Karla J. Leite & Daniel C. Fortier (2018)
The palate and choanae structure of the Susisuchus anatoceps (Crocodyliformes, Eusuchia): phylogenetic implications.Â
PeerJ 6:e5372
Crocodyliformes is a group with a broad fossil record, in which several morphological changes have been documented. Among known transformations the most iconic is perhaps the series of changes seen in the structural evolution of the choanae. The change in the position of the choanae was important during the evolutionary history of the Crocodyliformes. This structure is relevant in the phylogenetic position of many crocodyliforms. The new skull of Susisuchus anatoceps from the Crato Formation of the Santana Group (Lower Cretaceous) is described and the preservation in the ventral view allows character encoding not yet observed for the species. The new specimen shows a typical eusuchian palate for Susisuchus anatoceps, in which the choana is fully enclosed by the pterygoid. The Susisuchidae clade has been placed in different phylogenetic positions: as a sister group of Eusuchia, advanced Neosuchia and in Eusuchia. In Isisfordia there are reports that the choana of this taxon is or is not fully enclosed by the pterygoid. The encoding of the ventral characters of S. anatoceps places Susisuchidae in Eusuchia. However, this position must be further studied, since the matrices showed fragility in the reconstitution of the NeosuchiaâEusuchia transition.
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Robert L. Cieri (2018)
The axial anatomy of monitor lizards (Varanidae)
Journal of Anatomy (advance online publication)
Because the musculoskeletal anatomy of the trunk is the framework for the behaviors of locomotion, ventilation, and body support in lepidosaurs, comparative study of trunk anatomy in this group is critical for unraveling the selective pressures leading to extant diversity in axial form and function among vertebrates. This work uses gross dissection and computed tomography to describe the muscular and skeletal anatomy of the trunk of varanid lizards (Varanidae, Anguimorpha). Gross muscle dissections were conducted to investigate the axial muscular anatomy of Varanus exanthematicus, Varanus giganteus, Varanus rosenbergi, and Varanus panoptes. Computed tomography scans of these and additional varanid lizards from the Varanus and Odatria subgenera were conducted to investigate rib and vertebral number and gross morphology. The number of vertebrae differs between species, with 27â35 presacral and 47â137 postsacral vertebrae. Although the number of floating and abdominal ribs in varanids is variable, most species examined have three to four cervical ribs and three true ribs. Attachment and insertion points of the epaxial and hypaxial musculature are detailed. The body wall has four main hypaxial layers, from superficial to deep: oliquus externus, intercostalis externi, intercostalis internii, and transversus. Varanids differ from other investigated lepidosaurs in having supracostalis dorsus brevis (epaxial) and levator costae (hypaxial), which independently connect each rib to the vertebral column. Although more basic muscle descriptions of the body wall in reptiles are needed, comparisons with the condition in the green iguana (Iguana iguana) can be made.
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Gerardo A. Cordero, Haibo Liu, Kokulapalan Wimalanathan, Rachel Weber, Kevin Quinteros & Fredric J. Janzen (2018)
Gene network variation and alternative paths to convergent evolution in turtles
Evolution and Development (advance online publication)
Diversification of the turtle's shell comprises remarkable phenotypic transformations. For instance, two divergent species convergently evolved shellâclosing systems with shoulder blade (scapula) segments that enable coordinated movements with the shell. We expected these unusual structures to originate via similar changes in underlying gene networks, as skeletal segment formation is an evolutionarily conserved developmental process. We tested this hypothesis by comparing transcriptomes of scapula tissue across three stages of embryonic development in three emydid turtles from natural populations. We found that alternative strategies for skeletal segmentation were associated with interspecific differences in gene coâ_expression_ networks. Notably, mesenchyme homeobox 2 (MEOX2) and HOXA3â5 were central hubs driving the activity of 2,806 genes in a candidate network for scapula segmentation, albeit in only one species. Even so, scapula muscle overgrowth corresponded to the activity of similar myogenic networks in both species. This and other derived developmental processes were not observed in the third species, which displayed the ancestral (unsegmented) scapula condition. Differential gene _expression_ tests against this reference lineage supported histological and network analyses. Our findings illustrate that molecular underpinnings of convergent evolution, including during the diversification of the atypical turtle "body plan," are influenced by variation in underlying developmental processes.
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Chelonoidis dominicensis sp. nov.
Nancy A. Albury, Richard Franz, Renato Rimoli, Phillip Lehman, and Alfred L. Rosenberger (2018)
Fossil land tortoises (Testudines, Testudinidae) from the Dominican Republic, West Indies, with a description of a new species.
American Museum Novitates 3904: 1-28
ÂA new fossil tortoise, Chelonoidis dominicensis, is described from a flooded cave in La Altagracia Province in the southeastern Dominican Republic on the island of Hispaniola. The holotype, and only known specimen, includes a nearly complete shell, skull, and appendicular skeleton. The new Dominican species, Chelonoidis dominicensis, shares morphological features with the Bahamian tortoise, Chelonoidis alburyorum, and the Cuban tortoise, Chelonoidis cubensis. Chelonoidis dominicensis can be distinguished from C. alburyorum by its weak prognathous-shaped rostrum, stronger and sharper vomerine septum, more angular posterior skull margins, distinctive caudal hump as seen in shell profile, the centrum of first dorsal vertebra narrow without a strong ventral keel, massive sacral buttresses, weak presacral and sacral ribs, more tapered anterior plastral lobe with prominent gulars, elevated gular shelf. An interclavicular sculpture (bird face) occurs on the internal surface of the entoplastron, composed of a massive brow-line and an elongated, narrow keel (beak). Chelonoidis dominicensis is distinguished from C. cubensis (based on incomplete specimens), by its more narrow anterior plastral lobe and gulars, oval entoplastron, a strong wedge-shaped xiphiplastral notch, and a slight indentation at the junction of the cervical sulcus. The West Indian tortoises are allied with Galapagos tortoises, Chelonoidis nigra species complex, and possibly Chaco tortoises, Chelonoidis chilensis, based on morphology. These relationships are further supported by DNA evidence.
A second tortoise, Chelonoidis marcanoi, was recently named from dry caves in Pedernales Province, in the southwestern part of the country. The designated holotype for C. marcanoi is a right humerus, but this element is inadequate to differentiate taxa in the West Indian genus Chelonoidis; thus, we consider C. marcanoi a nomen dubium. The concept of multiple populations of tortoises on Hispaniola has merit and is discussed in terms of biotic patterns associated with south and north paleo-islands, which are separated from each other by the Hispaniolan Rift Valley.
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Ardenna davealleni sp. nov.
Alan J.D. Tennyson and Al A. Mannering (2018)
A new species of Pliocene shearwater (Aves: Procellariidae) from New Zealand.
Tuhinga 29: 1â19
We describe two partial but well-preserved Late Pliocene fossil skeletons from Taranaki, New Zealand, as a new species of seabird. In structure, these bones match those of a shearwater (Procellariiformes: Procellariidae) but the new taxon is distinguished from all known extant and extinct taxa by a unique combination of features. It was a gliding species as large as the largest species of extant shearwater. It represents the first pre-Pleistocene record of a new shearwater taxon from the western Pacific and helps reveal the history of shearwater evolution. Today, New Zealand has the greatest diversity of breeding shearwater species in the world, and the new fossil adds weight to other evidence that shearwaters have a long history in this region.
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