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 2015) 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 2015

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.







Tuesday, September 9, 2014

Stranded On A Hot, Briny Desert Isle With Stem Birds... I'm In!!! Beasts Of Antiquity: Stem-Birds in the Solnhofen Limestone

Well hey now.... today I have a book review for ya'all. Well kind of. The book as it stands now Beasts of Antiquity: Stem-birds in the Solnhofen Limestone (available here for $12.99 only on kindle edition at Amazon) can be thought of as a little bit of taster for a series of similar format books that Matthew P. Martyniuk is planning where he will cover stem-birds from a variety of productive Mesozoic formations. It is small enough at a little over 100 pages - with many illustrated - that you can go through it in one Sunday afternoon as I did. If you are old enough to remember buying albums or cds you can think of this book as a bit of a short length ep if you will.



If you have not been paying attention Matt has started a bit of a cottage industry for all things stem-birds with his blog DinoGoss and his other self-published book A Field Guide to Mesozoic Birds and Other Winged Dinosaurs (2012). Now I really liked his field guide book and I intended to review it back in the day but never got around to it. Perhaps the most invaluable aspect of his field guide to Mesozoic birds is that it put all those wild and wacky basal birds, para-aves, dino-birds, bird-dinos - whatever you want to call 'em - all in one easily readable and navigable book. Cuz lets face it there are a lot of 'em and they often have some pretty complex names and its a bit hard to keep 'em straight. But this book is a little different.

Let's get right to what is on everyone's mind. Matt put a picture of a pterosaur on a book with the words "stem-birds" on the cover. What What WHAAAAT?!?!? As I am fb friends with Matt I was privy to some of the diatribe aimed at Matt for his choice of wording. "But you will confuse people into thinking birds evolved from pterosaurs... Nobody uses the term stem-bird like that NOOOO!!!"
Admittedly I was a little puzzled by it too until I looked at the issue with a more dispassionate head. Birds are the surviving crown group and pterosaurs are (controversially) archosaurs and more basal than the split that leads to birds but they still share an archosaurian common ancestor. I guess, following this line of thinking Stegosaurus is also a stem-bird? Correct me if I am wrong in the comments but this is how I am seeing it. Anyways I am in favor of the title, after all birds are the most diverse crown group archosaur and more species rich than dinosaurs and pterosaurs. If we had recognized dinosaurs as ancestral to birds right from the get-go (as some did) there would be no need for all these semantic discussions. Let me offer this: generally we are quite ok with referring to synapsids like Dimetrodon and other early synapsids as "stem mammals" that is they are on the stem leading to mammals but not necessarily ancestral to mammals. But consider that Dimetrodon,  occurring at about 295-272 mya (at least according to wiki) is separated from the first true mammals in the Triassic at about 220 mya (give or take a few million) which give a separation of about 50 million years. Or, if you want to get really picky, the dominant crown group of mammals - the placentals - arrived a bit later perhaps in the Jurassic but possibly as late as the KP boundary. That is potentially over 200 million years separating placental mammals from Dimetrodon. Pterosaurs and winged birds are separated by much less. I defend Matt's choice for the title. It goes against traditional parlance but it is a defensible choice. And it shakes things up a bit. And I am all for shaking things up a bit. I do have to wonder if Matt was trolling us all a little wee bit by putting a pterosaur on the cover of a book with the words "stem-birds".....? We just have to get used to saying I am going to the museum to look at stem-bird fossils.

Now finally to the book. I don't know if it is because I am getting older but the parts of the book that most interested me and where I learned the most had to do with geology of the Solnhofen and the history of discourse, discoveries and evolution of knowledge on the stem birds of Solnhofen. First the geology. Solnhofen is just one of those formations that anyone with a passing interest in paleontology will have heard of. It has always been recognized for its exquisite world class fossils. But what were the conditions that led to such preservation? Matt lays out several not necessarily mutually exclusive theories. My favorite is that sponge and coral reefs rising up to 50 meters from the sea floor created large basins and lagoons. The hot, briny water was heavily stratified with perhaps an anoxic or low oxygen bottom layer inhibiting scavenging and decomposition. Keeping in mind that these basins of salty/anoxic/stratified waters were nary disturbed by currents from the deeper Tethys to the south and sheltered by the proto Europe 'Mittledeutche' to the north. Occasional typhoons or tropical storms - this area was at a latitude equivalent to the Mediterranean back then - would bring in the water from the deeper surrounding oceans. But because the reefs acted as sort of a barrier and filter to particle size entering the lagoons only the finest carbonate would filter into the lagoons and hence the exceptional specimens. That is pretty cool and I had never heard of that theory before. The other theory is that stromatolites provided the finely laminated limestone of Solnhofen.

