Spinosaurus Unauthorized III: Run, Spino, Run!! & An Anatomical Incongruity

Faster Spino!! Run-Run-Run!! by Duane Nash click image for larger view

I am not completely averse to Spinosaurus bounding around on two legs. You will note I did depict the spinosaurs here as ontogenetically immature and their bipedalism really just a mad dash towards the relative safety of the water as two Rugops have their eyes set on baby spino dinner. Because abelisaurids always seem to roam paleoart as duets - ever notice that? Cenomanian North Africa was not so much a large herbivore based ecology but a fish and fish eater based ecology. And Spinosaurus, especially the juveniles, potentially formed a large part of the prey base for the carcharodontosaurids and abelisaurids that - possibly to some extent - were temporally and environmentally coincident.

As the close-up here attests I put the little spino in a semi-contorted posture with the head and torso pulled back to bring the center of gravity closer to the hips. With each forward lunge the body is in danger of toppling forward as the larger individual in the mid-foreground is getting perilously close to doing so. But by pulling the torso and head back with each footfall at a rapid clip I can picture this locomotion working for the youngins. To help with balance the arms are splayed laterally like a tight-rope walkers balance pole.


I still maintain belly sliding takes care of that pesky center of gravity question and also allows them to negotiate the muddy/intertidal terrain they lived in. But the bipedal heritage of Spinosaurus can not be denied and I find it very probable that - like young/small crocodiles today - smaller spinos had much more liberty in terms of locomotory options on land than the more ponderous, gargantuan adults.



To take you into my minds' eye I think that they would somewhat resemble the quick bipedal sprint of basilisks (Jesus Christ lizards) and frilled lizards.



However some, or even many, of you reading this are not convinced of Ibrahim et al's proportions for Spinosaurus nor are you convinced that a novel adaptation such as some form of quadrupedalism or as I proposed belly sliding need be invoked for this animal(s). Consensus has been agnostic or equicocal concerning Ibrahim et al's proportions for Spinosaurus. Which leaves us in a funny place because renderings and depictions of Spinosaurus continue to come about and for the most part the professional paleoartists have gone into a sort of compromised position of depicting Spinosaurus having somewhat shorter legs than other theropods but still being a good ol' biped. The recent artwork depictions of Spinosaurus by Julius Csotonyi , Mark Witton, and Sergey Krasovsky all hedge their bets towards a longer in body, shorter legged, but still fundamentally bipedal Spinosaurus. I call this compromised sort of depiction of Spinosaurus the true "chimera" in all of this for reasons I will elaborate later.

To what extent was Spinosaurus bipedal? Most would say "we need more data", I say we have enough already to dismiss Spinosaurus as a less than ideal biped on land.  An anatomical incongruity has been rather summarily dismissed or just glossed over in discussions which I will highlight later. 

To me everything circles back to one fundamental question we should ask when settling on the interpretation of an animal: does this animal make sense as an evolutionarily successful animal in it's environment? Can it, in a reasonable manner do things like forage, move, mate, evade predators and in general get along in none too friendly environment full of obstacles, competitors, and predators? This notion that some animals from the fossil records are "in the process of adapting" or "an unfinished product" is bogus to me. Not only does such a sentiment smack of neo-Lamarckism but it also begs the question: where are all the unfinished products in today's biota? Is a mudskipper a less than perfect transitional species on its way to becoming terrestrial? No it's an animal doing just fine in the environment it lives in. Are gliding animals inferior to flying ones or are they better viewed as just good enough for where and how they live?

The jack of all trades, master of none interpretation of Spinosaurus as mixed forger of land and water is not congruent with the wealth of anatomical attributes pointing towards a primarily aquatic existence. The reluctance to give up obligate or classical theropodian terrestrial bipedalism - as evinced by the artistic depictions I mentioned earlier - is at odds with Spinosaurus' peculiar pelvic anatomy. There is a layer of evidence - sitting in plain sight as is so often the case - that speaks against "classic" theropod bipedalism. This anatomical incongruous - especially when viewed in light of the animal's likely habitat of complex, intertidal estuarine fluvial systems - essentially creates a vanishingly small window of opportunity for the bipedal loyalists to maintain Spinosaurus as just another good ol' bipedal theropod. 



