Tet Zoo picture of the day # 25

i-6566f53317bfb8b03b8a0bd5464320df-Bearpaw Marine sample.jpg

My job at Impossible Pictures finished last week (though I am still doing the odd day here and there and am likely to go back to them in the future). Sigh, so much for digging myself out of that immense financial pit I'm still in. Anyway, today I start work on a new job involving... marine reptiles. I'll say more about it in the future. Partly as a result of this, I post here another picture very kindly supplied by Mike Skrepnick, and used with his permission (image © Mike Skrepnick, used with permission). Created for a new mural at Dinosaur Provincial Park, it depicts a scene in the Campanian Bearpaw Sea. We can see a plioplatecarpine mosasaur, assorted sharks and ammonites, and the elasmosaurid plesiosaur Terminonatator ponteixensis, recently described by Sato (2003)...

Terminonatator - the name means 'last swimmer' - is so named as it is the youngest plesiosaur known from the sediments of the North American Western Interior (younger elasmosaurs are known from the western and eastern coasts of North America, as well as from Europe and elsewhere: see Mulder et al. (2000)). Its remains include a very nice articulated skull that is particularly interesting in preserving the impressions of various parts of the brain.

Marine reptiles - and in particular sauropterygians (plesiosaurs and their kin) - are another group that I've hardly touched at Tet Zoo, and again this is something I'd like to remedy (there is an article on Oxford Clay tetrapods at ver 1 here). Planned articles cover giant pliosaurs, leptocleidines, the salvation of Elasmosaurus, and placodonts. It would also be a good idea to cover the whole internal nostril thing: Cruickshank et al. (1991) proposed that plesiosaurs channelled water into the internal nostrils on the palate and 'smelt' the water while it moved through the olfactory chamber. The water would finally exit via the external nostrils on the dorsal surface of the snout. One key feature that led to the proposal of this ingenious system is that the internal nostrils of plesiosaurs are located closer to the snout tip than are the external nostrils*. It all sounds very good and this theory of 'underwater sniffing' has been largely accepted among marine reptile workers: there have been a few challenges to the model (Buchy et al. 2003), but they propose rather more radical interpretations of internal nostril function and don't seem as likely.

* This is also true of some other sauropterygians, like placodonts. Consequently it has been argued that they also snorted in water via the internal nostrils for the purposes of olfaction (Rieppel 2001).

i-7529cb7a6be148aebdd39c1f5135158c-Terminonatator skull.jpg

What makes Terminonatator really interesting, then, is that its internal nostrils are not located further forward than its external nostrils (Sato 2003, p. 95). I know that this is the case in at least one other plesiosaur too - so, were these taxa oddballs that didn't rely on underwater olfaction, or had they developed some other solution to the problem? Thanks to Terminonatator's cerebral impressions, we know that it had an olfactory canal, and hence was presumably sniffing something - it wasn't... err, what's the name for things that lack a sense of olfaction? Is there such a word? [adjacent pic of Terminonatator skull borrowed from Adam Smith's The Plesiosaur Directory].

Oh dear, I've now said far too much. And hey... you see you can talk about plesiosaurs and not mention necks once. Many thanks for sharing the picture Mike. The picture shown here is - I presume - only one section of the whole mural.

Refs - -

Buchy, M.-C., Frey, E. "D.", Métayer, F. & Salisbury, S. W. 2003. Slicing plesiosaurs, part II: plesiosaurs' internal nares are no nares at all. In 1st EAVP Meeting (Basel, Switzerland), Abstract of Papers and Posters, With Programme. Natural History Museum Basel, p. 39.

Cruickshank, A. R. I., Small, P. G. & Taylor, M. A. 1991. Dorsal nostrils and hydrodynamically driven underwater olfaction in plesiosaurs. Nature 352, 62-64.

Mulder, E. W. A., Bardet, N., Godefroit, N., Godefroit, P. & Jagt, J. W. M. 2000. Elasmosaur remains from the Maastrichtian type area, and a review of latest Cretaceous elasmosaurs (Reptilia, Plesiosauroidea). Bulletin de l'Institut Royal des Sciences Naturelles de Belgique, Sciences de la Terre 70, 161-178.

