Abstract Detail

Paleobotany

Parrott, Joan [1], Upchurch, Jr., Garland [2].

Significance and Systematic Assignment Of Early Platanoid Fossil Woods from the McRae Formation.

Extant Platanaceae are composed of a single genus, Platanus, with 8 species native to North America, Europe, and Asia. Fossil woods indistinguishable from extant Platanus are assigned to the extant genus. Platanoids (Platanus-like woods) are reported from the late Tertiary and differ from Platanus by the incidence of solitary vs. grouped vessels, the incidence of simple vs. scalariform perforation plates and the distinctness of the growth boundaries, and are assigned to the fossil genus Platanoxylon. Platanoid woods from the Late Cretaceous to early Tertiary have been related to Platanaceae but differ from Platanoxylon and Platanus in features considered more primitive anatomically in the Baileyan model of wood evolution. Four platanoid woods from the McRae Formation, south-central New Mexico, of Late Campanion age (74–76 Ma) are compared to Cretaceous, Tertiary and extant platanoid woods to assess their evolutionary significance and systematic assignment. Woods from the crown group, Platanus, as well as probable members of the stem lineage (fossils), are assigned to Platanaceae on the basis of opposite intervessel pits, a combination of some exceptionally wide rays (>10 cells wide) along with very few or no uniseriate rays, and rays that are nearly homogeneous. McRae platanoid woods differ from Platanus and Platanoxylon by generally having exclusively solitary vessels and scalariform perforation plates, considered primitive in the Baileyan model, and no growth rings. However, several morphotypes show one or more intermediate features. One morphotype exhibits weakly developed growth boundary structure, while another has areas with somewhat narrower fibers and smaller vessels, both of which have a discontinuous distribution. One morphotype has some vessels in tangential groupings, while another has simple to scalariform combination perforation plates (i.e., a simple perforation plate opposite a scalariform plate at the zone of contact between two vessel elements). The diagnosis for Platanoxylon as amended by Suss and Muller-Stoll (1977) includes distinct or indistinct growth rings, a combination of simple and scalariform perforation plates (not simple to scalariform combination plates) and vessels solitary and in multiples. The McRae woods fall outside the generic diagnoses of Platanoxylon and do not have the exact combination of features of Platanus warranting assignment to a new genus. This is supported by the extensive and diverse record of fossil leaves, flowers and fruits, which document a major radiation of Platanaceae during the mid- to Late Cretaceous.

1 - Texas State University, Department of Biology, 601 University Drive, San Marcos, TX, 78666
2 - Texas State University, Department Of Biology, 601 University Drive, San Marcos, TX, 78666, USA

Keywords:
platanoid
Angiosperm woods.

Presentation Type: Oral Paper
Session: 7, Cookson/Moseley award presentations
Location: Sundance 4/Omni Hotel
Date: Monday, June 26th, 2017
Time: 11:30 AM
Number: 7006
Abstract ID:343
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award