Gene Mapes

Thucydiaceae Fam. Nov., with a Review and Reevaluation of Paleozoic Walchian Conifers

Abundant fossils of a single conifer species occur in a Pennsylvanian‐age deposit of eastern North America, providing the opportunity to describe a biological taxon of primitive conifers as well as to clarify the uncertain taxonomy and systematics of walchian conifers. Thucydia mahoningensis gen. et sp. nov. is represented by up to three orders of interconnected vegetative and fertile shoots that are preserved as coalified compressions with cuticles; some also display internal anatomy. The plant has an orthotropic stem, with two orders of plagiotropic lateral branches that all bear helically arranged simple leaves. Ovulate fructifications consist of compact zones of bracts with axillary ovuliferous dwarf shoots on otherwise vegetative branches. Pollen cones are compound shoots comprising helically arranged dwarf shoots in the axils of bracts on a main axis. Polliniferous dwarf shoots produce sterile scales, sporophylls with a terminal pollen sac, and in situ Potonieisporites grains. Stems have an endarch eustele with dense wood, periderm, and resin canals in the pith. There are two adaxial stomatal zones on vegetative leaves, but stomata are distributed over the entire adaxial surface of bracts and sterile scales. Thucydia is the only conifer with ovuliferous fertile zones, compound pollen cones, and dissimilar stomatal distributions on vegetative and fertile leaves. This novel combination of features characterizes the Thucydiaceae fam. nov. The currently confused state of primitive conifer taxonomy is reviewed, nomenclature is clarified, and revised approaches for inferring relationships are proposed. Thucydia provides a benchmark for developing sound taxonomic concepts and useful criteria for identifying specimens of walchian species and for resolving phylogenetic relationships among fossil and living conifers.

Hanskerpia gen. nov. and phylogenetic relationships among the most ancient conifers (Voltziales)

A new fossilized walchian (Voltziales) conifer plant from the Late Pennsylvanian Hamilton Quarry of Kansas, U.S.A. combines morphological characters of the morphogenus Walchia and the fossil plant genus Otovicia, with cuticular characters like those of the fossil plant genus Ernestiodendron, and seed cone morphology like that of the fossil plant genus Emporia. Internal anatomical characters are basically similar to the other walchian genera for which such features are known, but some are taxonomically informative. Numerical cladistic analysis reveals that this novel combination of characters defines a new fossil plant genus and species of walchian conifers Hanskerpia hamiltonensis. This analysis provides a test of hypotheses for relationships among walchian and other ancient conifers. Results of this analysis support some previously proposed relationships among the most primitive conifers and other Paleozoic coniferophytes. However, the analysis also calls to question the validity of all previously proposed familial circumscriptions for walchian conifers, and highlights the perplexing systematic challenges posed by the most ancient fossil conifers. The unexpected species richness of voltzialean conifers is interpreted as having resulted from the evolutionary ecology of unstable environments.

Late Paleozoic conifers of North America: structure, diversity and occurrences

Abstract Late Paleozoic conifer communities originated in moisture-stressed environments along the paleoequator on the Laurussian continent. By Late Permian time, northward movement of the continent displaced these communities toward subequatorial regions. North American deposits provide the most abundant and best preserved pre-Permian conifer fossils. They represent a wide spectrum of preservational modes including compression/impression, mold/cast, and cellular permineralization by carbonates, phosphates, iron sulfides, iron oxides and iron hydroxides. Some modes are associated with distinct biotic assemblages, and to some extent each can be correlated with certain depositional environments and taphonomic histories. Exceptional floras containing extensive conifer remains occur in the Rocky Mountains, the Midcontinent, and the Appalachian regions. These include: estuarine carbonates at Hamilton and Pomona, Kansas; transitional terrestrial to marine clastics at Kinney Brick Quarry, New Mexico, Garnett, Kansas and the 7–11 Mine in northeastern Ohio; and offshore marine shales in Kansas, Oklahoma and Texas that were deposited in dysoxic environments. Most specimens have been assigned to the form genus Walchia , but exceptionally well preserved specimens conform to species of Emporia (Emporiaceae) and to one or more undescribed species that may represent additional genera and/or families. These species add significantly to the growing diversity of Paleozoic conifers, and provide valuable data for testing hypotheses of conifer and coniferophyte relationships.

