TR-J Cover.p65 - City of St. George

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Harris et al., eds., 2006, The Triassic-Jurassic Terrestrial Transition. New Mexico Museum of Natural History and Science Bulletin 37.
PRELIMINARY REPORT ON THE EARLY JURASSIC FLORA FROM
THE ST. GEORGE DINOSAUR DISCOVERY SITE, UTAH
WILLIAM D. TIDWELL 1 AND SIDNEY R. ASH 2
1
Earth Science Museum, Brigham Young University, Provo, UT 84602;
2
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87122
Abstract—A small, diverse flora occurs in the Lower Jurassic Dinosaur Canyon Member of the Moenave Formation
at the St. George Dinosaur Discovery Site at Johnson Farm locality in St. George, Utah. The flora consists of
poorly preserved impressions that represent seven species of conifers, ferns and horsetails. The coniferous fossils
are assigned to Araucarites stockeyi n. sp., Saintgeorgeia jensenii n. gen. and n. sp., Pagiophyllum sp., Milnerites
planus n. gen. and n. sp., and cf. Podozamites. The horsetail stem is assigned to Equisetum sp. and the fern leaf is
assigned to Clathropteris sp. Typically, the identifiable plant fossils found at this locality are rare and fragmentary,
and represent plant remains that were washed onto mudflats or into a lagoon where they were buried. These
fossils demonstrate that a variety of plants, many new to science, lived in this area during Early Jurassic time. No
other flora of this age is known in western North America, and it is quite unlike the floras of the Upper Triassic
Chinle Formation and Upper Jurassic Morrison Formation that occur in adjacent areas.
INTRODUCTION
This paper contains a description of the identifiable plant fossils
that are associated with the tracks and other fossil remains in the Lower
Jurassic Moenave Formation at the St. George Dinosaur Discovery Site
at Johnson Farm (SGDS) and vicinity in St. George, Utah (Fig. 1). The
flora consists mostly of poorly preserved impressions of coniferous
foliage and fertile structures. A short fragment of a horsetail stem and
fragments of a fern leaf are also present. The flora is noteworthy for
several reasons. First, it is the only Early Jurassic land flora known in
the western United States and, although small and poorly preserved, it
provides evidence that a variety of land plants were present in this area
about 200 million years ago, in the early part of the Jurassic. Furthermore,
the flora, which comprises mostly new genera and species, helps
fill a 60 million year gap in the megafossil record of plant life in this
region during the early Mesozoic. The next oldest flora in the region is
the well known Chinle flora of Late Triassic (Carnian-Norian) age (Ash,
1980); the next youngest is the Morrison flora of Late Jurassic age
(Tidwell et al., 1998).
MATERIAL AND METHODS
The plant fossils described here are preserved as iron stained
impressions in soft gray to white siltstone. Although no organic matter
seems to be preserved on the fossils, enough relief is present that their
gross features are evident. Consequently, it is possible to identify most
of the forms. In this article we classify the fossils using the system
outlined by Taylor and Taylor (1993). The identifiable forms found at
and near the SGDS are listed below.
Division Sphenophyta
Order Equisetales
Equisetum sp.
Division Pteridophyta
Order Filicales
Clathropteris sp.
Division Coniferophyta
Order Coniferales
Araucarites stockeyi n. sp.
Saintgeorgeia jensenii n. gen., n. sp.
Pagiophyllum sp.
Milnerites planus n. gen., n. sp.
cf. Podozamites? sp.
FIGURE 1. Index map of the St. George Discovery Site (A-B) and
stratigraphic section (C). A, Overview. B, Some of the localities in the
study area. The localities are: 1) SGDS, 2) Hildale track site, 3) Darcy
Stewart plant locality, 4) JFP.1 plant locality, and 5) JFP.2 plant locality. C,
Stratigraphic section through the Moenave Formation at the SGDS. Arrows
indicate plant horizons. The main track-bearing bed occurs near the contact
between the Dinosaur Canyon Member and the Whitmore Point Member.
The fossils were studied in reflected light with dissecting microscopes
and are deposited in the collections at the SGDS.
