Abstract Detail

Paleobotanical Section

Klassen, Rachel [1], Shelton, Glenn W.K. [2], Bishop, Megan [1], Tomescu, Alexandru M.F. [1].

Gymnosperm-associated ascomycetes in the Early Cretaceous (Barremian-Aptian) Budden Canyon Formation, California.

Four types of ascomycete fruiting bodies are found associated with gymnosperms in the Early Cretaceous of California.  The fossil material is preserved by permineralization in nearshore marine deposits of the Budden Canyon Formation (southern edge of Klamath Mountains), in late Barremian - early Aptian layers (ca. 125 Ma).  Two of the fruiting body types are associated with cupressaceous shoots, a third is found on a cupressaceous seed cone, and the fourth occurs on bennettitalean foliage.  Type 1 includes spheroidal fruiting bodies (90-300µm diameter) embedded subepidermally in cupressaceous leaves and occurring singly or in tightly appressed pairs.  Their walls are up to 60 µm (10 cells thick), and consist of large cells (6-12µm).  Narrow ostioles open where the fruiting bodies push against the epidermis.  Type 2 fruiting bodies occur singly or in groups of up to five, attached superficially to stems around leaf axils.  They are spheroidal to irregularly shaped, 160-370µm in diameter.  The fruiting body wall is 30-90µm thick and consists of small cells (2.4-6.0µm) forming a darker outer layer up to 10 cells thick and an inner layer of delicate cells (up to 16 cells thick); these fruiting bodies open through a short neck.  Type 3 fruiting bodies occur on a cupressaceaous cone but their relationship to the plant tissues is unclear due to preservation.  They are spheroidal (124-130µm diameter), with pseudoparenchymous walls 30-45 µm thick.  Type 4 occurs subepidermally on bennettitalean pinnules as solitary fruiting bodies.  They are spherical (85-135µm diameter), with walls 12-20 µm thick consisting of large cells (6-12µm).  In all four types, the lack of contents (asci, spores) makes it difficult to determine whether the fruiting bodies are ascocarps or pycnidia and renders taxonomic placement challenging.  However, some features of types 1 and 2 suggest potential affinites.  The simple wall structure of type 1 fruiting bodies resembles that of unilocular dothideomycete ascostromata, which are diverse and commonly found subepidermally in living leaf tissue of modern conifers.  The wall structure and grouping of type 2 fruiting bodies, as well as their mode of association with stem tissues (hyphal proliferation through the bark, connecting fruiting bodies to the cambium), is reminiscent of stromatal perithecia of sordariomycete canker fungi, such as Nectria.  Perithecioid fruiting bodies are scarce in the fossil record, known from only a handful of pre-Cenozoic occurrences; the addition of four new types from the Budden Canyon flora contributes significantly to the ascomycete fossil record.

1 - Humboldt State University, Department Of Biological Sciences, 1 Harpst Street, Arcata, CA, 95521, USA
2 - Humboldt State University, Biological Sciences, 120A 13th Street, Arcata, CA, 95521, USA

Keywords:
Fossil
Ascomycota
Cretaceous
California
conifer.

Presentation Type: Oral Paper:Papers for Sections
Session: 8
Location: Whitewater/Grove
Date: Monday, July 28th, 2014
Time: 10:30 AM
Number: 8008
Abstract ID:809
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award