Belated Tree-following at Fossil Lake

A lake in southwest Wyoming, lined with palm trees!

This month there's little to report about the trees I'm following aside from a bit of green in the aspen canopy—emerging leaves I think (forgot binoculars). Instead I have news about a tree I tried to follow five years ago, a Wyoming palm. This was not an extreme cultivar able to survive -10º to -40 °F average annual minimum temperature but a native. However, Wyoming palms went extinct millions of years ago, and now exist only as fossils.

Powell Palm, Sabalites powellii, at the U. of Wyoming Geology Museum (also called Palmites sp.).

That year (2017) I had hoped to visit Fossil Butte National Monument in southwest Wyoming, where the palms used to grow. I would go after finishing a field project nearby. But a June blizzard intervened. Three weeks ago, there was another opportunity, on my return trip from the Great Paleozoic Sea, but again a blizzard threatened. This time I ignored it, for awhile.

Above, Fossil Butte National Monument in the high dry desert of southwest Wyoming (NPS, Tyra Olstad photo). Below, same general area 52 million years ago.

Lotus plants (Nelumbo sp.) in foreground; click to view dragonfly and mosquitos.

My first stop was the Visitor Center, small but packed with fossils and information. A ranger greeted me and offered a tour. "Absolutely!" I replied. "Can we start with plants?" I followed him to the Plant Wall. In addition to the familiar palm leaves, there was a palm inflorescence and many other plant fossils, with modern genera surprisingly (to me) well represented.

Plant Wall at Fossil Butte NM (NPS photo). Below left of the palm leaf on the right is a palm inflorescence.

Like today's palms, those at Fossil Lake had large inflorescences with hundreds of tiny flowers.

Fossilized palm inflorescence.

Fossilized palm flower (NPS photo), c. 8 mm across.

Fifty-two million years ago, in what would become southwest Wyoming and adjacent Utah and Colorado, there were three large lakes, larger even than our Great Lakes. These were Lake Gosiute, Lake Uinta, and Fossil Lake. The last was the smallest, but its sediments were especially rich in plant and animal remains. The now-lithified sediments of Fossil Lake are famous for abundant well-preserved fossils.

Petrified Fish Cut near Green River, Wyoming, excavated in 1868 during construction of the transcontinental railroad. William H. Jackson photo, 1869 (Hayden Survey) (source).

Fossil Lake's Knightia (the many small fish in this photo) is said to be the most common of vertebrate fossil in the world. It's also the state fossil of Wyoming (photo by Mike Nelson).

This ray fossil is an example of the exceptional preservation at Fossil Lake (NPS photo). As I learned on my visit, rays usually aren't well preserved because they have cartilage rather than true bones.

We finished the tour at a diorama showing southwest Wyoming 52 million years ago. Dioramas of ancient worlds have enchanted me since I saw my first, 60+ years ago. I've never outgrown them, though I now know there can be a fair amount of informed speculation involved.

The many diverse creatures and plants preserved in Fossil Lake sediments indicate the climate was warm and humid. Vegetation along the shoreline was lush, with forests of palm, cinnamon, maple, and oak inhabited by mammals small and large, including some of our ancestors.

Yikes! Is that a giant oreodont approaching upper left?

As we finished, I asked the ranger about his background. Just five days earlier he graduated from university in California, then drove for two days to Wyoming, and went to work the next day. He was eager to share the joy of visiting the distant past, and his enthusiasm was contagious. Lucky me!

Next I hiked the nature trail, past high desert cushion plants blooming profusely in light snow and howling wind. The blizzard was closing in. I decided to skip the old quarry, where I would have seen remnants of Wyoming palm habitat up close. That and much more await another visit. I raced home ahead of the storm, easy to do on Interstate 80 with a ferocious tailwind. Good mileage too.

Sources

Grande, L. 2013. The lost world of Fossil Lake. University of Chicago Press.

McGrew, PO, and Casilliano, M. 1975. The Geologic History of Fossil Butte National Monument and Fossil Basin. NPS Occasional Paper No. 3.