Barthelia furcata gen. et sp. nov., with a Review of Paleozoic Coniferophytes and a Discussion of Coniferophyte Systematics

A conifer‐like plant occurs among the rich fossil biota at the Late Pennsylvanian–age Hamilton Quarry in southeastern Kansas. Barthelia furcata gen. et sp. nov. has irregularly branched shoots with both forked and simple leaves, simple pollen cones, and compound ovulate fructifications. Stems have an endarch eustele with dense wood surrounding a septate pith. Leaves range from ca. 1 to 5 cm long, display size‐related dimorphism, and have papillate epidermal cells with numerous trichomes and two adaxial stomatiferous bands. Stomatal complexes range from solitary to crowded, occur in longitudinal rows, and are represented by four to seven papillate subsidiary cells. Polar subsidiary cells are elongated parallel to the stomatal rows. Pollen cones are simple and have helically arranged sporophylls with a perpendicularly inserted shank, adaxial pollen sacs, and a forked distal lamina. Prepollen is monolete, monosaccate, and eusaccate. Ovulate fructifications comprise a compound conelike fertile zone of axillary dwarf shoots and extend into a vegetative zone distally. Ovuliferous dwarf shoots are radial, have numerous sterile scales, and occur in the axils of helically arranged bracts with forked tips. Ovules are apparently erect and borne on narrow sporophylls. They have a dense megaspore membrane and rounded micropylar end. The new species has a diagnostic suite of characters that falls outside the familial concepts of previously described spermatophytes. Bartheliaceae fam. nov. is compared to walchian conifers, ginkgophytes, cordaiteans, and other coniferophytic plants. The coniferophyte concept is reviewed, and the uncertain systematic relationships among coniferophytes are discussed.

An herbaceous fossil conifer: Gymnospermous ruderals in the evolution of Mesozoic vegetation

Abstract Fast growing conifers have been recognized in disturbed habitats of the transitional Lower Middle Triassic Gres a Voltzia delta from the Buntsandstein in eastern France. These herbaceous conifer fossils reveal that some Mesozoic seed plants were capable of opportunistic growth and rapid prolific reproduction long before the origin of flowering plants. Such ruderals indicate that certain gymnosperms came to characterize river terrace floras by the evolution of reduced size and enhanced reproductive allocation, while others dispersed to dominate more arid expanses of the Mesozoic landscape before the rise of flowering plants. The widespread occurrence and quantitative distribution patterns of pollen similar to that of Aethophyllum in the Middle Triassic suggests that Aethophyllum and related conifers may have played an important role in the evolution of distinctive Mesozoic wetland communities.

The seed cone Eathiestrobus gen. nov.: Fossil evidence for a Jurassic origin of Pinaceae

PREMISE OF THE STUDY Pinaceae and nonpinoid species are sister groups within the conifer clade as inferred from molecular systematic comparisons of living species and therefore should have comparable geological ages. However, the fossil record for the nonpinoid lineage of extant conifer families is Triassic, nearly 100 million years older than the oldest widely accepted Lower Cretaceous record for Pinaceae. An anatomically preserved fossil conifer seed cone described here extends the stratigraphic range of Pinaceae nearly 30 million years, thus reducing the apparent discrepancy between evidence from the fossil record and inferences from systematic studies of living species. METHODS Material was prepared as serial thin sections by the cellulose acetate peel technique, mounted on microscope slides, and viewed and photographed using transmitted light. KEY RESULTS A large cylindrical cone consisting of bract-scale complexes that diverge from the cone axis in a helical phyllotaxis has bracts and scales that separate from each other in the midregion and are of equal length and of nearly equal width. The cone has two inverted and winged seeds that are attached to the adaxial surface of each cone scale and, thus, represents an early member of the Pinaceae. CONCLUSIONS Eathiestrobus mackenziei gen. et sp. nov. extends the fossil record for well-documented members of the family Pinaceae from the Lower Cretaceous to the Kimmeridgian Stage of the Upper Jurassic. This species also clarifies the set of characters that are diagnostic for seed cones of Pinaceae and reveals possible plesiomorphic characters for seed cones of the family.

Medullosa steinii sp. nov., a seed fern vine from the Upper Mississippian

Three specimens of a medullosan seed fern stem with attached leaf bases, from the Chesterian Series of Arkansas, USA, are the earliest unequivocal occurrence of the genus Medullosa and form the basis for a new species Medullosa steinii. The stems have numerous features characteristic of vines, including stem diameters of only 2–3 cm in diameter, numerous wide, plate-like rays, relatively wide tracheids, the presence of cortical spines and variable but numerous stelar segments. In M. steinii vascular segment numbers vary from two to eight. Primary xylem bundles consist of one to several protoxylem poles with metaxylem and abundant parenchyma; each bundle is surrounded by secondary vascular tissue. Leaf traces typically diverge from a vascular segment as pairs, with the resulting bundles separating from each other at an angle of 90–100°. Paired leaf traces are separated from each other by a wedge of secondary vascular tissue, thus producing a distinctive mode of leaf trace production for the new species. Leaf traces divide repeatedly to produce the Myeloxylon rachis base configuration at the margin of the stem cortex. Rachis bases are decurrent and are separated from one another by a discontinuous row of sclerotic bundles and from the stem by a prominent periderm. The discovery of this plant demonstrates that scrambling and climbing seed ferns were part of some plant communities by Mississippian time.

