AN APTIAN CYCADEOID FROM THE BUDDEN CANYON FORMATION, ONO QUADRANGLE, CALIFORNIA

2007·4.2 MB·English

by  Barbara M Going

Madrono, Vol. 54, No. 2, pp. 167-171, 2007
AN APTIAN CYCADEOID FROM THE BUDDEN CANYON FORMATION,
ONO QUADRANGLE, CALIFORNIA
Barbara M. Going\ Robert Hilton^ and Bruce H. Tiffney^
^Department of Environmental Science and Policy, University of California,
CA
Davis, 95616
[email protected]
'Department of Geology, Sierra College, 5000 Rocklin Road, Rocklin, CA 95677
CA
^Department of Earth Science, University of California, Santa Barbara, 93106
Abstract
We describe a cycadeoid trunk from the Aptian Chickabally Member, Budden Canyon Formation
inOno, California. Ourdiagnosisofthespecimenasacycadeoidwasinitiallybased onthepresenceof
mucilage canals in the pith and the structure of the secondary xylem. This determination was
subsequently supported by recognition of the distinctive morphology of the surface of the primary
body of eroded cycadeoid trunks. The latter may aid in the identification of otherwise enigmatic
Mesozoic fossils. This specimen is the third cycadeoid to be reported from northern California and
slightly extends the known geographic range ofthe group within the state.
Key Words: Aptian, California, Cretaceous, cycadeoid, gymnosperm, trunk.
The cycadeoids (Bennettitales) are an extinct traces, which are a characteristic feature ofmost
group of seed plants that evolved during the cycads, although they are lacking in the cycad
Triassic (248-206 Ma [mega annums]) following Antarcticycas (Smoot et al. 1985). In addition,
the formation of the supercontinent Pangea and cycadeoids commonly had bisporangiate repro-
the emergence ofother seed plant groups, such as ductive structures (although those of William-
Cycadales, Ginkoales, and Glossopteridaceae sonia were monosporangiate) with microsporo-
(Willis and McElwain 2002). They becameextinct phylls and ovules within the same cone (e.g.,
by the end of the Cretaceous (—65 Ma). Cycad- Delevoryas 1968; Crepet 1974). By contrast, most
eoids attained a cosmopolitan distribution in the cycads are dioecious (Stewart and Rothwell
Mesozoic; growing abundantly in tropical and, to 1993).
a lesser extent, warm temperate climates (Taylor Cladistic analyses have placed the Paleozoic
and Taylor 1993; Willis and McElwain 2002). As medullosans as a possible ancestor to cycadeoids,
a group, cycadeoids appear to have grown in based on similarities in wood structure and
disturbed habitats, particularly on levees (Retal- vascular bundle patterns (Nishida 1994; Willis
lack and Dilcher 1981). Their seeds were small and McElwain 2002). Earlier cladistic analyses
and wind dispersed, commensurate with an early suggested that cycadeoids are most closely related
successional status (Tiffney 1986). Cycadeoids to angiosperms and Gnetales (Doyle et al. 1994;
ranged in habit from low barrel-shaped or multi- Nixon et al. 1994). More recent studies (e.g.,
branched shrubs to erect, often thick, sparsely Doyle 2006) generally link Gnetales with conifers
branched trees. Most bore pinnately compound, (but see Hilton and Bateman 2006), while
coriaceous foliage (Tidwell 1998); the petioles retaining a cycadeoid-angiosperm link. While
were surrounded by lignitic scales at their point some studies place cycadeoids as the sister group
ofinsertion on the trunk; these scales formed the to angiosperms, reflecting their bisexual, flower-
exterior surface ofthe trunk. Internally, the trunk like reproductive structure, the lack of morpho-
consisted of a large central pith, limited primary logical intermediates and the presence of one,
xylem, prominent to poorly developed secondary rather than two integuments, suggest some
xylem, and a thick cortical area. The secondary distance between the two groups (Willis and
j xylem was manoxylic, with files of tracheids McElwain 2002).
separated by medullary rays that were one to While the group embraced a range ofmorphol-
three cells wide (Stewart and Rothwell 1993). ogies throughout its history, the dominant
Leaf traces arose from the primary xylem and western North American Cretaceous taxon was
passed through the secondary xylem into the Cycadeoidea, a genus of squat, barrel-trunked
cortex and directly out to the leaves. Cycadeoids plants (Ward 1900; Wieland 1906 1916; Delevor-
were generally differentiated from the distantly yas 1968; Rothwell and Stockey 2002); although
related Cycads based on their vascular, repro- some specimens originally attributed to Cyca-
ductive, and stomatal structures (Nishida 1994). deoidea have been segregated into a separate
Cycadeoid stems generally lacked girdling leaf genus, Monanthesia (Delevoryas 1959), and other
I
MADRONO
168 [Vol. 54
genera of cycadeoids were present (e.g., Stockey
and Rothwell 2003). Cycadeoid fossils from
California are exceedingly rare; to date, only
two specimens have been reported. Ward et al.
