A new fossil assemblage shows that large angiosperm trees grew in North America by the Turonian (Late Cretaceous) - PubMed (original) (raw)

A new fossil assemblage shows that large angiosperm trees grew in North America by the Turonian (Late Cretaceous)

Nathan A Jud et al. Sci Adv. 2018.

Abstract

The diversification of flowering plants and marked turnover in vertebrate faunas during the mid-Cretaceous transformed terrestrial communities, but the transition is obscured by reduced terrestrial deposition attributable to high sea levels. We report a new fossil assemblage from multiple localities in the Upper Cretaceous Ferron Sandstone Member of the Mancos Shale Formation in Utah. The fossils date to the Turonian, a severely underrepresented interval in the terrestrial fossil record of North America. A large silicified log (maximum preserved diameter, 1.8 m; estimated height, ca. 50 m) is assigned to the genus Paraphyllanthoxylon; it is the largest known pre-Campanian angiosperm and the earliest documented occurrence of an angiosperm tree more than 1.0 m in diameter. Foliage and palynomorphs of ferns, conifers, and angiosperms confirm the presence of mixed forest or woodland vegetation. Previously known terrestrial vertebrate remains from the Ferron Sandstone Member include fish teeth, two short dinosaur trackways, and a pterosaur; we report the first turtle and crocodilian remains and an ornithopod sacrum. Previous studies indicate that angiosperm trees were present by the Cenomanian, but this discovery demonstrates that angiosperm trees approaching 2 m in diameter were part of the forest canopies across southern North America by the Turonian (~92 million years ago), nearly 15 million years earlier than previously thought.

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Figures

Fig. 1

Fig. 1. Cretaceous woods.

Map of Turonian localities in western North America with angiosperm woods >10 cm in diameter and stacked area curve showing the contribution of this discovery (indicated by star) to the global record of Cretaceous angiosperm woods. Ages are midpoint estimates. The gray area indicates the maximum observed angiosperm diameter through the Cretaceous. Dashed box indicates Turonian occurrences shown in the map above. Inset shows the new angiosperm log in the field (Photo Credit: M.D. D’Emic, Adelphi University). During much of the Late Cretaceous, the Western Interior Seaway divided North America into Appalachia in the east and Laramidia in the west. Map modified from Blakey (38).

Fig. 2

Fig. 2. P. cf. alabamense UF 19462-69143.

(A) Photograph of the log in the field. (B) Transverse section (XS) showing diffuse porous wood with vessels in short radial multiples of 2 to 11, growth rings absent, axial parenchyma rare, radial bands of fibers, and rays roughly the same width. (C) Tangential longitudinal section (TLS) showing crowded, hexagonal pits on the vessel wall. (D) TLS showing closely spaced lens-shaped 2- to 4-seriate rays among elongate fibers. (E) Radial longitudinal section showing rows of procumbent and upright ray parenchyma cells. (F) XS showing thin-walled ray cells (at left) and medium thick-walled fibers (at right). Scale bars, 500 μm (B), 100 μm (C), 250 μm (D), 200 μm (E), and 50 μm (F). (Photo Credits: A: M.D. D’Emic, Adelphi University; B to F: N.A. Jud, University of Florida)

Fig. 3

Fig. 3. Plant compression fossils from the Ferron Sandstone of Utah.

(A) Leafy shoot of E. curvifolia (Dunker) Nathorst; UF 19523-70170. (B) Close-up of (A). (C) Indeterminate angiosperm leaf; UF 19523-70171. (D) Isolated fern pinnule; UF 19523-70170. Scale bars, 5 mm (A to C) and 3 mm (D). (Photo Credits: N.A. Jud, University of Florida)

Fig. 4

Fig. 4. Vertebrate fossils from the Ferron Sandstone of Utah.

(A) Tooth of C. crassidens BMRP 2017.8.1. (B) Crocodyliform teeth 2017.8.5 (left), 2017.8.4 (center), BMRP 2017.8.3 (right). (C) Dorsal turtle scute BRMP 2017.8.6. (D) Ornithopod sacrum BMRP 2017.8.2. (Photo Credits: S.A. Williams, Burpee Museum of Natural History)

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