Evolution of the Earliest Horses Driven by Climate Change in the Paleocene-Eocene Thermal Maximum

Secord, Ross; Bloch, Jonathan I.; Chester, Stephen G. B.; Boyer, Douglas; Wood, Aaron R.; Wing, Scott L.; Kraus, Mary J.; McInerney, Francesca A.; Krigbaum, John

doi:10.1126/science.1213859

Cited by 193 publications

(150 citation statements)

References 31 publications

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“…When a sequence is modeled as a directional trend, for example, it is assumed that the trend holds with the same strength over the entire temporal span of measured fossil populations. Paleontologists have long explored explanations that violate this kind of uniformity (10,17,18), and several have warned of the limitations of trying to coerce a broad variety of evolutionary phenomena into a few, too-simplified models (16,(19)(20)(21).…”

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confidence: 99%

Simple versus complex models of trait evolution and stasis as a response to environmental change

Hunt

Hopkins

Lidgard

2015

Proc. Natl. Acad. Sci. U.S.A.

126

170

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Previous analyses of evolutionary patterns, or modes, in fossil lineages have focused overwhelmingly on three simple models: stasis, random walks, and directional evolution. Here we use likelihood methods to fit an expanded set of evolutionary models to a large compilation of ancestor-descendant series of populations from the fossil record. In addition to the standard three models, we assess more complex models with punctuations and shifts from one evolutionary mode to another. As in previous studies, we find that stasis is common in the fossil record, as is a strict version of stasis that entails no real evolutionary changes. Incidence of directional evolution is relatively low (13%), but higher than in previous studies because our analytical approach can more sensitively detect noisy trends. Complex evolutionary models are often favored, overwhelmingly so for sequences comprising many samples. This finding is consistent with evolutionary dynamics that are, in reality, more complex than any of the models we consider. Furthermore, the timing of shifts in evolutionary dynamics varies among traits measured from the same series. Finally, we use our empirical collection of evolutionary sequences and a long and highly resolved proxy for global climate to inform simulations in which traits adaptively track temperature changes over time. When realistically calibrated, we find that this simple model can reproduce important aspects of our paleontological results. We conclude that observed paleontological patterns, including the prevalence of stasis, need not be inconsistent with adaptive evolution, even in the face of unstable physical environments.evolutionary mode | stasis | gradualism | punctuated equilibrium | climate change P aleontologists have long sought to document patterns of trait change within fossil species and to infer from these patterns their underlying evolutionary drivers (1-3). However, only recently have sufficient case studies accumulated to assess what the aggregated fossil record has to say about phenotypic evolution occurring on the 10 5 -to 10 7 -y timescales routinely captured in paleontological sequences. Several factors have contributed to this cumulative increase, including advances in geochronology that more readily permit time-calibrating evolutionary sequences, better morphometric practices for documenting trait change, and new analytical tools to examine the resulting data. Perhaps most important, however, is that paleontologists were motivated to capture many additional examples of trait evolution in fossil lineages in response to the intense debate centered around punctuated equilibrium (4-6)-the notion that species do not usually evolve gradually over long periods of time but instead emerge in a discontinuous pattern, in bursts of change associated with cladogenesis followed by longer intervals of morphological stasis.Punctuated equilibrium proponents and critics disagreed about how best to interpret the same patterns of trait evolution, and thus early reviews (7, 8) did little to reso...

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mentioning

confidence: 99%

Simple versus complex models of trait evolution and stasis as a response to environmental change

Hunt

Hopkins

Lidgard

2015

Proc. Natl. Acad. Sci. U.S.A.

