Sunday, September 28, 2014

Green is Good: Slaying the Uber Mega-Sauropod


So I noticed I have not written much about plants lately but have been instead looking at marine reptiles and of course Spinosaurus in recent months - and thats ok (its my blog after all and expect MUCH more on Spinosauridae in the future). However I have been watching my feed and noticing a lot of hits coming in from various dino chat boards/ "dino fanboy" sites/ reddit etc. etc. - probably a lot to do with my Spinosaurus posts.  And this concerns me a bit in that I don't want this blog to turn into Carnivora forum type of place - but if you are from one of the JP forums/ Carnivora forums please stick around and hopefully I can convert you to a more egalitarian view of the past. So as an antidote to this concerning trend I am going to talk about plants (and at the end maybe a word or two about dinosaurs). 'Cause nothing should scare dino fanboys away more than talk about boring ol' plants, am I right? People coming in from DeviantArt you guys are cool, open-minded, and generally not of the same ilk please stay around. 

I want to post some pics of the Norfolk Island Pines (Araucaria heterophylla) in my backyard. And if you don't know why trees like this are important in Mesozoic paleoecology GTFO.  The cones these guys produce are pretty neat looking and just recently have started going to seed. They take a LOOOOONG time to mature. Wikipedia said they take 18 months to mature but I have pictures of these same cones from at least January of 2013 so that number from wiki may in fact be at the low end.

Same tree with cones coming in Jan 2013
Now I have seen an invasive Fox squirrel (Sciurius niger) rampaging about in my backyard for several months and although I have yet to see it in this tree I would not put it past a known predator of pine seeds to pillage these guys. There is a tasty and nutritious seed inside the woody, protective husk. Humans themselves will feast on the seed of related species. And I have seen ravens dropping kernels from a large Bunya-Bunya pine in the path of oncoming vehicles to crack the husk so that they can get at the tasty kernel. Students of Mesozoic life should not miss the potential for beaked ornithopods, stout jawed sphenodonts, various proto-aves, and multiberculates to have behaved in a like-wise manner.




Araucariaceae occurred throughout the Mesozoic and there is much to suggest that the family has changed very little. In the book Plants in Mesozoic Time Ch-5 Carole T. Gee and William D. Tidwell document the preserved whole plant remains of Araucaria delevoryassi from the Howe-Stephens Quarry of the famed Morrison Formation (i.e. big sauropod country). As you noticed they placed it in the same genera as modern species of araucariaceae and noted a suite of characters suggesting a mosaic of primitive and advanced features in it. Digestibility tests suggest the foliage of these trees offered an abundant and nutritious option for sauropods provided that they digested it for long enough periods of time.

I think that this is a reasonable option, especially for high-browsing sauropods. What I find interesting and a bit of a conundrum is that modern members of Araucariaceae are not particularly fast growers. Now one can make the argument that with their main predators - the sauropods - long extinct modern members of this family have divested from fast growth rates but I personally don't find this argument compelling. Why lose the fast growth rate if you ever had it to begin with? I have experimented with trimming some branches off of a larger A. heterophylla in my backyard. New growth will sprout out from the where the old branch was snipped off, but often from several latent nodes creating a bushier effect.



Artists of Mesozoic foliage striving to show how sauropod modified araucariaceae trees look should take note - what was once one branch has, after pruning, turned into a much more bushier "shelved" habit of several branches for the tree. What should be noted is that this modest growth - occurred over several years since I initially pruned it - not a spectacularly high rate of re-growth from pruning. If Mesozoic araucaria trees had similar growth speeds, and I find no compelling reason that they should not, this suggests to me that heavy sauropod browsing was mitigated to an extent by  predators/parasites/water needs necessitating constant nomadic movements as not to put their primary food source in a negative carbon balance.

Images like this, depicting sauropod herds ravaging the landscape, toppling trees, and devouring ad infinitum should be balanced with a more nuanced view of sauropod (and other dino megaherbivores) and plant coexistence. Admittedly I am arguing the negative a bit here. Of course sauropods (and other megaherbivorous dinos) toppled trees, disrupted/compacted roots systems, and plowed paths through the vegetation. Of course these things happened - it was just a matter of course for such large animals. But what I fear is happening is that we are seeing a parallel to the hypercarnivorous, all consuming semi-mythologized uber-theropod of recent years, except this time happening with megaherbivorous dinosaurs. Large sauropods and other dino megaherbivores may have just as well fostered diversity and heterogeneous patches in their landscape, huge piles of feces may have acted as recruitment sites for young plants - especially via seeds and spores that passed undigested through their digestive tract - and consumption of faster growing species allowing slower growing species to thrive. Large sauropods and other megaherbivorous dinosaurs may have in fact fostered and benefited the exact plant community that they depended on for food.