GEOLOGY
In the St. George area, the Moenave Formation is about 102 m
thick, divided into the lower Dinosaur Canyon and upper Whitmore
Point members. The formation overlies the Upper Triassic Chinle For-

mation and is in turn overlain by the Springdale Sandstone Member of
the Lower Jurassic Kayenta Formation (Fig. 1C; Kirkland et al., 2002;
Lockley et al., 2004; Lucas et al., 2005). The Springdale Sandstone
Member was originally considered the upper member of the Moenave
Formation (Hintze, 2005). The Triassic-Jurassic boundary is probably
located within the Dinosaur Canyon Member (A. Milner, personal
commun.). The Dinosaur Canyon Member is a reddish-brown siltstone
and sandstone, and the Whitmore Point Member a recessive unit of red
and white siltstone, mudstone, and limestone near the main track-bearing
bed in which the fossil plants occur. At many of the track sites, numerous
fossil track-bearing horizons have been identified, two associated
with the fossil plants described herein. The fossil plants have been collected
from near the top of the Dinosaur Canyon Member and near the
base of the Whitmore Point Member (Fig. 1C). Other types of fossils at
the track sites include arthropod, horseshoe crab, and beetle trackways,
fish remains, fish swim trails, and algal mats (A. Milner, personal
commun.).
SYSTEMATIC PALEONTOLOGY
Division Sphenophyta
Order Equisetales
Family Equisetaceae
Genus Equisetum Linné
Discussion: Harris (1961) discussed the usage of the generic
terms, Equisetum vs. Equisetites, for fossil forms similar to living Equisetum.
Although he had used Equisetites previously (Harris, 1926, 1931),
Harris reconsidered this decision and decided to use Equisetum, because
“no morphological differences have ever been proved between Equisetum
and Equisetites…” (Harris, 1961, p. 14). In fact, the fossil and extant
forms he examined exhibit strikingly morphological similarities. We follow
Harris (1961) and assign the single known equisetalean fossil known
from this locality to Equisetum because we cannot see any difference
between the stem of living Equisetum and the specimen at the Johnson
Farm locality.
Equisetalean fossils are poorly known in the Triassic and Jurassic
of North America. They include a few specimens of small stems described
from the Upper Triassic of Arizona by Daugherty (1941) and
Ash (2005). Daugherty (1941) also described some Late Triassic spores
that he attributed to Equisetum, but they were later found in small coniferous-like
cones by Ash (1972). The Jurassic representatives of Equisetum
described from western North America are found at a few localities
in the Upper Jurassic Morrison Formation (Brown, 1972; Tidwell, 1990;
Ash and Tidwell, 1998; Tidwell et al., 1998), as well as the Jurassic of
Oregon and Montana (Fontaine, 1905a, b) and Oaxaca, Mexico (Wieland,
1913; Delevoryas and Gould, 1971, 1973)
Geologic range: Triassic to Recent.
Equisetum sp.
Figure 2A
Material: SGDS.569.
Description: This species is represented by a single specimen of
a narrow stem about 5 mm wide and about 5 cm long that shows a single
node. The axis is furrowed and the node is marked externally by the
proximal ends of narrow commissural furrows and by a ridge formed by
an in situ nodal diaphragm. Internodes are at least 34 mm long and, as a
result, the leaves do not overlap adjacent nodes. The leaf sheath is 15
mm in length and is composed of 16 tapering, acutely pointed leaf teeth
(eight on each side of the flattened axis). The free teeth have a single ridge
above the midvein and extend beyond the node for about 9 mm.
Comparison: Equisetum sp. is somewhat similar to E. doratodon
Harris, E. muensterii (Sternb.) Schimper, E. laevis Halle, and E.
grosphodon Harris from the Rhaetic flora of Scoresby Sound, East
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FIGURE 2. Equisetales (A) and Filicales (B, C) from the Johnson Farm
locality. A, Stem of Equisetum sp. (SGDS.569). A single node is present on
this narrow stem as well as eight longitudinal ridges. B-C, Fragments of the
palmate leaf Clathropteris sp. B, Bases of several pinnae. The strong midribs
of the pinnae are prominent in this fossil (SGDS.465, x 1). C, Central part
of a leaf showing the net venation characteristic of this leaf (SGDS.503).
Greenland (Harris, 1931). It differs by being narrower (6 vs. 15-20 mm)
than E. doratodon, having shorter free teeth (9 vs. 12 mm), a larger
number of leaves (16 vs. 12 leaves) than E. muensterii, having a ridge
above the midvein rather than a furrow as in E. laevis, and a thinner stem
(6 vs. 25 mm) and far fewer leaves (16 vs. 30-40 leaves) than E.
grosphodon.
