If you've been paying attention you'll know that I've been absent for a little while: I've been at the Sea Dragons of Avalon conference, held at Street in Somerset and focusing on the evolution of marine reptiles (and other organisms) across the Triassic-Jurassic boundary. The meeting also included a tribute to Arthur Cruickshank, a day of 'Arthur-themed' talks, and a public lecture by Ryosuke Motani. And then there were collection visits and field trips; all in all, a major event. It went well and I have a lot to talk about: more details soon (for information on the sign shown in the adjacent photo, go here).
That's Golden Cap, Charmouth, in the fog. The weather on the field trip was pretty lousy (our initial quarry-visit plans were rained off), but the rain was light, not heavy.
A big temnodontosaur skull, with Adam Smith for scale. We saw a lot of ichthyosaur material!
Now for a swim with Sea Dragons.
I wonder if the ichthyosaurs ever developed big, killer pliosaur-like forms, as the younger groups of marine reptiles did. The mosasaurs were virtually all big killers, with the exception of maybe some of the smaller species and Globidens, while the plesiosaurs...well, they produced the pliosaurs, after all. Perhaps Shonisaurus would fit the bill, though I wonder how it would hunt with that long rostrum and fat body of its.
Shonisaurus was probably toothless at adult stage (Nicholls & Manabe, 2004). The biggest ichthyosaurs with meat cutting dentition are Temnodontosaurus, reaching 12m, Shastasaurus (from 2 to 8m) and Himalayasaurus (also a big one but poorly known genus, Motani, 1999).
Here's a question: what was ichthyosaur skin like? I constantly and consistantly see ichthyosaurs restored with smooth, dolphinlike skin. But since they're reptiles, I wonder if perhaps they actually had scales?
Aw, I never got a picture of the road sign. Ichthyosaurs up to the eyeballs. Ichthyosaurs, plesiosaurs and ammonites, oh my!
(#2) Anonymous: Intergirdle and rib length isn't known for Shonisaurus popularis but it probably wasn't deep-bodied since S. sikanniensis appears to have a Cymbospondylus-like body shape.
(#4) MOE: Darren wrote a post about that very topic
"Darren wrote a post about that very topic"
Actually, that post is mostly about the internal structure of ichthyosaur skin; Darren does not mention weather or not ichthyosaurs had epidermal scales.
I can't help but admire the scientific enthusiasm on Darren's face in the first picture, you can practically hear him shouting "Wahey!" at the top of his lungs.
I'm not a scientist, but I can field Michael's question with some experience at illustrating.
As far as I know, ichthyosaurs didnt have scales. The Jurassic stuff I've seen pictures of has the film, but there's alot of different deposits with alot of different preservational Biases. Judging from "reptile" evolution in general, I would be surprized if Ichthyosaurs had scales except for the very primitive kinds. Leatherbacked turtles have no scales except vestigial ones, so why would ichthyosaurs, the most hydrodynamic of "reptiles", have scales?
Then again, we have all kinds of scales for whatever "reptiles" have the right impression. Generally I as an Illustrator would say it's impossible, except for the triassic chinese ones.
Well, I never said that ichthyosaurs should have had scales, I was just wondering if there was actually a reason for protraying them as smooth-skinned, other than the constant comparisons to dolphins. I guess there is: a loss of scales would make them more hydrodynamic.
Judging from "reptile" evolution in general, I would be surprized if Ichthyosaurs had scales except for the very primitive kinds. Leatherbacked turtles have no scales except vestigial ones, so why would ichthyosaurs, the most hydrodynamic of "reptiles", have scales?
Why do fish have scales? They have a need to be hydrodynamic, much as Ichthyosaurs, dolphins, and Leatherbacked turtles - yet nearly all fish have scales.
Ichthyosaur skin does seem to have been scale-less, judging from the patches that have been preserved. This data comes from Early Jurassic forms: it's possible that older, Triassic forms were scaly, but there's no data on this yet (that I can recall).
Big ichthyosaurian macropredators (comment 2): it's likely that some large species were orca-like predators of other marine reptiles. The holotype of the robust-skulled Temnodontosaurus eurycephalus has bones from a much smaller ichthyosaur preserved within its jaws, and this might represent the remains of its last meal.
a loss of scales would make them more hydrodynamic
That depends on the shape of the scales. If they're keeled in the right way, like shark or mosasaur scales, or in fact "microsaur" and Micromelerpeton* scales, they can actually help.
* An aquatic temnospondyl.
As Cameron notes, Shonisaurus was probably not particularly deep-bodied, that misconception comes from a skeletal reconstruction by Camp based on fragmentary material.
Several Monte San Giorgio ichthyosaur specimens preserve soft tissue, none of which exhibit obvious evidence of scales. Neither do specimens of Early Triassic ichthyosaurs that preserve soft tissue, to my knowledge, but the soft tissue in those cases is fairly poorly preserved.
Himalayasaurus may have approached 15 m in size and has truly nasty looking teeth. There is another large Triassic ichthyosaur with similarly blade-like teeth that will hopefully be formally described soon!
I'm looking forward to more posts about the conference, I really wish I could have been there!
A new paper on trilobites
with the exception of maybe some of the smaller species and Globidens, while the plesiosaurs...
[url deleted again: stop spamming]