Sunday, June 28, 2015

Southern Discomfort: Violent Interactions of Antarctic Toothfish and Colossal Squid

A few months ago I wrote a post called Black, White, and Red All Over: Orcas Penetrate the High Arctic detailing how orcas are making inroads into habitat formerly off limits to them due to global warming. The ice melting earlier and staying clear longer allows killer whales to exploit ice specialist cetaceans such as narwhal and beluga and we may be seeing killer whales replace polar bears as top predators of the high arctic. This ecological shuffling of the deck is something we should expect to see more of in a rapidly changing climate and for this post I want to concentrate on the interesting predator ecology of the southern Antarctic and subantarctic waters with special emphasis on two predators in particular - Antarctic toothfish (Dissostichus masoni) & colossal squid (Mesonychoteuthis hamiltoni).

Antarctic toothfish. Alexander Remeslo (c) used w/permission
They say a pic is worth a thousand words right? The above ugly maw belongs to an Antarctic toothfish, kissing cousin to the Patagonian toothfish, and both often times labelled as "Chilean Seabass" to entice gourmands to eat such a brutal looking creature at 20$ lb. Nice video on the fishery. What should not go unnoticed is the large sucker scars from colossal squid - are some of those healed scars? A more nuanced relationship between these two southern juggernauts than previously recognized is the focus of a study by Russian researcher Alexander Remeslo and others looking at the sometimes prey, sometimes predator relationship.

Alexander Remeslo (c)
What Alex and his colleagues did, and many marine researchers do who study remote ocean organisms do,  was to hitch a ride on an oceanic trawler, in this case South Korean longliners, fishing for the south poles equivalent to pelagic sharks - Antarctic toothfish. They had the express purpose of looking at depredations by squid on hooked toothfish. But in looking at damage incurred on toothfish by colossal squid and taking a peek inside the belly of the toothfish these researchers were able to document a variety of interactions more complicated than the traditional view of toothfish as the obligate prey of colossal squid.

Colossal squid hook/suckers taken from stomach
of toothfish (c) Alexander Remeslo
Not surprisingly colossal squid, which in recent years has turned out to be a cryptic, sluggish, low metabolic ambush predator of the  s  l  o  w  e  s  t  order does take advantage of toothfish caught on longlines, evinced by the distinctive swivel hook scars from their suckers and chunks taken out of the fish by its beak. In light of the fact that colossal squid are not pursuit predators but ambush predators
(or possibly they lure prey with bioluminescence?) it does make sense that they would feed on  toothfish in a weakened state caught on longline, according to the study depredation rates of about 1%.

But what was not so expected was the rate at which colossal squid was found inside the tummies of the toothfish. In the various Antarctic seas that they collected data from colossal squid was found inside the stomachs of toothfish from .33% to 6.30% (interestingly the Ross sea did not have interactions between toothfish and squid in any form?). This equated to 11 - 20% by bulk weight of the fish's diet. Now that is substantial.

(not so) Colossal squid hooks from inside stomach's of toothfish (c) Remeslo
Now usually the squid remains indicated an animal smaller than the fish in question (colossal squid get up to about 500 kg, toothfish about 80 kg) but there was an important exception that was recorded in this study.

The complete tentacle with club as well as two arms was retrieved from the stomach of a toothfish as pictured on the left. As you can see these remains - which weight in at about 7 kg - hint at consumption of part of a particularly large colossal squid by a toothfish that weighed 70 kg.

Was this a predatory event or scavenged?

Now the authors - as well as the article in deep sea news about this paper - suggest that this parcel of colossal squid was either scavenged or taken off of an ailing individual. Possible predators the authors note that could have set the table for such a morsel ending up in the stomach of the toothfish include; sperm whales - which were witnessed at least once by the authors; and other colossal squid - the authors note that  cannibalism is common in teuthids and most attacks concentrate on the mantle, leaving the tentacles behind which are then easily scavenged.

Another predator that consumes colossal squid is the southern sleeper sharks.  Studies of the shark genus Somniosus suggest a capable - if very cryptic and sluggish - predator of large, active, and agile prey including large fish, cephalopods and marine mammals. Indeed dietary analysis of the southern sleeper shark suggests colossal squid is a mainstay of its diet and it takes larger squid on average than sperm whales. Now it is possible that southern sleeper sharks were simply scavenging these large squid but consider that we have evidence of southern sleeper sharks taking on the largest mammalian carnivoran of all time - the southern elephant seal.

Now whether or not attempted attacks on elephant seals by southern sleeper sharks are ever successful is debatable - but given colossal squids' adaptation as a very slow, drifter I think we should consider sleeper sharks as a predator of even large adult individuals. Regardless, data does not suggest southern sleeper sharks even range  far enough south into the habit of Antarctic toothfish. And, although data is lacking, maybe toss in killer whales and various pinnipeds as potential predators of colossal squid - especially elephant seals, southern fur seals, and leopard seals.

But there is another possibility, one that both the authors of the study and the deep sea news out-right dismiss, that the Antarctic toothfish bit those arms off of a healthy colossal squid itself.

The reason why they assume that these remains do not evince a predation event is that the colossal squid is larger and that the teeth of a toothfish are ill-equipped to wreak such carnage i.e. "too needle like". Let's unpack this a bit.

