Abstract Detail

Paleobotanical Section

Parrott, Joan [1], Upchurch, Garland [1], Wheeler, Elisabeth [2], Mack, Greg [3].

Forest of Giants: An In situ Angiosperm Forest of Late Cretaceous South-Central New Mexico.

Leaf and pollen records document the abundant occurrence of Late Cretaceous angiosperms in a variety of sedimentary facies, including channel and floodplain environments. Interpretations of Cretaceous angiosperm stature vary, in part because of limited reports of large angiosperm woods, especially in situ assemblages. A newly discovered fossil forest of well-preserved, in situ angiosperms provides important data on Late Cretaceous angiosperm stature, diversity and ecology. The assemblage, from the Jose Creek Member of the McRae Formation, south-central New Mexico, is of late Campanian age (>74 to 75 myr, zircon U–Pb dating). It consists of at least 18 in situ angiosperm stumps and 6 angiosperm logs that represent riparian forest preserved in a sequence of fluvial sandstones. Preliminary study indicates two angiosperm wood morphotypes. The first is a eudicot characterized by vessels that are solitary and in radial multiples of 2 – 3, intervessel walls that are substantially thicker than vessel walls adjacent to parenchyma cells, simple perforation plates, alternate intervessel pits, paratracheal axial parenchyma, banded parenchyma, uniseriate rays of square and upright cells and heterocellular rays, 2 – 3 cells wide, with a body of procumbent cells with one to many marginal rows square or upright cells. Possible related families include Sapotaceae, Myrtaceae and Cornaceae. The second morphotype resembles Paraphyllanthoxylon. Its features include vessels that are solitary and in radial multiples of 2 – 3, simple perforation plates, alternate intervessel pits, scanty paratracheal axial parenchyma, rays 2 – 3 (up to 5) seriate, and septate fibers. However, the rays of many specimens contain numerous thick-walled cells, which are not known from the type species of Paraphyllanthoxylon. The new fossil forest contains the world’s largest known Cretaceous angiosperm tree (2.0 m diameter at the top of the buttress roots). Stem diameters range from 0.4 m – 2.0 m (average = 1.0 m), with buttress root diameters up to 3.0 m. Tree height is estimated at 12 – 29 m using the 1994 equation of Niklas, and 20 – 64 m using the 1986 equation of Rich et.al. Both morphotypes have features that are common in tropical woods, including the absence of well-defined growth rings and presence of large vessels vulnerable to freeze-induced embolisms. The Forest of Giants adds to a growing body of evidence from in situ assemblages for large angiosperm trees during the Late Cretaceous, especially in regions of warmer climate such as the southern Western Interior of North America.

Broader Impacts:

1 - Texas State University, Department of Biology, 601 University Drive, San Marcos, TX, 78666, USA
2 - DEPT OF WOOD & PAPER SCIENCE, 710 Dixie Trail, Raleigh, NC, 27607, USA
3 - New Mexico State University, Department of Geological Sciences, P.O. Box 30001, Las Cruces, NM, 88003

Keywords:
angiosperm
fossil wood
Late Cretaceous.

Presentation Type: Oral Paper:Papers for Sections
Session: 16
Location: Melrose/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 9:30 AM
Number: 16006
Abstract ID:451
Candidate for Awards:None