# First report of a nearly complete comatulid crinoid (Comatulida, Echinodermata) from the Cretaceous of Australia

## TL;DR

A nearly complete fossil of a stalkless crinoid from the Cretaceous of Australia is described, marking the first of its kind found in the Southern Hemisphere.

## Contribution

This study presents the first nearly complete comatulid crinoid fossil from Australia and the Southern Hemisphere, including arms and pinnules.

## Key findings

- The fossil includes a centrodorsal, arms, and pinnules, assigned to Solanocrinitidae gen. et sp. indet.
- The fossil shows variation in arm branching due to regeneration after autotomy.
- It is the first opalized comatulid crinoid found worldwide and the second articulated comatulid from the Southern Hemisphere.

## Abstract

Finds of stalkless comatulid crinoids in the Southern Hemisphere are extremely rare and are almost exclusively of their centrodorsals. Complete or nearly complete specimens (centrodorsal with articulated arms, cirri and/or pinnules) are known from only a few localities. Here we report a comatulid fossil comprised of a centrodorsal, arms, and pinnules, assigned to Solanocrinitidae gen. et sp. indet. The shape of the centrodorsal; the arrangement, shape, and size of radials; and the morphology of the radial cavity suggest similarity of this fossil to Solanocrinites or Archaeometra rather than to Comatulina, Pachyantedon, or Palaeocomaster. It cannot be ruled out that the studied specimen belongs to Decameros with its relatively low and discoidal centrodorsal. In the light of last phylogenetic analysis both Solanocrinites and Decameros were recovered as part of a clade comprising Himerometroidea, Tropiometridae, and Asterometridae + Ptilometridae. The preserved arms of the Australian specimen reveals variation in the branching pattern, that can be attributed to the inaccurate regeneration of arms after autotomy. This find represents the second articulated comatulid (except of uintacrinids) which consists not only of the centrodorsal, but also having more or less complete arms and pinnules, from the Cretaceous of the Southern Hemisphere. It is also the first found from Australia. The only opalized crinoid known in the world is the stalked isocrinid (Isocrinida) Isocrinus australis. Thus, the present find is also the first record of an opalized comatulid crinoid worldwide. Additionally, the thin sections reveal the occurrence of transversal sections of pelagic roveacrinids (saccocomids), which are also the first from the Australian continent.

The online version contains supplementary material available at 10.1038/s41598-025-90111-2.