You may or may not recall that paleo-super hunk and Papa John spokesman Paul Sereno starred in a very well done promotional video that coincided with the infamous Spinosaurus Science publication. In this video Paul offers some really great and captivating sound bites and a little background on this most fabled of dinosaurs. For our purposes here he makes special emphasis on the femur of FSAC-KK-11888:

On lacking a marrow cavity: "It didn't have a marrow cavity. We had never seen this in any predatory dinosaur. they all have good marrow cavities. And that resembles animals that are actually spending a lot of time in the water. They want to be a little heavier than the water so they don't float all the time and they can control their swimming movements."



On the proportion of the thigh bone (femur) vs shin bone (tibia): "This thigh bone is shorter than the shinbone by several inches.... In animals that are sitting on top of the water and using their limb to paddle that thigh bone becomes short and stocky."



On the caudemofemoralis attachment "On that thigh bone we noticed that the attachment for the muscle that moves it back is huge. So what were looking at is an animal that has adapted it's hindlimb largely for paddling in water."

A couple of things here. While it's old hat that Spinosaurus lacked a marrow cavity I want to point out an inconsistency in Paul's thinking. In one instance he asserts that such animal's want to be a "little heavier than the water so that they don't float all the time" and to "control their swimming movements". This makes sense and I mostly agree with what he is saying here. But then later on Paul - when talking about the use of the hind limb and it's expanded musculature to paddle through the water contradicts himself saying, "In animals that are sitting on top of the water and using their limb to paddle that thigh bone becomes short and stocky".

Did you catch that? We can't have it both ways - Spinosaurus is either a floater or sinker. It's either heavier than the water (a sinker) or lighter than the water (a floater). In order for Spinosaurus to be a floating paddler like a duck or seagull we would not expect such dense bones. Spinosaurus is therefore - as I have been arguing for a while now - a sinker and when dense bones are combined with a dense dermis, which is not unparalleled,  it is more tenable to interpret Spinosaurus as an animal that sinks right down to the bottom. Which is where the true nature of Spinosaurus' unique and powerful pelvic anatomy come to fruition as an underwater walker.

Before I go into how and why Spinosaurus was such a superbly and beautifully adapted underwater walker one final nail in the coffin of this notion of Spinosaurus as floating paddler. Surface area. One of the most important concepts in paleo - functional analysis is the square-cube law.  As an animal increases in size the volume (read bulk) increases at a much higher rate than the surface area. Therefore a structure that is dependent on surface area to do it's job efficiently - such as a paddle - must hold pat and increase at a concurrent rate as size increases. In other words a 5 ton duck should have relatively larger paddles than a 2 lb duck. Like crazy huge paddles. Spinosaurs is a big, heavy and long animal. Even the most rudimentary, intuitive spitball analysis looking at it's paddling arsenal shows that it does not really have the type and spread of foot paddle needed to even move at the relative speed of a duck on the top of the water - much less the type of speed needed for a predator that, you know, had to go out and catch stuff. Just check out the huge rear foot paddles on a true rear foot paddler in the beaver pictured below.

Beaver on bank lower Kern River. credit Ryanx7. CC3.0

"The pelvic girdle and hind limb are considerably reduced in Spinosaurus. The surface area of the iliac blade is approximately one-half that in most theropods, and the supracetabular crest that supports the hind limb is low."

This is a crucial point that the bipedal loyalists have seemingly glossed over. The musculature and skeletal framework that are exactly crucial for standing bipedally (on terra firma) are diminished in Spinosaurus. Not only are the legs proportionately smaller in FSAC-KK-11888 (the proposed neotype) but the legs are relatively diminished in their capacity to support and maintain bipedality.

From Ibrahim et al.:

"The femur in Spinosaurus has an unusually robust attachment for the caudofemoral musculature, which is anchored along nearly one-third of the femoral shaft, suggesting powerful posterior flexion of the hind limb. The articulation at the knee joint for vertical limb support, in contrast, is reduced. The distal condyles of the femur are narrow, and the cnemial crest of the tibia is only moderately expanded."

What we have here in FSAC-KK-11888 is an incongruity that needs explaining. On one hand the femur and musculature attached give us a signal for massive power in the horizontal plane. Discordant with this observation is the relatively weak and diminished musculature and skeletal structure for the vertical plane that would be needed to support a biped of this size. How to explain this seeming contradiction?

