Hulettia

Hulettia is an extinct genus of prehistoric bony fish found in the Morrison Formation in the western United States, measuring approximately three to four inches in length. This fish genus contains one species, H. americana. Its body was covered in thick prominent scales, and its name is based on Hulett, Wyoming, a locale which is near the Morrison Formation. Discovered specimens show evidence of predation upon the smaller species of fish Todiltia that inhabited the Jurassic Lake Todilto, and another specimen discovered in the Bathonian coastal sandstone, in the Sundance Formation of South Dakota. Both specimens are complete skeletons with no fragmentary remains or dubious anomalies amongst the bones recovered.[2]

Hulettia
Temporal range: Early Jurassic
Hulettia fossil displayed in the New Mexico Natural History Museum
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Actinopterygii
Order:
Palaeonisciformes[1]
Genus:
Hulettia
Species:
H. americana

Paleobiology

It lived in an ecological niche similar to minnows and other small forage fish. The most noticeable quality of the Hulettia is its extremely durable and compact scales, providing protection from lepidophagy, external parasites and predation by fish which could not swallow it whole.[3] It prominently fed upon smaller fish, shrimp and other crustaceans, gastropods, worms and aquatic insect nymphs. Its mouth was lined with short tiny teeth that could scrape algae and other plant matter from solid surfaces, suggesting that it was an opportunistic forager that didn't solely depend on ingesting smaller creatures.[4]

Natural threats & uranium deposits

Hulettia, after reaching their maximum size of 4 inches (10 cm), had no threats from predators other than each other, or Todiltia which inhabited the same ecosystem (which could only prey upon the fry of Hulettia,) making it one of the smallest apex predators to ever exist during the Jurassic. In spite of the commonness of piscivorous Jurassic birds, large ammonites and marine reptiles (pliosaurs and ichthyosaurs), the environment in which Hulettia and Todiltia inhabited were completely devoid of any fossils of the respective carnivores. It is believed that the colossal deposits of uranium that are found in Todilto Formation and the Morrison Formation deterred other organisms from the area, and isolated the two species, protecting them from predation and trophic competition until their disappearance from the fossil record in the Cretaceous.[5]

See also

References
  1. "Palaeonisciformes". Paleobiology Database. Retrieved November 17, 2012.
  2. http://fossilworks.org/cgi-bin/bridge.pl?a=taxonInfo&taxon_no=212144 C. R. Eastman. 1899. Jurassic fishes from Black Hills of South Dakota. Geological Society America Bulletin 10:397-408 9/22/14
  3. http://earthphysicsteaching.homestead.com/Jurassic_Fossil_Fish.html Hulettia; Guadalupe County
  4. http://nmnaturalhistory.org/hulettia.html Archived 2014-09-08 at the Wayback Machine New Mexico Museum of Natural History, 1999
  5. https://nmgs.nmt.edu/publications/guidebooks/downloads/54/54_p0179_p0189.pdf New Mexico Geological Society Guidebook, 54th Field Conference, Geology of the Zuni Plateau, 2003, p. 179-189.
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