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Abstract Detail



Paleobotany

Atkinson, Brian [1].

Initial diversification of rosids: Fossil evidence for a Cretaceous origin of the Mahogany family, Meliaceae (Sapindales).

The rosid clade consists of over 70,000 extant species within two major clades: the fabids and malvids. Despite having an extensive fossil record extending back into the mid-Cretaceous (~100 Ma), it is notoriously difficult to accurately place fossils within the current rosid phylogenetic framework, apart from Fagales (fabids) and Brassicales (malvids). Thus, our understanding of the Cretaceous diversification of rosids is murky at best. In this study, a new rosid assignable to Meliaceae (Sapindales, malvids), the Mahogany family, is characterized based on a permineralized fruit (with attached abraded floral parts) from the Upper Cretaceous (~79 Ma, Campanian) of western North America. The fruit consists of a fleshy mesocarp and a thick woody endocarp with dorsal ridges and a hollow center. Serial sections of the fruit indicate that there are nine locules, some of which are abortive. The mesocarp is composed of palisade-like parenchyma with amber-colored contents. The endocarp consists of interlocking sclereids and uni- to biseriate layers of circum-locular fibers. Opposite of each locule there is a loculcidal suture. Within the hollow center there are vascular bundles that run along the ventral surface of each carpel. There is one sub-apically attached seed per locule, each with a somewhat swollen hilum. Seeds appear to be abortive and have a thin integument. Comparative analysis indicates that fruits with syncarpous multicarpelate (>five) fruits with thick sclerenchymatous endocarps that have a hollow center and one sub-apically attached seed per locule are highly indicative of Meliaceae, more specifically the genus Melia within the subfamily Meliodeae. However, the Cretaceous fruit differs from other Melia species (fossil and extant) by having interlocking sclereids comprising the endocarp wall rather than interwoven elongate fibers. Thus, the fossil described in this study represents a new taxon and is likely a stem member of Melia. This fossil fruit is the first evidence of Meliaceae from the Cretaceous and is among the earliest representatives of the order Sapindales, which sheds light on the timing of phylogenetic diversification within the malvid clade.


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1 - University of Kansas, Ecology and Evolutionary Biology and Biodiversity Institute, 1200 Sunnyside Drive, Haworth Hall, Lawrence, Kansas, 66045, United States

Keywords:
Cretaceous
Meliaceae
rosids
malvids
core eudicots
fruit
anatomy.

Presentation Type: Oral Paper
Session: 24, Late Mesozoic and Cenozoic Paleobotany
Location: 109/Mayo Civic Center
Date: Tuesday, July 24th, 2018
Time: 10:45 AM
Number: 24003
Abstract ID:327
Candidate for Awards:None


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