skip to content

Department of Zoology

 

A fossil species discovered in a new exceptional fossil deposit near Llandrindod Wells in mid-Wales, has been described by Dr Stephen Pates, Postdoctoral Fellow in the dept of Zoology, in collaboration with Dr Joseph Botting and Dr Lucy Muir, honorary research fellows at the museum of Wales, and Dr Joanna Wolfe, a postdoctoral researcher at Harvard University. Named using the Welsh language, Mieridduryn bonniae shares many features with Cambrian ‘weird wonder’ Opabinia but is 40 million years younger.

 

 

Figure 1: Mieridduryn bonniae – the larger specimen shows evidence for a spiny proboscis and annulated triangular lobopod ‘legs’

 

 

 

 

Two opabiniid-like specimens were described in the paper Ordovician opabiniid-like animals and the role of the proboscis in euarthropod head evolution” published in Nature Communications. Both specimens display a distinctive annulated proboscis at the anterior of the head, triangular, the larger specimen shows squishy lobopod ‘legs’ along its body for interacting with the sediment, and the smaller specimen preserves a tail fan with blades similar in shape to Opabinia’s sister taxon, Utaurora, described earlier this year by Pates, Wolfe and colleagues. However other features recognised in these specimens—such as sclerites covering the head – as well as the presence of spines on the proboscis— were not known from any opabiniid and instead hinted at possible radiodont (including Anomalocaris) affinities. Differences between the two specimens added further complications—were these due to changes during the growth of one species, or did they instead suggest that two distinct species were present in this new deposit?

 

 

 

Figure 2: The smaller specimen may be a juvenile of the same species or a new species altogether. It also shows a spiny proboscis, in addition to a tail fan at the posterior.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The researchers used phylogenetic analyses, comparing the new fossils with 57 other living and fossil arthropods, radiodonts and panarthropods, to determine their place in the history of arthropod evolution.  Crucially, these results suggested that a proboscis—thought to represent a fused pair of head appendages—was not unique to opabiniids but instead was present in the common ancestor of radiodonts and deuteropods (more derived, modern arthropods), and through evolutionary time may have reduced to become the labrum that covers the mouth in modern arthropods.

However, the second-best-supported position for these specimens was as true opabiniids, so the authors tested the robustness of this first result. If some, or all, the features shared between the Welsh animals and radiodonts were instead considered to have evolved convergently, the analyses strongly favoured these specimens being considered true opabiniids – the first from outside North America and the youngest by 40 million years.

Whatever the eventual conclusion, the fossils are an important new piece in the arthropod evolutionary jigsaw and hint at the value to be gained from further study of this exciting new fossil site in Wales.