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[dinosaur] Early onset of Permo-Triassic extinction in Karoo + Delorhynchus + lizard skulls + more

Ben Creisler

Some recent (and not so recent) non-dino papers that may be of interest:

Pia A. Viglietti, Roger M.H. Smith & Bruce S. Rubidge (2018)
Changing palaeoenvironments and tetrapod populations in the Daptocephalus Assemblage Zone (Karoo Basin, South Africa) indicate early onset of the Permo-Triassic mass extinction.
Journal of African Earth Sciences 138: 102-111
doi: https://doi.org/10.1016/j.jafrearsci.2017.11.010Â ÂÂ


Revised environmental change in Karoo Basin prior to Permo-Triassic mass extinction.
Wet floodplain and lacustrine conditions in Lower Daptocephalus Assemblage Zone.
Evidence for early onset of climatic drying in Upper Daptocephalus Assemblage Zone.
Extinction of index taxa and Lystrosaurus maccaigi appearance associated with drying.
Climatic changes associated with extinction occur earlier than previously reported.


Important palaeoenvironmental differences are identified during deposition of the latest Permian Daptocephalus Assemblage Zone (DaAZ) of the South African Beaufort Group (Karoo Supergoup), which is also divided into a Lower and Upper subzone. A lacustrine floodplain facies association showing evidence for higher water tables and subaqueous conditions on the floodplains is present in Lower DaAZ. The change to well-drained floodplain facies association in the Upper DaAZ is coincident with a faunal turnover as evidenced by the last appearance of the dicynodont Dicynodon lacerticeps, the therocephalian Theriognathus microps, the cynodont Procynosuchus delaharpeae, and first appearance of the dicynodont Lystrosaurus maccaigi within the Ripplemead member. Considering the well documented 3-phased extinction of Karoo tetrapods during the Permo-Triassic Mass Extinction (PTME), the facies transition between the Lower and Upper DaAZ represents earlier than previously documented palaeoenvironmental changes associated with the onset of this major global biotic crisis.


Yara Haridy, Mark J Macdougall & Robert R Reisz (2017)
The lower jaw of the Early Permian parareptile Delorhynchus, first evidence of multiple denticulate coronoids in a reptile.
Zoological Journal of the Linnean Society, zlx085 (advance online publication)
doi: https://doi.org/10.1093/zoolinnean/zlx085

We describe the lower jaw of the parareptile Delorhynchus from the Early Permian of Oklahoma, on the basis of a complete, isolated right ramus, and histological thin sections. The lower jaw of Palaeozoic amniotes is generally less well known than other parts of the cranium, largely because they are often preserved in tight occlusion with the skull. Thus, complete information about the dentition and other features of the lower jaw are rarely available. This specimen allows us to recognize for the first time the presence of two coronoid ossifications in a Palaeozoic reptile. Both coronoids bear numerous small teeth, a feature that is commonly found in anamniotes, but rare in amniotes. The distribution of these two features among amniotes reveals that they represent a reversal, and a synapomorphy of the parareptile clade Lanthanosuchoidea, possibly associated with specialized feeding behaviour among these small predators. In addition, Delorhynchus has a coronoid process that is anatomically distinct from those in other parareptiles, indicating multiple, independent origins of this feature within Parareptilia. Furthermore, the complete mandible of Delorhynchus allows us to recognize that the genus Bolterpeton is a junior synonym of the genus Delorhynchus, whereas the species Bolterpeton carrolli is a nomen dubium.


Free pdf:

Sean A. Williamson, Roger G. Evans, S. Charlie Manolis, Grahame J. Webb & Richard D. Reina (2017)

Ecological and evolutionary significance of a lack of capacity for extended developmental arrest in crocodilian eggs.

Royal Society Open Science2017 4 171439

DOI: 10.1098/rsos.171439



Hypoxia within the oviducts maintains embryonic arrest in turtles at the pre-ovipositional stage, which expands the timeframe over which nesting can occur without compromising embryo survival. The arrest can be extended post-oviposition through incubation of eggs in hypoxia. We determined whether crocodilian embryos have this same capacity. We also tested whether increased oxygen availability during incubation alters hatching success. We incubated freshly laid saltwater crocodile (Crocodylus porosus) eggs (Nâ=â83) at 32ÂC in one of five treatments; control (normoxia; 21% O2), 3-day and 6-day hypoxia (1% O2), or 3-day and 6-day hyperoxia (42% O2). Incubation (approx. 82 days) was then completed in normoxia. There was a significant effect of treatment on survival of embryos through to hatching (pâ<â0.001). The hypoxic treatments resulted in almost no hatching (6.7% and 0% survival for the 3- and 6-day treatments, respectively), while the hyperoxic and control treatments resulted in normal to high hatching success (86.6%, 100% and 64.2% for the control, 3- and 6-day hyperoxic treatments, respectively). Unlike turtles, hypoxic incubation of crocodile eggs failed to delay development. Our results provide the first experimental evidence that, unlike turtles, crocodiles do not exhibit embryonic arrest when incubated under hypoxic conditions immediately following oviposition. An absence of embryonic arrest is of ecological and evolutionary significance, as it implies that crocodilians lack an ability to avoid adverse environmental conditions through delayed nesting and that, unlike turtles, embryonic arrest may not be a potential explanation for the lack of viviparity in the order Crocodylia.