Following a Tree, from Fronds to Rebar

April 7 has arrived, and being a tree-follower, I’m posting the latest news of my tree at the monthly gathering kindly hosted by The Squirrelbasket. If you like trees and would like to join us, check out the links above (it’s interesting and fun, with no obligation).

This year I’m following an extinct tree—Sabalites powellii, a palm that grew in southwest Wyoming 50 million years ago. I discovered it in December in our Geology Museum, and in May I will visit its ancient habitat. In the meantime, tree-following consists of learning about Sabalites and its world. This month, I decided to look into its wood. The Green River Formation—the rock layers where fossilized fronds have been found—also contains fossilized palm wood. It’s common, beautiful, and popular with collectors.

Fossilized palm wood is the state rock of Texas (source).

However, my search for “Sabalites wood” was futile, both in Google and the scientific literature. That’s because fossil palm wood is called Palmoxylon. Is this weird? Are paleobotanists exceptionally obsessed with publishing new names?

Sabalites powellii, a fossil palm frond “species” from southwest Wyoming.

Palmoxylon includes 200+ “species” of fossil palm wood (source).

Plant fossil names proliferate because paleobotanists are faced with an unfortunate situation. Most fossilized plants are actually fossilized plant parts—leaves, branches, flowers, etc., that fell off some plant. Generally there’s no way to know if different parts came from the same species, so they’re given different names.

Palm wood usually is easy to recognize. Cutting a petrified palm trunk cross-wise reveals a characteristic pattern of scattered dots—the vascular bundles that conduct water and nutrients up and down trees.

Cross-section through petrified Palmoxylon log (click on image to view dots; source).

Length-wise view of Palmoxylon (source). Xylon means “one having (such) wood—in generic names” (Merriam-Webster) … in this case, having palm wood.

In most trees (dicots), vascular bundles are arranged near the perimeter, but in monocots, they're scattered through the stem (diagram below). Monocots include orchids, grasses, lilies and more. Most are herbaceous, but a few produce wood and grow large, e.g. yuccas, bamboos and palms.

Cross-sections through dicot and monocot stems (source, modified).

Wait a minute!!! As botany students we're taught that monocots don’t make wood. Wood is produced by secondary growth in the vascular cambium (below), and monocots have no vascular cambium. Yet palms are monocots and obviously woody … ??

In dicots, wood develops from secondary growth via the vascular cambium (source, modified).

Large monocots are said to produce strong trunks through abnormal secondary growth. I think we call it “abnormal” because it’s disorderly and hard to categorize … and poorly understood. Webpage after webpage explains that palms thicken their trunks through diffuse secondary growth, in which parenchyma cells divide and enlarge. And yet a recent study revealed that at least some palms have a vascular-cambium-like meristem! (Botánico & Angyalossy 2013; article here):

“… we analysed palm stems of four species, with the aim to understand the possible presence of such secondary growth. We found that a meristematic band occurs between the cortex and the central cylinder and gives rise to new vascular bundles and parenchyma internally, producing parenchyma and fibres externally. … In fact, a meristematic band is present and may be more common than currently believed, but uneasy to detect in certain palms for being restricted to specific regions of their stems.”

Palms’ tough rigid tissue may not be “true wood,” but it’s called wood and functions as wood. Some kinds are used in construction, including that of the coconut palm. Wood from the outer part of the trunk, where the vascular bundles are dense, is harder even than oak and Douglas fir (source).

In fact, sometimes palm wood is better than true wood. It's more flexible—palms can bend 40º without breaking! The tough fibrous vascular bundles scattered through the trunk serve as plant rebar—like the steel rods that give strength and flexibility to reinforced concrete.

Flexibility is a great adaptation in hurricane-prone environments. Courtesy US Navy.

When a tropical cyclone tore through this rainforest, the palms were left standing (source).

We'll stop here. Once again, tree-following has taken me on a winding journey, this time to fossil palm wood, woody monocots, meristems, vascular bundles and finally rebar. We’re lucky there’s so much of interest in this world!

Thanks to Mike of CSMS Geology Post, for continued paleontological guidance.

A Powell Palmetto Perhaps?

Am I following a palmetto?

