Research : PaleoBios

Abstracts (vols. 14 to 20)

PaleoBios 14(1), April 24, 1992
© 1992 University of California Museum of Paleontology

Reworked Cleiothyridina sp. in the Seymour Canal Formation (Jurassic-Cretaceous), southeatern Alaska

1Department of Integrative Biology and University of California Museum of Paleontology, University of California, Berkeley, California 94720, USA. 2Department of Geological and Geophysical Sciences, Princeton University, Princeton, New Jersey 08544, USA


Miocene land mammal faunas from the Caliente Formation, Cuyama Valley Badlands, California

1Vertebrate Paleontology Section, Natural History Museum of Los Angeles County, 900 Exposition Blvd., Los Angeles, California 90007, USA. 2Paleo Environmental Associates, Inc., 797 New York Dr., Altadena, California 91001, USA


A scimitar cat (Homotherium serum) from the Late Pleistocene Merrell Locality, southwestern Montana

University of California Museum of Paleontology, University of California, Berkeley, California 94720, USA


Two new species of Pseudolarix Gordon (Pinaceae) from the Middle Eocene of the Pacific northwest

University of California Museum of Paleontology, University of California, Berkeley, California 94720, USA

Two new species of golden larch, Pseudolarix wehrii sp. nov. from Republic, Washington, and P. arnoldii sp. nov. from the Princeton Coalfield of British Columbia, are described. Pseudolarix wehrii replaces P. americana Brown which is a nomen nudum. These two species differ from each other principally in the relative size and morphology of the cone scale bract. The Republic and Princeton floras are considered coeval in age [at approximately 49 Ma (early Eocene)]. Winged seeds that compare favorably to P. wehrii might be ancestral to P. arnoldii, or the two species might represent distinct lineages. Pseudolarix arnoldii closely resembles the living P. amabilis and might be ancestral to it.

PaleoBios 14(2), July 27, 1992
© 1992 University of California Museum of Paleontology

Clemensodon megaloba, a new genus and species of Multituberculata (Mammalia) from the Upper Cretaceous Type Lance Formation, Powder River Basin, Wyoming

Department of Anatomical Sciences, State University of New York, Stony Brook, New York 11794, USA

Two P4s from the Upper Cretaceous type Lance Formation of the Powder River Basin, northeastern Wyoming, both previously referred initially to ?Mesodma sp. and later to Kimbetohi campi, are shown to belong to neither taxon. Along with a previously undescribed but fragmentary P4, these teeth are referred to a new genus and species, Clemensodon megaloba. Evidence from the size and number of serrations of P4, and its enamel microstructure, indicates that Clemensodon is either a derived taeniolabdoid or a primitive ptilodontoid. Determination of which of these two alternatives is correct must await the recovery of teeth from other positions.

PaleoBios 14(3), March 22, 1993
© 1993 University of California Museum of Paleontology

A review of the Lonchorhynchine trematosaurs (Labyrinthodontia), and a description of a new genus and species from the Lower Moenkopi Formation of Arizona

University of California Museum of Paleontology, University of California, Berkeley, California 94720, USA

The labyrinthodont superfamily Trematosauroidea is diagnosed. It includes only the family Trematosauridae, which includes the subfamilies Trematosaurinae and Lonchorhynchinae, each of which is diagnosed. The several previously described genera and species of Lonchorhynchinae are reviewed in chronologic order. A new genus and species is described from a skull, lacking the otic region, from the Meteor Crater Quarry in the Wupatki Member of the Moenkopi Formation, Spathian, of Northern Arizona. Isolated fragments of skulls and jaws from Algeria, Australia, India, Madagascar, and Nova Scotia are diagnosable only to subfamily, but indicate a broad geographic distribution of Lonchorhynchinae and show its geologic range to be from the Griesbachian up into the Anisian.

PaleoBios 14(4), April 23, 1993
© 1993 University of California Museum of Paleontology

Hyaenodontidae (Creodonta, Mammalia) from the Early Eocene Four Mile fauna and their biostratigraphic implications

University of California Museum of Paleontology, University of California, Berkeley, California 94720, USA

Hyaenodontid creodonts from the Four Mile Local Fauna of northwestern Colorado are reexamined in light of recent work in the Bighorn and Clarks Fork Basins. Prototomus phobos, P. martis, P. secundarius, P. robustus, P. deimos, Arfia opisthotoma, A. shoshoniensis, Prolimnocyon haematus, and Acarictis ryani are now known from Four Mile. Acarictis, previously known only from lower teeth, is now known from an upper molar. These taxa suggest that the Four Mile Fauna is early Wasatchian in age and corroborate a Wa2 or Wa3 biochronologic age assignment. The species Prototomus secundarius and P. robustus initially suggest a Wa5 age for the Sand Quarry locality, but evidence provided by Gunnell (1989) suggests that this locality is actually Wa2 or Wa3 in age and the presence of these two species at Sand Quarry represents a biostratigraphic range extension. It is possible that the two species, which are significantly larger than other species of Prototomus, may have been in competition or ecologically partitioned from the similar sized species Arfia shoshoniensis and A. opisthotoma. The former two species do not co-occur with the latter two species at any locality. The presence of Arfia in Wa2 and Wa3 at localities in the Bighorn Basin may explain the absence of Prototomus robustus and P. secundarius there.

PaleoBios 15(1–4), May 24, 1993
© 1993 University of California Museum of Paleontology

New additions to the Pleistocene vertebrate record of California

Terminal Pleistocene–Early Holocene fishes from Tulare Lake, San Joaquin Valley, California, with comments on the evolution of Sacramento squawfish (Ptychocheilus grandis: Cyprinidae)


Preliminary list of the marine fishes and other vertebrate remains from the Late Pleistocene Palos Verdes Sand Formation at Costa Mesa, Orange County, California


Fossil lizards from Rancho La Brea in the collections of the University of California Museum of Paleontology


Fossil lizards from the Elsinore Fault Zone, Riverside County, California


Arctodus simus (Cope, 1879) from Riverside County, California


The Late Pleistocene record of Homotherium (Felidae: Machairodontinae) in the southwestern United States


Harlan's ground sloth (Glossotherium harlani) and a Columbian mammoth (Mammuthus columbi) from Stevenson Bridge, Yolo County, California


Preliminary report on a Late Pleistocene vertebrate assemblage from Bonita, San Diego County, California


A preliminary note on the Arvin Landfill local fauna (?Holocene), Kern County, California


PaleoBios 16(1), February 9, 1994
© 1994 University of California Museum of Paleontology

Two Pliocene (Blancan) vertebrate faunas from Douglas County, Nevada

Vertebrate Paleontology Section, Natural History Museum of Los Angeles County, 900 Exposition Blvd., Los Angeles, California 90007, USA

