Diane M. Erwin

Biomarker reconstruction of the early Eocene paleotopography and paleoclimate of the northern Sierra Nevada

We reconstruct ancient temperature and elevation gradients across the early Eocene (52– 49 Ma) northern Sierra Nevada (California, United States) using organic molecular proxies that record atmospheric and ground-level effects of topography. Paleoelevation was determined by reconstructing the change in the hydrogen isotopic composition of precipitation (Δδ ΔδD precip ) and mean annual temperature (ΔT GDGT ) (glycerol dialkyl glycerol tetraethers) from the isotopic composition of fossil angiosperm leaf n-alkanes and the distribution of microbially produced soil tetraethers preserved in leaf-bearing sediments. Organic molecular data produce equivalent range-scale (δD n-alkane ) and channel (T GDGT ) paleoelevation estimates that show the northern Sierra Nevada was a warm (>6–8 °C warmer than modern), high-elevation (>2 km), and moderate- to low-relief landscape at the Eocene Climatic Optimum. Modern northern Sierra Nevada topography likely refl ects post-Paleocene reduction of mean surface elevation and late Cenozoic increases in relief.

Diversification of Ceanothus (Rhamnaceae) in the California Floristic Province

High diversity and endemism in the California Floristic Province (CFP) are an alleged response to the late Cenozoic advent of Mediterranean-type climate in this region. Ceanothus comprises two divergent subgenera with centers of diversity in the CFP. We reconstruct the evolution of Ceanothus by using DNA sequence data from the nuclear gene nitrate reductase. We find that the timing of diversification events is related to geological and climatic history. In both subgenera, diversification is characterized by recent divergence of extant taxa and geographically structured phylogenetic relationships. A strong north-south divergence of subgenus Cerastes across the Transverse Ranges indicates that phylogenetic relationships may be structured by climatically divergent regions of the CFP. Divergence-time estimation suggests that the age of extant diversification in both subgenera is ∼6 Ma. This agrees with the fossil record but predates the hypothesized Quaternary (2-Ma) origin of Mediterranean-type climate in the region.

NEW MIOCENE OAK GALLS (CYNIPINI) AND THEIR BEARING ON THE HISTORY OF CYNIPID WASPS IN WESTERN NORTH AMERICA

Abstract Two leaves of Quercus simulata Knowlton from the Miocene of Oregon each show a new type of cynipid gall. Antronoides cyanomontanus n. sp. is described from six elongate and narrowly spindle-shaped galls, 7.0 mm long, and 2.0 mm wide tapering to a narrow tip. They have expanded rim-like bases with most galls scattered throughout the midsection adjacent to or partially straddling a secondary vein. Antronoides oregonensis n. sp. is known from 20 galls, 4.0–5.0 mm long, 1.8–2.0 mm wide and weakly clavate, appearing C-shaped with a rounded apex and circular to oval-shaped base. Galls occur primarily in the basal third of the leaf in a single file along each side of the midrib. Contrary to previous studies, we found A. schorni Waggoner and Poteet, A. polygonalis Waggoner, and A. cyanomontanus to be morphologically closer to Cynips cornifex Hartig on Q. pubescens (European white oak), whereas the new gall A. oregonensis most closely resembles X. clavuloides. The presence of Antronoides indicates the evolution and dispersal of Cynipini wasps was well underway in western North America by the Miocene. However, the new galls leave open the possibility that X. clavuloides and related species may have evolved during the Paleogene in higher-latitude mesic forests of western North America, rather than in the southern Great Basin as suggested by Kinsey and Waggoner and Poteet.

Pinus baileyi (section Pinus, Pinaceae) from the Paleogene of Idaho, USA

Pinus baileyi from the Paleogene of Idaho was initially related to the bristlecone pine P. longaeva (subgen. Strobus, sect. Parrya, subsect. Balfourianae) from western North America. Unlike the centromucronate condition in P. longaeva, P. baileyi cones have raised umbos that are excentromucronate, i.e., the mucro positioned in the upper umbo field above the keel. Cone size and scale morphology shows that P. baileyi more closely resembles excentromucronate pines of subsects. Halepenses and Pinus sensu Gernandt et al. (2005, Taxon 54: 29-42), but is most similar to P. resinosa, P. kesiya, and P. massoniana of subsect. Pinus. Morphologically, P. baileyi resembles the fossil species P. princetonensis and P. arnoldii from the Eocene Princeton Chert, British Columbia, Canada. Pinus baileyi extends the western North American range of ovulate cones resembling subsect. Pinus from the middle Eocene of British Columbia, Canada and Washington, USA to the Oligocene of Idaho, USA. Pinus baileyi, and possibly P. princetonensis and P. arnoldii, indicates the presence of early populations of subsect. Pinus-type pines in the western cordillera of North America, raising the possibility that P. resinosa and P. tropicalis may have evolved from this group.

