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Roger A. Close, Roger B. J. Benson, John Alroy, Matthew T. Carrano, Terri J. Cleary, Emma M. Dunne, Philip D. Mannion, Mark D. Uhen and Richard J. Butler (2020)
The apparent exponential radiation of Phanerozoic land vertebrates is an artefact of spatial sampling biases.
Proceedings of the Royal Society B: Biological Sciences 287(1924): 20200372
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https://doi.org/10.1098/rspb.2020.0372http://dx.doi.org/10.1098/rspb.2020.0372
There is no consensus about how terrestrial biodiversity was assembled through deep time, and in particular whether it has risen exponentially over the Phanerozoic. Using a database of 60 859 fossil occurrences, we show that the spatial extent of the worldwide terrestrial tetrapod fossil record itself expands exponentially through the Phanerozoic. Changes in spatial sampling explain up to 67% of the change in known fossil species counts, and these changes are decoupled from variation in habitable land area that existed through time. Spatial sampling therefore represents a real and profound sampling bias that cannot be explained as redundancy. To address this bias, we estimate terrestrial tetrapod diversity for palaeogeographical regions of approximately equal size. We find that regional-scale diversity was constrained over timespans of tens to hundreds of millions of years, and similar patterns are recovered for major subgroups, such as dinosaurs, mammals and squamates. Although the Cretaceous/Palaeogene mass extinction catalysed an abrupt two- to three-fold increase in regional diversity 66 million years ago, no further increases occurred, and recent levels of regional diversity do not exceed those of the Palaeogene. These results parallel those recovered in analyses of local community-level richness. Taken together, our findings strongly contradict past studies that suggested unbounded diversity increases at local and regional scales over the last 100 million years.
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http://digitallibrary.amnh.org/handle/2246/7102We used mitochondrial and nuclear DNA sequences to examine patterns of differentiation and evolution in the Musophagidae, an avian family endemic to sub-Saharan Africa; attention was focused on the subfamily Musophaginae, the turacos, or louries. Phylogeographic analysis of 410 individual ND2 sequences from throughout the ranges of the currently recognized species revealed multiple instances of unexpectedly large genetic divergences and cryptic taxa. Within both montane and lowland species, including Tauraco hartlaubi and T. schalowi, Menelikornis leucotis, Musophaga macrorhyncha, and Gallirex johnstoni, fixed private haplotypes were found in disjunct portions of the ranges, suggesting negligible recent gene flow and evolutionary independence of populations. Two taxa originally described as subspecies (T. schalowi loitanus and T. s. marungensis), but not recognized for over 50 years, were found to be 100% diagnosable based on the mitochondrial sequences. The data also revealed the existence of two polyphyletic traditional species, Tauraco livingstonii and T. schuettii, as well as the polyphyly or paraphyly of all traditional superspecies complexes involving members of the genus Tauraco. Overall, our analyses of genetic and morphological variation revealed substantial and unexpected geographic diversity within the Musophagidae. We recognize 33 species-level taxa that represent the appropriate units for phylogenetic and biogeographic analyses (phylogenetic species). We used complete mitochondrial ND2 sequences and nuclear DNA sequences of an Aconitase intron and of the RAG-1 exon to infer the phylogenetic relationships among those species. The results include all the phylogenetic species and, for the first time, nuclear data. We present a new classification of the Musophagidae based on our phylogeographic and phylogenetic results. We allocate the 33 species to seven previously recognized genera, an average of 4.7 species per genus.
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