An unnamed formation comprised of fluvial and lacustrine deposits is exposed along the east side of the Carson Valley and on the western flanks of the Pine Nut Mountains, Douglas County, Nevada. The unnamed formation has yielded two fossil vertebrate faunas. The Fish Spring Flat Local Fauna, which occurs in the upper part of the unnamed formation, is comprised of the following taxa: Gila cf. bicolor; Ptychocheilus sp.; Catostomus sp.; Chasmistes sp.; Catostomidae, gen. and sp. indet.; Oncorhynchus sp. indet.; Hypolagus furlongi; Satherium ingens; Canidae, gen. and sp. indet.; Mammut americanum; Equus simplicidens; Equus giganteus; Gigantocamelus spatula; Camelidae, gen. and sp. indet.; Spermophilus howelli; and Thomomys carsonensis n. sp. The Buckeye Creek Local Fauna, which occurs in the lower part of the unnamed formation, is comprised of the following taxa: Gila cf. bicolor; Chasmistes sp.; Catostomidae, gen. and sp. indet.; Hypolagus gidleyi; Alilepus vagus; Ursus abstrusus; Felidae, gen. and sp. indet.; Megalonyx leptostomus; Proboscidea, gen. and sp. indet.; Equus simplicidens; Hemiauchenia cf. blancoensis; Camelidae, gen. and sp. indet.; Odocoileus sp. indet.; and Spermophilus sp. indet. The Fish Spring Flat Local Fauna is late Pliocene in age (late Blancan North American Land Mammal Age) and the Buckeye Creek Local Fauna is middle Pliocene in age (early Blancan North American Land Mammal Age). These faunas represent the first record of vertebrate fossils from Douglas County.

PaleoBios 16(2), June 6, 1994
© 1994 University of California Museum of Paleontology

The 15 Ma floristic crisis at Gillam Spring, Washoe County, northwestern Nevada

1Department of Botany, University of California, Davis, California 95616, USA. 2University of California Museum of Paleontology, University of California, Berkeley, California 94720, USA

A major floristic change in western Nevada at approximately 15 Ma is marked by the rapid disappearance of abundant deciduous hardwoods allied to those now in the eastern United States and eastern Asia, and their replacement by taxa similar to modern western North American species. Whereas this shift is shown elsewhere by floras moderately separated geographically and stratigraphically, we present here the first evidence for the rapid change in composition between two floral horizons separated by scarcely 120 m stratigraphically at Gillam Spring, Nevada. The shift is attributed to a decrease in summer precipitation below 35-40% of the pre-15 Ma annual total.

PaleoBios 16(3), July 4, 1994
© 1994 University of California Museum of Paleontology

Amelanchier hawkinsae sp. nov. (Rosaceae, Maloideae) from the Middle Miocene of Stewart Valley, Nevada, and a review of the genus in the Nevada Neogene

University of California Museum of Paleontology, University of California, Berkeley, California 94720, USA

Amelanchier hawkinsae sp. nov. grew in west-central Nevada from approximately 15-12 million years ago. The earliest records of the species at Purple Mountain and Stewart Valley coincide with a widespread global change in vegetation and floristics that took place at approximately 15.0-14.5 Ma, at what corresponds to the initiation of the Seldovian-Homerian transition. In the western conterminous United States this change brought on relatively drier conditions that were more pronounced earlier in the southwestern United States than to the north. During this period of change it is inferred that A. hawkinsae dispersed into the Nevada region, replacing the earlier A. magnifolia var. desatoyana (Axelrod) comb. nov. Prior to the 15.0-14.5 Ma period of change, A. magnifolia var. desatoyana in Nevada was contemporaneous with A. magnifolia Arnold var. magnifolia at Succor Creek to the north in Oregon. After the change, when A. hawkinsae occupied west-central Nevada, the A. magnifolia-complex continued on in Oregon and Idaho where conditions were more mesic than in contemporary Nevada.

PaleoBios 16(4), December 8,1995
© 1995 University of California Museum of Paleontology

Comparative cranial anatomy of Seymouria sanjuanensis (Tetrapoda: Batrachosauria) from the Lower Permian of Utah and New Mexico

Department of Zoology, Erindale College, University of Toronto, Mississauga, ON, L5L 1C6, Canada (Current address: Museum of Paleontology, University of California, Berkeley, CA 94720, USA)

The Lower Permian seymouriamorph (Tetrapoda: Batrachosauria) Seymouria sanjuanensis was erected on the basis of several specimens from Utah, and specimens from New Mexico were subsequently described. Further preparation of two specimens of S. sanjuanensis reveals additional differences between S. sanjuanensis and the better known S. baylorensis. These include the exclusion of the supratemporal from the tabular horn, a shorter and narrower anterior process of the jugal, a vertical jugal-squamosal suture, a palatine wedged in the pterygoid, and a larger lateral exposure of the articular in S. sanjuanensis. As in S. baylorensis, there is no mandibular fenestra. Seymouria is more similar to the “discosauriscid” Ariekanerpeton than previously recognized. However, most similarities between S. sanjuanensis and Ariekanerpeton are probably size-related, ontogenetic, or primitive. Presence of posteroventral and anteroventral notches in the orbit of S. sanjuanensis and S. baylorensis indicates that these two species are more closely related to each other than to Ariekanerpeton.

A fossil Sigmodon from the San Francisco Bay Area, Solano Co., California, with comments on additional fossil material from Kern Co., California

1Department of Integrative Biology, Museum of Vertebrate Zoology and Museum of Paleontology, University of California, Berkeley, California 94720, USA. 225505 Sierra Ave., Richmond, California 94805, USA

A small, Pleistocene vertebrate fauna from a terrace deposit along the south flank of the Montezuma Hills near Collinsville, Solano County, California includes a unique record of the cotton rat genus Sigmodon. The specimen is a right M1 with three distinct roots and is identified as Sigmodon sp. Additional Sigmodon material from the Elk Hills, Kern County, California is reported. These records demonstrate that a more severe range contraction of the genus took place between the early Pleistocene and the present time in California than in the Great Plains.

PaleoBios 17(1), 1996
© 1996 University of California Museum of Paleontology

A redescription of the cranial anatomy of Seymouria baylorensis, the best known seymouriamorph (Vertebrata: Seymouriamorpha)

Department of Zoology, Erindale College, University of Toronto, Mississauga, ON, L5L 1C6, Canada; Current address: Museum of Paleontology, University of California, Berkeley, California 94720, USA

Seymouriamorphs are generally thought to be closely related to amniotes. Preparation of several specimens of Seymouria baylorensis from the Lower Permian of Texas requires a reevaluation of the affinities of seymouriamorphs. Contrary to previous reports, S. baylorensis has a long cultriform process but lacks mandibular fenestrae, and the transverse flange extends ventrolaterally, as in amniotes, rather than horizontally. The epipterygoid is not fused to the pterygoid. Mature specimens of S. baylorensis lack lateral-line canal grooves. In all these respects, Seymouria is more similar to amniotes than previously considered, but these similarities do not necessarily imply that seymouriamorphs are closely related to amniotes. The presence of a paired atlantal pleurocentrum and other primitive character states suggest that seymouriamorphs do not belong to the crown group Tetrapoda.

