Showing papers in "Journal of Paleontology in 1981"

Conichnus and Schaubcylindrichnus; redefined trace fossils from the Upper Cretaceous of the Western Interior

Abstract: Two distinctive trace fossils from the Blackhawk and Star Point Formations of Utah, heretofore known only by the informal field names "plug-shaped burrows" and "plural curving tubes," are formally designated Conichnus conicus Myannil and Schaubcylindrichnus coronus n. gen., n. sp., respectively. Reevaluation of C. conicus prompted emendations of the original generic and specific diagnoses; Amphorichnus Myannil is considered to be a synonym of Conichnus.

Neoceratodus forsteri from the Lower Cretaceous of New South Wales, Australia

Abstract: Ceratodont lungfish toothplates from the Cretaceous of Lightning Ridge, New South Wales, Australia are described. The specimens bear no resemblance to other fossil lungfish teeth from Australia or from other parts of the world. They cannot however be distinguished from the toothplates of the Recent Neoceratodus forsteri in length/breadth ratios, angles between the ridges, type of punctations, presence of pulp cavity in the ridges, form of the occlusal surface and position of the pterygoid bar.

A redescription of toxolophosaurus cloudi olson, a lower cretaceous herbivorous sphenodontid reptile

Abstract: Reexamination of the type mandible of Toxolophosaurus cloudi Olson, originally de- scribed as a trilophosaurid, indicates that this species is a member of the family Sphenodontidae. Toxolophosaurus shares a number of features with Sphenodon: 1, a close correspondence of mandib- ular elements; 2, acrodont implantation of the teeth; 3, evidence of two upper tooth rows, a lateral row located on the maxilla, and a medial row located on the palatine; and 4, propalinal movement of the jaws, with an anteriorly-directed power stroke. Most of the differences between Toxolopho- saurus and other sphenodontids seem related to adaptation for an herbivorous diet: 1, the mandible is relatively deeper; 2, the teeth are expanded transversely; 3, the teeth are more closely packed along the jaw; 4, the enamel has been greatly thickened. Toxolophosaurus cloudi is the only member of the family Sphenodontidae which shows clear evidence of an herbivorous diet.

Biotic relations in Early Cretaceous coral-algal-rudist reefs, Arizona

Abstract: In southeastern Arizona coral-algal-rudist patch reefs are exposed in the upper member of the Mural Limestone of early Albian age. These reefs were scattered upon the shallow shelf at the northern end of the Chihuahua Trough. Complex biotic relationships suggest that the reef paleocommunities were adapted to a stable, predictable environment, in which a complex trophic structure and food web developed. Two successive hermatypic coral communities are differentiated by coral growth forms and taxa. The basal community consists of massive-tabular corals and the reef frame community consists of lamellar corals that trapped and encrusted skeletal sediment. Other encrusting organisms, such as oysters, bryozoans, brachiopods, sponges, and foraminifers, occupied the protected and cryptic niches within the framework. Blue-green algal stromatolites accreted upon the corals and were volumetrically more important than the earlier encrusting green and red algae. Boring organisms were common and widespread. Algae-fungi produced micrite rims upon carbonate grains in the reef and in the lagoon. Clionid sponges infested reef corals and bivalve shells and boring bivalves were common in corals. In the final community of the reef recumbent caprinid rudists nestled between corals and reclined freely upon the loose sandy substrate. Upon the flanks or lee sides of the reef the elevated, thickwalled monopleurid, Petalodontiafelixi, formed large thickets. In the back reef lagoon Monopleura cf. M. marcida formed bouquets of elevated encrusted specimens, and the recumbent Toucasia texana formed densely packed biostromes. Albian reefs were the last built and dominated by corals and algae until the resurgence of corals during the Eocene. During Late Cretaceous time various rudists dominated reefs, banks, and biostromes.

