AN EVALUATION OF SPOROCARP STRUCTURE IN THE ...

Review of Palaeobotany and Palynology, 61 (1989): 341 345 341
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
Abstract
AN EVALUATION OF SPOROCARP STRUCTURE IN THE
TRIASSIC FUNGUS ENDOCHAETOPHORA
J.F. WHITE, JR.1 and T.N. TAYLOR 2
1Department of Biology, Auburn University at Montgomery, Montgomery, AL 36193 (U.S.A.)
2Department of Botany, The Ohio State University, Columbus OH 43210 (U.S.A.)
(Received March 13, 1989; revised and accepted June 5, 1989)
White Jr., J.F. and Taylor, T.N., 1989. An evaluation of sporocarp structure in the Triassic fungus Endochaetophora.
Rev. Palaeobot. Palynol., 61: 341-345.
Morphological and anatomical studies are made of three fossil fungi from silicified peat deposits of Triassic age from
Antarctica. Structural features of sporocarps are evaluated and compared to those of the previously described
Triassic fungus Endochaetophora antarctica. Features exhibited by these fossils suggests that they may be related to
E. antarctica. Increasingly evidence is accumulating that this type of fossil fungus is not related to the Ascomycotina,
but rather to an independent group, of which the extant Endogonaceae may be the sparse descendents.
Introduction
In recent years several investigators have
demonstrated that a wealth of information
about the natural history of fungi is available
from the fossil record (e.g., Dilcher, 1965;
Piorzynski, 1976; Wagner and Taylor, 1982;
Stubblefield et al., 1983; Taylor and White,
1989). The extraction of this information has
proven to be a slow process due in part to the
fact that most fungal specimens are incom-
pletely preserved and accurate interpretation
of morphology is often problematical. Interpre-
tation of structure is usually done under the
assumption that the fossil is classifiable in one
of the major groups of extant fungi (e.g.,
Ascomycotina, Basidiomycotina, Zygomyco-
tina). If a fossil possesses an enclosed sporo-
carp resembling a cleistothecium or perithe-
cium it is usually interpreted as ascomycetous,
since it is primarily the Ascomycotina which
produce such structures. This approach in
paleomycology is in part supported by the
0034/6667/89/$03.50 © 1989 Elsevier Science Publishers B.V.
belief that fungi are simple and evolutionarily
primative groups of organisms in which evolu-
tionary change has been conservative, i.e., that
fungi evolved relatively early and changed
little since their origins.
The idea of conservative evolution of fungi
may be a fundamental source of error in
paleomycology since it assumes that extinc-
tions of major fungal groups has not occurred.
Fossil evidence evaluated to date suggests that
this assumption may be incorrect (Taylor and
White, 1989). The peculiar morphologies of
several fossil fungi, such as Traquairia, Sporo-
carpon and Mycocarpon, from Paleozoic sedi-
ments do not correspond to extant species of
fungi (Stubblefield and Taylor, 1983; Stub-
blefield et al., 1983; Taylor and White, 1989).
This fact raises the possibility that periodic
extinctions, comparable to those hypothesized
for other groups of organisms, may have
occurred in fungi. This possibility compounds
the problem of the identification of fossil fungi
and suggests the need to reevaluate the

