By Mark Carnall, on 28 February 2014
It’s often said that seasons come and seasons go but fossil fish are forever*. However, sadly this isn’t as robust as it is commonly believed. Fossil fish, like Hollywood stars and small children need attention and that’s what this entire series is about, turning the spotlight on the nearly-made-its, the also-rans and the generally undistinctive. The mediocre, normal shaped and average sized. The fossil fish consigned to museum drawers and storerooms, their ‘heyday’ 100-odd years ago, consisting of a dry description in an obscure journal by a palaeontologist. Shed no tears for them for they are but rock. They shall go on to the end. You can find them in France, you can find them under the seas and oceans. You can find them on the beaches, on the landing grounds, in the fields and in the streets, in the hills; they shall never surrender. Here is yet another, especially underwhelming fossil fish of the month.
Whilst looking for this month’s fossil fish, this specimen jumped out as particularly unimpressive. At first glance, this specimen looks like a packet of M&Ms has been spilled on the floor, been faded by the Sun and then trampled on. Take the time to look a bit longer and that’s still what it’ll look like. According to the label for this specimen what we have here is a specimen of Glyptolepis leptopterus. The locality information is hard to work out but it could be Lethen, a locality in Scotland that other museums have similar specimens from, here’s a specimen from the Hunterian Museum in Glasgow that could be the twin of our specimen here. From the label on the specimen, this specimen came from an R.F.Damon. I haven’t been able to find out much about this collector but it appears he also donated specimens to Glasgow too.
Glyptolepis is a genus of porolepiform fish, an extinct group of lobe-finned fish, the most well known of which are probably the lungfish and the ‘living fossils’ the coelacanths. The term ‘living fossil’ is a problematic term that causes a lot of confusion, implying that ‘living fossil’ animals are ones that we can find living and in the fossil record. Whilst there are certainly many species which can be found in the fossil record and alive today, most of the common living fossil animals are actually highly derived species that are the last of their lineage that still exist today. Lobe-finned fish are fish with erm lobe fins and were the fish that evolved into the first animals with backbones to leave the sea and live on land. The origins of our limb girdles can be traced back to this group of fish. Although only represented by a handful of species alive today, the group was much more diverse in the past. The Porolepiforms flourished in the Devonian period, going extinct about 360 million years ago.
Preservation Although it doesn’t look like much we appear to have the front half of an individual preserved here. The white splodges are the scales of the fish, some of which have started to fall away but the majority of which are roughly in life position. On the left side (as it appears above) there are elements of the skull including the lower jaw and what appear to be tooth elements. I can’t discern the lobe fins here and it looks (to me) like the tail is missing. Like other fish of this species, this specimen has been preserved inside a nodule. Sadly we don’t have the other half.
Research This group was first described by Erik Jarvik (one of the ‘Stockholm School’ palaeontologists I’ve mentioned in a previous UFFoTM) and he described the Porolepiformes as the ancestors of salamanders and caecillians due to the shape of their ‘noses’. A theory that has subsequently lost favour. Additionally he described choanae, a nasal aperture associated with breathing air, in porolepiformes, specifically in Glyptolepis, which is a character thought to be unique to all tetrapods. However, this is debated in a thrilling paper, evidence for lack of choanae in the Porolepiformes (Clement 2001). For those of you not anatomically minded it might seem slightly absurd how a hole can be absent because when a hole is present it isn’t there. As far as research on this group and this species goes, there isn’t a lot after it was established that this group lies somewhat off the evolutionary line that leads to the animals that live on land, totally coincidentally the line that includes us humans. One day I’d love to look at the correlation between the amount of research done on animals depending on how important/close they are to our own species’ evolution. I have a suspicion that the research clusters around animals on the ‘road to us’ leaving animals like our poor Glyptolepis hitch-hiking on the roadside. Now it’s time for a gratuitous close up.
In Society Glyptolepis, like so many of its fellow fossil fish has had little to no impact on fish palaeontology and it’s fair to say it has had even less of an impact in wider society. You could go back in time, destroy all the Glyptolepis fossils before they were excavated and the only difference you’d notice on coming back to the present would be that this blog post wouldn’t be here. One theory for the relative obscurity of this genus is the fact that it’s very difficult to rhyme Glyptolepis with anything, keeping the genus out of nursery rhymes, poems and more recently rap. Wordsmiths, by all means submit your best efforts in the comments.
In Society 0
References Clement, G. (2001) Evidence for Lack of Choanae in the Porolepiformes Journal of Vertebrate Paleontology. Vol. 21, No. 4 (Dec. 14, 2001), pp. 795-802
Mark Carnall is the Curator of the Grant Museum of Zoology
* Including this time and interpreting the word ‘often’ very loosely.