California holds a deep prehistoric past. Millions of years ago, during the Mesozoic Era, ancient reptiles, including dinosaurs, roamed or swam in the region. While complete dinosaur skeletons are rarely found, fossil evidence provides glimpses into the creatures that once inhabited this dynamic environment.
California’s Ancient Past
During the Mesozoic Era, California’s geography differed greatly from today. Much of what is now California was submerged beneath the Pacific Ocean, forming part of an active volcanic island arc system. This geological setting was characterized by subduction, leading to volcanic activity and mountain building. The terrestrial areas were often narrow coastal plains bordering these ancient seas and volcanic highlands.
This prevailing marine environment largely explains why terrestrial dinosaur fossils are less common in California. Most land-dwelling dinosaur remains would have been exposed to decay or scavenging before fossilization could occur on dry land. The active geological processes, such as uplift and erosion, continuously reworked and buried potential fossil-bearing rocks. Any dinosaur carcasses that did end up in the ocean were typically swept out to sea and buried in marine sediments.
Dinosaurs Discovered in California
Paleontologists have unearthed evidence of several dinosaur types in California, often from fragmentary remains. The most significant discovery is Augustynolophus morrisi, California’s official state dinosaur. This duck-billed hadrosaur, a large herbivore, lived during the Late Cretaceous period, approximately 66 million years ago. Two fossil specimens of Augustynolophus morrisi have been found in California’s Moreno Formation.
Another identified dinosaur is Aletopelta coombsi, an armored nodosaurid ankylosaur. This herbivorous dinosaur was discovered near Carlsbad in the Point Loma Formation. Its remains, found in marine sediments, suggest the animal died on land and was washed into the ancient sea. Isolated bones of other hadrosaurs have also been found across the state, primarily from the Late Cretaceous period.
Fragmentary evidence also indicates the presence of theropods, a group of carnivorous dinosaurs. A bone fragment from a theropod leg was discovered in the Chico Formation, providing proof of these meat-eating dinosaurs in the state. These finds confirm that diverse dinosaur groups once inhabited ancient California.
Unearthing California’s Fossil Record
The fossil record of California’s terrestrial dinosaurs primarily consists of isolated bones, teeth, and occasional trackways rather than complete skeletons. This scarcity is largely attributed to California’s unique and active geological history during the Mesozoic Era. The state’s landscape was shaped by continuous tectonic activity, including subduction, uplift, and erosion, which tended to destroy or deeply bury potential fossil sites.
Many of the dinosaur fossils found in California were preserved in marine sediments, indicating that the animals likely died on land and their carcasses were then carried into the ocean by rivers or storms. For instance, a nodosaur specimen found in Carlsbad had fossilized oysters attached to its bones, showing it became a habitat for marine life after sinking to the seafloor. Key fossil-bearing formations include the Late Cretaceous Moreno Formation in the San Joaquin Valley and the Point Loma Formation near San Diego. The Chico Formation in northern California has also yielded dinosaur remains.
California’s Other Prehistoric Reptiles
While terrestrial dinosaurs are rare finds in California, the state’s fossil record is rich with other prehistoric reptiles that are often mistaken for dinosaurs. Given that much of ancient California was submerged, marine reptiles are far more common in the fossil record. These include ichthyosaurs, which were fish-shaped marine reptiles, and plesiosaurs, long-necked aquatic predators. Mosasaurs, large carnivorous marine lizards that dominated the oceans in the Late Cretaceous, are also frequently found.
Flying reptiles, known as pterosaurs, also soared through California’s ancient skies. These winged creatures, distinct from both birds and dinosaurs, had hollow bones making their fossilization rare, yet remains have been discovered in Butte and Shasta Counties. It is important to remember that marine reptiles and pterosaurs, despite living alongside dinosaurs, belong to separate branches of the reptilian family tree and are not true dinosaurs.