Thursday, November 26, 2015

What Do Face Biting Birds - Including Turkeys - Tell Us About Face Biting Dinosaurs?

This post will serve as a bit of a primer for a series of upcoming posts on theropod behavior and anatomy in which I introduce some new arguments and argue against some prevailing memes concerning their life appearance. I thought I could put it all in one post but I didn't make it to fedex kinkos before the holiday in time to scan my artwork so you know how that goes.

I wanted to make a Thanksgiving themed post today but I wanted to make it a little different. Instead of the usual "don't forget turkeys have some bad ass relatives" digression I wanted to make the argument that turkeys themselves are bad ass and they might teach us directly about some aspects of Mesozoic theropod behavior and appearance. Namely that male turkeys - in addition to their elaborate plumage & courtship displays - also regularly engage in combative behavior, including face biting behavior (insert discussion on abundant evidence for face-biting in Mesozoic theropods).

Pretty astounding behavior check out the full video here. Such behavior is not limited to wild turkeys as domesticated male turkeys will take on all kinds of foes including roosters as shown in this youtube video below. Now right here one can insert a whole discussion on cock fights, the long history of breeding fighter birds by humans, and the ethical issues raised. But for our purposes it should be noted that such behaviors are not without parallel in the wild fore bearers of these birds.

Or this particularly violent and prolonged battle between a Muscovy duck and some variety of fighting rooster (Asil?). As you can see in the comments someone mentions that this is how dinosaurs fought and I would have to concur.

Now I want to hit you with what this post is really all about. I will do this by pointing out - what is essentially staring at you literally right in the face - is that whether or not we are talking about tom turkeys, fighting cocks, or combative Muscovy ducks is that they all share one feature in common: abundant and garrulous, usually red, facial caruncles and a mainly naked head & neck.

credit The Photographer. Cairina moschata momelanotus. Margarita Island, Venezuela CC
credit Charles Toth youtube clip
What I am saying is that the convergence of a heavily adorned, wattled, dewlapped, caruncled, and combed cervical adornment in these three highly combative modern aves should not be glossed over. Usually interpreted as sexo-social signaling devices - and I am not disputing this adaptation - I think that they offer another, more functional usage. That is that in combat they offer up a convenient - and brightly colored - choice target to get bit upon. Why would a combative animal have such evolutionary pressure to offer up a choice morsel to get bit upon? Because losing a chunk of skin is preferable to losing an eyeball!! Feathers would be less than ideal because once plucked out little defense is left.

To embellish my point let's not forget to mention both old & new world vultures which are often bald headed and heavily caruncled. Except for these birds such features may offer more utility in fights over territory and food as opposed to sexo-social battles as in the other birds mentioned.

Red-headed vulture. credit Shepherd, Dayton OH CC
Andean Condor. credit Flickr Art G. CC
lappet-faced vulture. wiki-commons

Long time readers of this blog should not be surprised that I have been heralding both new and old world vultures as the best modern analogue to generalized, serrated toothed Mesozoic carnivorous theropods for quite some time now. People just need to get over the "scavenging" stigma for these animals - they offer more utility than sharks or monitor lizards in terms of how Mesozoic theropods behaved, moved across, and partitioned the landscape. Not only do sharks and monitor lizards fall down compared to theropods in terms of just about every meaningful gross anatomical/metabolic characteristic but the trait that is usually put forth as the unifying character linking these groups - serrated teeth - as I argued here both old & new world vultures (and giant petrels) have likely evolved an equivalent method of cutting and shredding carcasses: choanal grinding. Furthermore giant petrels, and both new & old world vultures are, you know, actually living derived theropods so there's that but it always seems to be that parsimony goes out the window with these things because TEETH. Get over teeth - modern day derived, soaring theropods are consuming more flesh on the African plains than all those "toothed" mammalian carnivores combined.

So when I stumble upon a youtube video (full video) showing essentially gang-turf warfare between two familial groups of black vultures (Coragyps atratus) and it has got "only" 711 views I got to raise a little ruckus. Not only are black vultures highly opportunistic and bold in their foraging - taking everything from turtle eggs to newborn calves - they also have evolved a kin-based group foraging method, are fairly terrestrial, and - as suggested by the author of this video - engage in territorial combat. Long story short this is the closest we are going to get to watching Mesozoic theropods engaged in combative face biting behavior. So I find it a little ironic that this window into the past is blatantly overlooked by a society supposedly obsessed with dinosaurs, especially face biting tyrannosaurids. Check out towards the end (about 20 second mark) where a chuck of one of the vulture's face gets ripped off and another vulture quickly gobbles it up.

"Now wait a second I thought group foraging was fairly rare in predatory birds and only Harris's Hawk regularly hunted in any sort of group hunting method?" 

Black Vulture wiki commons
Which brings me to my next point. Theropod interpretations both behavioral and appearance wise- especially dromaeosaurid - have been hoodwinked by the "hawk" analogy to a large degree. I presume this is because of the "predatory" nature of classic "raptorial clawed" accipitriformes. What is not in dispute is that hawks, eagles, owls, they do engage in some pretty startling and daring predatory ventures which I think capture the imagination and get us thinking about Mesozoic theropods. However  what should not go unstated is that "raptorial clawed" raptors of all ilks are dominated by a feet first method of predation. The head is almost never involved in the actual killing or subduing of prey except after the claws have sufficiently weakened the prey. This trend is immediately apparent in the startling video here of an eagle going after a very large ruminant and the prolonged battle. Never once does the eagle interface its head with the prey despite the rough and tumble engagement.

This trend of foot first predation with the head essentially not interacting with the prey until after it is killed or incapacitated is in stark contrast to generalized predatory theropods which all - even dromaeosaurids - maintained good sized jaws and serrated teeth. Dromaeosaurids never became >as specialized< in foot dominated predation as eagles, hawks and other raptorial birds of prey. The head remained a useful and probably necessary tool in prey acquisition and dismemberment, not to mention combat both intra & extraspecific.

credit Luis Rey. Maybe he was right all along? Link Deinonychus saga
Therefore, I argue, when restoring theropod heads - especially feathered - look more towards old & new world vultures, turkeys, chickens, muscovy ducks and other face biting highly combative birds than "classic" raptorial birds of prey. Give 'em mainly naked heads and necks, gnarly protuberances, grizzled bumpy ridges, combs, wattles, quills and frills. An apparent nape of thick feathers - like in many vultures and analogous to a lion's mane is quite defensible. In essence, make them less pretty. But please don't make 'em look like ground hawks because such birds don't kill or even really fight with their heads. Exception being theropods that lived in especially cool climates they likely had feathers all over just as cool adapted Lammergeiers have fully feathered heads. If you go look at all the artwork that came out surrounding the new Dakotaraptor it will very quickly become apparent that they are all just variations on the same "ground hawk" riff meme. The head is restored usually after a red-tailed hawk or peregine falcon.

Dakotaraptor Emly Willougby CC4.0

Ask yourself, what do we really have in terms of full body feather preservation for medium-largish generalized dromaeosaurids? Not much really. Microraptor hardly counts as it is small, fairly specialized, and lives in a cool environment anyways. So I say better to look towards the birds that actually do combative stuff with their heads as opposed to hawks and eagles which don't really engage their head in battle much at all...

Gobble, Gobble.

