''Ramskoeldia'' is a genus of amplectobeluid

radiodont Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. Radiodonts are distinguished by their distinctive frontal appendages, which are morphologically diverse and were used for a variety ...

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 ''Amplectobelua'' (meaning "embracing beast") is an extinct genus of late Early Cambrian amplectobeluid radiodont, a group of stem arthropods that mostly lived as free-swimming predators during the first half of the Paleozoic Era. Anatomy '' ...

''. The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

, ''Ramskoeldia platyacantha'', was discovered in the

Chengjiang biota The Maotianshan Shales () are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation or Heilinpu Formation, famous for their '' Konservat Lagerstätten'', deposits known for the exceptional preservation of fossilized orga ...

of China, the home of numerous radiodontids such as ''

'' and '' Lyrarapax''.

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. 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. 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 ''

''. 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.

Taxonomy

Two species of ''Ramskoeldia'' have been described, ''R. platyacantha'' and ''R.''? ''consimilis'', but the taxonomic placement of latter species within this genus has been consistently questioned by subsequent studies. 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 ''

Houcaris ''Houcaris'' is a possibly paraphyletic radiodont genus, tentatively assigned to either Amplectobeluidae, Anomalocarididae or Tamisiocarididae, known from Cambrian Series 2 of China and the United States. The type species is ''Houcaris saron'' ...

saron'' owing to their similar overall appearance. Due to the numerous shared characters with ''

'' (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. ''Ramskoeldia'' classified under Amplectobeluidae based on the diagnosis by Cong et al. 2018, while further

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analysis either suggest it to be a member of Amplectobeluidae (alongside ''Amplectobelua'', ''Lyrarapax'', and '' Laminacaris'') or a relatively basal

References

Radiodonta {{Paleo-arthropod-stub