The primary characteristic that classifies a lycopsid into the isoetalean clade is the presence of a non-branching, swollen or rounded root base (Pigg and Rothwell, 1983a, 1983b; Pigg,1992; Stewart and Rothwell, 1993). The extant group of Isoetales (Isoetes) represents the last remnant of a long line of isoetalean lycopsids whose origin is in the late Devonian to early Mississippian. Pre-Carboniferous isoetaleans are represented by the arborescent growth forms that include Lepidosigillaria and Protostigmaria (Stewart and Rothwell, 1993). The smaller, herbaceous growth forms of cormose lycopsids are now know to have arisen in the Middle Pennsylvanian (e.g., Chaloneria-type lycopods).

Chaloneria-type lycopsids have been the focus of study due to their predominance in late Carboniferous wetlands (Pigg and Rothwell, 1983a). Chaloneria cormosa is a permineralized isoetalean lycopsid, described as an unbranched, upright plant with a cormose base, from the Appalachian Basin. The height of this plant is estimated to have been approximately 2 meters, with a maximum diameter of approximately 10 centimeters. Leaves are known to spiral around the stem axis and, when broken off, produce irregular axial leaf scars. No leaf cushions are preserved on Chaloneria cormosa. The plant was heterosporous with fertile regions located towards the stem apex. Dispersed megaspores and microspores are assigned to Valvisisporites auritus and Endosporites globosa, respectively (Pigg and Rothwell, 1983a). In many ways, the Middle Pennsylvanian Chaloneria seems to bridge the gap between the upper Devonian tree-like cormose lycopsids and those herbaceous isoetalean lycopsids of the Triassic (e.g., Pleuromeia and Nathorstianella; Pigg, 1992).

In 1993, a large number of isoetalean-like lycopsids were discovered at a Lower Pennsylvanian outcrop in the Black Warrior Basin of Alabama. This material, which consists of cormose root bases, rootlets, decorticated stem segments, vegetative leaves, sporophylls, and sporangia containing megaspores, was loaned to Auburn University. The research project proposed herein intends to provide complete documentation and description of these recently discovered fossil plant remains in an attempt to fully reconstruct what is believed to be an isoetalean lycopod new to the fossil record. The specific objectives of my study are:

• to assess the character of each fossil plant organ represented within the study locale;
• to create a whole-plant reconstruction based on data obtained;
• to characterize the growth habit for the lycopsid in question; and
• to explore the implications of sedimentological data and other taxa present for an environmental restoration.

1.1 Stratigraphy

The outcrop, which is located southwest of Birmingham in the city of Homewood, Alabama, consists of two distinctive sandstone bodies each overlying what have been interpreted to be silty claystone paleosols. The extent of the outcrop appears to be highly localized because additional exposures of this interval have not been found within the Homewood area. If it were once traceable, industrial growth in the surrounding area has destroyed any potential data from adjacent outcrops. The orthoquartzitic sand bodies are massive (no thicker than 70 cm at the thickest point measured), and appear to be lobate.

1.2 Taphonomy

Lycopsid axes are found preserved erect as sandstone casts in the lower sandstone unit. Preliminary examination of thin sections made from these axes indicates that they were infilled by the enclosing orthoquartzitic sand. No plant remains have been documented in the uppermost sandstone unit, to date. Both the upper and lower paleosol contain well preserved compression fossils of stem axes, vegetative leaves, sporophylls, megasporangia, megaspores, and rootlets. A number of pteridosperm-type leaves and invertebrate bivalves have also been found within each paleosol.

2.0 METHODOLOGY

This research will focus on the analysis of both the sedimentological data and the five structurally distinct plant parts commonly preserved throughout the study area. To facilitate discussion, these materials will be grouped according to the methods by which they will be analyzed. Megaspores and other palynomorphs will be treated as a group; bases, rootlets, and axes will be treated as a group; and sporophylls, sporangia, and vegetative leaves will be treated as group. The fourth group to be examined will include non-lycopsid materials. These plants and invertebrates will be analyzed and catalogued separately according to their morphological features, and later used as possible paleoenvironmental indicators.

2.1 Outcrop Description

The outcrop will be thoroughly measured and described using basic field techniques. All sedimentological and fossil data will be recorded. Sandstone members will be examined petrographically in thin section, and compared with those data obtained from the sandstone that infills the casted stem axes. The claystone paleosol will be analyzed chemically using x-ray diffraction techniques and electron microscopy (EDAX). Sedimentological data obtained through these methods will be coupled with fossil plant and animal data, and used to create a possible paleoenvironmental reconstruction.

