LIFE AND DEATH ON THE EDGE: THE BIODIVERSITY, PALEOECOLOGY, AND TAPHONOMY OF ROCKY INTERTIDAL INVERTEBRATES

The rocky intertidal is a biologically diverse area between marine and terrestrial habitats where organisms are highly adapted to physical disturbance and complex biological interactions. The fossil record of these habitats is therefore important to understanding evolutionary and ecological patterns and processes. While the fossil record of the rocky intertidal is uneven through time and space, these habitats contribute significantly to knowledge of past biodiversity in tectonically active margins.

The quality of the fossil record, taphonomy, and biodiversity of rocky intertidal habitats are documented from the Cenozoic of western North America. Museum collection data and a review of the literature are used to quantify the deep-time record of these habitats. A case study in which the late Pleistocene record is compared with known biodiversity of the modern Palos Verdes Peninsula of California incorporates both field paleontology and extensive modern ecological data.

The Cenozoic molluscan fossil record of western North America is characterized by depauperate rocky shore diversity through most of the Paleogene and Neogene. Diversity rises significantly in the Pliocene (~200 spp.) as rock volume of nearshore facies increases, and again the Quaternary (~300 spp.) as coastal environments are influenced by eustatic sea level fluctuations. Fewer than 50 extant shelled molluscan species reported from the rocky intertidal of western North America lack a fossil record, owing to factors such as ecological rarity, geographic restriction, and small body size.

The modern rocky intertidal of the Palos Verdes Peninsula provides broader insight into the overall completeness and quality of the Quaternary fossil record. Of the more than 700 extant species of diverse marine invertebrates and algae reported from this well sampled region, only bivalves, gastropods, and chitons have a relatively complete fossil record. Arthropoda, Cnidaria, Bryozoa, and Echinodermata are poorly represented, while other invertebrate and algal phyla lack a fossil record entirely.