(1905) described Cycadeoidea stantoni from
Colusa County in northern California. Delevor-
yas (1959) later transferred this specimen to
Mononthesia based on vascular patterns. In
1998, an amateur fossil collector uncovered
a second Monanthesia from Vallejo in northern
California (Collecting fossils in Cahfornia 1998).
In this paper, we describe a cycadeoid recently
collected from Aptian age sediments ofnorthern
California. This find extends the geographic
range of cycadeoids within California. The
specimen also has an unusual mode ofpreserva-
tion, which led its initial discoverer to ally it with
arborescent lycopods.
Locality Description Fig. 1. This portion of a Cycadeoid stem was
uncoveredin Cottonwood Creek, nearOno, California.
The specimen was collected by Charles Dailey The stem has been strongly eroded so that the majority
from Cottonwood Creek, in the Chickabally ofpreserved tissue is pith. Leafscars occur in a spiral
Member ofthe Budden Canyon Formation near arrangement, about 50° offthe vertical axis.
Ono, California (Sec. 18, T30N, R6W). It was
found on the surface, and is presumed to be
derived from the immediately surrounding sedi-
ments. The Chickabally Member was determined General Description
to be of Aptian age (—120 to 112 Ma) by
Murphy and colleagues (Murphy et al. 1969; The specimen is a portion of a laterally
Murphy 1975), who provide a detailed descrip- compressed, silicified, stem that is 4.5 to 5.3 cm
tion ofthe local geology. The upper Chickabally long and 4.8 X 3.2 cm in cross section. The
Member is characterized by mudstone with a few specimen is strongly eroded and is primarily
sandstone beds and limestone concretions (Mur- composed of pith tissue (Fig. 1), with small,
phy et al. 1969). scattered portions of primary and secondary |
Marine invertebrate fossils associated with this xylem located on one side. This same side of
member include Potamides diadema, Plicatula the fossil is covered with spirally arranged leaf
variata, Nucula gabhi. Turbofestivus, and Tessa- scars. The specimen is assigned number TLLE 65
rokix bicarinata, all suggestive of a near shore in the Collection ofthe Natural History Museum,
marine environment. Chandler and Axelrod Sierra College.
I
(1961) described the following plant taxa as J
occurring in the Chickabally member, basing
Pith
their identifications upon Fontaine (in Ward et
al. 1905): Ckidophlebis, Ctenopteris, Sagenopteris, The pith was originally about 3.4 cm in diam.
!
Dioouites, Ctenophyllum, Cephcdotaxopsis, Sphe- and is poorly preserved in some areas due to cell
nolepidiimh and Acaciaephyllum. These attribu- degradation (Fig. 2). Intruding sediments have i
tions are a century old, and have not been re- occasionally permeated to the center ofthe fossil,
i
verified for accuracy of identification or system- and in one instance, contained a fungal spore. )
atic assignment. However, at face value, these The majority ofthe preserved portion ofthe pith
1
comprise three taxa of cycadophyte foliage, two consists of thin-walled parenchyma. These cells
i
of conifer foHage, and a single angiosperm leaf are roughly equidimensional, averaging 110 X
(Tidwell 1998). Chandlerand Axelrod (1961) also 105 \im. in cross section and 116 X 98 |am in long ,
described a putative angiosperm fruit from section. Scattered throughout the pith are muci-
a nearby locality (Sec. 17, T30N, R7W). More lage canals lined by small epithelial cells (109 X ;i:
recently, new specimens ofan osmundaceous fern 105 jim) and bearing dark resin within. Overall,
i
(Stockey and Smith 2000), a cyatheaceous tree these canals are larger in diameter than the i
fern (Lanz, Rothwell and Stockey 1999), and parenchyma cells, averaging 248 X 239 jum in
a cone ofthe Pinaceae (Smith and Stockey 2001) cross section and 405 X 205 jam in long section {i
have been collected from the same general area. (Fig. 3). :
2007] GOING ET AL.: AN APTIAN CYCADEOID 169
Fig. 2. Cross-section of specimen. Primary and
secondary xylem occur in the lower left section of the Fig. 4. Cross-section of secondary xylem. Strands of
specimen, below the intruded sediment. thick walled secondary xylem (.sc) alternatewith strands
of parenchyma (pa). The interface with the primary
Xylem body (pr) is at the top ofthe picture.
