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Paleobotany |
2School of Life Sciences, Arizona State University, P.O. Box 874501, Tempe, Arizona 85287-4501 USA; 3Department of Biological and Environmental Sciences, Georgia College & State University, Campus Box 081, Milledgeville, Georgia 31061 USA
Received for publication February 9, 2005. Accepted for publication June 23, 2005.
ABSTRACT
Paleoactea nagelii Pigg & DeVore gen. et sp. nov. is described for a small, ovoid ranunculaceous fossil fruit from the Late Paleocene Almont and Beicegel Creek floras of North Dakota, USA. Fruits are 5–7 mm wide, 4.5–6 mm high, 10–13 mm long, and bilaterally symmetrical, containing 10–17 seeds attached on the upper margin in 2–3 rows. A distinctive honeycomb pattern is formed where adjacent seeds with prominent palisade outer cell layers abut. Seeds are flattened, ovoid, and triangular. To the inside of the palisade cells, the seed coat has a region of isodiametric cells that become more tangentially elongate toward the center. The embryo cavity is replaced by an opaline cast. This fruit bears a striking resemblance to extant Actaea, the baneberry (Ranunculaceae), an herbaceous spring wildflower of North Temperate regions. A second species, Paleoactaea bowerbanki (Reid & Chandler) Pigg & DeVore nov. comb., is recognized from the Early Eocene London Clay flora, based on a single fruit. This fruit shares most of the organization and structure of P. nagelii but is larger and has a thicker pericarp. This study documents a rare Paleocene occurrence of a member of the buttercup family, a family that is today primarily herbaceous, and demonstrates a North Atlantic connection for an Actaea-like genus in the Paleogene.
Key Words: Actaea • Almont • London Clay • Paleocene • Ranunculaceae
Within the Ranunculales, a group of early diverging tricolpate flowering plants, the mostly North Temperate buttercup family, Ranunculaceae, is considered a relatively derived family (Hoot et al., 1999
; Magallón et al., 1999
; Judd et al., 2002
; Angiosperm Phylogeny Group, 2003
). In contrast to other ranunculid families such as the Menispermaceae and Berberidaceae that have a good Tertiary fossil record, the fossil record of the Ranunculaceae is poor prior to the Neogene (Cronquist, 1988
; Magallón et al., 1999
). One reason for this apparent rarity may be the typically herbaceous habit of the family today (Ziman and Keener, 1989
). Many extant members of the Ranunculaceae are woodland herbs that have less preservational potential and produce fewer leaves and flowers, less pollen, and a smaller number of seeds in comparison to forest canopy trees. Additionally, many taxa occur in environments less likely to be preserved in the fossil record, such as alpine areas (Ziman and Keener, 1989
). Fossil occurrences of this family, particularly prior to the Neogene, have not been comprehensively reviewed.
The oldest evidence for the Ranunculaceae are small, ribbed fruits or fruitlets from the lower Cretaceous (Early Barremian to Aptian) of Portugal that resemble Thalictrum (Tables 1, 2; "unilocular ribbed fruit," fig. 7a of Friis et al., 1994
). These elongate to elliptical specimens are 
3 mm long and 1.2 mm broad with 5–6 prominent longitudinal ribs per side that sometimes anastomose. Hyrcantha Krassilov, Shilin & Vachrameev, from the Middle Albian of Kazakhstan, is a small paniculate inflorescence thought to have affinities with the Ranunculaceae and Paeoniaceae (Krassilov et al., 1983
). Its infructescences are clustered follicles.
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). These seeds have a characteristic two-chambered body with a basal locule that houses the embryo and an apical chamber that serves to catch air and act as a flotation device. This unusual aquatic adaptation is unique to extant species of Caltha, and its presence in Late Cretaceous fossils suggests that, like today, early Caltha-like plants were adapted to an aquatic environment. Plant macrofossils referred to a "Caltha type" are also known from the Neogene of northernmost Arctic Canada (Matthews, 1987
; Matthews and Ovenden, 1990
). Ranunculaceous leaves of uncertain affinities have been preserved in a distinctive layer of the Late Cretaceous Hell Creek Formation, no doubt representing an unusual depositional environment that preserved a number of herbaceous elements of the flora (Johnson, 2002
).
