Late Cretaceous Mammals Research Articles

Oldest known eutherian stapes and a marsupial petrosal bone from the Late Cretaceous of North America

Cranial remains of Late Cretaceous therian mammals are rarely found in North America and are usually limited to isolated petrosal bones. The oldest known associated stapes and petrosal bone of a Late Cretaceous eutherian are reported here. Comparison with a Late Cretaceous marsupial petrosal bone gives a further indication of the probable condition of several character states of the ancestral mammalian (or at least therian) middle ear, and also indicates the antiquity of various aspects of the middle ear of extant eutherians and marsupials.

Prism Size in Tooth Enamel of Some Late Cretaceous Mammals and Its Value in Multituberculate Taxonomy

Teeth from specified members of the two suborders of Late Cretaceous Multituberculata and two Late Cretaceous therians were studied. The enamel was prismatic on all teeth. In the therian representatives and the representatives of the suborder Ptilodontoidea of the Multituberculata, the prism diameters and densities per unit area were similar to those of recent mammals. In the representatives of the suborder Taeniolabidoidea the prisms were very large and their density per unit area was 5 to 8 times lower than in recent mammals. It is suggested that gigantoprismatic enamel is a characteristic of Taeniolabidoidea and could be used as a taxonomic criterion in multituberculate systematics.

Is Deltatheridium a Marsupial?

THE family Deltatheridiidae was proposed by Gregory and Simpson1 to include two late Cretaceous mammals from the Djadokhta Formation of Mongolia (? Coniacian or Santonian2): Deltatheridium pretrituberculare, known from two partial skulls and associated lower jaws, and Deltatheroides cretacicus, known only by the facial part of a skull with upper dentition. They were believed to occupy a very central phylogenetic position among the eutherian mammals. Van Valen3 included them in the Palaeoryctidae, order Deltatheridia, but one of us (P. M. B.)4 has for some time doubted the correctness of these opinions.

Preliminary report on late Cretaceous mammals from the El Gallo Formation, Baja California Del Norte, Mexico

Preliminary report on late Cretaceous mammals from the El Gallo Formation, Baja California Del Norte, Mexico

Early Campanian (late Cretaceous) mammals from Alberta, Canada.

ALTHOUGH the occurrence of fossil mammals in North American Upper Cretaceous rocks has long been known1, only since the application in 1956 of new collecting techniques2 have large samples of skeletal—especially dental—remains of Late Cretaceous mammals been recovered3. Important systematic studies have been based on these samples during the past decade. Maestrichtian. (latest Cretaceous) assemblages from sites in New Mexico (W. Clemems, personal communication), Wyoming3, Montana4 and Alberta5 include several placental (Eutheria) orders, and many multituberculates (Allotheria) and didelphoid marsupials (Metatheria). Assemblages of late Campanian age in Montana6 and Alberta (unpublished results) are nearly as rich in multituberculates and marsupials, but are relatively poor in placentals, with only two orders (Insectivora and Deltatherida) represented.

Palynology of late Cretaceous mammal beds, Scollard, Alberta (Canada)

Fossil mammal bones have been located in Upper Cretaceous (Lance or Maastrichtian) Upper Edmonton Beds above the Kneehills Tuff in the Scollard area, Alberta (Canada). Samples from the mammal-bearing beds and from above and below, have been analysed for their palynological contents. Abundant microflora representing pteridophytes, gymnosperms and angiosperms have been recorded with an abundance of Aquilapollenites in varied morphological diversity. The microflora showed five paleoecological stages. The lowest Microfloral Assemblage I, representing mid-Middle Edmonton vegetation, indicates swampy, tropical and humid climate which was replaced by stages of a sere of cooler climate shown by Microfloral Assemblage II. Cooling increased still more, possibly due to descrease in the total solar radiation reaching the earth's surface, caused by the volcanic dust in the atmosphere as the bentonitic content is high. Microfloral Assemblage III from the bentonitic beds associated with the Kneehills Tuff shows little preservation of spores and pollen although comminuted fragments are present. Microfloral Assemblage IV (including the mammal beds) shows warming up and restoration of vegetation but of a cooler climate. Climate became warmer during the deposition of Microfloral Assemblage V and a rich woodland vegetation was established representing warm subtropical climate with warm temperate aspect during mid-Upper Edmonton deposition.

MESOZOIC MAMMALS AND THE POLYPHYLETIC ORIGIN OF MAMMALS

This is, in one way, a poor time to review the iViesozoic mammals and the origin of mammals. Discoveries and studies announced but not yet published fully, if at all, are extraordinarily rich and important. They include: late Cretaceous mammals from Wyoming (McKenna and associates at the University of California) ; Triassic mammals or very advanced mammal-like reptiles from England (Kermack and Mussett; preliminary notes have been published), China (Olson and Patterson) and South Africa (Crompton; the first of a series of studies has been published) ; and tritylodonts from Arizona (Lewis and Colbert). When available these prospective works will throw a flood of new light on the whole subject and will certainly greatly modify any conclusions that can now be reached. On the other hand, this pleasing prospect (complete fulfillment of which may be long delayed) makes it all the more interesting to survey what we do know now and what it may mean, to look at the base for the next advances. There are also several recent publications of major importance that merit review and that suggest reconsideration of various points, especially: Patterson (1956), Peyer (1956), Kiihne (1958), Crompton (1958), and Kermack and Mussett (1958 a, b). This review, centered on the affinities of the known forms, will consider those formis in sequence from later to earlier: Late Cretaceous. Although this situation is due to change rapidly, at present the published data on late Cretaceous mammals have not been really significantly increased in the last thirty years. The known specimens are from Mongolia (Simpson, 1928d, and references there) and North America (especially Silmlpson, 1929b; later studies by me and others so far add little of real importance). All fall into two very clear-cut groups, multituberculates and Theria with tribosphenic molars. The latter include unquestionable marsupials (e.g., Eodelphis) and placentals (e.g., Zalambdalestes). Some of the marsupials are closely similar to living opossuLms in the dentition and lower jaw. In spite of considerable diversity they represent or include very primitive forms from which any or all later marsupials could be structurally derived. The placentals are generally classed as Insectivora. They are, however, such not in the same sense as the later, specialized insectivores, but in the sense that they lack known clear-cut ordinal characters within the Theria and that Insectivora has been used as a convenient catch-all for such virtually nonordinal groups. Their degree of diversity and any special relationships to known later groups are yet to be established. Early Ciretaceotus. Endotlerium Shikama, 1947, was described as a placental mammal from the Jurassic of South Manchuria. Kiihne (1958) accepted Shikama's views as to age and affinities. He concluded that placentals arose in the Jurassic from pantotheres, and that marsupials arose in the early Cretaceous from placentals. Patterson (1956),' however, pointed out that Endotherium is probably