CONGRUENT PHYLOGENETIC AND FOSSIL SIGNATURES OF MAMMALIAN DIVERSIFICATION DYNAMICS

Computational methods for estimating diversification rates from extant species phylogenetic trees have become abundant in evolutionary research. However, there is virtually no direct test for the congruence between evolutionary rates obtained from this kind of data with rates estimated from the fossil record. This task is only achievable in clades with both a well-known fossil record and a complete phylogenetic tree. Here, we compare the evolutionary rates of ruminant mammals as estimated from their vast paleontological record —over 1200 species spanning 50 my— and their living-species phylogeny. Fossil-based evolutionary rates were estimated based on a cured dataset including 9186 occurrences using two approaches: the bin-based ’three-timers’ method and a birth-death Bayesian approach (PyRate). Phylogenetic rates were estimated using the yuleWindow function in the R package ape on 1 myr temporal bins. The phylogenetic analyses were run on two different published tree distributions with 500 trees each.

Our results revealed that the ruminant’s fossil record and phylogeny reflect congruent evolutionary processes. The concordance is especially strong for the last 25 my, when living groups became a dominant part of ruminant diversity. Also the high faunal replacement and lineage depletion in Eocene and Oligocene times marked the shape of the living ruminants tree to a great extent, restricting the number of lineages that it recovers from the fist half of the analysis interval. This is probably the case of other groups of land vertebrates.

Both increasing extinction or decelerating speciation can cause rate slowdowns in living taxa trees. Distinguishing between these alternatives is challenging if just neontological information is available. Interestingly, our combined analysis suggest that the early Miocene post-radiation slowdown detected in living ruminant trees was probably rendered by a speciation slowdown coupled with constant, moderate extinction. Thus, this slowdown in the living ruminant tree is rendered at the end of an expansion phase of the modern forms and not by extinction increasing above speciation. On the contrary, we detected a recent deceleration in phylogenetic rates that is probably connected to rapid extinction triggered by recent climatic fluctuations.