In the Tertiary, fruits assigned to Clematis L. were reported in the Oligocene of Germany by Weyland (1937)
. Leaves attributed to this genus are known by the Eocene in western North America (e.g., One Mile Creek, southern British Columbia, Canada; W. Wehr, Burke Museum of Natural History and Culture, personal communication). Leaves from the Oligocene Creede Formation of Colorado that were previously referred to the Ranunculaceae by Axelrod (1987)
were later removed from the family and reassigned to Potentilla L. (Rosaceae; Wolfe and Schorn, 1990
; Graham, 1999
).
Fruits of Myosurus L., Trautvetteria Fischer & C. Meyer, Hydrastis L., and Glaucidium Siebold & Zucc. are all recognized by the Oligocene in Europe (Li, 1952
; Mai and Walther, 1978
; Tiffney, 1985
; Collinson et al., 1993
). Achenes of Ranunculus L. occur from the Oligocene onwards in Europe and the former Soviet Union (Takhtajan, 1974
; Lan'cucka-Srodoniowa, 1979
; Mai, 1985
, 2001
) and the Early-Middle Miocene Mary Sachs Gravel of Banks Island, and the "high-level alluvium" of Ellesmere Island in Arctic Canada (Matthews and Ovenden, 1990
). Paeoniaecarpum hungaricum from the Miocene of Sarmatian, Hungary, in the Szelecsi Valley has been compared to both Ranunculaceae and Paeoniaceae (Andreánszky, 1961
; Collinson et al., 1993
). Anemone L. is known from Europe by the Pliocene (Reid and Reid, 1915
; Mai, 2001
; Martinetto, 2001
).
Fossil pollen of the Thalictrum-type has been reported from the lower Miocene and Pliocene of central Europe, the upper Miocene of Spain, the upper Miocene of Mexico, and the Pliocene of Turkey, Germany, and the Netherlands, and pollen of the Ranunculus-type is known from the upper Miocene of France (see Muller, 1981
, for a summary).
In the present study we describe Paleoactaea nagelii Pigg & DeVore gen. et. sp. nov., a distinctive fruit from the Late Paleocene Almont and Beicegel Creek floras of North Dakota; and a similar fruit Paleoactaea bowerbanki (Reid & Chandler) Pigg & DeVore nov. com. from the early Eocene London Clay flora of southern England. The occurrence of an Actaea-like fruit at these two Paleogene sites demonstrates the early presence of a ranunculid group that is represented today only by herbs and suggests a North Atlantic connection during the early evolution of this lineage within the family
MATERIALS AND METHODS
Fruits of Paleoactaea nagelii are anatomically preserved in silicified shale from two areas in central and western North Dakota (Bluemle, 1983
, 2000
). Most are from the original Almont site, Morton County, central North Dakota (Crane et al., 1990
), with one specimen from Beicegel Creek, MacKenzie County, approximately 120 km to the west (Manchester et al., 2004
). Both collecting sites occur within the Sentinel Butte Formation and are considered Late Paleocene (Tiffanian) based on mammal correlations (Kihm and Hartman, 1991
). At both sites, fossils occur in a brownish-tan, silicified shale that preserves both external morphological features of leaves and other plant organs and internal anatomy of fruit and seed remains.
