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Abstract Detail



Paleobotany

Fryer, Emma R. [1], Tomescu, Alexandru [1].

Conifer wood from the Lower Cretaceous of northern California: implications for Protocedroxylon taxonomy.

Protocedroxylon is a genus of fossil conifer wood established by Gothan in 1910. Characterized by an unusual combination of araucarioid radial tracheid pitting, transverse ray cell wall pitting (abietineentÜpfelung), simple crossfield pitting, and absence of resin canals, the genus has since been reported from across Laurasia and grown to over 25 described species. Over time, features contributed by new species have expanded the range of morphological variation well beyond that of the type species, for numerous characters, such as radial tracheid pitting seriation, tangential tracheid pitting, ray tracheids, traumatic resin canals, crossfield pit types, axial parenchyma, and tracheid septations, all of which now vary broadly within the genus. The concept of this genus has, thus, expanded to a significant degree, which led to problematic situations where Protocedroxylon species overlap partially with those of other fossil conifer wood genera and some features distinguishing species within Protocedroxylon are not always diagnostic. Two Early Cretaceous wood types from the Budden Canyon Formation of northern California share a number of features with one another and are relevant to the Protocedroxylon discussion. The first, a type assigned to Protocedroxylon, shares araucarioid radial tracheid pitting, abietineentÜpfelung, an absence of resin canals, and crossfield pit morphology with Gothan’s concept of the genus. The second type shares several significant features with Palaeopiceoxylon, including mixed radial tracheid pitting, crossfield pitting, abietineentÜpfelung, and non-traumatic resin canals. However, although both Protocedroxylon and Palaeopiceoxylon are valid genera, the differences in anatomy between the two Budden Canyon wood types fall well within the range of continuous variation in several characters spanned by species assigned to Protocedroxylon. This is due in large part to a proliferation of Protocedroxylon species as a result of taxonomic decisions based on characters that are known to vary within species and even within individuals. This situation has been compounded by longstanding lack of clarity in the terminology of some features and by international communication barriers. Recent efforts to address broader issues of similar nature in fossil wood studies have made progress with other genera, but efforts to establish the identity of the Budden Canyon woods highlight problems persisting within Protocedroxylon and the necessity of updating taxonomy within this genus. Reevaluation of currently described species to identify the types of characters used to distinguish them and to verify their suitability will enable the establishment of a more representative and functional taxonomic scheme for Protocedroxylon.


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1 - Humboldt State University, 1 Harpst Street, Arcata, California, 95521, USA

Keywords:
Protocedroxylon
conifer
fossil
wood anatomy
wood
Cretaceous
California
taxonomy.

Presentation Type: Oral Paper
Session: 5, Paleobotany Student Awards
Location: 204/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 8:45 AM
Number: 5003
Abstract ID:361
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award


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