Unexpected Bipedalism

Hopefully this will still work for future readers:

Most people seem quite unaware that pangolins even exist. Apparently, only three specimens are held in captivity legally as of 2005 - so it's really no small mystery why. Despite some bizarre notions that they are dinosaur-like reptiles, these are mammals and are closely related to carnivorans (dogs, cats, seals, etc.) forming the clade Ferae (Beck et al, 2006). These are united with Perissodactyla, Cetartiodactyla, Chiroptera, and Eulipotyphla (some "insectivores") to form the oddly diverse group Laurasiatheria. If you are familiar with Family/Order names of mammals, then this figure from Bininda-Emonds et al 2007 should be of interest:

You may want to click this...

You'll notice that other mammalian groups with tubular snouts that eat ants (Aardvarks - Afrotheria; Anteaters - Xenarthra) are not related but all belong to different super-orders. There was an enigmatic European Eocene species called Eurotamandua which is classified as an anteater on the German wikipedia and a pangolin on the English wikipedia but is currently in an unresolved position. It could be a sister group to sloths and anteaters, a stem Xenarthran (it doesn't posses the titular vertebral structure) or a pholidotan (pangolin) (Hunter & Janis 2006). Despite all the convergences, pangolins/pholidotans have sharp scales made out of agglutinated hairs covering everything but the bottom of the head and body, and the inside of the limbs (Heath, 1992). One of these days I'll probably talk more about the strange morphology of these mammals, but it is locomotion that I am focusing on here.

Pangolins normally roll up as an anti-predator defense (only exposing the sharp scales) but they are also known to curl up and roll down hills to elude predators (Tenaza, 1975). Since the only large predators on the island where that was observed were humans and pythons, perhaps this is an aberrant behavior. Didn't Stephen Jay Gould write an essay wondering why no animals moved around like balls?

As you may have noticed from the video, the large pangolin Smutsia temminckii is, in fact, a facultative biped. While most sources just mention that fact, the video is useful in showing that the tail is held somewhat strait out (not dragging on the ground) and the arms are tucked in - other bipedal mammals are saltatory (kangaroo, sifaka lemur, jerboa, kangaroo rat, springhare) or have a vertical posture (humans, gibbons - sifakas again) so this posture seems to be unique as far as I know. Walking quadrupedally, the large pangolin Smutsia temminckii puts weight on the knuckles of its forefeet and curls its claws inwards like anteaters (Heath 1992). That position normally is associated with clawed animals (chalicotheres, sloths) - so is the bipedal posture an alternate strategy in not wearing down claws, or is there another factor involved? S. temminckii has hips more suited for load bearing than other species (Heath 1992), and bipedalism appears to be a unique behavior for the species. I have not seen any references to bipedalism in S. gigantea, a similarly sized relative also living in Africa. Many other pangolins are arboreal, and I am not certain if any other large species engage in bipedal locomotion. Although not specifying a species, Filler 2007 noted that the LTP (Lumbar Transverse Process) of pangolins have the same homology as the hominiforms, uniquely among mammals. The implications of this have not been discussed to my knowledge. So why am I asking so many questions? As far as I know, the benefits and mechanics of such a posture have yet to be thoroughly analyzed. I know, I'm disappointed too.

Just in case the other video ceases working at some point, here is a backup pangolin video:





I won't just stop with pangolins. Chris Taylor wrote on bipedal postures in a relative of the camel recently, and my next group is somewhere more along those (herbivorous) lines. They were presumed to be relatives of pangolins earlier, but of course are actually quite distant. I'm talking, of course, about Megatheriid ground sloths. Darren didn't mention sloth bipedalism in his ten strange sloth facts post - which worried me immensely - but it does seem to be pretty widespread in the literature. Phew.

Megatheriid sloths having a bipedal posture when feeding shouldn't come as a shock in the context of mammalian diversity, others such as pandas and chalicotheres probably engaged in a similar posture. Also, just about every reconstruction I see of Megatherium puts it reaching up to a tree with its claws in a bipedal sort of posture. However, tracks indicating both bipedal and quadrupedal posture have been found (Casinos 1996) so there's something interesting happening here. The paper goes on to study the limbs and vertebral column of Megatherium sp. (different species were hard to discern) and the forces put on them in hypothetical quadrupedal and bipedal postures. Results for strength indicators were inconclusive as the hindlimb bones were stronger mechanically but the forelimb bones seemed more efficient in a quadrupedal posture. A study of the backbone movements fit well with bipedal mammals, although the bending was noted as being too high. The femur is pretty bizarrely shaped (it is four times wider in the transverse plane than the sagittal one) - this goes against mammalian and Xenarthran tenancies. This does appear to enhance dealing with stress and since such a drastic change in one bone makes little sense in a quadrupedal animal, Casinos concludes that this was a bipedally adapted animal.