Fruits were photographed from fractured surfaces and then embedded in Bio-plastic (Ward's Natural Science, Rochester, New York, USA) and wafered on a Buehler Isomet 1000 saw (Lake Bluff, Illinois, USA) into sections from 0.4 to 1.0 mm in thickness, and photographed under water with reflected light microscopy. Comparative material of extant fruits was hand-sectioned with a razor blade or embedded in Paraplast (Monoject Scientific, Sherwood Medical, St. Louis, Missouri, USA) and sectioned on a Buehler Isomet 1000 saw and photographed under water with reflected light. Figured specimens of extant fruits are from ASU 66642. The label information for this herbarium sheet is as follows: Actaea arguta Nutt. Ranunculaceae. New Mexico, Catron County; location—Willow Creek campground area, above Ben Lilly Forest Camp, Gila National Forest; habitat—Mountain stream, steep cliffs, spruce– aspen–ponderosa pine forest; collectors—D.J. Pinkava P12635, E. Lehto & T. Reeves. Determination. E. Lehto; date—15 August 1974. Fossil and comparative extant material was studied with scanning electron microscopy using a Hitachi (Tokyo, Japan) S-415A at 6 kV with 20 nm of gold coating and a Leica-Cambridge (Structure Probe, West Chester, Pennsylvania, USA) Stereoscan 360FE at 10 kV with 20 nm of gold coating.
Specimens of P. nagelii are housed at the Field Museum Chicago (FMNH; specimens prefixed PP), the Florida Museum of Natural History, Gainesville (UF; prefixed IU and UFLM), the University of Wisconsin at Stevens Point (UWSP), and Arizona State University (ASU).
The single specimen of P. bowerbanki was collected from the Sheppey locality of the London Clay (Reid and Chandler, 1933
; Collinson, 1983
). This locality is now considered Early Eocene (Collinson and Cleal, 2001
). The specimen was borrowed from the Natural History Museum, London, and photographed with reflected light under silicon fluid. The single specimen of P. bowerbanki is housed at the Natural History Museum, London.
Systematics
Family
Ranunculaceae.
Genus
Paleoactaea Pigg & DeVore.
Generic diagnosis
Fruits ovoid, elongate, bilaterally symmetrical, uniloculate, seeds borne along upper margin of fruit in 2–3 rows; fruit wall thin; seeds ovoid, flattened, pointed apically, and slightly pointed at chalazal end; anatropous, integument with outer layer of prominent palisade cells one cell thick.
Species
P. nagelii Pigg & DeVore (Figs. 1, 3–6, 8–10, 12, 14–15, 17–18).
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Prior citation
"Fruit of 9 to 11 Single-seeded locules" Crane, P. R., S. R. Manchester, and D. L. Dilcher, 1990
. Fieldiana Geology New Series, No. 20, Publication 1418. pp. 37–39; Fig. 25D–F.
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).
Stratigraphy
Sentinel Butte Formation, Late Paleocene (Tiffanian; Kihm and Hartman, 1991
).
Holotype
UWSP 1572 (Figs. 4, 10).
Paratypes
UF 15722-6277 and 6277' (Fig. 1); UWSP 6333 (Figs. 3, 5, 9, 17, 18); ASU # 2 (Fig. 6); UWSP 1788 (Fig. 8); UWSP 3972 (Fig. 12); UWSP 3973 (Fig. 14); ASU #12 (Fig. 15). Not figured: PP 34564; PP 34460; UWSP 1153; UWSP 3318; UWSP 3888; ASU #1, 3, 4, 5.
Etymology
The generic name "Paleoactaea" refers to similarities with the extant genus Actaea ("baneberry"). The species name "nagelii" is named in honor of the late Fred Nagel of New Salem, North Dakota, who provided paleobotanists access to the original Almont collecting site. He is remembered fondly for his unfailing generosity, kindness, and wonderful sense of humor.
Species
Paleoactaea bowerbanki (Reid & Chandler) Pigg & DeVore, nov. comb. (Figs. 19–26).
Synonomy
Carpolithus bowerbanki Reid & Chandler, 1933
; pp. 515–516, plate XXX, Figs. 38–41.
