Ursquilla (meaning "primeval Squilla", in comparison to the related modern genus) is an extinct genus of mantis shrimp that lived in Israel and Jordan during the Campanian stage of the Late Cretaceous period. It contains a single species, Ursquilla yehoachi.
Discovery and naming The first known specimen of Ursquilla (MNHN R. 62691) was discovered in Nahal Tze'elim (formerly known as the Ouadi Seiyal Valley), Israel near a road leading from Beersheba to Mount Sodom, likely in the vicinity of Arad, and is kept in the National Museum of Natural History, France. The deposits in which it originates are part of the Campanian-aged Chert Member of the Mishash Formation, and cover the southeastern flank of the anticline of the Judaean Mountains. This specimen was first described by Jean Marcel Remy and Moché Avnimelech in 1955, who identified it as the carapace of an eryonid crustacean. They designated this fossil as the holotype of a new species which they named Eryon yehoachi. The specific name honors M. Yehoach, who collected the specimen. In 1969, it was published in the Treatise on Invertebrate Paleontology that Martin Glaessner stated the Eryon yehoachi type specimen is not a carapace, but actually represents the telson and part of the sixth abdominal segment of a mantis shrimp. It was further stated that the specimen may belong to the extant genus Squilla, but was not complete enough for certain identification. This identification was further supported by Cees H.J. Hof, who formally redescribed the specimen in 1998 and established the genus Ursquilla, renaming the species as Ursquilla yehoachi. The generic name combines the prefix ur (meaning "primeval") with the genus Squilla, referencing its ancient age and similarity to the extant genus. Furthermore, Hof assigned three additional specimens to the species; one of which (GSI M-8113) belongs to the collection of the Geological Survey of Israel and was collected from the Chert Member of the Mishash Formation, in the northern flank of the Hazera anticline, Israel by Dr. S. Ilani in 1994. The other two specimens are preserved together in the same slab (BMNH I 7316) found in the outcrops of the Amman Formation east of Al-Karak, Jordan, presented in May 1906 and kept in the London Natural History Museum. All these fossils preserve only the tail fan of the animal. An epoxy resin cast of the type specimen is also kept in the London Natural History Museum and labelled as BMNH I 15472. A fifth specimen was found by Stan Natkaniec in the Negev Desert, Israel during a private trip and donated to the State Museum of Natural History Stuttgart. This fossil (designated as SMNS 67703) preserves the tail fan and last three abdominal segments of the animal. It was identified as a specimen of U. yehoachi by Günter Schweigert and described in a paper published in 2013, which also reevaluated the four previously known Ursquilla specimens.
Description Known specimens of Ursquilla have preserved only the tail fan and last three segments of the abdomen. Size of the telson varies between specimens from 2.4–3.2 cm (0.94–1.26 in) in length and 2.4–3.0 cm (0.94–1.18 in) in width, with the smallest specimens proposed to represent immature individuals. Taking 2.8 cm (1.1 in) as an average telson length and assuming the animal had body proportions matching modern squilloid mantis shrimp such as Squilla mantis, it has been estimated that Ursquilla reached a total length of 17–18 cm (6.7–7.1 in).
Abdomen Based on other mantis shrimp, the animal presumably had six abdominal segments, thus the known segments would be the fourth to sixth. The sixth abdominal segment is decorated with four pairs of keels designated as (in order of increasing distance from the center) the submedian, intermediate, lateral and marginal keels. Apart from the marginal keels, all are ornamented with a row of tubercles. The submedian keels are straight and show a gradual increase in height down the animal's length before abruptly ending at the hind margin of the segment. The intermediate keels are slightly curved and less pronounced. The lateral and marginal keels are preserved only in the sixth abdominal segment of one specimen (GSI M-8113), showing the lateral keels are straight while the marginal keels are positioned obliquely, fusing with the lateral keels at the back of the segment. The fourth and fifth abdominal segments are only preserved in one specimen (SMNS 67703) and not preserved as well as the sixth, but appear mostly similar to it in structure apart from having less pronounced ridges.
… excerpt ends here. Continue reading the full article.
