Global taxonomic diversity of living reptiles

Zoological Journal of the Linnean Society, 2020

Most species remain unknown to science and might go extinct before we recognize their existence. Although specimens belonging to many of these unknown taxa may already be housed in scientific collections, they can remain ‘shelved’ for years bearing the wrong name or without a formal name. We investigate factors underlying variation in time lag between collection and description dates for 2356 reptile species described worldwide between 1992 and 2017. We modelled the time to description using biological and sociological variables in a time-to-event analysis. Time lag between collection and description varied from zero to 155 years (median = 5). More than one-quarter of species involved specimens ‘shelved’ for 12 years or more. The time lag was shorter when the collector of the holotype – specimen serving as the name-bearer of the species – was an author of the description, while taxonomic revisions uncovered species with longer time lags. Unknown species collected by non-taxonomists and ‘shelved’ in scientific collections remained incorrectly identified for a much longer time. Taxonomic revisions are crucial to reverse this trend and improve benefits of the collecting performed by non-taxonomists. Our findings reveal the kinds of preserved reptile specimens that most likely represent unknown species in scientific collections.

2013

Molecular data offer great potential to resolve the phylogeny of living taxa but can molecular data improve our understanding of relationships of fossil taxa? Simulations suggest that this is possible, but few empirical examples have demonstrated the ability of molecular data to change the placement of fossil taxa. We offer such an example here. We analyze the placement of snakes among squamate reptiles, combining published morphological data (363 characters) and new DNA sequence data (15,794 characters, 22 nuclear loci) for 45 living and 19 fossil taxa. We find several intriguing results. First, some fossil taxa undergo major changes in their phylogenetic position when molecular data are added. Second, most fossil taxa are placed with strong support in the expected clades by the combined data Bayesian analyses, despite each having >98% missing cells and despite recent suggestions that extensive missing data are problematic for Bayesian phylogenetics. Third, morphological data can change the placement of living taxa in combined analyses, even when there is an overwhelming majority of molecular characters. Finally, we find strong but apparently misleading signal in the morphological data, seemingly associated with a burrowing lifestyle in snakes, amphisbaenians, and dibamids. Overall, our results suggest promise for an integrated and comprehensive Tree of Life by combining molecular and morphological data for living and fossil taxa.

Zootaxa, 2018

By August 2017 an estimated 13,047 species and subspecies of extant reptiles have been described by a total of 6,454 papers and books which are listed in a supplementary file. For 1,052 species a total of 2,452 subspecies (excluding nominate subspecies) had been described by 2017, down from 1,295 species and 4,411 subspecies in 2009, due to the elevation of many subspecies to species. Here we summarize the history of these taxon description beginning with Linnaeus in 1758. While it took 80 years to reach the first 1,000 species in 1838, new species and subspecies descriptions since then have been added at a roughly constant rate of 1000 new taxa every 12-17 years. The only exception were the decades during World Wars I and II and the beginning of this millennium when the rate of descriptions increased to now about 7 years for the last 1,000 taxa. The top 101 most productive herpetologists (in terms of "taxon output") have described more than 8,000 species and subspecies, a...

Aim Size is one of the most important and obvious traits of an organism. Both small and large sizes have adaptive advantages and disadvantages. Body size–frequency distributions of most large clades are unimodal and right skewed. Species larger than the mean or range midpoint of body sizes are relatively scarce. Theoretical models suggest evolutionary rates are higher in small organisms with short generation times. Therefore diversification rates are usually thought to be maximal at relatively small body sizes. Empirical studies of the rates of molecular evolution and clade diversification , however, have usually indicated that both are unrelated to body size. Furthermore, it has been claimed that because snakes are longer than lizards, the size–frequency distribution of all squamate species is bimodal overall. We examined the shape of the size–frequency distribution of nearly all Squamata and Rhynchocephalia species, and investigated how size affected diversification rates. Location Global. Methods We collected data on maximum body length for 9805 lepidosaur (squamates and the tuatara) species (99.7% of all species) and converted them to mass using clade-specific allometric equations. Using methods that test for relationships between continuous traits and speciation and extinction rates on a large, dated phylogeny (4155 species), we investigated the relationship between diversification rates and body size. Results Living squamates span six orders of magnitude in body size, eight when giant extinct snakes and mosasaurs are included. The body size–frequency distributions of snakes and lizards separately, and of all lepidosaur species combined, are unimodal and right skewed. Nonetheless, we find neither linear nor hump-shaped relationships between size and diversification rates, except in snakes, where specia-tion and diversification are hump shaped. Main conclusions Despite a clear modality and skew in the body sizes of lepidosaurs, we find little evidence for faster diversification of modal-sized taxa, perhaps implying that larger-sized clades are relatively young.

PloS one, 2012

Convergent evolution can explain similarity in morphology between species, due to selection on a fitness-enhancing phenotype in response to local environmental conditions. As selective pressures on body morphology may be strong, these have confounded our understanding of the evolutionary relationships between species. Within the speciose African radiation of lacertid lizards (Eremiadini), some species occupy a narrow habitat range (e.g. open habitat, cluttered habitat, strictly rupicolous, or strictly psammophilic), which may exert strong selective pressures on lizard body morphology. Here we show that the overall body plan is unrelated to shared ancestry in the African radiation of Eremiadini, but is instead coupled to habitat use. Comprehensive Bayesian and likelihood phylogenies using multiple representatives from all genera (2 nuclear, 2 mitochondrial markers) show that morphologically convergent species thought to represent sister taxa within the same genus are distantly related evolutionary lineages (Ichnotropis squamulosa and Ichnotropis spp.; Australolacerta rupicola and A. australis). Hierarchical clustering and multivariate analysis of morphological characters suggest that body, and head, width and height (stockiness), all of which are ecologically relevant with respect to movement through habitat, are similar between the genetically distant species. Our data show that convergence in morphology, due to adaptation to similar environments, has confounded the assignment of species leading to misidentification of the taxonomic position of I. squamulosa and the Australolacerta species.

Squamate reptiles (lizards and snakes) are a pivotal group whose relationships have becomeincreasingly controversial. Squamates include >9000 species, making them the secondlargest group of terrestrial vertebrates. They are important medicinally and as modelsystems for ecological and evolutionary research. However, studies of squamate biologyare hindered by uncertainty over their relationships, and some consider squamate phylogenyunresolved, given recent conflicts between molecular and morphological results. To resolvethese conflicts, we expand existing morphological and molecular datasets forsquamates (691 morphological characters and 46 genes, for 161 living and 49 fossil taxa,including a new set of 81 morphological characters and adding two genes from publishedstudies) and perform integrated analyses. Our results resolve higher-level relationships asindicated by molecular analyses, and reveal hidden morphological support for the molecularhypothesis (but not vice-versa). Furthermore, we find that integrating molecular, morphological, and paleontological data leads to surprising placements for two major fossil clades(Mosasauria and Polyglyphanodontia). These results further demonstrate the importance ofcombining fossil and molecular information, and the potential problems of estimating theplacement of fossil taxa from morphological data alone. Thus, our results caution againstestimating fossil relationships without considering relevant molecular data, and againstplacing fossils into molecular trees (e.g. for dating analyses) without considering the possibleimpact of molecular data on their placement.