Specimen dates and species longevity: an evaluation of temporal range data for questions of ancestry in the hominin fossil record

• In Event: Graduate Competition Oral Session 2

Abstract

Utilizing Australopithecus sediba as a case study, we evaluate statements implying that this taxon cannot be ancestral to Homo as the specimens from Malapa are found later in time (~1.98 Ma) than the earliest proposed examples of our genus (~2.8–2.4 Ma). For hypotheses about the ancestral nature of A. sediba to be plausible, two things must be established. First, it must be possible for ancestral and descendant taxa to coexist. Under a budding cladogenesis model of speciation a subset of a species differentiates into a new daughter taxon while the remainder of the species maintains cohesion. Among mammals, contemporaneous ancestral and descendant taxa are reported in the literature, ranging from rodents to proboscideans. Second, the amount of time represented by a “ghost lineage” must be reasonable. Many studies that have estimated the average mammal species duration have values ranging between 2-4 Ma, although these estimates are dependent on the dataset used and the taxonomic group. Utilizing published temporal range data of fossil hominin species, and incorporating proposed dating error, we calculate a conservative average hominin species temporal range of ~0.97 Myr. Using this estimate in a thought experiment wherein Malapa represents the first appearance date (FAD), midrange date, or last appearance date of the species, possible FAD’s for A. sediba range from 2.95–1.98 Ma. As these scenarios are all equally plausible, there is no a priori reason that A. sediba could not be ancestral to Homo based solely on the dates of the specimens currently known.

Authors

• Timothy Lee Campbell, Department of Anthropology, Texas A&M University

• Chris A. Robinson, Department of Biological Sciences, Bronx Community College

• Susanne Cote, Department of Anthropology and Archaeology, University of Calgary

• Darryl J. de Ruiter, Department of Anthropology, Texas A&M University