Discovery of the oldest South American fossil lizard illustrates the cosmopolitanism of early South American squamates
Bibliographic record
Abstract
Squamates have an extremely long evolutionary history with a fossil record that extends into the Middle Triassic. However, most of our knowledge of their early evolutionary history is derived from Laurasian records. Therefore, fundamental questions regarding the early evolution of squamates in the Southern Hemisphere, such as the origins of the extremely diverse and endemic South American fauna, remain unanswered. Here, we describe a new lizard species that represents the oldest fossil squamate from South America, demonstrating that squamates were present on that continent at least 20 million years earlier than previously recorded. The new species represents the first occurrence of the extinct squamate family Paramacellodidae in South America and displays an unusual limb morphology. Finally, our findings suggest early South American squamates were part of a much broader distribution of their respective clades, in sharp contrast to the high levels of endemicity characteristic of modern faunas.
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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 | 0.011 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".