wiki commons
As I mentioned earlier this book goes into some detail regarding the history of thought and idea regarding these beasts of antiquity. Generally I skim read sections like this in books where they get into the backgrounds of the people involved but Matt does a pretty good job of keeping the flow going and he always arrives at a very useful and succinct distillation of pertinent material. Case in poing: Matt reminds us that in the time of their discovery of these animals - the 17th and 18th century for many of the specimens - at the time these animals were interpreted as 'aberrant' forms of modern animals.

You have probably seen this picture before and had a slight chuckle at the thought of pterosaurs as flying marsupials and Matt does a fine job going over the errors of typological thinking and one is reminded of how easy it is to fall trap to this method of thinking. You probably thought of Archaeopteryx as the most important taxa from Solnhofen but a good case can be made for the relative historical importance of Pterodactylus antiquus and how this taxa, possibly more than any other, helped us arrive at our modern understanding of the evolution of animals in deep time. How so? Well you are going to have to buy the book!!

Pterodactylus antiquus. wiki
As for the stem birds themselves Matt goes into good detail on the half dozen or so pterosaur genera present as well as Compsognathus and the two(?) species of Archaeopteryx. His illustrations are, in my opinion, some of the best out there. Nothing special or outlandish to his style - he just makes very believable renditions of animals that seem plausible. You can tell Matt has spent a lot of time studying modern animal color patterns and anatomy, and especially modern birds, but the colors and patterns he picks never seem contrived or lifted wholesale from modern forms. One of the most useful things he does is illustrate not just the adults but several life stages of many of the animals as depicted below.


And I hope this method of rendering several life stages becomes more common. Indeed this realization of the importance of ontogenetic changes in stem-birds is a major theme of the book and although it has relieved us of a great deal of diversity it speaks to a greater truth regarding these animals which Matt does an excellent job of summarizing in my favorite paragraph from the book below:

"It may seem like this new era of research has resulted in a steep decline in overall stem-bird diversity in general, and especially pterosaur diversity in particular. In reality, we are really just re-thinking what diversity means in the context of their unique life histories. Diversity among stem-birds came mainly in the form of role shifting during their long period of slow growth, rather than the kind of high species diversity seen in modern birds and mammals, which have much faster growth rates. Stem-birds were highly successful to the point of dominating ecosystems on land for hundreds of millions of years, and they were able to do so in part thanks to the ability of each species to inhabit several different niches in the same ecosystem."

Hopefully I piqued your interest a bit to check out this book. It is a good blend of illustrations, history of knowledge, and the latest thought on these animals.

However I would not be doing my job I believe if I did not offer some constructive criticism. Me personally I would have liked the book to go a little further, even if speculative, on how this ecosystem may have functioned. Perhaps just a chapter on the vegetation, main types of sponges and corals present, ammonites, marine reptiles, fish, lizards etc etc- not in depth just a run through. These things would add some context to imagining the lives of these animals. From what I gather the xeric vegetation, hot briny lagoons, stratified water column - all these things suggest a very hard scrabble life for these animals. I would be interested in looking at possible marine resources asides from fish. Of course I am the guy that thinks everyone and their mother was eating a lot more ammonite than generally portrayed. I can easily imagine the slightly hooked rostrum of many of the pterosaurs probing into shelled cephalopods either caught or scavenged and pulling out delectable bits. Did turtles nest on these islands - perhaps offering a seasonal glut of eggs and hatchlings? What about all those sponges and corals - did they have reproductive orgies like modern corals perhaps offering a quick glut of eggs easily scooped up by pterosaurs especially guys like Gnathosaurus? I am intrigued by many of the crustacean remains from Solnhofen. Often described as lobsters they look a bit like some of the pelagic crabs we have today and could have offered up another food source for hungry pterosaurs or shore scavenging theropods.

