The potential evolutionary link between hairs in mammals, feathers in birds and scales in reptiles has been debated for decades. Today, researchers of the University of Geneva (UNIGE) and the SIB Swiss Institute of Bioinformatics, Switzerland, demonstrate that all these skin appendages are homologous: they share a common ancestry. On the basis of new analyses of embryonic development, the Swiss biologists evidenced molecular and micro-anatomical signatures that are identical between hairs, feathers and scales at their early developmental stages. These new observations, published today in Science Advances, indicate that the three structures evolved from their common reptilian ancestor.
Mammalian hairs and avian feathers develop from a similar primordial structure called a 'placode': a local thickening of the epidermis with columnar cells that reduce their rate of proliferation and express very specific genes. This observation has puzzled evolutionary and developmental biologists for many years because birds and mammals are not sister groups: they evolved from different reptilian lineages. According to previous studies, reptiles' scales however do not develop from an anatomical placode. This would imply that birds and mammals have independently 'invented' placodes during their evolution.
Microbiota and food residues including possible evidence of pre-mammalian hair in Upper Permian coprolites from Russia
Authors:
Bajdek et al
Abstract:
Coprolites (fossil faeces) provide direct evidence on the diet of its producer and unique insights on ancient food webs and ecosystems. We describe the contents of seven coprolites, collected from the Late Permian Vyazniki site of the European part of Russia. Two coprolite morphotypes (A, B) contain remains of putative bacteria, cyanobacteria, fungi, protists, invertebrate eggs, arthropod elements, undigested bone and tooth fragments, fish scales and elongated hair-like structures with hollow interiors. Content, size and shape of the coprolites together with the associated body fossil record suggest that the most probable scat-producers were carnivorous tetrapods; the bone-rich morphotype A reveals short food retention time and a fast metabolism and is therefore assigned to therapsid carnivores whereas morphotype B with rarer and degraded bones are assigned to archosauromorphs or other non-therapsid carnivores. The general coprolite matrix contains abundant micron-sized spheres and thin-walled vesicles which are interpreted as oxide and phosphatic pseudomorphs after microbial cells. From analyses of the undigested bones, we infer that they represent remains of actinopterygian fish, a therapsid and unrecognizable parts of amphibians and/or reptiles. Additionally, hair-like structures found in one coprolite specimen occur as diagenetically altered (oxide-replaced) structures and moulds (or partly as pseudomorphs) in a microcrystalline carbonate-fluoride-bearing calcium phosphate. This suggests that the latest Permian therapsids probably were equipped with hair-like integument or hairsuit. If true, this is by far the oldest evidence of this mammalian character in the stem group of mammals.
