Ancient dinosaur footprints reported in Mongolia nearly 70 years ago had almost vanished from science. The original account was only two pages long. It included no photographs, no exact location, and no detailed description, leaving later researchers with little more than a name: Saijrakh.
Now, that forgotten site has been found again.
In the Saizhurakh area of northern Mongolia, researchers identified 31 fossilized footprints preserved in a single layer of sand from roughly 120 million years ago. Two sauropod trackways stretch more than 15 meters across the ancient lakebed, while five separate theropod trackways cut across the same surface.
Together, the tracks provide the first direct physical evidence that large plant-eating dinosaurs and predatory dinosaurs moved through this region during the Early Cretaceous.
Mongolia’s Early Cretaceous Fossil Record Had Left a Long Gap
Mongolia ranks among the top five countries in the world for dinosaur fossil discoveries. Nearly all of that material, however, comes from the Late Cretaceous, a window running roughly 70 to 90 million years ago.
The Early Cretaceous, between approximately 100 and 120 million years ago, has produced far fewer specimens. Those that exist belong mostly to small- and medium-sized animals, including species such as Harpymimus, Psittacosaurus, and Choyrodon. No Early Cretaceous tracksite had ever been confirmed in the country before this study.
That gap mattered beyond Mongolia’s borders. During the Early Cretaceous, global temperatures ran warm, flowering plants were diversifying rapidly, and dinosaur populations in Asia were dispersing into North America. Mongolia sits directly along that movement corridor, making it a natural comparison point between the two continents.
Without physical evidence of large dinosaurs in the Mongolian section of that corridor, researchers could not say with confidence what animals occupied it or how populations on either side connected.
The Dinosaur Tracks Formed in a Fluctuating Lake Environment
The footprints lie within the Shinekhudag Formation, a sequence of rock built from sediment deposited in a large Early Cretaceous lake. Fine black clay makes up most of the deposit. Thin sand layers appear at intervals, pushed in during periods when the lake level dropped.
When the water retreated far enough, stretches of wet sand and mud were exposed at the surface. Dinosaurs moved across those flats, pressing their feet into the soft ground. Later sediment buried and preserved the impressions. The 31 documented footprints were pressed into one such sand layer.
Two sauropod trackways extend more than 15 meters across the surface. Both animals were close in size and left hind footprints approximately 70 centimeters long. One trackway largely overlaps the other, and the researchers concluded that a second sauropod followed almost the same route as the first at a slightly slower pace.
The team noted that modern elephants sometimes move in a similar way, stepping into the tracks of the animal ahead to follow established paths. The front-foot impressions preserved a mix of anatomical traits, including a medially projecting first-digit claw alongside a more advanced soft-tissue pad. The wide-gauge stance and overall track characteristics point to titanosauriform sauropods, a diverse group of long-necked herbivores known from multiple continents during this period.
Five Large Predators Crossed the Site Independently
Five theropod trackways are preserved on the same bedding surface as the sauropod prints. The largest single footprint measures 57 centimeters across, with toes spread wide.
Based on that measurement and the proportions of the tracks, the researchers estimated the body length of these carnivorous dinosaurs exceeded 8 meters. The team reported that this makes them the largest Early Cretaceous predators documented from the region.
The trackways point in different directions. The research team reported that no alignment among them suggests the animals moved as a coordinated group. Instead, the pattern indicates five large theropods crossed the site independently, likely within a short window before the mud fully hardened and fresh sediment sealed the prints.
Evidence for large Early Cretaceous theropods had previously surfaced in China, South Korea, and Japan. According to the study published in Ichnos, the Saizhurakh discovery extends that geographic range into northern Mongolia, closing a gap that had run across Mongolia and eastern Russia without a confirmed data point.
Nearby Sediment Layers Raise the Possibility of Skeletal Finds
Beyond the tracksite itself, the research team identified gravel-bearing sand layers in the surrounding outcrops. The team reported that those deposits create conditions where skeletal remains could be preserved.
Future surveys will target the area for bones, teeth, or other body fossils from the same animals that left the footprints. The researchers also plan to continue examining surrounding outcrops for additional tracksites.
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