Species diagnosis
Fruit 24 mm long, 18 mm wide; carpel wall 1.5 mm thick; seeds 9.5 mm long, 5 mm wide, 5.5 mm thick.
Holotype
V. 23175 (Figs. 19–26). Bowerbank Collection, Natural History Museum, London.
Type locality
Sheppey, England.
Stratigraphy
Early Eocene (Collinson and Cleal, 2001
).
RESULTS
Paleoactaea nagelii
The description of Paleoactaea nagelii is based on 17 specimens collected from the Almont fossil plant locality and one from Beicegel Creek. Fruits are 5–7 mm wide, 4.5–6 mm high in transverse section, ovoid, 10–13 mm long, contain 10–17 seeds each, and are characterized by a pointed hook on one side (Figs. 1, 3–6). The fruit is bilaterally symmetrical with the seeds borne in 2–3 rows (Figs. 3, 4, 10) and attached narrowly on the upper fruit margin with their major planes perpendicular to the fruit's length and parallel to one another (Fig. 3). Details of fruit organization and seed structure are markedly similar to those of extant Actaea (Figs. 2, 7, 11). Anatomical details of the fruit wall are not well preserved, however some specimens have a thin layer a few cells thick that surrounds the fruit and may represent remnants of a thin pericarp (Figs. 1, 5, 6) similar to that of extant Actaea (Figs. 2, 7). In the fossils this layer has a combination of dark areas and white crystalline areas.
Seeds are anatropous, such that the position of attachment to the upper fruit margin is very close to the position of the micropyle (Figs. 9, 12, 15). A simple raphe extends down to the chalazal end of the seed. Individual seeds are tightly packed within the locule of the fruit. Seeds each have a prominent outer layer of palisade cells, and the tight crowding of adjacent seeds within the locule results in a distinctive honeycomb-like appearance (Figs. 1, 3–6).
Seeds are 4 mm long x 1.8 mm wide x 3 mm thick, flattened, ovoid, anatropous, and triangular in longitudinal section, and have a pointed apex and somewhat pointed chalazal end (Figs. 1, 3, 4, 6, 8, 15). The seed coat has a prominent uniseriate outer layer 0.044 mm thick composed of palisade cells (Figs. 9, 17, 18) that is very similar to the comparable layer in extant Actaea seeds (Fig. 13). These cells typically show an inner thickening that by spacing and dimensions suggests that they are scleritized. Quartz crystals form within the cell lumina in fossils and sometime obliterate the details of this layer. To the inside of the palisade layer is a region of 6– 8 layers of isodiametric cells (Figs. 4, 6, 9, 12, 14) that surround the innermost 3–4 layers of tangentially elongate cells lining the embryo cavity (Figs. 12, 14). These inner regions of the seed coat are frequently only partially preserved (Figs. 3, 4, 9, 17). An opaline cast typically replaces the embryo cavity (Figs. 1, 3, 4, 6, 10, 14, 17).
Paleoactaea bowerbanki
The description of this species is based on a single specimen 18 mm across and 24 mm long recorded in Reid and Chandler (1933)
(Figs. 19–26). This fruit was originally found as a complete specimen and was later fractured. The outer surface is fairly smooth (Fig. 24) to somewhat rough (Fig. 21); however, it is unclear how reliably the texture represents the actual fruit surface and how much is due to weathering. Fragments of the specimen viewed with reflected light reveal a very similar morphological organization as that of P. nagelii; however, this fruit was considerably larger, with a much thicker carpel wall, up to 1.5 mm thick (Figs. 19, 20). Seeds are roughly twice the size of those of P. nagelii and extant Actaea (9.5 mm long x 5 mm wide 5.5 mm across), but of a similar shape (compare Figs. 19, 25 to Figs. 2, 6, 14, 16). Several fragments show the partially preserved seeds exhibiting the prominent outer palisade seed coat up against the fruit wall (Figs. 19, 23, 25) and fracturing through part of the inner spongy layer (Fig. 19, 22, 23, 26). Opaline seed casts like those seen in the Almont plant are not preserved.
