Bay Nature magazineSpring 2009


Dinosaur Plants

April 1, 2009

When dinosaurs roamed the earth, what we know as western California did not exist, and the waves of an ancient sea lapped against a beach where the Sierra Nevada foothills are now. In place of today’s Sierra Nevada range there were even larger mountains, complete with forests and active volcanoes.

We know from the work of paleontologists (scientists who study fossils to learn about life long ago) that dinosaurs, early mammals, tortoises, and many other creatures thrived in these ancient forests. We even have evidence that predatory dinosaurs related to Tyrannosaurus rex lived in California nearly 100 million years ago. But most of the land-dwelling dinosaur fossils unearthed in California have been herbivores (plant eaters) like the duck-billed giant Saurolophus.

Modern horsetails
Modern horsetails. Photo by Charles Kennard.

How do we know they were plant eaters? And what did these ancient vegetarians eat? Figuring that out takes sophisticated science and a lot of detective work. Some clues come from the shape of the dinosaur’s preserved teeth and jaws, or from what’s found in the animal’s fossilized gut. And there is even more evidence from the new science of “paleoscatology”–the study of fossil poop, called “coprolites” by scientists.

So far, paleontologists have not discovered coprolites from land-living dinosaurs in California. But they have found fossils of plants that once grew here, and we can assume the plant-eating dinosaurs must have eaten some of them.

You’ll never see a living dinosaur (though birds are their descendants), but you can see the relatives of ancient plants growing wild in the Bay Area today. The most unusual-looking are the horsetails, with straight stems resembling cartoon horses’ tails, some with whorls of short branches. Their leaves are almost invisible, and they have no flowers. Horsetail cells contain granules of silica (like sand), making the plants rough to the touch and inspiring another common name: scouring rush. For centuries, people have used horsetails to scour metal pots and sand wood. Because horsetails would have quickly worn down the teeth of any animals that ate them, they might not have been a big part of the dinosaur diet.

Horsetails are moisture-loving plants and grow along streams in many parts of the Bay Area. Gardeners who plant them often regret it; where there’s enough moisture in the soil, their roots spread far and wide and send up thickets of new horsetails as they go.

From fossils like this of Annularia, an ancestor of horsetails, paleontologists can learn about ancient plants. Photo by Sue Rosenthal.

Our local horsetails grow about three feet high, quite small compared to the 10- to 20-foot-tall giant horsetails of Central and South America. But even those “giants” would be dwarfed by their ancient relatives from before the dinosaurs, some of which towered 100 feet over the landscape.

Our many modern ferns are also descendants of plants that grew with the dinosaurs. At the time of the dinosaurs, many ferns had straight trunks up to 30 feet tall, while others grew lower to the ground, a good height for smaller hungry herbivores.

Also common when dinosaurs roamed California were the ancestors of our majestic redwoods. Ancient redwood relatives emerged on the scene more than 160 million years ago and grew from Alaska to Pennsylvania, as well as in Europe and Asia. A changing climate 10 million years ago left coast redwoods growing only in a narrow strip along the coast of California and Oregon and “Sierra redwoods” (giant sequoias) only in the western Sierra Nevada.

Luckily, we live in coast redwood territory, where many ferns and horsetails also grow, so we can travel back in time with these hardy survivors and imagine the days of the dinosaurs.

Get Out

You can see fossils of ancient plants (and dinosaurs) at the Sierra College Natural History Museum in Rocklin, east of Sacramento [] or at the University of California Museum of Paleontology at UC Berkeley, normally closed to the public. The UC museum will host an open house on Saturday, April 18, 9 a.m.-4 p.m., with tours, demonstrations, and displays [, (510)642-1821].

To see the ancient plants’ nearest living relatives “in the flesh,” visit the newly redesigned Ancient Plants Garden at the San Francisco Botanical Garden. Follow the footprints of a plant-eating hadrosaur through millions of years of plant evolution along a meandering boardwalk lined with descendants of ancient plants [, (415)661-1316].

For even more of the feel of an ancient California landscape, use your imagination while visiting redwoods, ferns, and horsetails at Muir Woods [, (415)388-2595]. Or check out the 3-million-year-old fossil trees at the Petrified Forest near Calistoga. Blasted down by a huge volcanic eruption and then buried in ash, the trees of the petrified forest were fossilized when minerals in the ash gradually replaced their wood, turning them to stone [, (707)942-6667].

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