Search

A special section is devoted to the origin and evolution of life on earth. Topics include vertebrate paleontology, invertebrate paleontology, mass extinctions, geoarchaeology and human evolution, palynology or the study of pollen in paleoclimates, and paleobotany.

Over 80 specimens of a permineralized fruit referable to the Comaceae (Mastixioideae) have been recovered from the Princeton chert (Allenby Formation) of British Columbia, Canada. Specimens were studied using a modified cellulose acetate peel technique for hydrofluoric acid. Fruits with endocarps 11 mm long and up to 10 mm in diameter have a smooth stone surface, one U-shaped locule in cross section and a germination valve that extends the length of the fruit. An epicarp (exocarp + mesocarp) composed of thin-walled parenchymatous cells, 1.2-1.5 mm thick, was found on one specimen. Remains of an apical disc with remnants of perianth parts are seen in three specimens. The endocarp is composed of interlocking fibers with scattered resin ducts and vascular tissue that parallels the edges of the valve. Seed integuments consist of a single external layer of large cells with brown staining contents and an inner zone of 2-4 thin-walled cells of smaller diameter lacking contents. Numerous septate fungal hyphae are usually present in the integumentary layers. These fruits most closely correspond to the fossil genus Mastixicarpum Chandler and extant Diplopanax Handel-Manzetti and add to our knowledge of the diversity and distribution of North American mastixioids during the Tertiary.

Many of the problems involving taxonomic delimitation of extant Isoetes are inherent in the fossil record as well. As with living Isoetes, the reduced plant body of Isoetes-like fossils provides a limited number of morphological features that have been shown in extant forms to be highly variable and often convergent. The problem is compounded by a lack of concordance in the definition of both the family Isoetaceae and the genus Isoetes in light of the rich and long-ranging fossil record of the isoetalean clade. The tendency of fossil plants to be found as disarticulated fragmentary remains adds further to the problem. Although members of the isoetalean clade can be recognized by the Late Devonian, the oldest fossil plants that can be confidently interpreted as having a reduced plant body like that of extant Isoetes are Jurassic, with a variety of additional forms occurring in the Cretaceous and Tertiary. The most obvious feature distinguishing modern Isoetes and Isoetes-like fossils from all other members of the isoetalean clade is a reduced, non-elongating stem axis. Aside from this and possibly a few other features, most of the unusual morphological features of Isoetes are shared by the entire clade.

Thirty-one specimens of petrified Liquidambar-like infructescences (Hamamelidaceae) have been studied from the middle Miocene Yakima Canyon flora of central Washington State, USA. The infructesences are globose fruiting heads consisting of dense clusters with numerous fruits per head. Each fruit is a 2-carpelled capsule with each carpel containing 1-2 mature seeds and up to 10 variously shaped abortive ovules. Mature seeds are 1.5 mm high x 1.2 mm wide, winged, and triangular in cross section. Seed integuments have a prominent outer layer of palisade cells, a middle region of isodiametric cells, and an inner lining of tangentially elongate cells. These fossils are the first anatomically preserved reproductive remains of Liquidambar-like plants to be described from northwestern North America and demonstrate similarities both to Tertiary forms such as the European Eocene Steinhauera Presl and Neogene Liquidamber as well as extant forms of subfamily Liquidambaroideae (Hamamelidaceae).

Highly opalized petrified plant, fungal, and possible animal remains are described from a middle Miocene (15.1-15.8 million year old) deposit in the Virgin Valley of northwestern Nevada, known as the 'Cessily-Anne' locality. Plant remains from this site, thought to represent a lake margin environment, include conifer and dicot wood, vegetative buds, seeds assignable to cf. Decodon (Lythraceae) and abundant pollen and spores. Fungi are represented by well preserved ascomycete perithecia with bicellular ascospores, multicellular conidia and several types of spores, sporangia and hyphae. Unusual cuticular sheaths that bear pointed spines and cellular sheaths with geometrically patterned ornamentation may represent animal remains. The exquisite preservation of this assemblage is thought to be the possible result of rapid deposition of volcanic ash or ash fall and plant debris into a lake. This volcanic slurry was then gelled into a silicified deposit.

