Long before humans were here, prehistoric horses roamed the coastal San Diego region. We find their fossils in our local sedimentary deposits, many of which date within the last 65 million years known as the Cenozoic Era, when mammals—including horses—rose and diversified. The San Diego Natural History Museum houses a rich collection of regional horse fossils, which paint a detailed picture of how horses have evolved over the last 55 million years.
San Diego, Oceanside, and Carlsbad were home to some of North America’s earliest horses between 37 and 43 million years ago. Their fossils—partial skulls, jaws, and teeth—tell us these dog-sized horses were not yet grazing grasses like the horses we know today. Their cusped teeth were an adaptation for grinding tough leaves and twigs. By around five to seven million years ago, the horse diet was changing, at least for some species: fossil horse teeth from Oceanside’s Lawrence Canyon are larger, taller, and flatter, more like the teeth of a grazer.
By around 3.5 million years ago, several horse species—including a zebra-like animal—were sharing space in our region. Fossil teeth and foot bones found in Chula Vista document some of that diversity. This was true as recently as 500,000 to 100,000 years ago, with horses large and small roaming the coast from National City to Oceanside. Some of these would look very familiar to us today. With tall, flat teeth that could withstand the wear of abrasive grasses, and just a single toe bone on each foot where their ancestors had three or four, these larger newcomers were fleet-footed grazers. The modern horse had almost arrived.