The rise of the 'Dino-Chickens'

The first Archaeopteryx fossil was unearthed from a limestone quarry in Bavaria, in the early 1860s. This relatively small (Raven size as an adult), feathered, broad winged dinosaur is believed to have glided like a bird through the forests of the Jurassic period 145 million years ago, leading many palaeontologists name it the ancestor of modern birds. Phylogenetic study is never so clean-cut however. Therefore it is unsurprising that other species similar to archaeopteryx; Aurornis xui, and the four winged Anchiornis huxleyi for example, are also contenders for the title of the first bird. But why are our winged dinosaur friends relevant? Well in May 2015 scientists were able to 'alter' chicken embryos to produce a dinosaur-like snout, which was an amazing breakthrough given the lack of clarity in the evolution of dinosaurs into birds; there is no single physical feature that defines this phylogenetic change. One important phenotypical transition evidenced by fossils was the alteration of the premaxilliae in the reptilian snout, growing longer and fusing together to form the beak structure present in birds today. The research team from Harvard then looked at gene expression domains in the face of multiple bird and reptile species; the earlier frontonasal ectodermal zone (FEZ) and the later midfacial WNT-responsive region (they sound incredibly intellectual but rather arbitrary at the same time). From this the researchers reasoned that reptile and dinosaur snouts develop from premaxillae in a similar way, and that the developmental pathways that form the snout were altered in the course of the evolution of Aves. 2 proteins; FGF and Wnt, were found to be essential in the differing developmental process of reptile and bird faces, due to differential gene expression and therefore differential translation of these proteins. The proteins worked differently also, as in reptiles they were active across 2 small regions of the embryo's 'face', whereas in birds they were expressed across a larger band, but in the same region as in reptiles. This may be evidence that evolutionary alteration of expression of these proteins contributed to beak formation. To test this theory and the mechanism of the snout to beak transformation, the autapomorphic median gene expression region found in birds (the area of the genome coding for the beak) was altered in developing chicken embryos. Biochemical inhibitors were added to the chicken eggs to block the 2 vital proteins, thus reverting the chicken's beak to its ancestral reptilian snout, with the premaxillae formed showing a resemblance to fossil specimens, rather than beaked birds. If you're like me though, the term 'biochemical inhibitors' is far too vague. So what do they do exactly? I believe they alter the epigenome of the chicken embryo, perhaps removing methyl groups from CpG regions of long silenced genes, or they may involve acylation of the tails of histones (perhaps using histone acetyltransferase enzymes) to alter transcription rates of genes (See my previous posts for more on epigenetics, it's my favourite thing ever). Back on the Dino-Chickens; let's not get overexcited about a potential Jurassic World situation happening where we reverse engineer dinosaurs and splice them all together into ridiculously improbable 'combosaurs'. The team from Harvard was only seeking the mechanism behind ancestral amniote snout transformation. But perhaps in the future... My army of squid, poison dart frog, chameleon ankylosaurs will become a reality!