Archive for June 23rd, 2013

Wooster’s Fossil of the Week: A barnacle-bored belemnite from the Jurassic of Spain

June 23rd, 2013

Hibolites_barnacle_borings585Two subjects of previous Fossil of the Week posts are combined together here: a belemnite (the elegant Hibolites hastatus) and barnacle borings (the ichnofossil Rogerella). This specimen is from the Jurassic of Moneva Teruel, Spain.

(Living belemnites reconstructed by Bogdanov on Wikipedia)

(Living belemnites reconstructed by Bogdanov on Wikipedia)

Belemnites are extinct cephalopods, oddly enough. The specimen is the guard or rostrum — a calcitic internal skeleton that gave the squid-like animal rigidity. Because they are made of solid, stable calcite, these guards can be extremely common in the fossil record, especially in the Jurassic and Cretaceous. Some people call these “belemnite battlefields”, probably because the fossils look so much like bullets.

de_BlainvilleHibolites hastatus was named by Henri Marie Ducrotay de Blainville (1777-1850) in 1827. He was a French naturalist with many accomplishments, especially in anatomy and systematics. He spent most of his career in the Faculty of Sciences at Paris, where he was a colleague (and eventual ideological enemy) of the epic Georges Cuvier. In 1830 he took over from the “father of invertebrate zoology” Jean-Baptiste Lamarck as the chair of natural history. Clearly he ran in powerful circles.

The yellow features in this close-up above are holes drilled by acrothoracic barnacles, which were then filled with fine-grained dolomite. The trace fossil thus formed is known as Rogerella. It is found from the Devonian all the way to today. Its presence on these belemnite guards shows that these structures laid for enough time on the seafloor that they could be colonized by barnacles. They are thus an indicator of the taphonomy (or history from death to discovery) of these fossils.

References:

Doyle, P. and MacDonald, D.I.M. 1993. Belemnite battlefields. Lethaia 26: 65-80.

Lambers, P. and Boekschoten, G.J. 1986. On fossil and recent borings produced by acrothoracic cirripeds. Geologie en Mijnbouw 65: 257–268.

Mariotti, N. 2002. Systematics and taphonomy of an Early Kimmeridgian belemnite fauna from the Mediterranean Tethys (Monte Nerone, Central Apennines, Italy). Geobios 35: 213-232.