While ScienceDaily isn’t a science journalism site (it’s an aggregator for university press releases excited about a faculty member’s latest publication) that doesn’t mean there’s nothing of value there, it just means that the value varies wildly with the priority (and personnel) different universities assign to writing up good press releases.*1
My latest find there not only details a great new Devonian find (if it holds up, as always, IANAB), but it’s also fairly well written in that it details where and how the crucial fossils were found, why the authors believe they are significant, and what they might tell us, all in sentences constructed to be understandable. Joy!
So what’s up? In a South African location that was below the Anarctic circle during the latter Devonian, a road cut revealed some mudstone deposits from an estuary (probably), lagoon, or similar (possible but not expected) environment of relatively calm, salty water with regular influx of fresh water sediments. Within those deposits two new tetrapod species were found: Tutusius umlambo and Umzantsia amazana. Both are partial skeletons*2, with Tutusius (named after Desmond Tutu) being known from just a single shoulder girdle fossil. Both skeletons are in the 2-3 foot size range, with Tutusius apparently the larger. For comparison, some trackways of early tetrapods suggest body sizes over 7 feet in length were probably common for adults of at least a few species. Elginerpeton and Ichthyostega were each approximately 4.5 – 5 feet long. If adults, then, Tutusius & Umzantsia were modest in size.
The age of the fossils is also unexceptional at approximately 360mya. The trackways of stem tetrapods have been found that date to over 390mya. Tiktaalik is probably from about 375mya. There’s nothing unprecedented about the age of these animals.
What is unprecedented is that stem tetrapods have not previously been found in the antarctic. The Science Daily release includes this statement:
“Whereas all previously found Devonian tetrapods came from localities which were in tropical regions during the Devonian, these specimens lived within the Antarctic circle,” explains lead author, Dr Robert Gess of the Albany Museum in Grahamstown, and co-author Professor Per Ahlberg of Uppsala University in Sweden.
Elsewhere Ahlberg asserts that the environment in which these two species lived would be climatically similar to coastal Norway today. This is incredibly significant, because change in body plan is reasonably expected to be associated with a change in selection pressures, and selection pressures are likely to change when the climate changes. This can be due to direct effects, but it can also happen because in a different climate a genera is likely to encounter different competition or different food availability.
We don’t know yet whether undiscovered early stem-tetrapods will prove to have differentiated by spreading to different climates or environments, but with the relative uniformity of environment for previous finds, Tutusius & Umzantsia open up new research possibilities and make it reasonable to ask new and interesting questions about where, why, and how stem-tetrapods developed the traits that would lead to the rise of amphibians.
The limited claim that irregular but non-overlapping and relatively evenly spaced trackways likely represent the footprints of a single, bilaterally symmetrical animal is something that can easily be judged at least a reasonable inference by non-experts. However the fragmentary nature of these finds and the fine distinctions in, say, shoulder girdles between stem-amphibians and stem-tetrapods renders the conclusions of the Gess/Ahlberg study probably beyond any of us here to even judge as plausible. Still, Ahlberg has a good track record*3 and Science has the budget for good peer review, so these probably are fossils of stem-tetrapods, they probably do date to the late Devonian, and the environment probably was dramatically different (in at least climate) from the environments in which other stem-tetrapods have been found.
That’s enough to make these finds pretty exciting. I still remember the antarctic episode of Walking With Dinosaurs Spirits of the Ice Forest. I still remember the portrayal of the crocodile-like temnospondyl Koolasuchus*4. It’s exciting to think of a similar creature occupying a similarly antarctic latitude 240 million years before Koolasuchus.
Dig everywhere, people! You never know what you’ll find.
*1: The biggest concern with these stories, even where well written and accurately reflecting published research, is that they almost never bother to get an expert free of connections to the research or the journal in which the research is being published to give an independent assessment of the quality of the work and the reasonableness of the conclusions. That’s to be expected from a promotional press release, but it’s very different from what we would expect from science journalism and leaves the non-expert with little help in identifying bad research. In this case, the research itself is published in Science, so at least that testifies that something significant is likely to be found, though not that the press release gets everything right. Reuters also has a report, and though they contacted Per Ahlberg for comment their story, contacting a co-author doesn’t do anything to help the reader understand the quality of the research or likely soundness of the conclusions. It does a good job of describing a bit of the research findings, but does not do any better at science journalism than the original press release on Science Daily. Ahlberg deserves better than to be used like this.
*2: and remember that even “complete” skeletons in paleontology aren’t complete in the literal sense, merely complete enough to contain bone from all representative segments of an animal
*3: Good enough to make it into the bedtime stories I told my kids.
*4: a pre-amphibian tetrapod or possibly stem-amphibian that resembles a salamander living a the crocodile-like lifestyle of an ambush predator.