How a soft body part can change your identity

By Lucy Brown

The classification of the “hyolith” is to change for the first time in 175 years. It will now belong to a new family group, thanks to a discovery involving researchers at the University of Toronto, University of Cambridge, and our very own Dr. Martin Smith here at the University of Durham.

Recently discovered evidence of a soft tentacle like structure has changed the way we categorise the extinct sea creature, the “hyolith”. It was originally grouped with molluscs based on its tentacles, but, thanks to this new research, is now grouped with the brachiopods. Its classification has important implications for how we understand the evolution of animals alive today.

A hyolith would have lived in the sea, with a shell shaped like an ice cream cone, but with tentacles where you would have your ice cream. These tentacle-like structures can serve different purposes depending on how they develop and seem to be key in the classifying process. Tentacles can either be more of a body part, like arms or legs seen on molluscs (think squid and octopus), or be part of the mouth and digestive tract (like animals in the brachiopods grouping).

Scientists thought that these tentacles had developed from a foot like structure, and thus placed them in the mollusc grouping. But the soft tissue found in samples from Utah and British Columbia have actually shown that these tentacles were involved in feeding. This means that the hyolith was not a mollusc, but a brachiopod.

Due to the nature of the fossilisation process, it is very rare for soft tissue to make it to the present day intact. This explains why for most, the stereotypical image of fossils are often shells or bones. If we take humans for example, there is very little that can be gleaned from using just our bones that would be able to help us fully understand how we walk, talk or breath. So the task of determining what past species may have looked like and functioned, only from the solid stuff, is very difficult. Classification of species is often based on comparisons of similar aesthetics or functioning, although the fossil record has its limits. Therefore, placing these fossils in a group is an extremely hard task.

So, understandably, the discovery of soft tissue can leave scientists and palaeontologists “fan-girling”, as in the case of the hyolith.

The hyolith was a common sea creature and key to the functioning of the ecosystem (much like the honey bee is today), but became extinct in a past mass extinction. As we too are currently undergoing an extinction event with the pressures of climate change, this discovery can give us a greater understanding of how past life recovered and adapted to the loss of key species, and can greater prepare us for the future.

Photograph: Jiahe max luan

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