Caryosyntrips ("nutcracker") is an extinctgenus of stem-arthropod which known from Canada, United States and Spain during the middle Cambrian.[1] It was first named by Allison C. Daley and Graham E. Budd in 2010, with the type species being Caryosyntrips serratus.[3]
Etymology
The scientific name Caryosyntrips comes from Greek karyon, "nut"; and syntrips, "the smasher", a spirit from Greek mythology.[3]
Occurrence
Multiple species had been recovered from the Burgess Shale Formation, Canada, Wheeler Shale and Marjum Formation, United States, and Valdemiedes Formation, Spain.[1][4] The latter contains a large specimen, which was initially misidentified as a body remain of lobopodian ("Mureropodia apae").[2][1][5][6] While the assignment of "Mureropodia" as a misidentified appendage was controversial,[7] the previous lobopodian affinity was less tenable than the fossil being a Caryosyntrips appendage.[6]
Description
Fossil frontal appendages of C. serratus
Fossil frontal appendages of C. camurus
Fossil frontal appendages of C. durus
Fossil frontal appendage of C. cf. camurus (=Mureropodia apae)
Digitally enhanced image of C. cf. camarus (=Mureropodia apae)
Presumed grasping motion of C. camurus
Sizes of various Caryosyntrips specimens, based on the interpretation as radiodonts.[6]
Caryosyntrips is known only from its 14-segmented frontal appendages, which resemble nutcrackers, with the endite (ventral spine)-bearing margin facing each other, and the bell-shaped bases might represent movable articulations with the animal's head.[1] Details of the endites, terminal spines, segmental boundaries and outer margins differ between species.[1] It is thought to have used their frontal appendages in a scissor-like grasping or slicing motion, and were probably durophagous, feeding on hard-shelled organisms.[1] Other structures remain unknown, although a specimen with paired appendages possibly contains fragmentary head sclerites as well.[3][4]
The size of Caryosyntrips differed between each species. The largest species is C. serratus which is estimated around 20.5–30.2cm (8.1–11.9in) long. Other species are much smaller, with the body lengths of C. camurus and C. durus estimated up to 13.7–20.2cm (5.4–8.0in) and 12.2–17.9cm (4.8–7.0in) respectively. The largest possible specimen (MPZ 2009/1241), identified as C. cf. camurus, would have belonged to an individual measuring between 36.7–54cm (1.20–1.77ft) long.[8]
Taxonomic affinities
As of 2010s, Caryosyntrips was long considered to be a basal radiodont of uncertain position, usually resolved in a polytomy between euarthropod and radiodont branches.[9][10][11][6][12][13] however more recent papers have found that it may sit outside of the monophyletic Radiodonta all together.[13][14] Due to the unusual morphology of the frontal appendages and the limited extent of known remains, its position within the arthropod stem-group remains uncertain.[1][14]
12Gámez Vintaned, José Antonio; Liñán, Eladio; Yu. Zhuravlev, Andrey (2011), Pontarotti, Pierre (ed.), "A New Early Cambrian Lobopod-Bearing Animal (Murero, Spain) and the Problem of the Ecdysozoan Early Diversification", Evolutionary Biology – Concepts, Biodiversity, Macroevolution and Genome Evolution, Berlin, Heidelberg: Springer, pp.193–219, doi:10.1007/978-3-642-20763-1_12, ISBN978-3-642-20763-1{{citation}}: CS1 maint: work parameter with ISBN (link)
↑Pates, Stephen; Daley, Allison; Ortega-Hernández, Javier (2018). "Response to Comment on "Aysheaia prolata from the Utah Wheeler Formation (Drumian, Cambrian) is a frontal appendage of the radiodontan Stanleycaris" with the formal description of Stanleycaris". Acta Palaeontologica Polonica. 63. doi:10.4202/app.00443.2017. ISSN0567-7920.
↑José A. Gámez Vintaned; Andrey Y. Zhuravlev (2018). "Comment on "Aysheaia prolata from the Utah Wheeler Formation (Drumian, Cambrian) is a frontal appendage of the radiodontan Stanleycaris" by Stephen Pates, Allison C. Daley, and Javier Ortega-Hernández". Acta Palaeontologica Polonica. 63 (1): 103–104. doi:10.4202/app.00335.2017 (inactive 11 July 2025).{{cite journal}}: CS1 maint: DOI inactive as of July 2025 (link)
