Omar Rafael Regalado Fernández

By understanding the way Hox codes work in the

extant phylogenetic bracket, it might be possible to infer a

pattern for dinosaurs.

The study aims to establish a pattern with

Crocodilus nilotuicus and compare it with the already established model for Alligator

mississipiensis

As of today, Hox codes have been established for

actinopterygians, mammals, squamates and birds.

(Left) Mouse embryo showing somites; (Right) Adult mouse vertebral column. Colors show vertebrae with different identities. Regions of Hox gene activity are shown with brackets on the embryo. Wellik (2007).

Jacqueline Deschamps, and Johan van Nes Development 2005;132:2931-2942

Landmark set used in the geometric morphometric analysis. The numbered three-dimensional landmarks (red points) are shown on the fourth cervical vertebra of A. mississippiensis (three-dimensional scan).

Considerations:• Atlas exluded from the

analyses.• LM 13 and 14 are not

applied to chickens (fussion of the ribs to the centra)

Relative Warp analysis results.

Christine Böhmer et al. Proc. R. Soc. B 2015;282:20150077

PCO analysis results.

Christine Böhmer et al. Proc. R. Soc. B 2015;282:20150077

Neural tube

Whole-mount in situ hybridisation (WIHS) in the somites of Crocodilus niloticus

Christine Böhmer et al. Proc. R. Soc. B 2015;282:20150077

C3

C6

C3

D1

C5

D3

C5

C9

C8

D1

C9

D4

Schematic of the anterior Hox expression limits in modern archosaurs.

Conclusions

Hox-4 and Hox-5 paralogue genes are active in the cervical columns of recent archosaurs.

The anterior expression boundaries of the Hox genes in modern archosaurs was correlated with the boundaries of morphologically distinct subregions within each cervical column.

Neck elongation is a prominent feature in the evolution of ornithodiran archosaurs. This enlengthenment seems to play a role in the ecological success of birds and sauropodomorphs.

A posterior evaluation of the Hox gene expression in relation to the neck elongation seems feasible.