''Ramskoeldia'' is a genus of
amplectobeluid radiodont
Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. They may be referred to as radiodonts, radiodontans, radiodontids, anomalocarids, or anomalocaridids, although the last two original ...
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''.
It was discovered in the
Chengjiang biota of China, the home of numerous radiodontids such as ''
Amplectobelua'' and ''
Lyrarapax
'' Lyrarapax'' is a radiodont genus of the family Amplectobeluidae that lived in the early Cambrian period 520 million years ago. Its neural tissue indicates that the radiodont frontal appendage is protocerebral, resolving parts of the arthropod ...
''.
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 ''
Amplectobelua''.
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: ''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
''Anomalocaris'' ("unlike other shrimp", or "abnormal shrimp") is an extinct genus of radiodont, an order of early-diverging stem-group arthropods. The first fossils of ''Anomalocaris'' were discovered in the ''Ogygopsis'' Shale of the Stephen F ...
saron'' owing to their similar overall appearance.
[
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
'' Lyrarapax'' is a radiodont genus of the family Amplectobeluidae that lived in the early Cambrian period 520 million years ago. Its neural tissue indicates that the radiodont frontal appendage is protocerebral, resolving parts of the arthropod ...
'', a presumed amplectobeliud genus which lacking characters noted above. ''Ramskoeldia'' classified under Amplectobeluidae
''Amplectobeluidae'' is a clade of Cambrian Radiodonta, radiodonts.
Definition
In 2014, ''Amplectobeluidae'' was defined as the most inclusive clade including ''Amplectobelua, Amplectobelua symbrachiata'' but not ''Anomalocaris, Anomalocaris ca ...
based on the diagnosis by Cong et al. 2018, while further phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
analysis either suggest it to be a member of Amplectobeluidae (alongside ''Amplectobelua'', ''Lyrarapax'', and ''Laminacaris
''Laminacaris'' is a genus of extinct stem-group arthropods ( Radiodonta) that lived during the Cambrian period. It is monotypic with a single species ''Laminacaris chimera'', the fossil of which was described from the Chengjian biota of China ...
'') or a relatively basal radiodont
Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. They may be referred to as radiodonts, radiodontans, radiodontids, anomalocarids, or anomalocaridids, although the last two original ...
.
References
Anomalocaridids
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