Sabal palmetto (source).

I’m intent on learning more about palms, as I decided to follow a palm tree this year (unfamiliar with tree-following? click on the link). My tree has a name, Sabalites, but what kind of palm is it? No one is sure. There are lots of choices—the palm family (Arecaceae) is large and diverse. It includes five subfamilies, 16 tribes, 2500 species, and many products consumed by humans: coconuts, dates, oil, betel chew, rattan and more. Most palms grow in tropical or subtropical regions, and occasionally in deserts.

Selected palms of the world; click on image to view details (source).

Palm fruit are beautiful as well as delicious (Dransfield et al. 2008).

Desert fan palms near Twentynine Palms, California (source).

When I lived in California, I was familiar with palm trees—specifically the ones planted along highways and in cities, and the native fan palms of desert oases, Washingtonia filifera. Then I moved to Wyoming where currently it’s much too cold for palms. However, fifty million years ago they lined the shores of huge lakes in the southwest part of the state. Even though their leaves are beautifully preserved in rocks of the Eocene Green River Formation (more here), no one is sure what kind of palms they were. Since I started following this tree, I’ve learned that plant fossil identification is really tough. Even the most challenging living plants are easy compared to fossilized ones.

Fossil Lake of Early Eocene Wyoming (Chicago Field Museum).

In 1870, geologist Ferdinand Vandeveer Hayden’s exploratory expedition stopped near Green River Station, Wyoming, where they found lots of fossils. Some looked very much like palm leaves. In the expedition report, staff paleontologist Léo Lesquereux assigned them to Flabellaria Eocenica. I don’t know why … modern day Flabellaria is not a palm, nor do the leaves resemble palm leaves.

Later, Hayden sent the fossils to paleontologist John S. Newberry of Columbia College, who decided they looked enough like today’s palmettos, genus Sabal, to call them Sabal powellii (I presume in honor of geologist John Wesley Powell, then Director of the US Geological Survey, but I haven’t been able to confirm this). The Powell palmetto was one of ten new fossil plant species from the Green River area published by Newberry in 1882.

8. SABAL POWELLII, n. sp. Leaves of medium size, 4 or 5 feet in diameter, petiole smooth, unarmed, terminating above in a rounded or angular area, from which the folds diverge; beneath concavely narrowing to form a spike 3 to 4 inches in length; rays about fifty, radiating from the end of the petiole, perhaps sixty in the entire leaf, compressed to acute wedges where they issue from the petiole, strongly angled and attaining a maximum width of about 1 inch; nerves fine, about twelve stronger ones on each side of the keel, with finer intermediate ones too obscure for enumeration. Formation and locality. — Eocene strata. Green River Station, Wyoming.

Why did Newberry conclude that these fossils were palmettos? Because the leaves are clearly costapalmate. (Yes, this is an esoteric term, but the concept is easy and useful.)

Costapalmate leaf of the Puerto Rican hat palm, Sabal causiarum (source).

Palm leaves are huge, with blades divided into many narrow segments arranged in several different patterns. In palmate leaves, segments fan out from the base of the blade—like fingers from the palm of a hand. In costapalmate leaves, the leaf stem (petiole) extends up into the blade to form a costa, where leaf segments are attached. The costa is only visible on the underside of the leaf, and from above, leaves look palmate. [Here’s a helpful webpage devoted to costapalmate palm leaves.]

In a paper about extinct floras of North America (1898), Newberry included a photo of a Wyoming palm leaf fossil with an obvious costa. “In the figures given, that on Pl. LXIII, fig. 6, represents the under side of the leaf at its base, showing [a] pointed spike [costa] formed by the prolongation of the petiole.”

From Newberry 1898; no scale provided (leaves can reach 4-5 feet across).

Unfortunately, costas are not unique to palmettos, and in 1930, paleobotanist Edward W. Berry overrode Newberry’s decision, renaming the fossils Sabalites powellii:

[the leaves] “are superficially much like the leaves of the existing species of Sabal, and their northern range appears to afford some corroboration of such a relationship, but this is by no means established, and it appears to me to be a better practice to refer such remains to the form* genus Sabalites rather than to Sabal.”

