Ramskoeldia

Ramskoeldia is a genus of amplectobeluid radiodont described in 2018. It was the second genus of radiodont found to possess gnathobase-like structures (abbreviated as GLS) and an atypical oral cone after Amplectobelua.[1] It was discovered in the Chengjiang biota of China, the home of numerous radiodontids such as Amplectobelua and Lyrarapax.

Ramskoeldia Temporal range: Chengjiang–Middle Cambrian PreꞒ Ꞓ O S D C P T J K Pg N
Frontal appendages of R. platyacantha and R. consimilis
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	†Dinocaridida
Order:	†Radiodonta
Family:	†Amplectobeluidae
Genus:	†Ramskoeldia Cong et al, 2018
Type species
Ramskoeldia platyacantha Cong et al, 2018
Species
R. platyacantha R. consimilis

Morphology

Ramskoeldia is known only from a few frontal appendages, gnathobase-like structures (GLSs), disarticulated smooth and tuberculated plates interpreted as parts of their oral cones, as well as fragments of body flaps and head carapace complex.[1] The frontal appendage of Ramskoeldia is composed of 16 podomeres (3 shaft podomeres and 13 distal articulated region podomeres), with endites of podomeres 4 to at least podomere 12 bearing prominent auxiliary spines.[1] The endites of podomere 4 (first podomere of distal articulated region) is the largest compared to other endites, but not extremely enlarged like those of Amplectobelua.[1] The size of the endites alternates (those on even podomeres being larger than that of the odd podomere following it) and decreasing distally, except podomere 8 is larger than podomere 6 just like Amplectobelua. Compared to Amplectobelua, the GLSs of Ramskoeldia are wider and the three pairs of GLSs did not gradually alternate in size.[1]

Taxonomy

Two species of Ramskoeldia have been described: Ramskoeldia platyacantha and Ramskoeldia consimilis. The endites of R. platyacantha are stout and their length does not exceed the height of the podomere to which they attach. The shaft podomeres 2 and 3 of R. platyacantha also bore prominent endites resembling those of distal articulated podomeres. Conversely, in R. consimilis, the endites of the distal articulated region are slender and most of them have a length that exceeds the height of podomere to which they attach. The shaft of R. consimilis has only a simple endite on podomere 3. The frontal appendages of R. consimilis had been previously misidentified as Anomalocaris saron owing to their similar overall appearance.[1]

Due to the numerous shared characters with Amplectobelua (e.g. larger endites of podomere 8; irregular oral cone; presence of GLSs), the discovery of Ramskoeldia questioned the amplectobeluid affinity of Lyrarapax, a presumed amplectobeliud genus which lacking characters noted above.[1] Ramskoeldia classified under Amplectobeluidae based on the diagnosis by Cong et al. 2018,[1] while further phylogenetic analysis either suggest it to be a member of Amplectobeluidae (alongside Amplectobelua, Lyrarapax, and Laminacaris)[2] or a relatively basal radiodont.[3]

References

1. Cong, Pei-Yun; Edgecombe, Gregory D.; Daley, Allison C.; Guo, Jin; Pates, Stephen; Hou, Xian-Guang (2018). "New radiodonts with gnathobase-like structures from the Cambrian Chengjiang biota and implications for the systematics of Radiodonta". Papers in Palaeontology. 4 (4): 605–621. doi:10.1002/spp2.1219. ISSN 2056-2802.
2. Lerosey-Aubril, Rudy; Pates, Stephen (2018-09-14). "New suspension-feeding radiodont suggests evolution of microplanktivory in Cambrian macronekton". Nature Communications. 9. doi:10.1038/s41467-018-06229-7. ISSN 2041-1723. PMC 6138677. PMID 30218075.
3. Moysiuk, J.; Caron, J.-B. (2019-08-14). "A new hurdiid radiodont from the Burgess Shale evinces the exploitation of Cambrian infaunal food sources". Proceedings of the Royal Society B: Biological Sciences. 286 (1908). doi:10.1098/rspb.2019.1079. ISSN 0962-8452. PMC 6710600. PMID 31362637.