Evolution of the axial skeleton of early dinosaurs and the role of meristic and homeotic processes
- 1CAPPA, Universidade Federal de Santa Maria 1 , Santa Maria, Brazil
- 2Programa de Pós-Graduação em Biodiversidade Animal, Universidade Federal de Santa Maria 2 , Santa Maria, Brazil
- 3School of Engineering, The University of British Columbia 3 , Kelowna, Canada
Abstract
Changes in the axial skeleton played an important role in dinosaur evolution, with some of the oldest dinosaurs showing evidence of sacralization events. The increased number of early dinosaur discoveries over the last decade provides an opportunity to better characterize this phenomenon. It has led us to revise our understanding of axial evolution in early dinosaurs. Results support that the last common ancestor of Dinosauria would probably present 9 cervical, 16 dorsal and 2 sacral vertebrae (primordials). Early saurischians maintain a consistent number of vertebrae with presacral origin, and there is no evidence of meristic changes in these dinosaurs. A more complex scenario is observed in early ornithischians (including ‘silesaurids’). An insertion between the primordials occurs early in ornithischian evolution, and it appears to be maintained in ‘traditional’ ornithischians (Saphornithischia). Unambiguous evidence supports loss and gain of presacral vertebrae in ornithischians. Inserted sacrals across all dinosaurs are associated with a loss of a corresponding dorsal vertebra, supporting that these represent trunk vertebrae moved into the sacrum rather than novel vertebral unities. Changes in the axial skeleton of early dinosaurs are dominated by homeotic processes, with meristic processes restricted to derived members.
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BibTeX
@article{fonseca2026evolution,
title = {{Evolution of the axial skeleton of early dinosaurs and the role of meristic and homeotic processes}},
author = {André O. Fonseca and Iain James Reid and Maurício Silva Garcia and Rodrigo Temp Müller},
journal = {Royal Society Open Science},
year = {2026},
month = oct,
doi = {10.1098/rsos.261325},
url = {https://royalsocietypublishing.org/rsos/article/13/10/261325/483649/Evolution-of-the-axial-skeleton-of-early-dinosaurs},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Evolution of the axial skeleton of early dinosaurs and the role of meristic and homeotic processes
AU - André O. Fonseca
AU - Iain James Reid
AU - Maurício Silva Garcia
AU - Rodrigo Temp Müller
PY - 2026
DA - 2026/10/14
JO - Royal Society Open Science
DO - 10.1098/rsos.261325
UR - https://royalsocietypublishing.org/rsos/article/13/10/261325/483649/Evolution-of-the-axial-skeleton-of-early-dinosaurs
AB - Changes in the axial skeleton played an important role in dinosaur evolution, with some of the oldest dinosaurs showing evidence of sacralization events. The increased number of early dinosaur discoveries over the last decade provides an opportunity to better characterize this phenomenon. It has led us to revise our understanding of axial evolution in early dinosaurs. Results support that the last common ancestor of Dinosauria would probably present 9 cervical, 16 dorsal and 2 sacral vertebrae (primordials). Early saurischians maintain a consistent number of vertebrae with presacral origin, and there is no evidence of meristic changes in these dinosaurs. A more complex scenario is observed in early ornithischians (including ‘silesaurids’). An insertion between the primordials occurs early in ornithischian evolution, and it appears to be maintained in ‘traditional’ ornithischians (Saphornithischia). Unambiguous evidence supports loss and gain of presacral vertebrae in ornithischians. Inserted sacrals across all dinosaurs are associated with a loss of a corresponding dorsal vertebra, supporting that these represent trunk vertebrae moved into the sacrum rather than novel vertebral unities. Changes in the axial skeleton of early dinosaurs are dominated by homeotic processes, with meristic processes restricted to derived members.
SN - 2054-5703
ER -