Osteology everywhere: Pollicem verte(b)r(a)e [Latin puns are hard]

I just got back from the meetings of the European Society for the Study of Human Evolution in Florence. As you can guess, bones and genes and anatomy and apes and biomechanics and energetics and everything were on everyone’s minds. Even in the midst of an unseasonal surprise typhoon of lunch time ice:

Ambush of hail.

Aw hail no.

Along the way, I passed a gift shop window and this book cover immediately caught my eye:helert

No, it’s not an ancient Roman gladiator’s helmet. It’s clearly a lumbar vertebra, probably of some quadruped. We’re looking down onto the top (or front of it) from the cranial view. The body or centrum is the rounded part toward the bottom of the picture, the short transverse processes jutting off to the sides. The spinous process, pointing toward the top, is even thick and blunt distally as is characteristic of lumbar verts. Here’s a comparison:

Middle lumbar vertebrae, from the cranial view (modified from Figs. 3-4 of Moyà-Solà et al., 2004). 0=modern baboon, A=Proconsul nyanzae (KNM-MW 13142-J)(B) P. catalaunicus (IPS-21350.59). (C) Cast of Morotopithecus bishopi (UPM 67.28) from Moroto (Uganda). (D) D. laietanus (IPS-18000) from Can Llobateres (Spain). (E) Pongo pygmaeus

Middle lumbar vertebrae of various Miocene apes (A-D) in cranial view (modified from Figs. 3-4 of Moyà-Solà et al., 2004). 0=modern baboon, A=Proconsul nyanzae (KNM-MW 13142-J), B=Pierolapithecus catalaunicus (IPS-21350.59), C=Morotopithecus bishopi (UPM 67.28), D=Hispanopithecus laietanus (IPS-18000), and E= modern orangutan.

Modern apes use an upright posture more frequently than living monkeys, who are quadrupedal. An anatomical correlate of these postures is the position of the transverse processes. Compare the baboon (0 in the figure above) with the orangutan (E). In the monkey the transverse processes come off the sides of the centrum (below the horizontal line), while in the orangutan the processes come off the pedicle further back. In your lumbars the transverse processes arise a little bit more toward the back than in the orangutan.

This is a pretty characteristic pattern, meaning that we can reconstruct the habitual posture of an animal based on a single bone – even just part of a single bone as in the case of Hispanopithecus (D, above). Proconsul nyanzae (A), dating to around 19 million years ago and therefore one of the earliest apes, has a monkey-like lumbar vert; the rest of its skeleton is monkey-like and so we think many of the earliest apes moved around like modern monkeys. In contrast, Morotopithecus bishopi (C), at 20.6 million years ago, is also one of the earliest apes but has a more modern-ape-like lumbar. And so with Pierolapithecus and Hispanopithecus.

The vertebra gracing the cover of our gift shop book is clearly more monkey-like, presumably from a simian who long ago walked on all fours across the blood-soaked floors of a cacophonous Colosseum.

Molar? I hardly even know her!

I was recently at the State Zoology Museum of Munich, studying their amazing plethora of orangutan bones. Jaw bones are especially useful skeletal remains when you study growth, because different teeth come in at different points in one’s life. Remember when your 1st permanent molar teeth came in? You were probably 5 or 6 years old at the time. It was a big deal, your first permanent teeth! What about your 4th permanent molars, after your wisdom teeth, remember those?

An adult male orangutan mandible, with bilateral supernumerary molars. Or more simply, “an extra molar on both sides of the jaw.”
I hope not. As a good eutherian, you should never have more than 3 molars in each half of each jaw. And as a modern human, there’s a good chance you’ve only got 2 in each half (but that’s a whole other story). So when I was looking at orangutan skulls to get an idea of individuals’ ages, I was shocked to find specimen after specimen with at least one extra molar. So far as I could tell, 27 out of 181 (14.9%) adult orangutans in this collection had extra molars.
Supernumerary (fancy word for “extra”) molars manifest a number of ways in this collection. Sometimes there’s only one extra tooth. Sometimes there are extra teeth in both upper and lower jaws but only on one side. Sometimes there’s a full set (4). Et cetera. One poor bastard even had a 5th molar lurking behind one of his four 4ths! Deplorable.

An adult male with a fairly normal 4th (blue arrow) and even a weird, unerupted 5th (red arrow) molar. Gross!
This is rather strange, such a regular occurrence of supernumerary teeth – what gives? A starting clue is the fact that all specimens with extra molars are of the species Pongo pygmaeus from Borneo (173 of 181 specimens). The remaining eight specimens, with a normal dental formula, are Pongo abelii from the island of Sumatra. But how much of this difference in frequency is due to the fact we’re looking at 181 Bornean, vs. only eight Sumatran orangutans?
Resampling to the rescue! Is it weird that 27/181 (15%) Bornean orangutans have extra teeth, while 0/8 Sumatran orangs do not? Another way to ask the question is, what are the chances of sampling 8 Bornean orangs, none of which have extra molars? This is very easy to program and test in R:
Set up a vector (basically, a string of numbers) to represent your Bornean orangs, each entry representing an individual, assigning “0” for no extra teeth and “1” for at least one (this admittedly oversimplifies the nature of extra teeth). Then simply randomly sample – lots and lots of times –  eight individuals from this Bornean vector, to see how often you get a set in which 0/8 have extra molars.
“b” is our vector of Bornean orangutans, consisting of 0s and 1s for whether there are extra teeth. “n” tells us how many individuals had extra teeth in that subsample. The “(i in 1:10000)” means for each of 10,000 resamplings.
Following this resampling procedure, there’s about a 25.5% chance that none of them will have extra molars. That means the remaining 74.5% of the time, a random subsample of the Bornean orangutans will contain at least one individual with at least one extra tooth.
A number of interesting questions arise from this – if we were to examine more Sumatran orangutans, would we eventually find one with an extra molar? After all, the 25.5% chance of sampling 0/8 suggests maybe we just missed some Sumatrans with extra molars. Regardless, within the Bornean orangs, why is the frequency so high? Does one pattern of extra teeth (say, just in the lower jaw, or on both sides, etc.) predominate? Are there differences between the sexes? These are questions for another day….

Pongo amidst conservation and industry

The December issue of Current Biology has a short summary about collaborations between the palm oil industry and conservationists to preserve orangutan (Pongo pygmaeus) habitats in Borneo. As the palm oil industry has burgeoned, orangutan populations have lost contact due to deforestation for industry and agriculture. Apparently palm oil companies have made an agreement with the government of the Malaysian state of Sabah in Borneo, in which the companies will help construct corridors that will reconnect isolated populations of the orangutan.

Lethargic orangutan at the Zoo Atlanta, in Hottlanta GA. He was cool but boring because he didn’t do anything.

Good to see cooperation rather than conflict between conservationists and industries. Let’s hope it proves beneficial for the endangered orangutans.

Assuming the project works out, it will be interesting to see population genetics and behavioral studies documenting the results of renewed contact and gene flow of these erstwhile isolated apes. Since the prior isolation and future reconnection are anthropogenic, or due to human activity, it will be an interesting (and hopefully not too depression) lesson about how human behavior affects biodiversity.

On an aside, I just heard, “Goonies never say ‘die'” (Sean Astin, Goonies).
Williams N. 2009. Orang-utan plan. Current Biology 19: R1098