The first fossil cyphoderiid testate amoeba, in Dominican Republic amber (Eocene-Oligocene)

Department of Integrative Biology, University of California, Berkeley, CA 94720, USA

Bacteria and protists from Middle Cretaceous amber of Ellsworth County, Kansas

Department of Integrative Biology, University of California, Berkeley, CA 94720, USA

Microfossils of sheathed bacteria and amoebae are reported from the middle Cretaceous amber of Ellsworth County, Kansas. The sheathed bacteria are morphologically very close to the living genus Leptothrix. Testate amoebae resemble the modern genera Pontigulasia and Nebela; these are the oldest fossil representatives of these genera. Other microfossils represent unicellular protists of some sort but cannot be identified further. This microfossil assemblage, similar to that in late Triassic amber from Bavaria, probably indicates an aquatic, oligo-mesosaprobic paleomicrohabitat. It also provides direct confirmation of morphological stasis in the amoeban taxa, which has been previously inferred from comparative molecular sequencing and biogeographical distribution.

PaleoBios 17(2–4), September 13, 1996
© 1996 University of California Museum of Paleontology

The uses of vertebrate fossils in biostratigraphic correlation
A selection of papers presented at the 1994 regional meeting of the Cordilleran Section of the Geological Society of America, edited by Christopher J. Bell and Stuart S. Sumida

Biostratigraphic correlations between the Lower Permian of North America and Central Europe using the first record of an assemblage of terrestrial tetrapods from Germany

1Department of Biology, California State University San Bernardino, 5500 University Parkway, San Bernardino, California 92407, USA. 2Section of Vertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Ave., Pittsburgh, Pennsylvania 15213, USA. 3Museum der Natur, Parkallee 15, 99853 Gotha, Postfache 217, D-99856 Gotha, Germany

The vast majority of tetrapods known from the Early Permian of central, continental Europe have been obligatory aquatic amphibians recovered from grey sediments and black shales reflecting limnetic environments; representatives of terrestrial faunas are exceedingly rare. This report documents a well-preserved terrestrial or semi-terrestrial assemblage remarkably like those of late Paleozoic North American red beds both in taxonomic composition and in its origin from fluvial red-bed facies. The discovery site is the long-known "Bromacker" trackway locality in the Lower Permian Tambach Formation of central Germany. Although exploration of the site is ongoing, a number of terrestrial tetrapod taxa have been recovered which were heretofore known almost exclusively from the Late Pennsylvanian and Early Permian of North America. These include the seymouriamorph amphibian Seymouria sanjuanensis, a trematopid amphibian comparable to the genus Anconastes, the diadectomorph Diadectes, a small reptile of uncertain affinities, and the protorothyridid reptile Thuringothyris mahlendorffae. This material provides significant new information bearing on the early history of the supercontinent Pangaea by demonstrating a high degree of commonality among Early Permian tetrapod faunas worldwide and the probable absence of major physical barriers to their interchange. Further, the Bromacker assemblage promises to be extremely useful in assessing the biostratigraphic position and age of the Tambach Formation, the lowermost unit of the Upper Rotliegend of the Saale Basin of Germany. Present indications are that the Tambach Formation is of an earliest Permian (Wolfcampian) age.

Fossil mammals as a tool in Andean stratigraphy: Dwindling evidence of Late Cretaceous volcanism in the South Central Main Range

1Department of Geological Sciences, University of California, Santa Barbara, California 94720, USA. 2Departamento de Geología, Universidad de Chile, Casilla 13518 Correo 21, Santiago, Chile. 3Department of Geology, Field Museum of Natural History, Roosevelt Rd. at Lake Shore Drive, Chicago, Illinois 60605, USA

A major central Andean volcanic/volcaniclastic unit, the Abanico (=Coya-Machalí) Formation, was long considered Late Cretaceous in age—at least in part, and as lacking chronologically useful fossils. Recent unanticipated discovery of Cenozoic mammalian remains in this unit in central Chile, in conjunction with new isotopic geochronometric evidence, overturns both of these views, necessitating considerable revision of the accepted geotectonic history of the region. Two fossil mammal faunas have been recovered in the Río Tinguiririca drainage (34° 50' S) of the Andean Main Range. The first discovered and better sampled of the two faunas represents a new biostratigraphic interval, of transitional Eocene-Oligocene age (pre-Deseadan, post-Mustersan, South American Land Mammal Age, SALMA) (31.4–37.7 Ma); it is derived from a horizon directly overlying Mesozoic units. The second fauna is unquestionably significantly older (?Early Eocene, Casamayoran SALMA) than the first. This contradicts previous stratigraphic interpretations of the region which place horizons producing the older fauna some 2000 m higher in the local stratigraphic section than those producing the younger, indicating an unforeseen degree of tectonic complexity for this Andean segment.
Two additional Cenozoic mammal faunas have been discovered within the Abanico (=Coya-Machalí) Formation north of the Tinguiririca valley region. Aside from a preliminary description of a primate skull, neither of these faunas has yet been studied, but preliminary biostratigraphic and radioisotopic information indicates both to be younger than the younger fauna from the Tinguiririca region. This has important geological ramifications inasmuch as both faunas occur in what was previously considered the oldest part of the formation, its oft-cited "eastern strip" occurring north of about 34° 40' S. Consequently, deposition of much (if not all) of the Abanico (=Coya-Machalí) Formation cannot be atributed to an episode of Late Cretaceous volcanism generally posited for the region.
These finds of well-preserved, temporally distinct, and geographically widespread fossils in the Abanico (=Coya-Machalí) Formation are of demonstrated importance to the interpretation of central Andean tectonics, establishing fossil vertebrates as an important new source of geochronologic information for this region.