In fact a recent paper may provide some insight and suggest a much more nuanced relationship of herbivorous dinosaurs to the plant communities that they fed upon.  Plant Ecological Strategies Shift Across the Paleogene-Cretaceous Boundary. What this paper suggests is that the angiosperm plant regime shifted from a relatively slow growing, evergreen dominated strategy in the Cretaceous to a faster growing/higher vein density regime of deciduous angiosperms after the K-Pg event. This ecological reset would have selected against the slower growing angiosperms and shifted the balance towards the metabolically faster deciduous plant community we see today. And here it should be reinforced that this changing of the guards occurred over a relatively short span of time of less than two million years. The faster growing species were around during the Cretaceous yet it took the meteor impact to provide the disruption that gave them the toe hold that they needed. And keep in mind that during the Cretaceous the slow growing angiosperm community - itself making inroads on the even slower growing gymnosperm/pteridophyte community that dominated most of the Mesozoic - existed under the auspices of supposedly some of the most disruptive/all consuming/omnipotent herbivorous animals the world has ever seen - dinosaurian megaherbivores. But if megaherbivorous dinosaurs were so aggressive/all consuming/disruptive why did they themselves not shift the angiosperm regime to a more quickly growing regime and not the K-Pg event? For me this is very suggestive and opens up many other questions. Were dinosaurs themselves keeping the faster growing species at bay and thus allowing  slower growing species to proliferate? And, if true, then perhaps it was the extinction of the dinosaurs that allowed the faster growing species to proliferate after the extinction of their chief predators? Or did herbivorous dinosaurs not matter at all to large trends in plant evolution and climate change/evolutionary innovation/ and extinction events are really what matter?

Kenneth Lacovara Phd, Dreadnoughtus remains
And one final word on megaherbivorous dinosaurs. We were recently treated to the rollout of the most complete and well preserved mega-sauropod ever recovered Dreadnoughtus schrani. Of course I am a little late to the game on covering this guy but - you know it is over 65 million years old so I think time is relative... But to my point of being careful not mythologize megaherbivorous dinosaurus the same way we do to mega-theropods:

“With a body the size of a house, the weight of a herd of elephants, and a weaponized tail, Dreadnoughtus would have feared nothing,” Lacovara said. “That evokes to me a class of turn-of-the-last century battleships called the dreadnoughts, which were huge, thickly clad and virtually impervious.” 

My critique is aimed at the very name of the beast - implied to "fear nothing". To me the idea of an animal that fears nothing speaks to a very maladaptive trait. A dinosaur this size should still fear lots of things. It should fear crossing uneven ground and breaking a leg. It should fear getting mired in mud. It should fear other members of its own species that might fight it for mates, water, or food. It should fear too high a parasite load. And as I will explain in a second it should still fear theropods even if it had grown out of the ontogenetic stage where it fell in the range of prey.

One of my favorite bits from Greg Paul's Princeton Field Guide to Dinosaurs was where he mused on the challenges that a field expedition of humans into the Mesozoic would face:

"A herd of whale-sized sauropods would pose a serious danger of trampling or impact from their tails, especially if they were spooked by humans and either attacked them as a possible threat or stampeded in their direction. Sauropods would certainly be more dangerous than elephants, whose high level of intelligence allows them to better handle situations involving humans." GSP

And here I think it important to recognize that anger and aggression - in animals and humans - is often the result of fear itself. If an animal is truly without fear then it would not even bother with acting aggressive - such as stamping the life out of a theropod. And mega-sauropods, perhaps surviving several dozen theropod attacks over the course of their lives before attaining a size range putting them out of threat, had evolutionary impetus to fear theropods. And when achieving a size outside the prey range of theropods who is to say that they were even intelligent enough to recognize this fact? Many animals, including humans, have been suggested to have predator recognition hardwired into their brain. Again sauropods - having to grow through several different size classes - would have been vulnerable to theropods for much of their life. Their would be evolutionary impetus for these animals to have a built in hardwired innate fear of theropods. And with the conservative theropod bauplan and long evolutionary history between the two groups there is much space and time for sauropods to evolve an innate predator recognition of theropods. So images of sauropods crushing the life out of theropods are just as plausible as huge adult sauropods getting spooked and fleeing away from harmless, small theropods.



