Abstract Detail

Fossil plants at the intersection of evo-devo and phylogeny: celebrating the contributions of Gar W. Rothwell to biodiversity and evolution

Rothwell, Gar [1], Stockey, Ruth [2].

Penetrating the perplexing Upper Cretaceous Parataxodium plexus from the Price Creek Formation of north slope Alaska - Will the real Parataxodium please stand up.

A critical reexamination of the original “compression” specimens of Upper Cretaceous organs described as Parataxodium wigginsii Arnold and Lowther from a terrestrial limestone block collected along the Colville River in northern Alaska reveals both that the assemblage includes at least four distinct taxa of conifer remains, and that the material is actually permineralized. Preservation quality and taphonomic alteration vary among the specimens, such that only some specimens preserve anatomy of excellent quality. Up to the present, two distinct sets of anatomical features have been recognized among the specimens. One suite of characters occurs in shoots with variable opposite-decussate/helical phyllotaxis and taxodioid leaf morphology, and a second suite is common to specimens with cryptomerioid leaves. Specimens with the former have a relatively large pith of cells with clear lumens, dense cortex, and prominent hypodermal sclerenchyma; specimens with the other have a relatively small pith of dark cells, less densely packed cortical cells with scattered stone cells, and little or no hypodermal sclerenchyma.  Section views of the former reveal flattened leaves with thin laminae, a distinct midrib, and a prominent zone of sub-epidermal sclerenchyma. Axillary pollen cones are attached to shoots with this first suite of anatomical characters. Such specimens correlate with the morphology of the holotype specimen of P. wigginsii. Leaves on the cryptomerioid shoots are characteristically much thicker in section views, and have scattered stone cells, an abaxial palisade, and much less sub-epidermal sclerenchyma. Seed cones attached to short sections of vegetative leafy shoots with the second suite of characters are most similar to Taiwania. Three other types of seed cones have yet to yield anatomical features or connections to vegetative shoots with taxonomically diagnostic features. These are 1) subspheriodal-cylindrical cones with sequoioid cone scales that are attached to slender “peduncles” with small distantly-spaced leaves, 2) ellipsoidal cones with an Athrotaxis-like appearance that are attached to slender shoots with taxodioid leaves, and 3) a subspheroidal cone with toothed cone scale maragins attached to closely-spaced cryptomerioid leaves. Up to the present, seed cones of the P. wigginsii plant have not been identified with confidence, and therefore, systematic affinities of Parataxodium within Cupressaceae remain equivocal.

1 - Ohio University/Orgon State Universtiy, Environmental and Plant Biology, Department of Environmental and Plant Biology, 318 Porter Hall, Athens, Ohio, 45701, USA
2 - Oregon State University, Department of Botany and Plant Pathology, 2082 Cordley Hall, Corvallis, OR, 97331

Late Cretaceous
Morphology and Anatomy

Presentation Type: Colloquium Presentations
Abstract ID:164
Candidate for Awards:None

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