Abstract Detail

Paleobotany

Abidi, Shayda [1], Tomescu, Alexandru [1].

An anatomically preserved marsileaceous sporocarp from the Lower Cretaceous of northern California (Budden Canyon Formation, Barremian-Aptian boundary).

The Budden Canyon Formation is an Early Cretaceous marine unit exposed in northern California that contains plant fossils. The age of this unit is Valanginian-Turonian, based on invertebrate and radiolarian biostratigraphy. Layers of the Budden Canyon Formation dating to the Barremian-Aptian boundary (ca. 125 Ma) have yielded a rich anatomically-preserved flora near the town of Ono. This fossil flora includes bryophytes, fungi, gymnosperms, as well as pteridophytes. One of these fossils represents a thick-walled reniform reproductive structure ca. 3.1 mm long and 1 mm wide. The wall of this specimen consists of two layers with differing anatomy. The thick outer layer is a sclerenchymatous palisade layer with cells ca. 30 µm across and 90-150 µm tall. The inner layer, often compacted, is 2-3 cells thick and consists of small parenchyma ca. 6-8 µm across. Inside this reproductive structure, incomplete thin partitions protrude 80-500 µm from the wall toward the center. These partitions consist of thin elongated cells and most of them are bifurcated. The specimen shows evidence of a longitudinal slit, suggesting bi-valvate dehiscence. Additionally, the fossil features a conical protrusion at one end, in a region where the wall is much thicker. The protrusion is located above the site where the wall is traversed by a fine vascular bundle of scalariform tracheids surrounded by parenchymatous tissue. Although devoid of content, this reproductive structure is similar in morphology and wall anatomy to marsileaceous sporocarps. Like in the latter, fine, inconspicuous veins are present in the inner wall layer. Fossils of marsileaceous affinity can be traced to the base of the Cretaceous and few – represented by spores – cross into the Late Jurassic. Sporocarp records are sparse and known only from the Late Cretaceous onwards, with the notable exception of a Regnellites sporocarp occurrence from Japan, dated to the Late Jurassic - earliest Cretaceous. Anatomically preserved sporocarps are known only in two pre-Cenozoic taxa, Regnellidium and Rodeites from the Late Cretaceous. The Ono sporocarp is similar in its bi-valvate dehiscence to Marsilea, Regnellidium, and Rodeites and, like some species of Marsilea, it features an inferior tooth. However, unlike these genera, it has a palisade layer only one cell thick. The Ono sporocarp is the second pteridophyte component in the anatomically-preserved flora of the Early Cretaceous Budden Canyon Formation. This is only the second marsileaceous sporocarp occurrence that pre-dates the Late Cretaceous and the oldest to yield anatomical preservation.

1 - Humboldt State University, Biological Sciences, 1 Harpst St, Arcata, CA, 95521, USA

Keywords:
Marsileaceae
fossil
Cretaceous
California
sporocarp
anatomy
fern.

Presentation Type: Oral Paper
Session: 5, Paleobotany Student Awards
Location: 204/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
Time: 9:00 AM
Number: 5004
Abstract ID:877
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award