Monday, April 13, 2015

Plesiosaur Machinations VI: WE BITE!!

Plesiosaurs and the Misfits together at last!! I've done this occasionally in the past for this blog where a certain song fits and inspires the subject matter at hand. The song We Bite was one of the last songs recorded by the Glenn Danzig incarnation of The Misftis for the Earth A.D. period of the band and really captures the feral, almost proto thrash intensity of the band at the time. This was a shift from what can best be described as the more Ramones inspired, rockabilly punk rock the band had perfected prior to this unholy last gasp. Unlike many bands The Misfits got more intense, serious, and unhinged with age.

Carnivores Live For Pleasure - WE BITE!
Strike Out Like A Wolf's Endeavor - WE BITE!

Sea and Land J.W. Buel 1889

And I think a similar arms race was in effect with plesiosaur evolution culminating in the mighty elasmosaurids of the Cretaceous period. As I discussed in my last post I think plesiosaurs, and especially elasmosaurs, often times filled their tummies with ammonites wrenched from their shells through either rotational feeding, bashing them on the surface, or group feeding or some combination there of. I don't think it was a coincidence that the largest ammonites coincided with the largest elasmosaurids in the Cretaceous. 

Now some readers might be open to plesiosaurs/elasmosaurs preying on large, squishy cephalopods.... but why stop there?

A funny little social experiment played out in front of me on facebook the other day. A person I follow who has written a paleo inspired fictional novel posted the picture below on his feed.

Now if you are as much of a plesiosaur fanatic as myself you will see that not only is that T- rex skull too small for an adult skull but the purported "pliosaur skull" is actually a blown up Elasmosaurus skull. Yep you heard me right, it is the supposedly "gape limited, small fish only skull" of a long necked plesiosaur. What is interesting is that the picture got several hundred likes and comments on said thread and I had to be "that guy" that let people know that they were looking at a plesiosaur not a pliosaur. This tells me a couple of things - the distinction between the two groups is rather arbitrary and if they are so easily confused on general inspection maybe the line between the two was blurred ecologically as well... If one views pliosaurs as large game hunters with compromises in the skull that also allow exploitation of relatively small prey then maybe one could view long necked plesiosaurs as predators with a penchant for small prey but also the ability to exploit relatively large prey/carcassses on occasion. 

If you are keeping up to date on your pinniped behavioral ecology you probably are aware that for a while now a bit of a slow motion revolution has been occurring revealing that many pinniped species kill and consume prey of a size larger than generally presumed and quite frankly should make you a little leery with swimming with them. There was the recent documentation and publication noting grey seals as significant predators of harbor porpoises and seals. And just recently the publication: Intraguild predation and partial consumption of blue sharks Prionace glauca by Cape fur seals Arctocephalus pusillus pusillus (abstract).

Cape Fur Seal predating Blue Shark (photo Chris Fallows)
It was well known "Air Jaws" photographer Chris Fallows that witnessed the carnivoran on chondrichthyan carnage not one time but twice and on both occasions more than one shark was caught by the seal which ate only the energy rich viscera, especially the liver and stomach, disregarding the rest. From the Smithsonian article summarizing said study: " The behavior also suggests that traditional methods of diet estimation might be missing some key strands in the food web. Ecologists have long assumed that seals consume mainly small fish not exceeding about a foot long. But analyzing seal diets usually entails looking at what's found in their guts or in their feces, which in turn depends on recovering hard parts such as fish ear bones. If seals are selectively eating viscera from sharks - or any other large animal - that slippery evidence would have evaded scientists' detection methods, potentially leading to a biased picture of who's eating whom."

Now go back and read that last paragraph and replace the word seal with the word plesiosaur and you will see exactly what I am getting at. If plesiosaurs were leaving behind the hard parts of large prey (and it  should be tacitly obvious why they would do so due to possible choking) you will likely get a view of prey remains not too dissimilar to the small prey bias we see in plesiosaur stomach remains. And from a very small sample size of just a few preserved stomach remains that we have - which were biased from the start arguably - evolves the dogma that you will see repeated in just about every wikipedia page, every professional or popular article on plesiosaurs, every artistic depiction, and every animated feature: that "plesiosaurs (long necked) were a threat to nothing larger than a small squid or fish - specialists on exclusively small prey of the size that they could swallow whole in one bite and nothing larger." 

What do the nuts and bolts of plesiosaur skull anatomy suggest about plesiosaur (again when I say plesiosaur let us just assume I am talking about long necked varieties for simplicities sake) feeding ecology? Turns out that there is a rather extensive study of the jaw closing musculature and finite element analysis of the skull of the elasmosaur Libonectes morgani. An elasmosaurid from the Turonian stage of the early Late Cretaceous discovered in Texas, the preserved skull of Libonectes is generally considered the most complete elasmosaurid skull found to date. Almost as important is how creepy the picture of its excavation is below, almost as if it was dug out of a recent deposit representing some Lovecraftian beast brought to the light of day.

Libonectes morgani c/o T.W. Tidwell SMU College
Now what did the paper I talk about say? Well first of all the name of the paper is Plesiosaur Mastication: A biomechanical analysis of the skull and adductor chamber muscles in the Late Cretaceous Plesiosaur Albertonectes Paleontologica Electronica April 2013 (Araujo & Polcyn) and is online (link). The paper is pretty technical and I had to read it a couple of times to get the gist. There are several conclusions that the author come to best summarized in the exert from the abstract below:

Our results show that a larger physiological cross-section of the adductor muscles is achieved by an enlarged supratemporal fenestra which although it reduces mechanical performance of the skull, it is offset by increased strength of a taller parietal crest and temporal bar, given the loading is largely symmetrical, the lateral components are offsetting yielding a vertical force vector. This arrangement also increases the length of the adductor musculature and thus the total muscle mass. We propose that the reduced pterygoid flange indicates a diminished role for the pterygoideus muscle, reflecting a shift of the majority of the bite force to the adductor mandibulae externus, pseudotemporalis, and adductor mandibulae posterior muscles. Reduction of the pterygoideus falsifies the dual adductor system hypothesis, in which kinetic inertia and static pressure coexist.