Pelagic Red Crab

Mecochirus longimanatus
But these are just minor quibbles and reflect more on my own personal interests and biases. Check it out, $12.99 is less than it costs to see a movie,  and support independent natural history media!!



Cheers!!!

Sunday, August 31, 2014

Surf OR Turf: Can A Terrestrial/Aquatic Switchitter Really Exist?

Following on the heels of my Spinosaurus post I have been thinking about the aquatic/amphibious thing a lot lately and looking at the various levels of engagement in either realm animals partake in and have come to the conclusion that, at least for a terrestrial limbed tetrapod, being equally competent in the land and water at a high level is pretty darn hard to do if not impossible. (In the title I used the word switchitter to refer primarily to baseball players that are equally competent as hitters with both arms leading in case you miss the translation)

As a qualifier I stated this animal has to have limbs as numerous snakes are great in both realms - what comes to mind are garter snakes. I also stated that the animal has to be terrestrial i.e. not a bird as the dipper bird makes for a good case of being equally competent in both realms.

CA red-sided garter snake
I should also qualify my statement by clarifying what I mean when I say "equally competent". I would consider a predator that can both run down prey and swim down prey at high levels "equally competent".  Not just any prey though - this animals must outpace the fastest prey items in both respective realms. Or a prey species that could elude the fastest predators in either realm. Such an animal would be able to approach the cursorial capacity of canids or felids on land and in the water be on par with the fastest scromboids and dolphins.

For sure there are plenty of animals that hunt down and kill prey in both realms - bears, lots of mustelids, monitors, crocs, frogs - but when you really look at these animals they generally are geared primarily to one environment or the other. And in many cases they are utilizing stealth or elements of topography to gain an advantage. Remember I am looking for that animal that can capture - not by stealth but by speed - the quickest and most elusive prey in either environment with equal ease and efficiency.

I am starting to think there is very good reason such an animal does not exist nor could it ever.

The reason being that aquatic versus terrestrial movement asks the limbs to do very different things. Aquatic propulsion will tend to select for shorter and stouter limbs. Shorter and stouter limbs, being closer to the body, will create less drag than longer limbs during the recovery stroke. So if speed is something of importance in amphibious tetrapods shorter and stouter limbs will be selected for. This is seen very well in skeletons of otters. In addition a long torso works a bit like a hull of a boat to help cut through and displace water. Just look at the unique proportions of Michael Phelps - long arms and torso, but relatively short (read powerful) legs and flexible flipper like feet.


Now contrast this with what it takes to be an excellent cursor ; long legs, especially the lower leg elements; a deep thoracic cavity to house large heart and lungs; and compact torso for quick maneuvering. Seen against what is called for to be an efficient amphibious tetrapod it quickly becomes apparent that the two forms of locomotion are diametrically opposed. And also why Phelps, although a world class swimmer, would make a relatively poor runner. Compare and contrast the dimensions of Phelps with the ideal body dimensions of a runner and you will see that humans mirror the pattern seen in animals.


So although we have lots of examples of animals that dominate the aquatic and terrestrial realm in fiction - for example Dinocroc, Godzilla, Cloverfield Monster, Beast From 20,000 Fathoms, and the semi-mythologized JP 3 Spinosaurus - being equally proficient at a high level in both realms I don't see happening for a tetrapod.









Saturday, August 16, 2014

A Very Dated Picture of Baronyx from Way Back in the late 90's

I never date or sign my pictures - that way  I can create havoc for art dealers of the future when I am a bright shiny star worth gabillions - so you just have to take my word for it that I drew this back in the late 90's - maybe 97/98. But as evidence I offer the very dated look for a putative spinosaur for the given time table of rendering. I think I was going for Baryonyx walkeri - back in those days if I recall that was all we really had going for good remains of a spinosaurid dinosauri. Anyways Andrea Cau of the blog Theropoda left a comment on my last post that reminded me of this pic so I wanted to put it up in all of its embarrassing detail.


Gobbling up cute, little aestivating lungfish.