Even relatively big-brained mammals such as the deer in this video display latent fear of house cats arguably due to predator recognition. I would suspect smaller brained sauropods (and other dinos) acted  with much the same consternation, confusion, and stress when faced with a theropod. How they react - either fleeing or attacking is besides the point. It was fear that caused the reaction. And it was this perpetual "landscape of fear" that theropods maintained - whether or not they could even attack/prey upon the animal - that mitigated wholesale destruction/over browsing of Mesozoic plant communities.

Or you may disagree.








Friday, September 19, 2014

Spinosaurus: The Tidal Rover (aka How I Interpret the Sail)

*My thoughts on how I think the sail was used keep changing and evolving. I am going to leave the post the way I originally wrote it but if you go to the '*' at the end you will see my view has changed a bit.

Qualifier: If you are not yet on board with an increasingly aquatic adaptation in Spinosaurus aegyptiacus are paths may have diverged a bit ago and this post may not be of use to you. If you take serious objection to my use of intuitive methods, deductive reasoning, storytelling, argument from analogy, and parsimonious route taking - chances are you might take objection here. I won't change my style and it's my blog anyways.

But if you are largely on board with the increasingly aquatic adaptations of Spinosaurus aegyptiacus; if you believe the best approach to eco-morphological reconstruction is a blend of both environmental context and anatomy; and if my interpretation of belly sliding as a probable terrestrial movement for Spinosaurus aegyptiacus intrigues you;  this post may be of some interest to you.

By the Wind Sailors. thedangingress.wordpress.com

Around this time of year along the coast of California we usually get a very strange and unusual drifter washing up on the shoreline. Velella velella or "by the wind sailors" are purple hydrozoans (not actually jellyfish but aggregates of colonial creatures) that use a combinations of winds and currents to drift about and reach concentrations of plankton.

Jymm. public domain
Small relatives of the better known Portuguese Man-of -War this member of the pleuston (organisms that live partially in and out of the water) is often cited by fisherman as an indicator of good fishing. And there may be some truth to fisherman's observations: where you have currents and winds combine plankton will tend to congregate and hence fish to feed on the plankton. Additionally, strange Mola mola (largest bony fish in the world) also love to schlurp up these guys.

So what am I suggesting, Spinosaurus was a pelagic drifter of the high seas? No, no, no, no not at all, this is a bit of a red herring, but I did want to get your minds thinking about ways in which organisms can move with an economy of motion to reach food concentrations.

First off, based on the new material both use as radiator/temp control and use as a hump or fat store are unlikely due to the lack of vessels and muscle scars. So we can eliminate those possibilities. And before I get to what I interpret the sail was for I think it worthwhile to ask why we assume the sail was largely above water level at all? And so far, if you look at just about every popular image of Spinosaurus in the water (such as the awesome image by Bonadonna below) the sail is level with the water line or well above it with much of the torso out as well. This is also the manner in which it is interpreted by Ibrahim et al 2014.

Davide Bonadonna (c) used w/permission
But it should be stated that the sail prominently displayed is an assumption that has not been tested and there is plenty of reason to in fact question it. When we look at other large tetrapods in the water, even humans, only a small percentage of the body is above water. This is especially true when the animal is not swimming and not providing any forward propulsion lifting the body above water. Sleeping sperm whales for instance. And those thick bones, don't forget the bones in the leg and dorsal spines of Spino were thick (Ibrahim et al 2014).
(c) Wild Wonders of Europe
And my favorite - look at the way crocodiles will often use erect posture in the water or when using foot propelled locomotion. I have often thought the greater range of motion crocs use in the water than on land betrays the more varied and athletic maneuvers of their ancestors.

(c) Zebraduiker. Zoochat
My main point here is that is far as I know there has been no detailed study to determine where the sail sat when the animal was in the water at a neutral posture. Possible routes of investigation could include detailed study of all the bones; is there evidence for extensive air sacs; computer models; how swimming would interact with posture (foot and/or tail calculations)? So far I know that the long bones were very solid and in fact the bones in the sail were fairly solid too (Ibrahim et al 2014). Basically many options are on the table and having the sail fully exposed is an option just as defensible as putting most or all of it underwater.