Ok I do not disagree with anything they say there as far as anatomy and the results of their FEA. Probably the most important aspect of their paper is that Libonectes did not have a dual adductor system like crocodilians and that the pterygoideus muscle was diminished in importance compared to the muscles of the temporal region.  

So there was a shifting of importance away from pterygoideus muscles (i.e the big muscles at the rear of the lower jaw in crocodiles that make a big bulge) towards muscles of the temporal region (i.e. the notable forehead muscles of many predators). 

Araujo & Polcyn 2013.

As the temporal hole got larger in elasmosaurs this was associated with increased height of parietal crest and temporal bar that offset the mechanical compromise of the larger hole. This increased bite strength as well as mechanical performance. In other words the architecture of the whole temporal region grew not only to accommodate larger temporal muscles but to increase mechanical performance. And I do have to mention that Araujo et. al. did an exemplary job of running the stress & strain tests under the assorted variables at hand such as size of temporal hole, with or without various muscles etc etc that does convincingly show that these factors influence how the skull behaves mechanically.

At this point I should mention that I only give finite element analysis a little bit of leverage in terms of telling me what an animal can or can't do. The reason I don't put full faith in drawing strong conclusions from FEA is that the simulations treat the skull as if it is in a vacuum - always remember that a skull is attached to an animal. Muscles, tendons, skin, fat, bone, and ligaments can absorb and redistribute stress and strain throughout the body. FEA does not account for this. And when you have a long neck with 60 or 70 neck vertebrate that is a significant part of the body that can absorb and redistribute stresses incurred at the head. (BTW red means high stress and blue means low stress in the skull). What I do read from the FEA analysis here is that blue dominates, pressure is equally distributed across the biting portion with a strong vertical bite force. Nowhere in the paper do the authors address how much force Libonectes could bite with and this is unfortunate.

As mentioned earlier the paper discounts the dual adductor system of crocodilians due to the underdeveloped pterygoid attachments in Libonectes (and, by extension, other sauropterygians built the same way). Following form this they suggest an emphasis on speed rather than force in the jaw closing apparatus in these animals. As evidence they cite the fact that gharials also have diminished importance of the pterydoid muscles. As such the authors favor a prey choice of small teleost fish.

And here is where I disagree. There is a strong argument to be made that the importance of the pterygoid muscular apparatus in crocodilians has a lot to do with putting the bulk of the animal's anatomy under the water in order to conceal the head when approaching prey. Therefore in crocodilians  there is an adaptive constraint to shift the bulk of the jaw closing musculature underwater. Plesiosaurs were under no such constraint and, being obligate piscivores, gharials are under no such constraint as well. In fact the increase of the temporal hole and concurrent heightening of temporal and parietal bars speak to an increase in power and bite force. And if there was an abundance of slow twitch muscles in that ample temporal region we might be looking at a bite that could hold on for a long time...

So I don't really follow this line of logic to argue that Libonectes and plesiosaurs of a similar build were obligate piscivores. For me the strongest indicator of being an obligate piscivore is the shape of the jaw and teeth - and we see this pattern again and again in nature - long narrow jaws, with more or less homodont dentition. Dolphins do this, gharials do this, gar do this. Plesiosauromporph plesiosaurs fall outside of this pattern. In fact some genera of elasmosaurids such as Callawayasaurus, Terminonatator, and Zarafasaura developed increasingly shorter snouts with jagged heterodont dentition!!

Convergence in obligate piscivores. Dolphin, Gharial, and Gar. Credit Ariel Zambelich wired
As difficult as it is to imagine what plesiosauromorphs were it is also important to realize what they were not. To better illustrate this point I drew a hypothetical obligate piscivore plesiosauromorph as I imagine it should look based on what other obligate piscivores do.

This plesiosaur does not exist yet
I gave it a highly felxible mobile neck like an Anhinga, a longirostine jaw, binocular vision for accurate strikes, and rows of needle sharp dentition. A flexible and slim lower jaw that could flex open to assist in swallowing fish.

But it is hypothetical because no known long necked plesiosaur developed this suite of characteristics.

They could not fold their neck back like an Anhinga to dart after quick moving, small prey. Although there was stereoscopic vision in plesiosaurs most species show a tendency for the eyes to be directed upward which suggests capture and stalking from below. They did not evolve longirostine skulls to maximize their reach and speed at snapping up small, slippery prey. Although some species evolved needle like, slender dentition other species evolved jagged, well rooted 2" plus conical daggers that would not look out of place in the jaws of a nile crocodile. Long necked plesiosaurs did not loosen up the skulls of the lower jaws like their relatives snakes and lizards do as well as many fish eaters to help swallow fish. Instead the lower mandible became one solid bone basically sutured up completely and with a noted unification of the mandibular symphysis. I do think one lineage of plesiosaurs became obligate piscivores/small game only speicalists: the polycotlylids. Their jaws converge with other known fish specialists.

All in all the majority of plesiosauromorph plesiosaurs fail in many of the aspects that make obligate piscivores so successful. And I think we should be asking why is this?

The answer I believe is quite simply many of them were not the small prey specialists so often ascribed to them but opportunistic mesopredators able to subsist on a wide prey base. Again I make the analogy towards pinnipeds. Long purported to be exclusively piscivorous but now known to be capable predators of quite large tetrapod prey. And in order to push the envelope even a bit more I drew this depiction below of the Early Jurassic plesiosauromorph Occitanosaurus tournemiensis (usually sunk into Microcleidus) taking down the Early Jurassic pliosauromorph Hauffiosaurus. Both species were in the 3-4 meter range and as is pretty obvious Occitanosaurus was an elasmosaurid before it was cool to be an elasmosaurid and Hauffiosaurus was a polycotylid before it was cool to be a polycotylid. You should also take note of the fact that I am inverting the usual trope of "pliosauromorphs" handing "plesiosauromorphs" their asses.

