The fossil salamander<i>Proamphiuma cretacea</i>Estes (Caudata; Amphiumidae) and relationships within the Amphiumidae
Bibliographic record
Abstract
ABSTRACT A revised diagnosis and expanded description are presented for the amphiumid salamander Proamphiuma cretacea based on the original topotypic collection of vertebrae and on new atlantes, trunk vertebrae, and caudal vertebrae from the holotype locality. P. cretacea is the type and only species in the genus and is reliably known only from the Bug Creek Anthills (late Maastrichtian or early Paleocene in age), in the Hell Creek Formation, Montana, USA. A referred dentary originally believed to be from the same locality is shown to have come from the upper part (late Paleocene in age) of the Ravenscrag Formation of Saskatchewan, Canada, and is re-interpreted as belonging to an indeterminate amphiumid genus and species. Contrary to a recent claim, P. cretacea is a diagnosable amphiumid taxon and stands as the geologically oldest member of the family. Proamphiuma differs from the type and only other unequivocal amphiumid genus, Amphiuma (four species: late Paleocene–Recent, USA), in primitively retaining weaker vertebral crests and processes. Proamphiuma differs further from the three extant Amphiuma species (conditions unknown for the late Paleocene A. jepseni) in three character states that are potentially autapomorphic within the family—indistinct postzygapophyseal process on atlas, vertebrarterial canal closed posteriorly in trunk vertebrae, and spinal foramen present in anterior caudals—plus vertebral plesiomorphies and one vertebral character state of uncertain polarity. The following relationships are hypothesized within the Amphiumidae: Proamphiuma (A. jepseni (A. pholeter (A. means + A. tridactylum))). This phylogeny and fossil occurrences imply that the characteristic atlanto–cranial joint and elongate trunk and the unique vertebromuscular complex of amphiumids were established by the Cretaceous–Tertiary boundary, while elongation of the snout and associated cranial modifications seen in living amphiumids appeared after the late Paleocene. In terms of its morphology and provenance, Proamphiuma remains a good structural ancestor for, if not directly ancestral to, Amphiuma.
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 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 | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".