From Fossils to Molecules: The Metasequoia Tale Continues - Arnoldia

From Fossils to Molecules: The Metasequoia Tale Continues - Arnoldia

From Fossils to Molecules: The Metasequoia Tale Continues Hong Yang population in China using the techniques of cuticle micromorphology and populatio...

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From Fossils to Molecules:

The Metasequoia Tale Continues Hong Yang population in China using the techniques of cuticle micromorphology and population genetics have introduced new ideas about the evolutionary history of Metasequoia glyptostroboides, previously limited to hypotheses drawn from the fossil record. The new information suggests that the living Metasequoia trees may be recent immigrants to their remote valley in central China, rather than Tertiary relics dating back as far as 15 million years ago. Recent studies of the wild

with the genus more than fif, teen years ago when I was a college student in Wuhan, a city along the Yangtze River in the Hubei Province of central China. In a paleobotany lab session, I was shown a fossil of Metasequoia foliage collected from a Tertiary deposit in northeastern China; minutes later I was led outside to inspect the city tree of Wuhan-living dawn redwoods planted along roadsides. Seeing the close resemblance between a fossil imprint preserved in a rock for over 50 million years and the green leaves shining in front of my eyes was a breathtaking experience. Equally astounding to me was the story of Metasequoia glyptostroboides, the dramatic discovery of a living tree previously known to science only as a fossil, a story that had unfolded in that same province in the early 1940s (Hu 1948, Merrill 1948). What I could not foresee was that this college exercise had planted a seed in my mind that later grew into a strong professional attachment to this species. The dawn redwood legend has led me twice to "Metasequoia Valley" in central China and engendered a tremendous interest in pursuing its evolutionary history through both fossil records and DNA molecules.

y

V1 <

first

I

encounter

Metasequoia occurred

came to

the United States in 1988 for gradu-

training under Professor Charles J. Smiley at the Tertiary Research Center of the University ate

Idaho, and it was there, in Smiley’s personal library, that I read intensively in the literature on both modern and fossil Metasequoia.l Smiley had been a graduate student of Professor Ralph W. Chaney, the first Western scientist to travel to Metasequoia Valley, in 1948, and in Smiley’s files were copies of remarkable photographs that Chaney and his traveling companion had taken during their trip there shortly after the discovery of the living trees. In 1988, Smiley was conducting research on the Clarkia Miocene fossil site, an exceptionally well-preserved fossil deposit in northern Idaho of

that contained abundant Metasequoia fossils as well as other warm-temperate plant genera that Chaney had observed during his trip to Metasequoia Valley. I was interested in the theory of "Arcto-Tertiary flora" that Chaney had put forward to explain the origin and distribution of plants around the Pacific basin. He argued that Metasequoia and the plants associated with it originated in the high northern latitudes during the Cretaceous period, over 65 million years ago; then the whole assemblage was gradually pushed southward into the modern Metase-

1 After Dr. Smiley’s sudden passmg on January 1, 1996, his personal of Geology and Paleontology, the Chinese Academy of Sciences.

library was donated to the Nanjing Institute

61

to

complete

the journey from

Wanxian (known as Wan Hsien in the old spelling) to Moudao

(also known as Mo-tao-chi) that Chaney completed in three days in 1948. Still, the narrow road and steep slopes reminded me of a poem by Li Bai, the great poet of the Tang Dynasty, who described traveling in the mountains of Sichuan as being as difficult as climbing to the sky. Although the hardwood forest that Chaney had seen growing alongside the dawn redwoods had been cut down over the previous forty years, the enormous, centuries-old dawn redwood that Chaney had admired in Moudao still stood proudly in the middle of farmland, and I could not help but be amazed by its power to endure time and environmental change. Touching the tree’s reddish bark and looking up at its top branches, I had to wonder when and how it got there, and why the species survives only in this remote valley. The answers to my questions, it seemed, were to be found only in the fossil record. For Chaney, the discovery of

