[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

[dinosaur] Dating fossil teeth + Foxemys + Amaru + Madrynornis + more




Ben Creisler
bcreisler@gmail.com

Some recent non-dino stuff that may be of interest:


Stephanie Greene, Larry M. Heaman, S. Andrew DuFrane, Thomas Williamson & Philip J. Currie (2018)
Introducing a geochemical screen to identify geologically meaningful U-Pb dates in fossil teeth.
Chemical Geology (advance online publication)
doi: https://doi.org/10.1016/j.chemgeo.2018.04.022
https://www.sciencedirect.com/science/article/pii/S0009254118302031



Previous studies have shown that radiometric dating of fossils can be complicated by post-fossilisation alteration. A key challenge to obtaining geologically meaningful fossilisation dates in bioapatite is identifying regions that have remained relatively undisturbed since the time of fossilisation. In order to determine whether a geochemical indicator can be used to identify least-disturbed regions, we combine in situ trace element analysis and U-Pb geochronology of fossil teeth from the Arroyo Chijuillita Member, New Mexico, and the Dinosaur Park Formation, Alberta. The reliability of these U-Pb dates is supported by good agreement between the isotope dilution thermal ionization mass spectrometry (61.5âÂâ1.6âMa) and laser ablation ICP-MS (64.2âÂâ2.4âMa) dates for a targeted tooth region. Of fourteen teeth analyzed from these units, two record dates within uncertainty of the depositional age: one has a "diffusion" concave upward cross-sectional yttrium profile, the other a concave downward profile reflective of trace element loss. It was found for teeth from both units that smaller yttrium concentration ranges are correlated with younger U-Pb dates, likely the result of post-fossilisation alteration. A yttrium screen based on this relationship is proposed, and is found to be a better indicator of post-fossilisation open system behaviour in the samples analyzed than other geochemical features thought to be produced during fossilisation. This screen provides a new tool for identifying fossil material least disturbed since fossilisation, facilitating the use of bioapatite to date the time of diagenesis.

===



Foxemys

AdÃn PÃrez-GarcÃa & Francisco Ortega (2018)
Geobios (advance online publication)
Identification of the French Upper Cretaceous bothremydid turtle Foxemys mechinorum in the Spanish record.
doi: https://doi.org/10.1016/j.geobios.2018.04.002
https://www.sciencedirect.com/science/article/pii/S0016699518300032



Bothremydidae is the most abundant and diverse group of turtles in the upper Cretaceous fossil sites of southwestern Europe. Several species a priori recognized as exclusive of the Portuguese, Spanish and French records were defined. The most abundant and best preserved Spanish collection of pleurodiran turtles from the last Stages of the Upper Cretaceous comes from the fossil site of Lo Hueco (Cuenca Province, Central Spain). The bothremydid Iberoccitanemys convenarum, defined by a single specimen from the Maastrichtian of Haute-Garonne (Southern France), was subsequently recognized as a very abundant form in this Spanish site, corresponding to the only bothremydid so far identified as being part of the diversity of Bothremydidae of both countries. The presence of a second member of Bothremydidae was recognized in Lo Hueco, representing the only evidence of the synchronic and sympatric coexistence of two members of this lineage in a European site. However, very scarce information about this second form from Lo Hueco was available. Thus, its attribution to a new taxon or to a member of Foxemydina previously identified in the Spanish record, or in that of other European regions, could not be evaluated until now. New material from Lo Hueco, not attributable to Iberoccitanemys convenarum but to this second larger form, allows its generic and specific identification. Close paleobiogeographical relationships considering the fauna of pleurodiran turtles from Spain and France are recognized thanks to the findings performed in Lo Hueco: not only Iberoccitanemys convenarum is known in both countries, but also the French Foxemys mechinorum is identified in Central Spain.


