Ontogenetic Changes in Endocranial Anatomy in <i>Gorgosaurus libratus</i> (Theropoda: Tyrannosauridae) Provide Insight Into the Evolution of the Tyrannosauroid Endocranium
Bibliographic record
Abstract
Over the past two decades, increased accessibility to computed tomography (CT) scanners has greatly facilitated documentation of the endocranium in numerous extinct theropod taxa. However, most of these studies have focused on the morphology of mature individuals, thus changes or variation through ontogeny of the endocranium in theropods remains largely unknown. The current study sheds light on the endocranial anatomy of the eutyrannosaurian tyrannosauroid, Gorgosaurus libratus, in both an ontogenetic and evolutionary context. Based on CT scans of six Gorgosaurus braincases, including those of two recently discovered juvenile individuals, we virtually reconstruct and describe the endocranial morphology for a growth series of G. libratus. Despite considerable changes in skull architecture, relatively few ontogenetic changes occurred in the endocranium of Gorgosaurus. These changes include a subtle increase in the length of the hindbrain region of the endocast and increased inflation of the tympanic sinus diverticula in adults relative to juveniles. Among the most significant ontogenetic changes is a decrease in the distinctiveness of the brain morphology in endocasts as Gorgosaurus mature. The endocasts of juvenile Gorgosaurus exhibit better defined cerebral hemispheres, optic lobes, and cerebella than those of larger and more mature individuals. This suggests a closer correspondence between the endocast and the brain in juvenile tyrannosaurids, indicating the endocast of juvenile individuals provides a more accurate representation of the structure of the brain and its regions relative to the endocast of more mature individuals. The brain of Gorgosaurus displays a mix of basal archosaurian traits and more derived coelurosaurian traits. More primitive archosaurian features of the Gorgosaurus brain include large olfactory bulbs and tracts, a posteroventrally oriented long axis of the cerebrum, and posteriorly positioned optic lobes, whereas derived features include prominent hindbrain flexure, a somewhat enlarged cerebrum, and a cerebellum that at least partially separates the left and right optic lobes. An understanding of the evolutionary acquisition of such derived features leading to the avian brain may be further elucidated via the study of the endocasts of juvenile individuals (more reflective of the structure/organization of various brain regions) of earlier-diverging theropods (e.g., Allosauroidea, Megalosauroidea, and Coelophysoidea).
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".