Scaphites Hippocrepis (Dekay) in the Western Interior of the United States
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The Late Cretaceous Ammonites Scaphites leei Reeside and Scaphites hippocrepis (DeKay) in the Western Interior of the United States GEOLOGICAL SURVEY PROFESSIONAL PAPER 619 The Late Cretaceous Ammonites Scaphites leei Reeside and Scaphites hippocrepis (DeKay) in the Western Interior of the United States By WILLIAM A. COBBAN GEOLOGICAL SURVEY PROFESSIONAL PAPER 619 Three chronological forms each of Scaphites leei and Scaphites hippocrepis occur in dimorphic pairs and provide a means of correlating thin units of strata UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. GS 68-316 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 60 cents (paper cover) CONTENTS Page Page Abstract. _________________________ 1 Dimorphism in ammonites Continued Introduction- _____________________ 1 Scaphites leei and S. hippocrepis Continued Geographic distribution.-_.________ 1 Form_______ _________________________ 10 Sequence of fossils_________________ 6 Sculpture. ___________________________ 11 Dimorphism in ammonites._________ 6 Systematic descriptions._______________________ 13 Ammonites other than scaphites_ 6 Scaphites leei Reeside_--__----________-_--- 13 Scaphites _____________________ 7 Scaphites hippocrepis (DeKay)____________ 17 Scaphites leei and S. hippocrepis. References cited______________________________ 24 Size -- - - Index _-__-_______-____.________-_-_-___-__-- 29 ILLUSTRATIONS [Plates 1-5 follow index] PLATE 1. Scaphites leei and S. hippocrepis. 2, 3. Scaphites hippocrepis. 4. Scaphites leei and S. hippocrepis. 5. Scaphites equalis and S. hippocrepis. FIGURE 1. Index map of the western interior of the United States._________________________________________________ 2 2. Drawings of male and female Scaphites hippocrepis III_____________________________________-_-_--------_ 7 3. Histograms showing range in size of male and female Scaphites leei III and S. hippocrepis I_______._-_____-_- 9 4. Cross sections of female Scaphites hippocrepis III.._________________________________---______-------_--_ 10 5. Cross sections of female Scaphites hippocrepis I________________-___-__----____-_-__-_------_--------_--- 10 6. Drawings of phragmocones of male and female Scaphites hippocrepis I.____________________________________ 11 7. Cross sections of male and female Scaphites hippocrepis I__________________-___________-__-_--------_--_- 11 8. Graph showing average number of ventral ribs on Scaphites leei and S. hippocrepis- ______________---_-----_- 12 9. Cross sections of phragmocones of female Scaphites hippocrepis I_________________________-__-_-_-_-_-_-_- 12 10. Cross sections through body chambers of Scaphites hippocrepis I and S. hippocrepis III_______________-_---__ 13 11. Suture of Scaphites hippocrepis III___________________________-_______-._____--__----_----_-_---_------- 13 12. Sutures of Scaphites leei I_________________________________-_______-___-_---__---_-_------_----------- 14 13. Histograms showing node counts on Scaphites leei !!!_______.___________________-_-_-_--_-_--------_----- 16 14. Scatter diagram showing number of ventral ribs on Scaphites leei III_______-__________-____-_-----_--_---- 16 15. Sutures of Scaphites leei III_________________________________________________-_-_____---__-_------_-_- 16 16. Scatter diagram showing number of ventral ribs on Scaphites hippocrepis I______________________---------__ 18 17. Sutures of Scaphites hippocrepis I__ ____________________________________________-_------__------------- 19 18. Sutures of Scaphites hippocrepis II___________________________________________-_----_--_-----._--------- 21 19. Scatter diagram showing ratios of distances between rows of ventrolateral nodes and rows of umbilical nodes of Scaphites hippocrepis III_________________-____________________-_----_----------_---------------- 22 20. Scatter diagram showing number of ventral ribs on Scaphites hippocrepis III_________________-__-_--_--_--- 23 21. Sutures of Scaphites hippocrepis III______________________________-_-_-___-_---_-----_-_--------------- 23 TABLES Page TABLE 1. Localities at which fossils were collected___________________________ 3 2. Range in length and number of measurable male and female scaphites. 