Did Bakker Get Spinosaurus Right After All?

We all know and love the new Spinosaurus aegyptiacus reconstruction right? "Disenchanting" is how Douglas Henderson described it on facebook. And it does fall a little bit shy of the impressive dual land/water arch predator it has so often been posited to be, especially since a little movie came out (JP3 duh) and our friend the Spino terrorized everything from T-rex to estranged parents. Truth be told it looks a little clunky, a little too front heavy to work right - at least the way we expect theropods to work  since GSP started drawing them as svelte athletes rip roaring across the page. So, yeah I do want to comment on the new Spino reconstruction and yeah there are a lot of people - very knowledgeable ones at that - that would definitely disapprove of what I am going to do before publication of the new material. But I will argue that my interpretation on what was going on with Spino is in fact presaged by what we already know from other members of spinosauridae and yes, as suggested by the title, I think Bakker got the jump on all of us by suggesting way back when that Spinosaurus was a lot more aquatic than generally portrayed. But I will offer my little Antediluvian Salad spin on Spinosaurus and hopefully you find it interesting. And leave a comment.


Moss Landing/Elkhorn Slough US Army Corps. public domain
Before I get to Spino itself I want to tell a little story to help illuminate my point. A little tale about kayaking. I do like to kayak and one of the funner places to do so in California is a place called Elkhorn Slough in the Monterey Bay. It is a tidally influenced estuary and there is always open access to the ocean, especially because of the harbor at the entrance having to be maintained. It is noted for the unique population of sea otters that forage in an estuary as opposed to the ocean - often times within view of the highway that crosses the estuary. These estuarine sea otters have been shown to predate heavily on crabs and, in a classic trophic cascade, have bolstered stands of eel grass in the estuary. In addition to the otters, there are loads of harbor seal, water birds and miles of watery inlets to explore. It is the type of place that lets you imagine the California that once was - when coastal lagoons and estuaries dotted the entire coast, flocks of birds blackened the skies and grizzlies patrolled everywhere. Elkhorn Slough is so spellbinding in fact that as I kayaked it I lost track of the depth of water I was in and became grounded in mud in shallow water. This sucks I thought to myself as I considered the possibility of having to get out and push my kayak back into deeper water. Thankfully cooler heads prevailed. I did not make the rookie mistake of getting out of the kayak where I would have likely got mired waist deep in tidal mud in a sulphurous mess. In our best impersonation of saltwater crocodile plowing through tidal flats we shimmied left and right and paddled with short quick thrusts to get back to deep water. And if you imagine the long rounded body of the kayak as equivalent to the long low body of a crocodile, seal, or otter the analogy of moving through deep/sticky mud in a kayak is spot on. And if you think of large amphibious tetrapods moving through the mud, and I am talking deep/miring mud, they all get low and down in it and use their body surface area to prevent sinking too deep. Go look at saltwater crocodiles steaming through tidal mud flats in Queensland.



Large tetrapods that do not use this technique in deep mud risk getting mired. For large bipeds the risks are even more extreme as all of the weight is concentrated on just one limb when pushing off. As the picture above attests a very large American crocodile has some advantages over a bipedal hominid in deep mud (he survived btw). Whether you are a trained soldier or a simply like to take the Spartan Challenge one is quick to see the benefits of getting down into the mud to get through it. It might seem counter intuitive at first but just ask this guy.


Now following this line of thought of how to traverse muddy areas as a large tetrapods let us revisit Spinosaurus aegyptiacus - especially with respect to the new reconstruction c/o Paul Sereno.

