or "wings", that were likely covered in long feathers, may have been flapped by the dromaeosaur in order to stabilize its balance while restraining prey, along with this, the long, feathered tail probably worked as a counter-balance to the main body. Lastly, the snout would have been useful for finishing off its prey. With these observations, they established that dromaeosaurids and troodontids were niche partitioned as large and small prey predators, respectively. In 2020, Powers and colleagues re-examined the maxillae of eudromaeosaur taxa concluding that Asian and North American eudromaeosaurs were separated by snout morphology and ecological strategies. They found the maxilla to be a reliable reference when inferring the shape of the premaxilla and overall snout. For instance, most Asian species have elongated snouts based on the maxilla (animals like Velociraptor are known from complete skulls), indicating a selective feeding, such as picking up small, fast prey. Achillobator however, is an exception for Asian eudromaeosaurs, featuring a robust and deep maxillar morphology similar to North American eudromaeosaurs which also have stocky and deep snouts, and thus indicating relationships with these members. The adaptations of Achillobator and North American eudromaeosaurs indicate a diet based on large-sized prey. Paleoenvironment The remains of Achillobator were unearthed from the Burkhant locality of the Bayan Shireh Formation. This formation has been divided into upper and lower parts, with some localities representing Lower and Upper Cretaceous boundary. Burkhant, the type locality of Achillobator, has been identified as an Upper Cretaceous-boundary locality. Analyses on the magnetostratigraphy of the formation indicate that the entire Bayan Shireh lies within the Cretaceous Long Normal, which lasted only until the end of the Santonian stage, giving a Cenomanian-Santonian age. The recent calcite U–Pb analyses performed by Kurudama and colleagues in 2020 have confirm the age of the Bayan Shireh Formation from 95.9 ± 6.0 million to 89.6 ± 4.0 million years ago, also supporting a Cenomanian-Santonian age. Over the time, a strong correlation with the Iren Dabasu Formation has been proposed by numerous authors mainly based on the similar fossil assemblages. This hypothesis may be also supported by the similar ages. The environments that were present in the Bayan Shireh Formation and Achillobator inhabited were relatively humid and had extensive fluvial and lacustrine facies, that is, a well-watered region dominated by prominent meanders, rivers, lakes and streams. The climate of the formation was slightly semi-arid, as seen on caliche-based sediments.