The crinoid Eugeniacrinites cariophilites from the Late Jurassic of southern Germany: babies, cripples and enigmatic wing plates
| Autor: | Hans Hess |
|---|---|
| Rok vydání: | 2014 |
| Předmět: | |
| Zdroj: | Swiss Journal of Palaeontology. 133:121-140 |
| ISSN: | 1664-2384 1664-2376 |
| DOI: | 10.1007/s13358-014-0064-8 |
| Popis: | The material for the present paper is based on 50 kg of processed sediment from the Early Kimmeridgian of Geisingen. The most frequent crinoids comprise cups and brachials of the roveacrinid Saccocoma quenstedti while Crassicoma feifeli is represented by a few cups only; these remains are not described. Cups and primibrachials of Eugeniacrinites cariophilites are the commonest cyrtocrinids, while cups of Pilocrinus moussoni are rather rare and not further treated, as are columnals of the two species. The ontogenetic series of cups and axillary primibrachials of E. cariophilites starts from ossicles of about 0.5 mm in height; and growth is allometric in both types. Postlarval cups resemble phyllocrinids; the distinctive shape with lanceolate interradial extensions and wide articular facets appears at a later stage. The spearhead-shaped axillary primibrachials are synapomorphic. The youngest of these ossicles with a muscular facet proximally were able to form a flat roof over the radial cavity. First primibrachials with synostosial distal facet appeared at a slightly later stage with a width of 1 mm; growth is isometric. A significant number of cups are mutilated by bite marks. The predatory attacks were sublethal in most cases as shown by secondary stereom growth and regenerated facets. First primibrachials are not deformed, but deformations occur in a small number of second primibrachials. The results suggest that the predators, presumably fishes, targeted the soft parts in the cup. Enigmatic brachials with a large wing to one side and a facet to an arm are thought to belong to E. cariophilites and presumably attached to deformed cups; the wings may have been an antipredatory adaptation providing some shelter to the cup. The various antipredator morphologies in cyrtocrinid history are discussed. The presently available growth series of Eugeniacrinites invites discussion of early cyrtocrinid phylogeny. Eugeniacrinites seems to have been derived from Phyllocrinidae; and Sclerocrinidae with Cyrtocrinus as the first representative in the Middle Jurassic is thought to have originated from Early Jurassic Tetracrinidae such as Bilecicrinus. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|