Echidnacaris

Echidnacaris briggsi is an extinct species of radiodont known from the Cambrian Stage 4 aged Emu Bay Shale of Australia. Formerly referred to as "Anomalocaris" briggsi, it was placed in the new monotypic genus Echidnacaris in 2023.^[1] It is only distantly related to true Anomalocaris, and is instead placed in the family Tamisiocarididae.^[2]

Echidnacaris Temporal range: Cambrian Stage 4 PreꞒ Ꞓ O S D C P T J K Pg N ↓
Diagram of frontal appendage
Speculative body size estimation
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	†Dinocaridida
Order:	†Radiodonta
Family:	†Tamisiocarididae
Genus:	†Echidnacaris Paterson, García-Bellidob & Edgecombe, 2023
Species:	†E. briggsi
Binomial name
†Echidnacaris briggsi (Nedin, 1995)

Echidnacaris is primarily known from its frontal appendages which had 13 podomeres.^[1] The largest appendages measured up to 175 mm (6.9 in) long,^[1] which would have belonged to an individual measuring between 33.2–49 cm (1.09–1.61 ft) long.^[3] The first few segments of the appendages were substantially taller than they were wide, with podomeres 2-12 bearing long, slender posteriorly curving endites/ventral spines which bore numerous small auxiliary spines.^[4][5][6] Like other tamisiocaridids, it is suggested to have been a suspension feeder, using its frontal appendages to capture small prey. Isolated eyes attributed to the species suggest that they were not stalked, but instead were adhered directly to the head, and surrounded by sclerotised structures. There were more than 13,000 lenses in the largest eyes, which were over 3 cm in diameter. The individual lenses were large, with some exceeding 335 μm in diameter, which was possibly an adaptation to seeing in low-light waters.^[2] The oral cone was triradial with three large plates, with the plates being studded with numerous tubercules.^[1]

References

1. Paterson, John R.; García-Bellidob, Diego C.; Edgecombe, Gregory D. (10 July 2023). "The early Cambrian Emu Bay Shale radiodonts revisited: morphology and systematics". Journal of Systematic Palaeontology. 21 (1). doi:10.1080/14772019.2023.2225066. S2CID 259719252.
2. Paterson, John R.; Edgecombe, Gregory D.; García-Bellido, Diego C. (2020-12-04). "Disparate compound eyes of Cambrian radiodonts reveal their developmental growth mode and diverse visual ecology". Science Advances. 6 (49): eabc6721. Bibcode:2020SciA....6.6721P. doi:10.1126/sciadv.abc6721. ISSN 2375-2548. PMC 7821881. PMID 33268353.
3. Lerosey-Aubril, Rudy; Pates, Stephen (2018-09-14). "New suspension-feeding radiodont suggests evolution of microplanktivory in Cambrian macronekton". Nature Communications. 9 (1): 3774. Bibcode:2018NatCo...9.3774L. doi:10.1038/s41467-018-06229-7. ISSN 2041-1723. PMC 6138677. PMID 30218075. Dryad Data
4. NEDIN, C. 1995. The palaeontology and palaeoenvironment of the Early Cambrian Emu Bay Shale, Kangaroo Island, South Australia. Unpublished PhD thesis, University of Adelaide, 207 pp.
5. Vinther, Jakob; Stein, Martin; Longrich, Nicholas R.; Harper, David A. T. (March 2014). "A suspension-feeding anomalocarid from the Early Cambrian". Nature. 507 (7493): 496–499. Bibcode:2014Natur.507..496V. doi:10.1038/nature13010. hdl:1983/88f89453-e81f-4767-a74d-1794c33e6b34. ISSN 0028-0836. PMID 24670770. S2CID 205237459.
6. Daley, Allison C.; Paterson, John R.; Edgecombe, Gregory D.; García-Bellido, Diego C.; Jago, James B. (Mar 4, 2013). Donoghue, Philip (ed.). "New anatomical information on Anomalocaris from the Cambrian Emu Bay Shale of South Australia and a reassessment of its inferred predatory habits". Palaeontology. 56 (5): 971–990. doi:10.1111/pala.12029. S2CID 128955512.