Rieppel, O. 2001. The cranial anatomy of Placochelys placodonta Jaeckel, 1902, and a review of the Cyamodontoidea (Reptilia, Placodonta). Fieldiana, Geology (New Series) 45, 1-104.

Sato, T. 2003. Terminonatator ponteixensis, a new elasmosaur (Reptilia; Sauropterygia) from the Upper Cretaceous of Saskatchewan. Journal of Vertebrate Paleontology 23, 89-103.

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Ineresting theory about aquatic olfaction. Did anyone propose a gular pump model--you know, change the size of the oral cavity by moving the gular muscles down and up? That would flush water back and forth over the olfactory epithelium, but it assumes the creature has lips sufficent to seal the mouth. (We've all heard dogs sniff by pumping air using the diaphragm.) Just wondering. Neat stuff.

PS--anosmic means you can't smell (if memory serves me).

I love marine reptiles, so I look forward to your posts on them. We have a big mosasaur up here in Alaska, known only from a humerous. The whole animal was probably 20 feet long. We also (supposedly) had a Jurassic pliosaur, possibly of the Liopleurodon genus. I'm less familiar with what that specimen consists of. The vast majority of Alaska's vertebrate fossils are shipped down to Texas (don't know why) for preparation.

Chris is right...there is even an Anosmia Foundation. I'm looking forward to the details on your return to a 'first love' and especially a placodont post...might you squeeze some thalattosaurs in there too?

I used to take my kids to visit the Harvard Museum of Natural History's Kronosaur, almost 13 meters long [here].

It makes me wonder why the flippers are so densely boned. Could these things have dragged themselves up onto the beach to lay their eggs?

[from Darren: I think that all plesiosaurs were viviparous, and thus entirely marine. Go here and here for some of my thoughts on this]

By Nathan Myers (not verified) on 30 Jul 2007 #permalink

Ah, the Bearpaw. Many a happy day in the sun, scratching up Placenticerus and chasing short-horned lizards in the Bearpaw badlands south of the Cypress Hills.

I look forward to seeing more plesiosaurs on Tet Zoo (about time too), and you're teasing about another new job - sounds interesting.
As for the internal nostril thing, I have to agree that the alternatives proposed by Buchy et al are not as convincing, and I still interpret the traditional internal nares as such. Relative position of internal and external nares may not be the whole story. Muraenosaurus has a slightly more anterior external naris, but the duct leading up into the snout from the internal naris is inclined posteriorly towards a large chamber which is at the end of the olfactory canal. Must have been a bit of fancy soft tissue in there doing something.

By Mark Evans (not verified) on 31 Jul 2007 #permalink

The image of Ms. Kronosaur heaving herself onto the beach is terrifying enough without imagining, some weeks later, dozens of kronosaurlets snap-snap-snapping their way to the water. Vivipary I can believe, but then why else might the flippers have been so strong? Hard swimming, to snatch pterosaurs on the wing? Violent mating competition? Kronosaurlets humping from one swampy puddle to another until they're big enough for the open ocean? Is there any way to gauge these notions, or are we doomed to idle speculation?

By Nathan Myers (not verified) on 31 Jul 2007 #permalink

After dinosaurs and Pleistocene megafauna, Mesozoic marine reptiles are another favourite of mine. Awesome! =D

It's interesting that the 3 separate Mesozoic lineages - sauropterygians, ichthyosauria and mosasaurs independently evolved viviparity (ovoviviparity?), while the turtles never did, and I believe the marine crocodyliformes never did either. I wonder why. And I do wonder whether ALL sauropterygians gave birth, or whether it was a trait that popped up now and then. After all, extant squamates employ a wide range of techniques.

Hai~Ren: look up "viviparity" and "vivipary". As I understand it, the distinction is that the former involves a placenta or something like. Darren hints in his first link above at the reason crocs and turtles never developed vivipary, being "constrained to ovipary because their embryos derive calcium from the egg shell".

