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[dinosaur] 6 month incubation?

Gregory M. Erickson, Darla K. Zelenitsky, David Ian Kay, and Mark A. Norell (2017)
Dinosaur incubation periods directly determined from growth-line counts in embryonic teeth show reptilian-grade development.
Proceedings of the National Academy of Sciences (advance online publication)
doi: 10.1073/pnas.1613716114

I have several questions regarding assumptions made in this paper...but just one for now: von Ebner lines are assumed to be deposited daily. While circadian rhythms are observed in many animals, this is not universal. In a paper called: Ontogeny of dentinogenesis in the rat incisor...early deposition is ultradian (more than an hour/less than a day) and then after the second to third week after birth, circadian rhythms predominate. This makes sense to me: during gestation there is likely very little periodicity in light reaching the pup. And then, in a dinosaur embryo buried under substrate, light might also be an unreliable cue. And so, since circadian periodicity is apparently not universal in dentin deposition, I'm not sure the estimation of incubation time in this paper is reliable. Any thoughts?