Alioramini is a tribe of long-snouted tyrannosaurine tyrannosaurids from the Late Cretaceous epoch. It includes the tyrannosaurid genera Alioramus and Qianzhousaurus. Although tyrannosaurids are known from a variety of places around the globe, alioramins are currently restricted to Asia in mostly Maastrichtian strata.[1] Many of the fossils attributed to Alioramini are not from fully developed individuals.[2]
Alioramins are medium-sized tyrannosaurids, reaching around NaNm (-2,147,483,648feet) in length. They have a more gracile body plan as compared to most other tyrannosaurines.[3] [4] Alioramins have rather shallow snouts, a trait that is rather rare among tyrannosaurs but can be found in the early tyrannosauroid, Xiongguanlong.[5] Alioramins are unique when compared to contemporary tyrannosaurs from the same time, such as Tarbosaurus and Tyrannosaurus, because most of the longer snouted tyrannosauroids, such as Xiongguanlong, were found in deposits dating to earlier times during the Cretaceous. Members of the alioramins also have an elongated maxillary fenestra. Besides their elongated snouts, perhaps another major trait that makes alioramins stand out is their nasal ridges. While most other tyrannosaurids have nasal ridges, the nasal ridges in alioramins are pronounced and discrete. They form well developed bumps on the surface of the nasal bones, forming their nasal crest. Within the dentary bone, alioramins have 18 or more teeth. [6] [1]
The tribe Alioramini was first coined in 1995 by George Olshevsky only to contain the at-the-time uncertain Alioramus.[7] In 2014, the tribe was formally defined as a clade-based branch containing all tyrannosaurids more related to Alioramus than to Albertosaurus, Proceratosaurus, and Tyrannosaurus. Hence, the tribe Alioramini consists of three species, namely Alioramus altai, Alioramus remotus, and Qianzhousaurus sinensis. Some researchers have tried to synonymize Qianzhousaurus with Alioramus,[8] but many others maintain that they are separate genera. Alioramini is usually considered to be a part of the Tyrannosaurinae subfamily within the Tyrannosauridae family; however, some phylogenetic studies find them to be outside the Tyrannosauridae. Alioramini is a part of Tyrannosaurinae, based on several features. These features include a maxillary process of the premaxilla that points upwards; the deep joint surface in the maxilla conceals certain features related to tooth roots; the particular shape of the lacrimal, mostly hidden from view; and an ectopterygoid with a pneumatic recess that possesses a distinctive round or triangular shape.[9] Dryptosaurus, usually placed as a basal eutyrannosaur is found to be a member of Alioramini under a Bayesian analysis in 2016 Carr and Brusatte paper, but this is the only time in the 2016 paper an analysis yields such a result with the rest of the paper placing Dryptosaurus in its usual position.
Below is a cladogram showing the placement of Alioramini within the Tyrannosaurinae, according to Brusatte & Carr (2016).[10]
Another cladogram showing the relationships of Alioramini by Loewen et al. (2013) places Alioramini outside of the Tyrannosauridae.[11]
Alioramins, due to their relatively gracile build and long snouts, were likely specialized in hunting small-sized prey with quick turns. Such feeding strategies may have avoided direct competition with other tyrannosaurids. In contrast to robust tyrannosaurids, whose juveniles underwent drastic changes in their skull, the characteristic elongated snout morphology of alioramins was likely maintained throughout their ontogeny (growth).[12] [13]