eFfing Fossil Friday: Funky facial flanges #FFF

David Krause and colleagues announced in this week’s Nature the discovery of a new species of extinct mammal, Vintana sertichi, that lived in what is now Madagascar between 66-72 million years ago. The species is based on a very well-preserved cranium of an early gondwanatherian (if you want to impress your friends this weekend, gratuitously use the word “gondwanatherian”). I don’t know much about early mammals like this, but it sounds like it was a weird creature (see the Stony Brook press release). Just looking at it’s face there’s something that sticks out as strange:

Ventana sertichi cranium (Reich et al. 2014, Figure 1a). Left is a 3D CT reconstruction, right is a line drawing highlighting all the individual bones (so many cranial bones). The view is from the right side, so the nose is on the right, the eye is the big hollow in the middle, and the back of the skull is on the left. The jugal flanges are the downward projections.

Vintana sertichi cranium (Reich et al. 2014, Figure 1a). On the left is a 3D CT reconstruction, and on the right is a line drawing highlighting all the individual bones (so many cranial bones). The view is from the right side, so the nose is to the right, the eye socket is the shadowy hollow in the middle, and the back of the skull is on the left. The jugal flanges are the downward projections.

Jutting downward from the sides of the jaw are ‘jugal flanges,’ projections of bone on the homologs of human cheeks. Projections of like these usually serve as muscle attachment sites, and the size of the projection generally reflects the size of the muscle. These facial flanges anchor the masseter muscle, a major chewing muscle that helps close the jaw. The size of this flange in Vintana suggests its chomp packed a punch. A debilitating bite. A face not even a mother could love (so now they’re extinct).

Vintana‘s bony tear-catchers caught my eye because most primates I’ve seen have, you know, less heinous faces. Scouring the internet, big jugal flanges are a fairly rare sight, but can apparently be found in glyptodonts (giant, armadillo-like mammals that lived tens of thousands of years ago) and various sloths. The closest thing I’ve seen to this gross bony flange in Primates are on the zygomatic bones of some extinct, baboon-like animals, such as Dinopithecus ingens:

Fragmentary skull, viewed from the top, of Papio (a.k.a. Dinopithecus) ingens, from Swartkrans, South Africa. Photo credit: CalPhotos.

Fragmentary skull, viewed from the top, of Papio (a.k.a. Dinopithecus) ingens, from Swartkrans, South Africa. As a punishment for its zygomatic excess, its face was confiscated. Photo credit: CalPhotos.

and Theropithecus brumpti

Theropithecus brumpti from the Omo basin. Photo credit: CalPhotos.

Theropithecus brumpti from the Omo Basin, Ethiopia. Photo credit: CalPhotos.

So some primates dabbled in jugal flangery like Vintana, but Natural Selection was having none of it. Anyway, Vintana overcame this craniofacial adversity with characteristic Mesozoic moxie, and is an important piece in the puzzle of mammal evolution. It will be interesting to see what other mammalian surprises the Mesozoic has in store for paleontologists.

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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.

As promised, malaria resistance in baboons

Last week I started to mention a recent paper in Nature on the evolution of malaria resistance in baboons, but then went out and partied instead. Not wanting to be a bastard, I’d better make good. While I’ll try to pull a good lesson from this, be warned that I’m about to discuss a topic about which I am no expert.

Malaria sucks, you don’t want to get it. There are anti-malaria medications out there, but I understand that they can make you insane, or at least have crazy dreams. Fortunately for millions of humans, there is a genetic basis for malaria resistance, so they don’t have to buy the anti-malaria crazy pills. Now, the paper tells me that a polymorphism in part of the FY gene turns the gene off in red blood cells, and that individuals with this variant are then strongly protected from malaria. No Lariam for these folks.

Jenny Tung and colleagues analyzed the homologous region of the FY gene in almost 200 yellow baboons (Papio cynocephalus) from Kenya, as well as tested these baboons for Hepatocystis parasites–relatives of Plasmodium vivax, which don’t cause malaria in baboons, but does really suck for them. And wouldn’t you know it–this same region on the baboon FY gene is also associated with Hepatocystis infection, where individuals with certain genetic variants have a lower susceptability to infection!

