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[dinosaur] Archosaur cranium evolution + Smilodon canine evolution + marsupial evolution + more

Ben Creisler

New papers:

R. N. Felice, ÂA. Watanabe, ÂA. R. Cuff, ÂE. Noirault, ÂD. Pol, ÂL. M. Witmer, ÂM. A. Norell, P. M. O'Connor & ÂA. Goswami (2019)
Evolutionary integration and modularity in the archosaur cranium.
Integrative and Comparative Biology, icz052 (advance online publication)
doi: https://doi.org/10.1093/icb/icz052

Complex structures, like the vertebrate skull, are composed of numerous elements or traits that must develop and evolve in a coordinated manner to achieve multiple functions. The strength of association among phenotypic traits (i.e., integration), and their organization into highly-correlated, semi-independent subunits termed modules, is a result of the pleiotropic and genetic correlations that generate traits. As such, patterns of integration and modularity are thought to be key factors constraining or facilitating the evolution of phenotypic disparity by influencing the patterns of variation upon which selection can act. It is often hypothesized that selection can reshape patterns of integration, parceling single structures into multiple modules or merging ancestrally semi-independent traits into a strongly correlated unit. However, evolutionary shifts in patterns of trait integration are seldom assessed in a unified quantitative framework. Here, we quantify patterns of evolutionary integration among regions of the archosaur skull to investigate whether patterns of cranial integration are conserved or variable across this diverse group. Using high-dimensional geometric morphometric data from 3D surface scans and CT scans of modern birds (nâ=â352), fossil non-avian dinosaurs (nâ=â27), and modern and fossil mesoeucrocodylians (nâ=â38), we demonstrate that some aspects of cranial integration are conserved across these taxonomic groups, despite their major differences in cranial form, function, and development. All three groups are highly modular and consistently exhibit high integration within the occipital region. However, there are also substantial divergences in correlation patterns. Birds uniquely exhibit high correlation between the pterygoid and quadrate, components of the cranial kinesis apparatus, whereas the non-avian dinosaur quadrate is more closely associated with the jugal and quadratojugal. Mesoeucrocodylians exhibit a slightly more integrated facial skeleton overall than the other grades. Overall, patterns of trait integration are shown to be stable among archosaurs, which is surprising given the cranial diversity exhibited by the clade. At the same time, evolutionary innovations such as cranial kinesis that reorganize the structure and function of complex traits can result in modifications of trait correlations and modularity.


Oliver A. LÃpez-Conde, Juliana Sterli, JesÃs Alvarado-Ortega, MarÃa L.ChavarrÃa-Arellano & HÃctorPorras-MÃzquiz (2019)
The first record of Desmatochelys cf. D. lowii from the Late Cretaceous (Campanian) of Coahuila, Mexico.
Journal of South American Earth Sciences (advance online publication)
doi: https://doi.org/10.1016/j.jsames.2019.05.020


Reported the first record of Protostegidae in the Late Cretaceous of Mexico.
The new specimen of Desmatochelys from Coahuila (Mexico), is a semi-articulated specimen in ventral position.
This new specimen assigned to Desmatochelys cf. lowii not only extends the spatial record of this genus, but also provides important information about the posterior limb anatomy of the genus Desmatochelys.
This new specimen of Desmatochelys is relevant because is the southernmost record along the Western Interior Seaway during the Late Cretaceous.


In this work we describe a new marine turtle from the clade Protostegidae from Mexico recognized as a new specimen of Desmatochelys. This specimen was collected in the San Carlos quarry, near JimÃnez, Coahuila, in outcrops of the Austin Formation, Late Cretaceous (Lower Campanian). The quarries of this region are composed of marly limestones where numerous remains of fossil fish, shark teeth, ammonites and crabs were also found. This Protostegidae turtle from Mexico is a semi-articulated specimen in ventral position, that lacks the skull. This specimen is important because it preserves one of its forelimbs and both hindlimbs. The left anterior limb is fully articulated bringing new information of Desmatochelys and, in the same way, it is the first time that both articulated hindlimbs are reported. This new specimen of Desmatochelys is relevant because is the southernmost record for the genus along the Western Interior Seaway during the Late Cretaceous.


