It was first identified as an extinct 'saurian', then as a dinosaur, followed by a theriodont, and finally correctly identified as a sphenacodontid, a group of early synapsids (a group of tetrapods with no temporal fenestra, or holes, in their skulls, consisting of mammals today) which includes the famous extinct sail-backed reptile Dimetrodon grandis. It hails from the Lower Permian, 283-290 million years ago, and was called Bathygnathus borealis. The fragmentary nature of the fossil made it difficult to determine the exact affinities of this specimen. Over the years it has been studied by a number of people, and similarities have been identified with Dimetrodon, Sphenacodon, and Ctenospondylus, but the similarities have never been major enough to warrant an official change. That is, until now.
|ANSP 9524 - type specimen of 'Bathygnathus' borealis (Brink et al. 2015)|
|Cladogram showing position of 'Bathygnathus' borealis (Brink et al. 2015)|
The interesting and very important thing about this paper is related to the the rules of taxonomic nomenclature and priority. Bathygnathus borealis was named 20 years before Dimetrodon, meaning that by the law of priority, Bathygnathus should have priority and replace Dimetrodon. However, Dimetrodon is a well known and very famous fossil and no one wants to lose that name. Exceptions are occasionally made when there is a strong reason to retain initial names, and they have started a case with the International Commission of Zoological Nomenclature (ICZN), the group responsible for taxonomic names and problems like this. If they succeed, we won't lose Dimetrodon, but gain a new species of 'Dimetrodon' borealis!
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Brink KS, Maddin HC, Evans DC, and Reisz RR. 2015. Re-evaluation of the historic Canadian fossil Bathygnathus borealis from the Early Permian of Prince Edward Island. Canadian Journal of Earth Sciences 52: 1109-1120.