in their wrist. Safarti is a case in point. Normally, most creationists quotemine Richard Leakey when this comes up, however, with the passing of time all things change. So now the try to quotemine Richmond and Strait’s Nature article (along with Collard and Aiello’s Nature commentary). Anyway, here is Sarfarti’s version of the argument.

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Laetoli Footprints In Danger

Rex Dalton, in Nature, noted that the 3.7 million year old fossil footprint tracks at Laetoli are in danger due to erosion caused by heavier than normal rainfall:

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What We Can Learn From Bones: Paleodiets, Early Hominins, and Mole Rats, Part Two

Before going further, let me remind readers of the purpose behind “What We Can Learn From Bones.” Creationists like to make two main claims about paleoanthropology. First, they claim that all we have are bone fragments and teeth, and by implication, that we can learn nothing from bone fragments and teeth. Second, they claim that paleoanthropology is a historic science and since humans were not around to witness the events in question we can never really learn anything about the past. The point of “What We Can Learn From Bones” is to show that we can gain a lot of useful knowledge from bone fragments and that there are a number of sophisticated methodologies that allow us to test our inferences about the past. Previous posts in “What We Can Learn From Bones” can be found by scrolling down my sidebar and clicking on the “Bone Fragments” category.
I am also departing, somewhat, from the outline I mentioned in the first part of “Paleodiets, Early Hominins, and Mole Rats” mainly because of several recent papers that are relevant to the issue (which I will get to later).

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What We Can Learn From Bones: Paleodiets, Early Hominins, and Mole Rats

I have been fighting with the idea for this post for the last couple of weeks ever since I read this paper on the human amylase gene. Part of the reason for the delay in writing about the amylase paper is that I have come down with what I suspect is lateral epicondylitis and typing seems to aggravate it. Worse yet, the more I thought about the subject the longer and more complicated the post became. At this point I have decided to break it into a series of posts.

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