Paleocene Of Wyoming Research Articles

Revision of Piceoerpeton Meszoely (Caudata: Scapherpetontidae) and description of a new species from the late Maastrichtian and ?early Paleocene of western North America

AbstractThe scapherpetontid salamander Piceoerpeton is known from the latest Cretaceous to middle Paleogene of North America and was the last surviving member of that paedomorphic family. A suite of vertebral features differentiates Piceoerpeton from other scapherpetontids, including three atlantal features that are autapomorphic within the family: odontoid process reduced to an anteriorly short, nipple-like structure; ventral surface of odontoid process lacks an articular surface for contact with skull; and articular surfaces of anterior cotyles are deeply concave. Differences in inferred body size and vertebral structure permit the recognition of two congeners: P. willwoodense, a large-bodied species (estimated snout-vent length = 100 cm) from the late Paleocene of the Western Interior and early Eocene of the Canadian Arctic and the much smaller P. naylori new species from the late Maastrichtian and ?early Paleocene of Wyoming and Montana, USA. In terms of its older age, smaller size, and less derived vertebral features, P. naylori is potentially ancestral to P. willwoodense.

Phytogeographic implications of fossil endocarps of Menispermaceae from the Paleocene of Colombia

Fossil leaves of Menispermaceae were previously described from the Paleocene of Colombia. Because of strong homoplasy of leaf characters, the fossils could not be placed more specifically within recognized clades, and additional data were needed to specify intrafamilial and paleogeographic relationships during the Paleocene. Fossil endocarps of Menispermaceae were collected from the Cerrejón Formation, the recently discovered Bogotá flora, and Wyoming (∼60 Ma). We surveyed the endocarp morphology of almost all extant genera, conducted character optimization, a molecular scaffold analysis, and critically reviewed the related fossil genera. Parallel syndromes of fruit characters have appeared in unrelated clades of the family according to current phylogenetic reconstructions. However, mapping selected endocarp characters across those clades that contain horseshoe-shaped endocarps facilitates identification and phylogenetic assessment of the fossils. Three fossil species are recognized. One of them belongs to the extant genus Stephania, which today grows only in Africa and Australasia. Palaeoluna gen. nov. is placed within the pantropical clade composed of extant Stephania, Cissampelos, and Cyclea; this morphogenus is also recognized from the Paleocene of Wyoming. Menispina gen. nov. shows similarity with several unrelated clades. The new fossils from Colombia reveal a complex paleobiogeographic history of the recognized clades within Menispermaceae, suggesting a more active exchange among neotropical, paleotropical, North American, and European paleoforests than previously recognized. In addition, the new fossils indicate that neotropical forests were an important biome for the radiation and dispersal of derived lineages in Menispermaceae after the Cretaceous-Paleogene boundary.

Leaves of Cornus (Cornaceae) from the Paleocene of North America and Asia Confirmed by Trichome Characters

The identification of Cornus foliage in the fossil record previously has relied primarily on similarities in venation, particularly the eucamptodromous secondary veins and widely spaced, transversely oriented tertiary veins. These features, while consistent with Cornus, are not by themselves diagnostic for the genus. Double‐armed, acicular trichomes mineralized with calcium carbonate are an additional characteristic feature found in all extant species of the genus. The presence of such trichomes provides a means of confirming leaf impression fossils attributed to Cornus. Reexamination of previously described Cornus leaves from the Paleocene of the Rocky Mountains and Great Plains region leads us to reject Cornus nebrascensis Schimper (=Cornus newberryi Hollick) from the genus. Another species, Cornus hyperborea Heer, is provisionally accepted as Cornus based on its venation, although we were unable to confirm the trichomes in the type material from Greenland or in the assigned specimens from North Dakota. We also review other Eurasian Paleocene Cornus‐like leaf remains, including Cornus platyphylla Saporta and Cornophyllum hebridicum (Johnson) Boulter and Kvaček. We recognize two new Paleocene species, whose identity as Cornus is confirmed by the presence of characteristic trichomes and venation: Cornus swingii sp. n., from the Paleocene of Wyoming, Montana, and North Dakota, and Cornus krassilovii sp. n., from the Paleocene Tsagayan flora of Russia. These occurrences, along with fruit records, indicate that the extant genus was well established in the Northern Hemisphere early in the Tertiary.

