Messorocaris
| Messorocaris Temporal range:
| |
|---|---|
| Diagrammatic reconstruction as a habeliid | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Chelicerata |
| Order: | †Habeliida |
| Genus: | †Messorocaris Lerosey-Aubril & Skabelund, 2018[1] |
| Type species | |
| Messorocaris magna Lerosey-Aubril & Skabelund, 2018[1]
| |
Messorocaris is a monotypic genus of fossil arthropod. The only known species is Messorocaris magna from the Wheeler Formation of Utah, dating back to the Cambrian (Drumian) period.[1][2]
Morphology
As of 2020, Messorocaris known only by two specimens. The holotype UU 17042.01 preserved the cephalon (head) and anterior half of the trunk.[1] The second specimen KUMIP312406 preserved only the trunk region, and was previously assigned to the similar-looking Dicranocaris.[3] It is a large arthropod, with a trunk measured up to 12 cm long.[2]
The body consists of a cephalic shield and a long, segmented trunk. All of the dorsal exoskeleton (tergite) have well-developed axial regions (vaulted middle sections) and tergopleurae (lateral extensions). The cephalic shield possess an anteriorly constricted axial region and wide pleural region, giving it a lens-shaped outline. The trunk has 12 body segments, divided by a series of overlapping tergites. The tergopleurae are somewhat reduced on the first segment, widely spaced and sickle-shaped at the second to fourth segments, increasingly recurved and narrower posteriorly from the fifth, and eventually become 3 pairs of posteriorly projecting spines at the last 3 segments. The telson (tail) elongated and narrow at the base, widen and bifurcate posteriorly.[2]
Appendages are only known by the partially preserved cephalic endopods. The anteriorly clustered position, terminal claws and posteriorly increased size resembling those of a sanctacaridid.[1]
Taxonomy
Based on the aforementioned similarity, Messorocaris is tentatively classified as a member of Habeliida (Sanctacarididae in the original description[1]), a group that increasingly evident to be a member of stem-group chelicerates.[4][5][6] Within putative habeliids, Dicranocaris might be a close relative of Messorocaris, differ by its semicircular cephalic shield and non sickle-shaped tergopleurae. Outside of habeliids, another similar-looking arthropod is Falcatamacaris (identified as an artiopod), particularly its sickle-shaped tergopleurae, but distinct by multiple features such as flatten cephalon, abrupt change of width between tergite 8–9 and calcitic exoskeleton.[2]
References
- ^ a b c d e f Lerosey-Aubril, Rudy; Skabelund, Jacob (2018). "Messorocaris, a new sanctacaridid-like arthropod from the middle Cambrian Wheeler Formation (Utah, USA)". Geological Magazine. 155 (1): 181–186. Bibcode:2018GeoM..155..181L. doi:10.1017/S0016756817000504. ISSN 0016-7568.
- ^ a b c d Lerosey-Aubril, Rudy; Kimmig, Julien; Pates, Stephen; Skabelund, Jacob; Weug, Andries; Ortega-Hernández, Javier (2020). Zhang, Xi-Guang (ed.). "New exceptionally preserved panarthropods from the Drumian Wheeler Konservat-Lagerstätte of the House Range of Utah". Papers in Palaeontology. 6 (4): 501–531. Bibcode:2020PPal....6..501L. doi:10.1002/spp2.1307. ISSN 2056-2799.
- ^ Briggs, Derek E. G.; Lieberman, Bruce S.; Hendricks, Jonathan R.; Halgedahl, Susan L.; Jarrard, Richard D. (2008). "Middle Cambrian arthropods from Utah". Journal of Paleontology. 82 (2): 238–254. Bibcode:2008JPal...82..238B. doi:10.1666/06-086.1. ISSN 0022-3360.
- ^ Aria, Cédric; Caron, Jean-Bernard (2017-12-21). "Mandibulate convergence in an armoured Cambrian stem chelicerate". BMC Evolutionary Biology. 17 (1): 261. Bibcode:2017BMCEE..17..261A. doi:10.1186/s12862-017-1088-7. ISSN 1471-2148. PMC 5738823. PMID 29262772.
- ^ Aria, Cédric; Caron, Jean-Bernard (2019). "A middle Cambrian arthropod with chelicerae and proto-book gills". Nature. 573 (7775): 586–589. Bibcode:2019Natur.573..586A. doi:10.1038/s41586-019-1525-4. ISSN 1476-4687. PMID 31511691.
- ^ Lerosey-Aubril, Rudy; Ortega-Hernández, Javier (2026-04-01). "A chelicera-bearing arthropod reveals the Cambrian origin of chelicerates". Nature: 1–7. doi:10.1038/s41586-026-10284-2. ISSN 1476-4687. PMID 41922763.