Hominin fossil inventory: Quantification and comparison of discrete regional and element representation among early African fossil hominins prior to the emergence of Homo erectus

Abstract

For all but the past few hundred thousand years, skeletal and dental morphology is the only evidence we have of our extinct ancestors and close hominin relatives. With a few exceptions, most lists of early hominin fossils have been assembled for single sites, formations, or taxa, with little attention paid to how different regions of the skeleton contribute to taxon hypodigms. We recognize there are different ways to divide up the hominin fossil record into taxa, but here, we present an inventory of the fossil evidence for the hypodigms of 14 early African hominin taxa that predate the emergence of Homo erectus. The hypodigms are limited to specimens that have been published and unambiguously attributed to a species. We use a novel, fine-resolution coding scheme that allows us to provide detailed counts of element and subelement abundance by taxon. We then compare the element counts of the taxon hypodigms with each other and with a novel standard based on a perfectly preserved skeleton we refer to as ‘hominin expected.’ The resulting hypodigms generally support commonly held assumptions about the early hominin fossil record (e.g., teeth dominate the hypodigms of all taxa), but they do not support the conventional wisdom that there are differences in the regional representation of the hypodigms of taxa that are found exclusively in eastern versus southern Africa. These data and analyses are a first step in exploring the differences in the composition of early hominin hypodigms. They will allow researchers to focus their comparative research on skeletal regions that are well-represented in the early hominin fossil record, as well as serve as tools for developing and addressing hypodigm-scale hypotheses that are central to our understanding of hominin evolution.