Discussion: As has been noted by Seward (1898), the presence
of a transverse nodal diaphragm enables axes to resist total compaction in
the nodal region by burial. No cuticle, cones, rhizomes, or individual
transverse nodal diaphragms are present.
Division Pterophyta
Family Dipteridaceae
Genus Clathropteris Brongniart, 1828
Discussion: This fern has distinctive, palmately compound leaves
that are borne on the ends of stout rachises that arise from underground
rhizomes. The pinnae have coarsely toothed margins and the leaf has net
venation with blind vein endings in the meshes. Fertile specimens have
small, round sori scattered on the lower leaf surfaces within the vein
meshes.
Comparison: In Clathropteris and the similar genus
Dictyophyllum, the pinnae extend outward from rather long trusses that
formed from symmetrical divisions at the tip of the petiole. They then
bend in a horizontal plane (Oishis and Yamasita, 1936). The pinnae
margins are denticulate in both genera and the major distinction between
them is the more regular and rectangular shape of the meshes formed by
the secondary and tertiary veins in Clathropteris than in Dictyophyllum.
The secondary venation in Clathropteris also generates a pattern perpendicular
to the veins inserted to the rachis (M.E. Popa, personal
commun.)
Geologic range: Late Triassic through the Middle Jurassic.
Clathropteris sp.
Figure 2B, C
Material: SGDS.465, 503.
Discussion: This species is represented by only the two small
fragmentary specimens of leaves shown in Figures 2B and C. Although
small, enough is preserved to show that the specimens are the remains of
palmately compound leaves that have net venation and marginal teeth on
the pinnae. All of these features are characteristic of the genus
Clathropteris. However, not enough is preserved for comparisons or to
assign them to a species.

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Division Coniferophyta
Order Coniferales
Family Araucariaceae
Genus Araucarites Presl (in Sternberg, 1838)
Discussion: Although this genus was originally used for coniferous
twigs, it has come to be used for isolated cones and cone parts that
appear to be araucarian (Harris, 1935; Miller, 1977). Other genera used
less frequently for such fossils include Primaraucaria Bock (1954),
Dammarites Presl (in Sternberg, 1838), and Aachenia Knobloch (1972).
Somewhat similar fossils have been reported from the Late Triassic of
eastern North America by Bock (1954, 1969), but the fossils have been
lost and the discoveries cannot be confirmed. Although the fossils described
here are not the oldest known cone-scale complexes yet attributed
to the genus Araucarites, their presence in the earliest Jurassic
seems to support the contention by Miller (1977) that the Araucariaceae
extended into the Triassic.
Geologic range: Late Triassic-Cretaceous.
Araucarites stockeyi new species
Figure 3A-K
Holotype: SGDS.515A and counterpart SGDS.515B.
Paratypes: SGDS.557A, B, C.
Derivation of name: We take special pleasure in naming this
species after Dr. Ruth Stockey (University of Edmonton, Edmonton,
Canada) who has devoted so much of her professional career to the study
of the living and fossil Araucariaceae.
Diagnosis: Detached ovulate cone-scale complexes, bract wedgeshaped
in outline, about 8-12 mm wide, 11-12 mm long, base broad,
lateral margins straight and smooth, apical margin rounded and smooth,
bearing a free tip or distal beak about 1 mm long. Ovule medially placed
in proximal part of bract, obovate, base narrow, lateral margins slightly
curving, smooth, apical margin rounded, smooth, about 5-6 mm wide
near top, 8 mm long, 1 mm thick in uncompressed specimens, surface
showing narrow longitudinal striations.
Description: This species is represented by nearly a dozen impressions
of cone-scale complexes and isolated ovules, the best of which
are illustrated in Figure 3. The bracts are thick and sturdy and give the
impression of being woody. Typically, the ovules on the cone-scale
complexes are not totally compressed and show varying amounts of
relief (Figs. 3A, C, G). When first collected, the ovule in one specimen
was attached to the bract by a thin layer of carbonaceous material that
later disintegrated while being examined. The resulting isolated ovule
(Figs. 3F, G) compares closely with some of the isolated ovules occurring
naturally in the rock (Fig. 3I). No clear evidence of an ovuliferous
scale or ligule is present on any of the specimens.