Revision of Lyonothamnus A. Gray (Rosaceae) from the Neogene of Western North America

Lyonothamnus Gray is a monotypic genus of evergreen trees endemic to California’s Channel Islands. There is one species, L. floribundus, with two subspecies, ssp. floribundus and ssp. asplenifolius. Subspecies floribundus has simple and entire‐margined leaves, while leaves of ssp. asplenifolius are pinnate and composed of three to seven primary segments. Despite its restricted modern occurrence, three fossil species have been described from Neogene paleofloras in the far western United States. Lyonothamnus mohavensis Axelrod is known from California; L. parvifolius (Axelrod) Wolfe and L. cedrusensis Axelrod, from Nevada. However, the size ranges used to segregate these species were all found to fall within the range of L. parvifolius from Stewart Valley, Nevada. Study of intact leaves reveals that the combination of (1) number of primary segments, (2) length of primary segments, (3) number of medial secondary segments per primary segment, and (4) lengths and widths of medial secondary segments is important in segregating species. Using these characters, L. parvifolius and L. wolfei Erwin et Schorn sp. nov. are recognized from Nevada and Oregon, and two species, L. mohavensis and L. axelrodii Erwin et Schorn sp. nov., from California. This renewed taxonomy within an updated temporal framework provides an important first step toward understanding the evolution, diversity, paleoecology, and paleobiogeographic history of this unusual member of the Rosaceae.

Deviacer pidemarmanii sp. nov. (Polygalaceae) from the Late Eocene–Early Oligocene Badger’s Nose Paleoflora, Modoc County, California

Premise of research. Fossils of asymmetrically winged samaras, informally referred to as Acer negundoides MacGinitie (Sapindaceae), from the late Eocene–early Oligocene Badger’s Nose flora (∼34 Ma) of northern California, are described as Deviacer pidemarmanii Myers and Erwin sp. nov. The genus Deviacer Manchester is emended and attributed to the family Polygalaceae. Methodology. The morphological features of more than 40 samaras exquisitely preserved as compressions in lacustrine siltstone of the Badger’s Nose member of the Steamboat Formation were compared to similar extant and fossil-winged fruits. Pivotal results. Deviacer includes compressions of nonschizocarpic asymmetrical samaras with a small dorsal projection. Similar projections characterize the fruits of extant Securidaca (Polygalaceae) and the extinct genus Paleosecuridaca Pigg, Devore, and Wojciechowski, but Acer L. (Sapindaceae) fruits lack these structures. Morphologically, Deviacer is indistinguishable from the anatomically preserved fruits of Paleosecuridaca. Deviacer pidemarmanii sp. nov. is described based on overall fruit size; nutlet shape, size, and orientation to the wing; and wing size, form, and venation. Anatomical features such as locule and seed number in D. pidemarmanii are not preserved, but one specimen appears to be two-seeded, as in Paleosecuridaca. Conclusions. Deviacer is emended and assigned to the Polygalaceae. Paleosecuridaca may be congeneric with Deviacer, but Deviacer fruits are compressions and lack the nutlet anatomy described by Pigg, Devore, and Wojciechowski. Deviacer pidemarmanii records Securidaca-like plants in warm temperate regions of the Pacific Northwest (North America) at least until the latest Eocene–early Oligocene climatic and biotic transition, whereas today extant Securidaca and most other members of the Polygaleae are pantropical. Deviacer pidemarmanii closely resembles the liana Securidaca paniculata Rich. var. lasiocarpa Oort., today a native of northern South America. Recognizing asymmetrically winged samaras from well-dated Cenozoic sediments as related to Securidaca will advance our understanding of the evolutionary relationships and biogeographic history of Polygalaceae and the ecology of Securidaca-like plants in Paleogene vegetation at north temperate latitudes.

Leafcutter Bee Nests and Pupae from the Rancho La Brea Tar Pits of Southern California: Implications for Understanding the Paleoenvironment of the Late Pleistocene

The Rancho La Brea Tar Pits is the world’s richest and most important Late Pleistocene fossil locality and best renowned for numerous fossil mammals and birds excavated over the past century. Less researched are insects, even though these specimens frequently serve as the most valuable paleoenvironemental indicators due to their narrow climate restrictions and life cycles. Our goal was to examine fossil material that included insect-plant associations, and thus an even higher potential for significant paleoenviromental data. Micro-CT scans of two exceptionally preserved leafcutter bee nest cells from the Rancho La Brea Tar Pits in Los Angeles, California reveal intact pupae dated between ∼23,000–40,000 radiocarbon years BP. Here identified as best matched to Megachile (Litomegachile) gentilis Cresson (Hymenoptera: Megachilidae) based on environmental niche models as well as morphometrics, the nest cells (LACMRLP 388E) document rare preservation and life-stage. The result of complex plant-insect interactions, they offer new insights into the environment of the Late Pleistocene in southern California. The remarkable preservation of the nest cells suggests they were assembled and nested in the ground where they were excavated. The four different types of dicotyledonous leaves used to construct the cells were likely collected in close proximity to the nest and infer a wooded or riparian habitat with sufficient pollen sources for larval provisions. LACMRLP 388E is the first record of fossil Megachile Latreille cells with pupae. Consequently, it provides a pre-modern age location for a Nearctic group, whose phylogenetic relationships and biogeographic history remain poorly understood. Megachile gentilis appears to respond to climate change as it has expanded its distribution across elevation gradients over time as estimated by habitat suitability comparisons between low and high elevations; it currently inhabits mesic habitats which occurred at a lower elevation during the Last Glacial Maximum ∼21,000 years ago. Nevertheless, the broad ecological niche of M. gentilis appears to have remained stable.