Lepidochitona lioplax is one instance of a fossil chiton. It was initially described from Oligocene rocks belonging to the Sooke Formation of southern Vancouver Island in British Columbia. Solely 4 moderate-sized valves had been initially recognized: one head valve, one intermediate, and two tails (so at the very least two people had been concerned). The valves had a easy outer floor with out a sturdy distinction in look between the central and lateral areas. The insertion plates (lateral projections of the decrease floor of the valves that in life anchor them into the encircling girdle) had been very brief. The sutural laminae (anterior projections of the decrease floor of the intermediate and tail valves that articulate with the valve in entrance) had been low, broad, and divided within the center by a broad shallow floor. Slits within the lateral insertion plates had been quite a few, with a number of within the tail valves and doubtless two or three on both sides within the intermediate valves (Smith 1960). When first described, this species was thought distinct sufficient to belong in its personal genus Oligochiton.
Oligochiton lioplax would then go little reported on till 2011 when Dell’Angelo et al. described an assemblage of chiton fossil from the most recent Eocene or early Oligocene of the Lincoln Creek Formation in Washington State. Specimens of lioplax had been comparatively quite a few on this assortment and Dell’Angelo et al. had been capable of study near 100 valves. Their observations would result in one thing of a downgrade within the species standing. Fairly than deserving its personal extinct genus, Dell’Angelo et al. felt that lioplax could possibly be comfortably accommodated within the dwelling genus Lepidochitona. Its easy valves are uncommon inside Lepidochitona however not distinctive. The supposed a number of slits within the sides of the valves didn’t stand as much as scrutiny. As a substitute, intermediate valves of L. lioplax bore solely a single slit on both sides, in step with different Lepidochitona species. The unique inference of a number of slits was an error as a result of authentic specimen being nonetheless partially embedded within the surrounding matrix.
Lepidochitona lioplax is without doubt one of the earliest recognized representatives of its genus however its actual significance is obscure. It has been recommended as a direct ancestor of the fashionable subgenus Spongioradsia however this, once more, was primarily based on the supposed slits within the intermediate valves that Dell’Angelo et al. refuted. To understand how L. lioplax connects to the massive image of Lepidochitona evolution, we’d most likely want a greater image of Lepidochitona evolution general.
Dell’Angelo, B., A. Bonfitto & M. Taviani. 2011. Chitons (Polyplacophora) from Paleogene strata in western Washington State, U.S.A. Journal of Paleontology 85 (5): 936–954.
Smith, A. G. 1960. Amphineura. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt I. Mollusca 1: Mollusca—Basic Options, Scaphopoda, Amphineura, Monoplacophora, Gastropoda—Basic Options, Archaeogastropoda and a few (primarily Paleozoic) Caenogastropoda and Opisthobranchia pp. I41–I76. Geological Society of America, and College of Kansas Press.