HERENDEEN, PATRICK S.1* and SCOTT WING2. 1Department of Biological Sciences, George Washington University, Washington DC 20052; 2Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC 20560. - Papilionoid legume fruits and leaves from the Paleocene of northwestern Wyoming.
The fossil record of the Leguminosae is abundant and diverse in Eocene
and younger sediments. Caesalpinioideae, Mimosoideae, and
Papilionoideae were all diverse by the middle Eocene, and many fossils
are referable to extant genera. By contrast, the Paleocene record is
not diverse and the several taxa that have been reported are all
referable to the Caesalpinioideae. The fossils we describe here are
significant because they are Paleocene in age and are clearly
referable to the subfamily Papilionoideae. The fossil locality is a
fine-grained, abandoned channel fill deposit in the lower part of the
Willwood Formation in the northwestern Bighorn Basin of Wyoming.
Mammalian fossils from above and below the plant site indicate a
latest Paleocene age, probably not more than 100 ky prior to the
carbon isotope excursion that marks the Paleocene/Eocene boundary.
Other fossil plants from the site are consistent with a late Paleocene
age, including, Acer silberlingii, Deviacer,
Metasequoia, Corylites, Platanus raynoldsii, and
Macginitiea gracilis. The legume fossils at this site consist
of a single type of fruit and a single type of leaf, which are
inferred to represent the same plant species. The fossil fruits are
stipitate, membranous, and narrowly winged on the placental suture.
The fruits are ca. 10 cm long and contain numerous ovules. The seeds
are transversely oriented and have a prominent radicular lobe, below
which is the funiculus attachment. The co-occurring leaves are
imparipinnate and leaflet position varies from opposite to alternate
on a single leaf. This fossil taxon is not referable to an extant
genus, but it is most comparable to several genera in the tribe
Sophoreae, including Acosmium, Bowdichia,
Diplotropis, Sakoanala, and Maackia. A precise
understanding of relationships of this extinct taxon will require a
phylogenetic analysis that includes these and other basal woody
Key words: Leguminosae, Paleobotany, Paleocene, Tertiary