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Bever, G. S., T. R. Lyson, D. J. Field, and B.-A. S. Bhullar. 2016. The amniote temporal roof and the diapsid origin of the turtle skull. Zoology 119(6):471–473. DOI: 10.1016/j.zool.2016.04.005.
Two taxa, Eunotosaurus africanus and Pappochelys rosinae, were recently and independently described as long-anticipated stem turtles whose diapsid skulls would cement the evolutionary link between turtles and other modern reptile lineages. Detailed CT analysis of the stratigraphically older and phylogenetically stemward of the two, Eunotosaurus, provides empirical insight into changing developmental trajectories that may have produced the anapsid cranial form of modern turtles and sets the stage for more comprehensive studies of early amniote cranial evolution.
Lyson, T. R., B. S. Rubidge, T. M. Scheyer, K. de Queiroz, E. R. Schachner, R. M. H. Smith, J. Botha-Brink, and G. S. Bever. 2016. Fossorial origin of the turtle shell. Current Biology 26(14):1887–1894. DOI: 10.1016/j.cub.2016.05.020.
The origin of the turtle shell is a major evolutionary transition whose initial function was unknown. Lyson et al. present a strongly supported idea that a burrowing ecology and adaptations related to digging favored the initial transformations on the road to the modern turtle shell. Only later was the shell co-opted for protection.
Bever, G. S., T. R. Lyson, D. J. Field, and B.-A. S. Bhullar. 2015. Evolutionary origin of the turtle skull. Nature 525:239–242. DOI: 10.1038/nature14900.
Here we use high-resolution computed tomography and a novel character/taxon matrix to study the skull of Eunotosaurus africanus, a 260-million-year-old fossil reptile from the Karoo Basin of South Africa, whose distinctive post-cranial skeleton shares many unique features with the shelled body plan of turtles.
Field, D. J., J. A. Gauthier, B. L. King, D. Pisani, T. R. Lyson, and K. J. Peterson. 2014. Toward consilience in reptile phylogeny: miRNAs support an archosaur, not lepidosaur, affinity for turtles. Evolution and Development 16(4):189–196. DOI: 10.1111/ede.12081.
Previously, a study using microRNAs (miRNAs) placed turtles inside diapsids, but as sister to lepidosaurs (lizards and Sphenodon) rather than archosaurs. Here, we test this hypothesis with an expanded miRNA presence/absence dataset and employ more rigorous criteria for miRNA annotation.
Lyson, T. R., E. R. Schachner, J. Botha-Brink, T. M. Scheyer, M. Lambertz, G. S. Bever, B. Rubidge, and K. de Queiroz. 2014. Origin of the unique lung ventilatory apparatus of turtles. Nature Communications 5:5211. DOI: 10.1038/ncomms6211.
We show through broadly comparative anatomical and histological analyses that an early member of the turtle stem lineage has several turtle-specific ventilation characters: rigid ribcage, inferred loss of intercostal muscles, and osteological correlates of the primary expiratory muscle. Our results suggest that the ventilation mechanism of turtles evolved through a division of labor between the ribs and muscles of the trunk in which the abdominal muscles took on the primary ventilatory function.
Joyce, W. G., Schoch, and T. R. Lyson, 2013. The girdles of the oldest fossil turtle, Proterochersis robusta, and the age of the turtle crown. BMC Evolutionary Biology 13:article number 266. DOI: 10.1186-1471-2148-13-266.
Proterochersis robusta from the Late Triassic (Middle Norian) of Germany is the oldest known fossil turtle (i.e., amniote with a fully formed turtle shell), but little is known about its anatomy. A newly prepared, historic specimen provides novel insights into the morphology of the girdles and vertebral column of this taxon and the opportunity to reassess its phylogenetic position.
Joyce, W. G., I. Werneburg, and T. R. Lyson. 2013. The hooked element in the pes of turtles (Testudines): a global approach to exploring primary and secondary homology. Journal of Anatomy 223(5):421–441. DOI: 10.1111/joa.12103.
The hooked element in the pes of turtles was historically identified by most paleontologists and embryologists as a modified fifth metatarsal and often used as evidence to unite turtles with other reptiles with a hooked element. Some recent embryological studies, however, revealed that this element might represent an enlarged fifth distal tarsal. We herein provide extensive new myological and developmental observations on the hooked element of turtles and reevaluate its primary and secondary homology using all available lines of evidence.
Lyson, T. R., B.-A. S. Bhullar, G. S. Bever, W. G. Joyce, K. de Queiroz, A. Abzhanov, and J. A. Gauthier. 2013. Homology of the enigmatic nuchal bone reveals novel reorganization of the shoulder girdle in the evolution of the turtle shell. Evolution and Development 15(5):317–325. DOI: 10.1111/ede.12041.
The animation is based on the work by Tyler Lyson, PhD. The animation shows how the bone at the front and center of the turtle shell is derived from paired shoulder girdle bones (cleithra, blue). In addition, three of the bones found in the plastron (belly shell) are also derived from shoulder girdle bones (clavicles, pink; and interclavicle, green). The animation takes you through known fossil taxa that help bridge the morphological gap separating the highly modified shoulder girdle found in turtles from the more generalized shoulder girdle.
Lyson, T. R., G. S. Bever, T. M. Scheyer, A. Y. Hsiang, and J. A. Gauthier. 2013. Evolutionary origin of the turtle shell. Current Biology 23(12):1113–1119. DOI: 10.1016/j.cub.2013.05.003.
The animation shows how various fossils, particularly Eunotosaurus and Odontochelys, bridge the morphological gap between a generalized animal body plan to the highly modified body plan found in living turtles.
Lyson, T. R., E. A. Sperling, J. A. Gauthier, A. M. Heimburg, and K. J. Peterson. 2012. microRNAs support a Testudines-Lepidosaur clade. Biology Letters 8:104–107. DOI: 10.1098/rsbl.2011.0477.
Lyson, T. R., and W. G. Joyce. 2012. Evolution of the turtle bauplan: the topological relationship of the scapula relative to the ribcage. Biology Letters 8(6):1028–1031. DOI: 10.1098/rsbl.2012.0462.
Lyson, T. R., G. S. Bever, B.-A. S. Bhullar, W. G. Joyce, and J. A. Gauthier. 2010. Transitional fossils and the origin of turtles. Biology Letters 6(6):830–833. DOI: 10.1098/rsbl.2010.0371.
Lyson, T. R., and S. Gilbert. 2009. Turtles all the way down: loggerheads at the root of the chelonian tree. Evolution and Development 11(2):133–135. DOI: 10.1111/j.1525-142X.2009.00325.x.