===



Gerardo A. Cordero (2018)
Is the pelvis sexually dimorphic in turtles?
The Anatomical Record (advance online publication)
doi:Â https://doi.org/10.1002/ar.23831
https://onlinelibrary.wiley.com/doi/10.1002/ar.23831


Variation in the pelvis is intrinsically linked to life history evolution. This is perhaps best exemplified by sexually dimorphic pelvic variation in bipedal primates. Yet, whether this trend is applicable to other taxa is unclear. Using turtle anatomy as a model, I tested the hypothesis that the pelvis is also sexually dimorphic in eggâlaying tetrapods. I sampled a natural turtle population with femaleâbiased sexual size dimorphism (i.e. larger females). I show that the area of the egg canal (pelvic aperture) is greater in females. Morphological differences between sexes were predicted by body size, such that skeletal shape deformation of the female ilium increased proportionally with pelvic aperture area. These results suggest that sexual pelvic dimorphism might be indirectly maintained by selection for large female size, consistent with the pelvic constraint hypothesis in reptiles. However, subsampling of similarly sized individuals revealed that pelvic aperture area and shape may vary in disproportion to body size. Comparisons of pelvic ontogenetic trajectories across multiple lineages are needed to clarify the occurrence of sexual pelvic dimorphism in turtles and other eggâlaying tetrapods. My findings provide impetus to further explore how sexâspecific functional demands influence the architecture of the pelvic girdle.Â



===

Amaru scagliai nov. gen., nov. nov.

Adriana MarÃa Albino (2018)
New macrostomatan snake from the Paleogene of northwestern Argentina.
ÂGeobios (advance online publication)
doi: https://doi.org/10.1016/j.geobios.2018.04.005
https://www.sciencedirect.com/science/article/pii/S0016699517301328


The lower Eocene Lumbrera Formation in Salta province, northwestern Argentina, outstands for providing snake remains from a non-Patagonian Paleogene site. The material consists of articulated precloacal vertebrae that represent a new medium-sized macrostomatan snake, namely Amaru scagliai nov. gen., nov. nov. The vertebral characters of Amaru scagliai nov. gen., nov. nov., suggest affinities with advanced clades, which is consistent with the recognition of derived macrostomatans in the early Paleocene of Bolivia and early Eocene of Brazil. The new snake confirms the presence of macrostomatan snakes in South America as early as the Eocene and suggests that the southern continents may have played an unsuspected role in the origin and evolution of advanced macrostomatans during the earliest Cenozoic.


====

Federico J. Degrange, Daniel T. Ksepka & Claudia P. Tambussi (2018)
Redescription of the oldest crown clade penguin: cranial osteology, jaw myology, neuroanatomy, and phylogenetic affinities of Madrynornis mirandus.Â
Journal of Vertebrate Paleontology Article: e1445636Â
DOI: 10.1080/02724634.2018.1445636
https://www.tandfonline.com/doi/full/10.1080/02724634.2018.1445636

Madrynornis mirandus, one of the few fossil penguins known from a nearly complete articulated skeleton, represents a key taxon for understanding the stem-crown transition in penguins. Despite the wealth of morphological character data preserved in the holotype specimen, the phylogenetic placement of this early late Miocene taxon has remained controversial. Reexamination of the Madrynornis mirandus holotype provides support for placement within the penguin crown clade. However, this placement is highly sensitive to the molecular signal and Madrynornis falls just outside the crown clade when molecular data are excluded. The neuroanatomy of Madrynornis shares many derived features with extant penguins, including an airencephalic brain shape, highly reduced bulbus olfactorius, and absence of an interaural pathway. However, the brain endocast differs from all surveyed extant species in that the eminentia sagittalis (wulst) is less caudally expanded, the tectum opticus is relatively less developed, and the flocculus is stouter and more laterally disposed. The cranial osteology and reconstructed jaw myology of Madrynornis suggest a primarily piscivorous diet, which likely characterizes the clade uniting Madrynornis, Inguza, Eudyptula, and Spheniscus.


==