The story of Axolotl is amazing, endearing, and almost somewhat ridiculous; but we are not going to learn much more about Axolotl today as they are a means to an end for us here. I will share that they love uncooked beef liver. Also, I was inspired to talk about them today because a friend that works at the Boston Museum of Science shared a post about an upcoming exhibit featuring these adorable little salamanders. Salamanders in general are fairly recognizable by most, though there is sometimes confusion over names (e.g. newt vs. salamander) and appearance (think Axolotl vs. any other generic "salamander" that comes to mind). We could discuss how newts are salamanders and why Axolotl look different from Tiger Salamanders (which they are closely related to), but we are going to talk, now that we all have a picture of salamanders in our heads, about fossil salamanders from the Permian known as Apateon.
|Senckenberg Museum of Frankfurt|
Photo by Ghedoghedo
Often preserved as flat impressions on slabs, these Permian temnospondyls are primitive amphibians that, like the Axolotl, are neotenic; meaning that they retain juvenile traits, such as the external gills seen in Axolotls, in their mature adult forms. This is often referred to as pedomorphosis also. Researchers have shown that these traits are retained in large numbers of these animals and they were so populous that we have a wide swath of ontogenetic or life cycle examples of animals in this genus to show that we are not just looking at odd young from many different groups. We have, of course, living examples to draw from as well. Many interesting things are known from these fossils, but probably one of the most intriguing things, to me, is the number of large group fossils and the detail in both the large group fossil assemblages and single animal fossil slabs that exist for Apateon. The genus Apateon actually consists of 7 species with Apateon pedestris von Meyer 1840 containing the holotype for the genus. As with many exquisitely preserved slab fossils, Apateon was originally discovered in Germany, a country with a rich history of excellent freshwater fossil diversity and preservation, and specimens have been dated from 295.0 to 290.1 million years ago.
|Apateon pedestris Natural History Museum, Bonn University|
Photo by Ghedoghedo
The skeleton of these Permian amphibians can be seen in this image from the Natural History Museum of Bonn University, which is actually quite a feat. The skeletons of Apateon are very weakly ossified, so the identifiable vertebrae, ribs, and limbs are truly exceptional and speak directly to the preservation of the fossil. Additionally, the orbits are fairly identifiable and, because we can see where the eyes would have been, we can see that the snout and the area of the skull directly caudal, or behind the eyes, are very short. We can say that Apateon had a very small head rostrocaudally (front to back) but also a very wide skull and very large eyes. If we turn our attention to those limbs we can just make out the digits. We know from more splayed out fossils of the limbs that there were four digits on the forelimb (on the "hand") and the hindlimb as well.