It’s been a fact that has baffled scientists: other than relatively small species, scientists have been unable to find dinosaurs in the equator that is filled with vegetation and wildlife today, a seemingly perfect place for them to thrive. But now scientists think they know why.

As it turns out, the equator was a lot different back 200 million years ago when dinosaurs roamed the earth compared to how it is today, and scientists now think that the high heat and unpredictable climate of the equator probably kept the dinosaurs away, according to a Daily Mail report.

The equator probably would have resembled today’s western United States, and it would have featured droughts and wildfires interspersed with sudden wet seasons that would have made it nearly impossible for large, long-necked dinosaurs to survive. This would have made it unsuitable for large, herbivore dinosaurs who would rely on lots of vegetation — vegetation that would be pretty much unavailable in the harsh, arid climate. As a result, larger meat-eating dinosaurs probably wouldn’t have found a home there either. Instead, smaller, carnivorous dinosaurs were the only types that could be found near equator — much like the small, carnivorous species like lizards and scorpions you find in today’s deserts.

Scientists studied rock samples from the Ghost Ranch in New Mexico, which probably would have been a more tropical area during that time period — northern New Mexico was much closer to the equator back in the Triassic than it is in the modern day, according to the report. Large sauropods like the diplodocus and brontosaurus probably would have stuck to these lusher areas, scientists believe.