Nat Geo
So we got a couple things going on here. A very long, low body with some ridiculous looking shorty-shorts legs. Especially reconstructed in the Paulian push off mode the beast looks seriously in danger of tipping over. Combined with the strangely down turned head and the heavy arms the question is begged is this manoeuvre even possible? To further complicate the issue let us put this animals in its habitat - tidal/deltaic wetlands. (insert discussion on spinosauridae habitat choice, diet, you can find the evidence is compelling!) Now we have the issue of a massive, bipedal animal in a habitat full of mud - as discussed earlier large bipeds in thick mud can be an issue. What was the poor spino to do? What I am going to suggest is that Spinosaur and its ilk went to boot camp and learned how to combat crawl. Not entirely quadrupedal but not entirely bipedal but a bit of a compromise between the two. Lower the torso, push off with the short back legs - a bit like a penguin actually - and the coup de grace those bizarre and massively boned and muscled forelegs. Simply fold them in the manner all theropods are now known to do. The radius and ulna take the weight and the clawed digits are curled inwards. Take a look at this pic c/o Dave Hone of a Suchomimus arm. Spinosaur arms were robust but not as elongate as often depicted. But when the spino goes into this belly slide I will suggest the arms can assist in kind of a "combat crawl" motion. The elbow is where the movement happens and the radius and ulna take the weight.

Seen in this manner the long low torso, short legs, short but powerful forearms, and downward sloping neck shared by all spinosauridae now start to make sense. Chasing after stuff on terra firma these  animals were not. But if you were in the water, or a hapless dinosaur mired in the mud, spino could get the jump on you.

Duane Nash
Above is a very quick and punk rockish sketch I did yesterday of a spino moving through thick tidal flat mud. The black color on the underside is not some type of reverse countershading but the thick/clingy mud you find in such environments. I have been drawing theropods on and off for over 20 years but drawing spinosaurids you have to sort of unlearn what you are used to. Not tall and gracile, no graceful S-curve to the neck, not a compact torso but a long barrel shaped torso. They seem to go against the "birdy, svelte, uber athletic" theropod bauplan that has dominated reconstructions essentially as a result of Gregory S. Paul's influence. Hence the culture shock at the new reconstruction of Spinosaurus. In hind sight maybe we should have seen this coming. All of the known relatives of Spino tip forward a bit, have short heavy arms, and well just look oddly proportioned compared to other theropods. Spinosaurs took these attributes to the extreme. I would suggest all spinosauridae would utilize belly crawls in muddy situations and perhaps occasionally even on dry land. If you look at the list of large amphibious tetrapods that do not utilize the belly slide in thick mud the list is basically.... nil? Maybe hippos don't belly slide, but they do have four short powerful limbs and a long torso. Capybaras?


Below is a depiction I did of Spino with just the body showing and not obscured in the mud. It is a little difficult to draw as such and work kinematically where everything goes. But I think such a style of movement is a fair compromise considering what we know from these critters anatomically and ecologically.

Duane Nash
And again let us just look at the skeletons of other related spinosaurids. Like I said earlier some take objection to me writing about Spino before the publication but if you look at these skeletons in light of the argument I just put forth for belly sliding/combat crawling there is no reason to say that they may have all been doing it. And I seriously doubt Sereno and Nat Geo are going to suggest this mode of movement because, you know, they put their mount in a Paulian push off extreme cursorial stance. And finally Robert Bakker was suggesting that these guys were a lot more aquatic than generally portrayed. And usually ridiculed for his opinions. Last laugh may go to Bakker on this one.

As for how they moved in the water I think more or less like a hippo but bipedal running underwater. Not tail driven.

Subadult Spino. wiki. legs were likely shorter. Creative Commons Funkmonk
Baronyx walkerii. CC Funkmonk. Note heavy, but short forearms

Above is a skeletal by blogger/artist/researcher Jaime A. Headden. You will notice that of the material we have, the lower legs are missing. Never the less, as in this skeletal, they are usually rendered fairly long and gracile. But they may have been quite a bit stumpier.

Suchomimus tenerensis. CC AStrangerintheAlps
Again with Suchomimus we see that tendency to fall forward a bit. Almost as if it is begging to go belly slide in some primordial ooze.

Suchomimus tenerensis CC Belinda Hankins Miller

Getting low, getting low.





Friday, July 18, 2014

Scrummy for Scromboids: How Do Great White Sharks Catch Tuna Anyways?

Well all righty then todays post might seem a bit all over the place but bear with me there is a valuable point to be made out of all of it.