3. Ratios of lengths of largest and smallest male and female scaphites_ _ _ in THE LATE CRETACEOUS AMMONITES SCAPHITES LEEI REESIDE AND SCAPHITES HIPPOCREPIS (DEKAY) IN THE WESTERN INTERIOR OF THE UNITED STATES By WILLIAM A. COBBAN ABSTRACT countries in northern Europe. $. hippocrepis was des Scaphites led Reeside and 8. hippocrepis (DeKay) are closely ignated by Reeside (1944) as the index fossil for recks related ammonites found at many localities in Montana, in the western interior region equivalent in age to that Wyoming, South Dakota, Colorado, Utah, and New Mexico. Both of the Eagle Sandstone of the Montana Group. species have been found in Texas, and S. hippocrepis occurs also in Alabama, Georgia, Maryland, Delaware, and New Jersey, as Scaphites leei and S. hippocrepis, in the broad sense, well as in several countries in Europe and Africa. range through as much as 1,700 feet of strata in parts of Both species occur in dimorphic pairs which are herein in the western interior region. Collections of the scaphites terpreted as male and female. In any one collection, the adults from several levels within this thick sequence reveal of each sex show a considerable range in size so that the ratio subtle changes in sculptural features, such as density of the smallest specimen to the largest may be as much as 1: 4. The females attain a larger size than the males, but there is an of ribs and nodes. These changes, which are herein inter overlap in the size range of the sexes. The last whorl of the preted as subspecific in rank, are useful in subdividing female considerably overlaps the inner whorls, and this character the zones of S. leei and S. hippocrepis and thereby pro combined with an umbilical swelling at the base of the body vide a means for correlating thin units of strata. chamber almost dees away with the umbilical opening. The The present study was principally made possible by males, which lack this overlap and swelling, have a larger umbilicus and a concave umbilical wall. a large collection of Scaphites leei made by Glenn R. Each species can be separated into three chronological sub Scott, of the U.S. Geological Survey, and by the nuir^r- species to which Roman numerals I, II, and III are assigned. ous collections of S. hippocrepis made by James R. Gill, The oldest form, Scaphites led I, has a coarsely ribbed body also of the U.S. Geological Survey, in the course of his chamber and ventrolateral nodes on both the phragmocone and study of detailed stratigraphic sections in Wyoming, body chamber. Scaphites led II lacks nodes on the phragmocone. Montana, and South Dakota. James H. Smith, of the Scaphites led III is more densely ribbed than &. led II, and the females have fewer umbilical nodes. Scaphites hippocrepis I, Mountain Fuel Supply Co. (Salt Lake City), kindly the descendant of S. leei III, is more densely ribbed and has donated a large collection of the youngest form of S. weaker ventrolateral nodes which tend to be elongated. Scaphites hippocrepis from the Blair Formation near Rock hippocrepis II is more densely ribbed than S. hippocrepis I and Springs, Wyo., as well as several smaller collections has stronger and more circular ventrolateral nodes. Scaphites of older forms of the species from Colorado p.nd hippocrepis III, the youngest form in the /S. leei-S. hippocrepis lineage, is very densely ribbed and has an incipient third row Wyoming. William D. Greene and Nelson H. James, of nodes on the flank of the body chamber between the rows of Greybull, Wyo., donated many fine specimens of S. Lip- umbilical and ventrolateral nodes. pocrepis from the Alakali anticline area northwest of Greybull. All photographs were made by Robert E. INTRODUCTION Burkholder, of the Geological Survey. Charles C. Scaphites leei Reeside and 8. hippocrepis (DeKay) Capraro, also of the Geological Survey, skillfully re are easily identified Late Cretaceous ammonites char touched many of the photographs and prepared the acterized by the adult body chamber having ventro drawings of sutures, as well as text figure 2. The figured lateral and umbilical nodes, a nearly smooth flank, and specimens are in the U.S. National Museum in Wash a well-ribbed venter on which the ribbing tends to be ington, D.C. interrupted on the older part. S. hippoerepis is widely distributed in the western interior of North America, GEOGRAPHIC DISTRIBUTION in the Gulf and Atlantic Coastal Plains of the United In the western interior of the United States, Sca States, and in the Lower Campanian rocks in many phites leei and S. hippocrepis are known from many 1 Is al < GEOGRAPHIC DISTRIBUTION" localities in Wyoming and Montana and from fewer TABLE 1. Localities at which fossils were collected Continued localities in South Dakota, Colorado, Utah, and New U.S. Geol. Mexico. The localities described in table 1 and shown No. Survey Collector, year of collection, description of locality, (fig. D Mesozoic and stratigraphic assignment on figure 1 are those pertinent to the present report and locality probably represent about two-thirds of the U.S. Geo logical Survey's localities of these scaphites. 13_._.-_ D4220 J.