Reconsidering Relationships among Stem and Crown Group Pinaceae: Oldest Record of the Genus Pinus from the Early Cretaceous of Yorkshire, United Kingdom

This study describes a specimen that extends the oldest fossil evidence of Pinus L. to the Early Cretaceous Wealden Formation of Yorkshire, UK (131–129 million years ago), and prompts a critical reevaluation of criteria that are employed to identify crown group genera of Pinaceae from anatomically preserved seed cones. The specimen, described as Pinus yorkshirensis sp. nov., is conical, 5 cm long, and 3.1 cm in maximum diameter. Bract/scale complexes are helically arranged and spreading. Vasculature of the axis forms a complete cylinder with few resin canals in the wood, and the inner cortex is dominated by large resin canals. Bracts are short, with two resin canals, and separate from the scale base laterally. Distally, the ovuliferous scales broaden and thicken to form a rhomboidal apophysis with a dorsal umbo, characters found only in the genus Pinus among living conifers. Resin canals enter the ovuliferous scale abaxial to the vascular tissue, which divides distally to form a row of adaxially convex bundles. A short interseminal ridge separates two inverted and winged seeds on the adaxial surface of the ovuliferous scale. Seeds contain megagametophyte tissue and polycotyledonary embryos. Numerical cladistic analysis of anatomically preserved seed cones yields a well-resolved phylogeny of crown and stem group Pinaceae that is roughly concordant with the results of analyses that include living species only. All of the included species of Pinus form a clade with three very Pinus-like species that currently are assigned to the stem genus Pityostrobus. These results call to question the utility of traditional methods for assigning fossil seed cones to Pinus, resolve relationships among stem and crown group genera, and highlight the unnatural circumscription of Pityostrobus. This suggests that some species of Pityostrobus may actually represent the genus Pinus, and it demonstrates that the evolutionary diversification of Pinaceae began earlier than previously recognized from fossil evidence.

Growth Architecture of Thucydia mahoningensis, a Model for Primitive Walchian Conifer Plants

A large number of vegetative and fertile branching systems of Thucydia mahoningensis provide data for interpreting the growth architecture and life‐history pattern of a primitive Paleozoic conifer. Internal anatomy is similar to modern conifers, indicating an arborescent life‐history pattern. Three categories of vegetative plagiotropic branching systems are recognized, and these resemble developmental variations among lateral branching systems in juvenile trees of the extant conifer Araucaria heterophylla (Salisb.) Franco. Thucydia mahoningensis is considered to be a small tree on the basis of the size and branching pattern of the stem and lateral branching systems and on the basis of internal anatomy. Growth architecture of T. mahoningensis conforms to Massart’s model, but fertile remains reveal interesting differences from living species. The T. mahoningensis tree has an orthotropic stem that bears two orders of plagiotropic vegetative shoots. Fertile shoots have a compound ovulate fertile zone and lack vegetative lateral branches. Ovulate branches bear penultimate‐type vegetative leaves in the basal region, a compound ovulate fertile zone in the midregion, and ultimate‐type vegetative leaves in the distal region. Axillary ovuliferous dwarf shoots of the compound fertile zones correspond to ultimate branches of the vegetative systems. Compound pollen cones are terminal on branches. These and supplementary data from previously described walchian species reveal that the architecture of the most primitive conifers resembles juvenile araucarian conifers and suggest that giant conifers evolved from diminutive trees by the combination of an extended vegetative growth phase and hypermorphoses in leaf development.

Anatomically preserved vojnovskyalean seed plants in Upper Pennsylvanian (Stephanian) marine shales of North America

ABSTRAcr-Upper Pennsylvanian dysoxic marine shales of midcontinent North America yield permineralized remains of apparently extrabasinal vegetation. A large percentage of the plants are surprisingly unlike the well known swamp, fluvial and lacustrian floras of the late Paleozoic paleotropics, revealing numerous aspects of the morphology, anatomy and reproductive biology of plants that may have been ancestral to the dominant taxa of the Mesozoic. Included among the assemblages are ovulate coniferophyte remains that demonstrate the occurrence of vojnovskyalean seed plants in equatorial Euramerica. Specimens consist of simple ovulate cones that are more-or-less clustered along eustelic stems in the axils of helically arranged, strap-shaped leaf bases, and are described as Sergeia neuburgii new genus and species. Individual cones are up to approximately 2 cm long and 1.5 cm in maximum diameter, with helically arranged scales and sporophylls that diverge from a eustelic axis. Scales occur in the basal region of the cone, and are laminar and pointed. Sporophylls are borne distally. One specimen shows about 45 sporophylls, each of which terminates as one erect ovule. Most of the other cones have abraded apices, and terminate in relatively terete foliar appendages that are interpreted to be sporophyll bases. Ovules are flattened and winged, approaching 1800 rotational symmetry. Integument histology, vascular tissue distribution and pollen chamber structure are similar to those of cordaiteans and callistophytalean seed ferns. Sergeia adds to the number of late Paleozoic conifer-like plants that do not conform to the Pinopsida as traditionally circumscribed, and poses additional questions to assumptions of monophyly for coniferophytes and for conifers sensu lato.