Origin and Evolvability of the Arthropod Body Plan: Integrating Exceptional Cambrian Radiodont Fossils and New Approaches
Bibliographic record
Abstract
The dichotomy between the geologically sudden appearance of major bilaterian animal groups in the Cambrian explosion and the subsequent relative stability of their body plans represents an enduring evolutionary conundrum. Arthropods constitute an ideal model group for investigating potential ecological and developmental drivers of the Cambrian radiation, owing to their excellent fossil record, high disparity, and readily quantifiable morphology. Recent advances have given rise to a solidifying phylogenetic backbone for Cambrian arthropods, particularly within crown group clades like Chelicerata and Mandibulata. Informed by new exceptional fossil material from the mid-Cambrian Burgess Shale, housed at the Royal Ontario Museum, this thesis contributes to a similar revision of Radiodonta, the arthropod stem group including the iconic Anomalocaris. In Chapters 1 and 2, we describe two new genera of radiodonts, Cambroraster and Titanokorys, based on abundant material from recently discovered Burgess Shale localities at Marble Canyon and Tokumm Creek. These studies provide an opportunity to apply landmark-based morphometric approaches to quantify carapace shape and to reevaluate the evolution of ecological traits in radiodonts. Chapters 3 to 5 focus on older, predominantly unstudied collections of the radiodont Stanleycaris. The exceptional quality of the material enables investigation of the origin, homology, functional specialization, ontogeny, and moulting in these early arthropods. This provokes an evolution of our view of radiodonts, neither as enigmatic “weird wonders” nor a transient “primitive” offshoot, but as part of an early arthropod radiation that converged on many of the niches later explored by the crown group. Armed with the resulting phylogenetic framework, incorporating stem groups along with the crown group, I then return to the broader question of the uniqueness of the Cambrian radiation of arthropods in Chapter 6. I develop a new approach to quantify the evolutionary correlation of arthropod appendages, technically known as integration. I show that, counter to the general expectation that integration should decrease evolvability, it is associated with increased dispersion and directional displacement of lineages relative to their ancestors. Decreasing variance, and possibly mean, of integration since the Cambrian thus offer a plausible explanation for the initial divergence and later canalization of major arthropod body plans.
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 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 | 0.004 | 0.002 |
| Science and technology studies | 0.001 | 0.003 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".