Cassubia

''Peytoia infercambriensis'' is a species of hurdiid radiodont in the genus ''Peytoia''.

''P. infercambriensis'' is the geologically oldest known radiodont; its remains date to the third age of the Cambrian. The type and only known specimen, a partial appendage, was found in a core sample from a borehole nearly five kilometers deep in northern Poland. ''P. infercambriensis'' was previously regarded as belonging to a separate genus, ''Cassubia'', named after the historical region of Kashubia in which the specimen was found, but ''Cassubia'' is now considered a junior synonym of ''Peytoia''.

History of study

Discovery and naming

The holotype—and only—specimen was recovered from the Kościerzyna borehole, in the Cambrian Stage 3 aged Zawiszyn Formation. It was found in the Fallotaspis Zone making it older than the Chengjiang biota. It was described by Kazimiera Lendzion in 1975 and given the name ''Pomerania infercambriensis'', in reference to its Lower Cambrian provenance and the Pomerania region in which the specimen was found. In her initial description, Lendzion interpreted the fossil as preserving 11 thoracic segments and a chelicera of a ''Leanchoilia''-like arthropod. In 1977, Lendzion discovered that the name ''Pomerania'' had already been used by an ammonoid, so she renamed the genus ''Cassubia'', after the Kaszuby region of where the specimen was found.

Reinterpretations

In 1988, Jerzy Dzik and Kazimiera Lendzion reinterpreted the specimen as representing the appendage of an anomalocaridid. They interpreted both the "thorax" and "chelicera" as both parts of a single elongate appendage, similar to that of ''Anomalocaris''. Some researchers, such as Simon Conway Morris, suggested that it may even be synonymous with ''Anomalocaris'' itself. In 1995, E. L. Bousfield proposed a taxonomic arrangement of early arthropods in which ''Cassubia'' and ''Anomalocaris'' were assigned to the same class, Anomalocaridea, but ''Cassubia'' was given a subclass of its own, Cassubiata. Though recognizing ''Cassubia'' as related to ''Anomalocaris'', Bousfield followed Lendzion's original interpretation of the specimen as comprising a short appendage and long body. When the radiodont ''Tamisiocaris'' was discovered by Allison Daley and John Peel in 2010, they took note of its apparent similarity to ''Cassubia infercambriensis'', as it had been interpreted by Dzik and Lendzion. In 2012, Joachim Haug et al. interpreted ''Cassubia'' as similar to the megacheiran ''Occacaris''.

These diverse interpretations led Alison Daley and David Legg to restudy the original specimen. They concluded that the specimen did indeed consist of both a body and appendage, but that they did not belong to the same animal. Rather, the body was that of an indeterminate arthropod, while the appendage was that of a radiodont similar to ''Peytoia nathorsti''. As such, they synonymized ''Cassubia'' with ''Peytoia'', making the new combination ''Peytoia infercambriensis''.

Description

''Peytoia infercambriensis'' differed from its close relative ''Peytoia nathorsti'' in several characteristics of its frontal appendage, the only part of its anatomy known. The ventral spines are only half as wide as the associated podomere, and are estimated to have borne approximately 24 tightly-spaced auxiliary spines. The endites decrease sharply in length, such that the distalmost endite is only a quarter the length of the proximalmost.

Paleoecology

The Zawiszyn Formation, in which the only known specimen of ''Peytoia infercambriensis'' was found, dates back to the third age of the Cambrian, making ''P. infercambriensis'' the oldest known radiodont. ''P. infercambriensis'' predates the earliest known mineralized trilobites from Poland, but the trilobite-like nektaspid '' Liwia'' is known from close to the same layer as ''P. infercambriensis''. The enigmatic small shelly fossil ''Mobergella'' is abundant in the rock layers where ''Liwia'' and ''P. infercambriensis'' are found. The depositional environment was a shallower-water environment than typical of places with Burgess Shale-type preservation.

References

{{Taxonbar, from=Q5049517

Fossils of Poland
Anomalocaridids