Dale A. Winkler

Early Cretaceous (Comanchean) vertebrates of central Texas

ABSTRACT Vertebrates from the Comanche Series (Lower Cretaceous) in central Texas occur in the superposed Twin Mountains, Glen Rose, and Paluxy formations. Stratigraphie position and relationship to marine units are more clearly defined for the central Texas localities than for the classic mammal-producing sites in the Antlers Formation of north-central Texas. The diverse terrestrial to marine faunas include new records for the ray Rhinobatos, a ptychodont (cf. Hylaeobatis ornata), and the salmoniform Enchodus. Anurans, salamanders, lacertilians, and mammals representing early forms relevant to the emergence of extant higher taxa are present but fragmentary. Crocodilians are represented by at least three taxa and theropods by more than three. Eight species of mammals have been named from the Comanche Series, with perhaps as many as four other unnamed species represented. Paleoenvironments appear to control the distribution of taxa: dinosaurs are found in coastal settings and are abundant in some terrestri...

Depositional facies of the Miocene-Pliocene Ogallala Formation, northwestern Texas and eastern New Mexico

Deposition of the basal fluvial sediments of the Miocene-Pliocene Ogallala Formation in western Texas and eastern New Mexico was controlled by topography on the underlying erosional surface. Paleovalley-fill facies consist of gravelly and sandy braided-stream deposits interbedded with and overlain by eolian sediments deposited as sand sheets and loess. Uplands on the pre-Ogallala erosional surface are overlain primarily by similar eolian sediments. Calcic paleosols, consisting mostly of glaebules and rhizoconcretions of CaCO/sub 3/, occur throughout the eolian facies. Massive to laminated and locally pisolitic, brecciated, and recemented pedogenic calcretes occur primarily near or at the top of the Ogallala Formation. Eolian facies preserve numerous superposed calcretes and calcic paleosols, reflecting slow episodic aggradation on a savannah or grassland under arid to subhumid climatic conditions. The change from fluvial to mostly eolian sedimentation probably resulted from diversion of streams that deposited fluvial sediments of the Ogallala Formation to form the Pecos and Canadian rivers. Source areas for eolian sediments may initially have been flood plains of Ogallala braided streams and later the flood plains of the newly formed Pecos and Canadian rivers. 38 references.

A new species of Tenontosaurus (Dinosauria: Ornithopoda) from the Early Cretaceous of Texas

ABSTRACT Two articulated skeletons of an ornithopod dinosaur from the Early Cretaceous of Texas form the basis for description of a new species of Tenontosaurus. The new ornithopod, Tenontosaurus dossi sp. nov., is a sister species to Tenontosaurus tilletti Ostrom found in Montana and Wyoming. Specimens of the new species are temporally older than those of T. tilletti, and in most cases of unequivocal polarity they are more primitive. The Texas species is clearly the most primitive iguanodontian, and thus shares many primitive characters with the weakly supported clade Hypsilophodontidae. The specimens from Texas represent unscavenged carcasses entombed in a brackish-water lagoonal or estuarine sands.

A 17-My-old whale constrains onset of uplift and climate change in east Africa

Significance An enigmatic fossil representing the deep-diving, open-ocean whale family Ziphiidae found 740 km inland and at 620 m elevation in West Turkana, Kenya was rediscovered after it went missing for more than 30 years. This stranded whale fossil provides the first constraint on the initiation of east African uplift from near sea level at 17 Ma, limiting the timing and initial elevation of environmental change indicated by geodynamic and climatic modeling, paleosols, isotopes, paleobotany, and the mammalian fossil record. At 17 Ma, elevation was low, rainfall was high, vegetation was forested, and mammalian communities contained immigrants and native African species, including diverse primates. Uplift resulted in increasing aridity and open habitats that drove human evolution. Timing and magnitude of surface uplift are key to understanding the impact of crustal deformation and topographic growth on atmospheric circulation, environmental conditions, and surface processes. Uplift of the East African Plateau is linked to mantle processes, but paleoaltimetry data are too scarce to constrain plateau evolution and subsequent vertical motions associated with rifting. Here, we assess the paleotopographic implications of a beaked whale fossil (Ziphiidae) from the Turkana region of Kenya found 740 km inland from the present-day coastline of the Indian Ocean at an elevation of 620 m. The specimen is ∼17 My old and represents the oldest derived beaked whale known, consistent with molecular estimates of the emergence of modern strap-toothed whales (Mesoplodon). The whale traveled from the Indian Ocean inland along an eastward-directed drainage system controlled by the Cretaceous Anza Graben and was stranded slightly above sea level. Surface uplift from near sea level coincides with paleoclimatic change from a humid environment to highly variable and much drier conditions, which altered biotic communities and drove evolution in east Africa, including that of primates.