Let's revisit my contention earlier than an animal should work reasonably well in it's environment. If we put Spinosaurus in the large, complex mangrove/deltaic/intertidal habitat that is most likely for it and infer bipedalism we should expect the opposite pattern of limb development. That is, far from being diminished in size, the skeletal and muscular framework for bipedalism should be hypertrophied (larger & stronger). The reason is that pushing yourself through water, mud, thick sand, tangles of mangrove vegetation as a biped is hard work. So if Spinosaurus was indeed doing this as an obligate biped we should see greatly expanded musculature for bipedalism in terms of vertical support, which we don't.  I cite the remarkable robusticity and upper muscular development for the swamp lions of Botswana's Okavango delta. These impressive lions - the females of which are as big as male lions elsewhere - have expanded chest and shoulder musculature that assist in not only their main prey - Cape buffalo - but also in swimming, wading, and pushing through their swampy, flooded habitat. There is even some suggestion of a separate subspecies emerging.


So using simple deduction if we can eliminate paddling as a way to explain Spinosaurus' pelvic anatomy on the grounds that it simply did not have too great of a surface area for foot paddling and if we can eliminate terrestrial walking/wading on the grounds that the exact structures needed for such an adaptation are diminished in Spinosaurus - the exact opposite of what should occur in such a large biped in a swamp - then we are left with underwater walking or "punting".

Underwater walking is consistent with the dense bones, diminished size of pelvic area, and greatly expanded caudemofemoral attachment. Neither obligate bipedalism nor paddling addresses the unique and seemingly incongruous features in Spinosaurus. Furthermore the lack of vertical support at the knee joint as noted in the Ibrahim's et al. paper speaks against both bipedalism and quadrupedalism and is another line of evidence in support of belly sliding. Even if Spinosaurus were to have evolved some form of quadrupedalism there is no reason for such an adaptation to cause a decrease in the ability of the hindlimbs to hold weight.



Finally those puny legs - a seeming weakness - are actually superior to long legs for an underwater walker. In one of the few research papers that actually attempted to quantify and bring some discourse to the manner in which hippo run underwater it was found that short, quick steps or "punts" actually outpace the longer "gliding" paces in speed when measured in controlled observations of hippos walking underwater.

Comparing hippo locomotion underwater to humans moving in a "microgravity" environment (i.e. outer space) Coughlin & Fish wrote in their abstract:

"Ground contact time decreased with increasing horizontal velocity,"

Which translates to as the hippo moved faster underwater the amount of time that the foot hit the ground decreased.

"vertical displacement during the unsupported intervals increased with an increase in ground contact time,"

"vertical displacement" refers to how high the hippo rises off the bottom of the tank in their observations. Since longer ground contact time is associated with slower relative speed when the hippo is moving relatively slowly its foot contacts the ground longer and it rises higher in the water column (i.e. gliding phases).

"and time between consecutive footfalls decreased with an increase in horizontal velocity."

which is pretty straightforward - as the hippo increased in velocity footfalls became more frequent (but still relatively short in duration).



Spinosaurus likely had the same pattern of locomotion underwater. Slow speeds with increased foot contact time and longer gliding phases (how beautiful to imagine btw). Higher speeds had decreased foot contact time and shorter unsupported intervals. Some might poo-poo this line of reasoning "you can't compare a bipedal dinosaur to a quadrupedal mammal blah, blah" but much recent work has highlighted congruity in all forms of tetrapod locomotion - especially remarkable convergence in aquatic locomotion in tetrapods. Furthermore you can test it out yourself as a biped. Go to a pool or body of water up to your chest and run. You will quickly see that short, quick steps with little gliding phase outpaces longer paces with lengthier gliding phases. As the authors note in the paper: "Under conditions of microgravity, humans switch from a walk to a run at slower speeds. (Kram et al, 1997)"

And don't for a second dismiss underwater walking or "punting" as a less efficient or even speedy way of moving through water than swimming. Check out the speed and alacrity in which the hippos in this  clip move. Although you can not see them as the people are in a boat - you can surmise from the wake and relative speed of the boat that the animals are moving along underwater at quite a pace.



The short and powerful legs of Spinosaurus are therefore beneficial to walking underwater at speed since short and quick paces outperform long paces for underwater walking.

In the discussion from the hippo/microgravity paper the authors also highlight the importance of the animal in question being denser than the water,

"Effective bottom walking requires a body that is denser than water when submerged."