The collection also contains the compressed remains of two cones
that are tentatively referred to this species. Both specimens represent
cones that have been compressed somewhat laterally. One specimen
(Fig. 3J) shows 6-8 poorly preserved and loosely arranged cone-scale
complexes extending outward from the cone axis, which is about 2 mm
broad. The bracts are wedge-shaped and are about 7-9 mm long and
about 5 mm broad. They show faint, longitudinal striations but there is
no evidence of an ovule present on any of these bracts. The other cone
specimen is more difficult to interpret because the axis is not preserved
in the specimen (Fig. 3K). Evidently, the axis was in the counterpart,
which is not in the collection. Remains of a number of cone-scale complexes
are evident at various levels extending into the matrix of this
specimen and arranged as if they had been attached to an axis when
buried. The scales are not entirely exposed but they appear to have been
wedge-shaped and about 5 mm wide. The surfaces of the scales show
strong longitudinal plications about 0.7 mm wide, but once again there is
no evidence of ovules on the scales. The cone-scale complexes on both of
these specimens are smaller than the isolated forms.
FIGURE 3. A-H, Holotype of Araucarites stockeyi n. sp. (SGDS.515) and I-
J, cf. Araucarites stockeyi n. sp. from the SGDS. A, Unusually broad conescale
complex with clearly differentiated and slightly compressed ovule.
The edge of what is probably the cone scale is visible below (arrowhead).
Note the narrow longitudinal striations on the surface of the ovule. B,
Typical compressed cone-scale complex with a barely visible ovule
(SGDS.514B). The counterpart is shown in F. C, Paratype (SGDS.557B)
cone-scale complex showing the clearly defined mold of the uncompressed
ovule. A thick layer of carbonaceous material that was beneath the ovule is
visible in the ovule cavity. The counterpart and the ovule are shown in D.
The free tip on the apical margin is visible. D, Paratype (SGDS.557A)
counterpart of the cone-scale complex in C, and the cast of the ovule in the
lower right which became detached during examination of the fossil in C.
The mold of the seed is barely visible on the bract. Note the narrow
longitudinal striations on both the seed and in the mold. E, Strongly
compressed isolated ovule (SGDS.559). Compare with the isolated ovule in
H. The narrow medial ridge at the base of the fossil maybe the infilling of
the micropyle. F, SGDS.514A, counter-part of the specimen in B. Note the
well preserved apical tip on the upper margin of the bract. G, SGDS.552,
typical cone-scale complex and compressed ovule. Note that the ovule is
about the same size as the isolated ovule in E. H, SGDS.555, a virtually
uncompressed cast of an isolated ovule. The edges of the scale are visible
along the lateral margins of the ovule (arrow). I, SGDS.556B, lateral
impression of a cone that is tentatively referred to cf. A. stockeyi. In this
specimen, only the basal parts of the cone-scale complexes are preserved.
Note the strong longitudinal plications on the bracts. J, SGDS.516, lateral
impression of a cone that is tentatively referred to cf. A. stockeyi. In this
fossil, several more or less complete cone-scale complexes are preserved
and are attached to what appears to be the cone axis (arrow) by narrow
stalks (arrow head). K, Compression of incomplete cone showing attached
cone scales (arrows). Scale bar = 1 cm.
Comparisons: The fossils described here seem to compare fairly
closely with the ovulate cone-scale complexes assigned to section Eutacta
of the genus Araucaria because the bracts are broadly wedge-shaped and
bear a short, acuminate free tip on the rounded upper margin. In addition,
the scales are woody and bear a single, narrow, and medially located
ovule that is retained at maturity (Stockey, 1982). Particularly interesting
examples are the cone scales of Araucaria columnaris (Forster) Hooker
that were described in some detail by Pant and Srivastava (1968) and A.
cookii Brown reported by Seward and Ford (1906). The ovules in both
species are also close to those of A. stockeyi in outline and size.
