Evolution and development of parrot pseudoteeth

Abstract

Parrot embryos carry peculiar appendages at their developing beak that have been described as pseudoteeth. To better characterize the pattern of development responsible for the emergence of these dental appendages, we examined parrot embryos combining conventional histology and microtomography approaches. Using immunohistochemistry, we observed the epithelial and mesenchymal expression of several proteins involved in tooth development in mammals. Parrot pseudoteeth arose by epithelial and mesenchymal evagination, and their early development was similar to the ontogeny of scales and feathers. There was no enamel tissue, and the evaginations were surrounded by the rhamphotheca. In adults, the rhamphotheca covers entirely the appendages, now represented by bone evaginations, which were more numerous in the lower than in the upper beak, being similar to the osseous teeth of the fossil Pelagornithidae. These embryonic pseudoteeth resembled reptile's first‐generation teeth and dental appendages of chicken talpid2mutants. Proteins involved in mammalian odontogenesis, such as SHH, BMP4, PITX2, and PAX9, were found to be generally expressed in beak epithelium and mesenchyme during parrot pseudoteeth development, with clusters of high‐level expression in the pseudoteeth rudiments. This suggests that a similar, highly conserved gene expression program gives rise to the appearance of odontode derivatives in numerous species, despite their divergent developmental paths. These results provide new insights into the development and evolution of odontode‐derived structures in vertebrates.

Development of the Goose Tongue Filiform Papillae: Could it be Tooth-Like Sense Organs?

“…However, no specific protein expression was observed prior to the first apparition of papillae. These results could also be compared to similar data obtained during the parrot's pseudoteeth development (Louryan et al, 2021). These genes are known to be highly involved during mammalian tooth development (Peters & Balling, 1999).…”

“…The general morphology of tongue papillae, pseudoteeth and denticulations evokes odontodes, the ancestral unique rudiment of teeth, scales and feathers. Parrot's pseudoteeth, scales and feathers express some common genes involved in epithelial-mesenchymal interactions (Louryan et al, 2021), and tongue papillae are classically considered as odontode derivatives (Dhouailly, 2009). Furthermore, the histological morphology of the embryonic papilla is very similar to the fetal keratinized teeth of cyclostomes (Weichert, 1970).…”

“…Negative control experiments were performed by omitting the primary antibodies and suppress and provided in the supplementary material section. In the positive control experiments, primary antibodies were incubated with tissues known to express the corresponding proteins as described previously by Louryan et al (2021).…”

“…Furthermore, several fishes, as the salmon trout, possess tongue teeth (Berkovitz, 1978;Berkovitz & Shellis, 2017). It could thus be interesting to correlate the anatomy and development of the goose filiform papillae to those of bird denticulations and pseudoteeth, which exhibit during their development some gene expressions associated with odontogenesis (Louryan et al, 2021(Louryan et al, , 2023. The morphological features of papillae development in geese (Skieresz-Szewczyk et al, 2012;Skieresz-Szewczyk & Jackowiak, 2017) and in duck (Skieretz-Szeczyk et al, 2014) were described using histology and scanning electron microscopy.…”