As I argued in my first post in this series on Spino there is reason to make Spinosaurus denser than the water via dense bones and an extensive and dense epidermis not without parrallel to manatees, hippos, and possibly tapirs.

When we put Spinosaurus in it's proper environmental context which is completely underwater - not some bastardized giant heron nor an improbable jack of all trades switch-hitter of surf and turf - now a real functional use for the sail emerges. As I discussed in my last post the sail would not sit above water anyways as the display marker so many have championed, nor would it add any sort of propulsive power either. But what it would do, I suggest, is act as stabilizer - a dorsal keel - that helped prevent Spinosaurus from rolling when twisting and turning underwater. As much as I have championed the hippo as a useful model for Spinosaurus underwater movement, they differ in one fundamental aspect. Hippos do not have to move with much agility underwater because their primary food - grass - does not grow there nor would it swim away from them if it did. Spinosaurus as an underwater hunter of aquatic prey that did not want to get caught - needs relatively more agility underwater than a hippo. Additionally, because Spinosaurus moves as an underwater bipedal walker not a quadruped, if Spinosaurus changes course rapidly underwater and it's body starts rolling it has no way to correct itself with forelimbs (like a hippo). Now caught in an underwater body roll a Spinosaurus'hind limbs would lose contact with the substrate and it would lose it's main propulsive power since pushing off the substrate is required in underwater punting. A sail helps with this dilemma so that as Spinosaurus twists and turns underwater to either sides the sail pushes back against the water and helps prevent rolling.



Ha, ha I made Spino almost comically "fat" but really no more ponderous that a hippo. You will note that I actually depicted another, more subtle, use for the sail in the top pic. That due to it's swayback morophology the sail may have hydro dynamically made movement underwater more efficient. As the animal moves from right to left, as shown by the large arrow - water flows up and over the sail but forms little micro-eddies over each rise and fall of the sail. The effect is that a slipstream develops that allows Spinosaurus to recoup some of the energy dispensed moving through the water. If you think about the way competitive bicyclists use slipstreams or even the "shake and bake" tactic used in competitive race car events this is not far from what I am suggesting. In the biological realm birds flying in formation or even migrating lobsters moving in line take advantage of the energy saving features of slipstreams. Spinosaurus may have done the same with it's sail underwater in addition to it's movement stabilizing attributes and not altogether dismissing possible uses for bluff/intimidation/social signalling, thermodynamics, prey corral, buoyancy control, and mineral storage.

Oh yeah I almost forgot. What animal also has big flat unguals and partially webbed toes? Take a wild guess...

Ibrahim et al 2014

Also it is worth repeating how "barrel chested"Spinosaurus really is. This is an important point and another nick against trying to retrieve any meaningful terrestrial bipedality. The front of this animal was heavy. Furthermore it compares very well with the skeletal framework of - you guessed it - a hippo. Drape on some muscle, meat, and a thick skin and you will have a very voluptuous - and long - animal. The likes of which is going to be very maladapted for bipedal movement on land and even worse off trying to walk through thick tidal muds, sands, and tangles of swamp vegetation.

link Youtube Hippo 3d skeleton

In the water it was a superbly adapted underwater bipedal walker or "punter" - very graceful, powerful and daunting in that environment. On land, not so much. Smaller juveniles could have enjoyed more liberty in moving around terrestrially, perhaps even going into quick bipedal sprints. As I have maintained since before the actual publication of the Ibrahim material it was a belly sliding mud surfer, looking like an amalgamation of a giant saltwater croc, a penguin, and a loon.  But that was ok for what it had to do in life. It conceded terrestrial ability for aquatic proficiency. And that is not radical or revolutionary or even unique - every tetrapod lineage that transitions back into the aquatic realm concedes some or even all amount of terrestrial capability. Otters, beavers, crocodiles, pinnipeds, loons, penguins they all can move around on land but are much less proficient on land than their related terrestrial brethren.

CC 2.0 credit Mike Bowler. Spinosaurus & Onchoprostis

Well for now that about does it for all I want to say on Spinosaurus (although things always change). I am quite confident that my take on Spinosaurus - a belly sliding, underwater punting, primarily aquatic/piscivorous beast of tidal waterways - will prove to have much truthiness to it.

