Cranial anatomy of the Galápagos marine iguana <i>Amblyrhynchus cristatus</i> (Squamata: Iguanidae)
Bibliographic record
Abstract
Amblyrhynchus cristatus, the marine iguana, is unique among the ~7,000 species of living limbed lizards as it has successfully evolved adaptations that allow it to live in both terrestrial and marine environments. This species is endemic to the Galápagos Archipelago and has evolved a specialized feeding behavior, consuming primarily the algae that grow on the rocky seafloor. The intriguing questions arising around the evolution of the marine iguana concerns the use of exaptations of terrestrial features for aquatic and specifically marine adaptations. However, the lack of fundamental information about its anatomy currently prevents us from understanding how it became adapted to such a peculiar lifestyle in comparison to all other iguanids. The goal of this study is to provide the first ever description of the skull, mandible, and hyoid of Amblyrhynchus. We examined several specimens of marine iguana, including skeletal, wet, and ct-scanned material, and individuals at different ontogenetic stages. We also analyzed specimens of all other modern iguanid genera (Conolophus, Iguana, Ctenosaura, Cyclura, Dipsosaurus, Brachylophus, Sauromalus) in order to make comparisons between Amblyrhynchus and its closest relatives. We were able to identify several autapomorphic features that distinguish the marine iguana from all other iguanids. These unique morphologies are mostly associated with the modified configuration of the snout (nasal chamber), increased muscle attachments in the temporal-postorbital region of the skull, and dentition. Since Amblyrhynchus is the only nonophidian squamate currently able to exploit the ocean at least for some vital functions (i.e., feeding), we used comparisons to fossil marine lizards (e.g., mosasaurids) to discuss some of these unique traits. The new cranial features described for Amblyrhynchus may represent a source of novel morphological characters for use in future phylogenetic analyses of iguanian (or squamate) relationships, which will then serve as the foundation for the exploration of evolutionary patterns and processes that led to the development of such unique adaptations.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 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 teacher head, 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".