Abstract
•Although the molecular structure of β-keratins from the Archosaurs (birds, crocodiles), testudines (turtles) and squamates (lizards and snakes) has been studied for more than 50 years and the key parameters established by X-ray diffraction, infrared spectroscopy and sequence analysis, the research has lacked data on the Rhynchocephalia, the last branch of the lepidosaurs in the phylogenetic map.•This paper represents the culmination of the very considerable efforts that have been made over many years by a diverse group from New Zealand, Australia, Italy and the UK to collect and analyse the beta-keratin sequence data from tuatara, the sole representative of the Rhynchocephalia.•Also described is the X-ray diffraction pattern from tuatara claw and this is compared with those from other β-keratins.•In so doing this research advances the β-keratin story structure-wise for the sauropsids in general (birds and reptiles).•Now, at last, we have a totally consistent structural model across all members of the sauropsids.
The birds and reptiles, collectively known as the sauropsids, can be subdivided phylogenetically into the archosaurs (birds, crocodiles), the testudines (turtles), the squamates (lizards, snakes) and the rhynchocephalia (tuatara). The structural framework of the epidermal appendages from the sauropsids, which include feathers, claws and scales, has previously been characterised by electron microscopy, infrared spectroscopy and X-ray diffraction analyses, as well as by studies of the amino acid sequences of the constituent β-keratin proteins (also referred to as the corneous β-proteins). An important omission in this work, however, was the lack of sequence and structural data relating to the epidermal appendages of the rhynchocephalia (tuatara), one of the two branches of the lepidosaurs. Considerable effort has gone into sequencing the tuatara genome and while this is not yet complete, there are now sufficient sequence data for conclusions to be drawn on the similarity of the β-keratins from the tuatara to those of other members of the sauropsids. These results, together with a comparison of the X-ray diffraction pattern of tuatara claw with those from seagull feather and goanna claw, confirm that there is a common structural plan in the β-keratins of all of the sauropsids, and not just those that comprise the archosaurs (birds and crocodiles), the testudines (turtles) and the squamates (lizards and snakes).