Infaunal molting in calmoniids trilobites: the polyphyletic origin of a defensive character in the context of the Mid Paleozoic Marine Revolution

RUSTÁN, J.J.; FOGLIA, R.D.; BALSEIRO, D.; IWASAKI, Y.

Dublin

Congreso; 56th Palaoentological Association Annual Meeting, Dubin 2012; 2012

Infaunalism for molting in trilobites was firstly recognized based on a striking three-dimensional molt pattern of the phacopid Paciphacops, from the Silurian-Devonian of Argentina (Rustán et al. 2011). Later, the same molt pattern was identified in several Viaphacops species from the Devonian of Bolivia (Rustán et al, 2012). In turn, a throughout taxonomic revision indicated that one Argentinian species should be considered as Echidnops. Here we report the diagnostic molt pattern in several specimens of the calmoniid Pennaia verneuili from the Middle Devonian of the Sica Sica Formation, La Paz, Bolivia (AMNH collection, USA). Concerning a phylogenetical context, these evidences definitively confirm that the infaunal molt behavior, as ethological defensive character, appeared more than once in different trilobite families (i.e. phacopids and calmoniids) thus being clearly polyphyletic. This finding provides new insights for the understanding of the wvolutionary-ecological context of the “Middle Paleozoic Marine Revolution” (Signor and Brett, 1984), a major bioevent related with an arms race triggered by the sudden appearance of several groups of durophagous predators in Silurian-Devonian marine ecosystems.