Thus Spoke Zarafasaura

Seriously I need to start a plesiosaur legal defense fund. What other group of Mesozoic beasties has suffered such a profound and jarring hit to their reputation? Once depicted as worthy and regal denizens of the deep, able to hold their own against the other Mesozoic marine reptiles - everywhere I look now

Hawkins demonic plesiosaurs battling other sea monsters in eternal darkness. nice

all I see are pictures of plesiosaurs getting rag dolled by mosasaurs or decapitated by pliosaurs. Seriously its like everyone in the ocean is just taking out plesiosaurs left and right as if they were blundering insults to Darwinian evolution.

From Hero to Zero

Well I say it is high time we turn back these insults to plesiosaurs. 

Don't get me wrong we actually do know plesiosaurs were preyed upon. I just think all this violence perpetrated upon plesiosaurs glosses over the very real and very impressive predatory arsenal they had at their disposal. You heard me right plesiosaurs had an impressive predatory arsenal.

I think first and foremost this emerging image of plesiosaurs as little more than cannon fodder for the more impressive macropredatory saurians it shared the ocean with has a lot to do with two prevailing notions; that (1) long necked plesiosaurs (plesiosauromorphs) are often considered a bit "samey" and; (2) they are considered gape limited (can't expand their lower jaw out) predators of small prey (i.e. basically fish no longer than 20" for the largest elasmosaurids).

Well with regards to number #1 that they are a bit "samey" this is quickly discredited upon actually looking at the surprising diversity in both tooth/jaw morphology. Yes there were slight, fine toothed plesiosaurs - that potentially even sieved small prey out of the water/sediment - but at the other end of the spectrum there were some impressively toothed and jawed species that speak to a more robust capacity for predation. Which gets me to #2 that plesiosauromorphs were severely limited to a prey base of only smaller fish and cephalopods.

In order to challenge #2 I want to invoke a little heralded elasmosaurid from the Maastrichtian (Upper Cretaceous) pbosphate rocks of Morocco: Zarafasaura oceanis (Paper 2013 Lomax & Wahl). I just want you to take a good look at the skull; the robust mandible; strong piercing dentition; large temporal (jaw closing muscle) area; brevirostrine morphology. This was the bulldog of the elasmosaurids. 

Lomax & Wahl 2013. scale bar 10 cm

Lomax & Wahl 2013. scale bar 20 cm

Are you really confident that this was a mere predator of only small fish and cephalopods - harmless to anything bigger? So confident that you would go for a swim with it? Are you sure that sauropterygian brain would not take an opportunistic lunge at you? Or even worse if it travelled and fed in groups (a distinct possibility given live birth for this group) that you might meet your fate in a spectacularly gruesome Mesozoic version of being "drawn and quartered" by several  20 foot long sauropterygians?

What I think gets left out of the discussion with regards to prey dismemberment in carnivores that operate at 1 g versus carnivores that operate in water is the differing physics of each realm. In the water as food is being shook, rolled, or twisted the water itself acts as resistance to such movement. This higher viscosity of water compared to air allows the consumer to gain leverage and further increase the damage and bodily insults to the food item as it is being shook about violently in any number of ways (yanking, rolling, twisting). This extra bit of leverage that aquatic predators can use to dismember food is put to good use by various sharks, fish, eels, crocodiles and other critters. And as I have discussed before I think a number of long necked plesiosauromorphs may have engaged in food dismemberment strategies - including cooperative feeding/dismemberment and twist/rotational feeding - to increase the size envelop of food items that they can consume.

Neck flexibility is a tricky thing in plesiosaurs. They could not likely do the graceful "S" snake like strike pose but dorso-ventral flexibility of the amount pictured above by Mark Evans is possible give or take a bit depending on how much intervertebral cartilage was present. But for our purposes here the diagram above is useful in imaging how such animals may have used the puncture/pierce type teeth, long neck, and heavy rigid torso to get bite sized chunks off of  carcasses. 

1) Establish a good securing bite.

2) With neck extended and heavy torso acting as fulcrum/pivot point/ballast - yank neck away from food item. If flesh is soft and/or rotten this step might not even be needed. 

3) Conspecifics and/or water viscosity aids in leveraging off a bite size morsel. 

4) Swallow, rinse, & repeat

Is there any evidence for Zarafasaurus oceani engaging in rugged feeding events? Well maybe... In the paper I linked to earlier (Lomax & Wahl, 2013) there is specific mention of "vertical, serration like marks preserved on the inner side of the left dentary" and the "odd, strong rugosity that surrounds the base of the posterior premaxillary teeth". Picture below of both features.