Again, so much of this hinges on if you buy into a social adaptation for these animals - which is a very defensible argument as I went over before. And if you go down that rabbit hole it does in fact open up other rabbit holes to go down.

Now drowning is a time honored reptilian tradition. It does not have to be quick or easy but drowning  prey will get the job done. Once an animal is bitten and then latched onto - and Occitanosaurus did have the teeth to bite onto stuff - you have to wonder how the body, skull, and teeth will react to that

skull Occitanosaurus

forceful interaction. Again not as a single tooth, skull or muscle - but as an entire animal in which stresses and strains can be absorbed and redistributed throughout the entire body. I don't actually think that the jaws and teeth of pelsiosaurs have to be all that robust, strong, or tough at all to maintain a grip. Pythons and boas do just find latching onto and holding onto large, strong terrestrial prey. And python teeth and jaws are a lot more dainty than most plesiosaur teeth and jaws.

Python skull

In the ocean where animals are often a bit softer not operating at 1 g I see no compelling reason that the skull, teeth, and jaws could bite into and hold onto largish stuff. They had a wide gape, and some of those teeth were pretty impressive and temporal muscle size and strength seems to have increased over time as noted earlier. If the prey was too strong or large the plesiosaur would most likely lose a tooth and disengage before the skull itself suffered damage. Could it be possible that plesiosaurs had involuntary biofeedback processes that would disengage from the bite if it was too straining?

Again though, we have to imagine that if a long necked plesiosaur bit into a large and struggling prey item that as the prey item struggled those stresses would largely pass through the head of the plesiosaur into the long neck and ultimately the stout and strong torso of the animal. Remember that as the neck got closer to the body it got stiffer and heavier in these animals. The plesiosaur would simply roll along with the struggling prey and, especially if mob attacking said prey, simply outlast it.

Occitanosaurus tournemiensis. credit Hinweise link

In short I think the majority of typically long necked "plesiosaurian" plesiosaurs fit this dual functionality approach. Able to subsist on small and large food items this basically "mesopredator" niche faired well for them allowing them to outlast more specialized ichthyosaurs, sea crocodiles, leptocleidids, hypercarnivorous "pliosaurine" pliosaurs, and coexist with mosasaurs.

artist Charles Fuge c/o Love in the Time of Chasmosaurus

Thursday, March 12, 2015

Plesiosaur Machinations V: Despot Ammonite Slayer

A little synchronicity occurred for me in the weeks leading up to this post. Some providential events - developments that let me know the world is ready for a re-imagining of the plesiosaur as the tyrant despot cephalopod slayer king. I see visions from the interwebz... beware!!

First up was the video documentation of a grey seal taking down a pacific giant octopus. Now the press around this rarely documented occurrence sounded off like it was a clash of deep sea monsters but at no time in the event did the harbor seal look at all worried or in danger. It probably has done this before and we know that pinnipeds do kill fairly large stuff all the time. Of course if you are familiar with my thoughts on plesiosaurs I do imagine them as being a bit not unlike pinnipeds in rarely being heralded as the opportunistic marine mesopredators that they are. Anyways keep in mind the way that the octopus sucks onto the back end of the seal to evade it and the general tactic of latching onto your predator.

And then there was the video of a fairly large octopus slipping through a very small crack on the side of a boat to get back in the water. I know we have all heard that they could do this but to see them do it is a different thing!!

Of course I would be remiss not to mention the recent publication of TWO new giant Mesozoic cephalopods from Japan. One of them was a modest sized relative of vampire squids (which are not vampiric and not squids but closer to octopi) but the other, also found from solely the chitinous beak, suggests a squid approaching the larger squid found in todays oceans.

Lower jaw Haboroteuthis poseidon. 2015 Tanabe et. al.
So now that I have you a bit primed with all that cephalopod madness I want to dive into the gist of what this blog post is about and exploring how and to what extent plesiosaurs may have exploited ammonites during the Mesozoic.

Now it is no great mystery that plesiosaurs of all flavors exploited ammonites as they have been preserved in the stomach contents of both polycotylids and elasmosaurids. Such invertebrate prey was common and small enough to be swallowed whole or crunched in the palate with the gastric mill possibly doing the rest of the chewing. And although most wikipedia entries on plesiosaurs (long necked) usually emphasis fish, belemnites and squid as their primary prey it is generally not controversial that smallish ammonites were dined upon by plesiosaurs.

Aristonectes pursuing ammonite meal. Used w/permission christopher 252 deviantart
But I would say we need >more< pictures like the one above. Ammonites were so spectacularly successful and abundant in the Mesozoic that they are used as index fossils. While fish, squid, benthos, and a variety of prey were utilized by plesiosaurs it should be noted that some formations are noted for a lack of fish. One example is the Jurassic Spitsbergen formation of the famed "predator X" which was dominated by invertebrates at the prey base.

What I want to expand upon is an idea of mine that many plesiosaurs did not curtail dining on the larger ammonite species found throughout the Mesozoic and indeed that some species may have preyed upon the largest ammonites which were indeed monstrous. It is not a coincidence in my view that the largest elasmosaurids overlapped in time and space with the largest ammonites in the Cretaceous.

But first lets explore how plesiosaurs may have consumed more modest sized ammonites - species of which may have been one or two feet across and may have been more common than the big ones and therefore been more of a mainstay in plesiosaur diets. Let us go over some characteristics of ammonites that made them vulnerable to predation.

c/o Duane Nash. Western Foundation Vertebrate Zoology

Above is saggital section of an ammonite shell displaying the buoyant septae chambers but what should also be apparent is that the living chamber is broken off. In fact the vast majority of ammonites are missing the living chamber. Why is this? Predators may have broken it off but a more mundane and pragmatic reason is that diagenetic processes during preservation would have broken it off. Perhaps the living chamber being flooded with sediment and uffering less structural support to withstand crushing. To get an idea of how much bigger these animals would have been I zoomed in on some smaller, but more fully complete ammonites you can see in the bottom right on the slab above.

c/o Duane Nash. Western Foundation Vertebrate Zoology
And the photo below shows the living chamber even better and you can see how many preserved ammonites undersell how large the animal was to a large extent.