DISCUSSION
Interpretation and affinities of Paleoactaea
The fossils we designate here as Paleoactaea nagelii gen. et sp. nov. were illustrated and briefly described by Crane et al. (1990)
in their preliminary overview of the Almont flora. Their interpretation was based on a small number of specimens that were somewhat misleading because of their preservation. In fact, based on examination of available material at an earlier stage of this study, the authors initially believed these fruits may have had an affinity with a malvalean family (DeVore et al., 2001
). Our larger number of specimens, including those with better preservation, now allow us to identify the taxonomic affinities of these fruits and resolve several initially puzzling features.
Locule number
The fruit was originally described as "multilocular with 9–11 single-seeded locules" and "elliptical in transverse section" (Crane et al., 1990
). The "locules" were described as having a "continuous layer of columnar cells 0.088 mm thick with the septa formed from two such adjacent layers." Initially studied fruits had seeds with incompletely preserved seed coats surrounding a prominent opalized seed cast (Crane et al., 1990
). Our examination of the original material and additional specimens convinced us that the appearance of multiple locules in the fruit was superficial, and instead the fruit is actually unilocular. This superficial appearance of the fruit results from a combination of tightly abutted seeds, each with a prominent outermost palisade integumentary layer, a central opaline seed cast, and partial preservation of the cells that make up the internal integumentary layers between the outer integument and the central locule (Figs. 3, 4, 9). In better specimens now at hand the seed coats are more completely preserved and show that the palisade layer is the outermost layer of the seed (Figs. 6, 12, 14). Based on currently available material, the number of seeds per fruit is now 10–17 in contrast to the earlier estimate of 9–11 (Crane et al., 1990
).
Fruit symmetry
The fruit was also initially thought to have radial symmetry (Crane et al., 1990
); however, the position of a central axis with seeds surrounding it was not obvious. With the discovery of additional specimens, it became clear to us that fruit symmetry is bilateral, not radial, and that rather than being attached along a central axis, the seeds were attached in 2–3 rows along the upper margin of the fruit (Figs. 3, 9). Moreover, the specimen originally illustrated by Crane et al. (1990)
is an oblique longitudinal view of the fractured fruit surface, not a transverse section, giving the misleading perception of an elliptical transverse outline. Actual transverse sections are a somewhat flattened oval shape (Fig. 10).
Seed and morphology and orientation
Regarding the seed shape, Crane et al. (1990)
noted they were "basally rounded but strongly pointed at the micropylar end." They illustrated an individual seed cast (fig. 25E of Crane et al., 1990
) with cells of "adhering tissue" around what they interpreted as the chalazal end of the seed (Crane et al., 1990
). Reexamination of this material, along with additional specimens with orientation and preservation necessary for resolving seed morphology, shows that the area described as the chalaza in this specimen is actually the micropylar end. Both micropylar and chalazal ends of the seeds of Paleoactaea are somewhat pointed, making it difficult to figure out orientation in obliquely fractured fruits (Figs. 1, 6). Additionally, other specimens in the current study show the tendency of the spongy layer to adhere to either or both of these areas. The disparity in the size of seeds between that reported by Crane et al. (1990)
and that of the present study is because Crane et al. (1990)
were measuring the seed casts as seeds, while we are including the central spongy integumentary layer and the outer palisade integument. With respect to the seed coat, their "outer layer of 0.2 mm thick of spongy mass of ovoid cells" is equal to our central region.