Lomax & Wahl 2013

Interesting for sure, but nothing definite. Could those vertical serrations suggest habitual feeding of shelled/rugged prey? Ammonites, chondrycthians, turtles or all of the above? Sidedness? Who knows but the rugosities, serrations, and general rugged and robust morphology of the skull and skeleton as a whole suggests a capacity for certain violent feeding activities.

Wiki. CC

But what spurred me on to write about Zarafasaura today, as I have been wanting to write about this guy for a while now, is actually a paper: Mosasaurids (Squamata) form the Maastrichtian phosphates of Morocco: biodiversity, paleobiogeography, and paleoecology based on tooth morphoguilds. Bardett et al. 2014 Gondwana Research Abstract:

Mosasaurid squamates are the most numerically abundant, and taxonomically/ecologically diverse clade of marine amniotes represented in the Maastrichtian Phosphates of Morocco. With few exceptions, they are faunally typical of the Southern Mediterranean Tethys Margin (around palaeolatitude 25°N) and range from the base to the top of the stage. The Moroccan assemblages include at least 7 genera and 10 species representing a broad spectrum of sizes and morphologies that illustrate several ecological trends. Noteworthy is the predominance of Mosasaurinae which are widespread in contemporaneous outcrops worldwide and constitute 80% and 70% of the total genus/species number respectively. In contrast, Halisauromorpha and Russellosaurina (plioplatecarpines) are scarce and tylosaurines are presently unknown. All of the Moroccan mosasaurids exhibit characteristic tooth morphologies and can be placed into resource partitioning morphoguilds indicative of adaptations for piercing, crushing or cutting. Medium to large predators are found to distribute along the ‘Crush’–‘Cut’ axis of the morphoguild projection, and a new ‘Crush–Cut’ guild, previously unrecognised amongst Mesozoic marine amniotes, accommodates severalPrognathodon species. Also of importance is the lack of mosasaurids along the ‘Pierce’–‘Crush’ axis, potentially inferring that these ecological niches were occupied by other marine vertebrates such as selachians and plesiosaurians. In addition, the relative abundance of mosasaurids throughout the Maastrichtian series of the Gantour Basin evidences direct ecological competition or predation phenomena.

Did you catch that sentence towards the end? The one that says "Also of importance is the lack of mosasaurids along the ‘Pierce’–‘Crush’ axis, potentially inferring that these ecological niches were occupied by other marine vertebrates such as selachians and plesiosaurians." 

As the only other plesiosaurians known from the Moroccan phospates are dainty toothed polycotylids, who does that leave but Zarafasaura oceanis?

And as I said earlier we need to stem the tide of plesiosaurs getting man handled so here I drew a mob (siblings?) of Zarafasaura oceanis having a go at the carcass of an immature Ocepochellon bouyi. Did they kill it or scavenge it? You decide.

Putting a little of the alien, evil, otherworldly, Ctulhuish aspect back into plesiosaurs.

Cheers!!

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Laramidia: The Great Dinosaur Species Pump

Recently published in PLoS ONE and viewable online here is a new paper suggesting a mechanism for the incredible diversity of Campanian age Cretaceous dinosaurs in western North America. Because western North America has such a long history of dinosaur excavation and America has long dominated dino science the dinosaur faunas of Late Cretaceous western North America have been assumed to represent the typical dinosaur fauna worldwide. However worldwide dinosaur discoveries have since overturned this notion and Late Cretaceous North America is now seen as the anomalous situation in terms of dinosaur fauna in the global context. As emblematic as tyrannosaurs, ceratopsians and hadrosaurs are- worldwide titanosaur sauropods, derived iguanodonts and abelisaur theropods would have been more typical. And not only is the dinosaur fauna of western North America the strange one, it now appears that the Campanian peak of dinosaur diversity in western North America is a bit of an ecological anomaly in and of itself.

Modern large herbivores are characterized by large geographical ranges often ranging across several ecosystems. Take a look below of the nearly continental range of the African Elephant before large scale human hunting and habitat loss (in grey).