So unless you can see a fully preserved living chamber (the final and largest septae) in the ammonite you are looking at you can imagine the living animal may have been much larger. And the shell itself was vulnerable to high pressure - from either a predators bite or too much water pressure at great depth. That means if brought to great depths the shell will literally implode due to too high a pressure as is the case with modern nautilus. Could this have been a particularly ingenious predatory tactic? Dragging ammonites to great depth to make them implode? Its possible but plesiosaurs likely had other more sensible tactics.

So if an ammonite prove too large to swallow or crush through via biting how to evict your cephalopod meal from its shell? First and foremost is to grab an exposed part of the animal - a tentacle or whatever exposed bit the plesiosaur can get its teeth on. Here the stealth tactics and long neck of plesiosaurs come in handy in getting the jump on the ammonite before it can retreat into its shell. Remember with that long neck, especially in murky, dark, or deep conditions it allows the plesiosaur to get within biting distance without alerting its presence via a pressure wave.

A little bit here on ammonite anatomy. Although still controversial (as many things are regarding ammonite soft anatomy) the strange aptychus found associated with ammonite remains likely served as a protective two valved closing hatch to secure the animal away from outside danger.

Wiki. Diagram of possible use of aptychi as closing mechanism
I found this animation recently put up on david's really interesting pages showing what he has dubbed the "grandmother hypothesis" because the ammonite is pushing it's aptychus (homologous to a beak, and then homologous to grandma's dentures) out in front of the aperture for safety. Used with permission and credit to Robert Lamanis (update an updated version is coming up).

credit Robert Lamanis

Regardless of how this whole set up worked for ammonites they likely had a way to shut themselves into their shell so getting a securing bite is of paramount importance for plesiosaurs and many had the dental armament to do this. Indeed plesiosaur heads can be seen as squeezing as much teeth, eyes, and jaw closing muscles in as small a space as possible.

And now that the plesiosaur has a good grip on this ammonite (again we are talking midsized ammonite - couple feet across) it can give it a nice shake and sometimes this might be good enough to shake the morsel out of its shell. Ammonites may have been especially vulnerable as they outgrew their old living chamber they had to slither into their new living chamber and the muscle attachments to the new chamber were not secure.

But if shaking underwater did not do the trick and there were no other plesiosaurs around to help dismember the shelled cephalopod time to drag it the surface and start bashing it against the topside.

CA Sea Lion thrashing apart Mola mola Monterey Bay. credit Bill Schmoker
Now this is a time honored tradition, crocodiles love to use a similar tactic when breaking up prey. For a plesiosaur they need not raise their hole neck out the water, just maybe the first 1/4th of it or even just a few feet out of the water. And then just violently twist the neck laterally and bash that ammonite (or whatever really) until it is yanked free or simply smashed open and then enjoy a good feed.

Plesiosaurs were strong animals. It is unfortunate that so many of the more popular depictions of plesiosaurs depict them as way too gaunt, famished, and shrink-wrapped (that is a future post topic). They have thick, heavy muscular torsos, and tall, strong dorsal spinous processes that anchored strong ligaments and musculature - especially where the neck met the torso. These were powerful animals and could mete out a thrashing to whatever was impaled on their teeth. And don't forget, water is heavy.

Thalassomedon, Adam Smith. 
Just look at the relatively tall vertebral spinous processes forming a ridge on the neck and continuing onto the shoulder. Next look at the lateral processes lower down on the neck and imaging the whole space between the two filled with muscle. In the photo below you can see and follow the spinous processes and note the distinct hump where the neck meets the torso.

Thalassomedon. Adam Smith. Note tall vertebral processes that anchored strong musculature

Thalassomedon, a powerful predator. wiki
And also don't forget that a decidedly social adaptation in these animals - a defensible position to take given live birth - would have allowed cooperative feeding. They could simply dismember ammonites by pulling them apart in unison - a habit not overlooked to anyone familiar with crocodiles pulling apart large prey en masse.

Ok now that I have warmed you up maybe to plesiosaurs taking on medium sized ammonites - what about those big boys, massive ammonites that may in fact represent the largest invertebrates ever evolved? Yep I think plesiosaurs - especially elasmosaurids - were especially apt to consume huge ammonites. Too heavy to lift out and smash against the surface of the water plesiosaurs could have used  rotational twisting to leverage the animal out of its living chamber. Have you ever seen a guinea worm spun out of its home in human flesh? Yeah kinda like that. That long neck comes in useful because as the cephalopod wraps itself around it (see the video above of giant octopus and harbor seal) the neck serves as a sort of winch to spin out the cephalopod. If one plesiosaur could not get the proper leverage to evict the cephalopod then other plesiosaurs could have assisted in stabilizing the animal from spinning as one or more plesiosaurs twisted, yanked, and pulled the poor writhing beast from its shell. Let me remind you of the strange rugose markings noted on the lingual side of the jaw in Zarafasaura - perhaps from holding onto the shells of ammonites. Of course I went over all this before but I gots to keep beating that drum - plesiosaurs were some tough cookies and imo not at all the constant whipping boys of other marine reptiles and limited to "small fry" for prey. After all if they were actually gape limited predators why not evolve an elongated or "longirostine" style jaw like you see in gharials, alligator gar, or delphinids? We see polycotylid plesiosaurs develop this longirostine style of jaw - why not long necked plesiosaurs? Why do long necked plesiosaurs have fused mandibular symphysis and a lower jaw that is completely fused? After all having a flexible lower jaw that can bow out a bit and accept larger objects is useful (especially for swallowing fish) and clearly evolved in related lizards and snakes. These anachronisms make more sense if we invoke rotational feeding and a propensity to bite into and prey upon stuff larger than previously assumed. Brevirostine jaws, fused symphysis, and solid lower mandibles all speak to these jaws sustaining large strain. Strain which was transmitted down and absorbed by the large neck and robust body. And don't be fooled by the relatively small head and less than stout like teeth. In the largest elasmosaurs the head was still impressive and approached close to two feet long. Teeth were often two inches long, well rooted and would not look out of place in the jaws of a nile crocodile. And the teeth were far more robust than the teeth of modern boa snakes which latch onto quite large and vigorous terrestrial prey. We do have a lot of plesiosaur teeth interestingly still pretty sharp but broken off at the root - perhaps due to vigorous struggles? Anyways without further ado I present a better illustrated visage of what I imagine this scene would have looked like featuring a non-specific heteromorph ammonite and a non-specific elasmosaur. You should note the "girthiness" of the elasmosaurs I think they were actually that thick.