For balance, we might note that plesiosaurs never developed tree-climbing, which -- who knows? -- might have saved them from extinction. That said, I don't know that anyone has ever really looked for Nessie in the treetops.

By Nathan Myers (not verified) on 01 Aug 2007 #permalink

I had no idea that viviparity and vivipary meant different things: are you sure about this? In the herpetological literature, 'viviparity' is ordinarily used for all live-bearing species, and don't all viviparous reptiles have a placenta anyway? (in some lizards - notably some skinks - it is particularly complex and not all that different from the organ evolved independently in mammals).

As for arboreal nessies: at last, an explanation for the elusive drop-bear. Godammit, I feel a blog article on Loch Ness coming on...

Reading Wikipedia more carefully, I find that ovoviviparity and placental viviparity are varieties of vivipary. (If there are others, it doesn't say so.) I didn't know any reptiles had developed placentas. It mentions that sharks have managed it, but (most?) vipers haven't.

Isn't it odd that with so many species of bats, none have returned to the water, despite their having sonar already? Or, none we know of! Have the black lagoons' depths been adequately plumbed? Credit for naming the first penguin-bat species awaits.

By Nathan Myers (not verified) on 01 Aug 2007 #permalink

Walruses can exhale water from the nostrils (photo at ATT Photos page here.

Was it likely that the 2 sets of nostrils in plesiosaurs were for pressurized (instant) exhalation, like a whale's blowspout?

If plesiosaurs allowed water into their nasal cavities, was it for pressure equalization (as top human freedivers do)? Seb Murat, a pro free diver allows seawater into his sinuses, middle ears and nasal cavities just before a dive, to avoid the hassle of equalizing often. (I've done the same).

The aquatic olfaction in plesiosaurs may have been nearly insignificant (as in dolphins, where taste is far more important).

Did marine reptiles have air-filled middle ears (like humans do) or other air-filled cavities in the head?

Very heavy dense bones in marine animals usually indicates slow diving (non-chasing), as in manatees, walrus, coastal Homo erectus, and some others (kolpimos (sp).


[from Darren: the url you linked to doesn't work]

As I understand it, the presence of a placenta in a vivaparous reptile depends on the species, and sometimes the individual. At one extreme the embryo's chorion exchanges gases etc. with the mother's circulatory system through accidental juxtapasition, up to the formation of a true placenta. In some cases a sort of false placeta forms as chorion and maternal blood vessel sort of intermingle, but don't quite 'sync up".

A bit more on dense skulls & skeletons: (from M. Verhaegen)
"AFAIK, dense skeletons are seen in slow (probably fat) shallow divers in salt water, who dive(d) for sessile bottom foods: seacows, walrus, Odobenocetops, Kolponomos, some Thalassocnus spp & coastal Homo erectus. The bottlenose whale's dense skull (note: rostrum) does NOT clearly belong to this group".

C. McCormick has sent me a link to a paper, free pdf, on this subject, at my blog (click on DDeden).

Is it likely that the ancient marine reptiles had a thick layer of subcutaneous fat/blubber as do marine mammals and birds? Some extant reptiles store fat in their tail IIRC, do any have blubber? Marine iguanas don't seem very thick, but perhaps sea turtles have a layer of fat?

The sheer weight of a kronosaur would crush it on land. Imagine a whale dragging its enormous carcass onto land to give birth. It's just not gonna happen!

Pachyostosis -- the possession of heavy, dense, sometimes bloated-looking bones that (more or less) lack a marrow cavity -- is seen in many diving animals that are not extremely well adapted to an aquatic lifestyle. Probably it serves as ballast in animals that haven't evolved the ability to collapse their lungs. Sea cows are famous for their pachyostotic ribs. I bet that there are no pachyostotic humans, however, and I bet that pachyostosis in the dolphin Odobenocetops is limited to the snout, as it is in beaked whales.

The leatherback turtle at least has a fat layer.