[*In form classification, fossilized organisms or their fragments are classified based on appearance, not biological relationships. If different parts of a single species are not obviously from the same source, they may end up as different form species or even genera.]

Robert Read and Leo Hickey agreed with Berry in their 1972 Revised Classification of Fossil Palm and Palm-like Leaves. They were adamant that leaves alone are insufficient evidence:

“Numerous similarities in the form and gross external features of [fossil] palm leaves make it difficult or impossible to assign them to modern genera based only on their external morphology. The uncertainty … becomes even greater with the limited, incomplete collections available to the paleobotanist. A modern specialist might speculate that a given fossil closely resembled a modern genus such as Sabal, Geonoma or Thrinax. Such a suggestion would be debatable since it is almost impossible to distinguish these genera … without seeing flowers, fruit or other diagnostic characters. Forced identifications with modern genera contribute nothing to evolutionary theory but give instead a confused picture of the floristics of the geological record. Since it is very difficult to identify specimens of modern palms accurately from their leaves alone, no attempt should be made to place fossil palm fragments in genera of modern palms unless unquestionably identifiable with them.”

Maybe we shouldn’t give up just yet. After all, thousands of fossils are collected from the Green River Formation every year! Maybe some will reveal the true identity of Sabalites powellii. There’s reason for hope. Paleobotanist Sarah Allen has been working nearby on another fossil palm, in the Bridger Formation, and has enough fossils—leaves, flowers and even pollen—to confidently assign the trees to Phoenix, the genus that includes today’s date palms (Allen 2015). Will we be so lucky with Sabalites? Already its fossils include not just leaves, but also apical buds, flowers, inflorescences (flower clusters), and even inflorescences attached to leaves. Are more discoveries likely? When I visit the remains of Fossil Lake later this year, I'll look for some experts and ask them what they think.

Fossil terminal bud, from the Green River Formation (in palms, leaves originate from a single terminal bud at the top of the trunk); University of Wyoming Geology Museum.

Personally, I hope paleobotanists find that Sabalites powellii is indeed a palmetto, and that they resurrect Newberry’s Sabal powellii. “Powell palmetto” has such a nice ring to it ...

We’re off to Fossil Lake to see the Powell palmettos!

Sources

Thanks to the Biodiversity Heritage Library for providing easy access to older paleontological literature, and to Mike for continued guidance in paleontology.

Berry, EW. 1930. A flora of Green River age in the Wind River basin of Wyoming. USGS Professional Paper 165: 67.

Dransfield, J., et al. 2008. Genera Palmarum, the evolution and classification of palms. University of Chicago Press.

Newberry, JS. 1882. Brief descriptions of fossil plants chiefly Tertiary. Proceedings US National Museum 5: 504.

Newberry, JS (A. Hollick, ed.). 1898. The later extinct floras of North America. Washington: Government Printing Office.

Read, RW. and Hickey, LJ. 1972. Revised classification of fossil palm and palm-like leaves. Taxon 21:129-137.

“so many fossils that people cry”

Scallop fossils near Lopez Lake. Photo courtesy Monika Wieland Shields, Orca Watcher

Long ago, on our frequent trips to Lopez Canyon, we would often pull off the road just past the lake to comb for seashells. These were fossil shells—exciting treasures common enough for a child to find. But why were they there, far from the sea, high in the rugged California Coast Range? Three hundred years earlier, the great Nicholas Steno, one of the founding fathers of geology, had also pondered this mystery: “in what way marine bodies had been left in places far from the sea.”

Steno concluded that shell-like “bodies” in rock looked like shells because … they once were shells! This seems like a no-brainer today, but in the 1660s it was a profound realization. Marine bodies did grow in the rock, as many thought. Rather they were creatures that lived, died and were buried in sand and mud on the bottom of an ocean. Then disturbance moved the Earth, seas became dry land, muck turned to rock, and seashells ended up in high in the mountains far from the shore.

