REVISITING THE QUALITY OF CALIFORNIA'S FOSSIL RECORD

The marine fossil record has the potential to capture a very high percentage of once living species. Valentine’s (1989) classic study “How good was the fossil record?” reported that 538 of 698 living molluscs (77%) were known as Pleistocene fossils. That study suggested that species not found as fossils had traits such as rarity, small body size, or preference for deeper habitats, although these findings were based on largely anecdotal data.

Large-scale digitization of major paleontological and modern invertebrate collections lays the groundwork for much finer resolution assessment of the qualities of the Pleistocene fossil record, in addition to elucidating the traits of species that either succeed or fail to leave a fossil record. Here we reproduce Valentine’s study using a dataset of more than 1.8 million specimens (50,000 lots) digitized from the Natural History Museum of Los Angeles County’s (NHM) Invertebrate Paleontology collection, paired with rich data from NHM’s Malacology collection, and an exhaustive literature search on reported Quaternary occurrences.

A review of recent publications on molluscs of the Californian province, indicates the presence of more than 1590 named living species. A survey of literature on Quaternary molluscs (including the Gelasian) discovered 898 species bearing a fossil record from this region, of which 192 are now extinct. Adding data from NHM paleontology collections reveals an additional 171 named species for which a fossil record had not previously been reported, in addition to many as yet unnamed species. A difference of 524 represents the number of living species for which a fossil record cannot be established. Many of these occur in depths greater than 50 m (23%), are rare among living faunas (22%), are known only from their type locality (22%), and are less than 5 mm in maximum diameter (21%).

The digital revolution in natural history museum collections is mobilizing a vast quantity of historically inaccessible knowledge. Critical examination of these new data not only informs us about the quality of the fossil record, but can enable more precise estimates of geographic and stratigraphic ranges, the magnitude and selectivity of extinctions, and improved knowledge of the distribution of taxa across environmental gradients, among many other paleobiological themes.