''Shucaris'' ( ; meaning "Shu's shrimp") is a genus of

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 ...

of uncertain taxonomic placement from the

Lower Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovici ...

Maotianshan Shales 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 ...

Yunnan Yunnan; is an inland Provinces of China, province in Southwestern China. The province spans approximately and has a population of 47.2 million (as of 2020). The capital of the province is Kunming. The province borders the Chinese provinces ...

South China South China ( zh, s=, p=Huá'nán, j=jyut6 naam4) is a geographical and cultural region that covers the southernmost part of China. Its precise meaning varies with context. A notable feature of South China in comparison to the rest of China is ...

. The type and only species is ''S. ankylosskelos'', known from multiple specimens comprising frontal appendages, multiple endites, gnathobase‐like structures, a nearly complete body, a head carapace complex, and one body flap associated with setal blades.

Description

''Shucaris'' is known from multiple specimens which were all referred to ''S''. ''ankylosskelos'' by Wu ''et al.'' (2024). The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

, JS-0972B, consists of an isolated frontal appendage. The paratypes, JS-1950 and JS-0658, comprise a nearly complete body specimen, and one partial disarticulated assemblage of a frontal appendage, gnathobase-like structures, an oral cone, portions of the head sclerites, and a flap associated with setal blades, respectively.

Appendage morphology

File:20240904_Radiodonta_frontal_appendage_Shucaris_ankylosskelos.png, 2D reconstruction of ''Shucaris ankylosskelos'' frontal appendage File:3D model of Shucaris ankylosskelos appendage.png, 3D reconstruction of ''Shucaris ankylosskelos'' frontal appendages File:Shucaris ankylosskelos turntable.webm, Turntable animation of ''Shucaris ankylosskelos'' appendages File:Shucaris 1st DAR podomere turntable animation.webm, Turntable animation of the first DAR podomere The appendage morphology of ''Shucaris'' is unlike any other radiodont in many respects, which makes taxonomic placement difficult. The appendages consist of 2 shaft podomeres and 15 distal articulated region ("DAR", also referred to as the "claw" portion) podomeres, typically found in a furled position. Podomere height decreases distally, with endites roughly the same size as them. The endites are paired, and alternate in length, with odd-numbered podomeres bearing relatively longer spines. The endites of the more proximal podomeres curve strongly inward, with auxiliary spines facing inward and laterally These auxiliary spines become larger approaching the tip of the endite. Auxiliary spines are more numerous on the anterior edge of the endites, with up to 4 auxiliary spines anteriorly and 2 posteriorly on proximal podomeres, and fewer towards the distal portion of the appendage. The endites of DAR podomeres 8-14 (up to the terminal 15th DAR podomere) are poorly preserved, and probably only bear at most a single auxiliary spine each. The 1st DAR podomere shows characteristics that are unusual for radiodonts. It bears two pairs of endites lying on the same lateral axis, with one pair in between the other. The outer pair curves distally, while the inner pair is mostly straight and points posteriorly. Both pairs bear a single auxiliary spine on each endite on their distal margin. DAR podomeres 12–15 have dorsal spines, with the largest one on the 14th podomere. The 14th DAR podomere also bears a secondary dorsal spine. The terminal spine is paired, which isn't observed in any other known radiodonts.

Etymology

The generic name is ''Shucaris''. 'Shu' honours Professor Degan Shu, the pioneer in the research on 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 ...

and the academic leader of the Early Life Research Team at Northwest University. 'Caris', translating to ‘shrimp’ from

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

, is a commonly used suffix for marine euarthropods. The specific name, ''ankylosskelos'', derives from the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

words for 'curved' and 'leg' respectively, alluding to the curved frontal appendage.

Classification

In previous studies, ''Shucaris'' was referred to as "Radiodont C" and has been recovered as an amplectobeluid and a basal anomalocaridid. The results of some of these papers'

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 ...

studies have been reproduced below: Wu ''et al.'' (2024) recovered ''Shucaris'' as a

of uncertain relation—often as a member of the Anomalocarididae—in their

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

. Their results are shown below: Despite this however, Wu ''et al.'', (2024) discuss novel features ''Shucaris'' possesses such as "more podomeres in the claw region than all amplectobeluids and most anomalocaridids", leading them to recover ''Shucaris'' as "the most basal taxon within Anomalocarididae or a sister taxon to the clade comprising amplectobeluids and anomalocaridids".

Paleobiology

''Shucaris'' had an abnormally small oral cone, suggesting that it likely chewed up prey with its gnathobase-like structures and then swallowed it. This implies that it had a similar diet to amplectobeluids, with both being nektobenthic predators consuming hard-shelled prey.

References

{{Taxonbar, from=Q107751301 Fossil taxa described in 2024 Fossils of China Cambrian arthropods of Asia Radiodonta Cambrian China