Answer Monday

A fossil!

It’s the ophiuroid Geocoma carinata! (Synonyms include Ophiocten kelheimense, Ophiopinna derecta, Ophiopsammus kelheimens, Sinosura derecta, Sinosura kelheimense, and Sinosura kelheimensis, so give yourself partial credit if you mentioned any of them, but not full credit, since these are all now defunct names.)

Here’s a terminological oddity for you. Back in the 1960s, there was a discussion in astronomical circles about observed α-radiation in the night sky. It was agreed that the radiation emanated from the sun and was then scattered by hydrogen, but there was disagreement about the location of the hydrogen, with three rival hypotheses advanced: the interplanetary hypothesis, the geocorona hypothesis (with the hydrogen in the luminous part of the exosphere), and a third hypothesis, according to which the hydrogen was spherically distributed around the Earth—in what “can be called the ‘geocoma,’ by analogy with comets”—as well as in a “downward tail or ‘geotail.’” (I quote from John C. Brandt’s “Interplanetary Gas v. a Hydrogen Cloud of Terrestrial Origin” [1961].) Alas, nobody seems to have noticed the possibility of confusing a huge hollow sphere of hydrogen gas with a Jurassic brittlestar, and so the scientific community continues to teeter on the brink of terminological disaster. (To be described in a sci-fi epic entitled Brittlestar Jurassica, obviously.)

Anyhow, congratulations to Dan Coleman for being the first to identify the fossil as a brittlestar in the comments, although he toyed with but rejected the identification as Geocoma, and a tip of the slow-moving low-level epifaunal detritivorous-suspension feeding hat to Dan Phelps for the photograph.