Abstract Detail

Paleobotanical Section

Steenbock, Christopher M. [1], Tomescu, Alexandru MF [1].

Resurrecting Sphondylophyton, an Early Devonian taxon with whorled appendages.

Sphondylophyton hyeniodes was described from a single slab of Lower Devonian Beartooth Butte Formation by Shultes and Dorf (1938) and is known only from sterile specimens. Relying primarily on the presence of whorled appendages, they assigned sphenopsid affinities to the fossils. Based upon four new specimens, and a revised interpretation of the depositional environment, Tanner (1983) found reason to doubt the initial interpretation of Sphondylophyton. We examined known specimens and documented a previously unknown specimen, which provides the clearest perspective of the characteristic whorled appendages, as well as additional examples of branching systems. The axes reach 4.5 cm in length and ca. 1-2 mm across. Internode length ranges from 2 cm in the basal region to ca. 1 mm in the apical areas; with internodes most commonly spanning ca. 0.6 cm. Well preserved examples show Sphondylophyton to bear four discrete determinate appendages that are not basally bifurcate as described by past authors. The appendages can reach up to 1 cm in length but typically measure ca. 0.7 cm and 1 mm across. Branches are associated with the whorls of appendages but due to the mode of preservation, their relationship to the appendages cannot be discerned. The characteristic whorled appendages of Sphondylophyton compare poorly to the features of early sphenopsids of similar age. Appendages of Middle Devonian putative members of the sphenopsid lineage (e.g., Ibyka, Pseudosporochnus) are determinate branching systems and do not form whorls. Whorled appendages are first known in the Late Devonian Eviostachya and then the Early Carboniferous Archaeocalamites. Furthermore, whorled appendages are characteristic of charaleans, as well as some rhodophyte and phaeophyte taxa. Given the marine depositional environment inferred for the Beartooth Butte Formation, we regard the assignment of sphenopsid affinities to Sphondylophyton as questionable and the dismissal of algal affinities premature.

Broader Impacts:

1 - Humboldt State University, Department of Biological Sciences, Arcata, CA, 95521, USA

Keywords:
Sphondylophyton
sphenopsid
algae
Wyoming
Devonian
Fossil.

Presentation Type: Oral Paper:Papers for Sections
Session: 4
Location: 555B/Convention Center
Date: Monday, August 2nd, 2010
Time: 8:30 AM
Number: 4001
Abstract ID:219