Fans of cephalopod culture should catch the strong homage I made to the vampire squid in the speculative design of this heteromorph. By the way I want to give a shout out to the book you should have bought yourself last X-mas - the book is called Heteromorph - The Rarest Fossil Ammonites and boy is it a doozie. I can not recommend it enough to anyone with even the most casual interest of those most strangest of the strange heteromorph ammonites. I can't say I have seen a dino book that holds a candle to the quality of  this book put out in the last 20 years. Eventually I want to revisit it here for a book review. Below is one of many stunning full color pics from this excellent book.

Anyways I am gonna leave a purple version I did and cuz its like my birthday and shit so leave a comment for me you knuckleheads!!

Wednesday, February 4, 2015

Plesiosaur Machinations IV: He Is the Last You'll Know....

When Harrison Okene, the chef on the oil company ship Jascon 4, rose early at around 4:30 a.m. on the morning of May 26, 2013 he would have had no inkling of the ordeal he was about to go through. A rogue wave slammed into the vessel that morning capsizing the ship. Okene, already awake and moving about, was at an advantage compared to his shipmates asleep and locked away in their cabins as a precaution against pirates in the ocean off Nigeria. Although he linked up with several shipmates following the hit they were washed away by incoming water, "I saw the first one, the second one, the third one just washed away. I knew these guys were dead." As the vessel began it's plummet 30 meters down (100 feet) to the bottom of the tropical Atlantic ocean Okene was able to find an air pocket, panelling to create a float to get partially out of the cold water, a bottle of coke, that, along with his faith, sustained him for 60 hours until rescue. Cold, in pitch black darkness, horrendously thirsty with saltwater taking the skin off his body and tongue the trauma for Okene was not yet finished, "I was there in the water in total darkness just thinking it's the end.... I couldn't see anything but I could perceive the dead bodies of my crew were nearby. I could smell them." It did not take long for scavenging fish and large sharks to move into the vessel and begin consuming his deceased shipmates,"The fish came in and began eating the bodies. I could hear the sound. It was horror."

Okene's hand making contact w/stunned diver. Link here.
Now reading this blog post (hopefully you don't skim read here tiss tiss) it is maybe a little hard to truly imagine what Okene went through and felt. You probably are well rested, not thirsty, have ate recently, are warm, dry, and - even if you are not with another person right now - you have experienced some social contact within the last couple of hours. Harrison Okene had none of these things going for him. Pitch black, no visual input only tactile. Cold and exposed. Even though able to get some of his body out of the water the skin was starting to slough off like an extreme case of raisin hand. Salt whisking away the water from your body like a giant desiccating jar. Tongue splitting. Social isolation. Loss of all sense of time and space. It is no wonder that Okene cited his faith as the reason he got through this. I wonder if I, as someone lacking faith, would have the same resolve he did.

And then, to truly remind him he was in an alien place indifferent to his continued existence, the sound of fish and sharks, breaking into the boat and locked cabins to have at his drowned ship mates. At these latitudes one has their pick of some truly nasty and voracious elasmobranchians that may have plied the very some confines Okene found himself trapped in. The tiger shark, Galeocerdo cuvier, as well as any number of reef sharks and even oceanic white tips are possible. But what I think would be truly terrifying would be the thought of massive bluntnose six gill sharks (Hexanchus griseus) breaking into the Jascon 4 and starting their slow motion feast of his shipmates.

Bluntnose Sixgill Photo Credit Island School
When we think of sixgill sharks what comes to mind is a true monster of the deep - a primeval undertaker that, luckily for us, sticks to the abyssal depths. This is not true though. Bluntnose sixgills, stick to the deeper parts of the continental shelf during the day but are well known to cruise up into shallow waters during the night. 30 meters down is well within their range. In fact sharks are noted for being very impoverished in truly abyssal depths. There just are not too many sharks of the abyssal plain. Why is this? Lack of resources for one and sharks do have those fatty livers to maintain have  been proposed.

And if you are further interested in the bimodal range of bluntnose sixgills this fishing show actually has some pretty good natural history tidbits as fishermen and hunters often times offer if you are ok with watching this genre of recreation (at least he is catch & release).

Never the less it would appear that sharks have had the niche of dominant large scavenger on the continental slope on lock down for some time and really is there any reason to suggest otherwise? As I will get to in a second maybe there is....

But just imagine in your minds eye Okene, his sinking ship transported via a time worm hole to the bottom of a Cretaceous ocean, and the undertaker that greeted him grimly at the bottom of the ocean was not the unblinking eye of a six gill shark but the snaggly toothed grin of a Terminonatator elasmosaur probing at his water softened extremities...