Comparable fossil cone scales that have been assigned to
Araucarites are widely distributed in Jurassic strata in both hemispheres
of the Earth. For example, the fossils from St. George are rather similar
to the cone scales attributed to Araucarites brodiei Carruthers (1869)

from the Middle Jurassic of England. The British cones are about the
same size as the ones described here, have a similar wedge-shape, and
bear a single broad seed (Cleal and Rees, 2003). The poorly preserved
cone scale complexes described from Scotland as A. millerii Seward (1911)
resemble somewhat those considered here except that the seeds are relatively
narrow compared to the seeds of the new species. In the Southern
Hemisphere, similar cone scales have been illustrated by Stockey (1994)
from the Jurassic of New South Wales, Australia.
Triassic Araucaria-like cone scales are much less common than
Jurassic forms. Probably the best documented such fossils are the conescale
complexes assigned to Araucarites charcotii Harris (1935) from the
latest Triassic (Rhaetic) of East Greenland. Although they are nearly the
same age, they differ significantly from the specimens described here.
First, the fossils from Greenland are more or less diamond-shaped with
long, tapered distal halves that are delicate, wedge-shaped, and sturdy
with a short apical beak on the rounded apical margin in the present
material. Also, the ovules in the Greenland specimens dropped before
the cone scales were preserved, in contrast to A. stockeyi where most
ovules are retained. Furthermore, the ovules are much larger (5-8 mm
wide) in the new species than those in the Greenland specimens. The
latter were probably only about 4-5 mm wide since the shallow depression
in which they were located is the width of several of the cone scales.
The two incomplete cones here tentatively assigned to this species (see
Figs. 3J, K) resemble slightly the cone described as Aliostrobus traversei
Ash (1999) from the Upper Triassic of east-central New Mexico. The
plications found in the cone scales in the cones from both localities are
particularly noteworthy.
Discussion: It appears that the seeds of Araucarites stockeyi
were often retained on the scale complexes at shedding as in section
Eutacta. The absence of ovules in the cones and their small size maybe
an indication that these two fossils are immature compared to the dispersed
forms. The falling away of the seed in one specimen of the new
species (Figs. 3C, D) has also been reported by Stockey (1975) in Araucaria
mirabilis (Spegazzini) Calder (1953) from the Jurassic of Argentina.
The presence of what most certainly are araucarian cone-scale
complexes at the SGDS in the very Early Jurassic indicates that the
origins of the family must lie earlier in time, such as in the Late Triassic.
Interestingly, however, such fossils have not yet been identified with
certainty in the underlying Chinle Formation of Late Triassic age that is
widely distributed in the southwestern United States. However, the
majority of plant fossils that are known in the Chinle occur in the lower
part that is assigned to the Late Carnian/Early Norian. Thus it may be
that the earliest araucarians lie in the slightly younger (Late Norian/
Rhaetic) parts of the Chinle and equivalent strata in the Southwest and
elsewhere.
Family Uncertain
Genus Saintgeorgeia new genus
Type species: Saintgeorgeia jensenii n. sp.
Derivation of name: After the city of Saint George where the St.
George Dinosaur Discovery Site at Johnson Farm is located.
Diagnosis: Leafy shoot forming flattened spray, ultimate branches
in a single plane, leaves scale-like, opposite on penultimate branches,
spirally arranged on ultimate branches. Staminate cones attached to ends
of ultimate branches.
Geologic range: Early Jurassic in southwestern Utah.
Saintgeorgeia jensenii new species
Figures 4A-G, 5B, C
Holotype: SGDS.627A, B.
Paratypes: SGDS.517A.
Derivation of name: From the name of the present owner of the
type locality, Paul Jensen.
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Diagnosis: Leafy shoot, forming more or less flat sprays,
penultimate branches straight, 3-5 mm wide, more than 17 cm long,
ultimate branches slender, 2-3 mm wide, 3-5 cm long, opposite to
subopposite, arising from axils of lateral leaves on penultimate branches.
Leaves scale-like, single-veined, arising oppositely at intervals of about 5
mm, spreading, forwardly directed, falcate, recurved, distally free, acutely
pointed, base expanded, decurrent. Leaves on penultimate branches in
one plane, 5 mm long, 10 mm wide at base, leaves on ultimate branches 3
mm long, 10 mm wide at base and appear spirally arranged. Cones about
3 cm long, 1 cm wide, attached to the ends of ultimate branches, staminate,
sporophylls spirally arranged, closely attached.
