Endocranial development in non-avian dinosaurs reveals an ontogenetic brain trajectory distinct from extant archosaurs

Modern birds possess highly encephalized brains that evolved from non-avian dinosaurs. Evolutionary shifts in developmental timing, namely juvenilization of adult phenotypes, have been proposed as a driver of head evolution along the dinosaur-bird transition, including brain morphology. Testing this hypothesis requires a sufficient developmental sampling of brain morphology in non-avian dinosaurs. In this study, we harness, for the first time, brain endocasts of a postnatal growth series of the ornithischian dinosaur Psittacosaurus and several other immature and mature non-avian dinosaurs to investigate how evolutionary changes to brain development are implicated in the origin of the avian brain. Using three-dimensional characterization of neuroanatomical shape across archosaur reptiles, we demonstrate that (i) the brain of non-avian dinosaurs underwent a distinct developmental trajectory compared to alligators and crown birds; (ii) ornithischian and non-avialan theropod dinosaurs share..., Taken from manuscript's Methods section (in-text citations refer to references of manuscript):
Specimens
We amassed 85 previously published endocranial reconstructions that spans 52 species of non-avian and avian dinosaurs in addition to American alligators (Table 1). The data include interspecific sampling of 36 crown birds, a juvenile Archaeopteryx32, and 19 non-avialan dinosaurs1,3,17–20,33, plus ontogenetic series of the domestic chicken (Gallus gallus; n = 14), the American alligator (Alligator mississippiensis; n = 14), and the ornithischian Psittacosaurus lujiatunensis3,17,34 (n = 4). Among non-avialan dinosaurs, several isolated immature specimens of both ornithischian and non-avian theropod dinosaurs, including Lambeosaurus (ROM 758) and troodontids Zanabazar and an unnamed specimen IGM 100/112619–21,35–38 were sampled for both ontogenetic and phylogenetic diversity. The taxonomically ambiguous tyrannosaurid specimen, CMNH 7541, has been considered a relatively immature specime..., , # Endocranial development in non-avian dinosaurs reveals an ontogenetic brain trajectory distinct from extant archosaurs

[https://doi.org/10.5061/dryad.3n5tb2rs2](https://doi.org/10.5061/dryad.3n5tb2rs2)

The contents comprise:

1\. King_etal_2024_Analysis.R (R code for performing analyses presented in the associated article)

2\. SuppData1.csv (Procrustes-aligned endocranial shape data)

3\. SuppData2.csv (centroid size of endocasts)

4\. SuppData3.tre (phylogenetic tree file used in comparative analyses)

## Description of the data and file structure

SuppData1.csv and SuppData2.csv are CSV files where each row represents a specimen and columns are morphometric variables.

SuppData3.tre is a plain text file containing time-calibrated phylogenetic tree in Newick format.

## Sharing/Access information

These files can also be found on the author's GitHub page: [https://github.com/akiopteryx/analyses/](https://github.com/akiopteryx/analyses/)

## Code/Software

King_etal_2024_Analysis.R...