A diverse assemblage of Permian echinoids (Echinodermata, Echinoidea) and implications for character evolution in early crown group echinoids

Abstract

The Permian is regarded as one of the most crucial intervals during echinoid evolution because crown group echinoids are first widely known from the Permian. New faunas provide important information regarding the diversity of echinoids during this significant interval as well as the morphological characterization of the earliest crown group and latest stem group echinoids. A new fauna from the Capitanian Lamar Member of the Bell Canyon Formation in the Guadalupe Mountains of West Texas comprises at least three new taxa, includingEotiaris guadalupensisThompson n. sp. an indeterminate archaeocidarid, andPronechinus? sp. All specimens represented are silicified and known from disarticulated or semiarticulated interambulacral and ambulacral plates and spines. This assemblage is one of the most diverse echinoid assemblages known from the Permian and, as such, informs the paleoecological setting in which the earliest crown group echinoids lived. This new fauna indicates that crown group echinoids occupied the same environments as stem group echinoids of the Archaeocidaridae and Proterocidaridae. Furthermore, the echinoids described herein begin to elucidate the order of character transitions that likely took place between stem group and crown group echinoids. At least one of the morphological innovations once thought to be characteristic of early crown group echinoids, crenulate tubercles, was in fact widespread in a number of stem group taxa from the Permian as well. Crenulate tubercles are reported from two taxa, and putative cidaroid style U-shaped teeth are present in the fauna. The presence of crenulate tubercles in the archaeocidarid indicates that crenulate tubercles were present in stem group echinoids, and thus the evolution of this character likely preceded the evolution of many of the synapomorphies that define the echinoid crown group.

A new stem group echinoid from the Triassic of China leads to a revised macroevolutionary history of echinoids during the end-Permian mass extinction

“…Our analyses also show that stem group and crown group echinoids, which inhabited the same environments in the Permian [ 28 ], must have coexisted from the Roadian, when the first crown group echinoid is known from the fossil record, until at least the Anisian occurrence of Y. luopingensis ( figure 3 a ). This implies an overlap in stratigraphic ranges of approximately 23 Myr between stem group and crown group echinoids ( figure 3 b ), and potentially longer as suggested by disarticulated ossicles [ 7 ].…”

Phylogenetic analysis of the Archaeocidaridae and Palaeozoic Miocidaridae (Echinodermata, Echinoidea) and the origin of crown group echinoids

“…Thompson et al . () recently showed that crenulate tubercles are present in a number of Permian archaeocidarids, and that this character probably pre‐dated the origin of the crown‐group echinoids. Given that there are no archaeocidarid species in our analyses from the Permian, however, crenulate primary tubercles are limited to A. apheles and the miocidarids.…”

“…The geologically oldest crown group echinoids are the cidaroids of the family Miocidaridae Durham & Melville, , which confidently date to, at the oldest, the Roadian stage of the Permian (Thompson et al . , ). Fossil‐calibrated divergence time estimation analyses also consistently place the origin of the echinoid crown group in the Permian or Carboniferous (Smith et al .…”

The youngest ophiocistioid: a first Palaeozoic‐type echinoderm group representative from the Mesozoic

“…Reich & Smith ; Thompson & Denayer ; Thompson et al . ; Thompson & Ewin ). A few of these taxa have teeth elements adorally serrated ( Archaeocidaris , Fournierechinus , Hyattechinus , Polytaxicidaris , Proterocidaris ; Reich & Smith ; Thompson & Denayer ; Thompson et al .…”

“…A few of these taxa have teeth elements adorally serrated ( Archaeocidaris , Fournierechinus , Hyattechinus , Polytaxicidaris , Proterocidaris ; Reich & Smith ; Thompson & Denayer ; Thompson et al . ; Thompson & Ewin ) with a primary point flanked by 2–3 secondary points (cf. Reich & Smith , fig.…”