Susiea newsalemae Taylor, DeVore & Pigg gen. et sp. nov. is described for distinctive seeds referable to the water lily family Nymphaeaceae from the Late Paleocene Almont Flora of central North Dakota, U.S.A. Seeds are oval to barrel shaped, 5 mm long × 3 mm wide, and have an apical operculum and a prominent lateral raphe. The outer surface of the seeds is composed of palisade, shinglelike cells 40 µm high × 150 µm wide with smooth cell margins lacking papillae. The operculum is 1 mm across and surrounded by a narrow furrow, covering the micropyle but not the hilum. The raphe and micropyle are separated by several cells. Several specimens have a small embryo cavity surrounded by a small area of presumed endosperm below the micropyle and a well-developed perisperm filling the rest of the seed cavity. Susiea seeds are most similar to those of extant Euryale but differ in features of the epidermal cells, seed coat, and raphe morphology. They also share some features with Nymphaea, Nuphar, and Victoria. Susiea appears distinct from the permineralized fossil seeds of the middle Eocene Allenbya from the Princeton chert, Nuphar wutuensis from the Eocene of China, and Nuphar cf. wutuensis from the same Almont beds. Susiea is the oldest fossil taxon of the Euryale lineage, extending the previous Oligocene record back to the Late Paleocene and documenting a significantly older age for the Euryale/Victoria clade that is clearly a derived lineage based on phylogenetic analyses of modern taxa. [ABSTRACT FROM AUTHOR]

A developmental and anatomical study of the staminate flowers of Halophytum ameghinoi showed decussate tepal estivation; residual growth of the receptacle after stamen inception; monocotyledonous and basic types of anther wall development; secretory, binucleate tapetal cells; tetrahedral tetrads; and binucleate pollen grains. A vacuolate stage in the archesporial cells, the structure of endothecial thickenings, and a mechanism of anther dehiscence by connective contraction are new autapomorphies for this family. Anemophily is confirmed (Plantago-type syndrome), and field studies of pollen release showed a subtle mechanism involving rigid anther wall structure, versatile anther insertion, and abaxial subterminal pores. In air currents, while anthers flutter with pores directed upwind, pollen is extracted presumably by a cavitation effect of the hooded anther tip. In a phylogenetic context, anemophily of Halophytum is of isolated occurrence within Caryophyllales, and uniovulate ovaries in sister clades probably represent a prerequisite for evolution of anemophily. [ABSTRACT FROM AUTHOR]

The Quilchena fossil locality is dated (51.5 ± 0.4 Ma) to the Early Eocene Climatic Optimum, and this locality is reconstructed as the warmest and wettest of the Early Eocene upland sites from the Okanagan Highlands of British Columbia and northern Washington State. Mean annual temperature (MAT) is estimated from leaf margin analysis, using 55 dicot morphotypes, as 16.2 ± 2.1 °C/14.6 ± 4.8 °C. Using bioclimatic analysis of 45 nearest living relatives, a moist mesothermal climate is indicated (MAT 12.7-16.6 °C; cold month mean temperature (CMMT) 3.5-7.9 °C; mean annual precipitation (MAP) 103-157 cm/year. Leaf size analysis estimates MAP at 121 ± 39 cm/year. Estimates from the climate leaf analysis multivariate program corroborate these results, although with a slightly cooler MAT (13.3 ± 2.1 °C). Plants that support an interpretation of warm winters with minimal or no frost include Azolla, Glyptostrobus, Taxodium, Keteleeria, Pseudolarix, Eucommia, Dipteronia, Hovenia, Ternstroemia, and others. These thermophilous elements occur together with temperate genera such as Alnus, Betula, Ulmus, Calocedrus, and Fraxinus. Palynological assemblages at Quilchena are dominated by bisaccate conifers and Cupressaceae. Common angiosperms include Ulmus type, triporates, Pterocarya, and Alnus. Insect fossils at Quilchena that today inhabit tropical and subtropical regions also support warm and equable climate without significant frost, and include obligate palm-feeding beetles (Pachymerina), which indicate CMMT perhaps as high as 8 °C. These are found together with temperate aphids, wasps, giant lacewings, brown lacewings, and a panorpoid scorpionfly, supporting an interpretation of equable climatic conditions during the Early Eocene Climatic Optimum. [ABSTRACT FROM AUTHOR]