Mark J. Macdougall; Diane Scott; Sean P. Modesto; Scott A. Williams; Robert R. Reisz (2017)
New material of the reptile Colobomycter pholeter (Parareptilia: Lanthanosuchoidea) and the diversity of reptiles during the Early Permian (Cisuralian).
Zoological Journal of the Linnean Society (advance online publication)
Over 150 years of collecting in the Permian Basin of North America suggests that reptiles evolved in the shadows of Dimetrodon and related Early Permian synapsids. Research in recent decades has revealed an unappreciated ecological diversity in addition to taxonomic richness of Early Permian reptiles and recognition of a radiation of Palaeozoic–Triassic forms now known as parareptiles. Perhaps the most unusual parareptile to be described from the Permian Basin of North America is the lanthanosuchoid Colobomycter pholeter from the Richards Spur locality, Oklahoma, USA. Although initially described as a synapsid, this species was later reassigned to Parareptilia. Colobomycter is very distinct from all other known parareptiles, and coeval tetrapods in general, largely due to its extremely conspicuous and unique marginal dentition. The single, very large anteriormost tooth of the premaxilla and the paired enlarged teeth of the maxilla characterize the dentition of Colobomycter. Herein we describe new cranial material of C. pholeter that reveals previously unknown aspects of the skull and further increases our anatomical knowledge of this unique taxon. The new cranial data allow us to reassess the interrelationships of Early Permian parareptiles, which has critical implications for the diversity of parareptiles during the Early Permian. Parareptiles were a diverse clade of reptiles that were an important component of Middle and Late Permian ecosystems, having gained a cosmopolitan distribution by the Middle Permian. In contrast to their diversity during the Middle and Late Permian, parareptiles were historically considered to have a lower taxic diversity during the Early Permian, as well as being rare members of Early Permian fossil assemblages. However, with the numerous species that have been produced from the Richards Spur locality of Oklahoma in recent years, we now have a much better view regarding the diversity of parareptiles during the Early Permian, with their diversity coming close to matching that of Early Permian eureptiles. Richard Spur is also unique in that more than half of all known Early Permian parareptiles are found there, as well as in capturing representatives of all major lineages of terrestrial parareptiles present during the Early Permian.
Alida M. Bailleul & Casey M. Holliday (2017)
Joint histology in Alligator mississippiensis challenges the identification of synovial joints in fossil archosaurs and inferences of cranial kinesis.
Proceedings of the Royal Society B 2017 284 20170038
Archosaurs, like all vertebrates, have different types of joints that allow or restrict cranial kinesis, such as synovial joints and fibrous joints. In general, synovial joints are more kinetic than fibrous joints, because the former possess a fluid-filled cavity and articular cartilage that facilitate movement. Even though there is a considerable lack of data on the microstructure and the structure–function relationships in the joints of extant archosaurs, many functional inferences of cranial kinesis in fossil archosaurs have hinged on the assumption that elongated condylar joints are (i) synovial and/or (ii) kinetic. Cranial joint microstructure was investigated in an ontogenetic series of American alligators, Alligator mississippiensis. All the presumably synovial, condylar joints found within the head of the American alligator (the jaw joint, otic joint and laterosphenoid–postorbital (LS–PO) joint) were studied by means of paraffin histology and undecalcified histology paired with micro-computed tomography data to better visualize three-dimensional morphology. Results show that among the three condylar joints of A. mississippiensis, the jaw joint was synovial as expected, but the otherwise immobile otic and LS–PO joints lacked a synovial cavity. Therefore, condylar morphology does not always imply the presence of a synovial articulation nor mobility. These findings reveal an undocumented diversity in the joint structure of alligators and show that crocodylians and birds build novel, kinetic cranial joints differently. This complicates accurate identification of synovial joints and functional inferences of cranial kinesis in fossil archosaurs and tetrapods in general.
Jennifer V. Mills, Maya L. Gomes, Brian Kristall, Bradley B. Sageman,
Andrew D. Jacobson, and Matthew T. Hurtgen (2017)
Massive volcanism, evaporite deposition, and the chemical evolution of
the Early Cretaceous ocean.
Geology (advance online publication)
Early Cretaceous (145–100 Ma) rocks record a ∼5‰ negative shift in the sulfur isotope composition of marine sulfate,
the largest shift observed over the past 130 m.y. Two hypotheses have been
proposed to explain this shift: (1) massive evaporite deposition associated
with rifting during opening of the South Atlantic, and (2) increased inputs of
volcanically derived sulfur due to eruption of large igneous provinces. Each
process produces a very different impact on marine sulfate concentrations,
which in turn affects several biogeochemical phenomena that regulate the global
carbon cycle and climate. Here we present sulfur isotope data from Resolution
Guyot, Mid-Pacific Mountains (North Pacific Ocean), that track sympathetically
with strontium isotope records through the ∼5‰ negative sulfur isotope shift. We employ a linked sulfur-strontium
isotope mass-balance model to identify the mechanisms driving the sulfur
isotope evolution of the Cretaceous ocean. The model only reproduces the
coupled negative sulfur and strontium isotope shifts when both hydrothermal and
weathering fluxes increase. Our results indicate that marine sulfate
concentrations increased significantly during the negative sulfur isotope shift
and that enhanced hydrothermal and weathering input fluxes to the ocean played
a dominant role in regulating the marine sulfur cycle and CO2 exchange in the
atmosphere-ocean system during this interval of rapid biogeochemical change.