living Metasequoia provided

a

critical piece of evidence in The oldest Metasequoia tree m Xiaohe Commune, estimated at 440 support of his theory, but since years of age, photographed m 1997. Photographs taken m 1948 and 1980 his time, more fossil Metasecan be seen on pages 36 and 49, respectmely. quoia have been reported. I wanted to find out if Chaney’s theory was still quoia Valley during the Tertiary, beginning around 40 million years ago when the global clivalid in light of new findings from China, Japan, mate started to cool. A trip to Metasequoia Valand Russia. Shortly after our trip to Metaseto trace the ley Chaney’s steps among "living quoia Valley, I started to compile the Metaseflora" to both and me. Smiley quoia fossil record from the Cretaceous onward, Tertiary appealed and a more detailed picture of Metasequoia hisHistorical Biogeography Revealed by Its tory started to emerge (Yang and Smiley 1991).~. Fossil Record It is apparent that the story of this remarkable In June 1990 Professor Smiley, his wife Peg, Protree encompasses the entire history of the fessor Fred Johnson, a forest ecologist from the Northern Hemisphere over the past 100 million years, including the changes in land connecUniversity of Idaho, and I took only four hours

62

tions and climates and the evolution of

living

organisms. fossil record reveals the folfour major phytogeographic events in lowing the history of this genus: First, it is likely that Metasequoia first evolved in eastern Russia (about 60 degrees North) during the early Late Cretaceous period, around 100 million years before the present, as the earliest dawn redwood fossils were reported from this region. Thanks in part to the low temperature gradient across the Northern Hemisphere and the Bering land connection between North America and eastern Eurasia, Metasequoia spread very rapidly in two opposite directions shortly after its origin: southward to lower latitudes in eastern Russia, northern Japan, and northeastern China; and northward across the Bering land connection to North America. By the end of the Cretaceous, when dinosaurs became extinct, Metasequoia had traveled as far south as New Mexico (about 35 degrees North) in North America and had become a dominant tree in ancient forests of southern Japan (about The

36

up-to-date

degrees North) in Asia. Second, during the Paleocene,

about 60 million years ago, Metasequoia moved to the high latitudes of North America and invaded northern Europe to become a prominent member in ancient floras circumscribing the North Pole. At the same time, Metasequoia maintained the distribution pattern at lower latitudes around the Pacific basin that it had established during the Late Cretaceous. Third, when major global cooling occurred during the Late Eocene, 40 million years ago, and the cooler climate persisted, the distribution pattern changed dramatically: Metasequoia disappeared from high latitudes. By the Early Oligocene, 35 million years before present, Metasequoia had moved to lower latitudes and undertaken a longitudinal expansion to arrive in central Eurasia along the foothills of the Ural Mountains. During the Middle Miocene, when the climate again warmed up, Metasequoia re-entered the Arctic Circle. It had vanished from Eurasian fossil floras by the Middle Miocene and from North America by the end of the Miocene.

(continued on page 65)

63

Fossil Remains of Metasequoia The discovery of living Metasequoia in China more than fifty years ago shed light on the study of fossil Taxodiaceae, the family of redwoods and bald cypresses. After his trip to China, Chaney (1951) reassigned to the genus Metasequoia many fossils that had been misidentified as Taxodium or Sequoia. Since then, new Metasequoia fossils have been reported from

the Northern Hemisphere, the oldest dating back to the Late Cretaceous. Metasequoia foliage and cones are among the most common fossils in Paleocene and Eocene floras around the Pacific Ocean. From small branchlets to single shoots, the leaves of Metasequoia show morphological characteristics that differ from those of other members of Taxodiaceae. The graceful, opposite arrangement of leaves allows quick, sure identification in the field (figure aJ. However, reliable identification is difficult in pollen and wood fossils of Metasequoia : separated from the male cone, Metasequoia fossil pollen grains are almost indistinguishable from those of members of Cupressaceae, Taxaceae, or other Taxodiaceae; likewise, its wood anatomy is very similar to that of other members of the same family. Metasequoia fossils have been reported from exceptionally well preserved deposits, revealing morphological and anatomical details of dawn redwoods that lived millions of years ago. For example, three-dimensional Metasequoia fossil cones from the Clarkia Miocene lake deposit in Idaho yielded seeds that give an accurate

Metasequoia fossil Miocene

remains: shoots

deposit m northern Idaho.

description of Metasequoia seeds in Miocene (figure bJ. Mummified Metasequoia leaves found in an Eocene deposit on Axel Heiberg Island in Canada’s Arctic archipelago have pertime

mitted detailed anatomical studies of its soft tissue, and leaves trapped in amber for more than 50 million years at Fushun, a Paleocene-toEocene coalfield in northern China, offer a remarkably detailed snapshot of an ancient

Metasequoia.