Davide Bonadonna (c) w/permission

An argument can be leveled against the purported benefits of having the sail exposed as a social signal at all times. There are in fact many times where you don't want to be seen. If we imagine Spinosaurus as moving through several different eco-morpho-ontogenetic stages through its life; and if we infer the potential for cannibalism/mate/territory competitor antagonism in a large bodied, weaponized, and reptile brained archosaur; I would say the potential for intraspecific violence is high. But you may disagree.

If we look at highly combative male lions they are not born fully tufted - it grows in with larger bulk. There are many good reasons to be less visible - especially if your neighbors might kill and/or eat you.




But for my purposes here I am going to argue the predominant position when neutral or swimming slowly would be with the sail largely underwater. As I said earlier all options are on the table at this point. And with the largest bones and greatest muscle mass in the caudal region and the smaller forelimbs and lungs in the anterior of the thorax this is a tenable position.

(c) Marco Auditore From Theropoda c/o Andrea Cau
Ibrahim et al 2014

Now above are the two independently arrived at skeletals based on material and approved from the peer reviewed paper Ibrahim et al 2014. As such they are the best current reference for Spinosaurus aegyptiacus until further detailed studies/papers reveal otherwise.

A funny thing happens when you rotate both picture so that the eyes and retracted nares align with the surface of the water in the manner many amphibious tetrapods do (frogs, beavers, crocs, otters, capybaras). (Of course I am a luddite and had to print out the pics and draw on the water level and then rescan - but someone skilled in photoshop should do a better job)

Rotated image so that nares/eyes are above water (c) Marco Auditore

Rotated image Ibrahim et al so that eyes/nares are above water

Now that looks interesting and is not at all too dissimilar to a pose crocs often go into when in the water. And it lets the animal both breathe and watch the top side - which there are some obvious and real benefits to do so. Additionally you will notice the snout is still in the water allowing sensory input from the water to be collected.

(c) Davide Bonadonna used w/permission
(c) Davide Bonadonna used w/permission
Notice that in this posture foraging via the snout and forelimbs is still an option even in deep waters. In murky/vision limited waters/nocturnal situations this is one of several foraging possibilities (but not the predominant foraging strategy as I will argue later). And again, this foraging strategy is none too dissimilar to a noted foraging strategy of saltwater crocodiles C. porosus.. Crocodylus porosus (Saltwater Crocodile). Fishing Behavior


A further line of inquiry investigating possible tactical feeding would be to look for signs of enervation in the forelimb/hand.

Getting back to this posture in the water and what the hell the sail was up to is to coming up next but beforehand to complete my picture I find it useful to give a little context to the tidal/estuarine/deltaic/fluvial mosaic systems that Spinosaurus aegyptiacus resided in.


This is the East Alligator River in Northern Territory Australia. As a large, tidally influenced, river on a coastline neighboring a large tropical ocean with a monsoonal climate regime I think this environment offers some good context to the habitat of Spinosaurus. As you can see from my measurement ( I use GEOlocate) the river mouth is over 5 km wide. You will also notice the network of side tidal creeks/oxbow lakes/ backwaters/billabongs creating a rich labyrinth of varied aquatic habitats.



What I measured here is the distance, as the crow flies, from the river mouth to Cahill's Crossing which is over 55 km.


Cahill's Crossing is the main road connecting Kakadu and Arnhem lands. But depending on the tides and floods crossing can be dicey as the road essentially goes through the river. Yes, there is significant tidal influence at Cahill's of several meters despite it being over 55 km from the river as I mapped on GEOlocate. During periods of rising or lowering tides the road acts as sort of a choke point for fish coming or going out with the tide. And attracted to those fish are two competing predators - Homo sapiens and Crocodylus porosus. By all accounts the croc seems to fare better as a fisherman here, especially for barramundi,  highly coveted by both animals. And sometimes H. sapiens loses more than just a 'barra here.

(c) BOBINOZ
What I want to illustrate is how important the tidal influence is on the organisms that inhabit these tidally dominated rivers - both in terms of the daily rhythm they set and how organisms move with the tide for feeding opportunities. And this is true whether it be the small fish/crustaceans moving in to feed in the shallows or the large, larger, and largest predators that move in to feed on them. And how adept predators can hone in at certain choke points or geographic funnels that fish have to move through in order to not get stranded with the lowering tide. Adept human fishermen of tidally influenced habitats use this very knowledge of how tides and topography can create significant influence on where fish have to move through and they take advantage of it. "As the tide begins to fall, the water coming off these flats begins to funnel into small channels, leading into larger channels and eventually into the creeks and rivers. Fish sense the dropping water and will move out with the tide to deeper water. These tidal outflows to deeper water are where fishing can be great." Ron Brooks, Fishing with the Tide. 

