How does Heterochrony relate to the History of an Organ (Wing) Evolution?

[Uncommon Ancestor]

Hi everyone,

I've read a paper (open-access link below) about evolution and development in ratite wings. It compares the rates of development during embryo ontogeny of wing in ostrich and emu (wich is known that developed their flightlessness independently) and compares it to normal wing development in flighted birds. As the rates are quite normal for a flighted bird in ostrich, wing proportions ain relation to the body are only slightly below the normal and the ostrich has a very massive body, it concludes that it is due to general peramorphosis of the body. On the other hand, emu wing growth rates are very, very slow and wing/body proportions are far below normal, it concludes that neoteny afects emu's wing (wich is quite clear according to the few I know about the subject).

However, there's a furhter development of conclusions wich I don't trully understand. The paper says that data suggest that ostrich wings became primarly useless due to body outgrowth so it was too heavy to sustain in the air, while emu ancestor probably reduced it's wings while having a small body size, followed by growth of the already flightless body. How is that deduced from the heterochronic mechanisms displayed (peramorphosis/neoteny)?

I'd be glad someone give me a clue.

I've to say that I'm just a newbie, so I'm probably losing a whole lot of relevant well-known things, I figure. Anyways, here you've got the paper, I'ts scarcely 3 pages long, and most relevant information is on the last one:

Faux, C., & Field, D. (2017). Distinct developmental pathways underlie independent losses of flight in ratites. Biology Letters, 13(7), 20170234.