[Herpetology • 2019] A Species-level Phylogeny of Trachylepis (Scincidae: Mabuyinae) provides insight into their Reproductive Mode Evolution

Phylogeny of Trachylepis 

in Weinell, Branch, Colston, et al., 2019. 

 DOI: 10.1016/j.ympev.2019.04.002 

  twitter.com/JeffWeinell  

Highlights

• Species-level phylogeny of Trachylepis inferred. 

• Oviparity inferred as ancestral reproductive condition for Trachylepis.

• Multiple reproductive mode transitions supported within Trachylepis.

• Best-fit model supports controversial viviparity to oviparity transitions.

Abstract

Trachylepis (Mabuyinae) includes 80 species of fully-limbed skinks found primarily in Africa and Madagascar, but a robust species-level phylogeny for this genus is lacking and this impedes studies on a wide-range of topics from biogeography to character evolution. Trachylepis and its close relatives (which together form the Mabuya group or Mabuyinae) are notable in that they have undergone multiple transitions and remarkable specializations in their reproductive modes. A Trachylepis phylogeny will be particularly useful for investigating reproductive evolution, because it includes species that exhibit oviparity, viviparity, and bimodal parity (species with both oviparous and viviparous populations). We sequenced DNA at four mitochondrial and five nuclear loci for 67 (84% of) Trachylepis species to infer a phylogeny for this genus. We performed stochastic character mapping of parity mode under a variety of parity mode transition models to infer ancestral parity mode states and the number and type of parity mode transitions. We recovered a strongly supported phylogeny of Trachylepis that is generally consistent with earlier phylogenetic studies. The best-fit model of reproductive mode evolution supports an oviparous ancestor for Trachylepis, and supports at least three viviparity to oviparity transitions. We compared parity mode evolution under the overall best-fit model (no constraints on parity mode transitions) to the best-fit model among the subset of models that assume viviparity to oviparity transitions are impossible. Our results support a model of reproductive evolution that allows for reversibility from viviparity to oviparity, a process that is not generally accepted. Alternatively, the best-fit model of evolution among the set of models that eliminate reversals from viviparity to oviparity suggests that bimodal reproduction may have persisted for millions of years within multiple lineages.

Keywords: Dollo’s law, Viviparity, Oviparity, Bimodal parity, Stochastic character mapping, Squamata

 

Jeffrey L. Weinell, William R. Branch, Timothy J. Colston, Todd R. Jackman, Arianna Kuhn, Werner Conradie and Aaron M. Bauer. 2019. A Species-level Phylogeny of Trachylepis (Scincidae: Mabuyinae) provides insight into their Reproductive Mode Evolution.  Molecular Phylogenetics and Evolution. 136; 183-195.  DOI: 10.1016/j.ympev.2019.04.002  

 twitter.com/JeffWeinell/status/1118993207151480832

[Paleontology • 2015] Pelagic Neonatal Fossils support Viviparity and Precocial Life History of Cretaceous Mosasaurs

Figure 4. Clidastes liodontus giving live birth in an open pelagic setting ~85 million years ago,
 beneath the shadow of the toothed stem bird Ichthyornis.

Artist's interpretation of this study's principal conclusions || Illustration by Julius Csotonyi.

DOI: 10.1111/pala.12165

Abstract

Mosasaurs were large marine squamates that inhabited all of the world's oceans during the Late Cretaceous. Their success as apex predators has been attributed to their rapid acquisition of aquatic adaptations, which allowed them to become fully pelagic. However, little is known about the breeding biology of derived, flipper-bearing mosasaurs, as the record of neonatal mosasaur fossils is extremely sparse. Here, we report on the fragmentary cranial remains of two neonatal mosasaurs from the Niobrara Formation, referred to Clidastes sp. Comparison with other preliminary reports of neonatal mosasaurs reveals that these specimens are among the smallest individuals ever found and certainly represent the smallest known Clidastes specimens. The recovery of these extremely young specimens from a pelagic setting indicates that even neonatal mosasaurs occupied open oceanic habitats and were likely born in this setting. These data shed new light on the ecology of neonatal mosasaurs and illustrate the degree to which size-related taphonomic and collection biases have influenced our understanding of the early life history of these iconic marine reptiles. 

Keywords: mosasaur; viviparity; Niobrara; marine reptile; life history

Figure 1. The smallest mosasaurid remains from the Niobrara Formation, previously misidentified as toothed stem birds.
A, lateral and dorsal view of the left dentary of Clidastes, YPM VP.058125; lateral and dorsal view of the left dentary of Clidastes, YPM VP.058126. Scale bar represents 1 cm. B, size comparison of several of the smallest Clidastes dentaries from the Niobrara Formation, in lateral (left) and dorsal (right) views. Scale bar represents 1 cm. The newly discovered specimens reported here (YPM 058125, YPM 058126) are by far the smallest. C, comparison of maximum tooth diameters for juvenile Clidastes from the Niobrara chalk. The newly discovered specimens (YPM VP.058125, YPM VP.058126) represent the smallest mosasaurids known from the Niobrara Formation and are currently the youngest Clidastes specimens ever found. D, estimated body length of neonatal mosasaurs (YPM VP.058125 and YPM VP.058126) relative to an adult specimen of Clidastes liodontus. The adult is 3 m in length; the neonate is 0.66 m in length (see text).

Redrawn from Caldwell and Diedrich (2005, fig. 5) and Lindgren et al. (2011, fig. 12). Scale bar represents 1 m. Colour online. DOI: 10.1111/pala.12165

Daniel J. Field, Aaron LeBlanc, Adrienne Gau and Adam D. Behlke. 2015. Pelagic Neonatal Fossils support Viviparity and Precocial Life History of Cretaceous Mosasaurs. Palaeontology. DOI: 10.1111/pala.12165

http://news.yale.edu/2015/04/10/new-beginning-baby-mosasaurs-thanks-yale-research