"A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine

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Tuesday, November 10, 2015

#Brontosmash Now More Hyper-Violent, Brutal, and Disturbing Than Ever

credit (c) Brian Engh, used w/permision prints here
If you don't know already #Brontosmash is now a thing. Get yourself caught up to speed here, here and here. Essentially #Brontosmash (as dubbed by Mark Witton) is the bastard offspring of the SV-POW! brain trust and does a pretty dastardly job of explaining those incredible apatosaurine cervicals. Although the official paper is not out yet the picture above by Brian Engh of (prints here) and several others pictures/posts at SV-POW! convey an aggressively battle ready brontosaurian neck clobbering mobile armament.

Apatosaurus ajax cervical (Lview & anterior) credit Mike Taylor CC3.0
Those big, knobbly ventral bosses on the cervical may have even supported a larger growth extending out of the skin and becoming visible on the ventral surface of the neck... weird. The whole neck was strengthened and designed for powerful ventral excursions - like a giant fleshy hammer.

It seems like a pretty devastating weapon and very suggestive of some type of weaponized, ritualized combat of the sexo-social nature in these sauropods. And the very exciting and evocative artwork by Brian Engh and Mark Witton definitely capture this vibe. Pic below is available as print here.

credit Mark Witton used w/permission
However in this post I want to ratchet up the possibility for an insidiously weaponized apotosaurine war doctrine by not only invoking the neck anatomy - but also several other aspects of these animals' anatomy in a more holistic sense. What I will suggest will be startlingly brutal but also within the realm of possibility and not without comparison to several modern animal's combat technique.

As I mentioned earlier several of the depictions of #brontosmash have come to light and I like them all. What I think should be pointed out is that most of these depictions you see the sauropods coming at eachother head on or neck to neck. But others show the combat occurring with the animals more astride each other such as the one below by Brian Engh (print here).

credit Brian Engh
I want to go a little further and suggest that as the battle progressed apatosaurine combat changed realms from frontal pushing and shoving & neck strikes  - to side to side combat - and to finally the ultimate goal: pin your competitor by mounting them from above. This final act of debasement - the mount - is not without precedent in numerous animal species. Heck, anyone with even the most limited experience with dogs should be very familiar with it.

Cape Buffalo males mounting credit Jochen Van De Peer
It also should not go unnoticed that the robust foot claws of apatosaurine sauropods now come into play. The large foot claw of the front foot - a single large claw - that points medially is now firmly ensconced in the hide of the poor sauropod it is mounting. Even more devilishly brutal are the claws on the hind-feet. They have at least three good sized claws and the largest occur - what do you know - medially (or towards the midline of the body) right in the line of fire for a poor cohort getting mounted. And with all the weight involved when these claws got purchase the result could have been rib shattering and deep hide gouges.

credit Razzberyy2
Now apart from the many examples of dominance mounting in mammals there is also a group of lizards that practice mounting and grappling combat to a high level: monitor lizards.

What I really want to draw your attention to in the gif above (full video here) is how much the tail plays  a crucial role in the fight. Each lizard is constantly trying to gain leverage and tip the balance of power in its favor by using its tail as sort of a 5th limb.

Komodo dragon male dominance mounting credit NatGeo
Let's not forget that in addition to a big robust neck apatosaurines also had a big arse.... and that tail was possibly thicker around the base than the hips combined. Below is a pic of the famous ass only apatosaur mount from the Chicago Field Museum.

dat azz. Elmer Riggs' unfinished Apatosaur 1908-1958. Chicago Field Museum. stolen from this blog
So let me just show you my image of what the final outcome of an apatosaurine battle royale would have looked like.

credit Duane Nash
What I really wanted to convey is how all limbs and appendicular elements are involved.  The mounting bronto is rising up to drop the hammer down with its neck.

The two front claws are digging in like giant macabre crampons. Augmented by the huge amount of weight pushing them down into the poor pinned bronto the back claws likewise dig in deep.

The tails are active leveraging tools. The mounting bronto is using its tail as a stabilizing 5th limb and - at the same time - preventing the mounted bronto from getting a good leveraging grip with its tail to try and topple the mounting bronto.

As a final little detail I gave the whip tail a frayed/tattered appearance. Personally I do subscribe to the tail whipping bullcrack hypothesis and that they were constantly growing new skin to replenish the constant breakage and damage incurred by the whipping. I don't know where I first heard this idea - I think at the latest Society of Vert Paleo meeting I overheard it(?)... let me know in the comments if anyone knows where the idea came from.

It is not without reason to assume that one or both combatants could have received fatal or crippling trauma considering the strength and weights involved. But such may have been the risks that these animals need have taken to win the genetic sweepstakes. Especially in the live fast and die young sexo-social archosaurian battlefields. Maybe these animals had at most 5(?) years of achieving dominant social status and good mating opportunities. That is after surviving several decades of growth/theropod attacks/and aggressive conspecifics. It is also entirely possible that the combatants involved were not merely satisfied with achieving dominant status but were intending to do mortal harm to their competitors. It is a bit of a myth that ritualized social combat is always geared towards allowing the animals to survive. We also not need assume that this was strictly a male on male thing. Access to the best nesting sites and/or prime male access (especially if adult prime males were a limiting factor on the landscape) could have resulted in a strong sexual equity (and diminished sexual dimorphism) in terms of combative tendencies in apatosaurine sauropods.

Such a scene would have created quite a disturbance on the landscape. As I mentioned earlier there is every bit of a chance that the imperative was to not only dominant but dispense with your opponent entirely. This is why I think mortally combat wounded apatosaurines were one of the most consistent sources of sauropod flesh to the Jurassic theropod tribes. This is not without parallel today as carnivores will often key in on herbivores engaged in sexo-social combat in the hope of surprising them or lucking upon a wounded warrior.

Imagine the surreal scene of two 30 ton apatosaurines engaged a prolonged dispute. Maybe it took the better part of a day. For the winner best choice of mates and/or nesting grounds. For the loser a humiliating defeat and bone shattering & hide splitting injuries. Theropods attracted to the commotion - the older theropods privy to the knowledge that one of these combatants will not likely be walking away from the battlefield. A slow excruciating death as the bedraggled losing apatosaur is felled upon by opportunistic theropods. They don't even bother to make their own incisions but work their way into the wounds created by the dominant apatosaurs hand & foot claws...


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Monday, November 2, 2015

Spinosaurus Unauthorized II: Spino Identity Crisis & Island Hopping Hippos

Well now... a lot has transpired since my last post in which I suggested that Spinosaurus likely fit within a range of aquatic and semiaquatic tetrapods in having a very thickened skin to aide in ballast. I went to to SVP in Dallas where Paul Sereno discussed his findings on Spinosaurus' swim speed and likely neutral buoyancy in the water. Let's say that his findings - preliminary as they are and no doubt controversy will ensue upon publication - did nothing but bolster my contentions regarding how Spino sat, moved, and generally behaved as a physical body in the water. Based on Sereno's preliminary findings ol' Spino was just an ok swimmer at about 3 meters/second. That is just a tad bit faster than Michael Phelps but quite a bit slower than your average croc. Keep in mind that crocodiles for the most part are not actively chasing and pursuing fish in the water column like an otter or seal but are more often than not using sit & wait tactics. stalking, and using physical obstacles to corral fish. So the notion that Spino was actively paddling and dashing after fish in open water may not make much sense. That is not to say that Spino didn't have a way to actively pursue fish (underwater running hint, hint) but that will have to be a future post. Also - based on Sereno's preliminary findings - Spino sat low in the water in terms of buoyancy. In fact as I have been saying since the week the Ibrahim new look Spino was unveiled the WHOLE DARN SAIL WAS UNDERWATER when Spino was in deep water!! So I gots to feelz myself a bit here - told ya so, told ya so, told ya so. This really puts a damper on the prevailing notion, that in my opinion, has just kinda been accepted and not really questioned rigorously - that the primary use for the sail on Spinosaurus' back was for social signalling. Additionally keep in mind that Sereno's work on buoyancy - and I talked to him at SVP - does not infer that Spino likely had a thickened epidermis that further added density - his calculations were just using the bones. What I am trying to say is that Spino potentially sat a lot lower - like literally right on the bottom - in the water column. What this suggests is that some of the most startling and amazing artwork that came out with the Ibrahim reveal such as this piece by Davide Bonnadonna (used w/permission) might already be dated.