Devin M O'Brien (2019)
Static scaling and the evolution of extreme canine size in a saber-toothed cat (Smilodon fatalis).
Integrative and Comparative Biology, icz054 (advance online publication)
doi: https://doi.org/10.1093/icb/icz054

The canines of saber-toothed cats are a classic example of an extreme morphology, yet important questions pertaining to their evolution remain unanswered. Recent analyses suggest these structures functioned as tools of intrasexual combat where trait size acts as both a weapon of battle and signal of competitive ability. However, classic skeletal reconstructions suggest saber-tooth canines evolved as specialized hunting tools. Either scenario could have led to the evolution of extreme canine size and distinguishing between these hypotheses is therefore difficult. This is made more challenging by the fact that natural observation of saber-toothed cats is impossible, and biologists must rely on measures of static morphology to study the patterns of selection that favored extreme canine size.

Here I analyze the static intraspecific scaling relationship between canine size and body size in the saber-toothed cat, Smilodon fatalis, to determine whether or not extreme canine size functioned as a sexually selected signal. I review the literature surrounding the evolution of sexually selected signals and the methods recently established by O'Brien et al. (2018), show how static scaling relationships can be useful, reliable tools for inferring patterns of selection, especially in fossil organisms, and provide evidence that extreme canine size in saber-toothed cats was not the product of selection for effective sexual signals, but instead evolved as a either a pure intrasexually selected weapon or hunting tool.


Mark D. B. Eldridge, ÂRobin M. D. Beck, ÂDarin A. Croft, ÂKenny J. Travouillon Â& Barry J. Fox (2019)
An emerging consensus in the evolution, phylogeny, and systematics of marsupials and their fossil relatives (Metatheria)
Journal of Mammalogy 100(3): 802â837
doi: https://doi.org/10.1093/jmammal/gyz018

Marsupials and their fossil relatives, which collectively comprise Metatheria, have been of scientific interest for centuries, with many aspects of their evolution and systematics subject to intense research and debate. Here, we review progress over the last 25 years, which has included the description of many new species (modern and fossil), and major improvements in understanding of their phylogenetic relationships, as well as the overall evolutionary history and biogeography of Marsupialia (crown-clade) and Metatheria (total-clade). Significant advances have included the deployment of increasingly sophisticated molecular, morphological, and total evidence analyses, which have resolved most previously disputed relationships among and within the modern marsupial orders. A broad systematic consensus is now emerging, although several major areas of contention remain, particularly among fossil metatherians. New modern species continue to be described at an impressive rate, with almost 50 named in the last 25 years, and many more await discovery. There has also been an explosion in the discovery and description of fossil marsupials and non-marsupial metatherians (~270 species), principally from Australasia and the Americas but also from Antarctica, Europe, and Asia. Most are represented by dental specimens only, but some consist of complete and well-preserved material, which has led to major improvements in our understanding of the evolution of cranial and postcranial morphology. Improvements in the fossil record and advances in methods for inferring divergence times have helped clarify when and where key events occurred in metatherian evolution, and the patterns of subclade diversification. We also have improved understanding of biogeographical relationships among metatherians on different landmasses. Despite enormous progress, numerous key uncertainties remain due to major gaps in the fossil record (e.g., Antarctica, Late Cretaceous, and early Paleogene of Australia) and a comparative lack of studies that directly combine molecular and fossil data. Future advances will largely depend on improvements in the fossil record and studies that better integrate neontological and paleontological evidence.


S. Kathleen Lyons, ÂFelisa A. Smith Â& S. K. Morgan Ernest (2019)
Macroecological patterns of mammals across taxonomic, spatial, and temporal scales.
Journal of Mammalogy 100(3): 1087â1104
doi: https://doi.org/10.1093/jmammal/gyy171

The field of macroecology has made many contributions to our understanding of mammalian ecology and evolution through its use of big data and the examination of statistical patterns that emerge. Here, we review the advances in three areas of mammalian macroecology: 1) spatial and temporal patterns of assemblage structure and space use, 2) the processes and constraints underlying the evolution of body size and life history, and 3) advances in understanding and predicting loss of biodiversity. We highlight the important role that studies of mammals have played in the advancement of macroecological theories and patterns, and note that both mammalogy and macroecology are richer because of this linkage.

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