Birds & Dinosaurs – Joined at the Hip | Yale News

[Posted by Chuck Almdale, suggested by Edna Alvarez]

More evidence that those friendly feathered animals living around, above, even below us, are the direct descendants of those toothy cold-blooded killers who used to rule the world (not counting bacteria).

Birds & Dinosaurs — Joined at the Hip
Yale News | Jim Shelton | July 27, 2022 | 5 minute read

From the article:

All baby birds have a moment prior to hatching when their hip bone is a tiny replica of a dinosaur’s pelvis. That’s one of the findings in a new, Yale-led study in the journal Nature that explores the evolutionary underpinnings of the avian hip bone. It is also a modern-day nod to the dramatic transformation that led from dinosaurs to birds over tens of millions of years.

Link to list of publications by co-author and lab director Bhart-Anjan S. Bhullar
Sample title: The early origin of a birdlike inner ear and the evolution of dinosaurian movement and vocalization. Science 372(6542): 601-609. Hanson M*, Hoffman EA, Norell MA, Bhullar B-AS. (2021).

Link to the paper: The developing bird pelvis passes through ancestral dinosaurian conditions
Abstract:

Living birds (Aves) have bodies substantially modified from the ancestral reptilian condition. The avian pelvis in particular experienced major changes during the transition from early archosaurs to living birds. This stepwise transformation is well documented by an excellent fossil record; however, the ontogenetic alterations that underly it are less well understood. We used embryological imaging techniques to examine the morphogenesis of avian pelvic tissues in three dimensions, allowing direct comparison with the fossil record. Many ancestral dinosaurian features (for example, a forward-facing pubis, short ilium and pubic ‘boot’) are transiently present in the early morphogenesis of birds and arrive at their typical ‘avian’ form after transitioning through a prenatal developmental sequence that mirrors the phylogenetic sequence of character acquisition. We demonstrate quantitatively that avian pelvic ontogeny parallels the non-avian dinosaur-to-bird transition and provide evidence for phenotypic covariance within the pelvis that is conserved across Archosauria. The presence of ancestral states in avian embryos may stem from this conserved covariant relationship. In sum, our data provide evidence that the avian pelvis, whose early development has been little studied, evolved through terminal addition—a mechanism whereby new apomorphic states are added to the end of a developmental sequence, resulting in expression of ancestral character states earlier in that sequence. The phenotypic integration we detected suggests a previously unrecognized mechanism for terminal addition and hints that retention of ancestral states in development is common during evolutionary transitions.

Three more articles on this paper: Xeniasday, Wiley Analytical Science, Hartford Courant.