credit Davide Bonnadonna (c) used w/permission
Instead a more likely image for Spinosaurus I would argue is the one below (used w/permission)- created by Christopher DiPiazza of the blog Prehistoric Beast of the Week.

credit Christopher DiPiazza used w/permission
Now I have to hand it to Christopher for being very prescient in doubting the ability of Spino as a swimmer but inferring it instead as an underwater runner and being one of the first artists to depict it as such. The only knock I can give it is that the skin should be a tad thicker (as discussed in my last post) and overall morphology more rotund ala hippo...

And here is my version of the underwater running Spino which is a bit of teaser for an upcoming post on underwater running... (yes, yes I wanted to do just 2-3 posts on Spino but it keeps growing)

Underwater Running Spino "glowstick" (c) Duane Nash use w/permission
So now that that stuff is out of the way (again the sail & underwater running will be future posts) I want to get to what this post is really about and that is two separate topics that might at first appear mutually exclusive but I will link them together at the end of the post: the Evers et al. paper that has spurred on some interesting thought but also loads of misinterpretation on the "popular" front; and, stimulated by discussions provided by LeeB from my last post, the interesting topic of island hopping hippos.

I have waited a bit to really address the Evers paper and, to be perfectly honest, I did this because the paper is just too darn long!! Seriously if the Ibrahim et al. paper got knocks for being overly abbreviated this paper deserves to get some critique on being overly verbose and less than easy to follow as a document. I really doubt most of the people heralding it as the savior of the long-legged Spinosaurus have even read it.

It did not have to be this way as the primary take home message is that Sigilmassasaurus brevicollis is its own beast!! That is about it when it is all said and done. Keep in mind that for Sigilmassasaurus we are talking about vertebrae - no appendicular elements, no skull material, not even a rib. It should also be added that Spinosaurus maroccanus (vertebrae & premaxilary material) is now - according to this study - sunk into Sigilmassasaurus brevicollis. As you may recall the Ibrahim et al. study cleaned house on all North African spinosaurid material and just lumped it all into S. aegyptiacus. The Evers paper could have been much more effective if they just presented their character analysis of the vertebrae, made their arguments for what bones they represent in the vertebral series, and made a succinct and clean argument for North Africa hosting at least two spinosaurids in the Kem-Kem and Bahariya respectively.

This beefy 100 page paper can best be summarized with this paragraph here:

This paper should have just focused on retrieving S. brevicollis as a unique species and not have - I don't know how else to put it - used its bully pulpit to cast doubt on the unique morphology of Spino B and FSAK-11888 - especially since the monograph of the latter is not even published and we don't even have the former anymore. Instead, among other critiques of Ibrahim et al., the authors question the synonymy of Stromer's spinosaur material with Ibrahim et al's. FSAK-11888 and reject their claim of a neotype.

They also insist on describing the retrieval of FSAK-11888 as coming from an "allegedly" associated partial skeleton several times. Understandably this is because the monograph is not yet prepared addressing the taphonomy and collection of said specimen. At the same time Evers et al. seem to really run with this "chimeric" interpretation of FSAK-11888 casting doubt on its validity. Is it chimeric due to Moroccan fossil dealers pulling together disparate skeletal elements in order to make a sell? If this is the case then why give the animal diminutive pelvic elements? Andrea Cau has addressed this problem on his blog here. The second possibility is that the elements are chimeric not due to anthropogenic forces but due to taphonomic forces, a possibility the authors raise citing several studies alluding to the Kem-Kem having a notorious reputation for mixed elements. However let us reason this scenario out. In both Stromer's Spino B and the Ibrahim FSAK-11888 we have diminutive pelvic elements associated with lengthened dorsal vertebrae, and neural spines... what are the chances of that happening twice with either taphonomic or anthropogenic interventions? Again these critiques are not new, they should be addressed, but I think that they really obfuscate the prime - and very interesting - point of the Ever's paper: that is North Africa hosted two Cenomanian spinosaurids.

Evers et al. also fail to mention a very important layer of evidence in favor of FSAK-11888 representing a single individual. This line of evidence bears repeating - in fact it should have got trumpeted from the hill top loudly a long time ago - and that is that the vertebral and appendicular bone histology of FSAK-11888 both signal a relatively young, sub-adult ontogenetic age . Yup both the diminutive pelvic elements and vertebral column/ribs/gastralia suggest an immature individual. This is not what we should expect if the elements are chimeric. Let's review that bit from the supplemental materials section of Ibrahim et al.:

"Neurocentral sutures preserved in the vertebrae do not exhibit coocssification, nor is there coossification between sacral centra or between the ilium and sacral vertebrae." (pp.13 supp.)

"Two long bones (femur, fibula), a possible gatralium and the proximal end of a dorsal rib were selected for histological thin sections.... (pp. 13 supp.)

"An external fundamental system is not found in any of the four bones sectioned, and vascularization is still prsent in the circumferential layer. We infer a subadult ontogenetic stage for the neotype specimen. This interpretation is also based on the high amount of Haversian systems in the inner cortex, the decrease in density of vascularization towards the surface of the cross section and the decrease in spacing between LAGS toward the outer cortex. Maximum adult size would likely have entailed many years of subsequent growth." (pp. 14 supp.)

Not addressing these histological lines of evidence in the Evers et al. paper is a major omission in my view. As I have said before this paper should have just dealt with Sigilmassasaurus as a unique taxa and by going after Ibrahim et al. in totality in a none too circumspect way they really do themselves a disservice. If you are going to make critiques you can't just omit the stuff that you don't like i.e. the very pertinent bone histology congruency between vertebral and appendicular elements suggesting just one individual. Especially if your paper is 100+ pages long. But Evers et al. are not solely too blame on this front. If you go back and review the several very storied and infamous online critiques of Ibrahim et al. including - Switek's, Headden's, Hartman's, and Witton's - you will see that all four of them fail to mention the bone histology data suggesting FSAK-11888 is one, subadult individual. For all of these very vocal and visible blog postings not to mention this line of evidence is very interesting. Make of that what you will.

The unfortunate effect of this paper is that it adds fuel to the fire for those in the "popular realm" (i.e. JP3 Spino fanboys) who are hellbent on retrieving an upright bipedal Spinosaurus at any cost. "Look at this 100 page paper in PeerJ - the authors shoot down the Ibrahim paper!! Whoopee long legged Spino lives again!!"

