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Evolutionary processes, including selection, can be indirectly inferred based on patterns of genomic variation among contemporary populations or species. However, this often requires unrealistic assumptions of ancestral demography and selective regimes. Sequencing ancient DNA from temporally spaced samples can inform about past selection processes, as time series data allow direct quantification of population parameters collected before, during, and after genetic changes driven by selection. In this Comment and Opinion, we advocate for the inclusion of temporal sampling and the generation of paleogenomic datasets in evolutionary biology, and highlight some of the recent advances that have yet to be broadly applied by evolutionary biologists. In doing so, we consider the expected signatures of balancing, purifying, and positive selection in time series data, and detail how this can advance our understanding of the chronology and tempo of genomic change driven by selection. However, we also recognize the limitations of such data, which can suffer from postmortem damage, fragmentation, low coverage, and typically low sample size. We therefore highlight the many assumptions and considerations associated with analyzing paleogenomic data and the assumptions associated with analytical methods. ; This work resulted from a synthesis and writing retreat as part of ADAPT (Ancient DNA studies of Adaptive Processes through Time) Special Topic Network generously funded by the European Society for Evolutionary Biology (ESEB). ADF was supported by European Union's Horizon 2020 research and innovation program under the Marie Skłodowska‐Curie grant agreement No. 663830. ASM was supported by a European Research Council (ERC) grant. LD and MD acknowledge fudning from the Swedish Research Coucil (VR grant 2017‐04647)

Homotherium was a genus of large-bodied scimitar-toothed cats, morphologically distinct from any extant felid species, that went extinct at the end of the Pleistocene [1–4]. They possessed large, saber-form serrated canine teeth, powerful forelimbs, a sloping back, and an enlarged optic bulb, all of which were key characteristics for predation on Pleistocene megafauna [5]. Previous mitochondrial DNA phylogenies suggested that it was a highly divergent sister lineage to all extant cat species [6–8]. However, mitochondrial phylogenies can be misled by hybridization [9], incomplete lineage sorting (ILS), or sex-biased dispersal patterns [10], which might be especially relevant for Homotherium since widespread mito-nuclear discrepancies have been uncovered in modern cats [10]. To examine the evolutionary history of Homotherium, we generated a 7x nuclear genome and a 38x exome from H. latidens using shotgun and target-capture sequencing approaches. Phylogenetic analyses reveal Homotherium as highly divergent (22.5 Ma) from living cat species, with no detectable signs of gene flow. Comparative genomic analyses found signatures of positive selection in several genes, including those involved in vision, cognitive function, and energy consumption, putatively consistent with diurnal activity, well-developed social behavior, and cursorial hunting [5]. Finally, we uncover relatively high levels of genetic diversity, suggesting that Homotherium may have been more abundant than the limited fossil record suggests [3, 4, 11–14]. Our findings complement and extend previous inferences from both the fossil record and initial molecular studies, enhancing our understanding of the evolution and ecology of this remarkable lineage. ; This project received funding from the European Union's Seventh Framework Programme for Research, Technological Development, and Demonstration under grant agreement no. FP7-PEOPLE-2011-IEF-298820 and ERC Consolidator Award 681396—Extinction Genomics to M.T.P.G. Portions of this manuscript were prepared while W.E.J. held a National Research Council Research Associateship Award at the Walter Reed Army Institute of Research (WRAIR).

Only five species of the once-diverse Rhinocerotidae remain, making the reconstruction of their evolutionary history a challenge to biologists since Darwin. We sequenced genomes from five rhinoceros species (three extinct and two living), which we compared to existing data from the remaining three living species and a range of outgroups. We identify an early divergence between extant African and Eurasian lineages, resolving a key debate regarding the phylogeny of extant rhinoceroses. This early Miocene (∼16 million years ago [mya]) split post-dates the land bridge formation between the Afro-Arabian and Eurasian landmasses. Our analyses also show that while rhinoceros genomes in general exhibit low levels of genome-wide diversity, heterozygosity is lowest and inbreeding is highest in the modern species. These results suggest that while low genetic diversity is a long-term feature of the family, it has been particularly exacerbated recently, likely reflecting recent anthropogenic-driven population declines. ; The authors acknowledge support from the Science for Life Laboratory, the Garvan Institute of Medical Research, the Knut and Alice Wallenberg Foundation, and the National Genomics Infrastructure funded by the Swedish Research Council and Uppsala Multidisciplinary Center for Advanced Computational Science for assistance with massively parallel sequencing and access to the UPPMAX computational infrastructure. We thank the Natural History Museum at the University of Oslo for providing the Javan rhinoceros sample. We thank the Museum of the Institute of Plant and Animal Ecology (UB RAS, Ekaterinburg) for providing the sample of Siberian unicorn. M.T.P.G. was supported by European Research Council (ERC) Consolidator grant 681396 (Extinction Genomics). E.D.L. was supported by Independent Research Fund Denmark grant 8021-00218B. A.C. was supported by an Australian Research Council Laureate Fellowship (FL140100260). T.M.B. is supported by funding from the ERC under the European Union's Horizon 2020 research and innovation program (grant agreement 864203), grant BFU2017-86471-P (MINECO/FEDER, UE), "Unidad de Excelencia María de Maeztu" funded by the AEI (CEX2018-000792-M), Howard Hughes International Early Career, and Secretaria d'Universitats i Recerca and CERCA Programme del Departament d'Economia i Coneixement de la Generalitat de Catalunya (GRC 2017 SGR 880). L.D. was supported by the Swedish Research Council (2017-04647) and Formas (2018-01640). ; With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2018-000792-M). ; Peer reviewed