Colossal Squid (c) Alexander Remeslo
Above is nice hefty colossal squid specimen photo provided to me by Alexander Remeslo. It is probably not too dissimilar in size to the specimen that was partially consumed by the toothfish as discussed above. Again, keep in mind that these were very slow, unathletic predators.

Patagonian Toothfish (c) Alexander Remeslo
And above is a good sized Patagonian toothfish (very similar to the Antarctic species) . In my mind a fish of that size, with that musculature, with those teeth could easily take off a couple of tentacles from a large colossal squid by simply grabbing and shaking/spinning. I have discussed this issue before with respect to marine predators (esp long necked plesiosaurs) just because you do not have large, serrated teeth does not imply that you can not break apart large carcasses. Look at a crocodile death roll, or any number of eel species wrenching apart carcasses (including large cephalopods), or bichir fish in your home aquarium. If you have conical non-serrated teeth, a long muscular torso, and the bite to match - simply get the leverage right and rotational torsion does the rest.

To prime your mind just a bit just watch this insane clip below to see what a group of (smaller) Chinaman Leatherjacket (Nelusetta ayraud) do to a larger octopus that they corner.

When I watch some of the plethora of online videos showing toothfish longlining hauls they all seem to be of the same size class... do we know if toothfish travel in schools? If so that would tip the scale a bit in favor of a fish that has to deal with several potential Antarctic predators and also maybe suggest a way to tackle large prey...

And finally let's keep in mind that colossal squid are not top predators but better characterized as mesopredators and are prey for sperm whales among others. It would make sense for such a slow moving animal to develop defensive strategies such as jettisoning off one or more tentacles when bit by a predator, like this squid species does. Anecdotally I see this a lot when looking at interactions between large cephalopods and predators - remember some of the first video evidence of Architeuthis showed individuals missing one or more tentacles - it could be a very common tactic used by cephalopods to distract predators...

Giant squid missing two largest tentacles
Giant squid washed up in Japan. missing both large tentacles

Should we be so surprised that a fish that is often compared to sharks does a shark like thing? That in the icy depths an exceptionally old, experienced toothfish had suffered enough from its cephalopod tyrants and took the fight to a colossal squid and decided that hey I am going to take some of your arms off today how do you like me now?

I have not yet mentioned that the name of the paper by Remeslo et al. is titled Alien Vs. Predator: Interactions between the colossal squid (Mesonychoteuthis hamiltoni) and the Antarctic toothfish (Dissostichus mawsoni) Journal of Natural History (2015). That is of course an awesome title and the allusion to color changing in the predator and cephalopods should be recognized. But in the cold Antarctic depths we best imagine this battle played out in super slow motion unlike the hyper speed assault of the fictionalized version. A gelatinous blob with a ridiculously slow metabolism begat by a much smaller fish that bleeds clear blood with only an incipiently faster pace of life. A slow motion clash of fin, tentacle, tooth and beak.

And an ecological association we are only beginning to get a handle on just as the cast of players in the Antarctic and sub-Antarctic oceans might be changing radically due to climate change.

(c) Alexander Remeslo

Special thanks to Alexander Remeslov for his kind correspondence and generous sharing of imagery.

Wednesday, June 24, 2015

Do Drought Prone Beaver Populations Aestivate?

As some of my readers know I maintain a blog about both paleontology (antediluviansalad.blogspot) and beavers (southlandbeaver.blogspot). This post gives me a chance to actually merge the two blogs a bit!!


Take a second to watch the video I posted above. It is an exquisitely preserved synchotron rendered 3-D preservation of two Triassic animals; a stem amphibian Broomistega; and a stem mammal therapsid Thrinaxodon. The most parsimonious interpretation that the authors of the paper in question (link Fernandez V, Abdala F, Carlson KJ, Cook DC, Rubidge BS, Yates A, et al. (2013) Synchrotron Reveals Early Triassic Odd Couple: Injured Amphibian and Aestivating Therapsid Share Burrow. PLoS ONE 8(6): e64978. doi:10.1371/journal.pone.0064978) come to is that the two organisms coexisted in a burrow to survive a harrowing drought. Such a tactic is widespread in organisms that must persist through both seasonally cold and/or hot/dry conditions. Metabolism can be slowed a bit and even enter a state of torpor, or more appropriately termed in the dry season aestivation - which is pretty much the equivalent of winter hibernation. Now trying to parcel out where the distinction lies between rest, sleep, torpor, hibernation, aestivation is a hard nut to crack. Truth be told all these phases are probably best understood on a continuum from rest < sleep  < torpor < hibernation/aestivation <  dormancy.

Broomistega (grey) & Thrinaxodon(brown) preserved in burrow credit Fernandez 2013

From the paper:

Now hopefully the connection does not go over your head. As a putative "mammal ancestor" modern mammals share this genetic legacy of "torpor" which is still often used in many modern mammals - even primates - and which may have even allowed mammals to survive the Cretaceous mass extinction while non-avian dinosaurs did not.

And now onto the beaver part.....

