MASSIVE COLLECTIONS OF MICROVERTEBRATES—IS THERE EVER TOO MUCH OF A GOOD THING?

The fossil record is the most comprehensive archive of past life, yet is woefully incomplete. Paleontologists have long sought to overcome its weaknesses, not just by collecting additional fossils, but also by developing sophisticated analyses, mostly rooted in statistics, to account for its many biases. However, many of these techniques were developed for the nonmarine invertebrate record, which probably represents more homogenous (less biased) conditions and assemblages that are arguably more amenable to these analyses. By comparison, the nonmarine vertebrate record is far more stochastic in nature, especially when large, multitaxic attritional assemblages are considered. One commonly used technique to assess diversity in nonmarine systems is rarefaction, which posits that, once reaching an asymptote, additional collecting will only occasionally recover elements new to the assemblage.

A decidedly non-quantitative survey of multiple Triassic attritional assemblages from southeastern USA and beyond suggests that even enormous (>10,000 identifiable specimens) assemblages barely encapsulate important (publishable!) taxa. Examples include a microvertebrate assemblage from Moncure, North Carolina (>50,000 specimens), the Placerias-Downs’ quarry complex in Arizona (>25,000 specimens at three institutions), Driefontein in South Africa (>100,000 specimens) and a new Triassic site in New Mexico with a similarly large collection. In each case new and/or exceptionally rare taxa are represented by much less than 1% of the total specimens, yet affect our interpretations of paleobiodiversity, paleogeography, and biostratigraphy. At Moncure more than 50,000 fish scales were recovered, but the tetrapod assemblage includes the first Newark Supergroup lungfish and at least 10 tetrapod taxa. The Placerias/Downs quarry was collected both traditionally and using microvertebrate methods over multiple field seasons dating to the 1920s, but two novel archosauromorphs, Syntomiprosopus sucherorum and the aetosaur Kryphioparma caerula, were only identified and named since 2015. At Driefontein relatively rare records represent taxa new to the assemblage, Gondwana, or even science. Ergo, when it comes to microvertebrate fossil collections the mantra of 1980s MTV may apply: “Too much is never enough.”