BERRIOCHLOA GABELI AND BERRIOCHLOA HULETTI (GRAMINEAE: STIPEAE), TWO NEW GRASS SPECIES FROM THE LATE MIOCENE ASH HOLLOW FORMATION OF NEBRASKA AND KANSAS

Journal of Paleontology, Jan 2005 by Thomasson, Joseph R

Elias (1942) recognized a distinct area of demarcation at the junction of the fused upper portion or apex of the lemma (summit of Elias, 1942, p. 41) and the awn in living and fossil Stipeae with a disarticulating awn. Although he did not provide a specific term for the area (I designate it the awn disarticulation joint), he did call the soft portion within the summit of the lemma the diaphragm. He indicated that three vascular trace scars could be observed in the diaphragm, one at the back and two on the sides.

If the margins of the lemma summit were differentiated and expanded laterally Elias (1942, p. 41, 62) called the expanded portion the crown and the contracted portion below the crown the neck. If a crown was absent, he simply referred to the apex or summit of the lemma and considered the lemma to be crownless. Barkworth (1990) and Jacobs et al. (1995) have suggested that the term crown should be used for the apex of lhe lemma whether expanded or not, but there is no reason to do so, especially because the crown, as a distinctive feature, was present on some species at least by the middle Miocene and absent on others (Elias, 1942). Because some fossil and modern Stipeae lack the expanded portion at the summit of the lemma (hence are crownless), the term crown should be retained only for those anthoecia with an expanded upper portion of the lemma at the summit.

Both B. gabeli and B. huletii have well-developed crowns, and when sufficient diaphragm tissue is absent within the awn disarticulation joint area, a flattened structure, the labrum, is found immediately behind the prow of the palea at the forward edge of the diaphragm (Fig. 7.3, 7.4). The labrum in these specimens is always distinct from the crown.

Berrichloa gabeli and B. huletti were found together twice, in Nebraska at site 52 and in Kansas at site 48, where the fossils were reported as B. intermedia (Thomasson, 1979b). At site 50 all occurrences of B. gabeli were stratigraphically above that of B. huletti. Beriochloa huletti was collected only at sites 48, 50, and 52. The significance of these observations is unknown.

DISCUSSION

Paleoenvironmentally the fossil biotas at both the Kansas and Nebraska sites suggest the presence of subtropical grasslands with both mesic (aquatic to emergent aquatic) and woody (riparian to savanna) components being present at or in the vicinity of the sites during deposition of the fossils. The recovery along with B. gabeli n. sp. of thousands of individual grass fossils of a number of species at the three most productive sites (50, 54, and 106) (Table 2) provides ample evidence of grasslands, and a similar abundance of the borage Biorbia fossilia and the hackberry Celtis willistonii (Cockerell) Berry, 1928b suggests other significant herbaceous and woody components.

The occurrence of diatoms, ostraeods, charophytes, ricegrass (Archaeoleersia nebraskensis Thomasson, 1980b), sedges (Carex graceii Thomasson, 1983, Cyperocarpus pulcherrima Thomasson, 1983, and Cyperocarpus terrestris Thomasson, 1983), a pondweed, (Midravalva sp.), and Ambystoma tigrinum Green, 1825 larval vertebrae (with delicate processes intact) together in units 8 and 9 at site 50 suggests standing water, although the complete absence of any fish among the numerous vertebrate fossils recovered may indicate the water was seasonal, perhaps due to pronounced wet and dry seasons (Thomasson, 1983; M. R. Voorhies, personal commun.). Other vertebrates collected in association with B. gabeli at site 50 from units 7 and 8 were a large tortoise (Geochelone sp.), a browsing probocidean (cf. Gomphoterium sp.), grazing and browsing rhinoceroses (Teleoceras sp. and Aphelops sp.), at least one grazing horse (Neohipparion sp.), a canid carnivore (Epicyon sp.), and numerous as yet unidentified mammals, amphibians, and birds. This fauna is consistent with a grasslands environment, and the presence of the tortoise suggests moderate temperatures that rarely, if ever, fell below 32 degrees F (Brattstrom, 1961; Holman, 1971).