| Stanleycaris | |
|---|---|
 | |
| Reconstruction ofS. hirpex | |
 | |
| Complete specimen ofS. hirpex | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Order: | †Radiodonta |
| Family: | †Hurdiidae |
| Genus: | †Stanleycaris Pates, Daley & Ortega-Hernández, 2018 |
| Type species | |
| †Stanleycaris hirpex Pates, Daley & Ortega-Hernández, 2018 | |
| Species | |
Stanleycaris ("Stanley's shrimp") is anextinctgenus ofhurdiidradiodont from theCambrian (Stage 3 toMiaolingian). Thetype species isStanleycaris hirpex.Stanleycaris was described from theStephen Formation near theStanley Glacier[2] andBurgess Shale locality ofCanada,[3] as well asWheeler Formation ofUnited States.[4] A second species,S. qingjiangensis is known from theQingjiang biota of China.[1] The genus was characterized by therake-likefrontal appendages with robust inner spines.[5][3]
Stanleycaris was originally described only from frontal appendages and oral cone.[4] Its generic name means "Crab of Stanley Glacier";hirpex, L. "large rake", reflects therake-like nature of its spiny frontal appendages.[2] However, in 2022, 268 specimens ofStanleycaris, many of which were complete, were studied, makingStanleycaris a well documented radiodont.[3]Stanleycaris had three eyes, a bizarre configuration previously unknown among other radiodont genera; yet this head anatomy supports early differentiation among arthropod head and trunk segmentation.[3]
The original description of the taxon appeared in an online supplement to the article published byJean-Bernard Caron,Robert R. Gaines, M. Gabriela Mángano, Michael Streng and Allison C. Daley in2010.[2] That description did not satisfy of the requirements of theInternational Code of Zoological Nomenclature, as the Code did not accept taxa named in electronic publications as validly named until 2012;[4] the name was eventually validated by Pates, Daley & Ortega-Hernández (2018).[6]
The specimen KUMIP 153923 from the CambrianWheeler Formation (Utah,United States), which was described by Robison (1985) as a whole body of newlobopodian speciesAysheaia prolata, was reinterpreted as an isolated frontal appendage ofStanleycaris sp. by Pates, Daley & Ortega-Hernández (2017). They reported segmental boundaries between the structures previously thought to be 'lobopods' and curved terminal spines that resemble the frontal appendages of radiodonts, and thus they consideredA. prolata as anomen dubium and synonymised it withStanleycaris on the basis of their interpretation.[7]
Stanleycaris was a small radiodont, with whole body specimen measured around 10–83 mm (0.39–3.27 in) long, excluding the tail. Even based on the largest isolated frontal appendage, the upper body length was thought to be less than 20 cm (7.9 in) long.[3] Unlike mosthurdiids with large head and broad neck region, the body ofStanleycaris was streamlined like those ofanomalocaridids andamplectobeluids.[3]
The small head occupies about 15% of the total body length. Each lateralcompound eye was estimated to have around 1000ommatidia. In addition of a pair ofstalked lateral eyes, a third, large median eye was located behind its preocular sclerite (H-element). Similar structures were evident in the fossils ofPeytoia andLyrarapax, suggesting these genera possibly had a median eye too.[3] Contrary to the agreement around mid and late 2010s (based on the discovery ofLyrarapax since 2014) suggest radiodonts had onlyprotocerebrum on theircerebralganglion,[8] Theneuroanatomical evidence ofStanleycaris suggests radiodonts have both protocerebrum anddeutocerebrum, and circumesophageal connective that surround digestive system between them.[3] Unlike other radiodonts, the paired lateral sclerites (P-element) are not evident in anyStanleycaris specimens, suggesting they were exclusively absent in this genus.[3]
Thefrontal appendages, which are the most commonly found component of this taxon, range in length between 3.5–32.2 mm (0.14–1.27 in).[5] It comprises 14 segments (podomeres) with 5 long,rake-like curved blades (endites) protruding from the ventral surface of podomere 3–7, while podomere 2 and 9 have short endites. The upper surface bore a row of inner-facing, mostly forked robust spines (gnathites) which are unique to this genus.[5] Similar toPeytoia, the distal podomeres have claw-like dorsal and terminal spines.[5]
Themouth was surrounded by a tetraradialoral cone, which comprises 28 tooth plates instead of 32 like those of otherhurdiid genera.[5] Each of the 4 large plate have 2 additional nodes, and the mouth opening has no additional inner plates.[3]
The trunk region have 17 segments with paired lateroventral flaps, as well as 4 caudal filiform blades on the tail. The setal blades (band ofgill lamellae) were suggested to be positioned ventrally on each of the trunk segment,[3] contrary to the general reconstruction of radiodont with dorsal setal blades.[9]
Stanleycaris was most likely a visualpredator that specialized primarily on macroscopic, soft-bodied benthic prey. Based on itsstreamlined body shape and broad trunk flaps, it may have been able to chase relatively fast-moving prey.[3] With strong differentiation of lateral–medial, inner–outer, and proximal–distal morphologies,Stanleycaris was probably able to manipulate prey with distal raptorial portion, trap and masticate prey items using endites and gnathites.[5]
Stanleycaris was analysed to be one of the basalmosthurdiidradiodont, alongsidePeytoia andSchinderhannes which shares some anatomical similarities.[10][5][11][3] This suggests that theanomalocaridid/amplectobeluid-like traits (e.g. streamlined body; small head sclerites; frontal appendages with curved dorsal spines) found in these hurdiids represent radiodontancestral characters.[10][5][3]
The following cladogram by Moysiuk & Caron (2022) demonstrates the phylogenetic position ofStanleycaris:[3]
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