Late Cretaceous (Maastrichtian-Lancian) vertebrate paleontology of the McRae Formation, Elephant Butte area, Sierra County, New Mexico
— Donald L. Wolberg, Richard P. Lozinsky, and Adrian P. Hunt


Skeletal remains or traces of dinosaurs are known from very few localities in New Mexico. The McRae Formation of the Elephant Butte Reservoir area yielded interesting collections early in the century; unfortunately, most of these collections have been lost and the report of the ceratopsian Triceratops cannot be substantiated. Recent discoveries (1981-1986) have shed new light on the age of the fauna and its relationship to faunas elsewhere in the Western Interior.

McRae dinosaurs occur high in the Jose Creek Member and low in the Hall Lake Member. This fauna includes the titanosaurid Alamosaurus, Tyrannosaurus rex, a fenestrate-frilled ceratopsian, an ankylosaurid, and possibly other taxa. These dinosaurs clearly indicate a late Maastrichtian age for a portion of the McRae, probably equivalent to the Lancian "Land Mammal Age" and clearly equivalent to the lower portion of the Tomillo Group of the Big Bend of Texas, the Naashoibito Member of the Kirtland Shale of the San Juan Basin of New Mexico, and the lower portion of the North Horn Formation of Utah.

The McRae dinosaur fauna has a southern-terrestrial-community character. Elsewhere, this community is dominated by Alamosaurus, and contains Tyrannosaurus rex, archaic hadrosaurs, and the ceratopsians Torosaurus utahensis and/or Pentaceratops. This community was distinct from a northern community dominated by the ceratopsian Triceratops and containing advanced hadrosaurs, Tyrannosaurus rex, and Torosaurus latus. Although the precise mechanisms and chronology are unclear, it appears that the archaic character of the southern Alamosaurus community was maintained by geographic barriers produced by transgressing and regressing shorelines of the epeiric seaway. Access to new faunal elements became available with withdrawal of the seaway late in the Cretaceous. However, profound modernization of the southern faunal community ceased as dinosaur extinction progressed. The pace and timing of this extinction probably explain the total lack of a terrestrial fauna in the Raton Basin.

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Recommended Citation:

  1. Wolberg, Donald L.; Lozinsky, Richard P.; Hunt, Adrian P., 1986, Late Cretaceous (Maastrichtian-Lancian) vertebrate paleontology of the McRae Formation, Elephant Butte area, Sierra County, New Mexico, in: Truth or Consequences region, Clemons, R. E.; King, W. E.; Mack, G. H., New Mexico Geological Society, Guidebook, 37th Field Conference, pp. 227-234.

[see guidebook]