LOWER CAMBRIAN <i>RUSOPHYCUS</i> FROM ELLESMERE ISLAND, ARCTIC CANADA: ICHNOFOSSIL OF A PREDATORY, NON-TRILOBITE ARTHROPOD
Bibliographic record
Abstract
ABSTRACT Cruziana and Rusophycus are commonly assumed to be trilobite trace fossils, although associated exoskeletons are almost invariably absent from host strata. In the lower Cambrian Dallas Bugt Formation of Ellesmere Island, Arctic Canada, high-energy, cross-laminated sandstones locally with dense populations of large Skolithos are overlain by thin-bedded, bioturbated, argillaceous, medium-grained glauconitic sandstones of lagoonal aspect, yielding Rusophycus along with an assortment of other “worm” burrows. Some specimens of Rusophycus are located over small Skolithos shafts and the bottoms of Arenicolites, suggesting a predator-prey relationship. Many preserve the impression of a strongly vaulted carapace with a broad, triangular dorsal outline between 1 cm and 7 cm across. A blunt anterior “prow” projects slightly forward and arches dorsally, forming a keyhole-shaped notch. The arthropod dug into the sediment up to 5 cm deep with an antero-posterior angle of up to ∼ 45° from the sea floor; in some cases it dug obliquely laterally and rarely sideways. Retroverse scratches—preserved in hyporelief as sharp-crested ridges—suggest about 20 pairs of endopodites tipped by a pair of small claws typically dug in unison, the anterior ones starting with a V-angle of 140° and decreasing posteriorly to 90°, in rare cases more tightly. Limb length increased posteriorly, although none extended beyond the carapace. Leg muscles were strong enough to rake through the muddy sand and pull inwards either straight or in a slightly forward-curving arc, but were also slightly flexible to wiggle around obstacles. Some specimens show subsequent re-burrowing which produced cross-cutting and opposed scratches. No evidence for exopodite brushings is present. Successive carapace imprints and scratches organized in transverse rugae in some specimens suggest repeatedly plunging and digging as the arthropod pulled backward in the sediment. This was likely aided by a stout trunk and a fan-shaped uropod-like structure flanking the telson which increased grip and leverage. A pair of eye stalks may have projected from the anterior notch, and these could have been retracted during digging, but there is no evidence for antennae. The tracemaker was not a trilobite but an unrelated crustacean-like arthropod, although there is no known late early Cambrian body fossil to which it can be ascribed. The specimens are classified as Rusophycus jenningsi (Fenton and Fenton, 1937) and a neotype is selected for this ichnospecies from the Gog Group near where it was first collected. Its range extends from the southern Canadian Rocky Mountains north along depositional strike to Victoria Island and northwest to Ellesmere Island and northern Greenland. Two new ichnofamilies are established: Rusophycidae and Cruzianidae.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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".