Several years ago when I first started to get interested in beaver in California and other arid places one of my chief stumbling blocks was trying to grapple with the idea of putting such a water dependent critter into a habitat where water has a very ephemeral presence on the landscape. This was of course before I got into contact with Rick Lanman, Heidi Perryman and other beaver notaries and discovered that beaver not only can live in such areas but are doing so right now in places such as the Mojave River in San Bernardino county socal (here and here), Santa Margarita River in Orange/San Diego counties (here), and various river systems throughout Arizona/Nevada/Utah/and New Mexico.

And, among many others, the river system I am most familiar with in regards to beaver in arid lands: the Santa Ynez river in Santa Barbara county which I have covered extensively (herehereherehereherehere, and here). Based on my personal observations, communications, and GEOlocate mapping viewings the Santa Ynez beaver population might be in the hundreds or even more despite the fact that the river system is highly augmented by human flow discharges from Cachuma Lake and is prone to all the flooding/droughts/ and water shortages that characterize a river system in coastal central/southern California.

Long story short even in the best of years the river runs mainly dry during several months of the year and during drought times (as we are in now) the river might be mainly dry from May to late August/September (if Cachuma does a late season water release for downstream senior water rights entitled farmers). We are, at a minimum, looking at 4-5 months of dry river.

How do beaver survive in conditions waffling between this,

and this?

Now I have had a lot of pet hypotheses that I have been spinning around to explain this anachronism; Maybe beavers migrate downstream or upstream to areas of permanent discharge from wastewater treatment plants downstream or mandatory steelhead discharges from Cachuma upsteamMaybe beaver are not as territorial here and share these resources in drought timesMaybe they relocate to the several golf ponds on surrounding golf courses. 

But all of these hypotheses have their problems. Beaver are known to be terrritorial. Golf ponds do not line the whole river. And even if they did relocate up/downsteam that is still a trek of several dozens of kilometers for the beaver in the center of river course. And then this trek has to be done with kits in tow because kits stay with their parents for several years. This would be a very hazardous risk due to the abundant predators of the river: there are for sure bobcats, coyotes, and cougar - probably black bear too. I have seen predator track/activity such as this gnarled mule deer spine in the river bed.

likely predator activity, probably coyote. mule deer spine Santa Ynez River
I now think all those ideas are too flawed and what makes most sense to me is this: beaver along the Santa Ynez - and probably most arid condition beaver populations - hunker down in their bank burrows and go into a bit of torpor. They probably don't aestivate to the true definition of the word which is basically a summer version of hibernation - and we know that beaver do not hibernate.

Probably the best summary of known beaver "thermoregulatory" tactics is the one on the USDA page on beaver (Baker & Hill 2003 pdf link):

In a sense arid beaver simply "flip the script" in the parlance of the time and do what beaver do in winter in high latitude/frost prone areas of the range except that they do it in the summer as opposed to the winter. As most beaver in arid areas dig bank burrows this makes for more of cool temperature thermal refuge to inhibit water loss. Note that lodges - made of wood usually - would still swelter in the sun but several feet underground is a much cooler refuge. If beaver can position their burrow next to a small pool of water - either dug into the substrate or provided for by human activities - this provides a pool for defecation and drinking (eww I know both in the same pool). And if the the beaver can stockpile a food source or be close enough to find some forage this will provide the sustenance. But all in all I think beaver strategy is to hunker down, eat very little, drink very little, survive on fat, and most of all just stay out of sight as much as possible to avoid predator attention. A waiting game for the water which I fully think beaver are capable of.

And I have some photographs/videos to embellish my case:

from July 2014

Now this fetid pool was the last bit of water in an area usually brimming with beaver activity. If you look closely you can make out two probable bank burrows. You will also notice several logs/branches on the ground. The outer bark is chewed off and note that the tree above - which more or denotes how high the water would usually be here - has its outer bark chewed off. Again I don't think beaver eat very much in this period - probably only enough to keep their intestinal biome optimized - but live off fat stored in their body and especially their tail.

I believe the depth of this pool is maintained by the beavers themselves to serve as a water reserve during the drought. This area of the river is full of rocks and since this pool occurs on a very rocky/cobbly part of the river these beaver are actively moving the rocks out of this deep part to dam up other parts. It should also not go unnoticed that this deepening of the channel - some claim beaver do the opposite but I disagree here - would serve as a nice cold water refuge for salmonids in years where drought was not so intense. Unfortunately non-native bullfrog are fully established in this stretch of the river and that is all I saw in this pool were goobly-gobbly looking bullfrog tadpoles.

Rock dam near bank burrow and deep pool

Above is a video I shot showing this same area in April of that same year showing this pool in higher water times when I already suspected the usage here. You will note the two leaning trees that you can see in the pic above. I sound a little wheezy because at the time I was suffering a bit of iron deficiency.

And some beaver burrows upriver - remember this is in April of a drought year - so when I went back this area was completely dried up as you can see in the 2nd dry season pic above.

And then there was the documentation on the San Pedro River of Arizona of beaver, bank burrow, and small dug out pool that I covered before here.

Desert Beavers on San Pedro River AZ
And astute beaver readers can probably recall a none too dissimilar situation of a beaver bunkering down on the Guadalupe River of Santa Clara county in drought conditions surviving off of a leaky culvert which I read about on Heidi Perryman's Martinez Beavers blog.