Marc E. H. Jones, Flora GrÃning, Hugo Dutel, Alana Sharp, Michael J. Fagan, Susan E. Evans (2017)

The biomechanical role of the chondrocranium and sutures in a lizard cranium.

Journal of the Royal Society Interface 2017 14 137 20170637

DOI: 10.1098/rsif.2017.0637.




The role of soft tissues in skull biomechanics remains poorly understood. Not least, the chondrocranium, the portion of the braincase which persists as cartilage with varying degrees of mineralization. It also remains commonplace to overlook the biomechanical role of sutures despite evidence that they alter strain distribution. Here, we examine the role of both the sutures and the chondrocranium in the South American tegu lizard Salvator merianae. We use multi-body dynamics analysis (MDA) to provide realistic loading conditions for anterior and posterior unilateral biting and a detailed finite element model to examine strain magnitude and distribution. We find that strains within the chondrocranium are greatest during anterior biting and are primarily tensile; also that strain within the cranium is not greatly reduced by the presence of the chondrocranium unless it is given the same material properties as bone. This result contradicts previous suggestions that the anterior portion (the nasal septum) acts as a supporting structure. Inclusion of sutures to the cranium model not only increases overall strain magnitudes but also leads to a more complex distribution of tension and compression rather than that of a beam under sagittal bending.



Ana IvanoviÄ & Jan W. Arntzen (2017)
Evolution of skull shape in the family Salamandridae (Amphibia: Caudata).
JOURNAL OF ANATOMY (advance online publication)
DOI: 10.1111/joa.12759ÂÂ

We carried out a comparative morphometric analysis of 56 species of salamandrid salamanders, representing 19 out of 21 extant genera, with the aim of uncovering the major patterns of skull shape diversification, and revealing possible trends and directions of evolutionary change. To do this we used micro-computed tomography scanning and three-dimensional geometric morphometrics, along with a well-resolved molecular phylogeny. We found that allometry explains a relatively small amount of shape variation across taxa. Congeneric species of salamandrid salamanders are more similar to each other and cluster together producing distinct groups in morphospace. We detected a strong phylogenetic signal and little homoplasy. The most pronounced changes in the skull shape are related to the changes of the frontosquamosal arch, a unique feature of the cranial skeleton for the family Salamandridae, which is formed by processes arising from the frontal and squamosal bones that arch over the orbits. By mapping character states over the phylogeny, we found that a reduction of the frontosquamosal arch occurs independently in three lineages of the subfamily Pleurodelinae. This reduction can probably be attributed to changes in the development and ossification rates of the frontosquamosal arch. In general, our results are similar to those obtained for caecilian amphibians, with an early expansion into the available morphospace and a complex history characterizing evolution of skull shape in both groups. To evaluate the specificity of the inferred evolutionary trajectories and Caudata-wide trends in the diversity of skull morphology, information from additional groups of tailed amphibians is needed.


Chul Lee, Heesu Jeong, DongAhn Yoo, Eun Bae Kim, Bo-Hye Nam & Heebal Kim (2017)
Coelacanth-specific adaptive genes give insights into primitive evolution for water-to-land transition of tetrapods.
Marine Genomics (advance online publication)
doi: https://doi.org/10.1016/j.margen.2017.12.004

Coelacanth is a group of extant lobe-finned fishes in Sarcopterygii that provides evolutionary information for the missing link between ray-finned fish and tetrapod vertebrates. Its phenotypes, different from actinopterygian fishes, have been considered as primitive terrestrial traits such as cartilages in their fatty fins which are homologous with the humerus and femur. To investigate molecular evolution of coelacanth which led to its divergence into Sarcopterygii, we compared its protein coding sequences with 11 actinopterygian fishes. We identified 47 genes under positive selection specific to coelacanth, when compared to Holostei and Teleostei. Out of these, NCDN and 14 genes were associated with spatial learning and nitrogen metabolism, respectively. In homeobox gene superfamily, we identified coelacanth-specific amino acid substitutions, and also observed that one of replacements in SHOX was shared with extant tetrapods. Such molecular changes may cause primordial morphological change in the common ancestor of sarcopterygians. These results suggest that certain genes such as NCDN, MMS19, TRMT1, ALX1, DLX5 and SHOX might have played a role in the evolutionary transition between aquatic and terrestrial vertebrates.


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