Metasequoia leaves trapped m amber found Paleocene coal mme m Fushun, Chma

(a) and female

cone

with seeds

(b) from the Clarkia

in a

64

Metasequoia fossil distnbution through geotimes. NP: North Pole, C: Center of Origm, TC: Tropic of Cancer, EQ: Equator. (a) Late Cretaceous (100 milhon years before present, or MYPB); (b) Paleocene (65 to 54 MYBP); (c) Eocene (54 to 38 MYBP); (d) Oligocene (38 to 24 MYBP); (e) Miocene (24 to 5 MYBP); (f) Phocene (5 to 2 MYBP); (g) Early Pleistocene (2 MYBP to present). The square marks the modern Metasequoia Valley.

logical

65

The fossil record shown on the preceding page was compiled from published paleobotanical literature, using only clearly illustrated fossil leaves and cones. These records give a feeling for the extensive distribution of Metasequoia. The oldest was found in Late Cretaceous rocks (about 100 million years old) in northeastern Russia. At the other extreme, the youngest Metasequoia fossil was collected from Pleistocene deposits in southwestern Japan: the lower part of the Osaka Group-about 1.6 million years old-marks the extinction of Metasequoia from Japan. The highest latitude at which a Metasequoia fossil has been reported is 82 degrees North in northeastern Greenland, where abundant Paleocene fossils have been found. The prize for southernmost distribution goes to the Shihti Formation, a Miocene deposit in Taiwan at a latitude of 25 degrees North. To the west, Metasequoia fossils have been reported from Oligocene deposits in central Asia as far as 60 degrees

_

East. Possible Metasequoia

dispersal and migration (a) center of omgm; (b) Paleocene dispersal paths showmg invasion of higher latitudes ; (c) lateral Ohgocene dispersal paths, (d) Late Pliocene or Early Pleistocene migration

routes:

direction.

(continued from page 62)

Fourth, the post-Miocene history of Metasequoia has been less studied, yet it is

_

critical to the explanation for its survival in central China. Metasequoia fossils from the Pliocene and Pleistocene epochs-roughly from 5 to 1.7 million years ago-have been found only in central and southern Japan. Non-marine Pliocene and Pleistocene deposits have been commonly reported in eastern China, but no Metasequoia fossil has been found. If we read the fossil record literally, it suggests that the living Metasequoia is geologically a newcomer to its valley at the juncture of Sichuan, Hubei, and Hunan Provinces in central China, most likely having immigrated from Japan during the Late Pliocene or

66

the Tertiary fossil and the modern Metasequoia twig that I compared fifteen years ago in Wuhan.

Morphological Variation at the Population Level 1997, seven years after my first trip, I revisited MetaseIn

quoia Valley with colleagues from the Nanjing Institute of Geology and Paleontology, the Chinese Academy of Sciences. The aim of the second trip was to collect modern Metasequoia leaf samples from trees in the wild for study of both cuticle and genetic variations at the population level. In the past few years, China’s market economy has reshaped the country, and I was eager to see how these trees had weathered the environmental changes that accompanied economic reform. To my surprise, the rapid economic growth that has taken place elsewhere in China had not penetrated the remote

Metasequoia Valley.