Terminonatator skull (Sato 2003) c/o Adam S. Smith

The idea of scavenging plesiosaurs is not a new one. In fact there are loads of interesting old papers on plesiosaurs from the grand ol' fossil collecting days full of the great writing and that old school penchant for flair that so used to characterize scientific writing but for whatever reasons has been replaced by a less colorful tone in most contemporary scholarly writing. And below is a gem I found on the interwebz by S.W. Williston titled North American Plesiosaurs in which he presciently suggests short necked polycotylids evolving from longer necked plesiosaurs, all but spells out Elasmosaurus using shallow waters to raise young, and interprets long-necked plesiosaurs as scavengers:

Zdenek Burian. 1955 Elasmosaurs & Tylosaurus
A constant theme of these posts has been that although much of the first interpretations of plesiosaur got a lot wrong, maybe they got a lot right and we should be careful not to throw the baby out with the bath water. In fact maybe it is later interpretations that have got further from the truth in some regards. And with scavenging plesiosaurs we do have some bona fide proof that they did eat dead stuff.

You might remember a couple of years ago a plesiosaur from the Jurassic Sundance formation with the preserved bones of a prenatal ichthyosaur in its stomach? You can find the paper online although it  takes a while to download.

Phote credit Fossils and Other Living
Prenatal Ichthyosaur vertebrae in stomach of plesiosaur
Now for whatever reason the ichthyosaur embryo was voided - either in life or death - and the plesiosaur opportunistically gobbled it up. But what about larger stuff? There is the consistently mentioned observation by Barnum Brown of broken up pterodactyloid bones preserved in the gastirc region of a plesiosaur from the Niobrara formation (late Cretaceous):

You should note that not only is Brown very insistent on plesiosaurs foraging on invertebrates commonly (read ammonites) he suggests that gastroliths did the chewing - I AGREE!! But about that pterodactyloid - although he does not name a species we only know of Pteranodon (common) and Nyctosaurus (uncommon) from the Western Interior Sea. As adults both species sport huge head gear and pointy and robust finger and arm bones. A significant choking hazard for such a supposed "gape limited predator" unless it just broke the pterodactyl bones by bashing it against the surface of the water or tugging on it with a friend or simply chomping on it repeatedly. But both the "pterodactyloid" remains and the ichthyosaur point to a more opportunistic, wider scoped foraging strategy than the usual dogma of "gape limited predators of small fish and squid - hardly a threat to anything larger than a trout" that has become a bit of dogma if you ask me. Even if the animals scavenged were small enough to be swallowed without dismemberment how many gape limited scavengers do you know that >only< eat the dead stuff they come across that they can swallow in one gulp? I can't think of any. If you are an opportunistic scavenger/predator (which I infer to be the dominant signal we get from plesiosaur stomach remains) then you don't turn your nose up at a free meal of any size. You break it up into smaller pieces to swallow - like any self respecting giant petrel, nile crocodile, western gull, or tiger shark would do!!

And now back to the question of dominant large deep coastal/contintal slope scavenger in the Mesozoic. Large sharks were certainly around in the Mesozoic and were already among the top pelagic large predators of the time. But I will argue that there was a bit of competitive exclusion going on in certain environmental situations that tipped the scale of power towards plesiosaurs (and other air breathing marine tetrapods of the time mosasaurs, ichthyosaurs, marine crocs) and that was repeated and consistent anoxic episodes throughout the Mesozoic. Simply put: you can't be a very efficient gill breathing scavenger in anoxic waters because, ummm, well you still have to breathe. And even if you can operate at very low oxygen amounts you are going to be a lot more sluggish, a lot less battle ready than those air breathing marine reptiles that are outswimming you and outcompeting you to all those carcasses in oxygen limiting zones. And why might you have loads of carcasses in anoxic waters? Anoxic waters can occur because of lack of ocean mixing but they can also occur when nutrients in the water stimulate a super bloom of phytoplankton and the concurrent food chain upwards. This explosion of life, and more importantly decaying particles with respiring bacteria, simply suck up all the oxygen from the ocean. With lack of ocean mixing and large scale monsoonal events weathering continents and dumping nutrients like fertilizer down the Mississippi into the Gulf today into the oceans of the Mesozoic may have experienced both types with regularity. And if vast shoals of fish, belemnoids, ammonites and other victims were caught in once nutritious waters turning anoxic that was a veritable feast for any scavenger that could get to them. Air breathing marine reptiles were free to do so and could go where sharks simply could not. Of course this all a little dependent on marine reptiles being able to handle scavenged animals that had succumbed to "red tide" which today kills marine mammals and birds.

Of course this does not imply that sharks were not successful in the whole of the Mesozoic - it appears that there were indeed large sharks then - I am just suggesting that in certain times that anoxia prevailed plesiosaurs - and other marine reptiles - had a distinct advantage over sharks. Whether or not this purported advantage resulted in evolutionary success of marine reptiles over sharks in certain epochs - I don't know but it is an interesting thought. And we do know from loads of examples sharks were scavenging a lot of stuff back then - especially dead marine reptiles.

Above I have depicted such a hypothetical scene of marine reptiles and pterodactylids converging on windfall of ammonites that have died due to a local anoxic event. The plesiosaur is Meyerasaurus victor. I know, usually considered a rhomaleosaurid pliosaur, but come on now that distinction is completely arbitrary especially in this case. Whether you want to call it a short necked plesiosaur or a long necked pliosaur any grade school kid would point out that it looks like the Loch Ness Monter. The ichthyosaur it is competing with and harrying is an indeterminate variety of Temnodontosaurus - Darren Naish loves talking 'bout this guy on his blog and the genus is in a bit of flux so I just took some liberties and depicted a medium sized longirostine variety. For sure I did not want to convey the reptilian dolphin meme that dominates reconstructions of these guys - they had shark like/tuna like caudal fins for christ's sake - why should they not swim like a shark (and probably not "porpoise" while swimming anyways).

The Posidonia shale dating to the Early Toarcian of the Early Jurassic best known from the Holzmaden of Germany is interpreted as a somewhat anoxic area of the Tethys ocean. There was the large Dorygnathus which yeah I took some liberties with and made it a little larger (my Xmas wish in paleo is the discovery of a truly large marine rhamphorynchoid). To the left you see the more svelte but cool still Campylognathoides. And you know I gots to speculate that the heterodont, stout, and piercing dentition of this guy would be great to get into the certain shell of a certain marine invertebrate that was so common it is used as an index fossil throughout the Mesozoic.