A review of the biostratigraphy of Pliocene and Pleistocene sediments in the Elsinore Fault Zone, Riverside County, California

1Quaternary Studies Program, P.O. Box 5644, Northern Arizona University, Flagstaff, Arizona 86011, USA. 2Section of Earth Sciences, San Bernardino County Museum, Redlands, California 92374, USA. 3Department of Integrative Biology and Museum of Vertebrate Zoology, University of California, Berkeley, California 94720, USA

Three fossil-bearing sedimentary formations are known from the Elsinore Fault Zone within the Temecula basin. The Temecula Arkose, stratigraphically lowest of these formations, crops out primarily in the southeastern portion of the basin. An unnamed sandstone and conglomerate formation cropping out near Murrieta and the Pauba Formation, the uppermost formation, unconformably overlies the Temecula Arkose and the unnamed sandstone formation in the center of the fault trough. A kaolin deposit within the unnamed sandstone has been correlated with the Bishop Ash (0.785–0.002 Ma), but is not found in direct association with vertebrate faunas.
Assessments of the age of these three units have been based primarily on the composition of the vertebrate faunas recovered from localities throughout the fault trough. Recent analyses of mammalian fossils recovered from the region permit more detailed biochronologic interpretations of these formations. Faunas from the Temecula Arkose are referred to the Blancan land mammal age, based upon the presence of Onychomys gidleyi, Calomys arizonae and Neotoma (Paraneotoma) sawrockensis low in the section and the co-occurrence of Tetrameryx and Nannippus higher in the section. The age of the unnamed sandstone formation ranges from the late Pliocene (Blancan) to the middle Pleistocene (Irvingtonian); an interpretation based upon the identification of three recognizable and apparently distinct faunal components within this unit. These components are informally designated the Paraneotoma faunal unit (middle to late Blancan), the Mimomys faunal unit (latest Blancan), and the Microtus/Mammuthus faunal unit (early to middle Irvingtonian). The age of the Pauba Formation ranges from the middle Pleistocene (Irvingtonian) to the early late Pleistocene (latest Irvingtonian), based upon the superpositional relationship of this formation to the unnamed sandstone as well as the presence within the formation of Microtus and Mammuthus and the absence of Bison. Following the biochronologic interpretations of Lundelius et al. (1987), Repenning (1987) and Repenning et al. (1990, 1995), the Temecula Arkose ranges in age from possibly 6.0 Ma to ±2.7 Ma; the unnamed sandstone dates from ±3.5 Ma to ±0.75 Ma; and the Pauba Formation falls within the range of <0.6 Ma to >0.12 Ma.
In recent years, reevalution of the taxonomic composition of several faunas has resulted in important changes in the interpretations of the age of the formations; a summary of the significant vertebrate fossil localities from the Elsinore Fault Zone and their contained mammalian faunas is provided in an effort to resolve a long history of confusion regarding specific taxonomic affinities and chronologic assessments of faunas from the region.

The Fairmead Landfill Locality (Pleistocene, Irvingtonian), Madera County, California: Preliminary report and significance

1Museum of Paleontology, University of California, Berkeley, California 94720, USA; Present address: Department of Anthropology, University of Montana, Missoula, Montana 59812, USA. 2Department of Geology, California State University, Fresno, California 93740, USA. 3Department of Geology, University of California, Davis, California 95616, USA

A diverse vertebrate fauna, dominated by large herbivorous mammals, was discovered in May of 1993 at the Madera County Fairmead Landfill in alluvial fan, fan channel and marsh/lacustrine sediments representing the upper unit of the Turlock Lake Formation. Taxa identified from this fauna include: Clemmys marmorata, Anatidae, Glossotherium harlani, Nothrotheriops cf. N. shastensis, Megalonyx sp., Canis armbrusteri, Canis cf. C. latrans, Smilodon cf. S. fatalis, Homotherium sp., Thomomys sp., cf. Dipodomys sp., Lepus sp., Mammuthus columbi, Equus sp. (large and small), Camelops sp., Hemiauchenia sp., Tetrameryx irvingtonensis, Capromeryx sp., and Odocoileus sp. A late Irvingtonian age is indicated for the fauna based largely on the presence of Tetrameryx irvingtonensis coupled with the absence of Bison. The fossil bearing stratum is normally magnetized, and is inferred to have been deposited during the Brunhes normal magnetic polarity chron, placing an upper bound on the age of the fauna at 780,000 years before present (yr. B.P.). The Fairmead Landfill yields the first diverse latest Irvingtonian fauna from north-central California. Comparison to the older, coastal type Irvingtonian fauna will enhance our understanding of the Irvingtonian of California, permitting better comparisons and correlations with other North American Irvingtonian age faunas.

The importance of fine-scaled biostratigraphic data in addressing questions of vertebrate paleoecology and evolution

Department of Biology, Saint Mary's College of California, Moraga, California 94575, USA

Large-scale stratigraphic units, such as formations or members, create excessive time-averaging, where taxa that occur in different fine-scaled stratigraphic units are often consolidated. Important evolutionary or ecological events, major hiatuses in the record, or significant changes in accumulation rates, may go unnoticed if the scale used in sampling the stratigraphy is inappropriate for the question being asked by the study. Consequently, a finer scale of resolution in the collection of biostratigraphic data needs to be employed. Fine-scaled sampling of stratigraphic units can help establish the possible coexistence of taxa by their co-occurrence in the same packet of sediments. These data would provide for a greater ability to address current questions on paleoecology and evolution with an appropriate degree of resolution. Two case studies are presented here as examples of how fine-scaled biostratigraphic data can allow for greater accuracy in the interpretation of paleoecological and evolutionary studies.
Vertebrate community structure can be determined through ecological quantitative measures, such as relative abundance and diversity. However, for the paleontological record, the accuracy of this approach is dependent upon coexistence of species in the same time frame. Here, the community structure of fossil penguins from the late Eocene, La Meseta Formation, Seymour Island, Antarctic Peninsula is tested when biostratigraphic data of a smaller scale are applied. The results demonstrate that the relative abundances of six coexisting penguin species from Unit Telm 7 of the La Meseta Fm. are not significantly different from the corresponding relative abundance values taken from stratigraphic subsets within that unit. Additionally, the relative abundance values between the subunits do not differ from each other based on the results of chi-square analyses.
A second study investigates a topical evolutionary question of whether some mammalian taxa exhibit a decrease in body size (i.e., dwarfing) due to predation or resource limitations. Temporal overlap between large, intermediate and small forms in an ancestor-descendant lineage should be present to indicate a dwarfing effect. A previously proposed example of dwarfing among late Pleistocene to Holocene kangaroos is not supported by biostratigraphic and chronostratigraphic data from Madura Cave, Western Australia, as no intermediate forms are present. An alternative interpretation is proposed, which is more consistent with the data. It is proposed here that the larger kangaroo species went extinct due to a change in vegetation type, which could not sustain the large animals and was subsequently replaced by a smaller immigrant species. The smaller kangaroo species was better able to utilize the new plant resources, which were present after the preexisting plant community changed in response to more arid climatic conditions.

