Abstract
Although fossil conifer wood, leaves, and pollen have been known from the Upper Jurassic Morrison Formation of the Western Interior of North America for many decades, only a few conifer seed cones have been described as carbonaceous compressions and casts with little internal structure. Recently, however, over 60 silicified seed cones with preserved internal anatomy were amassed by collectors from 11 localities in northeastern and southern Utah and brought to the attention of palaeobotanists. Here we describe the silicified cones from Utah and compare them to one another in size, gross morphology and internal construction. The fossil material is sorted into five new morphotypes of seed cone. Morphotype 1 pertains to Araucariaceae, Morphotype 2 is most likely Pinaceae, and Morphotype 5 is Cheirolepidiaceae. The familial affinity of Morphotypes 3 and 4 cannot be determined at this time. Comparative size analysis based on volume calculations shows that Morphotypes 2, 3, 4 and 5 are extremely small, smaller than any Mesozoic araucarian seed cone, and that Morphotype 1 falls within the range of small fossil araucarian cones. Most cone-bearing localities are situated to the northwest, west, and south of Hanksville in southcentral Utah. With regard to palaeobiodiversity, if Araucaria delevoryasii Gee from Wyoming is included, there are now six morphotypes of seed cones that represent at least three conifer families in Utah and Wyoming. Because many conifers are arborescent and form forests, the new fossil evidence suggests that species-diverse conifer forests or woodlands were a major type of vegetation in the Morrison Formation during the Late Jurassic.
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Acknowledgements
This paper is dedicated to Johanna H.A. van Konijnenburg-van Cittert, fondly known as Han, a Mesozoic palaeobotanist and palynologist par excellence in Leiden, The Netherlands, as well as mentor and friend of C.T. Gee. All authors thank Homer Behunin, Dan Chure, Jalena Dayvault, Steven Hatch, Doug Moore and Martin Sander for help in collecting and the loan of fossil cones; Ken Carpenter for his outcrop map of the Morrison Formation which he has made freely accessible to researchers; Armin Schmitt, Peter Göddertz, Georg Oleschinski for technical assistance with microCT and image analysis; Armin Schmitt for image segmentation; Georg Oleschinski for conventional photography. We are also indebted to Hans Kerp and an anonymous reviewer for their helpful comments. This is contribution no. 161 of the Deutsche Forschungsgemeinschaft Research Unit 533, “Biology of the Sauropod Dinosaurs”, which generously provided fieldwork and meeting funding.
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This article is a contribution to the special issue “Green planet—400 million years of terrestrial floras. Papers in honour of JHA van Konijnenburg-van Cittert”
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Gee, C.T., Dayvault, R.D., Stockey, R.A. et al. Greater palaeobiodiversity in conifer seed cones in the Upper Jurassic Morrison Formation of Utah, USA. Palaeobio Palaeoenv 94, 363–375 (2014). https://doi.org/10.1007/s12549-014-0160-1
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DOI: https://doi.org/10.1007/s12549-014-0160-1