Description: This species is represented by several dozen, generally
poorly preserved specimens. Some of the best preserved of them
are shown in Figure 4. The oppositely arranged leaves are clearly evident
on the lateral margins of most specimens (see Figs. 4B, C, D, G), but
there is no evidence of them on the upper sides of the branches. The
attachment of the staminate cone-bearing ultimate branches to the
penultimate branches is shown on several specimens (e.g., Figs. 4B, D).
The cones are too poorly preserved to provide detailed description of
sporophyll morphology. In addition, the microspores of this species as
well as the ovulate cones and seeds are unknown.
Comparisons: The ultimate branches with attached cones are
similar to Elatides, but differ by having more flattened leaves with broader
basal attachment. Spirally arranged leaves occur on both penultimate and
ultimate branches in Elatides, whereas they are only present on the
ultimate branches of Saintgeorgeia. Also, the male cones are smaller,
nearly one-half the size, in Elatides than in Saintgeorgeia.
Discussion: The leafy shoots of this species appear to have been
FIGURE 4. Saintgeorgia jensenii n. gen, n. sp. from the SGDS. A, SGDS.627B,
longest specimen of the penultimate branch which shows several ultimate
branches and the typical short aciculate leaves. B, SGDS.517A, penultimate
branch showing two ultimate branches (a) terminating in cones (b). C,
SGDS.517C, counterpart of the lower part of the penultimate branch in B
illustrating opposite aciculate leaves. Note the twisted appearance of the
leaves. D, SGDS.517A, an ultimate branch arising from the axil of a leaf (a)
on a penultimate branch and terminating at the base of a cone (b). E,
SGDS.517A, apical region of a cone of this species. F, SGDS.517B, ultimate
branch with attached base of cone. G, SGDS.561A, long penultimate branch
showing a single ultimate branch on the right side and typical aciculate
leaves.

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FIGURE 5. Sketches of selected foliage at the Johnson Farm locality. A,
SGDS.558.I, the fragment of a fossil leaf in Figure 6C compared with a
sketch of the upper portion of a leaflet of Podozamites distans given by
Harris (1935). B, SGDS.517A, a short length of a branch showing small
spirally arranged leaves. C, SGDS.517A, fertile branch of Saintgeorgia
jensenii arising from the axil of a leaf on a penultimate branch of the
species. Drawn from the specimen in Figure 4D.
fairly robust. Since the penultimate branches that have been found are
more or less straight and thick, it is probable that they were rather rigid.
The opposite leaves and ultimate branches indicate that the leafy shoots
formed flat sprays, perhaps similar to those of some species in the
Cupressaceae. Most of the known staminate cones of this species are
attached to ultimate shoots (Figs. 4A, B, D, F, 5B, C), suggesting that
they were retained for sometime after formation.
Genus Pagiophyllum Heer, 1881
Discussion: Pagiophyllum is one of a series of morphogenera
based on leaf characters that are used for mainly Mesozoic sterile coniferous
foliage. As now employed, Pagiophyllum is distinguished from
other genera of coniferous foliage by having uni-veined leaves that are
narrowly triangular in plan view and that are less than five times their
width in length. In addition, the leaves are helically arranged and diverge
from the parent stem at a low angle.
Geologic range: Late Triassic into the Cretaceous.
Pagiophyllum sp.
Figure 6D
Material: SGDS.491.
Description: This species is represented by a single slender axis
about 1 mm wide and 10 cm long that bears more or less alternate lateral
branches that are 10-30 mm long and appear flexible. The axis and the
lateral branches are usually concealed by small, helically arranged leaves.
The leaves are lanceolate with obtuse to acutely pointed apices. The free
parts of the leaves are typically about 2 mm long and about 1 mm wide
at the widest near the base. The surfaces of the leaves are smooth.
Cuticle and cones are not preserved.
Discussion: Comparisons between this specimen and previously
described species of Pagiophyllum are essentially impossible because of
the lack of cuticle on the specimen. The species described by Harris
(1979) from the Middle Jurassic Yorkshire of England, for instance, is
based largely on cuticle, which allows for more accurate determination of
its species but does not allow for meaningful comparisons with
Pagiophyllum sp.
Genus Milnerites new genus
Type species: Milnerites planus n. sp.
Derivation of name: After Andrew R.C. Milner, City Paleontologist,
St. George, Utah.
