Evan T. Saitta, christopher S. Rogers, Richard A. Brooker, and Jakob Vinther (2017)
Experimental taphonomy of keratin: a structural analysis of early taphonomic changes.
PALAIOS 32(10): 647-657
The evolution of integumentary structures, particularly in relation to feathers in dinosaurs, has become an area of intense research. Our understanding of the molecular evolution of keratin protein is greatly restricted by the fact that such information is lost during diagenesis and cannot be derived from fossils. In this study, decay and maturation experiments are used to determine if different keratin types or integumentary structures show different patterns of degradation early in their taphonomic histories and if such simulations might advance our understanding of different fossilization pathways. Although different distortion patterns were observed in different filamentous structures during moderate maturation and ultrastructural textures unique to certain types of scales persisted in moderate maturation, neither of these have been observed in fossils. It remains uncertain whether these degradation patterns would ever occur in natural sediment matrix, where microbial and chemical decay happens well before significant diagenesis. It takes some time for remains to be buried, meaning that keratin may not be left for moderate maturation to produce such patterns. Higher, more realistic maturation conditions produce a thick, and water soluble fluid that lacks all morphological and ultrastructural details of the original keratin, suggesting that such textural or distortion patterns are unlikely to be preserved in fossils. Although different degradation patterns among keratinous structures are intriguing, it is unlikely that such information could be recorded in the fossil record. Calcium phosphates and pigments are the surviving components of integumentary structures. Thus, the results here are likely of more relation to the archaeological record than fossil record. Other noteworthy results of these experiments are that melanin may not be the leading factor in determining the rate of microbial decay in feathers but may reduce the rate of degradation from maturation, that the existence of rachis filamentous subunits similar to plumulaceous barbules is supported, and that previously reported dinosaur ‘erythrocytes' may be taphonomic artifacts of degraded organic material.
Lauren B. DeBey and Gregory P. Wilson (2017)
Mammalian distal humerus fossils from eastern Montana, USA with implications for the Cretaceous-Paleogene mass extinction and the adaptive radiation of placentals.
Palaeontologia Electronica 20.3.49A: 1-93
Postcrania of Cretaceous-Paleogene (K-Pg) mammals offer insights into richness, body size, and locomotor ecology that supplement patterns from well-sampled dental assemblages. Here, we describe and morphotype 50 distal humeri from Lancian-Puercan assemblages of eastern Montana. Using geometric morphometric analysis of a taxonomically broad sample of humeri from extant small-bodied therians of diverse locomotor modes, we constrain locomotor inferences of some morphotypes. We use this database to preliminarily assess body-size and locomotor diversity across the K-Pg boundary.
The seven Lancian humerus morphotypes include the multituberculates ?Mesodma sp., ?Cimolodon nitidus, and ?Meniscoessus robustus and the metatherian ?Didelphodon vorax. Morphotype richness decreased to four or five across the K-Pg boundary and rebounded in the late Puercan to six, mostly eutherian, morphotypes. Puercan morphotypes include the multituberculate ?Stygimys kuszmauli, the “plesiadapiform” primate ?Purgatorius, small and large archaic ungulates, a possible palaeoryctid, and a very large eutherian. Humerus size data imply a decrease in body size across the K-Pg boundary, followed by an increase by the late Puercan, a trend consistent with the dental fossil record. Geometric morphometrics analysis and functional morphology imply greater locomotor diversity among K-Pg mammals than previously recognized: we infer that most Lancian and Puercan multituberculates were arboreal; the Lancian eutherian was arboreal or semifossorial; the early Puercan palaeoryctid was semifossorial and the small archaic ungulate was terrestrial; and the late Puercan “plesiadapiform” primate was arboreal and the large archaic ungulate was scansorial. Taken together, these preliminary results expand our understanding of K-Pg mammals and our basis for testing ecological hypotheses of the K-Pg mass extinction and recovery.
Rémi Allemand, Renaud Boistel, Gheylen Daghfous, Zoé Blanchet, Raphaël Cornette, Nathalie Bardet, Peggy Vincent and Alexandra Houssaye (2017)
Comparative morphology of snake (Squamata) endocasts: evidence of phylogenetic and ecological signals.
Journal of Anatomy (advance online publication)
Brain endocasts obtained from computed tomography (CT) are now widely used in the field of comparative neuroanatomy. They provide an overview of the morphology of the brain and associated tissues located in the cranial cavity. Through anatomical comparisons between species, insights on the senses, the behavior, and the lifestyle can be gained. Although there are many studies dealing with mammal and bird endocasts, those performed on the brain endocasts of squamates are comparatively rare, thus limiting our understanding of their morphological variability and interpretations. Here, we provide the first comparative study of snake brain endocasts in order to bring new information about the morphology of these structures. Additionally, we test if the snake brain endocast encompasses a phylogenetic and/or an ecological signal. For this purpose, the digital endocasts of 45 snake specimens, including a wide diversity in terms of phylogeny and ecology, were digitized using CT, and compared both qualitatively and quantitatively. Snake endocasts exhibit a great variability. The different methods performed from descriptive characters, linear measurements and the outline curves provided complementary information. All these methods have shown that the shape of the snake brain endocast contains, as in mammals and birds, a phylogenetic signal but also an ecological one. Although phylogenetically related taxa share several similarities between each other, the brain endocast morphology reflects some notable ecological trends: e.g. (i) fossorial species possess both reduced optic tectum and pituitary gland; (ii) both fossorial and marine species have cerebral hemispheres poorly developed laterally; (iii) cerebral hemispheres and optic tectum are more developed in arboreal and terrestrial species.