On the basis of a statistical extrapolation, Faith & Surovell (2009) suggest the current sample is “consistent with the synchronous extinction of all taxa between 12,000 and 10,000 radiocarbon years” ago (Faith & Surovell 2009, pp. 20,643–44). Leaving aside the validity of the extrapolation, the timing of extinctions is being determined primarily by Last Appearance Dates (LADs), the youngest age available for a genus. But knowing that an animal was extinct by the end of the Pleistocene is not evidence that it went extinct at the end of the Pleistocene, as is routinely assumed (e.g., Fiedel 2009, Gillespie 2008, Grund et al. 2012, Sandom et al. 2014), nor does it necessarily aid in understanding why a genus went extinct.

This is so for several reasons. First, LADs are just a Last Date, not a Last Appearance. Given the vagaries of preservation and sampling, and the proposition that rare animals disappear from the fossil record before they go extinct (the Signor-Lipps Effect), the last mammoth dated was almost certainly not the last mammoth standing (Meltzer 2009; see also Boulanger & Lyman 2014, Haynes 2013, Waguespack 2013). In fact, the DNA of Pleistocene megafauna has been recovered from Holocene-age sediments in Alaska, revealing that some genera survived well after their last dated appearance as macrofossils (Haile et al. 2009).

More importantly, knowing when the extinction process ended is largely irrelevant: To understand what caused the process we need to know when and why it began (Meltzer 2009; see also Meltzer & Mead 1985). By way of analogy, on Saturday, November 18, 1995, the last Bethlehem Steel plant ceased operations and the company, billions of dollars in debt, went bankrupt. An explanation for why that happened is not the trading price of domestic steel the Friday before, but instead the commercial, economic, political, technological, and other forces that buffeted the company over more than a century. Likewise, to understand what caused mammalian extinctions it is vital to understand the processes that might have led to this outcome (Meltzer 2009; see also Boulanger & Lyman 2014, Bradshaw et al. 2012). An important step toward that goal will be tracking megafaunal population changes through time to identify when the population of an extinct genus began to trend downward. In effect, more will be gained by determining (for lack of a better phrase) the “Initial Decline Date” (IDD) of a genus than its LAD.