Growth patterns and ontogenetic variation of the teeth and jaws of the Middle Jurassic sphenodontian <i>Cynosphenodon huizachalensis</i> (Reptilia: Rhynchocephalia)
Bibliographic record
Abstract
Growth patterns in teeth and jaws of the Middle Jurassic sphenodontian Cynosphenodon huizachalensis are compared to those of the extant Sphenodon, showing extreme similarity. Both taxa share the unique presence of a hatchling tooth series divided into anterior uniform size and posterior alternating size tooth regions by the eruption of successional teeth early in life, an ever-growing second-generation successional tooth that becomes a caniniform tooth in adults, and a symphysial region that grows anteriorly but with a differential faster rate in the dorsal margin, enlarging considerably the length between the caniniform tooth and the anterior tip of the dentary, and increasing the angle of the anterior margin of the symphysis. The sister-group relationships of Sphenodon and Cynosphenodon have been supported by the simple presence of a single caniniform tooth, but this tooth is shown to be a complex structure involving several other ontogenetic related synapomorphies as follows: (i) it is a second-generation successional tooth that replaces a first-generation successional tooth; (ii) it emerges between the anterior hatchling teeth and the alternating size hatchling series, replacing some teeth of the latter; (iii) it grows continuously in height and width during life at a rate faster than that of tooth wear; (iv) it denotes regionalization in the symphysis, marking previously undetected growing points of the dentary; and (v) it shows the posterior limit of the edentulous anterior margin diagnostic to Sphenodontinae. New developmental information about the caniniform tooth strongly supports the structure as a homologous character, endorsing the sister-group relationships of Cynosphenodon and Sphenodon. Developmental comparisons can provide good evidence concerning the homology of a similar character present in two or more taxa. These studies are particularly useful if a clade is weakly supported by a single character.
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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 | 0.002 | 0.001 |
| 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".