Ping Wu, Yung-Chih Lai, Randall Widelitz & Cheng-Ming Chuong (2018)
Comprehensive molecular and cellular studies suggest avian scutate scales are secondarily derived from feathers, and more distant from reptilian scales.
Scientific Reports 8, Article number: 16766 (2018)Â
Amniote skin appendages such as feathers, hairs and scales, provide thermoregulation, physical protection and display different color patterns to attract a mate or frighten an adversary. A long-standing question is whether âreptile scaleâ and âavian leg scalesâ are of the same origin. Understanding the relation between avian feathers, avian scales and reptilian scales will enhance our understanding of skin appendage evolution. We compared the molecular and cellular profiles in chicken feather, chicken scales and alligator scales and found that chicken scutate scales are similar to chicken feathers in morphogenesis at the early placode stage. When we compared the _expression_ of the recently identified feather-specific genes and scale-specific genes in these skin appendages, we found that at the molecular level alligator scales are significantly different from both chicken feathers and chicken scales. Furthermore, we identified a similarly diffuse putative stem cell niche in morphologically similar chicken and alligator scales. These putative stem cells participate in alligator scale regeneration. In contrast, avian feathers have a more condensed stem cell niche, which may be responsible for cycling. Thus, our results suggest that chicken and alligator scales formed independently through convergent evolution.
Tomasz SzczygielskiÂ & Tomasz Sulej (2018)
The early composition and evolution of the turtle shell (Reptilia, Testudinata).
Palaeontology (advacne online publication)
The shell of the oldest true turtle (Testudinata) branch (Proterochersidae) from the Late Triassic (Norian) of Poland and Germany was built in its anterior and posterior part from an osteodermal mosaic which developed several million years after the plastron, neurals and costal bones. We provide the most detailed description of the shell composition in proterochersids to date, together with a review of the shell composition in other Triassic pantestudinates. A scenario of early evolution of the turtle shell is proposed based on new data, and the possible adaptive meaning of the observed evolutionary changes is discussed. These observations are consistent with the trend of shell simplification previously reported in turtles. Several aspects of proterochersid shell anatomy are intermediate between Odontochelys semitestacea and more derived turtles, supporting their stem phylogenetic position. Three additional ossifications were sutured to xiphiplastra and pelvis in Proterochersis spp. and at least in some individuals the nuchal bone was paired. The peripherals, suprapygals, and pygal bone are most likely to be of osteodermal origin and homologous to the proterochersid shell mosaic.