On a little tangent regarding flying marine reptiles. Make them more voracious, aggressive, and highly opportunistic in depictions. Flying around like a bat out of hell challenging other pterosaurs and foraging willy nilly even in the midst of larger marine reptiles. Like pelagic birds today. Especially large gulls, skuas, petrels, and albatross. Food doesn't come within reach at the surface all the time after all. Below are some pics I stole that best capture the fray that is feeding seabirds. The photographer made special mention that the most combative and violent bird was the smallest - the little Cape Petrels. All photos by Karim Sahai, link here. I tried to email him for permission to use but no reply. But to cool not share with the and if you got the cash go buy something from his website or comment there.

Cape Petrel (Daption capense) & Wandering Albatross (Diomedea exulans) feeding. Karim Sahai
Southern Giant Petrel (Macronectes giganteus) looks on at cape petrel quarrelling with
Southern Royal Albatross ( Diomedea epomophora)

Cape Petrel fighting next to Southern Royal Albatross
Anyways slight diversion but I think that needed to be said. Back to the marine reptiles. Meyersasaurus
was a pretty neat looking plesiosaur and interesting in its proportions. Check out this pic of Adam Smith from the Plesiosaur Directory next to one below used w/permission.

Adam Smith w/Meyerasaurus at Museum am Lowentor -Stutgart State Museum of Germany
Look at that nasty set of chompers!! This guy still had some heft to him - maybe the size of a bull stellar sea lion more or less? And those fins - is that a bit of a high aspect ratio to them I see? I think it is. I depicted Meyerasaurus as a bit like the oceanic white tip shark - an opportunistic, energy efficient cruiser of the open ocean. And I took this analogy a bit further and made Meyerasaurus to Temnodontosaurs a bit of like what the oceanic white tip shark is to pilot whales - a follow a long opportunistic scavenger/hunter. But I took the liberty of making Meyerasaurus a relatively more aggressive harasser and competitor of Temnodontosaurs. The adults of neither could safely attack each other - if you are a sight dependent deepwater forager like Temnodontosaurus likely was you could not afford to lose an eye to a well placed bite from Meyerasaurus.

Oceanic White Tip Shark & Pilot Whales

Anyways I want to wrap this post up. I do want to do a speculative story line here but I will save it for another time. I want to keep the posts kind of bite size. And I am sleepy. Say goodnight Bluntnose Sixgill.


Monday, January 26, 2015

Using Phytoliths to Determine Tree Cover in Ancient Ecosystems

Ok all you dinomaniacs its time to stop fapping over massive theropods, titanic sauropods, and feathered (or non-feathered) velociraptors and talk about some boring ol' plants. And not even whole boring ol' plants even, we are talking microscopic remains of plants called phytoliths. You may or may not be aware but there has been a bit of a slow motion revolution of sorts going on in paleoenvironmental circles for some time now - and knowing about it will ultimately help in potentially viewing dinosaurs - and other extinct beasties - with greater resolution. And that should be of some interest to you if you want to really get into the nitty-gritty of paleoecology.

Scanning Electron image Phytoliths Elephant Grass Parr et al 2001
Just published in the January issue of Science, Linked canopy, climate, and fauna in the Cenozoic of Patagonia lead author Regan E. Dunn.,

Yeah, as it turns out those boring silica based epidermal cells found in loads of plants and just kicking around preserved in sediments going back to the Devonian, yeah they might just be useful as a proxy for determining relative vegetative cover i.e canopy thickness for extinct environments. And even if you could care less about plants that's pretty cool for it's potential to elucidate characteristics of extinct ecosystems and also potentially infer habitat characteristics and ecologies of extinct animals - even dinosaurs.

From redOrbit review article:

"The new methodology provides a high-resolution lens for viewing the structure of ecosystems over the  deep history of our planet. This capability will advance the field of paleoecology and greatly improve our understanding of how future climate change will reshape ecosystems." Alan Tessier, director NSF Division of Environmental Biology.

"Vegetation structure links all aspects of modern ecosystems, from soil moisture to primary productivity to global climate. Using this method, we can finally quantify in detail how Earth's plant and animal communities have responded to climate change over millions of years, vital for forecasting how ecosystems will change under predicted future climate scenarios." coathor Caroline Stromberg, curator paleobotany Burke Museum.

As an independent test the researchers compared modern phytoliths collected from a variety of closed to open habitats in Costa Rica and the observed forest cover resolved quite nicely with the collected data. So that's a slam dunk right? We can now really get a handle on what some of the famed Mesozoic environments were like.. Was the Morrison forested or more open savanna type vegetation? The Hell Creek Formation? Well as I mentioned at the beginning of the post this has been a bit of a slow motion revolution (which is fitting as plants operate in a slower pace of life) and using phytoliths has been bandied about as a way to infer past vegetation for some time.

A quick internet sleuthing on my own part revealed this paper just published last year which cautions against too literal interpretations of phytoliths and calls attention towards soil type:

So, as always, things are a little more complicated than first imagined. Furthermore how much phytolith is produced by plants is variable; not all plants produce phytoliths. Notably for those interested in Mesozoic ecosystems many conifers, including Araucariaraceae and cycads lack phytolliths. But on balance phytoliths are common in Equisetaceae (horsetails) and Selaginellaceae (spike mosses) and several types of ferns. At least according to wiki and my quick investigation.

Anyways some stuff to think about and I find these papers and paleoenvironmental topics/paleobotany stuff get's a little underreported in the general paleoblogosphere. I wanted to write more but my stomach hurts.

So here is pic I took in Northern California

Sunday, January 18, 2015

Black, White, and Red All Over: Orcas Penetrate the High Arctic

You could say I have shifted a lot of my attention and interest onto aquatic stuff lately - hey I included the word salad in the name of this blog for a reason, a salad can have all manner of toppings including seafood!! So no plesiosaur machinations today nor spinosaurid stuff although plenty more to come this year in those regards so stay tuned. No today I want to focus on extant marine creatures/ecological communities of the Arctic. Namely recent range expansion of what I consider personally the penultimate marine predator of all time (sorry Megalodon fanboys), the killer whale or Orcinus orca while Ursus maritimus - the polar bear - diminishes.

