The Cambrian Era, when animal life exploded into stunning diversity 541-485 million years ago, has surprised biologists once again. The latest discovery is Titanokorys gainesi, a creature that today would be notable for its shape, but then stood out for its enormous size, relative to the small animals of its time.
Titanokorys was discovered in the famous Burgess Shale, a site in the Canadian Rockies that gave us the first detailed insight into the staggering diversity of forms that appeared around 508 million years ago. Many of these were so strange they some were named after acid trips and most were never seen again.
For all their diversity, however, most of the species entombed in the Burgess Shale were smaller than a credit card. Titanokorys, in contrast, was half a meter long (20 inches), a paper in Royal Society Open Science reports.
“The sheer size of this animal is absolutely mind-boggling, this is one of the biggest animals from the Cambrian period ever found,” Dr Jean-Bernard Caron of the Royal Ontario Museum said in a statement.
Although it has only now been scientifically described, Titanokorys has been known to a portion of the general public for two years, with its discovery featuring in the CBC documentary First Animals.
Titanokorys was a radiodont, a group of early arthropods whose most famous member was Anomalocaris. The radiodonts are identified by their multifaceted eyes, cone-shaped mouths filled with toothed plates, and nightmarish claws that seem to issue directly from the head to seize prey. They swam through the Cambrian oceans driven by flaps. Initially identified from the Burgess Shale, radiodonts have been found at other sites of similar age, indicating their status as Cambrian successes.
“Titanokorys 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. The head is so long relative to the body that these animals are really little more than swimming heads,” said co-author and University of Toronto PhD student Joe Moysiuk.
What exactly the carapace was for, let alone why they came in so many different shapes among the radiodont species is something of a mystery. However, the authors believe Titanokorys's broad flattened carapace, which falls midway between long and short-carapaced species, is indicative of a species that lived close to the seafloor.
“These enigmatic animals certainly had a big impact on Cambrian seafloor ecosystems. 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,” said Caron.
Ecosystems can only support small numbers of large predators. Although 12 (mostly fragmentary) Titanokorys specimens have been found, it was far rarer than the smaller radiodont, Cambroraster falcatus, which lived in similar locations and may have competed with Titanokorys for prey.