Evidence of cryptic lineages within a small South American crocodilian: the Schneider’s dwarf caimanPaleosuchus trigonatus(Alligatoridae: Caimaninae)

Abstract

Schneider’s dwarf caiman Paleosuchus trigonatus is one of the smallest living crocodilians. Due to its broad distribution, cryptic behavior, and small home range, the species is well suited for the study of phylogeographic patterns on a continental scale. Additionally, this species is under threat due to habitat loss, trade and harvest, but is considered at low conservation risk by the IUCN. In the present study we test the hypothesis that P. trigonatus is comprised of geographically structured lineages. Phylogenetic reconstructions of the mitochondrial cytochrome b gene and single locus species discovery methods revealed the existence of two well-supported lineages within P. trigonatus—an Amazonian and Guianan lineage. Fossil calibrated divergence of these lineages was estimated to have occurred in the Late Miocene (7.5 Ma). The hypothesis that the Atlantic coast drainages might have been colonized from the southeast or central Amazon is supported by demographic metrics and relatively low genetic diversity of the Coastal and upper Branco populations when compared to the Amazon basin populations. The Amazon basin lineage is structured along an east-west gradient, with a sharp transition in haplotype frequencies to the east and west of the Negro and Madeira rivers. These lineages are already under anthropogenic threat and, therefore, are conservation dependent. Recognition of these lineages will foster discussion of conservation future of P. trigonatus and these lineages.

Species richness and composition of snake assemblages in poorly accessible areas in the Brazilian Amazonia

“…These observations and conclusions reinforce the conclusions of Fraga et al (2014) and Guedes et al (2018) that Amazonia has a high potential to contain still-to-be-discovered and undescribed species, and parallel observations in other Amazonian herps (e.g. Carminer et al 2017, Muniz et al 2018, Bittencourt et al 2019). Our results further highlight the importance of standardized faunal surveys in poorly sampled areas in the Amazonian biome.…”

Phylogeny and systematics of the Proterodiplostomidae Dubois, 1936 (Digenea: Diplostomoidea) reflect the complex evolutionary history of the ancient digenean group

“…This is particularly interesting considering the recent advances in the phylogenetics of crocodilians and discovery of cryptic species based on both morphological and molecular criteria (e.g. Brochu, 1997 , 2003 ; Bittencourt et al, 2019 ; Brochu & Sumrall, 2020 ; Roberto et al, 2020 ). Molecular data also suggested a relatively recent radiation and active speciation of the true crocodiles (Oaks, 2011 ).…”

Quantitatively assessing mekosuchine crocodile locomotion by geometric morphometric and finite element analysis of the forelimb

“…An additional caveat to consider is that although the mekosuchine specimens appear to diverge from a morphology associated with semi-aquatic habit, this in itself is not unequivocal proof that the subsequent forms were associated with terrestrial habit. This issue could be resolved if more limb materials became available to establish a larger shape dataset for mekosuchines that could be tested against extinct taxa regarded as terrestrial (e.g., notosuchids) and extant taxa (e.g., Osteolaemus tetraspis Cope, 1861, or Paleosuchus trigonatus Schneider, 1801 that purportedly show greater aptitude with terrestrial locomotion (Pol, 2005;Eaton et al, 2009;Eaton, 2010;Pol et al, 2012;Bittencourt et al, 2019). A larger data set would also be necessary to test for any Oligo-Miocene morphological radiation in mekosuchine limb shape and quantify its extent.…”