A morphometric study of the cranium of the pachycephalosaurid dinosaur stegoceras

Abstract: Fifteen domal and braincase measurements on 29 specimens are analyzed to gain insight into the taxonomic structure of the pachycephalosaurid genus Stegoceras. Principal components analysis indicates that the genus as a whole is fairly homogeneous with respect to gross cranial dimensions; only one specimen, which previously has been referred to a new genus, stands out from the rest. However, the analysis reveals that the most common species, S. validus, is heterogeneous, consisting of two distinct phenons. The phenons share similarly shaped domes and braincases but are differentiated by the relative sizes of these character groups. Bivariate analysis indicates that the differentiation is caused by a slight increase in the growth rate of the dome relative to the braincase in one phenon; there is also a weak suggestion that this phenon acquired a relatively thicker dome by a similar slight increase in relative growth rate. On the basis of the phenons' general morphological similarity, their presumed sympatry, and the inferred function of their domes, it is concluded that the phenons do not represent distinct species but rather sexual dimorphs of a single species. Males con- stitute the morph with the relatively larger and thicker domes, which probably were used for head ramming during intraspecific combat.

Middle to late Eocene invertebrate fauna from the San Julian Formation at Punta Casamayor, Santa Cruz Province, southern Argentina

Abstract: The marine Tertiary faunas of the Patagonian region of Argentina are exceptionally diverse and contain a number of endemic taxa of biogeographic interest. These faunas have received little attention since the turn of the century and are in need of rigorous systematic revision. A number of problems concerning the age and stratigraphic succession of the "Patagonian" marine sequence still exists. The purpose of this paper is to describe the invertebrate fauna collected by the First Marshall Field Expedition to Patagonia during 1921-1924 from the upper Eocene to lower Oligocene San Julian Formation from Punta Casamayor. An historical account of the bitter controversy between J. B. Hatcher and A. T. Ortmann of Princeton University and Florentino Ameghino and Herman von Ihering of the National Museum of Buenos Aires (now Museo de Ciencias Naturales "Bernardino Rivadavia") is included to give a persepective to the causes for the problems that still exist concerning the stratigraphy and age of the Middle Tertiary of Patagonia. A summary of the recent stratigraphic and paleontologic work on the Patagonian sequence previously available only in Latin American literature is also included.

Late Cenozoic stages and molluscan zones of the U.S. Middle Atlantic Coastal Plain.

Abstract: Pliocene to Holocene deposits of the U.S. Atlantic Coastal Plain from Maryland to Georgia are divided into four stages and four substages using molluscan biostratigraphic data. These divisions are the Wiltonian and Burwellian Stages (early Pliocene), Gouldian and Windyan Substages of the Colerainian Stage (late Pliocene to early Pleistocene), and Myrtlean and Yongesian Substages of the Longian Stage (late Pleistocene to Holocene). These stages may be recognized from Florida to as far north as Massachusetts and will facilitate correlation with other regions.

Are these the oldest metazoan trace fossils

Abstract: The Precambrian Medicine Peak Quartzite of southeastern Wyoming is part of a largely marine sedimentary sequence which lies unconformably on gneissic basement rocks 2.41 ? 0.5 BY old and which is cut by 2.0 BY old granite. The Medicine Peak is almost pure quartzite with primary sedimentary structures which collectively suggest intertidal to shallow subtidal paleoenvironments. Among the primary structures are nine distinct morphological types of sediment-filled tubes distin- guished by: a, difference in grain size between the tube and the surrounding matrix; b, concentrations of mica, iron and/or distinct grain sizes at the tube boundary; and c, by sharp color contrast, the tubes being darker than the matrix because of limonite staining or mica concentrations. None of these tubes closely resemble metamorphic segregations, gas and water escape passages, or larger dewatering structures. All tube morphologies have broadly similar Cambrian and/or younger analogs accepted as burrows of invertebrate metazoan organisms; yet there is no unequivocal evidence that these are trace fossils. They are dubiofossils whose morphology, size-frequency, orientation, and distribution relative to bedding suggest a biologic origin. However, the known record of Precambrian life, and widely accepted interpretations of biologic, oceanic, and atmospheric evolution +2 BYBP strongly argue against a metazoan origin. The theory of "explosive" Late Precambrian metazoan evolution requires that these tubes be abiotic structures. The less popular theory of gradual Precambrian evo- lution makes metazoan affinities of the tubes possible. Are these the oldest metazoan trace fossils?

