Kenneth E. Campbell

Magnetic Polarity Stratigraphy And Mammalian Fauna Of The Deseadan (Late Oligocene-Early Miocene) Salla Beds Of Northern Bolivia

The Salla Beds contain a rich assemblage of Deseadan mammals that traditionally has been considered of early Oligocene age. These deposits, located 90-100 km SE of La Paz, Bolivia, consist of more than 540 m of principally fluviatile clays and silts with numerous interbedded tuffs. Paieomagnetic samples were collected from 104 sites spaced at stratigraphic intervals of about 6 m. As a result of thermal demagnetization (at 400°C or greater), unambiguous polarities were determined for 76 of the 104 originally sampled sites. The pattern of reversals, stage of evolution of the fossils, and preliminary isotopic dates (including a K/Ar age of

Magnetic polarity stratigraphy of the middle Pleistocene (Ensenadan) Tarija Formation of southern Bolivia

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Preliminary observations on the paleobiology and evolution of teratorns (Aves: Teratornithidae)

Ma and zircon fission track ages of ca. 22 Ma) from interbedded tuffs suggest that the Salla Beds correlate to chrons C10 through C6 of the magnetic polarity time scale, or an absolute time interval from about 28.5 to 24 Ma. Pyrotherium and caviomorph rodents occur throughout the section; the primate Branisella is known to occur at about 27 Ma. The Salla faunas seem to represent an earlier part of the Deseadan than faunas of this Land Mammal Age from Argentina. These data suggest that the early Deseadan should be shifted significantly upwards (by ca. 10 m.y.) to late Oligocene-early Miocene time.

A new species of late pleistocene lapwing from Rancho La Brea, California

Abstract A thick blanket of Holocene alluvium lies over southwestern lowland Amazonia, and may possibly occur throughout much of the Amazon Basin. These deposits resulted from massive, seasonal flooding from about 11,000 to about 5000 yr B.P. that was followed by two cycles of erosion and deposition. Interpretations based on these geologic data suggest that southwestern lowland Amazonia is ecologically an “island” in a state of supersaturated disequilibrium as a result of colonization from Pleistocene refugia on its perimeter, and that habitats of highest diversity may be the most recent in origin. Conservation efforts and studies of Amazonian biogeography, soils, and paleoethnography should be reevaluated in light of the geologic data.

The Pan-Amazonian Ucayali Peneplain, late Neogene sedimentation in Amazonia, and the birth of the modern Amazon River system

Abstract The Tarija Formation of southern Bolivia, which is well known for its classic vertebrate faunas, is of prime importance in understanding of the chronology of the Ensenadan Land Mammal Age. This formation consists of well-exposed and relatively fossiliferous sections of clays, clayey silts, sands, gravels, and tuffs which were deposited in a predominately fluviatile regime in a Pleistocene structural basin. Four stratigraphic sections, each measuring 110 m or less, were studied to establish a magnetic polarity stratigraphy. Paleomagnetic samples were collected from the finer-grained sediments at 100 sites spaced at stratigraphic intervals of 5 m or less. All paleomagnetic specimens were demagnetized in alternating fields of least 250 oersteds (oe). Some specimens were also thermally demagnetized at 200°C or more. Of the 100 sites, 77 were ultimately used to determine the magnetic polarity zonation. Based on the four sections sampled, the Tarija Formation spans a time interval from about 1 my to about 0.7 my B.P. or perhaps younger. The lower half of the composite section is of reversed polarity punctuated by a short normal event. This sequence probably represents the late Matuyama chron with the Jaramillo subchron. The upper part of the section is of normal polarity and represents early Brunhes time. A tuffaceous unit 43 m above the Brunhes-Matuyama boundary yielded a fission track (zircon) age of 0.7 ± 0.2 by B.P. These data indicate that the classic Tarija fauna is middle Pleistocene Ensendan in age.

Amazonian magnetostratigraphy: Dating the first pulse of the Great American Faunal Interchange

Abstract The antitrochanter is a uniquely avian osteological feature of the pelvis that is located lateral to the postero-dorsal rim of the acetabulum. This feature makes the avian hip joint unique among all vertebrates, living and fossil, in that a significant portion of the femoral-pelvic articulation is located outside of the acetabulum. This additional acetabular articulation occurs between the neck of the femur and the antitrochanter, and operates as a hinge joint or ginglymus. It is complementary to the articulation of the head of the femur with the acetabulum, which is a pivot joint or trochoides. The size, location, and spatial orientation of the antitrochanter were determined for 77 species of birds representing a variety of hindlimb functions (e.g., highly cursorial, vertical clinging, foot-propelled diving) and spanning a wide range of body sizes (swifts to rheas). The area of the antitrochanter is a good predictor of body mass in birds; its position and orientation are reasonably consistent within hindlimb morphofunctional groups, but not among all birds. The antitrochanter serves as a brace to prevent abduction of the hindlimb and to absorb stresses that would otherwise be placed on the head of the femur during bipedal locomotion. The drum-in-trough-like form of the antitrochanter-femur articulation tends to assist in the transfer of long-axis rotational movements of the femur to the pelvis. The avian antitrochanter is a derived feature of birds that evolved as an aid in maintaining balance during bipedal terrestrial locomotion. El Antitrocánter en las Aves: Forma y Función en el Equilibrio

IN MEMORIAM: HILDEGARDE HOWARD, 1901–1998

An analysis of the functional morphology of the skull of Teratomis merriami indicates that these giant flying birds were predaceous carnivores. This contrasts with prior assumptions that teratorns were scavengers like vultures. The large wingspans of teratorns limited them to savanna habitats. Teratorns probably originated in South America, sharing the dominance of the carnivore adaptive zone in the Tertiary of South America with the better known cursorial carnivorous birds collectively referred to as phorusrhacoids. Their evolution to such large flying birds was most likely directly tied to the progressive development of widespread savanna habitat in South America during the Tertiary. The soaring manner of flight of teratorns may have prevented their dispersal into North America until after the closure of the Central American land bridge. Expansion of savanna habitats in the Americas during Pleistocene glacial periods probably aided this dispersal.

Ccile Mourer-Chauvir (ed.): L'volution des Oiseaux d'aprs le tmoignage des fossiles

A new species of late Pleistocene lapwing (Aves: Charadriidae: Vanellinae) is described from the asphaltic deposits of Rancho La Brea, California. The new species is referred to the South American genus Belonopterus; it corresponds in size to small individuals of B. chilensis. This is the second paleospecies of lapwing reported for North America and the fourth described from the Americas.Abstract A new species of late Pleistocene lapwing (Aves: Charadriidae: Vanellinae) is described from the asphaltic deposits of Rancho La Brea, California. The new species is referred to the South American genus Belonopterus; it corresponds in size to small individuals of B. chilensis. This is the second paleospecies of lapwing reported for North America and the fourth described from the Americas. Nueva Especie de Avefria (Aves: Charadriidae: Vanellinae) del Pleistoceno Tardio de Rancho La Brea, California Resumen. Se describe una nueva especie de avefria (Aves: Charadriidae: Vanellinae) proveniente del pleistoceno tardio de los depositos asfalticos del pleistoceno tardio de Rancho La Brea, California. La nueva especie es asignada al genero sudamericano Belonopterus. Su tamano se corresponde al de individuos pequenos de B. chilensis. La nueva especie es la segunda paleoespecie de avefria descripta para America del Norte y la cuarta descripta para las Americas.