Again, while the new paper might be correct in there being two or more spinosaurids in N. Africa (maybe even a species complex of Spinosaurus?) and that their critique of Ibrahim et al. lumping all N. African spino material into S. aegyptiacus may be valid- the morphology for Spinosaurus that the Ibrahim et al. paper gave did not hinge on the Sigilmassasaurus or S. maroccanus material anyways (which is mainly isolated vertebrae). We still, at the end of the day have the congruence of morphology in Spino B and FSAK-11888 standing tall (pun intended). 

The authors even begrudgingly concede this in the last sentence below:

Furthermore, on a wider note, this movement to retrieve a long-legged, bipedally striding Spinosaurus (Hartman's skeletal is usually the one bandied about - but not a fan of it myself or his spinosaurids in general - too gracile imo) both on the popular and scientific front I predict will fall flat on its face eventually (pun intended). Two specimens - as controversial and questionable as they may be - both displaying similar gross morphology in the pelvic area > zero specimens of Spinosaurus showcasing "normal" sized theropod pelvic anatomy. One set, the one we do still have, shows ontogenetic congruence between the vertebral and appendicular elements i.e. not likely a chimera. That's right, there is exactly 0.0% verifiable evidence for a long-limbed, classically bipedal Spinosaurus or even spinosaurid in North Africa. None. Any assertions for this interpretation over something more in the Ibrahim et al. ballpark of gross morphology - without skeletal evidence - is an assertion of a mythical creature over something we do have (controversial as it is) evidence for. It's high time we flip the script on long-legged Spinosaurus being the de facto representation - there is no evidence for that animal at all.

Now with no clever segue at all (although I promise it will relate back to above discusssions) I want to go into into island hopping hippos.

What really started this off was me stating - as others notably the San Diego Zoo - that hippos can't, in the truest sense of the word, actually swim. They are denser than water and don't really have large flippered limbs that can grab and push back large volumes of water. The reason for their density is - and I will go into this more in depth in a future post - that their primary mode of locomotion is best achieved via their ability to stay low in the water column. Hippos use a foot propelled running/trotting locomotion "underwater punting" in which the foot pushes off the substrate to achieve long and slow gliding phases or when hippos want to move faster they actually take shorter and quicker steps. At first this might seem counter intuitive but try it yourself. Go into a body of water at least 2/3 up your chest. Now experiment with running underwater to achieve maximum velocity. You will quickly realize that short/rapid punting steps outpaces long, gliding paces. Therefore for hippos to take advantage of moving quickly in the water via short/punting steps they need to be substantially denser than the water or else gliding phases (which are slower) will take over due to relatively increased buoyancy.

Before we take a look at the various island hopping hippos and other lines of evidence that are cited in favor of hippos being able to swim let's take a closer look at an animal that I neglected to mention in my  last post but offers much utility to discuss here - the pygmy hippo (Choeriopsis liberiensis).

Pygmy hippo. public domain. Mt Kenya Wildlife park
The pygmy hippo is a startling contrast to its larger more celebrated cousin. Although of the same family they are not closely related being of different genera and perhaps diverging as long ago as 8 million years ago (Boisserie, 2005). Pygmy hippos are very much smaller, more reclusive, and less aggressive or boisterous than their larger relatives. Their range is very limited: this is likely, I muse, because of the general loss of dense forested habitat in Africa since the Pleistocene that is their preferred habitat. Which brings me to my next point - pygmy hippos are very much forest animals, another contrast between their more grassland/savanna loving larger counterparts. In fact the animal most often posited as ecologically analogous to the pygmy hippo is the tapir.

Let that last bit about the tapir analogue sink in a bit - as you should recall in my last post I suggested tapir provide a good proxy for an animal that is not yet quite as aquatic adapted as a hippo. Tapirs can underwater punt, they have thickened skin that likely aides as ballast, and a barrel shaped torso for underwater streamlining. They are likely more bouyant than a hippo and might be able to achieve a swimming stroke or even float in saltwater. To put it another way tapirs are just getting their feet wet in terms of dedication to an aquatic existence. All of this is less than rigorous but is worthy of more testing mind you...

Going further if we take this analogy to tapirs for pygmy hippos and the general observation that they appear less massive skeletally , have less skin, and can potentially float or even actively swim - then maybe pygmy hippos actually did colonize offshore islands via swimming/floating. This may have especially been the case when pygmy hippos had a more wider distribution in the past.

When I took the question of pygmy hippos actually being able to swim into my laboratory (i.e. youtube clips) I very quickly - within the first 2 or 3 videos - saw some behavior suggestive of swimming. Mind you I am yet to see any good footage of big hippos swimming in any form...

infant pygmy hippo swimming a little
Follow this link here to see some pretty good footage of a newborn pygmy hippo calf doing some ok swimming. It does appear to achieve limb assisted swimming in several instances in this clip. You will also notice that as soon as it stops moving its limbs it sinks like a stone. I know young hippos of the big species have been suggested to be a little more bouyant than their parents but am not quite sold and them being able to self propel across 10's or 100's of kilometers of open ocean. I am a bit skeptical of them having the strength and stamina to pull off such feats. But then again maybe saltwater provides just enough buoyancy to overcome their densisty...

Here is another youtube clip of an infant pygmy hippo that appears to get a little bit of limb assisted swimming going on... but as soon as it stops pumping those legs it sinks like a stone.

For comparison here is an endearingly cute video of an infant hippo (H. amphibius, larger species) moving in water. It always appears to sink like a stone after pushing off the bottom. There is one sequence towards the end where it looks like it is trying to paddle but doesn't really get anywhere.

Malagasy Hippos

Choreopsis madagascariensis w/ H. amphibius skull. public domain 1923
Now, I will concede that pygmy hippos show a little bit more promise for swimming or floating across deep saltwater bodies than their larger cousins which leads me to my next point. The famed Malagasy dwarf hippo - which represents several species of hippo that only recently went extinct on Madagascar -  may actually potentially be part of the same genus as the pygmy hippo. I am not going to pretend to be an overnight expert on Malagasy hippo taxonomy but let's just say that it is unresolved and that the putative ancestor(s) of the various - highly terrestrial or even mountainous - recently extinct hippos of Madagascar might have been quite a bit removed from the classic hippo (H. amphibius) we all know and love. Alternatively H. lemeriei is often compared to H. amphibius so it is possible that both genera of hippos made it to the island. So until the taxonomy of the species of hippos that were endemic to Madagascar - some of which may have been a lot closer to pygmy hippos than regular hippos - is sorted out (great grad student project btw) I can't really accept positing the existence of various hippo species on Madagascar as proof positive that hippos similar to modern H. amphibeus actually swam or floated there - but rafting is my favored scenario in any case.   However as I conceded earlier I do hold more hope for dwarf hippos to actually swim or float in saltwater than H. amphibeus.

The Hippos of Center Island, Lake Turkana

Lake Turkana. CC3.0
I have to admit that this one was pretty interesting and a little perplexing. How did hippos colonize Center Island in the middle of Lake Turkana which is the largest desert lake in the world? Investigating this did get me to finger through my old copy of Eyelids of Morning: The Intermingled Destinies of Crocodile and Man which I always wanted to blog about. It's a great book btw and I don't see books like it really written anymore - pick it up. Back then Lake Turkana was called Lake Rudolph and in the book there are several mentions of hippo in the lake and violent confrontations with the locals. Its an eerie place for hippos because it is a true volcanic desert and testimony to the adaptability of these animals as long as they have water.