An approximately 5 mm wide by 1 mm thick Leaf Scars
area of primary and secondary xylem adheres to
one side ofthe pith. A roughly 200 |am wide zone Spiral leaf scars occur on the same side of the
of poorly preserved cells that are interior to the specimen as the adherent secondary xylem. Five
secondary xylem and distinct in morphology vertical spirals are present, each with four scars
from the pith cells is inferred to represent the per spiral; the spirals incline at an angle of49-50
place of the primary xylem. Exterior to this are offthe vertical axis. Each scar ranges from 10 to
mm mm
radially oriented strands ofalternating secondary 15 in length and 2.0 to 3.0 in width;
mm
xylem and parenchyma. Each xylem band is one a horizontal distance of5 separates the scars.
to three cells wide, and is composed of dark, Leafscars aremost prominent in the centerofthe
lignified cells averaging 28 x 25 \im in cross specimen, fading to either side.
section. The largest band of secondary xylem
(Fig. 4) is 666 |am thick. In between these bands Discussion
of lignified cells are thin-walled medullary rays.
Each ray is one to two cells wide, and is This specimen was first presented to us as
composed of thin-walled parenchyma cells aver- a possible Mesozoic arborescent lycopod, and
aging 49.6 X 40.7 jam in cross section. The indeed the spiral traces show a strong similarity
limited amount of secondary xylem did not to the traces observed on decorticated specimens
permit serial sections ora section in the tangential of Lepidodendron. The structure of the pith,
or radial plane. however, argued against this interpretation.
Partially decorticated Cycadcoidea specimens
from the Cretaceous of Maryland illustrated in
Plate LXXXIX, Figure 2 of Ward et al.'s (1905)
Later Mesozoic Floras ofNorth America provide
a view of the surface of the primary body, and
exhibit a distinctive set ofspiraled leafscars, very
much like those on the surface ofthis fossil. This
led us to interpret the specimen as a cycadeoid,
a conclusion furthersupported by the structure of
the pith with its slightly elongate mucilaginous
canals, and the manoxylic structure of the small
amount of secondary xylem preserved.
To date, anatomically preserved cycadeoid
trunks have generally been recognized by the
structure oftheir secondary xylem and the direct
path of the leaf trace, together with their
reproductive organs, if present. Those with
Fig. 3. Cross-section of mucilage canal (mc) sur- external morphology are identified by the dis-
rounded by epithelial cells (ep). Note the dark contents tinctive arrangement of the surficial ramental
in the interior ofthe canal. scales and interspersed holes demarcating the
MADRONO
170 [Vol. 54
insertion of petioles. Recognition of the distinc- Hilton, J. and R. Bateman. 2006. Pteridosperms are
tive morphology of the exposed surface of the the backbone ofseed plant phylogeny. Journal of ';
vpirdiemsaraynobtohdery piontetnhteiaMllayryulsaefnudl scpheacraicmteenrs, parnod- Lanttzh,e TT.orCr,eyG.BoWta.niRcoatlhSwoecilelt,y a13n3d:1R1.9-A1.68S.tockey. ;i
one which allows us to ally this otherwise a19n9d9.theCornoalnetioofpftoesrsiislssicnhruecshomlavniinigtgheen.phetylsopg.ennoyv.o,f i
perplexing specimen with the cycadeoids. Recog- Cyatheaceae s.l. Journal of Plant Research 112: ^
nition ofthis pattern ofleaftraces on the surface 361-381. I
ofthe primary body may aid in the identification Murphy, M. A. 1975. Paleontology and stratigraphy
ofotheranomalous Mesozoic stems, and suggests of the lower Chickabally mudstone (Barremian- |
the need to examine previously described Meso- Aptian) in the Ono quadrangle. Northern Califor- j
zoic lycopsid axes. nia. University of California Publications in Geo- |
Cycadeoid specimens from California are logical Sciences 113:1-52. j
notably scarce. The present specimen is the third Geo,lPo.gyU.ofRotDhDeA,OnAoNDquDa.draMn.glMe,ortShoans.ta19a6n9d. j
known. The first Monanthesia species was dis- Tehama counties, California. California Division
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before the second specimen of the same genus NiSHlDA, H. 1994. Morphology and evolution of \
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i
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in photographing the specimen and preparing the for the seed cones of Bennettitales. American
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