The sponge pump as a morphological character in the fossil record
Bibliographic record
Abstract
Abstract The timing of early animal evolution remains one of the biggest conundrums in biology. Molecular data suggest Porifera diverged from the metazoan lineage some 800 Ma to 650 Ma, which contrasts with the earliest widely accepted fossils of sponges at 535 Ma. However, the lack of criteria by which to recognize the earliest animals in the fossil record presents a challenge. The sponge body plan is unchanged since the early Cambrian, which makes a sponge-type animal a good candidate for the earliest fossils. Here we propose a method for identifying an organism as sponge grade by translating the sponge pump character into a quantifiable morphological trait. We show that the ratio between the two major components of the aquiferous system, the cross-sectional area of the osculum (OSA) and the surface area of the whole sponge (SA), is an effective metric of the pump character of extant sponges and that the slope of this ratio is distinct for three classes of Porifera: Demospongiae, Calcarea, and Hexactinellida. Furthermore, this metric is effective at distinguishing as sponges both extant taxa and fossils from two extremes of the Phanerozoic, the Cambrian and Paleogene. We tested this metric on the putative Ediacaran sponge Thectardis avalonensis from Mistaken Point, Newfoundland, and found Thectardis fits both with Cambrian sponges and with modern demosponges. These analyses show that the OSA/SA ratio is a reliable character by which to identify fossils as sponge grade, opening up exciting possibilities for classifying new fossils as sponges.
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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 | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".