Tempo does not correlate with mode in the fossil record

Abstract

The dominating view of evolution based on the fossil record is that established species remain more or less unaltered during their existence. Substantial evolution is on the other hand routinely reported for contemporary populations, and most quantitative traits show high potential for evolution. These contrasting observations on long- and short-time scales are often referred to as the paradox of stasis, which rests on the fundamental assumption that periods of morphological stasis in the fossil record represent minimal evolutionary change. Investigating 450 fossil time series, I demonstrate that the nonaccumulating morphological fluctuations during stasis travel similar distances in morphospace compared to lineages showing directional change. Hence, lineages showing stasis are commonly undergoing considerable amounts of evolution, but this evolution does not accumulate to produce large net evolutionary changes over time. Rates of evolutionary change across modes in the fossil record may be more homogenous than previously assumed and advocated, supporting the claim that substantial evolution is not exclusively or causally linked to the process of speciation. Instead of exemplifying minimal evolution, stasis likely represents information on the dynamics of the adaptive landscape on macroevolutionary time scales, including the persistence of adaptive zones and ecological niches over millions of years.

Assessing adequacy of models of phyletic evolution in the fossil record

“…Time series of phyletic evolution in the fossil record represent important data for understanding evolutionary change spanning more than a few decades. Comparing how alternative models fit fossil time series has greatly increased our ability to understand evolution on macroevolutionary time‐scales (e.g., Hopkins & Lidgard, ; Hunt, , ; Voje, ), but Akaike information criteria and likelihood ratio tests cannot evaluate the adequacy of fit between the model and data. Investigating the relative and absolute fit of Hunt's () models stasis, random walk and directional change to 300 fossil time series showed that most of the analysed data on phyletic evolution in the fossil record are adequately described by one of the three models (73%), but more than a quarter is not.…”

“…The majority of the data analysed in this study overlap with the data analysed in Voje et al. (), Voje (), Hunt (), Hopkins and Lidgard () and Hunt et al. (), but were filtered to meet certain criteria: Each time series had to consist of at least 10 sample means and time had to be on an absolute scale (in stead of relative).…”

“…This changed when Hunt (Hunt, , ; Hunt, Bell, & Travis, ; Hunt, Hopkins, & Lidgard, ; Hunt, Wicaksono, Brown, & Macleod, ) developed a model framework that allowed an objective evaluation of relative fit of different models to fossil time series based on their AIC scores. Hunt's models of the canonical modes stasis, directional change and random walk are widely used when analysing phyletic time series and his model framework has greatly advanced our ability to interpret the fossil record (e.g., Brombacher, Wilson, Bailey, & Ezard, ; Hopkins & Lidgard, ; Hunt, ; Hunt et al., ; Pearson & Ezard, ; Spanbauer, Fritz, & Baker, ; Voje, ).…”

Developmental bias in the fossil record

“…They argue that "the remarkable stasis exhibited by most species during millions of years is ignored (as no data)" (Gould & Eldredge, 1993). Indeed, studies on patterns of change in the fossil record have confirmed that stasis is a far more common observation than phyletic gradualism (Hunt, , 2007Hunt & Rabosky, 2014), with stasis, in this sense, more accurately regarded as directionless or nonaccumulating morphological fluctuations rather than true stagnance (Gould, 1982;Gould, 2002;Voje, 2016). The assumption that discontinuities are artifacts of incompleteness implies that phyletic gradualism is synonymous with evolution.…”

Body size evolution in an old insect order: No evidence for Cope's Rule in spite of fitness benefits of large size

“…The problem of evolutionary stasis has been discussed at depth in the evolutionary literature (Merilä et al. ; Hansen and Houle ; Voje ). Here, we show using combination of field studies and phylogenetic comparative analyses that several of the proposed mechanisms that could generate stasis are unlikely to explain slow body size evolution in odonates.…”