342
structural and morphological organization of
many fossil fungi.
Recent studies of Triassic sediments from
Antarctica have revealed the presence of a
fossil fungus possessing sporocarps resembling
perithecia of ascomycetes. This fossil was
given the binomial Endochaetophora antarctica
White et Taylor and suggested to be ascomyce-
tous, or ancestral to that group (White and
Taylor, 1988). After the original description of
this fossil, three additional specimens
possessing characters similar to those of E. an-
tarctica were discovered. In this paper the
structural features of these fossils are evalu-
ated and compared to those of the original
E. antarctica.
Materials and methods
Specimens are preserved as silicified permin-
eralizations collected from the Fremouw Peak
locality of the Transantarctic Mountains
(Smoot et al., 1985). These sediments are
included in the Beacon Supergroup and re-
garded as early-middle Triassic (Barrett, 1969;
Barrett and Elliot, 1972). Specimens were
prepared for examination using hydrofluoric
acid-etched cellulose acetate peels mounted on
microscope slides. The peels and slides are
deposited in the Paleobotanical collections of
The Ohio State University under the acquisi-
tion numbers 18,836-18,842. Comparative data
is presented in tabular form (Table I).
Results and discussion
Previously described features of E. antarc-
tica include the following compliment of fea-
tures: sporocarp wall composed of three cellu-
lar layers, hyphal appendages possessing nar-
row lumina embedded in the sporocarp wall,
uneven development of the middle layer of the
wall, ostiole and spherical spores. While it is
evident that the specimens described in this
paper are not identical to E. antarctica they
show many similar features, including size and
shape of the sporocarp, multilayered nature of
sporocarp wall, size of wall cells and the
presence of hyphal appendages in wall (Ta-
bleI). The similarities between these speci-
mens and E. antarctica suggests that they may
be related and may be considered congeneric.
Structural studies of these specimens may give
insights concerning development and phylo-
genetic affinities of Endochaetophora.
Specimen 1 (Plate I, 1 3) is represented by
only two sporocarps which appear to have fully
developed tripartite walls. The middle layer of
the wall is composed of cells that compare in
size and shape to those in E. antarctica, how-
ever, the inner and outer layers are acellular,
in contrast to those layers in E. antarctica
which are cellular or porus (Table I). Hyphal
appendages in E. antarctica appeared to con-
tain narrow lumina (White and Taylor, 1988),
while there is no evidence of narrow lumina in
appendages of these specimens (Plate I, 3, 5). It
is possible that what was initially interpreted
as a narrow lumen in hyphae of E. antarctica
may instead be a preservational artifact.
Specimen 2 (Plate I, 4, 5) is represented by
several sporocarps demonstrating a range of
development stages. These stages suggest a
method of sporocarp development in Endochae-
tophora. Immature sporocarps are globose and
surrounded only by a thin wall which bears
hyphal extensions (Plate I, 5). Within this pre-
existing wall, a new layer forms and thickens
irregularly so that the sporocarp wall is
unevenly thickened in partially developed
structures. The presence of hyphal appendages
on the sporocarps prior to formation of the
middle layer of the wall (Plate I, 5) suggests
that the appendages may have functioned to
provide a skeletal support network for the
developing sporocarp wall. The appendages
also may have anchored the sporocarps in an
extracellular matrix which is suggested to
have been present surrounding the specimens
due to the absence of debris around many of
the developing specimens (Plate I, 4, 5).
Specimen 3 (Plate I, 6, 7) is preserved in what
appears to be an assemblage of similar sporo-
carps. However, these sporocarps were some-
what different from those of the other speci-
mens in that hyphal appendages are rarely