PaleoBios 18(1), April 2, 1997
© 1997 University of California Museum of Paleontology

Additional late Cenozoic (latest Hemphillian to earliest Irvingtonian) mammals from Douglas County, Nevada

Vertebrate Paleontology Section, Natural History Museum of Los Angeles County, 900 Exposition Blvd., Los Angeles, California 90007, USA

An unnamed formation, exposed along the eastern side of the Carson Valley and on the western flanks of the Pine Nut Mountains, previously yielded two fossil vertebrate faunas; the early Blancan (middle Pliocene) Buckeye Creek Local Fauna and the late Blancan (late Pliocene) Fish Spring Flat Local Fauna. A new fauna, the latest Hemphillian (earliest Pliocene) Washoe Local Fauna, is now recognized from the lowermost part of the unnamed formation of the Carson Valley-Pine Nut Mountains area. The Washoe Local Fauna includes the following taxa: Lepoides lepoides; Hypolagus gidleyi; Proboscidea, family indet.; Teleoceras sp. indet.; ?Felidae, gen. indet.; Dinohippus or Pliohippus, sp. indet.; Hemiauchenia sp. indet.; and ?Cervidae, gen. indet. Platygonus cf. P. pearcei is added to the Buckeye Creek Local Fauna. Two new faunas, the late Blancan Wellington Hills Local Fauna and the earliest Irvingtonian (latest Pliocene) Topaz Lake Local Fauna, are provisionally recognized from an unnamed formation that is exposed along the eastern side of Antelope Valley and on the western flanks of the Wellington Hills, Douglas County, Nevada. The Wellington Hills Local Fauna includes the following taxa: Leporidae, gen. indet.; ?Nerterogeomys sp. indet.; ?Thomomys sp. indet.; Spermophilus wellingtonensis n. sp.; Marmota or Cynomys, sp. indet.; Megalonychidae, gen. indet.; Proboscidea, family indet.; Felidae, gen. indet.; Equus idahoensis; Equus sp. indet.; and Camelidae, gen. indet. (small sp.). The Topaz Lake Local Fauna includes the following taxa: Leporidae, gen. indet.; Ondatra ?idahoensis; Felidae, gen. indet.; Proboscidea, family indet.; Equus idahoensis; Equus cf. E. giganteus; Equus (?Dolichohippus) sp. indet.; Hemiauchenia sp. indet.; Camelidae, gen. indet. (large sp.); and Euceratherium collinum.

PaleoBios 18(2,3), September 14, 1998
© 1998 University of California Museum of Paleontology

A new species of Microcosmodon (Mammalia: Multituberculata) from the Paleocene Tullock Formation of Montana, and an argument for the Microcosmodontinae

Department of Integrative Biology and University of California Museum of Paleontology, University of California, Berkeley, California 94720, USA

A new species of the multituberculate genus Microcosmodon Jepsen, 1930 from the Puercan Tullock Formation of Garfield County, Montana is described. Study of a relatively large sample of molars and premolars from both upper and lower dentitions indicates that derived characters distinguishing Microcosmodon from other multituberculate genera were developed by the early Paleocene. The presence of the new species suggests that microcosmodontine species richness in the Western Interior was as high at the beginning of the Paleocene as at its end. Phylogenetic analysis of species assigned to the Microcosmodontinae confirms the close relationship originally postulated between Microcosmodon and Pentacosmodon Jepsen, 1940, but indicates that Microcosmodon woodi Holtzman and Wolberg, 1977 does not belong to the genus or subfamily. This is consistent with the hypothesis that microcosmodontines diverged from other eucosmodontids before their dispersal from Asia to North America.

A probable Cerion (Gastropoda: Pulmonata) from uppermost Cretaceous Hell Creek Formation, Garfield County, Montana

1Museum of Paleontology, University of California, Berkeley, California 94720, USA. 2Energy and Environmental Research Center, University of North Dakota, Grand Forks, North Dakota 58203, USA

The new species Cerion acherontis (Ceriidae) is described from strata of latest Cretaceous age in the Hell Creek Formation, Garfield County, Montana, USA. The occurrence extends the known geographic range of Cerion northward from the Caribbean region and its geologic age from the early Miocene. The species appears to obey the "jigsaw constraint" previously proposed on the basis of the relation between whorl size and number in Recent Cerion species, but plesiomorphic shell shape in Cerion remains an open question.

New information on the skull of the Early Permian reptile Captorhinus aguti

Department of Zoology, Erindale College, University of Toronto, Mississauga, Ontario L5L 1C6 Canada; Current address: Bernard Price Institute for Paleontology and Paleoenvironmental Research, University of the Witwatersrand, Johannesburg, P.O. WITS 2050, South Africa

Well-preserved material of the early reptile Captorhinus aguti Cope, from the Fort Sill fissure-fill locality, Lower Permian of Oklahoma, permits correction and emendation of earlier interpretations of its cranial anatomy. Description of new material and reexamination of previously described specimens reveals that anterior cristae are not present in the braincase of C. aguti, nor is there evidence for the presence of these cristae in specimens of its sister species Captorhinus laticeps. The parasphenoid of C. aguti has broad basitubera which may have overlain the stapedial footplates, as described for its larger relative Labidosaurikos meachami. Evidence of a jaw-locking mechanism is lacking for both C. aguti and C. laticeps, despite such a mechanism having been proposed originally for the latter taxon. In addition to the well-known presence of multiple rows of teeth, C. aguti is distinguished from other captorhinids by the presence of ogival cheek teeth. The presence of ogival cheek teeth in isolated, single-rowed elements from Fort Sill supports assertions that C. laticeps is absent from the Fort Sill fauna and that there is a distinct stratigraphic separation between the two Captorhinus sister taxa. Similarly, single-rowed elements with ogival teeth from the Lueders Formation of Texas are reassigned to C. aguti from C. laticeps, thereby extending the stratigraphic range of the former species in Texas at the expense of the latter.

Turtles from the Middle Eocene (Uintan) of Saskatchewan, Canada

1Museum of Paleontology, University of California, Berkeley, California 94720, USA. 2Yukon Paleontologist, Heritage Branch, Department of Tourism, Yukon Government, P.O. Box 2703, Whitehorse, Yukon, Y1A 2C6, Canada

Trionychids, testudinids, emydids, baenids, anosteirine carettochelyids, and an indeterminate family are present in the Swift Current Creek local fauna, Cypress Hills Formation of Saskatchewan. These are the most northerly records of middle Eocene (Uintan) turtles in North America and indicate some provincialism compared to more southerly faunas.