The second species, P. bowerbanki from the Early Eocene London Clay locality of Sheppey was originally described by Reid and Chandler (1933)
as Carpolithus bowerbanki. These authors also interpreted the ovoid fruit to be radially symmetric with axile placentation. Their specimen was approximately twice the size of P. nagelii (24 mm long x 18 mm in diameter), and the carpel wall is considerably thicker (Fig. 26) than that estimated for the North Dakota specimens (Figs. 1, 3, 4, 6) and most species of the extant fruit (Figs. 2, 7). The seeds are also approximately twice the size of seeds of P. nagelii and most species of Actaea, and we estimate that a comparable number (of around 10–20) were mostly likely borne by P. bowerbanki. Reid and Chandler (1933)
interpreted the fruits to be syncarpous with an uncertain number of locules, although they allowed the possibility that there might be a single locule. Like Crane et al. (1990)
, Reid and Chandler (1933)
assumed the "septa" were carpel walls rather than the outermost integumentary layer of seeds within a simple fruit. They regarded features of the outer surface of the seed coat, particularly the "tuberacles," as being of great taxonomic significance and compared the fruit to several families with presumably similar features, including Sterculiaceae, Bromeliadaceae, and Melastomataceae. Because it is difficult to resolve whether these authors were actually looking at the outermost fruit layers, these possible assignments cannot be supported strongly.
During the course of our investigation, we discovered the striking similarity of our fruits with the extant ranunculid fruit Actaea. Both are ovoid follicles bearing tightly packed seeds with a prominent outer palisade layer that superficially resembles the septa of a multiloculate fruit. The fruit wall in Actaea is noteably thin, its typically lunate seeds are borne along the upper margin in 2–3 rows, and the stigmatic area is borne as a short knob-like structure on the side of the fruit. Although the stigma has not been observed in our fossils, the lack of a prominent style in association with the fruits is consistent with this type of arrangement. Because the fossils have these pronounced similarities with Actaea, yet lack details of the fruit wall and other characters that would definitively place them in the extant genus, we choose to designate the new genus Paleoactaea. We prefer to follow this more conservative course, particularly given the Paleogene ages of the two species. In addition to the lack of detail known for the fruit wall of P. nagelii, the considerably larger size and thicker wall of P. bowerbanki suggest this is the more prudent taxonomic course.
The two fossil species of Paleoactaea share morphological organization, seed shape, and anatomical features but differ in their size and thickness of the carpel wall. Additionally, because of the differences in preservation of the two localities, some anatomical details seen in P. nagelii were unavailable for study in P. bowerbanki. For these reasons, we recognize fossils from the two occurrences as two distinct, but probably closely related, species. The relative ages of the two species (North American: Late Paleocene; England: Early Eocene) are consistent with travel via the North Atlantic Land Bridge from North America to Europe (Tables 1, 2).
Comparison with extant Actaea and biogeographical implications
The existence of a fossil record for fruits representing tribe Cimicifugeae Torr. & A. Gray provides an opportunity to address character trends in fruits and seeds and critically look at biogeographic patterns in the context of phylogenetic studies. Compton and colleagues (1998a
, b
) completed phylogenetic analyses for Actaea and the related genera Cimicifuga and Souliea based on morphology, ITS, trnL-F sequence data and combined ITS and trnL-F data sets. Of all four of these analyses, only the strict consensus tree based on the ITS data possesses basal branches that do not collapse and are well supported by bootstrap and jackknife values. We therefore will use the results of the ITS analysis to address fruit and seed trends as well as biogeographic trends in the family. All four species of Actaea plus Cimicifuga racemosa form a well-supported clade (bootstrap value = 100) with C. racemosa being basal to Actaea. This clade is basal to all other taxa within the ingroup. Although Compton and colleagues (1998a
, b
) circumscribe Actaea to include Cimicifuga and Actaea, we elect to refer to these genera separately in our discussion since their classification has not been widely accepted (e.g., Flora of China, Li and Tamura, 2003
) and may not be familiar to most readers.