Dry Guadalupe Summer 2014 credit Roger Castillo
Beaver Gnawed Cottonwood on Dry Guadalupe credit Steve Holmes
Water culvert exploiting Guadalupe beaver credit Gred Kerekez (c)
Reed bed w/beaver in cool/hidden spot w/water nearby from culvert

So in conclusion I doubt arid adapted beaver aestivate in the truest sense of the word but by just slowing things down a bit, bunkering down in a cool burrow, and sequestering away a source of water and just enough food beaver can find a way to squeeze through dry spells. Again, as discussed in the paleo paper on stem amphibians/mammals in arid climes this adaptation need not necessitate a strong drop in metabolism in line with true aestivation but it can significantly aide in resource poor/hot environments. And this is not a radical new adaptation for this species - it is simply the inverse of what northern/cold climate beaver do. Instead of buckling down for a couple months in the winter time arid adapted beaver adopt this behavior in the summer.

Dried beaver pond. Santa Ynez River

and nile crocodiles digging into and surviving in caves dug into river banks to survive drought in Africa just because....

Sunday, June 21, 2015

Triassic Systems Collapse

Time for nice, happy upbeat post that is going to reassure you that everything is going to be all right for us here on little ol' planet earth - NOT!!! Heed the dire proclamations sallying forth from scientists and,  even religious leaders, who have their ear to the ground concerning imminent systems collapse of both natural and artificial systems on earth. As a man wiser tham me once said: "history does not repeat itself, but it certainly rhymes."

The impetus for this post is a paper recently published in the Proceedings of the National Academy of Sciences (PNAS) Extreme Ecosystem Instability Suppressed Tropical Dinosaur Dominance Whiteside et. al. 2015. Popular write up here with depressing comments from climate change denier nutters.

The central question at hand and which guided this study is why do low latitude late Triassic formations   lack herbivorous dinosaurs while higher latitude formations document them?

To address this intriguing question the authors took a multi-proxy approach looking at numerous lines of evidence including pollen (palynology), carbon isotopes, sedimentary evidence, CO2 levels, and species composition of the famed Chinle formation of Western North America (including Coelophysis Ghost Ranch quarry).

What they found of is nothing short of a violently oscillating ecosystem that, they suggest, was incapable of supporting large bodied, fast growing, high metabolic dinosaur herbivores (a tenable assumption that they make regarding high metabolism). Instead a paucity of relatively small bodied theropods coexisted with a dominant fauna of pseudosuchian archosauriformes or as I used to hear them more often referred to as - thecodonts. You know your phytosaurs, rynchosaurs, aetosaurs, rauisuchians and other quasi croc-like beasties of lore which the authors assume a deliberately more slow paced metabolism (and therefore better able to endure unstable/extreme environments).

credit Victor Leshyk
A decidedly harsh world with CO2 levels three to four times above modern levels. From the paper:
"One of the major predictions of models of elevated atmospheric CO2 levels is the increased frequency and magnitude of events comprising very high temperatures, an enhanced hydrological cycle, and increased precipitation extremes" and such "climate extremes might be expected to profoundly influence biogeographic patterns".

In a world already likely dominated by world wide mega-monsoon the vicissitudes of low latitude Triassic climatic conditions created a tinder box condition that may have ultimately proven incapable of supporting abundant, tachymetabolic large herbivores. In a generally semiarid climate intense bouts of rain - likely leading to extreme flooding and weathering - may have spurred on abundant plant growth. But this set up a surplus of material that, when the intense heat coupled with crippling drought arrived, created a perfect set up for intense and wide ranging fires which the authors found abundant evidence for in the form of preserved charcoal. To add in my own personal 2 cents if we assume that weather patterns were likely cyclical such environments may have seen years, decades, or even centuries of slightly more humid conditions (which is why there was big trees preserved at the petrified forest) but which were likewise countered by equally long periods of drought conditions. Such conditions, the authors maintain, would have proven too unstable and inconsistent to allow populations of large herbivorous dinosaurs.

Lead author Jessica Whiteside: "Our findings demonstrate that the tropical climate swung wildly with extremes of drought and intense heat," and that the intense wildfires "swept the landscape," which constantly "reshaped the vegetation available".

Now the situation in the Chinle makes a little bit more sense to me with a fauna largely dominated by archosaurs with a smattering of small predatory dinosaurs. What I personally am intrigued by is the dominance of phytosaurs - water loving crocodile mimics - in the drought prone Chinle. But hey, you can still have large river systems in arid continents. And one can imagine that when it poured it really poured on Pangea. And with the continents still amassed in large blocks when the interior of these large land masses got inundated with large monsoonal rains and if we presume large swaths devoid of vegetation or fire decimated then that rain is going to create torrential rivers when they do run.

It does beg the question in my mind - and it is a question I hope to revisit in future posts - what sort of coping mechanisms did phytosaurs and other Triassic archosaurs have to deal with such climatic oscillations. If their water supply dried out could they aestivate for long periods of time? Maybe even years buried in drying mud with only that nostril opening on the top of the skull sticking out to breathe? What about the giant amphibious temnospondyls?

Nile Croc Caves of Katuma River

Now you can take what you want from this study. It would be remiss of me not to mention the obvious parallels in the situation faced by Triassic dinosaurs with the situation faced by an extant bipedal, dominant, high energy demanding hominid living in the tropics in a regime of increased climatic, ecological, and political systems collapse.

