No abstract

The recovery of identifiable plant remains intimately associated with a skeleton of Tyrannosaurus rex in southwestern Saskatchewan, Canada, provides the basis for interpreting the latest Maastrichtian (65.5–65 Ma) paleoenvironment of the region. Fossil plants from the site are described, and fruits formerly known as Aesculus antiquus Dawson or Ficus ceratops Knowlton are transferred to a new taxon, Spinifructus antiquus (Dawson) comb. nov. Study of the sediments of the Frenchman Formation that host the bones and plants, in combination with analysis of the plants, indicates that the regional climate was mesothermal and without winter frost, but with seasonal drought. The T. rex is believed to have roamed a broad river valley abundantly vegetated by a largely deciduous flora. The deciduous nature of the Saskatchewan paleovegetation, interpreted as a response to low winter light levels at high latitude, contrasts strongly with the contemporaneous vegetation of a few degrees latitude further south and leads to questions about how a dinosaur fauna survived in a region where the bulk of the vegetation entered an extended period of dormancy.

Fossil foliage and seed cones of Thuja (Cupressaceae) have been discovered in early Tertiary (Paleocene) sediments of the Eureka Sound Group on Ellesmere Island, Canadian Arctic Archipelago. Vegetative remains of the fossil species, Thuja polaris sp.nov., bear alternately branched, moderately divided, flattened, and pinnatelike sprays with scale-like, decussate leaves. Seed cones are oblong, bearing 8 – 9 pairs of thin, probably leathery cone scales with distinct, reflexed umbos. Fossil cones and foliage resemble closely those of extant Thuja plicata. However, fossil seed cones have twice as many pairs of scales as do extant species of Thuja. A review of the fossil record indicates that most Thuja-like vegetative remains which have been reported from Cretaceous and Tertiary deposits in the Northern Hemisphere are best assigned to form taxa and not to extant genera. Reproductive material from four Tertiary localities can be assigned to Thuja on the basis of seed cone structure. The evolutionary history of the genus, based on fossil and extant seed cone morphology, appears to include a reduction in the number of cone scales. Extant species form a closely related, natural group and, with the exception of T. sutchuenensis, may have arisen from an ancestor similar to T. polaris. Although Thuja was widespread in the Northern Hemisphere during much of the Tertiary, the genus is now confined to northeastern and northwestern North America, and to Japan, Korea, and central China.

Fossil cedar foliage of the Cupressinocladus interruptus type, with associated seeds and cones, is locally abundant in Paleocene deposits of the Ravenscrag Formation, southwestern Saskatchewan, Canada. Vegetative remains of this type occur frequently in early Tertiary plant assemblages throughout the northern hemisphere, indicating that this now extinct cedar was once widespread. For the first time this cedar can be described on the basis of both vegetative and reproductive morphology. Foliage is frond-like with a characteristic opposite branching pattern. Seed cones are globose and woody and bear four equal and decussate scales with prominent umbos. Seeds bear large, equal, semicircular wings. The fossil cedar appears most closely related to extant Cupressaceae such as Thuja, Chamaecyparis, and Heyderia. Foliage closely resembles that of Thuja, while cones are most similar to those of Chamaecyparis. The fossil differs sufficiently in foliage and seed cone structure to preclude assignment to an extant genus and is here assigned to Mesocyparis borealis gen. et sp. nov. Similarities among such extant genera as Thuja, Chamaecyparis, Heyderia, and Thujopsis and the fossil Mesocyparis borealis suggest that all may belong to a single natural group. Furthermore, this group may be more closely related to the southern hemispheric genera Libocedrus, Papuacedrus, and Austrocedrus than present classification schemes imply. Our examination of the Cupressaceae indicates that a revision of present systems of classification is required to accommodate evidence from both extant and extinct cedars.

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.