Paleontologists have described the largest Cambrian hurdiid radiodont known so far, named Titanokorys gainesi, from the Burgess Shale, British Columbia, Canada.
Reconstruction of Titanokorys gainesi. Image credit: Caron & Moysiuk, doi: 10.1098/rsos.210664.
Radiodonts, a group of primitive arthropods that evolved during the Cambrian explosion, were among the largest and most diversified Paleozoic predators.
These animals were widespread geographically, occupying a variety of ecological niches, from benthic foragers to suspension feeders and apex predators.
The most iconic representative of this group is Anomalocaris, which may itself have approached 1 m (3.3 feet) in length.
Like all radiodonts, Titanokorys gainesi had multifaceted eyes, a pineapple slice-shaped, tooth-lined mouth, a pair of spiny claws below its head to capture prey and a body with a series of flaps for swimming.
Within this group, some species also possessed large, conspicuous head carapaces, with the new species being one of the largest ever known.
“Titanokorys gainesi is part of a subgroup of radiodonts, called hurdiids, characterized by an incredibly long head covered by a three-part carapace that took on myriad shapes,” said Joe Moysiuk, a Ph.D. student at the University of Toronto and the Royal Ontario Museum.
“The head is so long relative to the body that these animals are really little more than swimming heads.”
Titanokorys gainesi carapace. Image credit: Jean-Bernard Caron, Royal Ontario Museum.
With an estimated total length of 0.5 m (1.6 feet), Titanokorys gainesi was a giant compared to most animals that lived in the seas at that time, most of which barely reached the size of a pinky finger.
“The sheer size of this animal is absolutely mind-boggling, this is one of the biggest animals from the Cambrian period ever found,” said Dr. Jean-Bernard Caron, also from the University of Toronto and the Royal Ontario Museum.
Why some radiodonts evolved such a bewildering array of head carapace shapes and sizes is still poorly understood.
The broad flattened carapace form in Titanokorys gainesi suggests this species was adapted to life near the seafloor.
“These enigmatic animals certainly had a big impact on Cambrian seafloor ecosystems,” Dr. Caron said.
“Their limbs at the front looked like multiple stacked rakes and would have been very efficient at bringing anything they captured in their tiny spines towards the mouth.”
“The huge dorsal carapace might have functioned like a plough.”
A paper describing the discovery was published in the journal Royal Society Open Science.
J.-B. Caron & J. Moysiuk. 2021. A giant nektobenthic radiodont from the Burgess Shale and the significance of hurdiid carapace diversity. R. Soc. open sci 8 (9): 210664; doi: 10.1098/rsos.210664