Dinosaurs and other prehistoric creatures

[Vertigo]

Theropod wrists couldn't be turned so the palms faced downwards (pronating), so none of them were quadrupedal, including spinosaurids. The skeleton does give that impression though, right? I'm wondering if the legs might be some kind of perspective trick.

It is pretty common for spinosaurid legs to be underdeveloped compared with overall body length, though. Part of the explanation is that they spent a lot of time in water - some spinosaurids spent even more time submerged than contemporary turtles and crocodiles. And obviously, an underwater animal's weight is supported for it, so it doesn't require strong, load-bearing legs.

Spinosaurus itself seems to have spent more time on dry land than its relatives - making its apparently super-spindly legs pretty mysterious - but still less than other theropods.

[DoomRulz]

What indication is there that Spinosaurus spent more time on land than a Suchomimus or a Baryonyx? Is it something in the bones? As for a quadrupedic spinosaurid, I doubt the arms could support that much weight behind them.

[Blacklabel]

...or....

could it be that "THAT" particular Spinosaurus had a genetic anomaly, and that it managed to survive until adulthood, despite the weaker legs?

I think there's a trick of perception in that photo of the skeleton anyway.... 

[Vertigo]

What indication is there that Spinosaurus spent more time on land than a Suchomimus or a Baryonyx? Is it something in the bones?

The reason we know spinosaurids were semi-aquatic is a 2009 study which measured the amount of isotopic oxygen in twelve well-preserved spinosaurid fossils. The theory is, an underwater animal is exposed to less oxygen, so preserve less of the isotope.

The full study's only accessible under an expensive subscription, so I've only been able to find a couple of charts which show the main data. I've annotated it with the species which I think may correspond to the fossils, based on when they were alive.
There are a lot of Cenomanian results, so Spinosaurus and Oxalaia could be any one of them (or none).



Oxygen isotope ratios vary over time, due to differing atmospheric conditions and other crap. So they're not all on the same scale. The main point of comparison is using crocodylomorphs, turtles and non-spinosaurid theropods, from the same time and place. The spinosaurid is then plotted on the scale to determine which group it gets closest to.

As you can see, the earlier spinosaurids tend to be the most aquatic, and the late ones (of which Spinosaurus is the best-known example) are often the least. The last of them is even less aquatic than the theropod control group.
If I had some way of reading the regions each fossil is from, I'd be able to be more specific. I know the full article does state them.
In any case, the Wikipedia page on spinosaurids does corroborate my analysis.
(Wikipedia also directly states that Siamosaurus is result #1, but I can't find an exact date for that genus.)

[DoomRulz]

I already knew about the isotope levels. I'm wondering why exactly the earlier ones were more aquatic than the later ones. My guess would be because either water beds were more shallow and there were fewer of them (or at least it varied by region) and that land-based prey was more readily available.

[Vertigo]

You'd think it would vary depending on the species and ecosystem, and the results I have access to are annoyingly non-specific. Some genera may have been better-adapted for an aquatic lifestyle than others, and most spinosaurids are extremely poorly-known.

I've been watching through Planet Dinosaur recently, and they posit that Spinosaurus died out after the regional river system changed, depriving access to the large fish it primarily subsisted on. It could be that they had a brief final period eking out an existence as exclusive land predators (which their carcharodontosaur and abelisaur peers were better adapted for).

[DoomRulz]

I can't imagine it's because they were too heavy to walk on land (not saying you are Vertigo; just throwing it out there). Saying such a thing makes me think back to the days when paleontologists said that sauropods spent time in the water for just that reason. Spinosaurids almost seem to be the amphibians of the dinosauria, if you will, because they could live on land and in water.

[Vertigo]

I'm sure they could get around just fine on dry land (as evidenced by that last isotope reading), it's just that terrestrial hunting wasn't their strong suit. Their legs are neither chunky for power nor long for sprinting.


Also:

I can't imagine it's because they were too heavy to walk on land (not saying you are Vertigo; just throwing it out there)

I'm very proud of my weight loss, damnit.






New development in Spinosaurus 2014: Luis V. Rey illustration based on the new remains.



It's a modification of an older picture, so spot the difference. The stiffened neck is an interesting feature that I hadn't picked up on.



(Rey has a tendency for weird and slightly speculative imaginings of dinosaurs, but it should give you some idea of the new view. Just don't read anything into the sail spikes or throat pouch.)

More info on his blog: http://luisvrey.wordpress.com/2014/08/13/that-was-then-this-is-now/

[DoomRulz]

I can't imagine it's because they were too heavy to walk on land (not saying you are Vertigo; just throwing it out there)

I'm very proud of my weight loss, damnit.

Most archaeocetians are

New development in Spinosaurus 2014: Luis V. Rey illustration based on the new remains.

https://luisvrey.files.wordpress.com/2014/08/spinosaurus-serenob.jpg

It's a modification of an older picture, so spot the difference. The stiffened neck is an interesting feature that I hadn't picked up on.



(Rey has a tendency for weird and slightly speculative imaginings of dinosaurs, but it should give you some idea of the new view. Just don't read anything into the sail spikes or throat pouch.)

More info on his blog: http://luisvrey.wordpress.com/2014/08/13/that-was-then-this-is-now/

Weird and speculative doesn't begin to describe it. It looks like a fat, toothy duck. How the hell would something that (appears to be) sluggish survive long enough to grow up to 11 tons?

[Effectz]

Probably only a handful of the hatchlings survive to grow to adulthood like Crocs and Gators.

[DoomRulz]

Perhaps but I'm also thinking about staying one step ahead of your prey. Spinosaurus was primarily a fish-eater but when it came time to hunt on land, I can't see it lasting for too long if it really had that sort of gait.

[Effectz]

It probably didn't actively hunt on land,it would probably scavenge though only really leaving the water when it began to dry up,also gators and crocs do this.

[OmegaZilla]

Rey is one of my least favourites when it comes to paleontological reconstructions. I prefer Martin, Marshall, Beneteau, Bonadonna...

[DoomRulz]

It probably didn't actively hunt on land,it would probably scavenge though only really leaving the water when it began to dry up,also gators and crocs do this.

It would have also hunted when need be. There's no such thing as a pure hunter and/or a pure scavenger.

[Effectz]

It probably didn't actively hunt on land,it would probably scavenge though only really leaving the water when it began to dry up,also gators and crocs do this.

It would have also hunted when need be. There's no such thing as a pure hunter and/or a pure scavenger.

I'm sure it was opportunistic,but there is such things as pure hunter and scavengers in nature,namely Vultures.