Leaves and Fruits of Celtis aspera (Newberry) comb. nov. (Celtidaceae) from the Paleocene of North America and Eastern Asia

One of the most widely distributed and distinctive leaf types of the Paleocene in North America and eastern Asia, previously named Viburnum asperum Newberry, is shown to represent Celtis (Celtidaceae). Leaves of Celtis aspera (Newberry) comb. nov. exhibit a suite of features diagnostic of Celtidaceae, including pinnipalmate venation, successive abmedial branches of the lower pairs of secondary veins, and blunt to right‐angle, regularly spaced teeth with the principal vein of each tooth entering submedially. The leaves differ from those of modern species of Celtis by having strictly craspedodromous (rather than semicraspedodromous to camptodromous) secondary veins; yet, they occur in close association with unequivocal Celtis fruits at nine sites in the Paleocene of Wyoming, Montana, North Dakota, Saskatchewan, and eastern Russia (Kamchatka and Amur Region). The fruits are preserved as globose to ovoid endocarp impressions with four longitudinal ribs and reticulate surface sculpture diagnostic of the genus. Previously, the oldest record of Celtis confirmed by endocarps was from the Paleocene of Brazil in South America. Occurrences of C. aspera foliage and endocarps in eastern Russia as well as in the Great Plains region of the United States and Canada indicate that Celtis was already widely distributed in the Paleocene of the Northern Hemisphere, from ca. 64 to 56 million years ago.

Eostangeria Barthel (Extinct Cycadales) from the Paleogene of Western North America and Europe

Fernlike leaflets from the Paleocene of Wyoming and Eocene of Oregon are recognized as cycad foliage based on diagnostic epidermal structure. The fossils conform to Eostangeria Barthel, an extinct genus based on Eocene foliage from Germany, and are described as a new species, Eostangeria pseudopteris Kvaček et Manchester. Eostangeria resembles the extant South African cycad Stangeria T. Moore (Stangeriaceae) in gross morphology (featherlike leaflets with dentate margin), but the fossil more closely resembles Zamiaceae in epidermal structure. Convergence in pinnule form and venation makes it difficult to distinguish Eostangeria from Allantodiopsis Knowlton et Maxon, a fern common in the Paleogene of North America, whose epidermal anatomy remains unknown. However, the cycad can be distinguished in well‐preserved specimens by the presence of interstitial fibers and secondary veins that occasionally fuse at the margin. The occurrence of Eostangeria in the Tertiary of both Europe and North America indicates that it may have spread across the North Atlantic region.

An Extinct Genus with Affinities to ExtantDavidiaandCamptotheca(Cornales) from the Paleocene of North America and Eastern Asia

A new genus of Cornales is recognized based on infructescences and foliage from the Paleocene of Wyoming, Montana, and North Dakota in the United States; southern Alberta, Canada; Heilongjiang, northeastern China; and Kamchatka and the Koryak Upland, northeastern Russia. Amersinia obtrullata gen. et sp. nov. has globose to ellipsoid infructescences with four or five basal deciduous bracts and numerous obtrullate, trilocular fruits with epigynous calyces. Each locule bears one seed and has a dorsal germination valve near the apex. The infructescences and fruits show many similarities to those of extant Camptotheca, but the extant genus is distinguished by only one or two locules and the absence of infructescence bracts. Fossil leaves previously assigned to “Viburnum” cupanioides (Newberry) Brown, Viburnum kingiensis Chelebaeva, and Viburnum pseudoantiquum Golovneva are transferred to the extinct foliage genus Beringiaphyllum gen. nov. They are distinguished from Viburnum by their long petioles and compare favorably to the leaves of extant Davidia. The fossil leaves are elliptical to ovate with pinnate secondary veins, percurrent tertiary veins, and obtuse teeth. Beringiaphyllum leaves and Amersinia fruits are considered likely to represent a single extinct genus because of their shared cornalean affinity and co‐occurrence at numerous sites both in North America and Asia. Although the leaves share more characters with Davidia, the Amersinia fruits share more characters with Camptotheca. The existence of Amersinia and Beringiaphyllum both in Asia and North America, together with their absence or rarity in the Paleogene of Europe, indicates that this plant probably dispersed across Beringia in the late Cretaceous or early Tertiary.

Reproductive and vegetative morphology of Polyptera (Juglandaceae) from the Paleocene of Wyoming and Montana

The morphology, systematics, and ecology of the extinct juglandaceous genus Polyptera are interpreted on the basis of infructescences, fruits, staminate catkins, pollen, and compound leaves from the Paleocene of Wyoming and Montana. The elongate infructescences of Polyptera manningii bear numerous helically arranged sessile fruits. The fruit is a pyramidal nut with a vascularized husk and a multilobed disk-like wing adaptive for wind dispersal. Associated staminate catkins bear numerous helically arranged florets, each with six or more stamens. Pollen from the anthers is triporate and isopolar, with ultrastructure diagnostic of Juglandaceae, but with a pattern of exinous thinning characteristic of the extinct dispersed pollen type Maceopolipollenites anellus (Nichols et Ott) comb. nov. The correlated leaves, Juglandiphyllites glabra (Brown ex Watt) comb. nov., are deciduous, pinnately compound, and have five to seven petiolulate finely serrate leaflets. Systematically, Polyptera shows relationships both with the Hicorieae and the Juglandeae. Occurrences in the Torrejonian and Tiffanian stages of the Paleocene place Polyptera as the oldest unequivocal record of Juglandaceae. Polyptera manningii typically occurs in low-diversity assemblages of 8-15 species, and usually is a dominant or subdominant constituent of floodplain assemblages. It may have been an early-successional colonizer.