BAGAHI-RIDING, NINA L. Department of Biological Sciences, Delta State University, Cleveland, MS 38733. - A study of megafossil leaves from the Aguja Formation, Big Bend National Park, Texas.
The North American records of Campanian (Upper Cretaceous) megafossil
plant localities are known primarily from the Atlantic Coastal Plain,
the central and northern Rocky Mountains and California. A
significant gap exists concerning plant megafossil localities that
border the southwestern margin of the former Western Interior Seaway.
A rare collection of leaf impressions, from the Upper Shale Member of
the Aguja Formation at Big Bend National Park, helps to reduce this
gap. These megafossils are preserved in tan to dark orange-brown,
oxidized shales and consist of extinct forms of Hamamelidaceae,
Lauraceae (Persea-tribe), Palmaceae, Zingiberales,
Cheirolepidiaceae, and Taxodiaceae. Specimens of juvenile and mature
leaves belonging to the Hamamelidaceae represent an undescribed genus.
This extinct genus has affinities to several extant genera of the
Hamamelidaceae including Corylopsis, Hamamelis,
Fothergilla, and Parrotiopsis. For example, major and
minor marginal venation patterns resemble those of Parrotiopsis
jacquemontiana Rehder; tooth apical projections are similar to
those of Corylopsis spicata Siebold and Zucc.; and the pattern
of secondaries, tertiaries, quaternaries and finer veins throughout
the middle portion of the lamina are similar to cleared leaf specimens
of Hamamelis virginiana L. The plant megafossils are
characteristic of plants that thrived on well-drained, channel levee,
or floodplain environments that experienced a pronounced dry season.
Key words: Aguja Formation, Campanian, Hamamelidaceae, Hamamelis, Lauraceae