Biology:Bannykus

Bannykus is an extinct monotypic genus of alvarezsauroid from the Early Cretaceous Bayin-Gobi Formation of Inner Mongolia, China. It includes one species, Bannykus wulatensis.

Discovery

Scaled reconstruction

The holotype of Bannykus wulatensis is IVPP V25026, a partially-articulated incomplete skeleton of an 8 year old subadult. The holotype comes from the Bayin-Gobi Formation in Chaoge, Wulatehouqi, Inner Mongolia, China. It was discovered in 2009 and in 2012, its remains were displayed in Japan under the unofficial name "Wulatesaurus". It was given the binomial name Bannykus wulatensis in 2018; its generic name comes from the Mandarin word Ban (Chinese: 半), meaning half, and the Greek word onyx, meaning claw. This refers to the transitional characteristics seen in this theropod. The specific name refers to Wulatehouqi (Wulate Rear Banner), the county that the holotype was found in.

Description

Bannykus holotype showing the intestinal contents (yellowish conglomerate)

Bannykus is large for an alvarezsaurian theropod, with an estimated length of 2.77 metres (9.1 ft) and body mass of approximately 24–30 kilograms (53–66 lb) for the immature holotype. The forelimb of Bannykus shows significant reduction and modification compared to Haplocheirus, but less shortened and specialized than later alvarezsaurs like Shuvuuia. In 2025, Wang and colleagues identified hard tissue debris and possible soft tissues in the intestinal contents of the holotype (represented by the yellowish conglomerate) based on scanning electron microscopy, which was consistent with further Raman spectroscopy analysis that detected "characteristic peaks indicative of bone-derived material", suggesting that Bannykus probably had a carnivorous diet. The authors concluded that both the forelimb reduction and the dietary shift from carnivory to probably insectivory among alvarezsaurians occurred later in their evolution.

Classification

Bannykus, along with Xiyunykus, fills a 70-million year gap in alvarezsaur evolution by exhibiting morphologies intermediate between the typical theropod forelimb of Haplocheirus and the highly reduced forelimbs and minute teeth of Late Cretaceous alvarezsaurids.

The cladogram below is the latest and most comprehensive analysis of alvarezsaurian evolution, following Meso et al. (2024).

Alvarezsauria

Shishugounykus inexpectus       Aorun zhaoi       Haplocheirus sollers         Bannykus wulatensis       Xiyunykus pengi     Tugulusaurus faciles           Alnashetri cerropoliciensis   Alvarezsauridae   Patagonykinae   Bonapartenykus ultimus     Patagonykus puertai         Achillesaurus manazzonei     Alvarezsaurus calvoi       Parvicursorinae   Ceratonykus oculatus       Khulsanurus magnificus       Qiupanykus zhangi       Dzharaonyx eski         Linhenykus monodactylus     Parvicursor remotus     Mononykini   Shuvuuia deserti       Mononykus olecranus       Ondogurvel alifanovi     Albinykus baatar

Palaeobiology

The forelimbs of Bannykus were biomechanically capable of generalised motions, and the animal likely used them for a variety of digging styles.

References

Wikidata ☰ Q56256254 entry