Abstract Detail

Paleobotanical Section

Fryer, Emma Rose [1], Tomescu, Alexandru M.F. [2].

Early Cretaceous permineralized wood with araucarioid characters in the Budden Canyon Formation of California.

The Budden Canyon Formation of northern California contains late Barremian – early Aptian near-shore marine calcium carbonate concretions that have yielded an abundance of plant fossils. One of these, the second type of wood to be described from this unit, is a fragment of coniferous wood. Tracheid pitting is exclusively radial, uniseriate to biseriate (in 51% of tracheids); pits are alternate, closely spaced and compressed against each other, sometimes forming hexagonal outlines. Callitroid thickenings are absent and opposite arrangement of pits is rare. Crossfield pits are cupressoid and taxodioid, 1-2 pits per crossfield. Growth rings are indistinct, with thin-walled latewood, one to two cells deep. Axial parenchyma are present but rare, with pitting on transverse walls. Resin canals are absent. Frequent resin plates are diffuse throughout the xylem. Rays are uniseriate to partly biseriate (29% of total), with a mean height of 15 cells. Ray parenchyma are pitted on the transverse walls and ray tracheids are absent. Among extant conifer families, this fossil only compares favorably to the Araucariaceae, based on the presence of biseriate alternate tracheid pitting devoid of callitroid thickenings, the absence of resin canals, and the lack of ray tracheids. The three extant genera of Araucariaceae also share with the Budden Canyon wood similar crossfield pit anatomy and resin plates. However, in contrast to the fossil, none of the extant Araucariaceae exhibit pitting on the transverse wall of ray parenchyma, and most of them lack axial parenchyma. Of the fossil wood types that possess both alternate, araucarioid tracheid pitting and ray parenchyma with transverse wall pitting (and taking into consideration recent taxonomic revisions and significant synonymization) the Budden Canyon fossil resembles Planoxylon (known only from the Cretaceous of Gondwana) and Protocedroxylon (a Laurasian Mesozoic genus), with which it shares the same type of ray pitting, radial tracheid pitting, crossfield pit type, and a lack of normal resin canals. However, differences in tangential tracheid pitting, number of pits per crossfield, distribution of axial parenchyma, and ray height, make conclusive placement of the Budden Canyon wood in either Planoxylon or Protocedroxylon tenuous, suggesting that it could represent a different taxon. The similarity of this fossil to the Araucariaceae is noteworthy considering the well-documented record of the family in the northern hemisphere during the Jurassic and Cretaceous, as well as the presence in the Budden Canyon Formation of a seed cone that exhibits some araucariaceous characters.

1 - Humboldt State University, 1 Harpst Street, Arcata, California, 95521, USA
2 - Humboldt State University, Department of Biological Sciences, 1 Harpst Street, Arcata, California, 95521, USA

Keywords:
fossil
Wood
Conifer
Anatomy
Araucariaceae
Cretaceous
California.

Presentation Type: Oral Paper:Papers for Sections
Session: 11
Location: Salon 5/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 11:15 AM
Number: 11005
Abstract ID:523
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award