Were all trilobites fully marine?

Trilobites, the poster-fossil of the Paleozoic, have long been considered to be invariably fully marine. Collaborative work between Dr. Mángano, Dr. Buatois, and Argentinian colleagues questions this assumption. Through the integration of multiple datasets they report uncontroversial evidence of the exploration of tide-dominated estuaries by some trilobite groups (olenids & asaphids) throughout the Furongian to Middle Ordovician. Thick siliciclastic successions in northwest Argentina expose vertically-repeating nearly-identical environments and allowed for the comparison of body-fossil and trace-fossil data in tide-dominated estuaries through time. Their research indicates two forays into brackish water, first the colonization of the outer portion of estuaries by olenids, followed by the colonization of inner to middle estuarine zones by asaphids.

The full article is available in the Proceedings of the Royal Society B (including some fantastic photos of trilobite trace fossils in the Supplementary Info!).

Figure. Time-environment matrix showing protracted trilobite expansion into marginal-marine estuarine settings. (From Mángano et al., 2021)

Written by Brittany Laing

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