 Orcinus orca. Uploaded by EvaK. CC 2.5 Senckenberg Museium Frankfurt Germany
The polar bear, Ursus maritimus, has become a bit of a symbolic linchpin for anthropogenic global warming. As a top predator at the top of the world which is inherently dependent on pack ice as a platform to hunt it's more aquatic capable phocid prey this choice is an obvious one. As the ice goes, so does the polar bear. And in our ramped up, high velocity anthropogenically driven world ecosystem there is a bit of an asteric at the question of polar bears surviving in an increasingly ice free Arctic - can they even adapt that fast with the pace of current climate change? I do lay out one possibility here. Never the less we should not consider the possibility of an ice free Arctic or the extinction of the polar bear as the end of an "ecosystem" so much as merely the start of a strange, new one. And quick to move into and usurp the polar bear as king of the Arctic is the killer whale, a shifting of the guard we may in fact be witnessing currently and which might become a veritable reality in this century.


Compared to the three most notable Arctic whales (bowhead, beluga, and narwhal) the killer whale is at a bit of a disadvantage in ice- it has a huge dorsal fin, especially among the males where it might be 2 meters tall. So although they do move up to the edge of the pack ice in the Arctic and Antarctic they do not penetrate very far into the pack ice or areas with large amount of floating ice due to obviously painful scrapings and cuts that constant abrasion against ice would incur. So not only is ice a hunting platform for polar bears and a resting/birthing stations for seals - it a sanctuary of sorts for Arctic whales from killer whales. But a spate of incidents suggests that the sanctuary that ice provided whales in the high Arctic Canadian archipelago and Hudson Bay is no more. There is a bloodbath in paradise.

Glenn Williams. Narwhals jousting

"We saw this big bloodstain in the water", and "You could smell the blubber in the air. And the killer whales were moving onto the next one, like nothing had happened." so describes a witness to an increasingly familiar but previously rare event - killer whales moving into Hudson Bay and targeting beluga whales in the estuaries and bays that they traditionally stayed in during the summer months in relative safety. Orcas Pop Up near Churchill, Feed on Beluga.  What was at most an ephemeral and rare predatory encounter between the two species is looking more and more like a deliberate hunt by the killer whales. The ice disappears earlier and arrives later allowing the orcas to move in and stay longer. There has been the suggestion that some recovering populations are being suppressed and others may be further diminished. Sometimes the killer do not make it out of the Bay in time, as occurred last year when a pod was trapped - but eventually freed by currents.

photo credit Davidee Mina. killer whales trapped Hudson Bay
What is obvious is that killer whales are increasing their presence in the Arctic, especially the eastern Canadian Arctic, and that they are targeting more than just belugas.

Invasion of the Killer Whales. Nature PBS December 18, 2014.

The portrait painted by the above highly recommended Nature documentary is one of an ecosystem in flux. Polar bears scrounging for carcasses on the beach, sea bird eggs, and fishing for Arctic char in rivers. And killer whales moving into an ecosystem in which they had previously been kept at bay. Moving with a purpose, covering over 200 km a day to seek out narwhal populations in the Canadian Archipelago from which they could not reach before. Bowhead whales evincing massive scars and bites from killer whales and switching their movements towards areas that retain ice year round to avoid the killer whales. Playing a game of cat and mouse the two whales listen to eachother across vast expanses of ocean.

Tagged killer whales (red) versus tagged Bowhead whales (yellow) showing avoidance patterns
Bowhead fluke w/killer whale maulings
And a third archpredator of the Arctic, Homo sapiens of the Inuit culture, seeking answers and context to an archpredator which had only previously been an ephemeral visitor but which now increasingly shapes the prey and the ecosystem that they are dependent on. Will the seals and whales that this culture depends on shift range and habits to deal with their new predator? How will this affect the ability of these people to find them? Are we looking at an example of killer whales competitively excluding humans?

"I was hunting these narwhals and they were fleeing from some killer whales. The killer whales were travelling fast and upside down. And they breached the water chasing the narwhal. When they got close to the shore where the narwhal were they took bites out of two of them very quickly. This is when I realized that they are supreme hunters." Inuit elder.

"We knew changes were happening and wanted to understand them... We anticipated a change from the bottom up... We recognized the killer whale as that top predator that was all of a sudden making these huge changes in the Canadian Arctic. And it was something we didn't really think about at the start but there it was staring us in the face." Steve Ferguson, Canadian fisheries biologist on realizing that simultaneous with a bottom up trophic cascade in the Arctic a top down trophic pressure via killer whales was also occurring.

While killer whales in the eastern Canadian Arctic appear to be expanding their range to include areas westward and northward and capitalizing on prey/feeding grounds previously out of their reach between Alaska and Siberia on a group of islands called the Diomedes they have been documented predating on walrus recently. The following clip I scrounged up on Youtube is to the best of my knowledge the first video documentation of such an occurrence.

Walrus, which are themselves recognized as keystone species due to the significant bioturbation they do when digging up benthic prey and are significant in the diet of Inuit, are also highly dependent on ice for resting upon. Loss of ice concentrates walrus in large herds on the land which might further enable killer whales to find and target these large seals.

Polar bears have also been documented targeting these concentrations of walruses, although concentrating usually on the young. Another food source grounded polar bears have been utilizing during the summer months are runs of a type of arctic salmon called arctic char.

Polar Bears hunting Arctic Char. Nature
 Harkening back to their brown bear roots...

Global ecosystem change is already afoot. Some will adapt. Some will move. Some will benefit. And some will perish. How this will all play out and what surprises await who can say?

(c)US Navy. public domain. USS Honolulu 450 km (280 mi) from N. Pole

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