Evaluating the Impact of Anatomical Partitioning on Summary Topologies Obtained with Bayesian Phylogenetic Analyses of Morphological Data.

Morphological data are a fundamental source of evidence to reconstruct the Tree of Life, and Bayesian phylogenetic methods are increasingly being used for this task. Bayesian phylogenetic analyses require the use of evolutionary models, which have been intensively studied in the past few years, with significant improvements to our knowledge. Notwithstanding, a systematic evaluation of the performance of partitioned models for morphological data has never been performed. Here we evaluate the influence of partitioned models, defined by anatomical criteria, on the precision and accuracy of summary tree topologies considering the effects of model misspecification. We simulated datasets using partitioning schemes, trees, and other properties obtained from two empirical datasets, and conducted Bayesian phylogenetic analyses. Additionally, we reanalyzed 32 empirical datasets for different groups of vertebrates, applying unpartitioned and partitioned models, and, as a focused study case, we reanalyzed a dataset including living and fossil armadillos, testing alternative partitioning hypotheses based on functional and ontogenetic modules. We found that, in general, partitioning by anatomy has little influence on summary topologies analyzed under alternative partitioning schemes with a varying number of partitions. Nevertheless, models with unlinked branch lengths, which account for heterotachy across partitions, improve topological precision at the cost of reducing accuracy. In some instances, more complex partitioning schemes led to topological changes, as tested for armadillos, mostly associated with models with unlinked branch lengths. We compare our results with other empirical evaluations of morphological data and those from empirical and simulation studies of the partitioning of molecular data, considering the adequacy of anatomical partitioning relative to alternative methods of partitioning morphological datasets. [Evolutionary rates; heterogeneity; morphology; Mk model; partition; topology.].

Insectivory leads to functional convergence in a group of Neotropical rodents.

The mandible of vertebrates serves as insertion area for masticatory muscles that originate on the skull, and its functional properties are subject to selective forces related to trophic ecology. The efficiency of masticatory muscles can be measured as mechanical advantage on the mandible, which, in turn, has the property of correlating with bite force and shape. In the present work, we quantify the mechanical advantage of the mandible of akodontine rodents, which present a diverse radiation of insectivorous specialists, to assess their relationship to the estimated bite force and diet. We also tested the degree of morphofunctional convergence in response to insectivory on the group. We found the mechanical advantages to be convergent on insectivorous species, and associated with the estimated bite force, with higher mechanical advantages in species with a stronger bite and short, robust mandibles and lower mechanical advantages in insectivorous species with weaker bites and more elongated, dorso-ventrally compressed mandibles. Insectivorous species of Akodontini are functional specialists for the consumption of live prey and may exploit the resources that shrews, moles and hedgehogs consume elsewhere.

Evolution and biogeographic history of the Saguinus mystax group (Primates, Callithrichidae).

The Saguinus mystax group traditionally includes three species, S. mystax, S. labiatus, and S. imperator. The additional inclusion of S. inustus is argued on molecular grounds, which have an important impact on our comprehension of the phenotypical evolution and biogeography of the group. Here, we investigate the evolutionary events leading to the diversification of the S. mystax group, integrating phylogenetic, temporal, and geographic information with the current knowledge of the Amazonian paleogeographical history. The examination of 208 specimens of Saguinus resulted in 25 morphological characters, of which 13 were used for the first time in a phylogenetic analysis of the genus. Morphological characters were also combined with molecular data and analyzed using Bayesian and Maximum Likelihood methods. Trees resulting from morphological and combined data recovered a monophyletic S. mystax group, including S. inustus, whose inclusion was supported by two morphological synapomorphies. Molecular based age estimates place the origin of Saguinus in the middle Miocene (17.4-13 million years ago [mya]), whereas the S. mystax group originated in an interval between 12 and 6 mya. Our results also suggest that the ancestral area of Saguinus was western Amazon, from where they dispersed to their current distribution after the end of the Pebas lakes system. The diversification events in the S. mystax group are related to the Pliocene development of the modern Amazon river network associated to the uplift of Fitzcarrald Arch.

Morphology of the tongue of Vermilingua (Xenarthra: Pilosa) and evolutionary considerations.

The tongue of anteaters (Xenarthra, Pilosa, Vermilingua) is a highly specialized for myrmecophagy. Here, we describe the topography and histology of the tongue, and compare it to that of other xenarthrans and other myrmecophagous eutherian mammals. The tongue of Vermilingua is long and slender, with an apical protuberance, which differs between Myrmecophagidae and Cyclopes didactylus. In the former, the rostral region is conical, and in the latter, it is dorsoventrally compressed, as observed in sloths. The tongue of Vermilingua has filiform and circumvallate papillae on the surface; foliate and fungiform papillae are absent. The filiform papillae of Myrmecophaga tridactyla are simple all over the tongue, differing from Tamandua tetradactyla and Cyclopes didactylus, which present composed filiform papillae in the rostral and middle regions. Histologically, the tongue has a peculiar organization of muscular and neurovascular tissues, differing from the usual mammalian pattern. However, the tongue structure is less divergent in Cyclopes. The presence of two circumvallate papillae is common to the three major clades of Xenarthra (Cingulata, Folivora and Vermilingua). In each group, the tongue may reflect functional features related to myrmecophagous (anteaters and some armadillos), omnivorous (remaining armadillos) and folivorous (sloths) feeding habits. The similarities between the tongues of Vermiligua and other non-xenarthran eutherian myrmecophagous mammals are somewhat general and, under close inspection, superficial, being an example of different lineages achieving the same morphofunctional adaptations through distinct evolutionary pathways.

Response to comment on "The placental mammal ancestor and the post-K-Pg radiation of placentals".

Tree-building with diverse data maximizes explanatory power. Application of molecular clock models to ancient speciation events risks a bias against detection of fast radiations subsequent to the Cretaceous-Paleogene (K-Pg) event. Contrary to Springer et al., post-K-Pg placental diversification does not require "virus-like" substitution rates. Even constraining clade ages to their model, the explosive model best explains placental evolution.

The placental mammal ancestor and the post-K-Pg radiation of placentals.

To discover interordinal relationships of living and fossil placental mammals and the time of origin of placentals relative to the Cretaceous-Paleogene (K-Pg) boundary, we scored 4541 phenomic characters de novo for 86 fossil and living species. Combining these data with molecular sequences, we obtained a phylogenetic tree that, when calibrated with fossils, shows that crown clade Placentalia and placental orders originated after the K-Pg boundary. Many nodes discovered using molecular data are upheld, but phenomic signals overturn molecular signals to show Sundatheria (Dermoptera + Scandentia) as the sister taxon of Primates, a close link between Proboscidea (elephants) and Sirenia (sea cows), and the monophyly of echolocating Chiroptera (bats). Our tree suggests that Placentalia first split into Xenarthra and Epitheria; extinct New World species are the oldest members of Afrotheria.