Chris Taylor's post showed that an animal can be adapted towards standing bipedally, so its not like this sloth was an exclusive biped. The possibility of claw prints being somehow erased in the bipedal tracks was not raised, but presumably since there were examples of both tracks types they could be easily distinguished. Maybe this sloth was adapted towards standing bipedally while feeding on trees and switched between quadrupedal and bipedal locomotion like...the pangolins in the videos. Even having a living example doesn't always help since apparently we're not sure what advantage this switching would give.

I tried and tried to find a Youtube video of a bipedal sloth but failed. Also, I realized that the title should have specified "in Mammals", but it sounds snazzier this way.


-Cameron


References:

Beck, Robin MD et al. 2006. A higher-level MRP supertree of placental mammals. BMC Evolutionary Biology (6) 93. Available

Bininda-Emonds, Olaf et al. 2007. The delayed rise of present-day mammals. Nature 446, 507-512. Available

Casinos, Adria. 1996. Bipedalism and quadrupedalism in Megatherium: an attempt at biomechanical reconstruction. Lethaia 29 (1), 87-96. Available

Filler, Aaron G. 2007. Homeotic Evolution in the Mammalia: Diversification of Therian Axial Seriation and the Morphological Basis of Human Origins. PLoS ONE. Available (Open Access)

Heath, Martha E. 1992. Manis temminckii. Mammalian Species 415, 1-5. Available

Hunter, John P and Janis, Christine M. 2006. Spiny Norman in the Garden of Eden? Dispersal and early biogeography of Placentalia. J Mammal Evol 13, 89-123. Available

Tenaza, Richard R. 1975. Pangolins Rolling Away from Predation Risks. Journal of Mammalogy p. 257. Available



I can't access the article, but this abstract mentions how large and derived Glyptodonts possibly engaged in "strenuous locomotor activities" bipedally! Darren mentioned this first, of course.

One Year of The Lord Geekington

61 published posts.

That's what I'm measuring my year by. At a rate of a post a week I feel somewhat accomplished. Cutting and pasting things into Word revealed that I have written something like 87,000 words and filled out around 300 pages so far. By either count, this is roughly the length of an average novel. Granted somebody like H. P. Lovecraft could pump out a letter of a similar length in about a week, but given the subjects covered I feel that I've accomplished something. At least one monstrous post took over a dozen hours to illustrate and write, for instance. I feel that I'm being self-congratulatory here, this feels bizarre.



Reflections Upon the Lord Geekington


So how did this all begin anyways?


I remember as a little kid how I'd always ramble on about every science fact I knew to who ever had the tolerance to listen to me. This blog seems to be a direct continuation of that, now that everybody has the capacity to write about everything to everybody else. As you may recall, the first few months of this blog were rather uneven and, well, geeky. I talked about video games, weird paintings, art, forteana, my own personal speculative evolution, and even a bizarre type of, um, -craft. In retrospect, it really doesn't feel all the worthwhile writing to me. Sure art is nice, but there are much finer websites out there covering it. I had reached the realization that with 100 million other bloggers out there (big numbers scare me) I might want to write something more worthwhile. What is worthwhile to me isn't worthwhile to everybody of course, but at least I feel writing about overlooked natural science is a lot more fulfilling. I hope that it is at least an occasionally interesting read to some people occasionally, I'd hate for this just to be some self-centered exercise, or, er, more so. But hey, I don't get paid for this so at least I feel a little altruistic!

From about February on I had shifted more towards science blogging, writing about cephalopods and cryptid amphibians and other things Darren Naish hadn't posted on yet (or ever). Being dangerously under-qualified compared to Dr. Naish, I didn't my blog to just just wind up a Fooling Grandma* (or worse yet, a Deceiving Great-Grandma) of his creation. I think now that there is information, probably far more than enough, to go around for everybody. Since starting to blog Darren has moved to Scienceblogs and some other very fine Zoology/Paleontology based blogs have arisen such as, ooh, say Laelaps and the Catalogue of Organisms. These blogs and others have given me an unprecedented opportunity to learn about science in a way that I would never have been able to do in the past. What a golden age of information we live in.

