A tiny dinosaur with long arms leads to rethinking the miniaturization of dinosaurs

However, the real surprise came when the researchers realized that Alnashetri It was not a highly specialized late-stage Alvarezsauroid. Instead, despite living in the Late Cretaceous, it occupied an early branching position among the earlier basal members of the clade.

This combination of tiny size and early branching state fundamentally breaks our previous model of how these animals evolved. If the miniaturization of the Álvarezsauroids was strictly linked to their lifestyle as eaters of stubby-armed insects, a species that diverged early as Alnashetri it should have some transitional features in a steady march of the entire clade toward that extreme endpoint. But it didn’t seem like that.

“It’s a very long-limbed animal, so it was probably pretty fast. My best analogy would be something like a roadrunner from the American West,” Makovicky said.

arms and teeth

Late Alvarezsaurids had small, robust forelimbs that measured less than half the length of their femurs. AlnashetriHowever, it sported comparatively long forelimbs that were 61 percent of the length of its entire hindlimb. While it had three-fingered hands with a robust first finger, a hallmark of its group, it still retained slender second and third digits, unlike its later cousins.

Other features that challenge the established evolutionary model of miniature dinosaurs are AlnashetriThe jaws and teeth. Its dentition presents non-toothed teeth placed in alveoli, but the most important thing is that these teeth are not extremely small, as they were in later Álvarezsaurids such as Enthusiasm either jaculinykus. “This decoupled the evolution of small body size from anatomical specializations,” Makovicky explained.

The team concluded that extreme miniaturization in Alvarezsaurids did not necessarily coevolve with the evolution of smaller arms better suited for digging or with small teeth built for crushing ants and/or termites. Instead of a clade-wide trend in which the entire lineage steadily declined over time, a new evolutionary model that includes Alnashetri suggests that the body mass of Álvarezsaurids fluctuated repeatedly. AlnashetriIt turns out that it achieved its 700-gram frame independently of other highly specialized alvarezsaurid species.