Object of the Month

 
Plamen, PhD student within the School of Geography, Earth and Environmental Sciences, talks about his choice of the Object of the Month
Video transcript here

Hemicyclaspis murchisoni

Much of the morphological gap that separates extant jawless from jawed fish was once filled by a diverse group of jawless fishes now known only as fossils from Palaeozoic rocks from around the world. These fossils are therefore of fundamental importance for helping us to reconstruct the origin and early evolution of jawed vertebrates—one of the most significant evolutionary events in vertebrate history and, by extension, our own evolutionary history. A group of central importance in this context is the Osteostraci. This bizarre looking group of fish are the sister group to all jawed vertebrates - that is the most derived, or ‘advanced’ in crude terms, fish that don’t have jaws. Understanding the biology of these long dead fish is therefore of considerable importance in documenting this major evolutionary transition.

This is one of many specimens of osteostracans we have here in the Lapworth Museum, but is of particular importance as articulated specimens (with this incredible bony headshield attached to the rest of the body) are extremely rare. This specimen is from the Downton Castle Sandstone at Gornal, near Dudley in the Black Country, and was a crucial specimen in determining the correct age of the geological formation. During a visit to a quarry at Gornal with students from the Geology Department at the University of Birmingham, Professor L.J.Wills noticed the specimen on the desk of the quarry owner and immediately recognised its significance. The specimen was later donated to the Lapworth Museum.

Looking at this model of a closely related osteostracan, these paired pectoral fins are one of the more obvious features of this group of fish that represent a major step on the way to vertebrates acquiring jaws, and it is largely through articulated specimens such as this specimen from the Lapworth Museum collection that we are able to uncover these important evolutionary narratives.