Early Cenomanian Rhyncholites

Remarks

• Collector:    Adam Armstrong, donated to the MMNS.
• Collection:   Mississippi Museum of Natural Science.  Photos by Curator George Phillips.  Thanks!
• Formation:  Washita Group, Grayson Formation
• Location:     McLennan County, TX

General Info

• Rhyncholites are intriguing fossils.  They have been known since the early 1800's, but there still isn't complete agreement on what they are or what they belong to.  The current thought is that they are the "hoods" (also known as "jaws") of fossil nautiloids.  There is at least one example of a Eutrephoceras associated with it's hood (Campbell, 1996 below), which provides some evidence that these fossils are indeed nautiloid parts.

• Compare with the living Nautilus, which has a lower and an upper jaw (Griffin, 1900 and Teichert, et al., 1964 below).

• The only nautiloids reported from the Grayson are cymatoceratids, so we've tentatively placed Adam's specimens in this family.

Synonyms (older names and misidentifications in the literature)

• Nautiloid "hood"

• Nautiloid "Jaw"

Stratigraphic Occurrence

• The ones shown are from the Grayson Formation, Texas.

• Rhyncholites have been reported from the Permian, Triassic, Jurassic, and Cretaceous Periods and Eocene and Miocene Epochs from around the world.

Age

• The genus Cymatoceras ranges from the Late Jurassic to Early Tertiary (Oligocene Epoch) Period.

• The genus Paracymatoceras ranges from the Late Jurassic Period to the Early Cenomanian Stage in the Cretaceous.

• The rhyncholites shown are from the Graysonites lozoi Young or G. adkinsi Young zone in north-central Texas.

Geographic Occurrence (not an all-inclusive list)

• The specimens shown are from McLennan County, Texas

Remarks

         For identification and descriptions, see:

• Campbell, D. C.  1996.  The Riddle of the Rhyncholites, a Possible Culprit fro mthe Eocene of the Carolinas.  Geological Society of America, Abstracts with Programs 28 (7), 293 (abstract only).
• Griffin, L.  1900.  The Anatomy of Nautilus pompilius.  National Academy of Science Memoir 8, 103–197.
• Tanabe, Y. Fukuda, Y. Kanie, and U. Lehmann.  1980.  Rhyncholites and Conchorhynchs as Calcified Jaw Elements in Some Late Cretaceous Ammonites, Lethaia 13, 157-168.
• Teichert, C.; Kümmel, B.; Sweet, W. C.; Stenzel, H. B.; Furnish, W. M.; Glenister, B. F.; Erben, H. K.; Moore, R. C.; Nodine Zeller, D. E.  1964.  "Rhyncholites".  Moore, R. C., ed.  Treatise on Invertebrate Paleontology, Part K, Mollusca 3, Cephalopoda-General Features-Endoceratoidea-Actinoceratoidea-Nautiloidea-Bactritoidea.  Boulder:  Geological Society of America and University of Kansas, K467–K484.