But why are there so many fossils near Lopez Lake … and off and on for miles to the north? This contradicts basic knowledge. Fossils are rare. In fact, fossils are so rare that Charles Darwin worried they would undermine his theory of evolution:

“Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and gravest objection which can be urged against my theory. The explanation lies, as I believe, in the extreme imperfection of the geological [fossil] record.” On the Origin of Species, 1859.

Not long after Darwin published On the Origin of Species, access to the fossil record grew dramatically. Pioneering paleontologists excavated thousands of fossils, taking them back to their respective institutions. The pace accelerated through the twentieth century and continues today. Even so, fossils remain rare. Though zillions of creatures have come and gone during the 3.65 billion years since life began, precious few died where they or their parts could be preserved. Most decayed. I’ve read that only 1% of all organisms that ever lived have been fossilized, though I wonder … how can we know?

There are spectacular exceptions, sites where fossils number in the millions. These are lagerstätte, meaning “storage places.” German miners use the term for rich seams of ore—mother lodes in English. There are two kinds of fossil mother lodes. In concentration lagerstätten, fossils are exceptionally abundant, but are mainly disarticulated bones or fragments that aren’t always useful in reconstructing organisms.

Above, bones from a dried-up waterhole, during a severe drought circa 20 million years ago. Below, reconstructed Dinohyus (Agate Fossil Beds National Monument Visitor Center).

Most highly prized are conservation lagerstätten, where fate stepped in to preserve quality as well as quantity. Fossils include articulated (connected) skeletons, soft tissues of various kinds, even entire organisms (e.g., flies in amber). Soft tissue fossils can be quite beautiful, with minute details of hair, feathers, muscle tissue, even ovaries with eggs! And soft tissue preservation immortalizes organisms that have no bones or shells, such as insects, spiders and plants.

Above, Jack hunts for sea scorpions (Eurypterus) that swam the seas 400+ million years ago. These are extinct marine arthropods, and not true scorpions. After finding a claw on his first try, he uncovered two beautiful scorpions on his second (below)! Photos courtesy Jack Share of Written in Stone.

Here in Wyoming, we have a world-renown conservation lagerstätte, in the Green River Formation. It's a grand accumulation of exceptionally-preserved fossilized creatures that were buried in lake-bottom muck about fifty million years ago. Some layers are especially rich. The Fossil Butte Member, just 20 m thick, has yielded millions of exquisite fossils of fish, flies, bats, snails, spiders, parrots, mosquitos, crocodiles, and (best of all) plants.

Exceptional preservation requires exceptional conditions. In the case of Green River fossils, frequent floods may have deposited enough sediment on the lake bottoms to quickly bury the dead. Perhaps lake water periodically turned noxious, killing scavengers and microbes that would otherwise devour soft tissues. Whatever the causes, we’re lucky.

We share the Green River Formation with adjacent states (source).

Articulated skeleton of a clawed bat, in beautiful detail (NPS).

Sabalites powellii, an extinct palm (NPS).

Macginitiea wyomingensis, an extinct sycamore.

Plant fossils are especially valuable, for they provide clues for diciphering paleo-environments. A diverse flora with palms, ferns, horsetails, sycamores, sweetgums, catalpas, lotuses and more suggests Wyoming was subtropical (or at least mild) during early Eocene times.

Southwest Wyoming 50 million years ago (artist’s reconstruction; Chicago Field Museum).

Wyoming citizens are rightly proud of the Green River Formation. It’s considered one of three great conservation lagerstätte in the world (Nudds & Selden 2008), the other two being an oil shale deposit near Darmstadt, Germany, and the Florissant Formation of Colorado. But the order may be rapidly fading.

In Patagonia, Argentina, paleontologists are removing thousands of beautifully-preserved fossils from the Lago del Hunco Formation. Like our Green River Formation, it dates from the early Eocene, roughly 52 million years ago, and is composed of lithified lake sediments—specifically a lake in a caldera, a huge volcanic crater. Reports verge on ecstatic:

“There are white rocks that are jam-packed full of fossils, so many fossils that people cry when they see them. I’ve never seen so many beautiful fossils in one place.” —paleontologist Peter Wilf, to a New York Times reporter (italics added)

(Tearful?) paleontologist at a Lago del Hunco quarry (source).