PaleoBios 18(4), December 15, 1998
© 1998 University of California Museum of Paleontology

"Self-organizing" stress-stabilizing behavor and the co-evolution of interacting species and ecosystems: The quest for a fundamental law of evolution

Petrobras-Cenpes, Cidade Universitária, 21949-900 Rio de Janeiro, Brazil (current address); and Geologische-Paläontologisches Institut der Universität Heidelberg, Im Neuenheimer Feld 234, D-69120 Heidelberg, Germany

Current research provides insights into the rules of self-organization, complexity, and evolutionary dynamics of natural systems. New theoretical studies that combine evidence drawn from ecology (ecosystem interactions and selective forces) and the geological record (mass extinctions, biotic/ecosystem recovery and phylogenetic/evolutionary patterns) strongly suggest that evolution follows a fundamental law that melds spontaneous order and natural selection. The evidence discussed in this paper indicates that complex, non-linear webs of biotic-abiotic interactions (ecological linkages), established at the population and community levels, form complex ecosystem "fitness" templates. These templates dictate, in a deterministic manner, the overall patterns of physiological and phenotypic traits and behavioral structure within an ecosystem and consequently, produce patterns of "seemingly-adaptive" speciation events. A primary evolutionary mechanism, here termed the "self-organizing" stress-stabilizing behavior, is proposed as a driving force for stabilizing "stress" or "pressures" of internal or external character to an ecosystem. This behavior conforms with different levels of ordered complexity according to the degree of interaction dynamics. The process is wholly autocyclic, inducing a near simultaneous avalanche of random geno-/phenotypic changes through genetic transposition and point mutations within the population and community (co-evolution of interacting species and ecosystems). The evolutionary impact at the community level depends on the complexity of ecological linkages. Darwinian natural selection is seen as an omnipresent "fitness" template threshold which acts subsequently on the resultant variations, further molding and refining the outcome and interactions at a slower pace.

Secondary tiering among Silurian epibionts in the Waldron Shale, Indiana, USA

Geology Department, Milwaukee Public Museum, 800 West Wells St., Milwaukee, Wisconsin 53233, USA

Epibionts in the Silurian (Wenlockian) Waldron Shale, Indiana, lived as secondary tierers on crinoids, brachiopods and platyceratid gastropods. Bryozoans were the dominant epibionts, followed by cornulitids, small crinoids, corals, spirorbids, and brachiopods. Crinoid holdfasts exposed to encrustation from 0 to 5 mm above the sediment surface have fewer epibiont species than taller brachiopods (to 2 cm height) and gastropods (to 5 cm height). Upright crinoid columns elevated higher than 5 cm above the bottom hosted encircling coral and bryozoan colonies, as well as other crinoids attached by distal coils of their columns. The platyceratid Naticonema niagarense lived, at least in part, on crinoid crowns at heights of up to 1 m above the bottom and hosted its own encrusting fauna dominated by bryozoans and cornulitids. The bryozoan-cornulitid assemblage on N. niagarense is the same as that on Strophostylus cyclostomatus, a platyceratid which has not been found on Waldron crinoids and was probably a bottom-dweller. The same association of encrusting epibionts occurred through all primary tier levels in the Waldron fauna, and host selectivity among epibiont groups was low.

Holodiscus lisii (Rosaceae): A new species of Ocean Spray from the late Eocene Florissant Formation, Colorada, USA

University of California Museum of Paleontology, University of California, Berkeley, California 94720, USA

Holodiscus lisii is described as a new species of fossil Ocean Spray from the late Eocene lacustrine shales at Florissant, Colorado. This new species, with the lamina narrowly decurrent on the petiole, and with well developed subsidiary teeth, has a combination of morphological features that are typically found in leaves of the extant H. discolor-complex. The narrowly decurrent lamina on the petiole is shared with leaves of H. discolor sp. dumosus, whereas the presence of subsidiary teeth is shared with leaves of H. discolor ssp. discolor. The Florissant species is inferred to be systematically part of the root plexus from which the discolor-complex is derived. The climatic conditions inferred for the Florissant paleoflora suggest that H. lisii sp. nov. lived at the upper range of microthermal climate at a mean annual temperature of approximately 11–13° C, and that the later growing season was relatively dry. The small leaf size of the H. lisii sp. nov. reflects adaptation to the climatic conditions that existed at Florissant during the latest Eocene.

PaleoBios 19(1), April 15, 1999
© 1999 University of California Museum of Paleontology

A reexamination of Thalattosaurus and Nectosaurus and the relationships of the Thalattosauria (Reptilia: Diapsida)

Royal Tyrrell Museum of Palaeontology, P.O. Box 7500, Drumheller, Alberta, Canada T0J 0Y0

The genera Thalattosaurus Merriam and Nectosaurus Merriam are described and reviewed following acid preparation of the type material. In both forms, a supratemporal fenestra is present, although it is reduced to a narrow slit by the greatly enlarged supratemporal bone and the posterior extension of the frontal. There is no quadratojugal and the quadrate is streptostylic. Tooth implantation is thecodont in Nectosaurus, and ankylothecodont in Thalattosaurus. While tooth replacement is not yet fully understood, it appears to differ from the normal thecodont pattern. Thalattosaurs are modified diapsids and can be identified as saurians (sensu Laurin, 1991). Their relationships within the Sauria is left unresolved. A phylogenetic analysis of 39 characters suggests that within the Thalattosauriformes (new taxon), Endennasaurus and Askeptosaurus form the primitive sister group of all other forms. The Thalattosauria is defined as the stem group including all members of the Thalattosauriformes more closely related to Nectosaurus and Hescheleria than Endennasaurus and Askeptosaurus. Within the Thalattosauria, Nectosaurus is the sister group of the Thalattosauridae, which includes Clarazia, Thalattosaurus, Paralonectes and Agkistrognathus.

PaleoBios 19(2), August 20, 1999
© 1999 University of California Museum of Paleontology

New Pterodontinae (Creodonta: Hyaenodontidae) from the late Eocene-early Oligocene Jebel Qatrani Formation, Fayum province, Egypt

Museum of Paleontology, University of California, Berkeley, California 94720, USA; Phone: (303) 642-3733, Fax: (303) 642-1822

Reanalysis of existing pterodontine creodont collections and study of new finds from the late Eocene to early Oligocene Jebel Qatrani Formation, Fayum Province, Egypt, reveals greater diversity than previously recognized and provides the first opportunity in nearly 80 years to revise these taxa. All the taxa previously considered members of the subfamily Hyaenodontinae are formally recognized as belonging to the subfamily Pterodontinae. The genus Pterodon is revised and restricted to one European and three African species, one new. A new genus is erected to accommodate material previously referred to P. leptognathus. The genus Hyaenodon is no longer recognized in the Fayum sequence. Material previously referred to that genus is transferred to Metapterodon, and two new species are described. The presence of an additional, diminutive pterodontine and at least three medium- to large-sized taxa are noted from fragmentary material.

