Titanokorys

''Titanokorys'' is a genus of extinct hurdiid radiodont (a grouping of primitive stem arthropods which lived during the early Paleozoic) that existed during the mid Cambrian. It is the largest member of its family from the Cambrian, with a body length of long, making it one of the largest animals of the time. It bears a resemblance to the related genus ''Cambroraster''. Fossils of ''T. gainesi'' were first found within Marble Canyon in 2018. The fossils were not named until 2021 because they were assumed to be giant specimens of ''Cambroraster''.

The creature was one of several genera of radiodonts known from the Burgess Shale, with some of the others being ''Cambroraster'', ''Anomalocaris'', ''Peytoia'', and ''Hurdia''. ''Titanokorys'' is distinguished from other Burgess Shale radiodonts because of its large anterior sclerite (head covering carapace) and a pair of spines on the anteroventral sides. Based on the shape of its appendages, ''Titanokorys'' is speculated to have used them to sift through the sand looking for prey. It is believed to have fed by using its anterior sclerite to scoop up organisms from the sea floor. Then it would use its frontal appendages (long grasping structures that all radiodonts possessed) to trap the prey item so it could start consuming it. Because of its size, ''Titanokorys'' was one of the dominant predators of the Burgess Shale and one of the largest animals in its ecosystem.

Etymology and history of research

The genus name refers to the Titans of Greek mythology in combination with the ancient Greek ''κόρυς'' (''korys'' = "helmet") and alludes to the unusual size of the central carapace element. The species name "gainesi" honors the American geologist Robert R. Gaines, who was instrumental in the discovery of new fossil deposits in the Burgess Shale in 2012.

The first description of the genus and type species was made in 2021 by Jean-Bernard Caron and Joseph Moysiuk. This study was based on twelve specimens that came from the Marble Canyon area of Tokumm Creek in the northern part of Kootenay National Park in British Columbia. All previously known specimens are kept at the Royal Ontario Museum (ROM) in the Department of Invertebrate Paleontology (ROMIP). Before the animal was named, researchers often nicknamed it the "mothership" or " spaceship" in reference to its massive head looking like a starcraft.

Description

Fossils of ''Titanokorys'' are known from the Burgess Shale, a famous Lagerstätte from British Columbia dating to around 508 million years ago. Only disarticulated head sclerites, frontal appendages and oral cone (radiodont mouthpart that somewhat resembled a camera aperture) had been discovered. Due to the limited discovery, little is known about the oral cone of ''Titanokorys'', but the tooth plates have smooth surfaces like most other hurdiids. Based on the largest sclerite (measured about ) and ratio inferred from the closely-related ''Cambroraster'', the complete animal was estimated to be about long. ''Titanokorys'' is readily dintinguised from other radiodonts by the anterior sclerite (H-element) with trifurcate anterior region and lateral sclerites. The frontal appendages are almost indistinguishable from those of ''Cambroraster.'' Which have short podomeres with 5 long endites, each associated with a row of long, densely-packed auxiliary spines. These appendages suggest a specialized “ sweep feeding” behaviour that would allow the radiodont to catch and eat both microscopic and macroscopic food. ''Titanokorys'' lived alongside other Burgess Shale radiodonts, such as ''Anomalocaris'', ''Hurdia'', and ''Peytoia''. The fact that so many large predatory radiodonts lived together suggests that Cambrian communities at the time were very diverse and could hold many large macro-predators.

Comparison to ''Cambroraster''

File:20210516 Radiodonta head sclerites Cambroraster falcatus.png, Head sclerite of ''C. falcatus''
File:20210909 Radiodonta head sclerites Titanokorys gainesi.png, Head sclerite of ''T. gainesi''
File:20191229 Radiodonta frontal appendage Cambroraster falcatus.png, The grasping appendage of ''C. falcatus''
File:20210909 Radiodonta frontal appendage Titanokorys gainesi.png, The grasping appendage of ''T. gainesi''
File:Video animation of Cambroraster.webm, A video reconstruction of ''C. falcatus''
File:Titanokorys reconstruction video.webm, A video of a hypothetical reconstruction of ''T. gainesi'' based on ''Cambroraster''

Living alongside ''Titanokorys'' was a similar-looking hurdiid radiodont called ''Cambroraster''. This closely related genus is so similar to ''Titanokorys'' that the latter was originally thought to have been a giant specimen of the former genus and not a distinct genus. The main difference between them is size, with ''Cambroraster'' reaching in length, while ''Titanokorys'' reached a length of around . Another difference is the shape of the sclerite, with ''Cambroraster'' having a horseshoe shaped sclerite that was in width for the largest specimen. On the other hand, Titanokorys had a more pointed, larger head sclerite which reached in length. The grasping appendages of the two genera are almost identical, though the secondary spines on the appendages of ''Titanokorys'' are longer than, and possibly not terminally hooked, as the ones seen in ''Cambroraster''.

Classification

''Titanokorys'' is a radiodont belonging to the family Hurdiidae. Hurdiids can be distinguished from other radiodonts by the rake-like frontal appendages which each bore a single row of elongated endites with only anterior auxiliary spines, alongside the combination of enlarged head sclerites and tetraradial mouthparts (oral cone). ''Titanokorys'' was found to form a derived clade with '' Cordaticaris'', ''Cambroraster'' and possibly also '' Zhenghecaris''. While ''Stanleycaris'' and ''Schinderhannes'' were found as the most basal hurdiids.

Ecology

Like many other hurdiid radiodonts, ''Titanokorys'' was most likely a nektobenthic animal that swam slowly above the seabed and sifted through sediments. It is presumed that the animal dug up the sediment with its huge protruding carapace and guided the prey into its mouth with the front appendages to form a cage-like structure. Since fossils may be preserved together alongside ''Cambroraster'', it is presumed that ''Titanokorys'' lived in the same areas as ''Cambroraster''. ''Titanokorys'' is a relatively rare find at Marble Canyon, because of this it is thought that this fossil site possibly occurred near the edge of the species range in life.

Based on differences in size, ''Titanokorys'' probably escaped competition with ''Cambroraster'' by hunting larger prey, thereby exploiting a different ecological niches. Aside from ''Cambroraster'', other creatures lived alongside ''T. gainesi''. The fauna in the region included the hymenocarine pancrustaceans '' Tokummia'' and ''Balhuticaris'', the primitive chordate ''Metaspriggina'', the problematically interpreted arthropod ''Kootenichela'', and the isoxid arthropod '' Surusicaris''. Like all stem and total group arthropods, ''Titanokorys'' had to shed its outer skin to grow larger. This is evidenced by the holotype specimen (ROMIP 65415) which probably represents a collection of molted remains.'''' Sometimes, fossils of these exuvia are found alongside numerous specimens of the agnostid Trilobite genus '' Peronopsis'' in the immediate vicinity or directly on the exuvia. Why the trilobites were on the exuvia is unclear, but they could have been eating from the molting residues or grazed on a possible biofilm that was growing on it.

References

{{Taxonbar, from=Q108472656

Anomalocaridids
Articles containing video clips
Prehistoric arthropod genera
Burgess Shale fossils
Cambrian arthropods
Cambrian genus extinctions