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Crocodilian play behavior + keratins in feather and claw formation (free pdfs)
Two recent non-dino papers that may be of interest (with free pdfs):
Vladimir Dinets (2015)
Play behavior in crocodilians.
Animal Behavior and Cognition 2(1): 49-55
Play behavior in crocodilians is not uncommon, but it remains
virtually undescribed in scientific literature. I present the first
overview of play behavior of three types (locomotor play, object play
and social play) in crocodilians based on original observations,
published reports and anecdotal evidence. Object play is the type most
often reported; social play can include interactions with conspecifics
and mammals. Apparently, play behavior is not particularly rare in
crocodilians, but is underreported due to the difficulties of
observing it and interpreting the observations.
Matthew J Greenwold, Weier Bao, Erich D Jarvis, Haofu Hu, Cai Li, M
Thomas P Gilbert, Guojie Zhang and Roger H Sawyer (2014)
Dynamic evolution of the alpha (α) and beta (β) keratins has
accompanied integument diversification and the adaptation of birds
into novel lifestyles.
BMC Evolutionary Biology 14:249
Vertebrate skin appendages are constructed of keratins produced by
multigene families. Alpha (α) keratins are found in all vertebrates,
while beta (β) keratins are found exclusively in reptiles and birds.
We have studied the molecular evolution of these gene families in the
genomes of 48 phylogenetically diverse birds and their expression in
the scales and feathers of the chicken.
We found that the total number of α-keratins is lower in birds than
mammals and non-avian reptiles, yet two α-keratin genes (KRT42 and
KRT75) have expanded in birds. The β-keratins, however, demonstrate a
dynamic evolution associated with avian lifestyle. The avian specific
feather β-keratins comprise a large majority of the total number of
β-keratins, but independently derived lineages of aquatic and
predatory birds have smaller proportions of feather β-keratin genes
and larger proportions of keratinocyte β-keratin genes. Additionally,
birds of prey have a larger proportion of claw β-keratins. Analysis of
α- and β-keratin expression during development of chicken scales and
feathers demonstrates that while α-keratins are expressed in these
tissues, the number and magnitude of expressed β-keratin genes far
exceeds that of α-keratins.
These results support the view that the number of α- and β-keratin
genes expressed, the proportion of the β-keratin subfamily genes
expressed and the diversification of the β-keratin genes have been
important for the evolution of the feather and the adaptation of birds
into multiple ecological niches.