Simply put, you need to go where the fish are.

East Alligator River tidal tributaries
And I will suggest  Spinosaurus aegyptiacus was especially adept and skilled at finding and exploiting these tidal outflows/inflow channels.

By concentrating at these particular spots where the fish have to come to it Spinosaurus aegyptiacus could key in on a particularly easy, dependable, and rich food source. Note as well in this scenario  Spinosaurus is facing into the flow of water. Fish have to swim past it to either rich feeding areas with the incoming tide or go past it to escape the out-flowing tides. And if the jaws do not get the fish the hands - behind the jaws of course - still get a shot at passing fish or can assist with gaffing larger ones. Seen in this manner oncoming fish have to face a gauntlet of gaffing hand claws or rosette toothed jaws. Of the neck Ibrahim et al (2014) noted "The horizontal cervicodorsal hinges created by these broad centra facilitates dorsoventral excursion of the neck and skull in pursuit of prey underwater." Of the forelimb it "has hypertrophied deltopectoral and olecranon processes for powerful flexion and extension." and "that the manus is proportionately longer than in earlier spinosaurids."

What I envisage is an animal that had a predatory strike a bit like a xenomorph, fairly long fingers with gaff hooks, and a hug that you did not want to be the recipient of. With the long neck, dorsal sail, relatively flexible tail and immense size and length these guys could block off entire creeks pinning outgoing fish in a death trap formed by its own body. Again crocodiles are known to do this (on a smaller scale).

(c)Holmesontheroad. Saltwater Croc at Cahills Crossing Northern Territory Australia

In this discussion it should not be left out that current thought is that the moon has been moving away from us, stealing rotational energy from us (via tides) and giving us longer and longer days. Following from this there is potential for much greater tidal swings in the Cenomanian with both a higher maximum tide and a lower low tide. I don't know or have any data on how much bigger it was then but I did find this interesting discussion on the old DML where a suggestion was made for potentially high tides adjacent to the Tethys - take it for what it is. I would like to look more in depth at this issue.

And finally the sail. I am going to maintain that the pose I used above is a nice approximation for Spinosaurus aegyptiacus in a neutral relaxed floating/slow swimming position. The observations that; most large amphibious tetrapods maintain most of their body under the water; the eyes and nares both naturally surface in this posture; and that the thick bones, heavy caudal musculature, and buoyancy of the lungs/lighter forequarters may likely dictate this posture are my main reasonings.


And in this neutral swimming posture I am going to suggest that Spinosaurus aegyptiacus used the sail to ride tidal currents with both the rising and lowering tides to reach choice feeding opportunities.* Both tail and/or hindlimb could assist in movement and/or direction. With pedal/tail propulsion the body - and therefore the sail - can best be directed in a manner most useful to the animal in terms of where it wants to go. It has not gone unnoticed that the strange morphology of the sail may offer hydrodynamic properties that would further support this hypothesis and this may be a fruitful area of study to anyone with better physics knowledge than myself. This underwater sail interpretation also is suggestive of a method of dispersal via ocean currents. Again saltwater crocs use currents and tides to their advantage in movements in rivers and oceans. A quote from Dr. Campbell who tracked the movements of saltwater crocodiles (link), "They have an extraordinary ability to calculate the direction the currents are flowing and whether they will take them in the direction they want to go." additionally "We (were) looking through the data and found their movements correlated with the tidal flows in the rivers and that they were getting out onto the river bank when the tide changed direction."

Note that this interpretation does not preclude the use of the sail for social cues. But as I argued earlier there are often very good reasons to remain hidden. If you are the king of the estuary - or a hopeful to the throne - then I can well imagine you blowing yourself up as big as possible especially by exposing that big sail. Again, crocodiles do a similar thing inhaling air and ballooning up bigger.

