Ian M. Miller

Leaf economic traits from fossils support a weedy habit for early angiosperms

Many key aspects of early angiosperms are poorly known, including their ecophysiology and associated habitats. Evidence for fast-growing, weedy angiosperms comes from the Early Cretaceous Potomac Group, where angiosperm fossils, some of them putative herbs, are found in riparian depositional settings. However, inferences of growth rate from sedimentology and growth habit are somewhat indirect; also, the geographic extent of a weedy habit in early angiosperms is poorly constrained. Using a power law between petiole width and leaf mass, we estimated the leaf mass per area (LMA) of species from three Albian (110-105 Ma) fossil floras from North America (Winthrop Formation, Patapsco Formation of the Potomac Group, and the Aspen Shale). All LMAs for angiosperm species are low (<125 g/m(2); mean = 76 g/m(2)) but are high for gymnosperm species (>240 g/m(2); mean = 291 g/m(2)). On the basis of extant relationships between LMA and other leaf economic traits such as photosynthetic rate and leaf lifespan, we conclude that these Early Cretaceous landscapes were populated with weedy angiosperms with short-lived leaves (<12 mo). The unrivalled capacity for fast growth observed today in many angiosperms was in place by no later than the Albian and likely played an important role in their subsequent ecological success.

A Morphotype Catalogue, Floristic Analysis and Stratigraphic Description of the Aspen Shale Flora(Cretaceous–Albian) of Southwestern Wyoming

Abstract We describe 28 fossil plant morphotypes from the Aspen Shale flora (Cretaceous: middle to late Albian) in southwestern Wyoming. This impression flora includes 6 ferns, 1 sphenopsid, 2 conifers, 17 dicotyledonous angiosperm (dicot) leaves and 2 dicot reproductive structures. The Aspen Shale megaflora is most similar to that of Subzone IIB of the Potomac Group of the eastern United States. Analysis of the Aspen Shale sedimentology and botanical composition shows occupation of open, paludal sites by a succession of progressively more complex plant communities. Like other middle Cretaceous floras, these data suggest that early angiosperms were weedy, herbaceous to shrubby, early successional competitors to ferns on open substrates. The description and illustration of the Aspen Shale morphotypes is presented as an example of how an entire flora can be described and analyzed before full taxonomic determinations have been made.

Plant Ecological Strategies Shift Across the Cretaceous–Paleogene Boundary

The End-Cretaceous Impact Winter Killed Off Slow-Growing Plants The end-Cretaceous mass extinction caused the selective extinction of plant species with slow-growth strategies, consistent with an impact winter hypothesis.

The Fossil Flora of the Winthrop Formation (Albian-Early Cretaceous) of Washington State, USA. Part II: Pinophytina

ABSTRACT The Winthrop Flora is of middle to late Albian age (Early Cretaceous) and occurs in the Methow basin of north-central Washington State, USA. With an estimated diversity of more than 150 species, the Winthrop is the most diverse flora yet described from the Early Cretaceous of North America. This paper deals with the 38 species of gymnosperms or Pinophytina of the Winthrop Formation, consisting of three species of Pteridospermopsida, three of Cycadopsida, three of Ginkgoopsida, nine of Bennittopsida, 15 of conifers or Pinopsida, and five species whose assignment is uncertain below the level of the gymnosperms. We describe four new genera and 21 new species of Pinophytina. Overall, the gymnosperm component of the flora is concordant with that of other late Early Cretaceous floras of the Northern Hemisphere. However, several of its species are similar to those found in Jurassic sediments from Mexico and Central America and some of the cycadophytes and conifers have what we interpret as xeromorphic foliage.

The Fossil Flora of the Winthrop Formation (Albian–Early Cretaceous) of Washington State, USA. Part I: Bryophyta and Pteridophytina