An Early Jurassic microvertebrate fauna from the Kayenta Formation of northeastern Arizona: Microfaunal change across the Triassic-Jurassic boundary

Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley, California 94720, USA

The tetrapod faunal transition across the Triassic-Jurassic boundary is characterized by the extinction of dominant Late Triassic taxa (non-dinosaurian archosaurs) at or near the end of the Triassic, the rise of their dinosaurian contemporaries to dominance in the Jurassic, but few originations of new taxa in the Early Jurassic (Liassic). Thus the beginning of the Jurassic Period is characterized among terrestrial vertebrates primarily by negative evidence. We report on the Žrst Early Jurassic microvertebrate fauna from the southwestern U.S. Microvertebrate fossils from four localities in the Kayenta Formation (Liassic) of Arizona are compared to the known macrovertebrate diversity of the Kayenta Formation and to a large and diverse Late Triassic (Carnian) microvertebrate fauna from the Placerias and Downs quarries (lower Petrified Forest Member, Chinle Formation) of eastern Arizona. The Kayenta faunule consists of anurans, sphenodontids, and pseudosuchians, including crocodilians, already known from the Kayenta Formation, and chondrichthyans and urodeles, which were not previously reported from the formation, as well as a great number of forms that elude positive identiŽcation and differ substantially from unidentiŽable taxa in the Chinle microfaunas. Comparison of the Kayenta and Chinle microvertebrate faunas supports our present view of faunal change across the Triassic-Jurassic boundary; the known temporal ranges of vertebrate taxa that became extinct at or near the end of the Triassic are not extended into the Jurassic by the Kayenta microfauna. Crocodiles are the only pseudosuchians positively identiŽed in the Kayenta microfauna. Urodeles, anurans, and other lissamphibian remains present in the Kayenta faunule (but not positively identiŽed from the Chinle fauna) are among the most ancient members of the living amphibian taxa known in North America. Facies differences may partly account for the taxonomic differences among the microfaunas.

PaleoBios 19(3), December 15, 1999
© 1999 University of California Museum of Paleontology

Late Cretaceous sea turtles from the Chico Formation of California

1Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley, California 94720, USA. 2Museum of Vertebrate Zoology, University of California, Berkeley, California 94720, USA

New chelonioid sea turtle specimens from the Late Cretaceous (Campanian) Chico Formation of Northern California include taxa from the clades Cheloniidae and Dermochelyidae. The dermochelyid material represents at least one undescribed species. These specimens are the oldest PaciŽc occurrence of cheloniids and dermochelyids, and one of the oldest records of their association. No protostegids are known from the Chico Formation, highlighting the taxonomic differences between the pre and post-Campanian PaciŽc Ocean turtle faunas. The turtles of the Chico Formation exhibit biogeographic afŽnities with both Japanese and Eastern North American Late Cretaceous chelonioids.

Fossil oak leaf galls from the Stinking Water paleoflora of Oregon (middle Miocene)

Department of Biology, University of Central Arkansas, Conway, Arkansas 72035, USA

Complex galls, Antronoides polygonalis n. form sp., are documented on a leaf of the fossil oak Quercus simulata, from the Miocene-age Stinking Water flora of southeastern Oregon. These galls are assignable to the Cynipidae (Hymenoptera), and can with some conŽdence be allied to the extant genus Antron. This affinity is consistent with the modern geographic distribution of the genus. The fossil host species has been linked with fourteen different extant analogues in the past, including extant Asian species in the subgenus Cyclobalanopsis (cycle cup oaks). Modern Antron is known only from PaciŽc species of white oaks (section Quercus sensu stricto). These fossil galls support evidence from fossil acorns that Q. simulata does not belong in Cyclobalanopsis, and suggest that its affinities lie with the PaciŽc white oaks.

Evolution of enamel microstructure of archaic ungulates ("Condylarthra") and comments on some other early Tertiary mammals

Department of Integrative Biology and Museum of Paleontology, University of California, Berkeley, California 94720, USA

The enamel structure of early Tertiary mammals, and in particular the Hunter-Schreger bands (HSB), is surveyed and discussed in light of the correlations between HSB occurrence and body size, chewing mechanisms and other factors. The previously proposed positive correlation between body size and HSB occurrence is generally supported, as well as the previously stated exceptions; a causal relationship is not assumed. A positive correlation between the occurrence of HSB and divergence from the structure of the primitive tribosphenic molar and insectivorous feeding is also observed, but exceptions do occur. Poorly-developed HSB, well-developed HSB, and a specialized bending of prisms in advanced periptychids probably evolved independently and directly from radial enamel. Observations indicate convergent evolution of HSB within different families of archaic ungulates as well as in other mammalian groups, such as Pantolesta, Pantodonta, Primates, Rodentia, and Tillodontia. Within Ungulata underlying synapomorphies or developmental constraints may facilitate parallel acquisition of HSB in several families. It is hypothesized that co-occurring changes in dental morphology, body size, overall ecology, and chewing pattern in eutherian mammals of the early Tertiary resulted in the evolution of HSB. However, combinations of these factors differed in different lineages. Through biomechanical constraints, either one factor or a combination of factors could have caused the alteration of the enamel structure to HSB or specialized bending.

PaleoBios 20(1), April 15, 2000
© 2000 University of California Museum of Paleontology

Terminal Pleistocene armadillo (Dasypus) remains from the Ozark Plateau, Missouri, USA

1Geology Section, Research and Collections Center, Illinois State Museum, Springfield, Illinois 62703, USA. 2Earth and Space Sciences, Denver Museum of Natural History, Denver, Colorado 80205, USA

Seven osteoderms, tentatively referred to Dasypus cf. D. bellus, were recovered from excavations in the entrance of Little Beaver Cave (LBC), Missouri. Morphologically, D. bellus (beautiful armadillo) is a poorly deŽned species and its relationship to other extinct Dasypodidae and the extant D. novemcinctus (nine-banded armadillo) has not been adequately established. An accelerator mass spectrometer radiocarbon date (11,000 ± 60 yr B.P.) on a buckler osteoderm from LBC represents a new terminal date for Dasypodidae in the contiguous United States, prior to the historic invasion by D. novemcinctus in the latter half of the 19th century. The LBC nonanalog fauna ranges in age from ~13,000-10,000 yr B.P., and is composed of >30 mammal species with four extinct and eight extralimital taxa. Morphological similarities suggest that late Pleistocene Dasypus had thermal tolerance levels like D. novemcinctus. If this inference is correct, the association of a strong boreal component with Dasypus at LBC suggests high levels of equability (reduced seasonality) for the terminal Pleistocene Ozarks.

