Abstract Detail

Paleobotany

Contreras, Dori [1], Upchurch, Garland [2], Looy, Cindy [3].

Diversity and distribution of Monocots from a single tuff layer in the upper Campanian Jose Creek Member, McRae Formation of New Mexico.

Monocotyledons are well represented in Late Cretaceous floras and form a prominent part of the vegetation from the upper Campanian Jose Creek Member, McRae Formation, south-central New Mexico. Here we describe monocots preserved in an extensive horizon of recrystallized volcanic ash and reconstruct their presence across the landscape. The fine-grained ash layer, dated to 74.7 Ma, was deposited on an alluvial plain located over 200 km inland of the Western Interior Seaway. It preserves a diverse flora in relative growth position, including leaves, stems, reproductive material, and in-situ stumps. Quantitative sampling of leaf macrofossils from over 20 quarries spanning the ~1.2 km exposure demonstrates an angiosperm-dominated flora (95%of species; 74% of specimens; 84% of total leaf cover). Monocots represent 26% of the total specimens but only eight species (6% of total diversity). The most common monocot is the ground cover rosette plant Zingiberopsis, an early representative of Zingiberales, which occurs across the deposit and represents over 16% of the specimens in the flora and 32.5% of leaf cover. The costapalmate palm leaf Sabalites occurs in several quarries across the deposit, accounting for 6% of specimens and 8% cover. Also present are probable palm petioles with thick spines assignable to Bactricites. Three taxa with strap-shaped leaves are also present but not widely distributed and only locally abundant. These include Pandanites, which has leaves that are M-shaped in transverse section, one order of parallel veins, irregularly spaced and oriented transverse veins, and marginal and midrib spines. Pandanites probably represents a rosette shrub or rosette tree, based on similarities in leaf architecture with members of Pandanales (Pandanaceae and Velloziaceae). A second taxon is also M-shaped in transverse section but has entire margins with four orders of parallel veins and short perpendicular cross veins. Uncommon elements include Araceae and/or possible stem relatives, including leaves of Orontiophyllum mackii and a second taxon, and sporadic permineralized monocot stems. The JCM monocots lived alongside diverse non-monocot angiosperms, four species of conifers, a cycad, and low-abundance ferns. There was a strong dominance structure in which only a few species are common across the landscape, the most common being Zingiberopsis, Sabalites, a sequoid conifer, a Brachyphyllum conifer, and the eudicot Dryophyllum (Fagales). The JCM flora demonstrates that monocots were important elements of a stable floodplain of the southern Western Interior and that they formed a major component of ground cover relative to ferns and other free-sporing plants.

1 - University Of California Berkeley, UC Museum Of Paleontology, 1101 Valley Life Sciences, Berkeley, CA, 94720, United States
2 - Texas State University, Department Of Biology, 601 University Drive, San Marcos, TX, 78666, United States
3 - Integrative Biology, 3060 Valley Life Sciences Bldg #3140, Berkeley, CA, 94720, United States

Keywords:
angiosperms
monocots
Campanian
Cretaceous
fossil leaves
paleobotany.

Presentation Type: Oral Paper
Session: 28, Cookson Award Session I
Location: 109/Mayo Civic Center
Date: Tuesday, July 24th, 2018
Time: 2:15 PM
Number: 28004
Abstract ID:953
Candidate for Awards:Maynard F. Moseley Award