"What We Find Belongs to the Public Domain of Science": The Boy Paleontologists and the Irvingtonian Land Mammal Stage

 

Mission Peak from the Sabercat Trail in Fremont, California

I can just hear the script writers arguing about one of the scenes in an Indiana Jones movie...

George Lucas says "How about 'What we find belongs to the public domain of science'?"

Someone, presumably Harrison Ford in disguise says "George, you can type this s**t, but you sure can’t say it.”

Someone else pipes up and says "Shorten it to 'That belongs in a museum'" and history was made.

I'm sure it never happened that way, but "What We Find Belongs to the Public Domain of Science" was in fact the motto of the Boy Paleontologists, who prior to last weekend I had never heard of. As adventurers, they were far more real than Indiana Jones, and ended up contributing far more to science than a glorified tomb raider. And to my surprise, I learned a lot more in an unexpected moment of serendipity.

Interpretive sign on the trail describing the paleontology efforts at Sabercat Trail

To begin with, Irvington simply is not a city that I've ever heard of in California. There's Irving, Texas, and Irvine, California, but no Irvington. But there is a part of the geological time scale called the Irvingtonian North America Land Mammal Stage. And that means there's an Irvington somewhere in North America, but a moment of research reveals that there are hundreds of fossil sites of Irvingtonian age scattered across the continent (and in fact the world). I never really thought to look up the actual location (and yes I see that Irvington, NJ is a place). 

The Irvingtonian North American Land Mammal Age (NALMA) on the geologic timescale spans from 1.9 million to 250,000 years ago. The Irvingtonian is usually considered to overlap the Lower Pleistocene and Middle Pleistocene epochs (basically the middle of the ice ages). The Irvingtonian is preceded by the Blancan and followed by the Rancholabrean NALMA  (which I absolutely knew about; I wrote about it tangentially just months ago).

The beginning of the Irvingtonian is defined by the first appearance of Mammuthus south of 55° N in North America, and the beginning of the succeeding Rancholabrean is defined by the first appearance of Bison.

Source: Barnosky et al., Prelude to the Anthropocene: Two new North American Land Mammal Ages (NALMAs). The Anthropocene Review. 1. 1-18. 10.1177/2053019614547433.

So how do these land mammal stages happen? Basically someone finds a huge number of fossils in a particular locality, and the assemblage turns out to be correlated to lots of other fossil sites across the continent to the extent that any fossil site with the same assemblage can be confidently dated. 

My son has been encouraging me for months to come and visit and walk the path in a Fremont park called the Sabercat Trail. He said they dug up a bunch of fossils there and it was preserved as a historical park now. I was intrigued, but COVID cut down on the opportunities to visit so it didn't happen until last weekend.

We got there and I was confused. I was in Fremont, but I was in Irvington. It turns out that Irvington once did exist as a village, but it was incorporated into the larger city of Fremont, but retains its character as the Irvington Neighborhood. And suddenly I realized this Sabercat Historical Park was a lot more important than I took it for. It wasn't just a fossil dig, it was THE Irvingtonian fossil dig. And what a story it had!

The fossils were first reported in 1867 when a local dentist named Lorenzo Gordin Yates found bones on Mission Creek (Sabercat Historical Park is just a few blocks from Mission San Jose). He sent them to Yale University because there was no one yet on the west coast who could identify them. His samples apparently included horses, camels and mammoth bone fragments.

Decades passed, and despite being just a few miles north, paleontologists from U.C. Berkeley didn't visit the site until the 1930s. The head of the Paleontology department at Berkeley, Ruben Stirton collected an assemblage of fossils and published a report in 1939 that first referred to the Irvingtonian fauna. It was defined as a land-mammal age as a result of Don Savage's studies in 1951.

A very large mammoth tusk at the Bell Quarry. Source: Pleistocene Ecosystem (msnucleus.org) by Wesley Gordon

The Boy Paleontologists entered the scene in middle 1940s when Wesley Gordon brought his sons and several of their friends on a fossil-collecting trip to the site. By now the locality was an active gravel quarry (the mind reels at the number of specimens that must have been destroyed over the years). A weekend hobby turned into a major excavation using young volunteers from the local community. The digs continued for around 15 years, and were even the subject of a Life Magazine article. They ultimately recovered 150,000 specimens of 58 species. 

The site unfortunately lay in the path of "progress", or more specifically the 680 freeway. Most of the quarry is covered by pavement now, although the account mentions that Wes Gordon convinced CalTrans to slightly divert the route to preserve a Short-faced Bear locality. My son mentions that the Ohlone people fought a 20-year legal battle to preserve an ancient burial site from the same freeway.

What exactly did they find? Who was living in the San Francisco Bay region between 1.9 million to 250,000 years ago? The trail provides some very nice interpretations of the ecosystem that existed at the time.

The cast of creatures ranges from mammoths larger than today's elephants to frogs and toads. During the ice ages, San Francisco Bay didn't exist as such because sea level was hundreds of feet lower than today. The area was broadly similar to what it would be today, if not cooler and slightly wetter. The grazing animals were dominated by camels, horses, deer, mammoths, mastodons, peccaries, and a unique species of four-horned antelope first discovered at Irvington. There were also gigantic ground sloths many times the size of their cousins today in Brazil. Rodents and rabbits would have been as common as today, and their remains are part of the assemblage that was discovered. Because of the delicate nature of their bones, only a few birds, a Canada Goose and Mallard duck, have been found as fossils. There were undoubtedly hundreds of species as there are today.

The carnivores were diverse and imposing. Sabertooth cats have been found (hence the name of the park), as well as scimitar cats, dire wolves, coyotes, foxes, badgers, and raccoons. The most terrifying must have been the short-faced bear, which makes grizzlies look small. It is considered the largest terrestrial mammal carnivore known. 

The park is a different place today. Bobcats and coyotes have replaced the bears, wolves, and sabertooth cats. It offers a network of trails that wind in and out of Sabercat Creek, and there is a smaller wilderness area in adjacent Mammoth Creek. Most all the trails are paved and accessible except for the actual remains of the quarry overlooking the freeway. Most of the fossiliferous layers were eliminated by the construction of the freeway, but the view from that end of the park is far-ranging (below).

I have a feeling that the park is an underutilized birding site. 84 species have been reported so far, but that is probably far fewer than what is actually there, given the excellent riparian habitat. We saw 18 species during our short visit including a very accommodating Western Bluebird.

I'm glad my son dragged us out to the Sabercat Trail. It was quite a revelation and answered some questions I've always wondered about!