The Platycarya Perplex and the Evolution of the Juglandaceae

Abstract

We report on the leaves, fruits, inflorescences, and pollen of two fossil species in the genus Platycarya. The association of these dispersed organs has been established by their repeated co‐occurrence at a large number of localities, and for two of the organs (fruit and pistillate inflorescence, and pollen and staminate inflorescence) by apparent organic attachment of compression fossils. Each of the two species can be distinguished by characteristics of all the known megafossil organs. We also review the fossil record of dispersed platycaryoid fruits and inflorescences, recognizing three additional species of Platycarya and two of Hooleya. Two of the fossil Platycarya species are morphologically very different from the living Platycarya strobilacea Sieb. et Zucc., but they show the diagnostic features of the genus. Hooleya is a generalized member of the Platycaryeae that is probably close to the ancestry of Platycarya. The two Platycarya species known from multiple organs provide a remarkable example of mosaic evolution in which fertile and foliar structures have attained different levels of morphological specialization. The leaves, often considered the most plastic of plant organs, retain several features that are otherwise seen only in the Engelhardieae. These similarities in leaf architecture between the fossil Platycarya species and Engelhardieae are advanced features for the Juglandaceae, and thus indicate a sister‐group relationship between the two lines. In contrast to the leaves, the fruits, inflorescences, and pollen of the fossil Platycarya species are almost as specialized as those of the extant P. strobilacea and bear little resemblance to the same structures in other genera of the family. The morphology, taphonomy, sedimentary setting, and geographic and stratigraphic distribution of three of the fossil platycaryoid species suggest that they were wind‐dispersed, early successional plants that grew in thickets. This habit is retained by Platycarya strobilacea and is typical of many of the amentiferae (e.g. Myricaceae, Betulaceae). The r‐selected life‐history pattern of the Platycarya line may well have contributed to its low diversity through geologic time.

Two large meteorite impacts at the Cretaceous-Paleogene boundary

“…Borehole 42/11 records minor weathering of the Boltysh impact suevite prior to the formation of a crater lake and deposition of the oldest sediments (associated with a mean δ 13 C value of −30.5‰), accompanied by an early-mid successional community of ferns and angiosperms (Wing and Hickey, 1984). Parallels with inter-lava fl ow durations in large igneous provinces (Jolley et al, 2008) and from modern lava fi elds (Vitousek, 2004) suggest that such communities can occur in sedimentary interbeds of 2-5 k.y.…”

The Earliest Remains of Grasses in the Fossil Record

“…Paleoclimatic and paleobiogeographic data suggest that these events took place under dry tropical to semitropical conditions (e.g., Upchurch and Wolfe, 1987). Modernization ofsome elements of the Normapolles lineage began at the Cretaceous-Tertiary boundary, and was followed in the Paleogene by the evolution of modern families and some genera (e.g., Juglandaceae, Betulaceae, Fagaceae; Crane, 1981;Wing andHickey, 1984, Dilcher andManchester, 1986;Manchester, 1987). By the uppermost Cretaceous, the first evidence of insect-pollinated Fagaceae appears in the fossil record with Paleocene-Oligocene evidence suggesting windpollinated taxa evolved and diversified during the latter interval -again in a warm dry climate (e.g., Crepet and Nixon, 1989a, b;Nixon and Crepet, 1989).…”

Palaeoenvironmental significance of marine and terrestrial Tertiary sediments on the NW Scottish shelf in BGS borehole 77/7

“…In contrast, areas of newly created saturated swamp will have been dominated by Momipites spp. (Juglanaceae), perhaps forming a late hydrosere of early successional vegetation (Wing and Hickey 1984). In drier areas of greater environmental stability, 'climax' stable swamp forests dominated by a mixture of deciduous and evergreen broadleaved angiosperms are developed.…”