Morphology and relationships of Mesocyparis umbonata sp.nov.: fossil Cupressaceae from the Late Cretaceous of Alberta, Canada

Abstract

Late Cretaceous silicified Cupressaceae remains, recently recovered from the Horseshoe Canyon Formation of Alberta, Canada, include three-dimensional leafy twigs of the Cupressinocladus interruptus type with attached seed cones, seeds, pollen cones, pollen, and woody stems. The abundance and excellent preservation of the remains allows detailed description of most aspects of the plant, including foliage, reproductive organs, epidermal features, and wood. Foliage of the fossil is frondlike and flattened, with an opposite, less commonly alternate, branching pattern. Seed cones, borne in decussate pairs, are globose, woody, about 4.0 mm in diameter, and bear four approximately equal-sized cone scales with small umbos near the scale center. Each seed has two broad, semicircular wings. Pollen cones are typical for the Cupressaceae; pollen grains are structurally comparable, but small, for the family. Fertile branches and seed cones are not identical to any extant member of the Cupressaceae, but they are sufficiently similar to those of the Paleocene cedar Mesocyparis borealis from Western Canada to be referred to that genus. Dissimilarities justify assignment to Mesocyparis umbonata sp.nov. Seed cone structure of Mesocyparis umbonata resembles most closely that of the northern hemispheric taxon Chamaecyparis nootkatensis; the leaves resemble those of Thuja and Chamaecyparis. Other features, including the number of seed cone scales, branching pattern, and wood anatomy, are more comparable to those of taxa of the southern hemispheric Libocedreae. New information, based on these remains, indicates that the relationship between some northern and southern hemispheric taxa is closer than previously proposed, supporting the premise that present systems of classification separating these taxa do not reflect phylogeny. Key words: Cupressaceae, Mesocyparis, Late Cretaceous, fossil, seed cones, evolution, phylogeny.

Ecological Aspects of the Cretaceous Flowering Plant Radiation

“…An approximately coeval flora from the Almond Formation in southern Wyoming occurs in an ashfall within a coal and is similar to the Meeteetse floras both in species composition and dominance by non-angiosperms (Tiver et al 1994). Further north, megafioras from the Late Cretaceous of Alberta found in the Horseshoe Canyon Formation are dominated by conifers (Mclver & Aulenback 1994).…”

An early Chamaecyparis (Cupressaceae) from the Late Cretaceous of Vancouver Island, British Columbia, Canada

“…5, 7). Leaves of Chamaecyparis corpulenta are comparable to those of Mesocyparis umbonata in both length and width, while those of Mesocyparis borealis are slightly longer (McIver and Aulenback 1994).…”

“…Lateral leaves of Mesocyparis are closely appressed to the facial leaves for about two-thirds of their length; the upper third of the leaf, including the mucronate tip, is free (McIver and Basinger 1987;McIver and Aulenback 1994). Lateral leaves of Chamaecyparis corpulenta are closely appressed to the facial leaves, and only the mucronate tip is free (Figs.…”

“…Chamaecyparis corpulenta (Bell) comb.nov., like the Late Cretaceous and early Tertiary species of Mesocyparis McIver & Basinger (McIver and Basinger 1987;McIver and Aulenback 1994), bore seed cones with four scales. In fact, for all Cretaceous Cupressaceae presently known, seed cones bore four scales (McIver and Basinger 1987;Golovneva 1988;McIver and Aulenback 1994). Chamaecyparis corpul e n t~, the earliest available Cupressaceae revealing seed-cone morphology, provides a n appropriate basis for reconsidering proposed hypotheses o n the evolution and origin of extant lineages.…”

Introduction to the Special Issue commemorating the 30th anniversary of the Royal Tyrrell Museum of Palaeontology, with a summary of the museum’s early history and its research contributions

“…Also notable is the discovery of an ironstone-hosted plant locality in the late 1980s by then-RTMP technician Kevin Aulenback, just east of the museum and within the upper Campanian portion of the Horseshoe Canyon Formation. Kevin developed an acid bath technique (Aulenback and Braman 1991) that permitted the recovery of hundreds of silicified, three-dimensionally preserved plant fossils, such as stems and cones (e.g., McIver and Aulenback 1994;Aulenback and LePage 1998;Bogner et al 2005;Aulenback 2009). …”