* Humble boast time, just broke 300,000 page views. I have a lot more stuff to post on in the nearish future and am pleased with many requesting/asking about if I will cover certain topics. Unfortunately due to this thing called life it will be a little quiet around here in the next month - I will be doing field work on beavers in Monterey county on the Arroyo Seco creek. If you don't know already beaver in California is a topic of intense interest to me which I discuss on my other blog southlandbeaver.blogspot Anyways if I was getting paid to write this blog I would have a lot more time to devote to it and would love to do it full time. But you know the story money is allergic to the topic of paleontology - unless you create a fictionalized monster movie full of cliches then it falls like mana from the sky.

Cheers and don't worry I have more plesiosaur machinations, dinosaur ecology, and Spino stuff planned but don't be surprised if it takes me until August!!

Friday, June 12, 2015

Plesiosaur Machinations X: Senior Water Rights

Brontosaurus credit Charles R. Knight wiki
When I ponder long necked plesiosaurs, especially the stupendous elasmosaurids, my mind can't help but wander towards the other notable clan of Mesozoic long necked beasties - sauropods. Now obviously the differences between these two are profound in terms of ecology, habitat, and evolutionary history. However where I do think a congruence can be made between these two groups is in terms of the history of opinion - both popular and professional - of these two long necked dynasties.

Dr. Robert Bakker. wiki commons

I do remember once hearing a profound Bakkerian quote from of course the inimitable Robert Bakker on dinosaurs in some dino doc I can't recall, to paraphrase; "There is a lot of explaining away going on with dinosaurs."

Now to focus on sauropods in particular let's look at how this group, right or wrong, has been "explained away" in particular throughout their history of study.

"They are so big and heavy that they could not support their weight on land".... 
"With their puny teeth and head they could only subsist on soft water plant mush".... 
"The preposterously long necks were a failed evolutionary experiment, dooming sauropods to evolutionary and ecological insignificance"....
"Their huge bulk and long ungainly neck limited them in maneuverability and they were easy pickings for any predator"....
"They could not raise their heads and neck above horizontal due to constraints imposed on the circulatory system getting enough blood to the head"....
"Sauropods were replaced by more sophisticated ornithischian herbivores in the Cretaceous"...

Now any student of sauropod knowledge should be aware that almost all of these claims have serious problems with them - and this "explaining away" of sauropods - especially by noted researchers - has throughout the history of thought on this group really established a number of pitfalls in arriving at the more nuanced understanding of this group that we have today. But what should not go unnoticed is that, with an economy of word change, almost all of these once cherished dogmatic"truisms" for sauropods, that have been more or less discounted over time, can be applied to plesiosaurs. And just how sauropods were often "explained away" despite their prolonged and spectacular evolutionary success so, likewise, have plesiosaurs been "explained away" despite their even longer relative tenure in the oceans.

"With their puny teeth and jaws, long necked plesiosaur could only subsist on small, soft bodied fish and squid"....
"The absurd necks of plesiosaurs, and especially elasmosaurs, were a failed evolutionary experiment - condemning them to ecological and evolutionary insignificance"....
"Their slow swimming speed, lack of maneuverability, and long vulnerable necks left them vulnerable to predators"....
"The plesiosaur neck was so stiff, weak, and inflexible that it imposed a significant burden on these animals for survival"....
"Plesiosaurs were replaced by the more advanced, aggressive, and dominant mosasaurs at the end of the Mesozoic"....

All right so a lot of the above interpretations I have dealt with before on several posts - especially concerning a wider foraging scope and potential defensive strategies - for this post I want to unpack that last one, a claim often made of plesiosaurs, that "plesiosaurs were replaced by the more advanced, aggressive, and dominant mosasaurs at the end of the Cretaceous".

As a bit of a primer let us address the claim which was often made of sauropods in the Cretaceous - that they were replaced by more advanced ornithischian herbivores (namely hadrosaurids and ceratopsids). This has been shown to be a complete farce with the advent of a more global survey of Cretaceous dinosaur faunas. Sauropods, most importantly the titanosaurs, actually held sway in Gondwana throughout the Cretaceous. It is in fact Laurasia, especially Laramidia, that is the anomaly with it's aberrant fauna of diverse ceratopsids and hadrosaurids. Take a trip to Maastrichtian Gondwana and you are going to be looking at sauropod dominated habitats. It has also been increasingly recognized that titanosaurs were making inroads into Laurasia by the end of the Cretaceous reclaiming lost territory. In retrospect it is not too difficult to parcel out why this paleontological faux pas occurred - some of the best Cretaceous dinosaur formations and most qualified researchers/amateurs/collectors of the time hailed from North America. Therefore the ornthischian dominated faunas of North America, especially Laramidia, were held up as the standard for what Cretaceous faunas looked like world wide - American exceptionalism. Time has not borne this idea out.