And in closing I leave you with a depiction of an adult Spinosaurus closing off a tidal outlet and using it's length, size and sail to corral aquatic animals trying to exit with the outgoing tide. The experienced adult has enmeshed itself between two thickets of the mangrove fern Weishchelia reticulataand completely dammed off the outflow channel from a tidal mudflat that fish came up through to feed during high tide. Contrary to the vast majority of Spinosaurus/ Kem-Kem paleoart which feature towering cypress canopy relatively low and shrubby cheirolepidiacean conifers and Weischelia should dominate the flora. Some of the fish - Lepidotes - even swim out of the water to escape the hungry maw of the Spinosaurus while other fish such as the sawshark and various sarcopterygians attempt to vault over the striking theropod to get to the deeper safer water on the other side. I would suggest that this form of fishing - not too dissimilar to what modern crocs do - would be a very efficient and likely manner of fishing for Spinosaurus especially amongst the older, larger, and more experienced Spinos that knew how to take advantage of such tidal choke points. A chunk has also been taken out of the Spino's sail. Also take note of the pterosaurs and dromaeosaurids attracted to the commotion and easy feed provided by the spino.

Tidal Harbinger Negative Brown by Duane Nash click image for larger view

Tidal Harbinger Shocked Pink by Duane Nash click image for larger view

I have actually amassed quite a lot of posts on Spinosaurus going back nearly to the start of this blog. Going back and reading these may be of interest to see the evolution of my ideas - including ideas I have since abandoned.

Spinosaurus Unauthorized II: Spino Identity Crisis & Island Hopping Hipposfrom November 2, 2015 in which I go into Sigillmassasaurus and what this animal means and does not mean for the "new"Spinosaurus and highlight a pivotal point generally overlooked in discussion of the veracity of FSAC-KK-11888. More on hippos and what island hopping hippos tell us and don't tell us about swimming ability and lack there of.

Spinosaurus Unauthorized I: Hippos Are Not Really Fat and Can't Swimfrom October 12, 2015. I return to the spino debacle and begin building my case that Spinosaurus works most effectively as an underwater walker/punter. In order to do so I have to spend a lot of time on hippos and a whole lot of effort arguing that hippos can not actually swim. I also argue that Spinosaurus sported a very thick and heavy dermis that assisted as ballast control along with the thick bones similar to manatees, hippos, tapirs, and walrus.

Time For the Giant Heron Spinosaurid Analogy to Bite the Dust Part 2: Getting More Than Just Your Feet Wetfrom November 7, 2014 in which I elaborate on why the heron/spinosaur comparison is very much less than ideal and not at all the best of all candidate analogs. Also why depictions of spinosaurids  standing on the edge of riverbanks hoping for big fist to blunder on by is patently ridiculous.

Time For the Giant Heron Spinosaurid Analogy to Bite the Dust Part Ifrom November 2, 2014. In which Thomas Holtz says I make a straw man argument.

"Last Man Standing... el Ultimo Hombre": As the Dust Settles on the Spinosaurus BombshellfromSeptember 14, 2014. Well the dust is still settling and well, sometimes you have to push the issue to get people to take notice.

Adding Some Context to the Middle Eastern Attack Today. from September 11, 2014. Do you see what I did there? Very meta.

Surf OR Turf: Can a Terrestrial/Aquatic Switch Hitter Really Exist?from August 31, 2014. Skeptical of the notion that Spinosaurus ala JP3 could function equally proficiently in the water or land.

Did Bakker Get Spinosaurus Right After All?from August 16, 2014 in which - upon seeing the leaked Nat Geo photos of the new Spino reconstruction - first mused that Bakker got Spinosaurus right in the animal being very aquatic and where I first argue the belly sliding hypothesis. I am now equivocal on how much the forelimbs - if at all - assisted in belly sliding or a "combat crawl" type of movement or some combination there of. In either case the post is one of my most popular and still gets lots of links and hits never mind the fact that I feel how Spino moved terrestrially is among the least interesting aspects of the animal.

Planet Predator II: Kem Kemfrom September 7, 2012 in which I muse on the ecology of the Kem Kem & Cenomanian North Africa and Spinosaurus' place in the ecosystem as prey, competitor, and provider of fish dinners for other kleptoparasitic theropods.



References

Coughlin, Brittany & Frank, E.  Hippopotamus underwater locomotion: reduced gravity movements for a massive mammal. (2009) Journal of Mammalogy 90(3) 675-679