ABSTRACT: Taphonomy of a living fossil: The lingulide brachiopod Glottidia palmeri Dall from Baja California, Mexico.


Kowalewski, M.
Palaios 11:3, pp. 244-265.


Glottidia palmeri Dall, a Recent lingulide brachiopod, inhabits intertidal flats of the Colorado Delta plain in Baja California, Mexico. Live lingulides occur in patches across the intertidal zone. Patches are dominated by single cohorts with unimodal size-frequency distributions. The oldest cohorts appear to be between four and five years old. Dead specimens of G. palmeri occur in three modes: (1) In situ shells remaining after death in their burrows. These undergo decay and maceration, are blacken, soften, and eventually disintegrate. They persist up to at least a year and represent a slightly time-averaged, but strictly in place record of a single patch; (2) Surface shells removed from their burrows before or soon after death. These are deposited d on the surface as single valves and undergo quick mechanical disintegration. They disappear within days, or at most weeks, and are a synchronous but spatially mixed record of different patches coexisting on the flat; (3) Beach shells represented by dried shells with mummified soft bodies. These specimens were washed out by storms and deposited on supratidal beach ridges. They disappear within weeks to months and are a synchronous, but spatially mixed record of different patches.

This study offers criteria for the recognition and interpretation of preservation modes in fossil lingulides. Moreover, it confirms previous notions that Recent lingulide brachiopods have a very low fossilization potential and suggestions that high to catastrophic sedimentation rates are needed to preserve them. Thus, large-scale aspects of lingulide history (e.g., global taxonomic diversity, stratigraphic ranges) must be poorly recorded in the fossil record. At the same time, extensive time-averaging or significant transport of lingulide shells are highly unlikely. Therefore, on those rare occasions when lingulide shells are preserved, they record outcrop-scale, short-term aspects of their history with high fidelity. The literature on the Paleozoic lingulides suggests that they had a higher fossilization potential than their post-Paleozoic relatives. Thus, this study is most applicable to Mesozoic and Cenozoic lingulides. Most importantly, this study suggests that the fossil record of the lingulides may be affected by a taphonomic megabias -- their decrease in diversity and ecologic importance after the Paleozoic may be, in part, a taphonomic artifact.


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