Posts Tagged ‘paleontology’

I just don’t know enough paleontology

Wednesday, August 26th, 2009

I just read this post by John Hawks this morning over my morning coffee.  I totally agree with this sentence:

Many years ago, I got used to the fact that paleontologists and geneticists live in separate realities.

and I find this quite disturbing.

I’m one of the geneticists trying to figure out the ancestry of apes and trying to date the speciation events, and I just cannot read the paleontology papers.  Well, I can read them, but I really don’t understand them, so I often end up just scanning for estimates of speciation times without being able to judge how they come about.

Just last week I tried to figure out the divergence time between humans and orangutans to relate it to the estimates we get in the orangutan genome project.

For example, following a reference from another paper I read this one that, according to the first paper was supposed to give a lower bound on the speciation of 18 million years ago.  First I just scanned the PDF for “18″ but the units where “18″ appear are mm so not exactly what I was looking for.  So I tried actually understanding the paper… I probably failed, ’cause as far as I understand it it gives an upper bound of 20 million years ago.

Scanning the supplemental information of the first paper I then found that they use the 18 mya both as an upper and a lower bound, depending on which table you look at, and that just makes it that more confusing.

As a side remark, here I agree with John Hawks again:

After quoting from their online supplement (once again, grumbling that the essential details are hidden online where nobody reads them!)

I hope that it is an upper bound, since a lower bound would be very inconsistent with our genetic estimate, but I just wish I could be sure I understood the paper…

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Are orangutans our closest living relatives? Part II

Tuesday, June 30th, 2009

Ok, as the comment in my previous post pointed out to me, the question was raised by this new paper:

Evolution of the second orangutan: phylogeny and biogeography of hominid origins
John R. Grehan and Jeffrey H. Schwartz
Journal of Biogeography
Abstract

Aim To resolve the phylogeny of humans and their fossil relatives (collectively, hominids), orangutans (Pongo) and various Miocene great apes and to present a biogeographical model for their differentiation in space and time.

Location Africa, northern Mediterranean, Asia.

Methods Maximum parsimony analysis was used to assess phylogenetic relationships among living large-bodied hominoids (= humans, chimpanzees, bonobos, gorillas, orangutans), and various related African, Asian and European ape fossils. Biogeographical characteristics were analysed for vicariant replacement, main massings and nodes. A geomorphological correlation was identified for a clade we refer to as the ‘dental hominoids’, and this correlation was used to reconstruct their historical geography.

Results Our analyses support the following hypotheses: (1) the living large-bodied hominoids represent a monophyletic group comprising two sister clades: humans + orangutans, and chimpanzees (including bonobos) + gorillas (collectively, the African apes); and (2) the human–orangutan clade (dental hominoids) includes fossil hominids (Homo, australopiths, Orrorin) and the Miocene-age apes Hispanopithecus, Ouranopithecus, Ankarapithecus, Sivapithecus, Lufengpithecus, Khoratpithecus and Gigantopithecus (also Plio-Pleistocene of eastern Asia). We also demonstrate that the distributions of living and fossil genera are largely vicariant, with nodes of geographical overlap or proximity between Gigantopithecus and Sivapithecus in Central Asia, and between Pongo, Gigantopithecus, Lufengpithecus and Khoratpithecus in East Asia. The main massing is represented by five genera and eight species in East Asia. The dental hominoid track is spatially correlated with the East African Rift System (EARS) and the Tethys Orogenic Collage (TOC).

Main conclusions Humans and orangutans share a common ancestor that excludes the extant African apes. Molecular analyses are compromised by phenetic procedures such as alignment and are probably based on primitive retentions. We infer that the human–orangutan common ancestor had established a widespread distribution by at least 13 Ma. Vicariant differentiation resulted in the ancestors of hominids in East Africa and various primarily Miocene apes distributed between Spain and Southeast Asia (and possibly also parts of East Africa). The geographical disjunction between early hominids and Asian Pongo is attributed to local extinctions between Europe and Central Asia. The EARS and TOC correlations suggest that these geomorphological features mediated establishment of the ancestral range.

See also Humans More Related To Orangutans Than Chimps, Study Suggests at Science Daily.

Here they look at physiological features of apes and conclude that we, humans, look more similar to orangutans than the African apes.

Of course, this conclusion only flies if we discard the molecular evidence as artifacts.  The molecular evidence is pretty clear in putting us closer to chimps, then gorillas, than orangutans.

Quoting from the Science Daily piece:

Schwartz and Grehan contend in the Journal of Biogeography that the clear physical similarities between humans and orangutans have long been overshadowed by molecular analyses that link humans to chimpanzees, but that those molecular comparisons are often flawed: There is no theory holding that molecular similarity necessarily implies an evolutionary relationship; molecular studies often exclude orangutans and focus on a limited selection of primates without an adequate “outgroup” for comparison; and molecular data that contradict the idea that genetic similarity denotes relation are often dismissed.

“They criticize molecular data where criticism is due,” said Malte Ebach, a researcher at Arizona State University’s International Institute for Species Exploration who also was not involved in the project but is familiar with it.

“Palaeoanthropology is based solely on morphology, and there is no scientific justification to favor DNA over morphological data. Yet the human-chimp relationship, generated by molecular data, has been accepted without any scrutiny. Grehan and Schwartz are not just suggesting an orangutan–human relationship—they’re reaffirming an established scientific practice of questioning data.”

Personally, I put more faith in the molecular data, but then I don’t know that much paleontology…

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Dinosaurs may not be the ancestor of birds

Saturday, June 13th, 2009

Story here: Discovery Raises New Doubts About Dinosaur-bird Links

Researchers at Oregon State University have made a fundamental new discovery about how birds breathe and have a lung capacity that allows for flight – and the finding means it’s unlikely that birds descended from any known theropod dinosaurs.

The conclusions add to other evolving evidence that may finally force many paleontologists to reconsider their long-held belief that modern birds are the direct descendants of ancient, meat-eating dinosaurs, OSU researchers say.

Sadly I know too little to really follow the arguments, so I am not sure how strong they are, but it is interesting nonetheless.

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Last week in the blogs

Monday, May 11th, 2009

Another week, another list…

Computing/programming

Flu

Genetics

Genomics

Paleontology

Research life

Statistics

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