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[dinosaur] Amniote marine colonizations + Crocodylia transverse processes and limb proportions + bat terrestrial limb loading

Ben Creisler

Some recent non-dino papers:

Geerat J. Vermeij and Ryosuke Motani (2018)Â
Land to sea transitions in vertebrates: the dynamics of colonization.
Paleobiology (advance online publication)

Vertebrates with terrestrial or freshwater ancestors colonized the sea from the Early Triassic onward and became competitively dominant members of many marine ecosystems throughout the Mesozoic and Cenozoic eras. The circumstances that led to initial marine colonization have, however, received little attention. One hypothesis is that mass extinction associated with ecosystem collapse provided opportunities for clades of amphibians, reptiles, birds, and mammals to enter marine environments. Another is that competitive pressures in donor ecosystems on land and in freshwater, coupled with abundant food in nearshore marine habitats, favored marine colonization. Here we test these hypotheses by compiling all known secondarily marine amniote clades and their times of colonization. Marine amniotes are defined as animals whose diet consists primarily of marine organisms and whose locomotion includes swimming, diving, or wading in salt water. We compared the number of clades entering during recovery phases from mass extinctions with the rate of entry of clades during nonrecovery intervals of the Mesozoic and Cenozoic. We conservatively identify 69 marine colonizations by amniotes. The only recovery interval for which prior mass extinction could have been a trigger for marine entry is the Early Triassic, when four clades colonized the sea over 7 Myr, significantly above the rates at which clades entered during other intervals. High nearshore productivity was a greater enticement to colonization than was a low diversity of potential marine competitors or predators in nearshore environments of a highly competitive terrestrial or freshwater donor biota. Rates of marine entry increased during the Cenozoic, in part because of rising productivity and in part thanks to the participation of warm-blooded birds and mammals, which broadened the range of thermal environments in which initial colonization of the sea became possible.


Rafael Gomes de Souza (2018)
Comments on the serial homology and homologues of vertebral lateral projections in Crocodylia (Eusuchia).
The Anatomical Record (advance online publication)
DOI: 10.1002/ar.23802Â

The literature on crocodylian anatomy presents the transverse process in an ambiguous meaning, which could represent all lateral expansions derived from the neural arch, including vertebrae from cervical to caudal series, or in a more restrictive meaning, being applied only to lumbar vertebrae. The lateral expansion of sacrals and caudals vertebrae usually referred to as the transverse process has been discovered to be fused ribs, bringing more ambiguity to this term. Therefore, with the lack of a definition for transverse process and other associated terms, the present work aims to propose a nomenclatural standardization, as well as definitions and biological meaning, for vertebral rib related structures. Vertebra obtained from museum collections from a total of 87 specimens of 22 species of all extant Crocodylia genera were studied. All vertebrae, except cervicals and first three dorsals, exhibit transverse processes. The transverse process is more developed in dorsals and lumbars vertebrae than in sacrals and caudals vertebrae in which it is suppressed by the fused ribs. The serial homology hypotheses here proposed can also be aplied to other Crurotarsi and saurischian dinosaurs specimens. This standardization clarifies the understand of the serial homology among those homotypes and, reduces the ambiguity and misleadings in future work comparisons.Â


Free pdf:

Masaya Iijima, Tai Kubo &Â Yoshitsugu Kobayashi (2018)
Comparative limb proportions reveal differential locomotor morphofunctions of alligatoroids and crocodyloids.
Royal Society Open Science. 2018 5 3 171774
DOI: 10.1098/rsos.171774

Although two major clades of crocodylians (Alligatoroidea and Crocodyloidea) were split during the Cretaceous period, relatively few morphological and functional differences between them have been known. In addition, interaction of multiple morphofunctional systems that differentiated their ecology has barely been assessed. In this study, we examined the limb proportions of crocodylians to infer the differences of locomotor functions between alligatoroids and crocodyloids, and tested the correlation of locomotor and feeding morphofunctions. Our analyses revealed crocodyloids including Gavialis have longer stylopodia (humerus and femur) than alligatoroids, indicating that two groups may differ in locomotor functions. Fossil evidence suggested that alligatoroids have retained short stylopodia since the early stage of their evolution. Furthermore, rostral shape, an indicator of trophic function, is correlated with limb proportions, where slender-snouted piscivorous taxa have relatively long stylopodia and short overall limbs. In combination, trophic and locomotor functions might differently delimit the ecological opportunity of alligatoroids and crocodyloids in the evolution of crocodylians.


M. C. Granatosky (2018)
Forelimb and hindlimb loading patterns during quadrupedal locomotion in the large flying fox (Pteropus vampyrus) and common vampire bat (Desmodus rotundus).
Journal of Zoology (advance online publication)
DOI: 10.1111/jzo.12538ÂÂ

Adaptations for flight have greatly modified the forelimbs and hindlimbs of bats compared to other mammals so that terrestrial and/or above branch quadrupedal locomotion is awkward and unusual for most species. However, suspensory quadrupedal gaits are quite common for bats, but little is known about this type of movement and no data are available on how these animals load their limbs and support the body. Values for vertical, fore-aft and mediolateral peak forces were collected for the forelimb and hindlimb during suspensory quadrupedal locomotion in the large flying fox (Pteropus vampyrus) and common vampire bat (Desmodus rotundus), and during terrestrial locomotion in the common vampire bats. During suspensory quadrupedal locomotion in both species, the hindlimbs serves as the primary weight-bearing and braking organ, whereas the forelimb has a reduced weight-bearing role and acts as the primary propulsive limb. Mediolateral forces are dominated by medially directed forces by the animal that likely serve to help maintain âgripâ while moving below supports. Kinetic patterns of terrestrial locomotion in the common vampire bat are completely opposite, and resemble data that has been reported for most mammals with the exception of relatively high lateral forces. The data presented here add to the growing body of knowledge that suspensory quadrupedal locomotion does not represent a neuromuscular mirror to non-suspensory quadrupedal gaits. Furthermore, this study demonstrates that suspensory quadrupedal gaits are not the same across mammals, and species have adopted multiple mechanical strategies for moving quadrupedally below a support.


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