A Late Pleistocene biota from the Arco Arena site, Sacramento, California

1Dept. of Geology, Sierra College, 5000 Rocklin Road, Rocklin, California 95677, USA. 2Dept. of Biology, Sierra College, 5000 Rocklin Road, Rocklin, California 95677, USA. 3Hagerman Fossil Beds National Monument, 221 North State Street, Post Office box 570, Hagerman, Idaho 83332, USA

A small, Late Pleistocene biota was recovered from an excavation of a professional outdoor sports stadium adjoining the ARCO Arena in Sacramento, California. The fossils were recovered from overbank deposits in the less than 600,000 year old Riverbank Formation (Wagner, et al., 1981). This is one of a handful of Pleistocene sites in the northern half of California that include a signiŽcant number of genera and this site helps to give us a clearer picture of the Late Pleistocene paleoecology of the Sacramento Valley. The fossils include: Harlan's ground sloth, Paramylodon harlani; bison, Bison antiquus; coyote, Canis cf. latrans; horse, Equus sp.; camel, Camelops hesternus; a squirrel, cf. Sciurus sp.; an antelope (Antilocapridae) or deer (Cervidae); and mammoth, Mammuthus sp. Plant fossils include an unidentiŽed leaf and a holly leaf cherry seed, Prunus cf. ilicifolia.

New material of the basal Thyreophoran Scutellosaurus lawleri from the Kayenta Formation (Lower Jurassic) of Arizona

Museum of Paleontology, University of California, Berkeley, California 94720, USA

As a basal member of the thyreophoran lineage of ornithischian dinosaurs, Scutellosaurus lawleri is important, yet still incompletely known. Material recovered from the Lower Jurassic Kayenta Formation of Northern Arizona in 1983 reveals new details about its anatomy. Portions of the skull, ankle, forearm, and pelvis are particularly important because they were incompletely preserved or missing in the holotype. The phylogeny of the Ornithischia has been modiŽed cladistically since Colbert's description, warranting a reassessment of the comparative morphology and phylogenetic position of S. lawleri. Skull fragments indicate an emendation to the clade Thyrephora is necessary. New limb material suggests that S. lawleri was not an obligate quadraped. Histological observations indicate that S. lawleri grew slowly throughout its life.

PaleoBios 20(2), September 25, 2000
© 2000 University of California Museum of Paleontology

Systematic revision, skeletal anatomy, and paleoecology of the New World early Tertiary Presbyornithidae (Aves: Anseriformes)

Swedish Museum of Natural History, P.O. Box 50007, SE-104 05 Stockholm, Sweden

Since the family Presbyornithidae was first described from the Eocene Green River Fm. of Utah, fossils referred to this genus have been collected from many Paleogene localities around the world. Fossils of this family are extraordinarily abundant and permit detailed studies of all parts of the skeleton. This paper describes the osteology of the Presbyornithidae based upon virtually all the prepared material known from the New World. The family is revised and found to comprise four species placed in the two genera Presbyornis (three species) and Telmabates (one species). Presbyornis pervetus is by far the most common and widespread member of the family. The large size variation in the skeleton of P. pervetus is attributed to sexual dimorphism. Phylogenetic analyses of the Presbyornithidae have shown it to be a member of the order Anseriformes (ducks, geese, swans, and their allies). In addition to derived anseriform characters, the presbyornithid skeleton has many features in common with other late Cretaceous and early Tertiary birds. Nearly all presbyornithids have been collected from lacustrine environments. Avian egg-shells associated with the fossils at certain localities suggest P. pervetus was a gregarious breeder along the shores of freshwater lakes. At several localities large numbers of presbyornithid fossils form mass-mortality layers in which the skeletons are disarticulated. Although the cause of death is unknown, avian botulism or catastrophic volcanism may have contributed to the mass death of the birds.

PaleoBios 20(3), December 15, 2000
© 2000 University of California Museum of Paleontology

Magnetic stratigraphy of the type Montediablan Stage (Late Miocene), Black Hawk Ranch, Contra Costa County, California: Implications for regional correlations

1Department of Geology, Occidental College, Los Angeles, CA 90041, USA. 2Department of Vertebrate Paleontology, American Museum of Natural History, Central Park W. at 79th St., New York, NY 10024, USA

The faunas and strata of the Black Hawk Ranch Quarry in the Sycamore Formation on the south žank of Mount Diablo, Contra Costa County, California, were the original basis of Savage's (1955) late Miocene "Montediablan Stage." Magnetic samples of the Sycamore Formation were taken at the quarry level, and up to 100 m (300 feet) below and 250 m (750 feet) above it. Although some samples had unremovable normal overprints (easily distinguished from primary remanence because of the near-vertical dip of the beds), all of the samples with primary directions had simple one-component reversed magnetizations held in magnetite. Our results are compared to other sections in California where similar faunas occur in a single long zone of reversed polarity. Based on comparison with distinctive faunas from the Dove Spring Formation in Red Rock Canyon, Kern County, California, and with assemblages in the High Plains of North America, the long reversed magnetozone is correlated with Chron C4Ar (9.0-9.7 Ma). This interpretation differs from the conclusions of Wilson and Prothero (1997), who argued that the single, apparently conformable reversed magnetozone in the Tejon Hills, which contain superposed faunas assigned to the early and late Clarendonian land mammal ages, was correlative with Chron C5r (11.0-12.0 Ma).

Neuralethopterids (Trigonocarpalean Pteridosperms) from the Early Pennsylvanian of eastern North America

1Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA 19104-6316, USA. 2West Virginia University, 916 Churchill Circle, Charleston, 25314-1747

The genus Neuralethopteris Cremer ex Laveine is common in terrestrial strata of Late Mississippian and Early Pennsylvanian age in the Euramerian Floral Realm. This is the first study of the genus as a group in North America where it has biostratigraphic, phylogenetic, paleoclimatologic, and paleoecologic significance. Most of the material examined was collected from the area of the "proposed Pennsylvanian System stratotype" project (PSS) in West Virginia and Virginia, but some additional material and records from other areas of North America have been included. Six species can be recognized in the North American material: Neuralethopteris schlehanii (Stur, 1877) Laveine (1967); N. pocahontas (White, 1900) n. comb.; N. smithsii (Lesquereux, 1880) n. comb.; N. sergiorum n. sp.; N. pentias (White, 1900) n. comb.; and N. biformis (Lesquereux, 1880) n. comb. Paleobiogeographically, the distribution of the six species shows differences. Neuralethopteris pocahontas has been reported in West Virginia and in the Southern Anthracite field, N. pentias in the Anthracite fields, N. schlehanii throughout North America, N. smithsii throughout the Appalachian basin, and N. sergiorum and N. biformis in West Virginia and Alabama. The consistent occurrence of foliage of N. pocahontas with Aulacotheca-like prepollen organs and Trigonocarpus-like ovules allows for a partial plant reconstruction. These results are a step towards better species delimitation within the genus Neuralethopteris and a better understanding of its natural affinities, including its relationship to the genera Alethopteris, Cardioneuropteris, and Crossopteris.

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