*Coined by Russell Shepherd, date unknown. Signifies a product made in imitation of an actual franchise (Action Rangers --> Power Rangers). Most kids and adults realize the difference, so apparently these products were making profits solely by fooled grandmas. Deceiving Great-Grandma. Older people also have great difficulty reading white on black and this footnote is likely nigh-unreadable.

It has come to my surprise that not only do people read what I write, but two fellows (Darren and Chris Taylor (Cat. of Org.)) have given me the "thinking blogger" award, much to my astonishment. If I had heard about such a thing at the outset of blogging, the thought of receiving it would never have crossed my mind. Instead of making me feel pretentious (!!??!) it makes me live in fear of betraying this title. And I don't believe I've ever formally thanked Chris yet, well, thanks! As for awarding others...I don't think I carry any sort of authority, so I'll trust other better bloggers to make their decisions.

Here I am writing this post, just to give you all a glimpse of the magic in progress. I'm sitting on the floor, not even in my own room, and hammering away. Oh yes, I cut my hair rarely, usually shaving my head on Maine Day. This is why I don't talk about or show my personal life.

Random Highlights

As if the structure of this post wasn't convoluted enough...


Disappointments.

Judging by my comments, I have had some uninteresting posts here. I've got to hand it to my sister for commenting enough to basically be a co-blogger of sorts. No zero comments for me! My "scientific" racism, dang! I though that was a pretty good topic. Maybe my "Proto-Europoid" mug scared everybody off. My post on pseudopapers was also just, blah, not needed. There are others, but a cursory glance should give them away.

I'm often rather self-critical, so that coupled with feedback (or lack thereof) will hopefully drive me to improving this blog. I have the drive to improve things, although recently the motivation to do much is more difficult to come by (severe money related troubles, yeesh).


Successes - or at least better posts.

Despite my oft-critical perspective, I'm surprised by how popular some posts were. Anything dealing with large animals (here and here) were surprisingly popular. They were a topical overload and kinda jumpy, but hey, they were pretty fun. As for my favorite posts, I'd say that they were the Omnivore vs. Hypercarnivore post, the choristodere post, and the Meganthropus post - the one that launched me into using peer-reviewed articles. The super-long and semi-technical posts were my favorites, but unfortunately they have to be rare due to the time involved. Sigh...

And now for highlights in picture form:

Choristoderes!

Me and some rather large catfish.

My interpretation of three bigfoot "types" according to Hall/Coleman/Huyghe.

Some very large squids. Hmm, no 108 footers as far as I can tell...

A fictional temnospondyl from a quasi-abandoned project.

That ever-strange cetacean centipede.

The amazing blanket octopus. Taken by Marcello Conticelli off Ponza, Italy.

The obscure Barra carcass, one very strangely decomposed whale.

And I course, I give my thanks to everybody that I have failed to mention in this post. And if you find this slightly interesting, please visit the links to the right.


Let's hope I can write another one of these

-Cameron

Swimming Opossums

Let's start off with a mystery:

In a 1999 field report by Angel Moran Forés (readable: here) he claimed to have found and photographed a strange aquatic animal in Macas, Ecuador. He said it had white fur with brownish spots, was 35-40 cm long with no tail, had webbed fore and hind-feet, no pouch, and a proboscis. The specimen was never sold, so all we have to go on is a photograph and that description:

"Mystery Animal" photograph by Angel Morant Forés.

And now to make things interesting, here is a photograph of a Water Opossum or Yapok:

Taken from Wikipedia

While living yapoks seem to have much darker fur (see here) for some reason either preservation makes the fur lighter or there is a light colored morph. Either way, both specimens have the same striking bodily coloration pattern (down to the barely visible dorsal stripe), which Forés did not mention. The size would be a little large, unless the legs were counted; but the main problem is with the weird anatomical features. Yapoks do have pouches (rear-opening, so maybe it was missed?) and tails and also lack webbed fore-feet and a proboscis. I for one can't see a proboscis in that picture, but I'll take the author's word for it. While new species are being discovered at a fairly impressive rate in this region of the world, I think this is more likely a poor case of taxidermy than anything. Of course with many things of a cryptozoological nature, this one doesn't appear to be wholly resolvable any time soon.

Aquatic adaptations in marsupials appear to be quite unusual. There don't seem to be any species of mammals that can't swim to some degree (except giraffes), but marsupials seem conspicuously unable to adapt to a semi-or fully aquatic niche. Apparently the logistics of keeping the young alive in a pouch while diving kept the marsupials from adapting in that direction. That is, except the yapok (Chironectes minimus) is the only species of marsupial to be adapted towards this lifestyle (Fish, 1993). I'll get into its tricks later.