Now, the underlying genetic architecture and subsequent mechanisms of infection resistance are not exactly the same. But here’s the take home message from the paper:

“These results suggest that the genetic basis of phenotypic variation in different primate species can exhibit a remarkable degree of parallelism. In this case, not only are the similarities present at the molecular level . . . but they also extend to the mechanism that links molecular and phenotypic variation”

In other words, closely related species are equiped with very similar (or often the same) genetic or developmental “hardware,” and so evolution can cause them to come up with similar solutions to the same problem. In this case, there’s a similar genetic basis underlying infection resistance in humans and baboons. But I think this is a lesson that can be extended to, or at least kept in mind when considering, phenotypic evolution generally.

I’ve always (well, for the past three and a half years since I’ve been studying physical anthropology) thought that such a situation might characterize the “robust” australopithecines of East and South Africa. It is possible that these groups are not each others’ closest relatives, but that they evolved many craniodental characters in parallel, in response to selection for a heavy-chewing diet. This becomes even more plausible if it should turn out that many of these cranial and dental features are morphologically integrated–something I’m working on at the moment (if anyone reads this and scoops me, you will pay).

So, interesting paper. Reference

Tung, J. et al. Evolution of a malaria resistance gene in wild primates. Nature, in press.

Fatherhood

No, Dr. Bill Cosby (of Cliff Huxtable fame), I’m not trying to plagiarize the title of your book. Rather, I’m talking about an article published online today in PNAS by Charpentier and colleagues about paternal care in yellow baboons (Papio cynocephalus). I’m no expert on primate behavior (even though when I GSIed Primate Social Behavior last semester I read a billion student papers, many of which were about various forms of baboondom), so I won’t get too in depth here. The interesting finding of the authors’ study was that paternal investment in this species (or subspecies of P. hamadryas, if you lump like me) can have a “non-trivial” (to quote a famous primatologist) effect on offspring’s reproductive success. Paternal presence in the offsprings’ social group tends to cause offspring to mature faster, though only if the father was of high rank for male offspring. Faster maturation means one can begin his/her reproductive career earlier, potentially increasing reproductive success.

Paternal care is, arguably, a normal thing in modern human life, so it might be surprising to some that the behavior is relatively rare in the mammal world. But in many mammal, viz. primate societies, there are lots of reasons why it may make more sense for males not to invest in parenting. For starters, males have countless sperm, which are produced throughout their mature lifetime, whereas females are born with a set amount of eggs: gametically, males are millionaires, but females more penurious. On top of that, females bear the burden of pregnancy and nursing, which are very resource-draining. So females have more to lose from negligent parenting than males. Furthermore, in many primate societies, especially polygamous ones, it can be near-impossible for males to be certain of their paternity–why care for an infant that might belong to someone else? Plus, time spent taking care of one potential offspring is time that could be possibly better spent trying to sire a new one. Thus, in the primate world, paternal care is a fairly rare behavior, though the authors note that when there is paternal care, the species tend to be ‘monogamous.’

Yellow baboons are not monogamous, and they live societies with many mature males and females. But these baboons are fairly adept at knowing which offspring are theirs, and males often behave in ways beneficial to their offspring, through protection from both agonistic interactions and infanticidal males, and by helping forage. The authors show that such paternal behavior helps offspring reach sexual maturity earlier (hybird females also tend to mature faster, possibly a heterotic phenotype…?)

In some episode of The Simpsons whose details I forget, Lisa Simpson berates her father, calling him, “Baboon, baboon, baboon!” But perhaps this such a slur was not so slanderous. Perhaps his involvement in parenting (or his coresidency in the polygynandrous town of Springfield) will in some way bolster her reproductive success (though not in earlier maturity). Indeed, it would be interesting to determine exactly what role parental care played in human origins. Lovejoy posited that it was the watershed event that led to the emergence of hominins–something about females dropping so many babies (“Hey, wha’ happen?!”). . . . While the Charpentier et al. study suggests that the behavior could well have been a good paternal reproductive strategy, I don’t know that the idea is easily testable.

References
Charpentier MJE, van Horn RC, Altmann J, Alberts SC. 2008. Paternal effects on offspring fitness in a multimale primate society. Proc Nat Acad Sci 105: 1988-1992.

Lovejoy CO. 1981. The origin of man. Science 211: 341-350.