March 12th’s DpSU, Researchers Find Fossil Salamanders’ Last Meals, is a combination of the living fossil argument with the soft tissue preservation one. We have some fossil salamanders, dating at around 150 million years old, that “look almost the same as living salamanders, and they apparently ate the same food.”
This is unsurprising. Salamanders are an entire order of life – making the change required to make them look significantly different rather difficult – that has been around for a good 164 million years. As for the soft tissue:
Publishing in the Chinese Science Bulletin, three paleontologists described the fossils as being “well-preserved as articulated skeletons, even retaining soft tissue impressions.” The fossils showed more than just impressions in mudstone, however. The study authors wrote, “It is obvious that more organic residue (shown by the darker color) is preserved on the surfaces of the carapaces in the gut of the salamander than on those outside, providing further evidence for their being the food of the predator.”
The paper is Two Jurassic salamanders with stomach contents from Inner Mongolia, China. Denied here any definitive example of original organic tissue, Thomas goes on to list others:
They did not test whether the dark fossil material was original and not mineralized soft tissue, but other fossils from the same area appear to have original organics. For example, researchers described lizard skin impressions that may preserve original skin in dark patches. Also, two different Daohugou spider fossils have dark-colored exoskeleton outlines, and one Daohugou specimen contains pterodactyl skin fibers. If direct tests verify biological materials such as protein and chitin, as other similar fossil troves have shown, they wouldn’t support the millions-of-years age assignment because such tissues only last hundreds of thousands of years at most.
How do you know that? These examples are tiny residues, not slightly-rotten meat.
But back to the living-fossil side:
The fact that these fossil salamanders look much the same as their living counterparts also fails to show millions of years’ worth of evolutionary modifications. The Chinese study authors wrote, as an example, “The Jurassic cryptobrachid [sic] Chunerpeton has a flat skull, as does its living relative the Chinese giant salamander, Andrias davidianus, which is benthic [bottom-dwelling].”
Evolution contends that organisms can change – not that they have to. And there are differences: nobody’s saying that the specimens are identical to extant species. And again, ‘salamander’ is an order, which means that classification into it will be quite broad.
So, if salamander bodies have not really evolved, have their diets? Apparently not, according to the authors: “It is not surprising to discover that a Jurassic salamander ate conchostracans [clam shrimp].”1 Living salamanders also eat these.
No, it isn’t – conchostracans are three orders, and have been around since the Devonian, 400 million years ago. Why shouldn’t they have eaten them?
Even the tiny fossil insects preserved in the fossil salamander stomachs looked the same as living insects called corixids, also known in the United States as “water boatmen.” The authors wrote, “Extant [living] corixids mostly inhabit ponds and slow-moving streams where they forage on the bottom ooze; this was probably also true of the corixids at Daohugou.”
Corixidae is, at least, a Family (a level or three more specific, depending on how you count). I see no reason why they too couldn’t have been around a hundred million years ago.
To return to Mr Thomas’ question in his second paragraph:
And since it could only eat those creatures that lived at that time—creatures that had not yet evolved into today’s life forms—wouldn’t it have had a different diet?
There are two species being eaten here: “juveniles of the conchostracan Euestheria luanpingensis” and the “corixid Yanliaocorixa chinensis“. Both the species and even the genii in this case appear to be long extinct – these salamanders were indeed eating contemporary creatures. They just don’t have to be all that different from what is around today: successful organisms are successful.