Diagnosis: Flattened leafy shoots, leaves arranged in two ranks
on opposite sides of axes, leaves decurrent, triangular to falcate in lateral
view, containing a single vein.
Geologic range: Early Jurassic in southwestern Utah.
Milnerites planus new species
Figure 6A-B
Material: SGDS 513A, 558A.
Derivation of name: From the Latin, planus, flat, level, in reference
to the appearance of the leafy shoot of this species.
Diagnosis: Shoots robust, flattened, single plane, leaves close, 2-
ranked, opposite to subopposite, decurrent, coriaceous, triangular to
falcate in lateral view, 3-5 mm long, 1-4 mm wide at base, apex acute,
occasionally slightly curved, attached by entire base, abaxial surface
convex, somewhat rounded, but not keeled; single vein, immersed, continues
to near apex.
Discussion: Specimens are incomplete. They are not typical conifer-type
foliage and, in some cases, they appear to be more fern-like in
outline. The fact that the shoots are flattened with the leaves attached in
two ranks on opposite sides of axes, rather than arranged in a helical,
whorled, or decussate pattern, is rather unique. It is similar in this context
to some foliage of Metasequoia, but differs by not being petiolate
FIGURE 6. Milnerites planus (A, B), cf. Podozamites (C), and Pagiophyllum
sp. (D) from the SGDS. A-B, In these specimens of Milnerites planus (A is
SGDS.558A; B is SGDS.513A), the triangular-shaped leaves are clearly
opposite and single veined. The upper leaf shoot in A is not connected with
the specimen in the lower part of the specimen, although it represents the
same species. C, SGDS.558I, fragment of a leaflet that compares fairly
closely with Podozamites. Note the parallel veins in the specimen that are
typically of this genus. Compare with the drawing in Figure 5A. D, SGDS.491,
leafy shoot of Pagiophyllum sp.

and having broader, shorter leaves rather than linear, needle-like leaves of
the latter. Milnerites planus differs from Saintgeorgeia jensenii by having
different shaped leaves that are closer together and not as curved and
by a flattened shoot.
Genus Podozamites (Brongniart) Braun in Munster, 1843
Discussion: Like Pagiophyllum, Podozamites is another in a series
of morphogenera based on leaf characters that are used for mainly
Mesozoic sterile coniferous foliage. Podozamites, as it is usually employed,
is distinguished from the others by having linear, lanceolate
leaves containing numerous parallel veins that converge apically. They
are borne alternately or spirally on long shoots.
Geologic range: Triassic throughout the Cretaceous.
cf. Podozamites
Figures 5A, 6C
Material: SGDS.558A.
Description and Discussion: Several small fragments of lamina
showing narrow parallel veins apparently represent Podozamites. The
size of the whole leaf is unknown, but the dimensions of the fragments
indicate that it was probably rather small. These fragments are comparable
to Podozamites distans (Presl) Braun and P. punctatus Harris from
the Rhaetic Scoresby Sound flora of East Greenland (Harris, 1935) (Fig.
5A). Although the lower part of the leaf shows elongate cells over the
veins, no other epidermal cells are visible.
SUMMARY
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The flora from the SGDS is the first Early Jurassic flora reported
from western North America. The majority of Early Jurassic floras are
found in Eurasia. Early Jurassic floras are marked by an ascendance of
many Triassic types in Europe (Vakhrameev, 1991). Ferns were common,
as were conifers and bennettitalean forms, in many floras of this
age. Podozamites, Clathropteris, and Equisetum, present in the St. George
flora, were well represented in Early Jurassic floras in Eurasia. This flora
and fragments of other plant material which occur at the SGDS suggests
the flora was much more diverse when living and that more taxa will
likely be uncovered with additional collecting at other sites within and
adjacent to St. George.
ACKNOWLEDGMENTS
We are grateful to Andrew R.C. Milner (City Paleontologist, St.
George, Utah) who was responsible for collecting the material described
here and providing additional data, and to Dr. James I. Kirkland (State
Paleontologist, Utah Geological Survey) for inviting us to study this
flora. We acknowledge the assistance of Darcy Stewart, Paul Jensen and
the late Layton Ott for allowing collection of fossils on their properties,
Professor M.E. Popa (University of Bucharest) for reviewing the manuscript,
and to Dr. Brooks Britt (Department of Geology, Brigham Young
University) for his assistance with the illustrations.
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