May 21, 2016

by Brian Switek

Ask to see dinosaurs at the La Brea asphalt seeps and you’re likely to get a quick correction. The standard museum line is that are no dinosaurs in the tar pits, and the institution is adamant enough about it that they’ve had comedian Will Ferrell derisively point it out in a new ad campaign. This, of course, is untrue. Birds are dinosaurs – not just "descended from," but are properly classified as dinosaurs in the same way that bats are mammals – and the sticky deposits of La Brea are rife with them.

Admittedly, these aren’t the dinosaurs most visitors are looking for. The word "dinosaur" is still overshadowed by the likes of Tyrannosaurus and Triceratops, both of which snarl at each other in the foyer of the Natural History Museum of Los Angeles. And this is strange place for these dueling dinosaurs to be. The La Brea birds are locals. Those feathery dinosaurs lived and died in the area thousands of years ago. But most of the more ancient fossils that populate the NHMLA’s halls come from Montana, Utah, and other distant spots, and this raises a question about a state so geologically well-endowed as California – where are all California’s dinosaurs?

You can find one of the locals tucked away in an alcove on the upper deck of the museum’s Dinosaur Hall. Skull bones suspended on a metal armature present Augustynolophus morrisi, a duckbilled dinosaur that trod California sometime between 72 and 66 million years ago. Drive a few hours south to the San Diego Museum of Natural History and you can find what’s left of another SoCal dinosaur under glass against the wall. This is Aletopelta coombsi, an armored dinosaur discovered during the construction of the Palomar-McClellan Airport in 1987. From the invertebrates, shark teeth, and other clues, this Carlsbad County dinosaur had been washed out to sea and had a short afterlife as a reef before being interred for over 75 million years.

Augustynolophus and Aletopelta are about as good as it gets, though. In the San Diego museum, for example, a gorgeous model of the svelte tyrannosaur Gorgosaurus menaces the other inhabitants of the hall. The evidence such a dinosaur lived nearby? Part of a tooth that may very well have come from a tyrant as-yet-undiscovered. Paleontologist Richard Hilton’s 2003 book Dinosaurs and Other Mesozoic Reptiles of California lays out some of the other finds, many of which are unimpressively scraptacular– fragments of other duckbills, teeth of raptors, tantalizing tidbits from Baja, and a partial skeleton of a carnivorous dinosaur named Labocania anomala that is undoubtedly unique but has so far defied definitive classification in the dinosaur family tree.

The basic answer is geological. “We just don’t have many of the right kinds of rocks,” Farke says, noting that “A lot of the rocks that produce fossils in California are too old, or too young, or from the places, like deep seas, that dinosaurs just didn’t live.” That means that paleontologists have uncovered a good record of marine reptiles from the Age of Dinosaurs that includes sea turtles, long-necked plesiosaurs, and sinuous cousins of Komodo dragons called mosasaurs, but the few dinosaurs known seem to be the rare ones whose bodies were washed out to sea in ancient storms, beaten and broken to leave only chunks and shards behind.

But this doesn’t mean that the record of California’s non-avian dinosaurs is unimportant. Quite the contrary. All of those tantalizing fragments and isolated bones hint at a lost world that paleontologists have really only just started to put back together.

Many of California’s dinosaurs come from Late Cretaceous rocks between 75 and 66 million years ago. Not only was much of what would become California covered by ocean during this time, but further to the east there was a great shallow body of water called the Western Interior Seaway that split the continent in half, making states like Utah and Idaho beachfront property. The great seaway was receding during this time, changing habitats as it went, but this had a profound impact on dinosaur evolution.

If you were to travel North America’s western subcontinent, called Laramidia, around 75 million years ago, you’d find different dinosaurs almost everywhere you went. Over a century of fieldwork and research, including some spectacular finds in the last twenty years, have shown that the dinosaurs that lived in Alaska were distinct from those in Alberta, which were in turn different from those in Montana, Utah, Texas, and Mexico. There were pockets of dinosaur evolution that spun off vastly different species all the way down the landmass. The communities would be the same – with tyrannosaurs, duckbills, horned dinosaurs, ankylosaurs, and so on – but the species were often very different. Why this was so isn’t yet known. Some researchers have suggested that there were physical barriers like river systems or mountain ranges that separated dinosaurs. Others have proposed that it was variations in vegetation and habitat that tied particular dinosaur species to narrow ranges. Whatever the cause, though, the Late Cretaceous saw a profusion of dinosaur species, and California has an as-yet-untold part in that story.

“Paleontologists don’t know much at all about land animals that lived on the west coast of North America during the Mesozoic”, Farke says. And yet when paleontologists uncover relatively complete specimens, those animals turn out to be different from those found to the north and the east. Augustynolophus, Aletopelta, and Labocania were all distinct from dinosaurs living elsewhere at the same time, and, based on the dinosaur discoveries around the west, it’s likely that California was home to a hidden diversity of terrible lizards. Whether we’ll get to know any of these dinosaurs is unclear. The right rocks are few, the fieldwork is difficult, and the returns may be meager. Still, the known fragments promise that there may be more out there, and we may yet get a little more clarity in envisioning the lost world of California’s dinosaurs.

https://www.kcet.org/redefine/the-dinosaurs-of-californias-lost-world