While the unique North American "Laramidia" fauna historically dominated much of our concept of what Cretaceous dinosaur fuanas "should" look like it is the Great Western Interior Sea that has most dominated thought on what late Cretaceous marine ecosystems "should" look like. And the biggest signal we get from the GWIS is that it was mosasaur country. Mike Everhart has documented the dominance of mosasaurs in the GWIS very well in several papers and articles on his Oceans of Kansas web site. Elasmosaurs, although present in the GWIS, typically form only a minority of the fossils pulled from the ground there - often attributed as 1% of the fauna by Everhart and others. Go further south along the gulf, Alabama, and the situation does not improve for elasmosaurs and mosasaurs are spilling out of the ground everywhere.

Some "medium" sized mosasaurs c/o Memo Koseman, from top-bottom Platecarpus,
Clidastes, Plioplatecarpus, Halisaurus. used w/permission
Does this pattern suggest that mosasaurs were replacing elasmosaurs on a world wide scale? As discussed earlier with the pitfalls regarding sauropods supposedly diminishing due to advanced ornithischians in the Cretaceous we should be cautious not to ascribe too much weight to this idea based on just one locality. What can other formations tell us about elasmosaur abundance/diversity waning at the end of the Cretaceous?

Maastrichtian Californian Elasmosaurs

What do we see on the other side of Laramidia along the putative coast of California (largely submerged) along the west coast of Laramidia? Wait, let's back up a bit - are you aware that California boasts a fairly decent roster of late Cretaceous marine reptiles? Yup even in the waning Cretaceous period going surfing in California was not without risk of being "tasted" by toothy predators. The best formation for marine reptiles is the Moreno formation of the San Jauquin valley representing a good transition from the Maastrichtian into the early Eocene. And just as the California coast today boasts significant upwelling of cold nutrient rich waters furnishing a robust food chain that attracts large pelagic megafauna - including blue whales - the proto-California coast (which would have been more inland coming against the rising Sierras) also seems to have been a productive area of upwelling hosting pelagic megafauna. We know this, because um well oil. From the abstract (AAPG, C. Fonseca 1996) "The hydrogen rich organic matter, high amount of biogenic silica and diatom assemblage in the Marca Shale (Moreno formation), indicate the latest Cretaceous coastal upwelling along the California margin resembles analog systems described from Recent and Neogene deposits along the Pacific coasts of North and South America." So it appears that during the latest Cretaceous early California already was characterized by the high productivity we see today. Additionally anoxic conditions were frequent (AAPG, C. Fonseca May 1996). Dedicated readers should recall that I suggested persistent bouts of anoxia inhibited large gill breathing predators (esp. sharks) allowing marine reptiles advantage to forage in such zones, especially as scavengers during mass die offs (Plesiosaur Machinations IV: He Is the Last You'll Know...).

Upwelling creates the conditions that puts dinosaurs in whale mouths. link
Humpback whales, Heermann's Gulls, Brown Pelicans. credit Connie Tran.
San Luis  Harbor CA
note the brown pelican stuck in jaws of whale
So what do we see regarding marine reptiles here? Well there is always suggestions of higher diversity in mosasaurs, indeed a lot of work needs doing in the Moreno, but we have at least two genera, representing three species; Plesiotylosaurus crassidens which looks like a bit of a generalist decent sized mosasaur although I have heard it suggested as a turtle specialist (there were three marine turtles in the Moreno at least); and at least two species of Plotosaurus - P. bennisoni & P. tuckerii. Plotosaurus is often recognized as the most advanced mosasaur, seemingly caught in the act of trying to mimic advanced ichthyosaurs both in form and likely function.

I really like Ken Kirkland's take on Plotosaurus bennisoni. Kirkland does the illustrations for the book Dinosaurs and Other Mesozoic Reptiles of California which was a useful reference for this post. Especially fond of the incipient dorsal fin. Hey, why not? Tetrapods that return to the water converge on a number of anatomical features.

Plotosaurs bennisoni. (c) Ken Kirkland
And what of the plesiosaurs? There are no polycotylids described (but maybe in the future?) and large morph "pliosaurs" seem to have bitten the dust a while ago. But elasmosaurids abound. Most references point to at least 4 genera (although w/plesiosaur taxonomy!?!) with several known from great remains; Aphrosaurus furlongi from some fairly sparse postcranial remains; Fresnosaurus drescheri named after Fresno county and simultaneously the coolest thing from Fresno county - also scrappy, postcranial; Morenosaurus stocki some pretty good remains, only missing the head and bits of paddles - on display at LACMNH; and the cream of the crop, and actually one of the best preserved elasmosaurs known, Hydrotherosaurs alexandrae remains including most of the skeleton including the snaggle toothed skull!! Remember I featured Hydrotherosaurus in my illustration for my first machination Introducing the Plesiosaur Phalanx Attack.

In fairness it should be noted that all four elasmosaurs were discovered and named by one individual Samuel Paul Welles in just one year!! Could there be a little redundancy here in number of species or genera?  Most likely. However we still have more and better specimens of elasmosaurs than mosasaurs in the Moreno. Elasmosaurs were kicking butt right here when they should be at their lowest if we accept the premise that mosasaurs were outcompeting them. At least in California  elasmosaurs seem to be doing better than mosasaurs!! (BTW the title of this post, senior water rights, is a play on the divisive rights to water that early settlers of CA maintain - from groundwater or  river diversion - to this day in spite of our crippling drought.)