Lake Turkana is the largest of the eastern rift valley lakes. It is also a relatively recent lake in terms of origin - 200,000 years old is the most commonly cited age. And research suggests that what we see today - the largest desert lake in the world - might have been in fact two or more smaller lakes and dried up completely as recently as 7,500 years ago. Follow this link if you want a good overview of the complex and dynamic geological history of this lake Paleogeography of Lake Turkana. Even before "Mega-Lake Turkana" nearly dried up 7,500 years ago the Lake Turkana basin hosted several ghost lakes and rivers. Long story short we have a more parsimonious solution to why there are hippos on Center Island.  They need not have swam, floated or rafted there - they most likely were always there - a hold out from when the lake level was a lot lower as has happened several times in the lakes geologic history. Which might happen again as the main incoming tributary for the lake - Omo river - is set to be dammed.

Mediterranean Isle Hippos

composite mounted skeleton H. minor. George Lyras 3.0
Shaking my head on this one.... the problem as I see it is the taxonomy of these beasts is a mess. Yes, we have definite "dwarf" island hippos on Crete, Malta, Sicily & Cyprus. But what can definitely be said about the hippo(s) that they evolved from? Most of the literature I see linked to these animals dates to the early 19th century or even 18th century. They need a revision for sure!!

Compounding the issue is that not only do we have fuzziness on the ancestry of these beasts is that the geological history of the Mediterranean basin is horribly complex. Events like the Messinian salinity crisis of the Miocene in which the whole basin literally dried up could have allowed the ancestor(s) of the Mediterranean "dwarf" hippos to literally walk up to the various isles. High evaporation rates in the Mediterranean also may have provided just the amount of buoyancy needed to float a putative ancestral hippo type beast - especially if not built as heavily as modern H. amphibius and possibly more along the lines of Archaeopotamus.

What can be said about the Mediterranean isle hippos species for sure? From what I gather not much definitely. We can't be precise in terms of who they evolved from or when they evolved? Are they really dwarfed? Do they represent a more ancestral stock of hippo and just evolved in convergence to look superficially like modern hippos? What can be said definitely in terms of their biogeographic origin? Not much really only that they got on those islands somehow.

My final thoughts on the debate of island hopping hippos is somewhere between Mazza (2015) and Van der Geer (2015). If you follow the links at the end of the post you can read their interesting exchange. Neither paper addresses the geological history of Lake Turkana which suggests that the hippos that live on Center island need not have swam their but arrived when lake levels were lower. Furthermore neither paper addresses the many unresolved issues in hippo taxonomy and that - especially when variable of skin thickness and bone thickness are taken into account - there may have been a spectrum of densities and therefore differing buoyancy in fossil hippos. Some of the Malagasy hippos might be closer to pygmy hippos. Who knows about the Mediterranean hippos and what they evolved from and how the geological history of that area affected their biogeography. Basically it is not so simple to look at what modern H. amphibius does or does not do and infer that fossil hippos had similar capabilities or limitations. Especially so in light of the real possibility that pygmy hippos might have a different buoyancy than H. amphibius.

Hippos Best Equipped Large Bodies Mammals For Rafting

All things being equal - and even if in especially high salinities or invoking putatively  >less dense< ancestral hippos that could float or dog paddle - I still prefer rafting to colonize far flung islands as opposed to deliberate swimming and/or floating to them. Rafting solves the buoyancy issue which let's remind ourselves that no hippo of either species adult or immature has ever been observed to float or swim in fresh or saltwater for any length of time - that fact can't be ignored especially for a species so common in captivity and well observed as H. amphibius. Hippos are known for a relatively slow metabolism - especially for a mammal - and this preadapts them for oceanic voyages floating on rafts. Because hippos are known to live in estuaries and saltwater beaches they are in direct line of fire for the occasional, but inevitable, mega tsunami. mega-flood or mega-typhoon. The study of these events and how they reshuffle the deck ecologically is in its infancy. The historical and scientific record is not deep enough to document many of these events. But the geological record is. And over the course of long enough periods of time such events become not happenstance but statistical eventualities. Hippos, as long as they can get secured on a floating pile of debris or large tree, are well equipped - perhaps the best equipped out of all large mammals - to survive and take advantage of such events sporadic as they are.

The Spinosaurus Biogeography Question

Early Cretaceous. Albian
Now I finally want to tie in the two seemingly disparate narratives of this post - a potentially diverse fauna of spinosaurids in N. Africa and the likely rafting capabilities of hippos. As I mentioned in my last post I find it likely that Spinosaurus probably plots pretty close to hippos in terms of buoyancy i.e. spino is likely a sinker and not a floater. My reasoning is that underwater running/walking is most efficient with a heavy/dense body. It is quite possible that Spinosaurus did not only swim poorly - it did not even swim at all. This creates a bit of biogeographical issue as well because it could not likely disperse over land that well either. At least in the adult morph bipedalism can't currently be retrieved and it most likely moved in awkward belly sliding shuffle. Therefore Spinosaurus was limited in dispersing itself actively over deep channels of water and over long patches of dry ground.

However just because Spinosaurus could not move itself over deep channels of water or across long patches of terra firma does not mean that other geologic agents could not do the moving for it... Keep in mind that the Cenomanian was a hothouse world and the mega-typhoons/mega-floods/mega-tsunamis and just general slosh between the land/intertidal/ocean realms must have been unprecedented. All Spino had to do was hold onto that floating clump of debris/tree and sail away perhaps even to South America (hello Oxalia).

What I predict was going on is that each major river system and adjacent estuaries/mangroves would start to evolve its own unique "flavor" of spinosaur. Whether or not you would call these different species or subspecies... its a bit subjective. Once in a while environmental perturbations would shuffle up the groups so that new colonists would be spit out and formerly isolated populations would reengage. This might be what we are seeing in the differences between Stromer's spino & Spino B and FSAK-11888 that Evers et al. note -  different members of a "species complex".  Sigilmassasaurus might be its own "species complex" and it is interesting that Evers et al.'s work shows it close to several baronychines . So North Africa might just have its own giant, bipedal spinosaur that is not Spinosaurus proper!! It might also eventually prove useful to designate FSAK-11888 as a separate species from Stromer's S. aegyptiacus but still cogeneric.

However, especially in light of the taxonomic mess that is hippo taxonomy, I wouldn't hold my breath expecting Spinosaurus or N. African spinosaurid taxonomy to be sorted out neatly any time in the near future or even in your life time.


Evers SW, Rauhut OWM, Milner AC, McFeeters B, Allain R. (2015A reappraisal of the morphology and systematic position of the theropod dinosaur Sigilmassasaurus from the “middle” Cretaceous of MoroccoPeerJ 3:e1323 

Mazza, PD (2015) To swim or not to swim, that is the question: a reply to Van Der Geer et al. Lethaia Focus V-48 pp 288-290

N. Ibrahim, P. Sereno, C. Dal Sasso, S. Maganuco, M. Fabbri, D.M. Martill, S. Zouhri, N. Myhrvold, D.A. Iurino (2014). Semiaquatic adaptations in a giant predatory dinosaur. Science 26 September 11, 2014

Van Der Geer AAE, Anastasakis G, Lyras GA (2015) If hippopotamuses cannot swim how did they colonize islands: a reply to Mazza. Lethaia Focus V-48 pp 147-150

Hippopotamus, H. amphibius & Pygmy Hippopotamus, Choreopsis liberiensis 2001. revised 2011. San Diego Zoo Hippopotamus Fact Sheet


Sunday, October 18, 2015

#2015SVP Everything Is Bigger In Texas

I just did my second pilgrimage to an SVP meeting. While my first attendance in L.A. was basically right next door to me (I live in the county north of L.A.) this one required a little bit more travel prep. Luckily I had saved up enough money from my last job doing data entry at a museum to get my expedia ticket and hotel room done for a reasonable amount and I got the discount rate for the preregistration ticket on the last day of that offer so those savings helped. Of course finances is a constant theme for why people do or do not go to this and other events and the #paleo-economy is a topic I do intend to discuss in the future. Fortunately the next two SVP meetings are in North America (Salt Lake City, Utah & Alberta, Canada) so, especially since I just got a solid job, I aim to make both of those.

