Intraspecific variation in Forresteria

Forresteria alluaudi (Boule, Lemoine & Thevenin) 1907, from depressed, evolute, spinose to compressed, involute, almost smooth, a nice range of intraspecific variation. Is it any wonder why these, and some like these, were placed in 4 separate species in 3 separate subgenera (Reeside, 1932), Barroisiceras (Forresteria) forresteri, B. (F.) stantoni, B. (Alstadenites) sevierense, and B. (Harleites) castellense. Kennedy, Wright and Klinger (1983) put them all in synonymy with F. alluaudi.

Many ammonoids show intraspecific variation, including, for example, Placenticeras from the Cretaceous and, at least in my mind and experience, Anasibirites and Wasatchites from the Early Triassic. Found in the same bed or group of beds worldwide, to see one would tell you precisely what age the rock they were in is. Unlike the Triassic example, where there are differences in ornamentation and shape from one part of the world to another (maybe some kind of latitudinal or provincial thing), F. alluaudi is basically the same, that is different, wherever found.

Forresteria was named after the late Robert Forrester of Salt Lake City, Utah, who found the type material in southern Castle Valley, eastern Sevier County, Utah.

Scaphites hippocrepis and S. leei

Scaphites hippocrepis and S. leei, Early Campanian (Late Cretaceous) Scaphitids. A row of ventrolateral tubercles, an inner row of tubercles on the body chamber and a constricted collar at the aperture. Best seen on the micromorph of S. leei in #22 below, and on the macromorph in #27, are dorsal lappets.


Below is a drawing of the dimorphs of S. hippocrepis. The collar shows well but the dorsal lappet does not, at least not as well as on some of the other figures.

The lappets and their dorsal location on the aperture of the adult micromorph is the question at hand, just how much plasticity is there in the location of the lappets around the collar? Especially in their ancestors and descendants.

Figures from:

Cobban, W.A., 1969, The Late Cretaceous ammonites Scaphites leei Reeside and Scaphites hippocrepis (DeKay) in the western interior of the United States: U.S. Geological Survey Professional Paper 619, 29 p., 5 pls.

Juvenile heteromorph

Another small heteromorph from the Cretaceous Mancos Shale. This one has the body chamber preserved so it is freshly hatched or up to a few weeks old. 1mm diameter at widest point.

SR2 Anasibirites Bed

Like at all other localities, about as thick as the hammer. The lower beds at this locality are a lot less fossiliferous than at any other, they have also been baked by the nearby igneous intrusions, so I don't think they are worth collecting in detail.

A closeup. All the small circular spots are drippings from the Pinyon tree above

Tirolites ?

? Tirolites body chamber cast

From above the "Clam Wall" and below the "Spathian Gap", geographic outcrop nicknames that don't mean anything to anyone unless you have a copy of my field notes from 15 years ago, sorry. Even below M109 of anothers' notes. Not a very good fossil, but it may be important.

Calcite Heteromorph

A small portion of a heteromorph ammonoid, possibly Allocrioceras. This thing is only about 1.5mm long, photo taken through the eyepiece of my microscope. Dorsal side toward viewer, without impressed zone so it was completely evolute and probably open whorled, not enough preserved to tell if it was helical or not. From the Upper Cretaceous Mancos Shale, lower Upper Turonian Scaphites whitfieldi Zone.

Rudolftruempyiceras Guex & Bylund 2010

The name Boreoceras Dagys & Ermakova (1988), has been replaced with Rudolftruempyiceras Guex & Bylund 2010, Family Columbitidae, see Guex, J., Hungerbuhler, A., Jenks, J., O’Dogherty, L., Atudorei, V., Taylor, D., Bucher, H., Bartolini, A., 2010, Spathian (Lower Triassic) Ammonoids from Western USA (Idaho, California, Utah and Nevada), Memoire de Geologie (Lausanne), No. 49, on page 29. The name Boreoceras is used for an Ordovician Endocerid Nautiloid by Miller & Youngquist (1947). The ammonoids in this old post and this update, will probably be referred to Xenoceltites and not the new genus.

Link

Cephalopods - Present and Past

Cephalopods - Present and Past:



Stephen, D.A., Bylund, K.G., Bybee, P.J. and Ream, W.J.: Ammonoid beds in the Lower Triassic Thaynes Formation of western Utah, USA, p. 243-252

In the 20 years since I located the Triassic fossil bearing beds in the Confusion Range of western Utah, I have only co-authored papers on sponges and gastropods. Now, a paper on the Ammonoids. The first of many I hope.