Spirophyton in alluvial-tidal facies of the catskill deltaic complex: possible biological control of ichnofossil distribution

Abstract: The trace fossil Spirophyton occurs in rocks of the alluvial-tidal facies of the Devonian Tully clastic correlatives in east-central New York. It is absent from nearshore and offshore deposits in the Tully equivalents, although the similar form Zoophycos is abundant in these facies and Spi- rophyton is found in offshore siltstones of the underlying Hamilton Group. In areas other than New York Spirophyton occurs in nearshore and offshore facies. The fact that Spirophyton is found only in alluvial-tidal siltstones and very fine grained sandstones of the Tully clastic correlatives and is absent from equivalent rock types in nearshore and offshore facies suggests that energy and substrate conditions did not entirely determine the distribution of the Spirophyton producer. Kitchell (1979) and Kitchell and Clark (1979) suggested that the distribution of deep-sea traces may be controlled by ecological factors such as competition and predation, and the same may have been true for the Devonian Spirophyton. Facts consistent with the interpretation of its producer as a r-selected opportunist competitively excluded from more benign deeper water environments include: 1, it is absent from its normal facies where the similar Zoophycos is abundant and it occurs profusely locally in the marginal marine facies where Zoophycos is absent; 2, it is restricted to rocks which, by analogy with the present, were deposited in harsh unpredictable environments which favor r-selected species; and 3, the pattern of its occurrences and its densities fit previously delineated characteristics of opportunistic fossil species.

The nasal cavity of lambeosaurine hadrosaurids (Reptilia; Ornithischia); comparative anatomy and homologies

Abstract: The structure of the lambeosaurine nasal cavity is discussed and revised on the basis of ontogenetic and new anatomic information. The ascending tract from the external nares to the lateral diverticula is homologous with the vestibulum nasi in recent reptiles. The lateral diverticula and common median chamber are together homologous with the cavum nasi proprium. The descending tract is homologous with the nasopharyngeal duct. Species of Parasaurolophus differ greatly in nasal anatomy from Lambeosaurus lambei, Corythosaurus casuarius, and Hypacrosaurus altispinus. Lambeosaurus lambei differs from C. casuarius and H. altispinus in some features and the last two species possess similar nasal cavities. Juveniles of C. casuarius and L. lambei lack lateral diverticula and possess a common median chamber within the supracranial, partially swollen crest.

A new species of hadrosaurian dinosaur from the Upper Cretaceous of Baja California; ?Lambeosaurus laticaudus

Abstract: A new species of Late Cretaceous hadrosaurian dinosaur, ?Lambeosaurus laticaudus, is described. ? Lambeosaurus laticaudus has an open narial canal on the premaxilla like that of Lam- beosaurus lambei, but greatly elongate neural and haemal spines on the caudal vertebrae similar to those of Hypacrosaurus altispinus. This latter characteristic illustrates morphological parallelism between the two genera. Sedimentologic, taphonomic and morphologic data indicate that ? L. laticaudus was dominantly aquatic and lived in near shore estuaries along the Pacific margin of Baja California during the Campanian.

Priscansermarinus barnetti, a probable lepadomorph barnacle from Middle Cambrian Burgess Shale of British Columbia

Abstract: Priscansermarinus barnetti n.gen., n.sp., from the Middle Cambrian Burgess Shale of British Columbia is probably a lepadomorph cirriped. If so, it is the oldest barnacle known, pushing back the known age of the cirripeds 140 million years. Priscansermarinus has a remarkably modern aspect with a rounded, irregularly ovoid capitulum and a smooth, thick peduncle ending in a thickened collar or attachment disc. The capitulum appears to have a thick, leathery wall with two large teardrop shaped chitinous plates similar in shape to the scuta of Lepas. The apparent presence of chitinous plates on Priscansermarinus supports the proposal of Newman, Zullo and Withers (1969) that the lepadomorph ancestor was of the Cyprilepas grade of construction with a chitinous shell, rather than that of Foster (1978) who proposed a non-shelled lepadomorph ancestor. The similarity in size and shape of the Priscansermarinus capitular plates to the scuta of Lepas suggests that in the phylogeny of the lepadomorph barnacles the scuta appeared before the terga and carina. Because barnacles are so highly modified compared to other crustaceans, a considerable length of time was needed for them to evolve from the ancestral crustacean. It is evident, therefore, that the presence of a probable lepadomorph barnacle in the Middle Cambrian, particularly one of such modern aspect, demonstrates that crustacean diversification began well before the Middle Cambrian, most likely during the late Precambrian arthropod radiation postulated by Whittington (1979).