Monterey Bay Aquarium. tuna & great white

I have had a bit of a predilection with all things aquatic lately as you may have noticed - plesiosaurs, pliosaurs, ammonites, and all things gishy, gushy, and squidy - have been on my mind of late. And here in the states it is summer and that means one thing and one thing only - SHARKS!! An immature great white shark has already bit a swimmer who blundered into it as the shark was trying to free itself from a fisherman's hook in southern California. And Discovery Channel is set to break new highs (lows?) in shark carnage in their annual Shark Week marathon. The ambassador to sharkdom, great white sharks, have a bit in common with T- rex in that the attention and coverage both animals receive is a bit fantastical and overshadows other shark/theropod species in popular media. That is not to say I personally have or will ever tire of learning new insights into both species. So I say hogwash to notions of overexposure as both species are stupendously cool and actually quite unique in the evolutionary framework of their respective pedigrees. But other types do need more attention and to let you know now, I will be talking about great whites in terms of one specific aspect of their predatory behavior that is little explored. But to set the stage I need to talk about something seemingly completely incongruous with great white sharks - spotted hyena predation.


The book above was one of the foundational pieces of natural history literature that really captured my attention as a youngster. I recently became reacquainted with the book. At the research institution where I work at doing data entry, The Western Foundation of Vertebrate Zoology (despite the name the museum  specializes in birds eggs), was cleaning out old books one of which was Innocent Killers. So I quickly scooped up the free copy of this brilliant text only to discover that it was a copy signed by author Jane Goodall . And yes that is the Jane Goodall I am talking about - the Jane Goodall best known for her work with primates. Less well known is that for several years she worked with wildlife photographer Hugo Van Lawick documenting the social and predatory ecologies of spotted hyenas, wild dogs, and jackals in east Africa. While common knowledge now what Jane revealed concerning spotted hyenas was an intensely social, intelligent, and capable predator that operated largely under the cover of darkness. This data went contrary to previous assertions of spotted hyenas as consummate scavengers - characterizations due to diurnal observations and entrenched negative cultural views of hyena. I know the decline in the quality of natural history documentaries has been well noted (mermaids, Megalodon) but the Nat Geo channel has produced a very interesting film entitled Night Stalkers - Hyena Gangs which is on youtube check it out.


The take home message is that a significant misunderstanding of spotted hyena predatory behavior and ecology went unchecked right up until the 1970's when actual long term field studies, including nocturnal observations, were made. And this is for a particularly well known large predator that lives in open habitats.

Check your privilege, mate

With this example in mind what might we be missing in terms of behavior for great white sharks at night? The challenges of documenting the behavior of this massive, complicated predator are even more  compounded by its aquatic realm - where even during the day turbidity and lack of vision are par for the course. And this is a bias that I think can't be overstated to your typical arm chair naturalist (myself included) - bad visibility, even in tropical waters, is the rule rather than the exception. When you watch undersea documentaries you are seeing the rare, exceptional times where visibility is good. Otherwise tides, currents, plankton blooms, and storms muck up the water a good part of the time - and give predators a decided advantage. Just as hyenas and lions have a decided advantage over their ungulate prey at nightfall.

As a kid in the eighties I watched every documentary I could find on great white sharks in hopes of getting a glimpse of their predatory behavior. But all I saw where rather sedate looking whites gathered around human induced feeding opportunities. I could not figure out how such a languid looking fish captured smart, agile, and quick pinnipeds. Boy was I wrong!! Nat geo captured white shark predatory behavior via stationary underwater cameras in the 90's but it was not until the "air jaws" phenomena off South Africa via Chris Fallows that we really saw unadulterated white shark predatory behavior. What's more not only were white sharks doing acrobatic full breaches, extended chases - they were also hunting this way at night!!

Nat Geo
And I now I want to get to the heart of this post. We have good footage and data on the ways that white sharks go after and capture pinnipeds, even varying their tactics based on the type of pinniped. But how do they capture the other, other white meat? I am talking about those hyper-streamlined, hyper vigilant, super charged, warm blooded super-fish - tuna. Of the genus Thunnus these fish, most notably bluefin, albacore, and yellowfin are super tasty to certain hominids as well as anything else that can get a jump on these most speedy of pescados.