Another critique I will offer is that bone is expensive to grow and maintain. If visual signaling is the primary use for the sail why not have a couple of thin rods of bone with just skin. Like a sailfish?

sailfish. Benjamint444
All in all, as you can probably guess, I would elect the saltwater crocodile, Crocodylus porosus, as the most useful analogue to Spinosaurus aegyptiacus. Basically a saltwater crocodile writ large, S. aegyptiacus, had the advantage over the croc in terms of relative strike range via the neck and gaffing forelimbs. I interpret the sail as being largely underwater bringing the nares and eyes above water level. The sail, used to take advantage of currents/tides, furthermore offered an energy efficient mode of transport and dispersal.* Like the saltwater crocodile I do not interpret S. aegyptiacus as a particularly good pursuit predator and the relatively stiff thoracic region do not speak to the nimble maneuvering useful in aquatic pursuit. Instead non-visual detection of prey via sensory receptors in the snout and possibly hands was predominate encountered during stalking/drifting (esp in turbid/nocturnal conditions); and adept use of physio-fluvial constraints (i.e. banks/channels/tidal constraints on fish movement) offer more pragmatic and economic options in foraging behavior. Foraging on terrestrial sediments was likely not important as the skeletal features outlined by Ibrahim et al (2014), especially diminished pelvic region, suggest terrestrial movement was not important to S. aegyptiacus. Underwater running in a classic bipedal  theropod mode was likely predominant mode of locomotion in shallower waters (although still potentially pretty deep) where the feet could touch down. 

Again you may differ in your interpretation, or you might not be convinced Spino was this aquatic -that's ok. You might not like my approach but I think the picture I have conveyed is very believable and in line with the known anatomy and environment of Spinosaurus aegyptiacus, and not without analogue. It offers a foraging and dispersal strategy exceptionally thrifty and energy efficient. And all in all I can't help but mention this picture I have painted speaks to a far more interesting, nuanced, and amazing animal than anything suggested so far.

And finally here is a young Homo sapiens imitating a saltwater crocodile/spinosaur in a tidal creek in Australia.



Cheers!!

*Update 9/21/14 After receiving some valid criticism regarding the use of the sail to be pushed with tidal currents I have changed my thoughts. The reason for this is that unlike a sail in the wind being used to help push along an object on the water - a sail in the water being used to push an object already in the water is not necessary. The body will float along naturally anyways with the current as the body is less dense than the water it is immersed in. This still does leave open possible hydrodynamic properties for greater maneuverability via the sail, and using the tides for movement is a possible strategy, and I do think in a neutral floating/slowly swimming position much of the sail would be underwater - but further tests are needed.









Sunday, September 14, 2014

"Last Man Standing... El Ultimo Hombre" - As the Dust Settles on the Spinosaurus Bombshell

One of my favorite (among many) scenes in No County For Old Men is when Moss (Josh Brolin) first comes across the scene of the drug deal gone bad while hunting in the desert scrub.
Upon further inspection and questioning of a mortally wounded combatant Moss asks him "Where is the last man standing... el ultimo hombre?" Presumably because Moss has deduced somebody got away with the money and he stands a good chance of retrieving it.
Which he does retrieve from the now deceased "last man standing".

Upon the disclosure several days ago of the new and revamped Spinosaurus aegyptiacus (Ibraham et al. 2014) there was something of a wild west shootout on social media - which I followed largely on facebook - but which spilled over on to many platforms. Oh and the debates, conjectures, criticisms, postulates, and endless musings were fun to watch. Like any shootout some just panicked and/or ran away in denial. Some were caught unaware. Some sprayed shots every which way and that. And some shot with pinpoint accuracy but were gunned down none the less.

As the dust settles on the Spinosaurus revelations I have seen no reason to discredit the chief findings of the paper - an unorthodox theropod morphology in a primarily aquatic animal. Some of the details, the P's and Q's, of this situation will undoubtedly change. Perhaps the hind limbs were not as dramatically reduced as some restoration suggest. But I think by and large the exceptionally elongated body, reduced  hind limb length, retracted nares, supple tail, skull and tooth morphology, elongated neck, heavy bones, isotopic data, geologic setting and sedimentary setting of fluvial/deltaic/tidal river environment, inferred diet, adaptations of foot for spreading tetradactyl design become too large a body of evidence to ignore and gloss over. This was an animal that had crossed the tipping point of being partially amphibious to being largely aquatic to an extent no other known non-avian dinosaur has done so.

