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A recent study by Keifeng Yu and his colleagues, in Acta Geologica Sinica, describes the discovery and identification of 12 new dinosaur teeth from the Upper Cretaceous Nenjiang Formation. The Cretaceous dinosaurs were identified as belonging to five different taxa, including tyrannosaurids, dromaeosaurines, velociraptorines, hadrosauroids, and titanosaurs.

In addition to providing insights into previously identified dinosaurs from the Songliao basin, three new ones were identified, extending the paleogeographic range of these taxa.

According to Dr. Wenhao Wu, one of the paleontologists involved in the study, the Songliao Basin was chosen for study due to the possibility of numerous dinosaur fossils likely still lying undiscovered.

Dr. Wu elaborates, "The Songliao Basin, one of East Asia's largest Late Mesozoic continental sedimentary basins, hosts a continuous sequence of Late Cretaceous continental strata. This makes it an exceptional location for studying Cretaceous continental climate change, paleoenvironmental evolution, and associated biota.

"However, dinosaur fossil records in the Songliao Basin are relatively scarce. Previously documented dinosaur remains are primarily from the lower Upper Cretaceous Quantou Formation (Cenomanian), leaving a significant gap in the fossil record for the Upper Cretaceous strata of the basin.

"In contrast, abundant dinosaur fossils from the Upper Cretaceous have been discovered in regions such as Mongolia and North America. This suggests that numerous dinosaur fossils likely remain undiscovered in the Songliao Basin, awaiting further exploration and study."

The 12 dinosaur fossils that formed part of the study were found in a thin layer, only around 10 cm thick. Though representing isolated teeth, they could only be identified to taxa, not species.

"Among vertebrates, mammals can often be identified to the genus or species level based on tooth characteristics due to their complex dental structures. In contrast, the teeth of dinosaurs and other vertebrate groups, whose morphology is relatively simple, have different groups within the same family exhibiting highly similar tooth forms. Consequently, identifying dinosaurs to the genus or species level based solely on tooth fossils is generally not feasible," explains Dr. Wu.

Four of the teeth were identified as belonging to carnivorous theropods. Of these, two belonged to Tyrannosauridae and were identified based on their unique combination of tooth features, including their large, robust appearance with chisel-like denticles.

The remaining two teeth were identified as dromaeosaruinae and velociraptorinae, a subfamily within dromaeosaurinae.

While dromaeosaurids have been recovered in Nong'an, China, the tooth from the Nenjiang Bei'an site is located over 500 km northeast and significantly extends the known range of the taxa in China.

Similarly, the veloceraptorid tooth is the first to be discovered in the Nenjiang formation.

The majority of teeth came from herbivorous sauropods. Sauropods' geographical distribution was highly dependent on temperature, preferring hotter climates compared to theropods.

On the northern continents, sauropods are mainly found in the warmer lower altitudes, with a few exceptions of fossils found at higher altitudes.

Three of these sauropod teeth belonged to Titanosauria. These teeth are unique not only for being the first of this taxon to be found in the Nenjiang formation, but also for having been found in the Songliao basin, which is situated at a relatively high altitude and extends the northernmost occurrence of titanosaurs in the Campanian period.

The remaining five teeth belonged to various Hadrosauridae individuals. During the evolution of hadrosaurids, there was a simplification in their teeth. Their tooth crowns became narrower, the main ridge moved to a more central location, and the accessory ridges decreased in number from four to one or none.

The teeth found by Yu and his colleagues all had a slightly off-center ridge and only one or two small accessory ridges. This indicated that these teeth belonged to non-hadrosaurid hadrosauroids.

Hadrosauroids were initially an abundant and diverse group, found across the ancient continents of Laurasia and some regions in Gondwana. However, primitive hadrosauroids experienced a significant decline in numbers at the end of the Cretaceous period.

Non-hadrosaurid hadrosauroid specimens had previously never been found in the Songliao Basin.

However, the discovery of these teeth expands on our understanding of the distribution and evolutionary trajectory of these dinosaurs during the early Campanian.