Instead let me suggest that we flip the script. Elasmosaurs held the longer tenure in the oceans and were better adapted to aquatic life than the relative new comers the mosasaurs. Elasmosaurs were choosing the best places to live in terms of ocean productivity. Let the mosasaurs have the warm shallow epicontinental seas, elasmosaurs like the cooler, richer, and deeper waters of continental shelfs i.e. areas of active oceanic upwelling. This idea of linking to elasmosaurs to areas of upwelling has been suggested before and I happen to endorse it. We will revisit it later.

Northern Plesiosaurs of the GWIS

Technically still part of the GWIS Canada's Bearpaw Formation, sometimes referred to as the Bearpaw Sea, My first real exposure to this interesting body of water was via - Dale Russell and his epic tome "An Odyssey in Time - Dinosaurs of North America". A book, though largely outdated in terms of dino science, does not get the credit it deserves for immersive text and attention to paleoecology. And despite the name of the book there is ample attention paid to the inland seas of North America with special reference to the marine reptiles (and Dale Russell has done a lot of mosasaur work too). With regards to plesiosaurs in the famed Kansas chalk of the GWIS Dale notes: "Only 1 percent of all the skeletal fragments of backboned animals belonged to plesiosaurs... Their skeletons are so uncommon in the chalk that those that have been preserved may have belonged to animals that were only migrating through the midcontinental sea (pp. 132)." This idea that plesiosaurs used the GWIS as a migration corridor is an idea that I have mentioned before and one that I happen to subscribe to. It is not without analogy given the many species of marine mammals that migrate to more equitable climes to give birth. Things get a little more interesting Dale notes as our gaze shifts northward to what is now known as the Smoking Hills Formation located in the northern territories near what is now the edge of the Beaufort Sea: "Platecarpus is the only known mosasaur, and Clidastes and Tylosaurus are either rare or absent. Plesiosaur remains are three times as abundant as those of mosasaurs, and nearly half of the specimens of air-breathing vertebrates collected belonged to Hesperornis. No remains of pterosaurs or marine turtles have yet been found (pp. 135)."Interesting to note that both sea turtles and mosasaurs are often rare or absent - this leads to suggestions that temperature may have played a role in the sorting of species there. Going further south into Alberta at the famed Dinosaur Provincial Park, which episodically records marine transgressions one of which is the Lethbridge Coal Zone Phil Currie notes that: "The marine reptile assemblage of the Lethbridge Coal Zone differs from that of the Bearpaw Formation in the abundance of plesiosaurs relative to mosasaurs. Although plesiosaurs are present in the Bearpaw formation, mosasaurs are more abundant. The reverse situation is seen in collections from the Lethbridge Coal Zone. This tendency for plesiosaurs to be more abundant in the more coastal settings suggests that elasmosaurid plesiosaurs were typically more coastal in their distributions than were mosasaurs (pp. 497 DPP: A Spectacular Ancient Ecosystem V1)." 

I have to admit that I am not quite sold on elasmosaurs being  primarily coastal as their worldwide distribution does not speak to that. And, has occurred several times when writing these machinations, synchronicity strikes again allowing me to embellish my point of what I think was often going on with their habitat preference. Recently published in Nature (Lea et al. 2015 link) the title pretty much explains it all: Repeated, long-distance migrations by a philopatric predator targeting highly contrasting ecosystems.

Galeocerdo cuvier. Albert Kok. wiki

"... adult males undertake annually repeated, round-trip migrations of over 7,500 km in the northwest Atlantic. Notably, these migrations occurred between the highly disparate ecosystems of Caribbean coral reef regions in winter and high latitude oceanic areas in summer..."

What should be iterated with regards to the tiger shark study is to keep in mind that prevailing thought is that the tiger shark is primarily a shallow water animal of reefs and the continental slope - not the middle of deep ocean basins. But when you think about it should we really be that surprised that a large pelagic animal spends time in several very disparate habitats and often migrates huge distances? Large pelagic animals travelling huge distance through variable habitats seems to be more the rule than the exception if you ask me; numerous cetaceans; pinnipeds; lamniforme sharks, especially noteworthy are white sharks i.e. "white shark cafe" etc etc; sea turtles, especially leatherbacks that target upwelling zones; many large fish, esp tuna. Such a movement pattern may have served numerous benefits for elasmosaurs; optimal temperature ; feeding opportunities; nursery grounds; predator/competitor mitigation. Note the last one is very pertinent with regards mosasaurs.

Size Race Between Mosasaurs and Elasmosaurs?

credit Memo Koseman. Mosasaurs Blowing UP!! you can't handle the thickness from top to bottom Plotosaurus, Hainosaurus, Tylosaurus. used w/permission
Were mosasaurs and elasmosaurids engaged in a bit of a size race in the late Cretaceous? I don't know if this question has been studied in any kind of rigorous way. The largest elasmosaurs do seem to overlap a lot in time and space with the burgeoning in size and diversity mosasaurs. Personally I think young of both groups were not safe from either group. Although we do have evidence of polycotylid plesiosaurs attacked ending up in the belly of mosasaurs, evidence of interaction between the massive elasmosaurs and mosasaurs is minimal. I seem to recall reading about an elasmosaurid paddle showing mosasaur bite marks somewhere but can't find the reference now, help anyone? Because mosasaurs tend to go for prey that they can swallow I don't think that large elasmosaurs were thought of as prey by most mosasaurs. But then again when I look at the maw of Hainosaurus I could imagine it choking down a pretty good sized elasmosaur of maybe 4-5 meters?