126

170

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“…55 MYA), especially during the Miocene (Janis and Wilhelm, 1993;Edwards et al, 2010;Figueirido et al, 2012;Lovegrove, 2012b;Secord et al, 2012;Lovegrove and Mowoe, 2013). Moreover, during the Late Cenozoic, both unguligrade and digitigrade mammals showed body size increases (Alroy, 1998;Smith and Lyons, 2011;Lovegrove and Mowoe, 2013) and increased hypsodonty in unguligrade mammals (MacFadden, 2000;Jardine et al, 2012).…”

Section: The Evolution Of Micro-cursoriality In Elephant-shrewsmentioning

confidence: 99%

The evolution of micro-cursoriality in mammals

Lovegrove

Mowoe

2014

Journal of Experimental Biology

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In this study we report on the evolution of micro-cursoriality, a unique case of cursoriality in mammals smaller than 1 kg. We obtained new running speed and limb morphology data for two species of elephantshrews (Elephantulus spp., Macroscelidae) from Namaqualand, South Africa, which we compared with published data for other mammals. Elephantulus maximum running speeds were higher than those of most mammals smaller than 1 kg. Elephantulus also possess exceptionally high metatarsal:femur ratios (1.07) that are typically associated with fast unguligrade cursors. Cursoriality evolved in the Artiodactyla, Perissodactyla and Carnivora coincident with global cooling and the replacement of forests with open landscapes in the Oligocene and Miocene. The majority of mammal species, though, remained non-cursorial, plantigrade and small (<1 kg). The extraordinary running speed and digitigrady of elephant-shrews was established in the Early Eocene in the earliest macroscelid Prodiacodon, but was probably inherited from Paleocene, Holarctic stem macroscelids. Micro-cursoriality in macroscelids evolved from the plesiomorphic plantigrade foot of the possum-like ancestral mammal earlier than in other mammalian crown groups. Microcursoriality evolved first in forests, presumably in response to selection for rapid running speeds facilitated by local knowledge, in order to avoid predators. During the Miocene, micro-cursoriality was pre-adaptive to open, arid habitats, and became more derived in the newly evolved Elephantulus and Macroscelides elephant-shrews with trail running.

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“…When detailed climatic records for the global oceans OPEN ACCESS (especially the early oxygen isotope curves) became available as a proxy for North American climates, the claim that there was a strong association between climate and mammalian diversity appeared in papers such as those by Webb [4,5] and especially in papers by Janis [6][7][8] and Vrba [9,10]. In recent years, the number of studies asserting the climatic causes of Cenozoic mammalian diversity is increasing [11][12][13][14][15][16][17][18]. But Alroy [19][20][21], using similar methods of analysis but different statistical methods, concluded that there was no statistical relationship between North American mammalian diversity and Cenozoic climate proxies, such as the oxygen isotope curve.…”

Section: Introductionmentioning

confidence: 99%

Cenozoic Mammals and Climate Change: The Contrast between Coarse-Scale versus High-Resolution Studies Explained by Species Sorting

Prothero

2012

Geosciences

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Many paleontologists have noticed the broadly similar patterns between the changes in Cenozoic mammalian diversity and taxonomic dominance and climate changes. Yet detailed studies of fossil population samples with fine-scale temporal resolution during episodes of climate change like the Eocene-Oligocene transition in the White River Group, and the late Pleistocene at Rancho La Brea tar pits, demonstrates that most fossil mammal species are static and show no significant microevolutionary response to major climate changes. This mismatch between patterns seems best explained by species sorting. As the punctuated equilibrium model demonstrated, over long time spans most fossil species are stable and do not respond to climate change. Instead, change occurs at the next hierarchical level, with species sorting adding and subtracting to the total diversity pattern revealed by coarse-scale taxon counting, apparently responding to longer-term changes in climate as revealed by proxies like the oxygen isotope record.

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Evolution of the Earliest Horses Driven by Climate Change in the Paleocene-Eocene Thermal Maximum

Cited by 193 publications

References 31 publications

Simple versus complex models of trait evolution and stasis as a response to environmental change

Simple versus complex models of trait evolution and stasis as a response to environmental change

The evolution of micro-cursoriality in mammals

Cenozoic Mammals and Climate Change: The Contrast between Coarse-Scale versus High-Resolution Studies Explained by Species Sorting

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