The fruits of the two species of Paleoactaea are markedly similar to those of extant Actaea in their size, shape, and details of seed morphology and anatomy. As previously mentioned, discernment of the fruit type in Paleoactaea nagelii is difficult because of limited preservation of the fruit wall. However, based on the apparently thick-walled fruits of P. bowerbanki, the berries and follicles of extant Actaea and Cimicifuga may have arisen from a thicker-walled fruit type.
Aside from fruit type, the presence of scales on the seeds has also been used to delimit Cimicifuga from Actaea. If the condition present within Paleaoactaea is used to polarize this character state, then seeds with scales are the derived condition and arose at least twice within Cimicifuga. The exceptional preservation of Paleaoactaea from Almont and the presence of seeds within the thick fruit wall of the London Clay taxon are both conditions that would have most likely preserved seed scales if they were indeed present.
Seed shape of Paleoactaea is most similar to the flattened, luniform condition Compton et al. (1998a)
noted in both the Actaea clade and a second, more derived clade of Cimicifuga (C. bitemata, C. japonica, and C. purpurea). Seeds with oblong outlines were considered ancestral within Cimicifuga and that is the most common condition within the genus. The combination of seeds with flattened, luniform outlines and no scales is characteristic of the Actaea-Cimicifuga racemosa clade. The presence of both of these conditions in Paleoactaea suggests that this basalmost clade was distinct by the late Paleocene.
Extant Actaea includes four species of cosmopolitan herbs of North Temperate regions, including North America, Europe, and Asia and unlike Cimicifuga, are broadly rather than narrowly, distributed within the generic range (Compton et al., 1998b
). Actaea favors cool, moist, shady habitats and typically occurs at lower elevations at the northern edge of its range and shifts to higher elevations at the southern limits of its distribution (Ford, 1993
; Compton et al., 1998b
; Li and Tamura, 2003
).
Compton and colleagues (1998b)
attributed the restricted distribution of Cimicifuga species within the overall range of the generic distribution to be the result of poor dispersal ability tied with the follicle fruit type. In contrast, Actaea, with its fleshy berries, may have successfully been dispersed into recent habitats (most of the range of Actaea is within glaciated regions) after Quaternary glaciations. This makes using the present distribution, in the absence of a fossil record, difficult to determine the biogeographic patterns for the genus.
The occurrence of Actaea-like fruits in both the North Dakota Paleocene floras and London Clay strongly suggests dispersal of Paleoactaea across the North Atlantic land bridge. However, the method of dispersal as well as plant habit, probably differed from its descendents Actaea and Cimicifuga. Taxa belonging to Ranunculaceae today lack the development of secondary tissue to the extent necessary for supporting an arborescent growth form. However, some genera within the family are vines (e.g., Clematis). All of the angiosperm taxa represented in the Paleocene North Dakota floras are either woody (e.g., Cornus, Cyclocarya, etc.) or vine-like (Icacinaceae, Vitaceae, Securidaca-like fruit of Polygalaceae). We do not rule out the possibility that the fruits of Paleoactaea were produced by a vine or liana.
FOOTNOTES
1 We thank Peter R. Crane, John D. Curtis, Steven R. Manchester, Paul Kenrick, and Paul Davis for providing fossils for study; Gregory Erdos and William P. Sharp for access to scanning electron microscopy facilities and technical assistance; Donald J. Pinkava for comparative extant material; the late Fred Nagel and his wife Beth Nagel for access to the collecting locality; John C. Benedict, Stefanie M. Ickert-Bond, Steven J. Mouton, and Steven Moore for technical assistance; and Sara B. Hoot and Steven R. Manchester for helpful suggestions. This research was funded in part by NSF EAR-0345838, a Faculty Grant-in-Aid, College of Liberal Arts & Sciences, Arizona State University, and a Research Incentive Award, Arizona State University, to K.B.P.; and NSF EAR-0345569 and a Faculty Research and Development Award, Georgia College & State University, to M.L.D. 
4 Author for correspondence (e-mail: kpigg{at}asu.edu
)
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