A phylogeny of Plesiosauria (Sauropterygia) and its bearing on the systematic status of Leptocleidus Andrews, 1922
Why this work is in the frame
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Bibliographic record
Abstract
Leptocleidus Andrews, 1922 is a poorly known plesiosaur genus from Lower Cretaceous successions of the UK, South Africa, and Australia. Historically, there has been little consensus regarding its phylogenetic position within Plesiosauria, largely because of its seemingly aberrant combination of a relatively small skull and short neck. As a result, a diverse array of potential sister groups have been posited for Leptocleidus, including long-necked Cretaceous elasmosaurids, Early Jurassic “rhomaleosaurs”, and Middle to Late Jurassic pliosaurids. A cladistic analysis including Leptocleidus, and a new, apparently morphologically similar specimen from Alberta, TMP 94.122.01, was undertaken to assess their phylogenetic position within Plesiosauria. A character-taxon matrix was assembled afresh, consisting of 33 operational taxonomic units sampled broadly among plesiosaurs. 185 cranial and postcranial characters used in plesiosaur phylogenetics were critically reanalyzed, of which 152 were employed in the parsimony analysis. The results indicate a basal dichotomous split into the traditionally recognized pliosauroid and plesiosauroid clades. Nested within Pliosauroidea, a monophyletic Leptocleididae was recovered, consisting of L. superstes Andrews, 1922 and L. capensis (Andrews, 1911a). In contrast to earlier suggestions, Leptocleidus neither clusters with Rhomaleosaurus, which was found to be paraphyletic, nor with large-skulled pliosaurid taxa, such as Simolestes. Rather, a sister group relationship between Cretaceous Polycotylidae and Leptocleididae was recovered, which is here named Leptocleidoidea. Although TMP 94.122.01 is superficially similar to Leptocleidus, several discrete characters of the skull nest this new taxon within Polycotylidae. Compared to other phylogenetic hypotheses of plesiosaurs, these results are more congruent with respect to the stratigraphic distribution of leptocleidoids. A classification for Plesiosauria is presented.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 it