Elsewhere, Wilf declared Lago del Hunco to be one the most fantastic fossil sites in the world, because of the diversity of plants, insects, fish and amphibians. Gosses and colleagues (2006) called it “the world's most diverse Eocene flora.”

Fossils of the Lago del Hunco Formation record a time when a great diversity of plants—probably a rainforest—grew around a lake. Dead plant material that washed into the lake was frequently buried in sediments containing large amounts of volcanic ash and debris. That lake-bottom muck is now tuff containing beautiful soft-tissue fossils, and the rainforest is long gone. Paleontologists work amid dry desolate hills.

In 2003, Wilf and colleagues reported that the Lago del Hunco flora had a richness (number of species) that “exceeds that of any other Eocene leaf flora, supporting an ancient history of high plant diversity in warm areas of South America.” The known flora as of 2013 (listed here) includes ferns, cycads, ginkgos, several unidentified conifers, palms, eucalyptus trees, grasses, many members of the pea family, and more.

Fossils from the Lago del Hunco Formation (Wilf et al. 2003). Scale bars are 1 cm long.

Will Lago del Hunco fossils bump our Green River Formation from its standing as one of the three great conservation lagerstätte? It’s too early to say; much work remains to be done. But an especially charismatic plant appears to be making fossil numbers and quality irrelevant. In slabs of white tuff, Peter Wilf found two tomatillos. Exceptional preservation combined with the popularity of tomatillos among salsa-aficionados was enough to grab the attention of the press.

“Tomatillo Fossils, 52 Million Years Old, Are Discovered in Patagonia” (The New York Times). 

Tomatillos are tomato relatives, with smaller green fruit. They’re distinctive for their thin papery inflated husks. To find these delicate structures preserved in rock 52 million years after death is mind-boggling! This discovery also upsets current thinking about the evolution of the Solanaceae, the family that includes potatoes, tomatoes and nightshades (discussed here and in Wilf et al. 2017).

Garden tomatillo or Mexican husk tomato. The husk, or lantern fruit, is an inflated calyx (source).

One of our wild tomatillos, Physalis heterophylla (source).

“Eocene lantern fruit from Gondwanan Patagonia” (Wilf et al. 2017).

I have to admit, I'm in awe of paleobotanists. I’ve done floristic surveys myself, compiling species lists for areas large and small. We collect plants in identifiable condition, with flowers or fruit, and compare them to herbarium material to verify identification. Sometimes we analyze relationships to well-documented floras elsewhere to determine affinities, and try to tease out biogeographic history and paleoclimate. This isn’t easy, even with fresh specimens, so to identify and coax stories from 52-million-year-old fossilized plants seems magical! Are paleobotanists part shaman—able to bring the dead back to the land of the living? Maybe they're more like Virgil, who visited the past himself and then returned to tell he found.

You gods who rule the kingdom of the rocks! You soundless Shades! …

Grant me to tell what I have seen! With your assent,

May I reveal what lies deep in the gloom of the Underworld!

(Aeneid Book VI, modified only slightly)

Sources (in addition to links in post)

Thanks especially to Mike the rock guy, for help with paleontological issues!

Cutler, A. 2003. The seashell on the mountaintop; how Nicolaus Steno solved an ancient mystery and created a science of the Earth. A Plume Book.

Grande, L. 2013. The lost world of Fossil Lake. University of Chicago Press.

Montanari, S. 2016. What Darwin didn’t know about the fossil record. Forbes, Feb 12, 2016.

Nudds, J. and Selden, P. 2008. Fossils explained 56; fossil-lagerstätten. Geology Today 24:153-158. PDF

Wilf, P, et al. 2003. High plant diversity in Eocene South America: evidence from Patagonia. Science 300:122-125.

Wilf, P, et al. 2005. Eocene plant diversity at Laguna del Hunco and Rio Pichileufu, Patagonia, Argentina. The American Naturalist 165:634-650. PDF

Wilf, P, et al. 2017. Eocene lantern fruits from Gondwanan Patagonia and the early origins of Solanaceae. Science 355:71-75.