First of all Texas. This was actually my first time in Texas and was very impressed by the hospitality and niceness of the people of Dallas. Being a leftist Californian I was a little weary of Texas culture but I have to say I was proven wrong by the all around awesomeness of the people and workers of Dallas. They by and large were much nicer and more real than most Californians. Plus BBQ. I tried to keep my gluttony and bone chomping down to a minimum but I did have several feeding bouts at Sonny's in downtown Dallas. It was an epic bonesaw feast....  when in Rome. I also was very impressed with DART (Dallas Area Rapid Transit) that got me from the airport to downtown and from my hotel room at The Marriot to Hyatt convention center very quickly. At first I was a little stressed that I did not get a room at the Hyatt but in retrospect it worked out splendidly as it was usually only a 15 minute commute via DART and it forced me to get out and see more of Dallas. I talked to several people who stayed at the Hyatt and got the impression that they dumped a lot of money into over-priced hotel food and alcohol and did not get out on the city too much. Also by staying at the Marriot I was a block away from the free Aurora light/art installation public event that Dallas put on. The whole arts district was transformed into cool light shows, art installation, psychedielic animations screened onto the sides of a large building. The whole presentation was an interesting contrast because you felt like you should be at some drug-addled rave or burning man show but it was very much a family event. Plus a cathedral sized Catholic church was outfitted with ambient lights and misty smoke pots to create a chilling and surreal effect when you walked in... and people were still performing mass in the church. It was like some weird Fellini film. Also SVP collaborated with the Perot museum to provide free shuttles and catering to the museum on the first night. I have to say the museum was well done, very engaging, and had an interesting architecture too. I commented to several attendees about the museums namesake Ross Perot (the oil magnate and one time presidential hopefull) and they did not know who I was talking about. Made me feel kind of dated lol!! Let's just say ol' Perot was an outsider 3rd party candidate before it became cool to do so. So, yeah if you were wondering why the museum went so in depth into the science of hyrdocarbon exploitation...

Onto the meeting itself.

One of the highlights of course for any of these types of meeting is getting to rub-shoulders with the noted luminaries so to speak of the field. This event was certainly packed with them. Now at my last meeting I got to chat with James Kirkland, Thomas Holtz, Phil Currie, James Farlow, Julius Csotony, Darren Naish, Jack Horner and several others for this meeting I got to chat with many of these same people but also for this event with; Robert Bakker - who I will admit I did get a wee bit star struck over which I don't usually do anymore; Larry Witmer (pestered him about vulture, allosaur, and phorusrhauchid feeding mechanism); and even Paul Sereno (you could guess what I talked to him about)... they all were very nice and personable. Others who I got to meet, some of whom even came up to me recognizing my name which was a little humbling included Anthony Martin and Andrew Farke. Also it was great to meet facebook friends such as Brian Engh and Stevie Moore in real, face to face circumstances.

The whole mood was very polite and convivial which I have to admit I kind of like that but also don't like it. I like it because at my heart (despite occasional explosions) I myself am pretty mellow and relaxed and really don't like seeing people getting bullied, threatened or intimidated. What I don't like about it is that this ethic - which basically all attendees had to agree upon by going and which was constantly plastered all over the event - becomes a form of tone policing. Tone policing, in my view, is bad for science because it creates a situation where how you say something - potentially with anger, aggression, rage, spite, venom, or just too much passion - becomes more important than what you say. Potentially an emotionally delivered argument - even a correct one - can be shot down because it is delivered in the wrong tone. This is my issue with what I see as a creeping group think that science and scientific debate always has to be delivered in such a nice, formal, polite manner. Let me be careful with this because I can see how what I am saying can be misconstrued. I am not suggesting that openly hostile, mean, personal, vitriolic attacks are the way to go. We, myself included, should always aim to be polite and convivial but lettuce b realz not all people are like that and not all cultures are like that. What I fear is that certain peoples, groups, individuals will be shut out from discussion because they do not play by majority rules. A review of some of the top brass in any fields includes some - how should I put it - real assholes. Sometime assholes do some really brilliant, top shelf stuff. I don't know what the answer to this is. Certainly the majority rule in public events - keep it polite please - has a strong argument. But my critique is more of a warning in general. We should always be on guard from overly tone policing people in science. In science what you say should always trump how you say it.

For the talks I don't want to get into real specifics because I am still confused over the whole press embargo and what can or can't be said ( its a load of phooey if you ask me). What I do want to give are some very broad stroke trends or themes I noted and which should garner interest. As opposed to my last SVP where I made a mad dash from lecture hall to lecture hall in an attempt to get some of everything, this time I really just hung out for the archosaur talks ( and some shark, marine reptile stuff too). I do have to say that the sauropod talks might just have slightly edged out the ornithopod talks and that theropods were third in the dino sweepstakes imo. This might have a bit to do with the fact that the last couple of years have seen some truly stunning theropod reveals at SVP (Spino, Deinocheirus) so the bar was a little high. A running theme in several of the talks was that ontogenetic change is a dangerous pitfall in evaluating characters in cladistic analysis. Heterochrony also provides a challenging aspect towards cladistic analysis. the most succinct example I recall is the talk on the dwarf island sauropod Europasaurus by Schmitt A., Knoll F., & Tschopp E. (I don't know who actually gave the talk but probably Schmitt). The interesting thing here is that neural anatomy - the brain - was highly brachiosaurian but the body itself was signaling more basal - closer to something like Camarasaurus. Because it was dwarfed paedomorphic processes gave it more of a basal macronarian gestalt - very cool!! These and other examples of the pitfalls of cladistics also, at least in my mind, suggest that cladistics is every bit as contentious and prone to pitfalls as what I like to concentrate on - lifestyle & ecological reconstruction. I think that there is a general opinion that of the two - cladistics & lifestyle interpretation - that cladistics is the more rigorous, methodological, "hard science" venture but life-style reconstruction is the softer science more prone to baseless speculation, faults of bias, assumptions etc etc. However several of the talks I attended suggested that the dichotomy between the two might not be so sharp. Another theme, especially of the sauropod talks was freaking cute baby/ en ovo stuff (would make a good t-shirt or SVP artwork logo). I was joking with Stevie Moore that I wanted to ask several of the presenters of such topics after their talk who would win in a fight a baby titanosaur or a baby diplodocid as a little poke at carnivora forums/battle royale culture...