And thanks to the Metasequoia conservation program, most of the wild trees are still healthy, although I was sad to learn that These isolated trees are located m a field mside an iron fence m the eight huge trees under which remote Longshan area of Hunan Province, about 70 miles southeast of we picnicked in 1990 had died a Metasequoia Valley. couple of years ago. we made a special effort to travel 2 million or less On this years trip, Early Pleistocene, only to the remote Longshan area of Hunan Province, before the present. about 110 kilometers (70 miles) southeast of It is interesting to note that the morphology of Metasequoia has changed little during the Metasequoia Valley, to visit and sample leaves from several large, wild trees that have rarely 100 million years since its origin. A recent taxobeen seen by outsiders. We also sampled leaves nomic revision of Metasequoia fossils by Liu from large Metasequoia trees in eight natural of what were has et al. (1999) reassigned twenty M. dawn redwood groves in the provinces of formerly twenty-one species (excluding only M. occidentalis. This Sichuan and Hubei. Each sample was divided to a single species: millen) two sets: one for study of cuticle micromorof morinto a considerable degree merger suggests a slow and another for DNA analysis. Cuticle and rate of stasis phology implies phological morphological evolution. This would explain from each tree was prepared and examined under a scanning electron microscope by Qin the striking similarity in morphology between

67

Leng, a paleobotanist at the Nanjing Institute of

Geology and Paleontology. We were not surprised to find that the cuticular characteristics among living trees within Metasequoia Valley display little variation, but Leng did make an exciting discovery: the sample collected from an isolated wild tree in Paomu, Longshan, showed

In 1992, the post

office of the People’s’s Repubhc of China issued stamps celebrating dawn redwood as well as other promment Chmese comfers.

variation. Among other noticeable differences, the internal surface of the lower cuticle in the Longshan leaves possesses a uniquely some

cuticular membrane between the stomatal and the non-stomatal zone-a characteristic that is not observed in any of the groves.2 Moreover, compared with all other samples, the Paomu sample also showed variation in the micromorphology of its guard cells. The differences in these features are great enough to warrant designation of two separate cuticle types, and the data imply that the isolated tree in Hunan Province may have preserved some characteristics that do not exist in the trees in Metasequoia Valley. Is this an indication that this isolated dawn redwood possesses a slightly different gene pool? If so, it is exciting news for the endangered Metasequoia population, whose genetic variability is expected to be very low. New morphological features found in the wild population may signal an increase of genetic diversity, which would help to alleviate its even

zone

endangered state. Clues from DNA Molecules The past fifty years have witnessed the rapid development of molecular biology, and the impact of DNA-based biotechnology is felt in almost all subdisciplines of biological science. Earlier genetic work on Metasequoia has examined chromosome characteristics and, more recently, electrophoretic patterns of enzyme polymorphism (Kuser et al. 1997), but population structure at the DNA level for wild Metasequola remained unexplored. Accordingly, a set of leaf samples collected during our 1997 trip was used to assess genetic diversity; the project is still in progress, but some preliminary data are

intriguing.

As a small population with a very limited number of individuals living in a restricted geo-

would expect the modern Metasequoia population to display a very low level of genetic diversity, especially since the morphology of several of its features has shown considerable homogeneity at the population level. However, preliminary DNA analysis,

graphic

area,

we

RAPD

(random amplified polymorphic DNA) technique, by Dr. Qun Yang and his student Chunxiang Li at the Nanjing Institute of Geology and Paleontology indicates that the species possesses a moderate genetic diversity that exceeds that of other endangered Chinese conifers, such as Cathaya argyrophylla. Further, the RAPD analysis also reveals that the genetic differences among sampled Metasequoia trees is primarily related to the geographic distance between them (Li et al. 1999). This interesting revelation suggests several possibilities: First, using

a

the genetic constitution of isolated trees in Hunan Province may have helped to increase

the overall genetic diversity of the population. If this is true, the data from molecular analysis could fit with the findings in the comparison of cuticle morphology, which also imply a slightly different gene pool for the grove in Hunan Province from that of the groves in Metasequoia

Valley. Second, the unexpected level of genetic diversity may reflect a relatively recent establish-

2 Q. Leng, H. Yang, Q. Yang, and J-p. Zhou 1999. Variation of cuticle micromorphology Metasequoia glyptostroboides Hu et Cheng ~Taxodiaceae~ (m progress).

