Ben Creisler
Some recent non-dino papers that may be of interest:
Acresuchus pachytemporalis, gen. et sp. nov.Â
Jonas P. Souza-Filho, Rafael G. Souza, Annie Schmaltz Hsiou, Douglas Riff, Edson Guilherme, Francisco Ricardo Negri & Giovanne M. Cidade (2019)
A new caimanine (Crocodylia, Alligatoroidea) species from the SolimÃes Formation of Brazil and the phylogeny of Caimaninae.
Journal of Vertebrate Paleontology e1528450
The Miocene deposits of South America are notable for their diverse crocodyliform fauna, of which the giant caimanine Purussaurus is a well-known example. This contribution describes a new caimanine, Acresuchus pachytemporalis, gen. et sp. nov., based on an almost complete skull and mandible from the late Miocene SolimÃes Formation of the southwestern Brazilian Amazonia. This new taxon is based on a unique combination of characters, of which the presence of an upturned posterolateral margin of the squamosal throughout the entire lateral margin of the bone (a 'horn'), with a dorsoventral expansion in the posterior portion of the eminence, stands out. We conducted a phylogenetic analysis of Eusuchia, which showed the new taxon as sister to Purussaurus. This placement allows discussion about the evolution of gigantism in the Acresuchus-Purussaurus clade, which reveals several characters that may be related to gigantism. Additionally, Acresuchus was probably a medium-sized generalist caimanine that had an ecological niche similar to the extant Melanosuchus niger. Until now, crocodyliforms that had such niches were unknown from the SolimÃes Formation.
SUPPLEMENTAL DATAâSupplemental materials are available for this article for free at www.tandfonline.com/UJVP
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Marco Romano & Bruce Rubidge (2019)
Long bone scaling in Captorhinidae: do limb bones scale according to elastic similarity in sprawling basal amniotes?
Lethaia (advance online publication)
Captorhinids are a speciose clade of sauropsids that are crucial to understand several aspects of basal amniote general biology. Members of the Captorhinidae explored different diets and, amongst basal amniotes, were one of the first groups to demonstrate highâfibre herbivory. Several papers have been published on the cranial anatomy of captorhinids, but there are relatively few studies which focus on the postâcranium, especially on the appendicular skeleton and long bones. This contribution presents the first quantitative long bone scaling in Captorhinidae performed through morphometric analyses. From classical biomechanical research, it is wellâestablished that to accommodate an increase in size, gravity will result in elastic deformation of long bones. This outcome is especially significant in terrestrial tetrapods with a sprawling limb posture such as captorhinids, where great torsional stresses are applied to long bones, both during locomotion and in the resting phase. In this paper, we test whether the consistent evolutionary size increase in captorhinids led to major reâpatterning in long bone structure as theoretically expected, based on the theory of elastic similarity. Morphometric analysis shows that, apart from a small positive allometry in the humerus, captorhinid long bones scale geometrically as body size increases. Thus, the predicted elastic similarity to maintain similar levels in peak stress with an increase in dimensions does not seem not to apply to long bone evolution in captorhinids. We propose that, as already observed experimentally in largerâbodied varanid lizards, large captorhinids could also mitigate sizeârelated increases in stress by reducing femur rotation and increasing the percentage of the stride cycle during which the right hindfoot was on the ground (i.e. the duty factor). In this way, large captorhinids could avoid reaching peak stress thresholds by sacrificing speed during locomotion and without a substantial long bone reâpatterning or postural change.
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Lorenzo Alibardi (2019)
Organ regeneration evolved in fish and amphibians in relation to metamorphosis: Speculations on a post-embryonic developmental process lost in amniotes after the water to land transition.
Annals of Anatomy - Anatomischer Anzeiger 222: 114-119
Organ regeneration occurs in anamniotes (fish and amphibians) while is absent in amniotes (reptiles, birds and mammals). An evolutionary hypothesis is presented to explain the loss of organ regeneration in amniotes. The aquatic life in fish or the initial aquatic and later terrestrial life in amphibians requires complex life cycles after embryonic development. One or more larval stages that occupy different ecological niches are necessary in fish to reach the final adult stage, generally through metamorphosis. This is a post-embryonic process determined by genes that are constitutive of the genome of fish and amphibians, and that can also be re-utilized during adult life to regenerate injured or lost organs. During the adaptation to terrestrial niches, the larval stages disappeared and a direct development evolved with the formation of the amniote egg in reptiles and birds or the blastocysts in mammals. The genome for developing larvae and metamorphosis was therefore eliminated from the life cycle of amniotes. The loss of genes utilized for metamorphosis determined also the loss of the capability to regenerate organs in adults, especially of the neural organization of the nervous system. The cellular immune system that in anamniotes was operating in metamorphic destruction of larval tissues, in amniotes became no longer tolerant to embryonic-larval antigens. The loss of genes operating during metamorphosis and presence of intolerant immune cells determined the inability to regenerate organs in amniotes. Efforts of regenerative medicine must overcome these genetic and immune barriers to induce organ regeneration.