Speaking of the question section after the speeches - I think that they should just get rid of the option. Either get rid of the option for questions or give the speeches a five minute intermission for more questions also a chance for people to move between talks. The thing is that more often than not there was no time for questions etc etc. Additionally if you are not among the one or two people that have the luck of getting called on for a question it becomes challenging sometimes to keep track of where the talker goes to if you want to pin him/her down for more detailed discussion. Plus you end up feeling like a stalker... Here is what I suggest. Get rid of the whole question format. Give speakers the full 15 minutes for the talk. Require that speakers - at the end of the speaking session that they are a part of - convene in some predetermined room, or even the same room, to take questions after the symposium (this would allow the speaker & attendee to see the whole syposium). This could be 1/2 to 1 hour where they are mandated to be present to solicit questions from the attendees. This is less time than the poster presenters are required to be adjacent to their poster and I do not think it draconian to hold the speakers to the same standards of making themselves available to questions that the poster presenters have to abide by. Going back to the timing of the talks I also think it useful to have a bit of a buffer time between talks to give people a chance to move from different rooms. I know that it is accepted that people will be moving about but I can only imagine as a talker it be disconcerting seeing people moving in and out during your talk and as an attendee I can't help but feel rude. I hope I don't come off like SVP do a horrible job planning these things - they don't -and it must be a mountain of work to coordinate. At the same time any organization can always look for ways to improve and providing more of a forum for open questions and discussion opportunities can only be a good thing.

I don't have anything that immediately comes to mind to discuss regarding the posters... there was a lot of them, they covered a lot of topics, and the poster presenters were very good and gladly answered questions. Especially impressed by all the poster presenters from Europe, South America, and Asia - did not notice a lot from Africa/Australia. That's a big trip and kudos to you from investing to come to all the way!!

One aspect that I really did enjoy regarding the talks was the way several of the talks really built into and embellished the whole symposium creating a nice little forward momentum. But speaking of momentum I wish there was a mid-afternoon coffee break...

Anyways that was my broad stroke analysis. I hope I don't come off too critical - after all if I didn't like it why would I keep going? - but any venture can find ways to improve.


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Monday, October 12, 2015

Spinosaurus Unauthorized I: Hippos Are Not Really Fat and Can't Swim

Well now, it has been a little bit now - such is life. I was honestly surprised that my last post on Masiakasaurus received such positive feedback, no really problems with my interpretation at all, at least from the comments and feedback I received.

There shall be no such good feelings and consensus with these posts as I am wallowing back into the treacherous waters of Spinosaurus once again!!

credit Duane Nash
In these posts I want to lay out my most current ideas, speculations, theories, and thoughts concerning the new Spino as revealed by Ibrahim et. al. a little over a year ago. As such I hope it will serve as an impetus and inspiration for new and hopefully more rigorous research. So I am just going to put it all down here. I do have a standing offer that if any researchers want to publish on an idea or theory that I put forth in this blog simply get in touch with me and list me as a coathor/credit this blog.

My idea posted here that Spinosaurus was not fully bipedal, nor classically quadrupedal either, but is best characterized as a belly slider continues to get a lot of page views. I will embellish my case for that locomotion in these posts as well as some other possible locomotory modes used during the creatures' ontogeny. More importantly I will explore how this creature likely moved in its predominant habitat - the water - which is more important imo than how it moved on land anyways. If you are still holding out that spino was primarily terrestrial and only went into the water sporadically we obviously differ right from the get - go in which case you will probably not be convinced by my arguments here which treat Spinosaurus as primarily aquatic as a given. I have discussed the sail before here but my thoughts on the sail have changed pretty radically - which will also be detailed in these posts.

Anyways, I hope you have as much fun with this post as I had writing it!!

It is now officially October which basically translates here in southern California where I live to asking yourself is it cool enough that I should think twice about putting on shorts and sandals today? Over on the east coast they experience a little bit more of a seasonal bite, with Florida occasionally getting a twinge of frost by winter. What this means for people over there is that they actually have to dress for the seasons. But what this change in seasons means for a particularly interesting marine mammal is a question of life or death.

credit Ahodges7. Florida manatee @ Sea World Orlando CC3.0

The West Indian manatee (Trichechus manatus) is an obligate tropical water marine mammal. Sustained exposure to cold water (below 20 C or 68 F) will cause mortality. It is this sensitivity to cold water and not predators or even boat propellors that is the chief limit to the population of this species. This means that the Florida population - usually referred to as the Florida manatee - which can range as far north as Massachusetts must migrate south before the advent of substantial water cooling. Anthropogenic warm water refugia in certain enclaves of north/central Florida has created unique opportunities for these Florida manatees to remain in waters year round that they normally would have not persisted in.

However the question (unless you already know the answer) in your head should be why are these animals so deathly cold sensitive - shouldn't their blubber layer allow them to survive in cold conditions? The answer to this query is that manatees have only a slight, incipient fat layer. Despite their rotund appearance their blubber quotient is a far cry from the blubbery status of pinnipeds/cetaceans and other cold water tolerant marine mammals. What gives manatees that "fat" appearance is actually a very thick dermis i.e. they are thick skinned.

It could be argued that skin does not get the attention it deserves despite it being the most visible and exposed organ in vertebrates. It is also usually the largest organ. In fact if you ever want to show off your biological knowledge at a social event asking "what is the largest organ in the human body?" (snark, snark) is a good conversation starter because it is in fact skin.

So why do manatees (and, as I will discuss later, other aquatic tetratpods) develop such a thickened dermis? Manatees don't engage in combative behavior nor do they suffer from intensive predatory pressure. The reason for the dense and thick dermis is related to buoyancy control. While dense heavy bones (pachyostosis) have long been recognized as aides in achieving negative buoyancy in water what is less recognized is that a heavy, dense dermis is also an adaptation for achieving negative buoyancy.

In fact a paper (Kipps et. al., 2002) addresses this very issue. Titled Skin density and its influence on  buoyancy in the manatee (Tricheus manatus latirostrus), harbor porpoise (Phocoena phocoena), and bottlenose dolphin (Tursiops truncatus) this paper compares and contrasts the relative level of skin density as an adaptation to buoyancy control in these three mammals. In both the harbor porpoise and bottlenose dolphin skin density was less than sea water density and contributed a net positive buoyancy force. Thinking in terms of where these animals live - relatively deep water - this makes sense to be a little bit lighter than water so they are not always expending energy to stay afloat. However the manatee is notably different in terms of buoyancy. Its thickened dermis provides a net negative buoyancy to its body.

From the study:

What should be restated is that the skin of the manatee:

"equaled 70% of the negative bouyant force of their dense, pachyosteosclerotic ribs."

That is substantial. Also of interest is that the manatee's buoyancy changes with water depth - which is a known phenomena in diving marine animals:

"The manatee is positively buoyant at the surface and negatively buoyant at depths of less than 10 m."

Now think about this in terms of what and where a manatee is going to be living and foraging. When they are just resting, breathing, or just lolly-gagging about at the surface it makes sense for them to be just slightly buoyant at the surface. However since they are herbivorous and much of their food will be foraged below the surface of the water it also makes sense that once they dip below the surface they are negatively buoyant so that they are not expending loads of energy staying deep. But as manatees are not predatory but herbivorous they are not going to go much beyond the photic zone in terms of foraging which is why that 10 meter mark is so interesting - most of the plant mass will be in the upper, shallower levels where sunlight penetrates.

If you are still a little confused about how the densities of different body tissues can change with water depth maybe this paragraph can help you from the paper:

Additionally it is important to realize that lipid (i.e. fat or blubber) and air filled tissues will compress with increasing pressure i.e. depth. What this means is that in shallow water a blubbery tetrapod can be positively buoyant but with increasing depth both lungs and fat tissue will compress so that the diving animal becomes neutral or even negatively buoyant. As a general pattern the neutral or "gliding" phase of diving tetrapods is both energetically and ecologically optimal similar to basically moving around in a zero gravity environment, essentially outer space.