Figure 2 Ibrahim et al 2014

Not that the new morphology has created additional questions: chief among them was the use(s) of the sail and how it moved terrestrially. I will save my thoughts on the sail for a later post but here I want to address problems with the two dominant thoughts on how it moved - either bipedally or quadrupedally. The quadrupedal knuckle walking design that the authors postulated and featured in several of the animations surrounding the forthcoming NatGeo documentary has several serious flaws. Besides the constraints imposed by a relatively immobile shoulder girdle restricting limb movement and inability to pronate the hands,  there is the even more obvious limitation of rather slender wrist and hand bones - they do not look weight bearing at all. Does this leave us then with a classic bipedal posture? There are some serious problems here as well, not the least of which is the center of gravity question.

Figure S3 Ibrahim et al 2015. red dot denotes center of gravity
Now it has been argued (Hartman) that if the legs are lengthened and the tail made more robust the COG (denoted by the red dot) can be brought more towards the hip. I am not convinced by these arguments. There is good reason to believe the skeletons are not chimeras (Cau) and from what I have seen of the neotype it more or less falls within this morphology.


Personally I think we have a bit of ontogenetic shift going on here. Younger individuals (i.e. the immature neotype FSAC-KK 11888) were likely relatively more longer in leg than adults and potentially more closely resembled the stance of other spinosauridae.

I like the pangolin type of locomotion proposed by Darren Naish as one of several possible locomotory possibilities. But as you notice in the pic/video below, pangolins will still occasionally touch down with their forelimbs for extra stability when covering rough terrain and I think the same would have held true for Spinosaurus (and spinosauridae as well) when covering rough terrain. They are, after all, many orders of magnitude larger and a fall could have been a lot more impactful. My gut feeling is that this form of bipedalism - with occasional forelimb stability touches - is an option that may have been common in the family as a whole and possibly Spinosaurus as younger/smaller individuals. All in all more work is needed on this family in terms of posture and locomotion. And correct me if I am wrong in the comments but do we even have preserved distal leg elements for any other members of the family besides Spinosaurus? Again, correct me if I am wrong, but if we only have foot remains for Spinosaurus does this not imply that the most parsimonious option is to infer spreading/tetradactyl feet for all of spinosauridae?



Of course I think these stability touchdowns would have not been with the claws and hands but the forelimb - and chiefly the massive ulna - taking the weight along with the ventral body surface. Let's just look at those ulnas again by the way (from Suchomimus via Dave Hone):


And finally why I think obligate bipedalism has its flaws is that traversing tidal mud flats as a large bipedal multi ton animal raises some serious issues of getting stuck in the mud!!! Fairly maladaptive for an animal that would have had to get across some fairly difficult terrain if you ask me. If you don't believe me try it yourself. Puny human bipeds run into trouble in thick mud - imagine the difficulties as a 10 ton Spinosaurus!!

Hey I could have posted a pic of myself in the mud instead?
And what was the dominant sedimentary type documented for the stratigraphy of FSAC-KK 11888? A lot of fines - mudstone, siltstone, sandstone - hey go read it for yourself as the supplementary data is free right here and it has a lot of good stuff!!

So if there are significant problems with both obligate quadrupedalism and bipedalism then what are we left with? Who is the veritable Last Man Standing (or in this case waddling)? El Ultimo Hombre?

THE LOON WINS!!!


Belly Sliding/Combat Crawling/Mud Bank Sliding provides a nice and easy way to solve the problems of both the obligate biped/quadruped dichotomy.



Video By Dj Zemenick as noted by Holtz on FB

As I first proposed here on August 16th Spinosaurus could simply fold up its arms, lower it's belly and scooch along propelled by the back legs. This is not redesigning the wheel - it is essentially just a slight modification of known theropod resting anatomy. Hey maybe not too classy but it will work nice in a muddy environment. Some variation of this theme is what crocs, pinnipeds, otters, loons, navy seals and maybe even Amphicoelias utilized when moving across such terrain.

Stay tuned I will be delving into my interpretation of the funtion of the 'sail' next and I promise my interpretation here will be even weirder!!



Cheers!!!!











Thursday, September 11, 2014

Adding Some Context to the Middle Eastern Attack Today






Video Large Crocodile Sliding Down Mud Bank



You might want to turn down the music on this one but note how comfortable, agile, and at home tapirs are underwater and how quick they are with leg propulsion underwater.


I really get a kick out of this one. Those Squeals!!!


This really is an amazing video of the tapirs ability to use underwater running/propulsion.







Related Posts Plugin for WordPress, Blogger...