Underwhelming Fossil Fish of the Month: April 2016
By Mark Carnall, on 29 April 2016
Since the last Underwhelming Fossil Fish, we’ve been betrayed comrades. Last month, one of our own, a hitherto underwhelming fossil fish got interesting, as hacks reported. Of course, nobody remembers this news now but the underwhelming fossil fish of the month community was rocked so hard by this betrayal, et tu Tully Monster?, that there wasn’t an underwhelming fossil fish of the month for March 2016, the first ever break in the series. In a touching act of solidarity, appropriately for the series, nobody even seemed to notice. This month, there haven’t been any more turncoats so we can get back to the business of this blog series, that is to celebrate the unremarkable fossil fish in museum collections precisely for their distinctive uninterestingness.
This month, widely heralded on the Twitter as #TheReturnOfFossilFish, I’ve got a specimen that’s appropriately uncommemorating in any way, unless slightly resembling a bald person’s head whilst they are frowning, is at all commemorative.
This wonderful fossil, resembling a topographical map of a mushroom is, according to the label, in fact a tooth from a fish in the genus Ptychodus. Ptychodus and related fish are hybodont sharks, an extinct group of cartilaginous fish closely related to today’s modern sharks and rays. Ptychodus lived from the end of the Cretaceous period through to the Palaeocene epoch from 95 to 60 million years ago, surviving the mass extinction that did in for the ammonites, belemnites, plesiosaurs and some other obscure group of reptiles whose name escapes me. Ptychodus is a well known genus of fossil shark as the hard teeth, like this specimen, are more readily preserved than soft tissue and cartilage and each individual shark would have had numerous sets of these flat teeth throughout life and up to 550 teeth in the jaws at any one time. Similar in function to modern ray teeth, hundreds of these broad teeth arranged in a battery would probably have been used for crushing shells of marine molluscs and crustaceans (a durophagous diet). Unfortunately, we don’t know where this fossil was collected but one of the numbers written on the underside, indicates it was once part of the UCL Geology collections. Hybodont shark experts out there may be able to identify which species this tooth is from from the pattern of the raised bars on the tooth, if so, drop a comment down below!
Preservation All we’ve got here is the tooth so in terms of the whole animal the preservation isn’t fantastic however, what is preserved is what palaeontologists call ‘nice’. As this slightly zoomed in image of the surface of the tooth shows:
There’s even a little not so hidden angry face which is always a treat and quite distinctive as these ridges on the teeth.
Research Due to being quite common and readily identified as teeth, Ptychodus fossils have a long history when it comes to scientific research and there are some palaeontological luminaries who have pondered the fossils, albeit not for very long. Ptychodus was first described by legendary geologist Louis Agassiz in 1833. In 1868, palaeontologist American palaeontologist Joseph Leidy, better known for describing Hadrosaurus and the extinct dire wolf, commented on American fossil species of Ptychodus, distinguishable from European species by their “generic peculiarity” which is high praise in the world of underwhelming fossil fish (Leidy 1868). Although isolated teeth are fairly common it wasn’t until the discovery of an articulated set of teeth in 1976 that the structure of the teeth was described, each tooth possessing structures to interlock with adjacent teeth, giving the tooth battery strength for engaging in the business of crushing shelly animals (Macleod 1982). A more recent paper is a notable contribution to the history of Ptychodus, the first known example of a Ptychodus-bearing coprolite, that is fossilised faeces with a tooth in it. The discussion section in particular is of interest, the serious scientific examination of whether or not this was a tooth swallowed by a Ptychodus or that of a predator (Shimada 1997). Although there are hundreds of references mentioning Ptychodus, most merely mention that teeth were found during the more interesting business of describing extinct crocodyliform reptiles, crocodiles, lizards, mammals and even, for shame, other more interesting fossil hybodont sharks.
In Society Until recently, it was thought that Ptychodus and 16th Century Danish astronomer and astrologer Tycho Brahe may have been related because their names sound the same. Recent analysis has determined that Tycho Brahe, who lost his nose in a duel over a mathematical theory, owned one percent of the wealth of Denmark in 1580 and discovery of librations in the inclination of the lunar orbit plane was in fact nothing to do with the Cretaceous shark at all beyond the similar beginning part of the name.
Preservation 7 (+1 angry face bonus)
In Society 0.5
Leidy, J.. (1868). Notice of American Species of Ptychodus. Proceedings of the Academy of Natural Sciences of Philadelphia, 20, 205–208. Retrieved from http://www.jstor.org/stable/4059893
MacLeod, N.. (1982). The First North American Occurrence of the Late Cretaceous Elasmobranch Ptychodus rugosus Dixon with Comments on the Functional Morphology of the Dentition and Dermal Denticles. Journal of Paleontology, 56(2), 403–409. Retrieved from http://www.jstor.org/stable/1304466
Shimada, K.. (1997). Shark-Tooth-Bearing Coprolite from the Carlile Shale (Upper Cretaceous), Ellis County, Kansas. Transactions of the Kansas Academy of Science (1903-), 100(3/4), 133–138. http://doi.org/10.2307/3628001
Mark Carnall is the Collections Manager (Life Collections) at the Oxford University Museum of Natural History, and former Curator of the Grant Museum