Quote from: DoomRulz on Aug 13, 2014, 02:34:29 AM
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.)