However in aquatic tetrapods that are at most living in 10's of meters of water as opposed to 100's or 1000's meters of water depth, the pattern of the manatee - dense dermis and dense skeletal system - promises more optimization for that habitat choice. With a dense skeletal and dermal adaptation they do not have to expend energy diving - unlike positively buoyant deep divers which must expend at least some energy to get past the buoyant threshold of depth. Furthermore, since they are only living in water depths measured in the 10's of meters of depth it is not a challenge to push off the bottom or swim a bit to get a gulp of air.

At this point it should be apparent to readers where I am going with this. Spinosaurus, as most likely an inhabitant of estuaries, large river systems, possibly coastlines squarely falls more in the pattern of the manatee as opposed to the dolphins in terms of typical water depths (10's of meters) and therefore skin and skeletal density. Long story short give your Spinosaurus depictions a thick skin - looking at the skin of hippos and manatees is a great reference. And so the artists who speculated on the "Mr. Big" Spinosaurus countenance may have hit it closer to the mark than they even realized.

credit Duane Nash
To embellish my case, that Spinosaurus fits somewhere along this pedigree of dense skin/bone aquatic tetrapods of shallow water are there any other semi-aquatic tetrapods that exhibit a similar pattern of shallow water habitat, dense bone, and dense skin. Turns out there is and the best one to talk about next is the hippopotamus.

The Hippo: Can't Swim and Not Really Fat

Although I can't find any relevant literature on hippo skin it is fairly common knowledge that there skin is exceptionally dense and thick. While such a thick skin is no doubt useful to defend against predators and intraspecific combat I am going to suggest that such a thick dermis evolved in concert with those reasons to help the hippo achieve and maintain negative negative buoyancy.

The series Inside Natures Giants takes a look at hippo anatomy and anatomist Joy Reidenberg has some choice words describing hippos skin (start at about the 11:45 mark).

"That's really thick skin... and very, very tough. It feels almost like elephant skin but a lot, lot thicker. I think that's the toughest skin I ever had to cut."

When, after much effort, she finally gets a plug of skin removed you really get a sense of the thickness. She really makes a point that it is not fat but is all skin. The "fatness" of hippos is due to the thick skin. large stomach, and barrel chested torso. Don't fat shame hippos - they probably have a lower BMI than you do!!

Here is a really interesting photo-essay documenting an intrepid male hippo that got into a pretty dangerous situation moving through some rough coastal surf along the Mozambique coast of South Africa. The young male was observed fighting through strong surf and finally scrambling over sharp rocks for over 2 hours to make it around a point into a calm bay.

credit Angie Gullan, Dolphin Encounters & Research Center. Nat Geo
After the hippo finally made it into the bay it collapsed on the beach in sheer exhaustion.

credit Angie Gullan, Dolphin Encounters & Research Center. Nat Geo
These photos and documentation highlight a seldom discussed fact about the hippo - they can't really, in the truest sense of the word, swim. Try as you might (and I have) you will not find images or video of hippos actively swimming a dog paddle motion or other limb assisted paddling. What they do in the water is best described as an underwater run or trot. They use the bottom substrate to kick and push off the bottom - quite rapidly sometimes - and this allows them the ability to propel upwards for air or glide through the water for extended periods.

Underwater locomotion is the topic for another post and I am getting a little ahead of myself. What should be noted is that the correlation of thick skin and shallow water diving should be noted in both the manatee and the hippo.

Are there other aquatic/semiaquatic tetrapods that might suggest shared anatomical features in congruency with an aquatic habit?

Well, I am glad you asked because yes there are several strong candidates displaying various levels of dedication to a watery lifestyle.

Walrus public domain
The walrus (Odobenus rosmarus) is famously thick skinned and although I can't find any rigorous work in how this skin pertains to its buoyancy there is some suggestive data. Several entries on wikipedia mention large bulls with hides that weight over 1,000 lbs and skin that is 3.9 inches thick around the neck. With regards to diving and buoyancy Inuit hunters are quick to attach seal skin floats to a harpooned walrus as it is said to be negatively buoyant. In order to sleep on the water walrus inflate their pharyngeal sacs in order to remain afloat. In a large study of diving seabirds and pinnipeds walrus were observed to be among the most shallow diving pinnipeds never maxing out at about 80 meters (260 feet). This shallow water diving profile makes sense in terms of their primary diet of clams which are most abundant in shallow shelf waters. Remarkable convergence yet again of thick skin, relatively shallow diving (10's of meters), and pachyeosclerotic rib bones (like the manatee).

Malayan tapir. credit Sepht CC2.5
At the other end of the spectrum of aquatic animals are the tapirs. While tapir's penchant for water is well known we now have video showing tapir running along the bottom of bodies of water like hippos - they can achieve negative buoyancy. Furthermore they are noted for their thick skin. According to the San Diego Zoo tapir fact file tapirs are characterized by "thick, leathery yet supple skin with little hair (the exception being the mountain tapir with thinner skin and thick hair)." I want to draw attention to that last bit about the mountain tapir. If the mountain tapir is the >least< aquatic of the tapirs due to it living in elevation where marshes, large rivers, and lakes will be less common on the landscape then a less thick skin is exactly what should be expected according to the theory linking thick skin with shallow water habits. One of the hallmarks of a theory is that predictions can be made and tested.

Although more rigorous anatomical and behavioral studies are needed I think there is a strong suggestion of a trend in the animals I have listed. As we move from tapir to hippo to walrus to manatee  this should become apparent. Increasing aquatic adaptation in these animals is associated with increasing skeletal density and skin density. At the lower end of the scale would be tapirs and at the other end of the scale walrus and manatee. I suspect Spinosaurus sat somewhere between the hippo and walrus in terms of dedication to the water. Spinosaurus therefore likely had an extremely thick and dense skin. This dermis would have "fattened" the appearance of the animal, offered protection from intraspecific combat, predators, and retaliatory prey (sawfish rostrums for instance). I highly endorse the Mr. Big model for Spinosaurus. And if walrus and hippo can pack on over 1,000 lbs of skin on their frame, Spinosaurus with a much larger frame likely packed on a skin weight measured in the tonnage!!

In my next post I will further look into the way(s) Spinosaurus moved in the water. Can't promise when that will be and I apologize if I do not respond to comments quickly as I will be in Dallas this week... and if you read said abstract list for a certain convention you will note there is a study on spino swimming ability. As a little hint for next post I predict that spino will be shown to be just an ok swimmer - probably less efficient than a croc. But this does not imply that spino did not have other ways of moving rapidly in the water (hippo punting hint, hint) ...



N. Ibrahim, P. Sereno, C. Dal Sasso, S. Maganuco, M. Fabbri, D.M. Martill, S. Zouhri, N. Myhrvold, D.A. Iurino (2014). Semiaquatic adaptations in a giant predatory dinosaur. Science 26 September 11, 2014

Kipps, E.K.,  McLellan, W.A,  Rommel, S.A., & Pabst, D.A. 2002. Skin density and its influence on  buoyancy in the manatee (Tricheus manatus latirostrus), harbor porpoise (Phocoena phocoena), and bottlenose dolphin (Tursiops truncatus). Marine Mammal Science 18(3) 765-778. July 2002

"A Long habit of not thinking a thing wrong, gives it a superficial appearance of being right, and raises at first a formidable outcry in defense of custom". Thomas Paine

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