Lonchodomas

Lonchodomas
Temporal range: Ordovician
Lonchodomas mcgeheei, from the Bromide Formation, Carter County, Oklahoma
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Trilobita
Order: Asaphida
Suborder: Trinucleina
Family: Raphiophoridae
Subfamily: Raphiophorinae
Genus: Lonchodomas
Angelin, 1854
Species
  • L. rostratus (Sars, 1835) (type species) synonym Ampyx rostrata
  • L. carinatus Cooper, 1953
  • L. clavulus Whittington, 1965
  • L. mcgeheei (Decker, 1931) synonym Ampyx mcgeheei
  • L. retrolatus Ross jr. & Barnes, 1967
  • L. suriensis Harrington & Leanza, 1957
  • L. volborthi (Schmidt, 1894)

Lonchodomas is a genus of trilobites, that lived during the Ordovician. It was eyeless, like all raphiophorids, and had a long straight sword-like frontal spine, that gradually transforms into the relatively long glabella. Both the glabellar spine and the backward directed genal spines are subquadrate in section. Lonchodomas has five thorax segments and the pleural area of the pygidium has two narrow furrows. Lonchodomas occurred in what are today Argentina, Canada (Newfoundland), Estonia, Latvia, Norway, the Russian Federation (St. Petersburg region) and the United States (Oklahoma, Virginia).

Distribution

Lonchodomas suriensis, 4 mm long

Description

Like all raphiophorids, Lochodomas is eyeless. The headshield (or cephalon) and tailshield (or pygidium) are subtriangular in outline. Lonchodomas looks a lot like Ampyx but the glabella is diamond-shaped in outline, and it has a ridge along the midline (it is carinate). The glabella gradually transforms into the spine, which makes it difficult to determine where the spine begins. The long median glabellar spine is subquadrate in section and is directed horizontally forward, from the frontal tip of the glabella. The glabella has 2 pairs of muscle scars. The genal spines are also subquadrate in section. The thorax has 5 segments. The pleural regions of pygidium have 2 pairs of narrow pleural furrows.[7]

References

  1. Whittington, H. B.; I.I. Evitt, W.R. (1953). "Silicified Middled Ordovician trilobites". Geological Society of America Memoir 59: 1–139. doi:10.1130/mem59-p1. cited in "73341". Paleobiology Database.
  2. Whittington, H. B.; Kindle., C.H. (1963). "Middle Ordovician Table Head Formation, western Newfoundland". Geological Society America Bulletin 74: 745–758. doi:10.1130/0016-7606(1963)74[745:mothfw]2.0.co;2. cited in "104800". Paleobiology Database.
  3. Decker, C.E. (1939). "Genal spine attached to Ampyx (Lonchodomas) mcgeheei" (PDF). Journal of the Academy of science: 107–108.
  4. Ross, R.J. jr. (1967). "Brachiopods and Trilobites from the Basin Ranges, Western United States" (PDF). Contributions to Paleontology. Geological Survey Professional Paper 523-D.
  5. "Species Lonchodomas rostratus (Sars, 1835)". Baltoscandian fossils. Tallinn University of Technology, University of Tartu, Finnish Museum of Natural History, Swedish Museum of Natural History. Retrieved 14 September 2013.
  6. Harrington, H.J.; Leanza, A.F. (1957). Ordovician trilobites of Argentina. Department of Geology, University of Kansas Special Publication. Lawrence: University of Kansas Press. pp. 1–276. cited in "Lonchodomas suriensis occurrences listing". Paleobiology Database. Macquarie University. Retrieved 1 October 2013.
  7. Moore, R. C., ed. (1959), Treatise on Invertebrate Paleontology, Part O, Arthropoda 1, Trilobita, Boulder, CO & Lawrence, KA: The Geological Society of America & The University of Kansas Press, pp. xix + 560 pp., 415 figs., ISBN 0-8137-3015-5