Tiago R. SimÃes, Michael W. Caldwell, Mateusz TaÅanda, Massimo Bernardi, Alessandro Palci, Oksana Vernygora, Federico Bernardini, Lucia Mancini & Randall L. Nydam (2018)
X-ray computed microtomography of Megachirella wachtleri.
Scientific DataÂ 5, Article number: 180244Â
Understanding the origin and early evolution of squamates has been a considerable challenge given the extremely scarce fossil record of early squamates and their poor degree of preservation. In order to overcome those limitations, we conducted high-resolution X-ray computed tomography (CT) studies on the fossil reptile Megachirella wachtleri (Middle Triassic, northern Italy), which revealed an important set of features indicating this is the oldest known fossil squamate in the world, predating the previous oldest record by ca. 75 million years. We also compiled a new phylogenetic data set comprising a large sample of diapsid reptiles (including morphological and molecular data) to investigate the phylogenetic relationships of early squamates and other reptile groups along with the divergence time of those lineages. The re-description of Megachirella and a new phylogenetic hypothesis of diapsid relationships are presented in a separate study. Here we present the data descriptors for the tomographic scans of Megachirella, which holds fundamental information to our understanding on the early evolution of one of the largest vertebrate groups on Earth today.
Neil Brocklehurst & JÃrg FrÃbisch (2018)
A reexamination of Milosaurus mccordi, and the evolution of large body size in Carboniferous synapsids.
Journal of Vertebrate Paleontology e1508026 (advance online publication)
Milosaurus mccordi was described in 1970 as a large, pelycosaurian-grade synapsid from the latest Carboniferous of Illinois but has since received little attention. Here, the holotype and referred material of Milosaurus are reexamined and incorporated into a phylogenetic analysis. Milosaurus is resolved within Haptodontiformes, sharing with this clade a posterodorsally expanded ischium and a calcaneum with greater length than width. The more plesiomorphic ischium indicates a basal position within this clade. Most of the referred material shows very little overlap with the holotype and so most was not included in the cladistic analysis. However, what was originally described as a dorsal rib is here judged to be a femur that shares a highly distinctive morphology with the holotype. With its mass estimated as 41âkg, Milosaurus represents one of the largest Carboniferous synapsids. Large size evolved at least twice independently in Haptodontiformes during the Pennsylvanian: once in Sphenacodontidae and once in Edaphosauridae. Using phylogenetic comparative methods, Milosaurus is found to have evolved a large size independently of these two clades. As one of the largest Carboniferous amniotes, and the outgroup to one of the most diverse Paleozoic synapsid lineages, Milosaurus represents a crucial taxon for understanding early terrestrial ecosystems.
Steven E. Jasinski, Robert M. Sullivan, Asher Lichtig & Spencer G. Lucas (2018)
Baenid (Baenidae: Testudines) lower jaws from the Late Cretaceous and Paleocene of the San Juan Basin, New Mexico.
in Lucas, S.G. and Sullivan, R.M., eds., 2018. Fossil Record 6. New Mexico Museum of Natural History and Science 79: 311-318
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Two isolated lower jaws belonging to different baenid turtles are identified as cf. Boremys grandis from the upper Campanian (Late Cretaceous) Kirtland Formation (De-na-zin Member) and cf. Neurankylus torrejonensis from the Paleocene Nacimiento Formation (Puercan). Cf. Boremys grandis is the first lower jaw of a baenid to be documented from the Late Cretaceous (Kirtlandian) of New Mexico and may represent a temporal extension for this taxon. Cf. Neurankylus torrejonensis may be the oldest record of this taxon, which may suggest evidence for anagenesis. As turtle skull material, including lower jaw and cranial remains, are rare from the Cretaceous and Paleocene of New Mexico, these specimens provide new morphological information and potential extensions of the respective biostratigraphic ranges of these turtles. They also help us further understand the composition of turtle faunas during the Cretaceous/Paleogene transition in New Mexico and the southern United States. Durophagy may not have been as important to survival of the baenid turtles at the end-Cretaceous extinction as previously thought, at least in the southern United States, because durophagous turtles appear to be absent during the Late Cretaceous in this region. In addition, the percentage of nondurophagous turtle genera in the Paleocene of North America is larger than previously believed. Turtle paleoecology was obviously distinct in northern and southern North America during the Late Cretaceous, at least regarding the major niches held by turtles. This paleoecological separation became less distinct following the Cretaceous-Paleogene extinction event, with durophagous taxa present, potentially through migration or evolutionary events, to the south.Â
Asher Lichtig & Spencer G. Lucas (2018)
The ecology of Meiolania platyceps, a Pleistocene turtle from Australia.
in Lucas, S.G. and Sullivan, R.M., eds., 2018. Fossil Record 6. New Mexico Museum of Natural History and Science 79: 363-368
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The Australian Pleistocene turtle Meiolania platyceps was subjected to quantitative methods of inference of paleohabitus. These are based on the shell, forelimb, and femur morphology. All methods indicate that Meiolania was aquatic. This is further supported by the presence of a plastral fontanelle, known only from one extant terrestrial turtleâ Malacochersus torieriâ and no fossil turtles infered to be terrestrial, but known in many fossil turtles inferred to be aquatic. Further corroboration comes from the shape of the femoral head and the chelydrid-like distribution of armor. This analysis serves as an important reminder that qualitative analogies are no substitute for quantitative analysis of paleohabitus.
Jun Liu (2018)
Osteology of the large dissorophid temnospondyl Anakamacops petrolicus from the Guadalupian Dashankou Fauna of China.
Journal of Vertebrate Paleontology e1513407 (advance online publication)
Dissorophidae are terrestrial temnospondyls with conspicuous armor. All known Guadalupian dissorophid species, including Anakamacops petrolicus, are established based on incomplete materials. Here two new dissorophid specimens from the Guadalupian Dashankou Fauna of China are described and referred to A. petrolicus. They provide much more new osteological information of this species. Anakamacops petrolicus has the largest skull among all known dissorophid species. It exhibits knobby exostoses on the skull roof and mandible, a high suborbital bar that is greater than half of the skull height, a triangular, posteriorly closed otic notch with the anteroposterior length greater than the width, relatively smooth vomer with a few denticles on the lateral margin, two nuchal (occipital) ridges with short overlap where the right one is anterior to the left one, the interpterygoid vacuity far from the choana, low coronoid process, the medial ridge of the adductor fossa close to the ventral margin of the mandible, and the first inner osteoderm nearly triangular with concave margins in dorsal view. The Guadalupian dissorophid species form a monophyletic clade, Kamacopini, which was distributed in northeastern Pangaea, with the following synapomorphies to differentiate it from other dissorophids: suborbital bar high (subequal to or greater than the orbital height) and the interpterygoid vacuities far from the choanae.