Ben Creisler
Recent non-dino papers:
Species of the order Crocodylia are mostly large, predatory and semi-aquatic reptiles. Crocodylia, the closest living relatives of birds, first appeared in the Late Cretaceous period. In the present study, the complete mitochondrial (mt) genomes of 19 Crocodylia species, including two species (Melanosuchus niger and Caiman yacare) that have not been previously sequenced for mitogenomes, were processed through Illumina sequencing to offer genetic resources and compare with the mitogenomes of Crocodylia species reported previously. In addition, a high-resolution phylogenetic tree of nearly all current recognized species of Crocodylia is constructed based on mitogenomic data. Phylogenetic analyses support monophyly of three families: Alligatoridae (four genera: Alligator, Caiman, Melanosuchus and Paleosuchus), Crocodylidae (three genera: Crocodylus, Mecistops and Osteolaemus) and Gavialidae (two genera: Gavialis and Tomistoma). The tree topology is generally similar to previous studies. Molecular dating suggests that the first split within Crocodylia date back to the Upper Cretaceous (approx. 86.75 Mya). The estimated time to the most recent common ancestor (TMRCA) of Alligatoridae is 53.33 Mya and that of Crocodylidae and Gavialidae is 50.13 Mya, which might be closely linked to climate changes during the Late Palaeocene and Early Eocene. Additionally, this study proves that the diversification rate within Crocodylia began to increase from the Late Eocene (about 36 Mya) and two diversification peak periods of Crocodylia (0â10 Mya and 10â20 Mya) are disclosed, which is roughly consistent with the estimated crocodylian species richness through time. Combining all these clues, we can suggest that climate fluctuation may have played a decisive role in the speciation of Crocodylia.
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E. A. Buchholtz, Z. M. Yozgyur, A. Feldman, A. A. Weaver & T. J. Gaudin (2020)
The therian sternum at the lateral somitic frontier: Evolution of a composite structure.
Journal of Zoology (advance online publication)
doi:
https://doi.org/10.1111/jzo.12809https://zslpublications.onlinelibrary.wiley.com/doi/10.1111/jzo.12809The mammalian sternum plays key roles in structural support, locomotion and ventilation, but its evolutionary history has rarely been addressed. Unlike most other synapsids, the therian presternum lacks a discreet interclavicle, and the mesosternum is composed of a series of sternebrae. Here, CT scans of fossil and living therians are used to confirm that the therian presternum incorporates multiple elements, including the interclavicle and the anteriormost sternal bands of ancestral synapsids. A previously unrecognized transitional element that articulates with rib 1 is variably present and is hypothesized to permit the direct integration of the first rib and the sternum, despite their origins in different developmental domains. Sternebrae are found at sites where primaxial ribs interact directly with the abaxial sternum and locally inhibit skeletal maturation. Both presternal fusion and mesosternal subdivision are the products of small developmental changes that allowed the adaptation of ancestral structures to the lifestyles of therians.
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Free pdf:
Studies of soft tissue, cells and original biomolecular constituents preserved in fossil vertebrates have increased greatly in recent years. Here we report preservation of âskinâ with chemical and molecular characterization from a three-dimensionally preserved caudal portion of an aspidorhynchid Cretaceous fish from the equatorial Barremian of Colombia, increasing the number of localities for which exceptional preservation is known. We applied several analytical techniques including SEM-EDS, FTIR and ToF-SIMS to characterize the micromorphology and molecular and elemental composition of this fossil. Here, we show that the fossilized âskinâ exhibits similarities with those from extant fish, including the wrinkles after suffering compression stress and flexibility, as well as architectural and tissue aspects of the two main layers (epidermis and dermis). This similarity extends also to the molecular level, with the demonstrated preservation of potential residues of original proteins not consistent with a bacterial source. Our results show a potential preservation mechanism where scales may have acted as an external barrier and together with an internal phosphate layer resulting from the degradation of the dermis itself creating an encapsulated environment for the integument.