TABLE I
Characteristics of Endochaetophora sporocarps
Criteria Specimen 1 Specimen 2 Specimen 3 Endochaetophora
antarctica 1
Sporocarp shape globose globose globose globose
Sporocarp size (diam) (290)300- (310)350 (200)255- 350-500 IJm
Sporocarp wall
370(400) ~m 400(450) ~m 400(450) ~m
No. of layers
Composition
and thickness
of wall layers
3 3 2 3
Inner layer acellular, acellular, acellular, porus or cellular(?),
6 20 ~m 3 5 ~m 5 7 pm 11 18 ~m
Middle layer cellular, unknown, cellular, cellular,
45-60 ~m 9-80 ~m 19-70 ~m 55-76 ~tm
Outer layer acellular, acellular, not evident porus or cellular(?),
6-20 ~un 2-4 ~tm 11-14 ~m
Size (diam) (4)5-6(8) ~m cells not (2)4 6(10) ~m 3-10 ~m
of cells
in middle
layer of wall
Hyphal
appendages
preserved
Frequency frequent frequent infrequent frequent
Diameter (8)9-10(14) pm (6)8-10(11) pm (5)6 10(12) ~m 5-10 lam
1 Characteristic of E. antarctica are those given by White and Taylor (1988).
encountered and sporocarp walls seem to
contain only two layers (Table I). This speci-
men has an acellular inner wall layer and a
cellular outer wall layer (Plate I, 7) which
compares structurally to the cellular middle
wall layer of E. antarctica.
The walls of ascomycete sporocarps are
usually composed of pseudoparenchyma de-
rived from interwoven hyphae. Individual cells
in these walls often show a tangential flatten-
ing due to the shear of sporocarp expansion.
The cells in the wall of Endochaetophora
sporocarps are not tangentially flattened (Pla-
te I, 2, 7). This suggests that sporocarps of this
fossil fungus developed differently from the
usual method of ascocarp development in
which the wall forms before the sporocarp
expands. Endochaetophora sporocarps prob-
ably enlarged to near maximum size before the
cells of the middle wall layer proliferated, thus
the cells were not subjected to shear of
sporocarp expansion and did not become tan-
343
gentially compressed like the pseudoparen-
chyma of ascomycetes. Whether the cells of the
middle wall layer of these fossils are pseudo-
parenchymatous, i.e., derived from interwoven
hyphae, is difficult to assess with the present
material, however, interwoven hyphae have
not been observed in sporocarps.
Occasionally sporocarps of Endochaetophora
contain spores (e.g., E. antarctica; White and
Taylor, 1988), however, typically the sporocarps
are empty. The absence of spores is difficult to
explain since one would expect that spores,
which are often resistant propagules, would
preserve readily. Perhaps spores are not differ-
entiated within the sporocarp until just before
they are released. If this is the case, most
sporocarps either may not yet have produced
spores, or may have already released them.
With so little known about Endochaetophora
it is impossible to accurately classify it.
However, features of its development are
inconsistent with those of the Ascomycotina to

• ' ...... *
I

which it superficially bears some resemblance.
Since we know of no other morphological
equivalent among extant species of fungi it
seems evident that the fungi we identify as
Endochaetophora have become extinct. In a
previous article (Taylor and White, 1989) we
suggested that Endochaetophora may have
affinities to the zygomycete family Endogona-
ceae. This suggestion is based on: (1) the
presence of an acellular inner wall layer
(Plate I, 7), much like the wall of Glomus
chlamydospores, (2) the presence of a cellular
wall layer (Plate I, 2, 7) which may be equivalent
to the cellular mantles of zygospores of extant
species of Endogone (Gerdemann and Trappe,
1974) and (3) the abundance of fungi in Triassic
peat which corresponds to extant species of
Endogonaceae (White and Taylor, 1989).
Evidence is beginning to accumulate which
suggests that extant members of the Endogo-
nales may represent relicts of a larger group of
fungi which may have been important in the
terrestrial environment prior to widespread
diversification of the Ascomycotina in the
Tertiary (Pirozynski, 1976; Taylor and White,
1989; White and Taylor, 1989). The continued
study of fossil fungi, including their distribution
in time and space will no doubt yield new dis-
coveries of forms which will elucidate some of
the complexities associated with their evolution.
Acknowledgements
This research was supported by a National
Science Foundation grant (BSR-8516323).
PLATE I
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1. Collapsed sporocarp of specimen 1, C.B 540A (bot-1), × 176.
2. Detail of wall of specimen 1 showing acellular nature of the inner and outer wall layers (arrows) and cellular structure
of the middle wall layer, C.B. 540A (bot-1), × 1100.
3. Detail of specimen 1 showing cross-sections of hyphal appendages (arrow) embedded in wall, C.B. 540A (bot-1), × 1100.
4. Partially developed sporocarp of specimen 2 showing unevenly thickened wall. The arrow indicates a thin area of the wall
where numerous appendages attach, C.B. 10,236C (bot-2), × 176.
5. Detail of wall of specimen 2 showing attachment of appendages, C.B. 10,236C (bot-2) x 350.
6. Partially developed sporocarp of specimen 3, C.B. 10,028G (top-2), × 176.
7. Detail near a rupture in the sporocarp wall of specimen 3 showing the acellular inner wall layer (arrow) surrounded by a
layer composed of numerous cells, C.B. 10,028G (top-2), × 410.