Temporal range: Early Cambrian–Early Ordovician
Markuelia is a genus of fossil worm-like bilaterian animals allied to Ecdysozoa and known from strata of Lower Cambrian to Lower Ordovician age containing five species. A common nickname for Markuelia is 'Mark'.
An advanced X-ray imaging technique called X-ray tomographic microscopy has been applied to splendidly preserved, uncrushed Markuelia fossils found in Hunan province in southern China and in eastern Siberia. When details in features smaller than one micrometre across can be observed, these fossils are seen to represent many developmental stages, from the first cell divisions to the time of hatching; therefore they offer a unique opportunity to study the development of Lower Cambrian animals.
However the characters preserved are inconclusive regarding the genus' taxonomic affinity; it can at best be placed in the scalidophoran total group, since it is currently impossible to ally it with the Priapulids or other scalidophora.
Zhang, X. G.; Pratt, B. R.; Shen, C. (2011). "Embryonic Development of a Middle Cambrian (500 Myr Old) Scalidophoran Worm". Journal of Paleontology. 85 (5): 898. doi:10.1666/11-024.1. Duan, B.; Dong, X. -P.; Donoghue, P. C. J. (2012). "New palaeoscolecid worms from the Furongian (upper Cambrian) of Hunan, South China: Is Markuelia an embryonic palaeoscolecid?". Palaeontology. 55 (3): 613. doi:10.1111/j.1475-4983.2012.01148.x.
- Dong, X. ‐P.; Bengtson, S.; Gostling, N. J.; Cunningham, J. A.; Harvey, T. H. P.; Kouchinsky, A.; Val’Kov, A. K.; Repetski, J. E.; Stampanoni, M.; Marone, F.; Donoghue, P. C. J. (2010). "The anatomy, taphonomy, taxonomy and systematic affinity of Markuelia: Early Cambrian to Early Ordovician scalidophorans". Palaeontology. 53 (6): 1291–1314. doi:10.1111/j.1475-4983.2010.01006.x.
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