Elephants follow the Jarman-Bell principle in that they are large bodied herbivores and can subsist on relatively low quality fodder- and their range reflects this. However the dinosaurian megaherbivores of Campanian age western North America seem to break all the rules (as dinos often do). Take a look at this map:

A. Late Campanian 75mya B. Late Maastrichtian 65mya

The western "island-continent" of North America in pic A is called Laramidia and is divided by the Pacific Ocean to the west and the Western Interior Seaway to the east. All vying for real estate on Laramidia during Campanian times were up to a dozen rhino sized and up dinosaurian megaherbivores. Dinosaur park in Alberta Canada, for example, documents six to eight large herbivores living synchronously together at various times through the Campanian. Contrast this scenario with what is seen by late Maastrichtian times in pic B where much of the seaway has drained away giving a much larger piece of land to live on. Here we see the iconic "Hell Creek" fauna famous for T-rex and usually containing at most two large herbivores, i.e. a species of Edmontosaur and a species of Triceratops (up in da' salad we do not believe in Torosaurus). Compounding the situation in Laramidia is the recent revelation that there appears to be distinctive north/south faunas of dinosaurs. Recent findings in southern Utah and New Mexico of critters such as Kosmoceratops suggest a division between northern and southern dinosaur faunas in the Campanian that roughly coincides with modern day Colorado and Utah.

Kosmoceratops richarsoni. Copyright Lukas Panzarin

So not only were dino megaherbivores living together in great diversity on Larimidia- these large animals were also showing strong provincialism- individual species were not even spreading across the entire land mass... How ecologically could this be and, more importantly, how did this situation even arise?

What the authors argue is that orogonic activity (mountain building) effected the radiation of large dinosaur herbivore species. Involved are basically two mountain ranges. The first one is the Sevier Mountains which arose in the mid-Cretaceous and trended roughly north-south. Notice also that Laramidia trends north-south. Although a large range, the formation of the Sevier range did not significantly hamper dinosaur movements and there is no great north vs south disparity between dinosaur faunas at the time of its creation. However the Larimide orogonic event, a precursor to the Rocky Mountains, was a game changer. Unlike the Sevier range, these mountains arose longitudinally, east-west. The net effect was to "grid up" the whole of Laramidia, creating numerous small east-west basins hemmed in by ocean on either side. Coincident with the Larimide orogoney is the time of maximal dinosaur species diversity and also evidence of significant north-south provincialism. Long story short geographic barrier is in place and vicariance induced speciation takes over giving us the great species diversity of Campanian dino megaherbivores of Laramidia. When we get into the Maastichtian we see the Rockies start to rise further east, the inland sea drain away, and speciation rate/diversity levels drop off. The dinosaur species pump was turned off by the time of T'-rex.

The authors also speculate that changes in vegetation regimes with elevation/climate would have stifled dino megaherbivore movements between basins. Of course this flies in the face of the notion that all megaberhivores are generalists (something I want to address later)- but I don't dismiss it at face value. Dinos seem to break the rules a lot anyways. And even though there was a much more gradual temperature gradient north-south than in the present- we do see today even in the tropics dramatic changes in vegetation with elevation. Just look at the pic below of Mt. Kinabalu in Borneo, elevation 4, 095 meters (13,435 feet) where you can find alpine and even tundra biomes in tropical latitudes.

It should be noted that the authors concentrated their study on the two main groups of herbivorous dinos in the area- duckbills and horned dinos. This is not to suggest other groups were not following similar trends in radiation of species (dinos or other animals/plants)- its just that the data is best for these guys. Also their head ornamentation allows easy visual discrimination for us and themselves.

One final tid-bit, and this is my conjecture. Many herbivorous dinosaurs show strong nest site fidelity- nesting sites found show evidence they were used for many generations. Two separate populations of the same species with different nesting grounds probably had enough genetic flow between them to maintain species integrity. But now imagine that a mountain range appears that separates the two groups, even if not an impassible one, site fidelity to a nesting ground would further minimize genetic flow between the two populations. And voila- vicariance speciation follows.

Laramidia must have been a strange and wondrous place. A place of incredible diversity, not just of the small but the large as well. Anomalous, even for dinosaur standards, in the ridiculous variety of megafauna cohabiting in time and space. A place where by simply cresting an insignificant mountain pass one might find a whole separate flora/fauna waiting on the other side.

Pertinencia

Dinosaur Boom Linked to Rise of Rocky Mountains
http://www.livescience.com/22116-dinosaur-diversity-rocky-mountain-rise.html

Gates TA, Prieto-Márquez A, Zanno LE (2012) Mountain Building Triggered Late Cretaceous North American Megaherbivore Dinosaur Radiation. PLoS ONE 7(8): e42135. doi:10.1371/journal.pone.0042135

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0042135 

Copyright Sammy @ http://dino-art.blogspot.com/

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