Now I love to quiz fishermen on bits of natural history that they have observed - fisherman's tales notwithstanding they are a treasure trove of knowledge and experience. Lucky enough my uncle regularly goes on charter trips to catch yellowfin tuna at Guadalupe Island off of Baja California, Mexico. And any great white shark groupie should know that island well, it is a preeminent spot for eastern pacific white sharks. Indeed my uncle testifies the white sharks there are a bit of a nuisance, and snatch hooked tuna so often that they are dubbed "the taxman" (experienced surfers on California refer to white sharks as "men in grey suits" alluding to how commonly they encounter them with no incident spooky still though). A quick perusal of you tube clips verifies my uncles' testimony.


Also check out this vid of what is claimed to be an 18 footer at Guadalupe. Based on the girth that might not be an overestimate.

But when I ask my uncle if a great white can catch a free-swimming yellowtail he is quick to say no... only when they are hooked can the whites get a yellowtail as they are too fast.


At first this makes sense, tuna are very fast - faster than whites and faster than the pinnipeds that whites have been documented to hunt. But then again tuna are always put forth as a food of great whites, you have accounts of great white sharks actively following bluefin tuna, especially in the Mediterranean, or getting into tuna aquaculture pens as recently happened in Mexico where a massive shark was killed by tuna ranchers, and then you have loads of accounts of tunas being pulled out of the stomachs of dead great white sharks. Of special significance are the great white sharks of the Mediterranean, said to follow schools of tuna through the straights of Gibraltar and sometimes even being encountered in the traditional matanza tuna killing festivals. Interestingly the rare Mediterranean white sharks, including some of the largest ever captured, may subsist primarily on tuna - seals not occurring there in any large numbers. Here is a good blog post going deeper into this little known population of white sharks. Additionally the Mediterranean might be from a relict Australian population that got misdirected about half a million years ago.

So how does a great white shark go about hunting a tuna? Well I suspect, at least in the case of bluefin tuna, we are not witnessing the white shark in hunt mode because white sharks may only have the advantage at night. I want to draw your attention to this study: Electroretinographic Analysis of Night Vision in Juvenile Pacific Bluefin Tuna (Thunnus orientalis) published in the Biological Bulletin 2009. Basically, although the bluefin tuna has good vision and is a sight orientated predator, it's vision is geared towards diurnal activities and shows a marked decline for nocturnal vision. So marked in fact that collisions at high speed against underwater pen walls is a significant mortality factor in pen raised bluefin tuna. If this decline in nocturnal vision goes across the whole genus of tuna Thunnus, might this be the small window of opportunity that allows the larger, slower but nocturnally capable white sharks to predate speedier tuna? And hopefully now you see why I started with a discussion of hyena nocturnal habits and how for so long that animal was misinterpreted. It is not hard to imaging how the nocturnal habits of a large, rare oceanic predator might go unrecognized as well.



The 19 foot, 5000 pound female great white has been following the school of bluefin tuna for several weeks now but has not attempted an attack. During the day it stays below and behind the school, sometimes letting the school get several miles ahead of it as it slowly maintains course and conserves energy, living off of its fatty liver. But it is gravid and needs a good feed for its growing pups. Tonight is a new moon and under the cover of darkness the white shark will make its move. A few of the larger fish have become aware of something large following the school for several weeks now and are careful not to swim at the periphery of the school as they have experienced attacks before. But other fish are naive to white sharks. They have  ran into small blues and makos but had outgrown these predators in size and strength. This female white shark is experienced in bluefin hunting and knows that only a certain congruence of factors allows her to make a kill of the speedier tuna. Cloud cover, lack of moonlight, and a bloom of phytoplankton gives her the cover to slip into the school of tuna. Although technically not asleep, they are swimming in a sort of waking dream - like race cars at idle. Amazingly the white shark is able to blend into the school by mimicking the swimming rhythm of the school and evade detection. They may sense another large fish but register it as just another tuna. When the shark picks a victim the dash is barely over a distance of 10 feet, but conditions are so murky that even the great white shark misses its mark on a disabling bite to the tail. With the school now alerted it is like a hundred ferraris going from 0 to 50 mph. But the white shark knows that it can still exploit this chaos and when one startled tuna accidentally rams into another tunas gills, momentarily stunning it, the shark has its meal.




Cheers!!!




Related Posts Plugin for WordPress, Blogger...