Even less widely known than the yapok is the thick-tailed opossum (Lutreolina crassicaudata), also said to be quite competent in the water. It is the most carnivorous of all didelphids and is frequently compared to a mustelid ("mink-opossum") in appearance (Santori et al, 2005). The scientific name "Lutreolina" hints at an otter-like and thus semi-aquatic lifestyle as well. So is this an overlooked semi-aquatic marsupial?

The "lutrine opossum". Taken from this page. According to Walker's Mammals of the World this image (flipped) was taken from the New York Zoological Park through Joseph Davis.

A 2005 paper by Santori et al on the locomotion of the thick tailed opossum reveals that yes, there are some people who have considered this species semi-aquatic in the past. Didelphids as a group are apparently good swimmers, so the authors of the paper compared terrestrial species and the yapok to this species by using videotape. The climbing, jumping, and running capabilities of this species was also compared to the other opossums. L. crassicaudata actually does have some adaptations towards an aquatic lifestyle (buoyancy control, posture), and a unique gait separate from terrestrial opossums and the yapok, but curiously is not faster in the water than terrestrial opossums. It also lacks other adaptations such as webbed feet and the use of only the hind limbs (though some other semi-aquatic animals also use all their limbs). So while possessing some aquatic adaptations, the thick-tailed opossum is not even considered semi-aquatic. Apparently there isn't a term to reflect this semi-semi-aquatic condition. Perhaps a mustelid-like body plan has the side-effect of being able to travel in water slightly more efficiently than most terrestrial mammals.


So now on to (or rather, back to) the real McCormick, the yapok. Unlike lots of other didelphids, the yapok actually does have a pouch and a very unusual one at that. The pouch opens to the rear and has a powerful sphincter muscle able to keep water out, but maybe not necessarily airtight (somehow...) (Marshall, 1978). The young in the pouch are able to suspend breathing for a few minutes and tolerate low oxygen levels. Very oddly, there are some claims that opossums of the genus Didelphis (the Virginia opossum and kin) can also swim with young in the pouch, although how they were able to manage that has not been explained (Marshall, '78). The colossal Voss & Jansa 2003 phylogenetic study closely links the yapok and thick-tailed opossum with the genus Didelphis (plus Philander and Metachirus), so maybe a semi-aquatic or semi-semi-aquatic ancestor existed. Or maybe not. Regardless, the same authority with the unexpected fact concluded that maintaining the young in the pouch limits how far the marsupials can adapt to a semi-aquatic lifestyle. The fact that opossums managed it but Australian marsupials haven't (as far as I know) is remarkable enough as it is.

Marshall '78 has some other weird facts about the yapok worth mentioning. Despite being semi-aquatic, the species is still able to climb and uses its tail in a prehensile manner (the thick-tailed opossum can't, interestingly) and it is also capable of collecting nesting materials. These animals are also largely carnivorous and they are believed to use their un-webbed forepaws in the same manner as a raccoon. Despite apparently being considered nocturnal, the circadian rhythms of this animal are not apparent and it can be active day or night. The females somehow manage to have four to five teats...didelphids seem to have a tenancy towards an odd number of teats for some reason.

And there is a whole paper on just how weird the genitalia of the males are (Nogueiraet al. 2004). The males posses a rudimentary pouch which it protects its scrotum in only while moving quickly or moving in water. Unlike other didelphids, they also lack a cloaca. Weird, weird stuff.



It looks like another wretchedly busy week, so who knows when and what I'll write about.

-Cameron

References:

Fish, Frank E. 1993. Comparison of Swimming Kinematics between Terrestrial and Semiaquatic Opossums. Journal of Mammalogy 74 (2), 275-284. Available: Here

Marshall, Larry G. 1978. Chironectes minimus. Mammalian Species. 109, 1-6. Available: Here

Nogueira, Jose Carlos et al. 2004. Morphology of the male genital system of Chironectes minimus and comparison to other didelphid marsupials. Journal of Mammalogy 85 (5), 834-841. Available: Here

Santori, Ricardo Tadeu et al. 2005. Locomotion in Aquatic, Terrestrial, and Arboreal habitat of thick-tailed-opossum, Lutreolina crassicaudata (Desmarest, 1804). Journal of Mammalogy 86 (5), 902-908. Available: Here

Voss, Robert S. and Jansa, Sharon A. 2003. Phylogenetic studies on Didelphid Marsupials II. Nonmolecular data and new IRBP sequences: Separate and combined analyses of didelphine relationships with a denser taxon sampling. Bulletin of the American Museum of Natural History. 276, 1-82. Available: Here