First report of a nearly complete comatulid crinoid (Comatulida, Echinodermata) from the Cretaceous of Australia Mariusz A. Salamon, Tamas Kapitany & Bartosz J. Płachno

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 Archaeometrarather 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.

南半球无柄羽星海百合（stalkless comatulid crinoids）的化石发现极为罕见，且几乎仅保存有中背板（centrodorsal）。带有有关节的腕、卷枝和/或羽枝的完整或近乎完整的中背板标本，仅在少数产地被报道。本文报道一件产自澳大利亚的羽星海百合化石，其包含中背板、腕与羽枝，归属于索兰海百合科（Solanocrinitidae）未定属种（gen.et sp. indet.）。该化石的中背板形态、辐板（radials）的排列方式、形态与尺寸，以及辐射腔（radial cavity）的形态特征，均显示其与索兰海百合属（Solanocrinites）或古美羽星属（Archaeometra）具有相似性，而非羽星科（Comatulina）、厚羽星属（Pachyantedon）或古羽星属（Palaeocomaster）。无法排除该研究标本隶属于德卡海百合属（Decameros）的可能性，该属具有相对低平的盘状中背板。根据最新的系统发育分析（phylogenetic analysis）结果，索兰海百合属与德卡海百合属均被归入包含希美羽星超科（Himerometroidea）、热带海百合科（Tropiometridae）、星海百合科（Asterometridae）与羽枝海百合科（Ptilometridae）的演化支（clade）。该澳大利亚标本保存的腕部显示出分支模式的变异，这可归因于自割（autotomy）后腕部的不完全再生。本次发现是南半球白垩纪（Cretaceous）地层中，第二件不仅保存中背板，还带有近乎完整腕部与羽枝的有关节羽星海百合化石（不包含乌塔海百合科Uintacrinidae）；同时也是澳大利亚境内首次发现的该类化石。目前全球已知的唯一一件欧泊化（opalized）海百合化石为有柄等节海百合目（Isocrinida）的澳大利亚等节海百合（Isocrinus australis）。因此，本次发现同时也是全球首例欧泊化羽星海百合化石记录。此外，薄片切片（thin sections）分析显示存在远洋漫游海百合类（roveacrinids，囊海百合科saccocomids）的横切面，这也是澳大利亚大陆首次发现的该类化石。