2.2 Megaspores and other palynomorphs

The megaspores are one of the more interesting aspects of this study. They are robust, ranging in size between 1.0-2.8 mm, and are easily recognized by characteristically long, "hooked" spines that protrude from their surface. Cursory examination of the megaspores found in the lower paleosol has proved inconclusive with regard to their systematic identification. Documentation of megaspore-size distribution and surficial characteristics is, therefore, crucial to this current investigation. Palynological analyses may also provide necessary data regarding microspore characteristics, as well as other taxa present within the depositional setting.

2.2.1 Palynological Analyses

To date, approximately ten to fifteen 1-cm³ samples of paleosol have been subjected to palynological analyses. Preparation techniques were carried out using the following procedures (Traverse, 1988): (1) dissolution in 10% dilute HCl to remove carbonate minerals; (2) washing to neutrality followed by the addition of concentrated HF to remove silicate minerals; (3) washing to neutrality followed by a warm 10% dilute HCl bath to remove any neo-formed fluorides; (4) washing to neutrality; and (5) centrifuged to concentrate the organic matter. Recovered palynomorphs were then mixed with a warmed glycerine jelly on glass slides. Coverslips were added, and slides were placed on a warming plate for approximately ten hours to facilitate adhesion. The slides will be analyzed optically using a Zeiss Axioscope equipped with epifluorescence.

2.2.2 SEM Analyses

Megaspores and microspores will be further examined through the use of scanning electron microscopy (SEM). Spores will be affixed to an SEM stub and sputter coated with gold in order to prepare them for viewing with a Zeiss 240 SEM microscope (personal communication, M.T. Sadler). The megaspore data that will be collected include spine length, abundance, surficial distribution, and potentially internal spore-wall anatomy. Microspore data will include surficial ornamentation, and if possible, spore-wall ultrastructure.

2.3 Bases, Rootlets, and Stem Axes

Cormose bases, rootlets, and stem axes will be morphologically characterized using basic comparative techniques. Plant-base size, shape, and number of lobes will be carefully measured and recorded; points of rootlet initiation will be determined. These features will be compared with those of other known fossil isoetalean lycopsids.

Rootlet characteristics will be determined based on the consideration of rootlet diameter, presence or absence of taper, bifurcation characteristics, and, if possible, vascularization. These data may make it possible to establish a growth habit for this particular lycopsid ( i.e., shallow vs deep rooting, determinate vs indeterminate growth).

Stem axes will be studied on the basis of preserved height, diameter, and taper. Utilizing the allometric approaches outlined by Niklas (1994), estimates for growth height will be attempted. External features, such as leaf scarring, will be analyzed to determine leaf phyllotaxy and possibly vascularization.

2.4 Sporophylls, Sporangia and Vegetative Leaves

A comparative analysis of both vegetative and fertile leaves will be conducted to determine if any differences exist between these two organs. Leaf shape, size, and general character will be recorded. Leaf epidermal features will be studied through the use of scanning electron microscopy in order to identify if any cell or stomatal patterns are present. Sporangia will be examined to determine if these plants were heterosporous or homosporous. These data will be useful in determining the reproductive nature of these plants. Because it is not known whether these plants produced apical cones or possessed alternating zones of reproductive and vegetative organs, a compilation of these vegetative and reproductive data may answer this question. Only the presence of megasporophylls has been noted throughout the study locale; no microsporophylls have been identified to date.

2.5 Other Taxa

Apart from the various lycopsid organs, several specimens of pteridosperm-type leaves and invertebrate bivalves have been collected from the study area. Specimens of what appear to be marine bivalves may be useful, when coupled with sedimentological data, in establishing a depositional setting for the study area. All non-lycopsid specimens will be characterized, identified, and catalogued for whatever information they might supply.

3.0 SIGNIFICANCE OF STUDY

Results of the proposed study will provide precise documentation of an Early Pennsylvanian origin for a growth form of cormose lycopsid known only from Middle and Late Pennsylvanian-aged strata. Thus, by analyzing the reproductive structures and morphology of this earlier member of the isoetalean clade, information that this research provides should prove to increase our current understanding of lycopsid phylogeny.