Abstract A diverse fossil flora of middle to late Albian age occurs in the upper half of the Winthrop Formation of the Methow basin in north-central Washington State, USA. The formation represents a transition from marine to terrestrial conditions within what is inferred, on paleomagnetic and paleofloral grounds, to be an allochthonous tectonic terrane, known as the Baja BC block, which formed adjacent to western Mexico, about 3,000 km south of its present position. The fossil plants were deposited in a braided-stream setting, with the richest plant sites occurring just above incipient paleosols and within probable crevasse splays. The flora consists of approximately 145 species in the Hepaticopsida, Equisetopsida, Polypodiopsida, Pteridospermopsida, Cycadopsida, Ginkgopsida, Bennettitopsida, Pinopsida, and Magnoliopsida. Its floral diversity exceeds that of any other contemporaneous paleoflora in the Rocky Mountain region. Sixty percent of the species are angiosperms, with the ferns, the cycads, and the conifers each comprising from approximately 10% to 15% of the total. The present study treats the spore plants of the Winthrop Formation and is the first in a series of three papers to cover the complete flora. This first portion of the flora consists of one species of the Hepatcopsida; two of the Equisetopsida, including a remarkable occurrence of the relict genus Neocalamites; and 19 species of ferns, of which two belong to Blechnaceae, two to Dicksoniaceae, two to Gleicheniaceae, three to Matoniaceae, and 10 of uncertain relationship. Five species in this latter category belong in the problematical Mesozoic genus Cladophlebis. In the uncertain category, we also propose two new morphogenera for sterile fern leaves that will, hopefully, reduce some of the confusion caused by assigning fern leaves with such morphology to living genera. We describe 5 new genera and 10 new species of Pteridophytina here. Overall, the spore-plants of the Winthrop flora are concordant with those of other late Mesozoic floras from North America and Europe.

Earth history along colorado's Front range: Salvaging geologic data in the suburbs and sharing it with the citizens

the Denver Basin preserves >800 m of laramide synorogenic strata, which record basin accommodation, orogenic topography, and resultant orographic climatic effects. the basin also records the cretaceous-tertiary boundary event and the subsequent recovery of terrestrial ecosystems. Outcrops in the basin are modest and commonly consist of temporary constructionrelated excavations. the Denver Museum of nature & Science has coordinated a decade-long multidisciplinary program that includes paleontological research, stratigraphic studies, aquifer analyses, and basin evolution studies in this area. As part of this effort, the synorogenic strata were continuously cored in 1999. Unusually diverse floras exhibiting rainforest physiognomy, episodic sedimentation linked to pulsed orogeny, and stratigraphic controls on aquifer distribution and quality have emerged from beneath the urbanizing landscape. results of this work, summarized in painted reconstructions, have helped colorado residents and museum visitors gain insight into past climates and settings, and have helped inform decisions regarding the ongoing development of the region. INTRODUCTION the enigmatic laramide Orogeny can be analyzed through evaluation of the sedimentary debris shed from uplifted regions into adjacent basins. While the plate-scale genetic mechanisms responsible for the orogeny remain obscure (english and Johnston, 2004), increased precision in the analysis of synorogenic sediments can reveal patterns and trends that improve our understanding of regional tectonic development (Dickinson et al., 1988). During the laramide Orogeny, abrupt uplift of the eastern flank of the rocky Mountain Front range led to the dispersal of fluvial distributary systems carrying coarse clastic debris into the asymmetrically subsiding Denver Basin (Fig. 1) on the eastern periphery of the rocky Mountains. As the Front range mountains rose, >800 m of nonmarine strata accumulated in the basin. these sediments form the bedrock aquifers that are currently mined to supply drinking water to many communities along the Front range urban corridor. these same rock layers are also extremely fossiliferous: almost any excavation in the rapidly urbanizing Front range area yields exciting evidence of past flora, fauna, and landscapes. Fresh excavations are commonly only briefly available, so geological and paleontological work needs to be done on an opportunistic and expedient basis. For the past decade, a team of researchers from the Denver Museum of nature & Science (DMnS), supported by local, state, and national Science Foundation funding, has salvaged newly discovered fossils and worked to assemble the geologic history of the Denver Basin. During the same period, colorado’s population increased by 30%, with 80% of the state’s population concentrated in the Front range urban corridor (Mladinich, 2006). Dinosaurs are found in people’s basement excavations, and leaves from fossilized rainforests litter road cuts along busy freeways. Volcanic ash layers are found in city parks, and stratifigure 1. Geologic base map of the synorogenic strata in the Denver basin showing fossil plant localities and the K-t boundary. this map is a compilation of over 25 geologic maps with additional boundary information obtained by intersecting three-dimensional subsurface models created by using over 1400 oil, gas, and water well electric logs with the digital elevation model. Small outcrops of post-orogenic Castle rock rhyolite and Castlewood Conglomerate have been omitted for clarity.

The Snowmastodon Project: cutting-edge science on the blade of a bulldozer

GS A TO DA Y | SE PT EM BE R 20 15 Jeffrey S. Pigati, U.S. Geological Survey, Denver Federal Center, Box 25046, MS-980, Denver, Colorado 80225, USA, jpigati@usgs. gov; Ian M. Miller, Dept. of Earth Sciences, Denver Museum of Nature & Science, 2001 Colorado Blvd., Denver, Colorado 80205, USA; and Kirk R. Johnson*, Dept. of Earth Sciences, Denver Museum of Nature & Science, 2001 Colorado Blvd., Denver, Colorado 80205, USA