(contmued on page 69) m

native

population of

68

A

Glimpse of the Living Population

Cuticle is a waxy layer covering the outer cell walls of the plant leaf that serves as an effective barrier against water loss. Both botanists and paleobotanists are interested in plant cuticle because their faithful impressions of epidermal cells provide valuable physiological and sometimes taxonomic information. The cuticle’s stable chemistry allows it to be preserved in sedimentary rocks for millions of years; therefore, it is particularly valuable for paleobotanists, who use it to classify fossil plants and infer their paleoenvironment. However, for both botanist and paleobotanist, studies of fossil cuticle are greatly improved when preceded by analysis of the cuticle micromorphology of living plants, and the limited distribution of existing Metasequoia will simplify this task of examining the variability of cuticle micromorphology within the species. Thus, the results of these studies will be very useful for interpreting cuticular features in the fossil material. In the laboratory, cuticle from both sides of Metasequoia leaves can be prepared, and both internal and external surfaces of each piece can be examined. Cuticle is separated from the leaf by means of an acid solution. After the material is washed in distilled water and dried in the air, it can be coated with platinum and then amplified hundreds of times under a scanning electron microscope. In addition to the cuticle’s thickness, micromorphological features of taxonomic or physiological value include the shape of epidermal cells, size and shape of stomata, shape of guard cells around stomata, and patterns on various cell walls. Two types of cuticle micromorphology were observed by Qin Leng in the wild Metasequoia population. The isolated tree growing in the Longshan area of Hunan Province exhibits slightly different cuticle characteristics from those of trees in the Sichuan and Hubei groves, some 110 kilometers (70 miles) away. For example, epidermal walls in the Paomu sample from Longshan are more regular, with a defined boundary, and the shape of the guard cells around stomata differs from those of the Sichuan and Hubei samples. These differences point to a possible source of morphological variation in the wild population.

Cuticle micromorphology of Immg Metasequoia magmfied 200 times, both show the mternal surface of the cuticle on the underside of the leaf, comparing the two cuticle types: (a) from an isolated tree m Longshan, Hunan Provmce, (b) from Metasequoia Valley m Lichuan, Hubei Provmce.

DNA from

Metasequoia Only recently have molecular approaches been applied to the field of paleobiology, providing evolutionary biologists with an independent data set that helps compensate for the incomplete fossil record. In higher plants, DNA molecules reside in the nucleus and in two organelles, chloroplast and mitochondria. A biochemical procedure permits a mixture of the three types of DNA to be extracted and purified from plant cells. Then, using a new molecular technique called polymerase chain reaction (PCR)-a kind of molecular copy machine-selected portions of the DNA can be amplified into millions of identical copies. Depending on the goals of the research, amplified DNA fragments can be sequenced to reveal nucleotide base pairs or can be cut by various enzymes to detect variations. It is the variation in DNA molecules that is the genetic basis

69

(continued from page 67J of the living population. In theory, the longer a population exists in a confined area, the more homogeneous its genetic diversity would become as inbreeding increases. Third, the unexpected level of genetic diversity may also indicate divergent evolution of small, isolated populations due to habitat fragmentation from a once genetically homogeneous, large population. Unfortunately, our current data are insufficient to prove or disprove these possibilities. The RAPD technique used in this study is a rough, molecular-level survey and, moreover, the sample size is not large enough for a meaningment

Agrose gel electrophoresis pattern showmg RAPD

amphficatlons demved from Metasequoia

27

different mld

trees.

for

morphological variability and population diversity. RAPD (random amplified polymorphic DNA) analysis, a PCR-based technique, is a new molecular tool that has proved powerful in detecting genetic diversity at the population level. Primers-small synthetic pieces of DNA-will locate any regions of the chromosome ("priming sites") that exhibit sequences complementary to the primers’ sequences. PCR will amplify all complementary fragments of DNA; if, due to a mutation, a priming site is absent from an individual, then PCR will skip over it. Thus, by counting the number of fragments shared by two individuals we get a crude measure of their genetic difference. When fragments from each Metasequoia sample are separated and stained according to their size, a series of bands is created. Variations in amplification patterning among the samples mirror the underlying DNA variation of the Metasequoia population. Therefore, the amount of genetic variation within the population can be measured by the pattern of bandmg after

amplification. By comparing amplified bands, computer-based statistical programs are able to calculate the genetic divergence among exammed Metasequoia samples. For DNA collected from any two individual trees, the more differences among the bands, the larger the genetic distance. Only in the past few years has ancient DNA from amber been extracted and sequenced. I have cracked open an amber from Fushan containing a Metasequoia shoot similar to that shown on page 63, hoping to find ancient genes that had survived for over 50 million years. Despite repeated efforts, I have been unable to find DNA; perhaps this goal will be achieved in the future.