By David Marjanović (not verified) on 12 Aug 2007 #permalink

Thanks David Marjanovic,

AFAIK no extant (healthy) human population is pachyostotic.

Before the development of dug-out canoes, apparently coastal Homo regularly dove for sessile benthic foods, based on the skeletal density of some fossils, including the occiput of the skull.

Wiki, re odobenocetops:
"This, coupled with its broad snout, similar to that of a walrus, suggests that it was a bottom feeder, searching for gastropods and sucking them out of their shells with a powerful tongue."
Fast chasing was not required to eat, it's flexible neck allowed swift head movements while possibly the trunk stayed immobile. (like some plesiosaurs?)

Beaked whales seem to eat squid, chasing, so the slow diver sessile food eater feature in pachyostotic species doesn't fit.
You might be right, I haven't seen the density of odobenocetops snouts, though since it wasn't written about in the article, it probably wasn't noticeably denser than other similar taxons.

Regarding the Liopleurodon-sized Jurassic pliosaur from Alaska that Zach Miller mentioned, could it be the same as Megalneusaurus from farther south? It was also pretty big (about the same size as Liopleurodon), and closer to Alaska than Liopleurodon was.

[from Darren: yes, Alaskan pliosaur remains were referred to Megalneusaurus by Weems & Blodgett (1996). I don't recall the referral being particularly convincing, but would like to be corrected. See...

Weems, R. E. & R. B Blodgett. 1996. The pliosaurid Megalneusaurus: a newly recognized occurrence in the Upper Jurassic Neknek Formation of the Alaska Peninsula. U.S. Geological Survey Bulletin 2152, 169-175.]

By Jamie Stearns (not verified) on 28 Aug 2007 #permalink

Fast chasing was not required to eat, it's flexible neck allowed swift head movements while possibly the trunk stayed immobile. (like some plesiosaurs?)

Despite their many vertebrae, plesiosaur necks were very stiff, surprisingly.

By David Marjanović (not verified) on 24 Nov 2007 #permalink

I just saw a painting of a plesiosaur with a very curled neck, apparently that was not accurate. Stiff necks fit hydrodynamic "flight" like a long-tailed ray, giving vertical stability. Odd though, since they couldn't snoop in reef tunnels for fish or octopus, couldn't change speed or direction quickly, probably couldn't reverse. Did they eat jellyfish like sea turtles? Dense boned limbs indicate slow diving in shallow marine waters, but I don't know what they ate.

Did some long-necked plesiosaurs live in rivers (like river dolphins returned to rivers from coastal ancestors)?

riparian pleisosaur(?) fossils in Melbourne Aus

The idea that plesiosaurs sniffed water remains unlikely to me, what chemicals would they detect to their advantage, that would not be better done through the tongue?

I wonder if it wasn't more likely respiration or pressure equalization or suction feeding rather than olfaction while submersed. I guess air olfaction would be useful for detecting flood washed carcasses, if they lived at river mouths.

I just saw a painting of a plesiosaur with a very curled neck, apparently that was not accurate.

Indeed not.

Did they eat jellyfish like sea turtles?

With those teeth?

Traditionally, the small-headed plesiosaurs have been considered fish- and cephalopod-eaters, because this is what their teeth fit. Recently much more diverse stomach contents were found in a very long-necked one, however, indicating that that species at least grazed on the sea bottom and gobbled up all animals it found.

The big-headed ones (especially the pliosaurs) must have been top predators, on the other hand.

Did some long-necked plesiosaurs live in rivers [...]?


The idea that plesiosaurs sniffed water remains unlikely to me, what chemicals would they detect to their advantage, that would not be better done through the tongue?

Smelling underwater is the normal state of affairs. All vertebrates have nostrils, and those that haven't had land-living ancestors also have olfactory epithelium behind them and use them to smell.

I guess air olfaction would be useful for detecting flood washed carcasses, if they lived at river mouths.

A far too rare event for natural selection, and most lived far from river mouths.

By David Marjanović (not verified) on 27 Nov 2007 #permalink