Taphonomy of a middle Miocene autochthonous forest assemblage, Ngorora Formation, central Kenya

Abstract A 12.6 million year old forest assemblage of leaves, twigs, and rare fruit is preserved in the Ngorora Formation of central Kenya. The assemblage is autochtonous, preserved in airfall tuff and represents well the diversity, heterogeneity and richness of the original forest. The herbaceous component, not usually preserved in paleobotanical assemblages, is present. Nearest neighbor analysis and mapping of the vertical distribution of plant organs indicates that leaves and twigs are preserved near the parent plant and that there is no apparent size, weight, or species bias in deposition of these remains. Leaves occur isolated, in clusters, or attached to branches, and fell directly to the ground as a result of ashfall, most falling very soon after ashfall commenced. The absence of upright trunks and large stems is probably due to post-depositional weathering which may also be responsible for the absence of a leaf litter layer. However, leaf litter may have been absent at the time of ash deposition.

An azhdarchid pterosaur humerus from the Lower Cretaccous Glen Rose Formation of Texas

Pterosaurs are rare components of Texas Cretaceous faunas. The best known is Quetzalcoatlus northropi , from the Javelina Formation (Maastrichtian) of Big Bend National Park, with a wingspan of some 11-12 m (Lawson, 1975; Langston, 1986; Busbey and Lehmann, 1989). Texas pterosaur specimens of less spectacular proportions include a pteranodontid partial humerus (USNM 13804) from the Eagle Ford Formation (late Cenomanian-late Turonian) of Austin (Gilmore, 1935; Bennett, 1989) and a first wing phalanx of a pterodactyloid from the Buda Formation (Cenomanian) of Hays County (Langston, 1974; Lawson, 1975). Pterosaur bones were also recorded at localities near Forestburg, Montague County (Zangerl and Denison, 1950), in the Antlers Formation (Winkler et al., 1990), although these specimens are undiagnostic hollow bone fragments.

Life in a sand sea: Biota from Jurassic interdunes

Interdune deposits in the Navajo Sandstone of Arizona are identified as the source of most fossils known from the formation. They provide information on terrestrial life in a poorly known interval of the North American Jurassic. The biota includes sphenophytes, ostracodes, and four species of vertebrates, including a skeleton of the geologically youngest tritylodontid synapsid from western North America. Fossils and sedimentary rock localized in interdunes indicate areas of greater available moisture, and therefore greater carrying capacity, than surrounding dune deposits that compose the bulk of the formation. Environmental conditions in interdunes favor fossil preservation and thus provide a focus for future studies. The diversity and adaptations of fossils from Navajo interdunes support models of climatic amelioration during sand-sea evolution when wet interdunes were deposited.

First Occurrence of the Long-Snouted Crocodyliform Terminonaris (Pholidosauridae) from the Woodbine Formation (Cenomanian) of Texas

THOMAS L. ADAMS,*1 MICHAEL J. POLCYN,1 OCT VIO MATEUS,2 DALE A. WINKLER,1 and LOUIS L. JACOBS1; *Roy M. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas 75275, U.S.A., tladams@smu.edu; mpolcyn@smu.edu; dwinkler@smu.edu; jacobs@smu.edu; 2CICEGe, Faculdade de Ci ncias e Tecnologia, FCT, Universidade Nova de Lisboa 2829-516, Caparica, Portugal, and Museu da Lourinh , Portugal, omateus@fct.unl.pt

Vertebrate-bearing eolian unit from the Ogallala Group (Miocene) in northwestern Texas

The upper Couch Formation is part of the lower of two formations composing the Ogallala Group in Blanco and Yellowhouse canyons in northwestern Texas. An eolian origin for the upper Couch Formation is indicated by its mean grain size, pedogenic carbonate nodules, massive bedding, and blanketlike morphology. The unit conforms poorly to the usual eolian depositional models; it resulted from a combination of the processes involved in loess and sand-sheet formation. Grassland or savanna vegetation probably existed over the area and aided in sediment trapping. Vertebrates are unusual in eolian units, but the adaptations and mode of preservation of those in the upper Couch Formation also support an eolian interpretation. This and other widespread silty sand sheets in the Ogallala indicate major fluctuations in depositional style, possibly climatically controlled. Lateral continuity and preservation of vertebrates give silty sand sheets great potential as correlation tools.

Forelimb anatomy of Serengetilagus praecapensis (Mammalia: Lagomorpha): a Pliocene leporid from Laetoli, Tanzania

The forelimb elements of the leporid Serengetilagus praecapensis, from the famous Laetoli sites in Tanzania, occur in three stratigraphic levels. Most come from the Upper Laetolil Beds, the middle unit. Size frequency distributions of limb dimensions demonstrate one highly variable population with no clear trends through time. Statistical analyses cannot be used to support the presence of more than one species. Sexual dimorphism also is not apparent in the samples, but may have contributed to the variability in sizes. Anatomical traits of the forelimb ally Serengetilagus praecapensis with smaller, less cursorial leporids like the modern European rabbit Oryctolagus. Serengetilagus praecapensis has a predicted body mass in the range of 1.2–1.6 kg. Like some smaller modern rabbits, its forelimb suggests the capability for burrowing.