ful statistical

test. DNA sequences

of appro-

priate genes derived from individual Metasequoia may yield more quantitative information. Nonetheless, the available DNA data reveal an interesting level of genetic variation in the wild Metasequoia population. When Did Metasequoia Arrive There?

Traveling through Metasequoia Valley in 1948, Chaney thought that he had seen a Tertiary fossil flora

come to life. Based on the close resemblance between fossil remains that he had studied in Tertiary deposits around the Pacific basin and living plants that he encountered in Metasequoia Valley, Chaney believed that Metasequoia and its Tertiary associates had taken refuge in central China since Tertiary time. He asserted that Metasequoia "participated in wide migrations" from north to south and "continued down to the present Metasequoia valley" (Chaney 1948). In other words, he viewed the living Metasequoia as a Tertiary relic. However, the detailed fossil record seems to tell a slightly different story. The absence of post-Miocene Metasequoia fossils in China suggests that the dawn redwood is a relatively recent arrival in central China. The youngest Metasequoia fossils found in China are from Middle Miocene deposits (about 15 million years before present) in Jilin Province, more than 2,000 kilometers (1,240 miles) northeast of Metasequoia Valley, and in Taiwan, an island more than a thousand kilometers (620 miles) east of

70

the present native population. Despite fifty years of intensive searching (Li 1995), no postMiocene Metasequoia has ever been found in China. It is possible, of course, that younger Metasequoia fossils are waiting to be discovered in central China, but it is also conceivable that the chronological and geographical gap in the fossil record reflects the tree’s absence during the period of more than 15 million years between the Middle Miocene and Early Pleistocene. Pliocene and Pleistocene Metasequola fossils have been found only in central and southern Japan. Geological evidence shows that the land link between southern Japan and eastern China (at about 34 to 36 degrees North) was available most recently during the late Pliocene to early Pleistocene interval, during the same period that Metasequoia trees are known to have lived in southern Japan. This land connection could have provided a migration route for its westward relocation (Wang 1985). There is also evidence that, while the climate in Japan during the Pliocene appears to have been suitable for Metasequoia, the aridity of central China in that period would not have allowed it to survive. Conversely, during the Pleistocene "Ice Age," southern Japan may have become too cold for Metasequoia (Momohara

1992), while central China, which was not significantly influenced by continental glaciation, thanks to the intervening mountains, could have been a protected haven for the species. One possible interpretation of the fossil distribution and climate data is that Metasequoia migrated southward during the Late Pliocene or Early Pleistocene from Japan to the modern Metasequoia Valley. Finally, the preliminary RAPD data seem to be compatible with the fossil record, suggesting the recent establishment of Metasequoia in its present range. Unfortunately, it offers no precise information regarding the antiquity of the living population, but further molecular study may yield better data. Conservation Efforts

During my second visit to Metasequoia Valley, I was happy to see promising results from local conservation efforts, including preservation of trees in the wild, a plantation of grafted trees, and reintroduction of seedlings to other parts of China and throughout the world. Despite a very limited budget, a Metasequoia conservation station in Xiaohe, with Mr. Shenhou Fan as the director and only employee, has maintained a large Metasequoia seedling farm and a plantation grown from grafts of wild

large

groves and along roads m great numbers, and many nurseries have been estabhshed to produce seedlmgs for cuttings. The rooting efficiency of cuttmgs decreases with the age of the source tree; the best source of cuttmgs is from seedlmgs aged one to three years

Long He, Hubei, 1994. In Chma, Metasequoia has been planted m

71

Local

people still worship the giant trees, believing they bring the family good luck (nowdays translated into prosperity) and bless their children with healthy bodies and bright minds. Educational programs are increasing, as is local awareness of the significance of trees.

these trees. Many articles in the Chinese press have featured Metasequoia, describing its discovery, scientific value, and current conservation programs. Over the next fifteen years or so, the Metasequoia trees will witness the construction of the controversial Three Gorges Dam on the Yangtze River, not far from their native land. The huge manmade lake behind the dam is bound to

affect the local climate and related ecosystems. It is my hope that the remarkable resilience of this species will again enable it to cope with dramatic environmental changes, as it has so successfully done throughout its history.