Elasmosaurus replica. credit Black Hills Institute

And if we look at the Late Cretaceous and elasmosaur size there were some absolute bruisers in size. Elasmosaurus is usually quoted as the "largest" elasmosaur but I would caution with such sample sizes as we have and simply point out that there was a variety of late Cretaceous elasmosaurs that probably clustered in the 10-14 meter range and several tons of mass; Elasmosaurus in the Campanian; Hydrotherosaurus Maastrichtian of California; Futabasaurus Santonian Japan; Mauisaurus Haumurian(?) New Zealand. Killing a large adult elasmosaur was likely no easy task. And the significant teeth and bite of large elasmosaurs coupled with the distinct possibility of social defense was likely a significant deterrent to predators. More so than that visual predators could not afford to have damage sustained to, let's say an eye, from a deft elasmosaurid defensive strike from that capable neck.

Worldwide Maastrichtian Elasmosaur

I wanted to focus on these North American occurrences in particular because they are the most well studied. Turns out elasmosaurs are known from many places in the Maastrichtian - again not what we should expect if mosasaurs were displacing them. But if I can outsource my argument a bit I want to point to an obscure published "bulletin" that gives a pretty good review of elasmosaur distribution in the curtain call of the Cretaceous - the Maastrichtian. Elasmosaur Remains from the Maastrichtian type area, and a Review of latest Cretaceous Elasmosaurs (Reptilia, Plesiosauroidea) Mulder et al, 2000. Bulletin of Institut Des Sciences. pdf available online. In addition to what I have mentioned in California there are worldwide remains of elasmosaurs present in the Maastrichtian. Mulder et al. argue that the distribution and abundance of elasmosaurs was tied to upwelling and not to, as Bakker has argued, "dense algal forests" inhibiting their movements. So what Bakker has suggested is that basically kelp forests impeded elasmosaur movements in some areas. Kelp forests that we have no evidence for. Mulder et al. : "However, whether submarine vegetation barred plesiosaurs from epicontinental seas remains to be seen. The occurrence of plesiosaurs related to abundance of prey in oceanic upwelling areas is at least as plausible an explanation." and "From the distribution of Maastrichtian elasmosaurids worldwide it may be cocluded that , like mosasaurs, elasmosaurids were still widespread and diversified during the latest Maastrichtian... Even if precise stratigraphical extensions are often difficult to obtain for large vertebrate remains the extinction of elasmosaurids at the K/T boundary thus appears to be sudden rather than gradual."

So yeah, I agree with Mulder et. al. over Bakker at least here (see - I am not a total Bakker fan boy). Isn't it often said that great white sharks do not swim or hunt within kelp forests (interesting discussion)? And this pattern is what we see today with many of the oceans most dynamic and wide ranging high trophic consumers. Numerous whales, great white sharks, leatherback sea turtles, elephant seals - they all migrate vast distances to nursery grounds and/or high quality feeding grounds. The paucity of elasmosaur remains in many areas speaks to their ephemeral occurrence in these areas as they are simply passing through to more choice habitats. While mosasaurs were becoming more specialized towards the end of the Cretaceous to suggest that they were displacing elasmosaurs is not borne out by the evidence of plesiosaurs coexisting alongside mosasaurs for over 35 million years right up until the end of the Cretaceous.

Again moral of the post - where elasmosaurs are found seems to be correlated with upwelling and not mosasaur exclusion (not my idea but I agree with it). Certainly not an exhaustive survey on the subject but hopefully this post encapsulates the argument well enough.

And so to illustrate the bad-assery of elasmosaurs holding their own against the sea-lizards I depicted what is probably the second most iconic prehistoric clash after T-rex and Triceratops, a hypothetical encounter between a bivouac of Elasmosaurus platyurus and a marauding pair of Tylosaurus proriger. I imagine the mosasaurs travelling northward as the southern portions of the interior sea dries up. The elasmosaurs are holding up in a nice, productive rudistid reef full of tasty chondricthyans, shellfish, colonial crinoids, and crustaceans to eat in the Bearpaw Sea. The elasmosaurs do not take kindly to the sea lizards' intrusions and let them know their displeasure in no uncertainty.

How come no one draws this match up anymore?

credit Duane Nash

A quick note on reef like benthic structures and fauna. Rudistids are an under utilized reference for depictions of Cretaceous reefs. That is probably because good depictions are lacking. I used this page from Smithsonian and took some highly liberal interpretations regarding size. But they do add sort of an alien, "Gigeresque" sensibility.

"Elevator" Rudists. credit Mary Parrish/Smithsonian

"Recliner" Rudists. credit Mary Parrish/Smithsonian
credit Mary Parrish. Smithsonia
And those jellyfish looking animals getting disturbed are actually colonial crinoids that were free swimming. Did you know that even some seemingly sessile crinoids get up and swim around?

Colonial Crinoid GWIS. Mike Everhart credit


Tylosaurus vs Elasmosaurs. credit Zdeneck Burian

Related Posts Plugin for WordPress, Blogger...