(ed.). 1995. Fossil floras of Chma through the Geological Ages. Guangzhou: Guangdong Science and Technology Press, 695. Li, C-x., Q. Yang, J-p. Zhou, S-h Fan, and H. Yang. 1999 RAPD analysis of genetic diversity m the natural population of Metasequoia glyptostroboides, central Chma. Acta ScienLi,

X-x

tiarum

Naturalmm Umversitaus Sunyatsem

38/ 164-69. Liu, Y-j., C-s. Li, and Y-f Wang. Studies on fossil Metasequoia from northeast Chma and them taxonomic

Linnean

Mernll,

implications. Journal of the

Society (m press).

E. D. 1948. Another

"living fossil." Arnoldia

8~ 1 /:1-8. Momohara, A. 1992.

Late Pliocene plant biostratigraphy of the lowermost part of the Osaka Group, Southwest Japan, with reference to extinction of plants. The Quaternary Research (Tokyo)

Wang,

31(2): 77-89. (ed.). 1985. Atlas of the Palaeogeography of Chma. Beyng: Cartographic Pubhshmg

H-z

House, 143.

Fifty years may be short for the dawn redwoods, whose lifespans easily exceed hundreds of years, but it is long enough for political, economic, and technological changes to occur around their native valley. Our knowledge of these magnificent trees has grown substantially over the past fifty years, thanks to new technologies and to several generations of industrious scientists. As studies of the species continue to provide scientists with new inputs for new ideas and hypotheses, the fascinating Metasequoia tale will continue to evolve. Literature Cited

Chaney,

bearing of the living problems of Tertiary paleobotany. Proceedings of the National Academy of Sciences, USA 34/11): 503-515. R.

W.

1948. The

Metasequoia

1951. A m

on

of fossil Sequoia and Taxodmm North America based on the recent of Metasequoia Transactions of the

revision

western

discovery

Philosophical Society, New Senes, 40(3): 171-262 H 1948 How Metasequoia, the "hvmg fossil," was discovered m Chma. Journal of the New American



Hu, H.

"

York Botanical Garden 49: 201-207. D. L. Sheely, and D. R Hendricks. 1997. Genetic variation in two ex situ collections

Kuser, J. E.,

of the

rare

Metasequoia glyptostroboides

(Cupressaceae). Silvae 264.

Genetica

46(5) :

258-

Yang, H., and C. J. Smiley. 1991. The history of Metasequoia-Its omgm, early dispersal and migration. Proceedmgs of the First Canadian Paleontology Conference, Program with Abstracts Vancouver, B.C., Canada, 26.

Acknowledgments This article is dedicated to two scientists of previous generations whose work brought me to Metasequoia Dr. Ralph W Chaney, whom I never met, but whose thmkmg on Metasequoia and other fossil plants has always intrigued me; and Dr CharlesJ Smiley, with whom I shared the ~oys of both the Clarkia fossil site m Idaho and Metasequoia Valley m Chma. I would hke to thank my colleagues at the Nanjmg Institute of Geology and Paleontology and the Zhongshan University for their collaboration. The research is supported by a Bryant College course release and by summer stipends. My trips to Chma have been supported by grants from the Chmese National Science Foundation, Chma Bridge International, and the K. C. Wong Educational Foundation.

Dr. Hong Yang is on the faculty of Bryant College where he teaches biology and earth science. He is also an adjunct research professor at the Nanyng Institute of Geology and Paleontology, the Chmese Academy of Sciences. His research mterests lie at the mterface between paleobiology and molecular biology. The author can be reached at the Department of Science and

Technology, Faculty Suite C, Bryant College, 1150 Douglas Pike, Smithfield, Rhode Island 02917 or, via e-mail, [email protected]