|Qiupanykus zhangi |
Lü, Xu, Chang, Jia, Zhang, Gao, Zhang, Zhang & Ding, 2018
Illustration: Zhao Chuang.
An alvarezsaurid dinosaur skeleton was discovered from the Late Cretaceous Qiupa Formation of Luanchuan, Henan Province of centtral China. It represents a new alvarezsaurid dinosaur Qiupanykus zhangi gen. et sp. nov. A phylogenetic analysis recovers Qiupanykus nested within the unresolved clade, which includes Asian and north American taxa. The skeleton of the new specimen is preserved in association with eggshells. The eggshell morphologies show that these eggs belong to oviraptorid eggs, skeletal remains of which were discovered from the same area. The alvarezsaurid skeleton associated with eggshell fragments may indicate that these eggs were broken by the strong thumb-claws of the former and that alvarezsaurid dinosaurs may be egg-eaters.
Keywords: Vertebrate paleontology, alvarezsaurid dinosaur, Qiupanykus, Late Cretaceous, central China
|Figure 2. The photograph (a) and outline drawings (b) of Qiupanykus zhangi.|
Abbreviations: cd: caudal vertebrae; f: femur; hc: haemal arch; il: ilium; mt(II-IV): metatarsls II-IV; ti: tibia; p: pubis; pp: pedal phalanx; sv: sacral vertebrae.
Maniraptora (Gauthier, 1986)
Alvarezsauridae (Bonaparte JF, 1991)
Qiupanykus zhangi gen. et sp. nov.
Etymology: The generic name refers to the Qiupa town, Luanchuan County, where the specimen was discovered. The specific name is in honor of Shuancheng Zhang for his logistic support with fossil searching and excavations in the field.
Holotype: Incomplete skeleton comprising most posterior axial elements and most of hindlimb elements. The specimen 41HIII-0101 is housed in the collections of the Henan Geological Museum, Zhengzhou, China.
Holotype locality and horizon: The specimen (41HIII-0101) was found in Guanping, Qiupa Town, Luanchuan County of Henan Province; Qiupa Formation (Bureau of Geology and Mineral Resources of Henan Province, 1989; Lü JC et al., 2007)
Diagnosis: A small-sized alvarezsaurid dinosaur with the following combination of characters: posterior sacral vertebrae bearing a strong ventral keel; proximal caudals with transverse processes centrally positioned on centrum; pubic articular surface of the pubic peduncle of ilium is reduced and knob-like; fibular crest of tibia large and quadrangular; functional sacrum made up of eight vertebral elements (two anterior caudal plus six sacral vertebrae); a small pneumatic foramen is present in caudal vertebrae.
|Figure 4. Life scene of Qiupanykus zhangi. |
(drawn by Zhao Chuang)
Behaviour of alvarezsaurid dinosaurs
The skeleton of Qiupanykus is associated with an eggshell fragment near its tail. The thickness of the eggshell fragment is 1.8 mm. Some features, such as linearituberculate ornamentation type, including nodes and short ridges, two structural layers (non-prismatic), and relatively thick shell, are all identical to the Luanchuan oviraptorosaur eggshells (Tanaka K et al., 2011). Using the formula (Elongatoolithidae) by Tanaka K et al. (2016), the estimated egg mass of the eggshell is: Log10 egg mass = 1.569×log10 (1.8)+2.655, the thickness of the egg shell is 1.8 mm, then the Egg mass is 1136.377 g (95% CI: 715 g to 1809 g). The femur circumference of Qiupanykus is 17.09 mm. Based on the formula (log10 BM = 2.754×log10(femur circumference－0.683) by Campione NE et al. (2014), the estimated body mass for Qiupanykus: is 515 g (log10 BM = 2.754×log10 17.09－0.683). The estimated egg mass is much heavier than the estimated body mass of Qiupanykus. Thus, the egg could not be laid by Qiupanykus.
Alvarezsaurid dinosaurs bear highly specialized arms, whose purpose is still a mystery. They are regarded that the special arms were used to burrow (Perle A et al., 1993) or break open termite mounds (like modern anteaters), and possible to feed on insects (Senter P, 2005). However, the skeleton is associated with eggshell fragments from Luanchuan area, and the eggshell fragment morphologies indicate that those eggs belong to oviraptorid eggs (Tanaka K, personal communication, 2017). There is another case found from north-western Patagonia of Argentina, where an alvarezsaurid skeleton is preserved with eggs (Agnolin FL et al., 2012). Although Agnolin et al. thought the eggs associated with the alvarezsaurid Bonapartenykus ultimus were laid by an alvarezsaurid dinosaur, they pointed out that the external ornamentation patterns of Arriagadoolithus expressed on the outer shell surface is similar to elongathoolithid eggs. Arriagadoolithus was possibly laid by oviraptorosaurid dinosaurs. Thus, there are three possibilities about the relationship between the alvarezsaurid skeletons and eggs (egg fragments) associated with them: (1) Eggshell fragments were buried with alvarezsaurid skeleton by coincidence, and the eggshell is nothing to do with the skeleton. (2) The eggs were laid by alvarezsaurid dinosaurs and (3) The eggshell fragments were from eggs broken by alvarezsaurid dinosaurs and the eggs were not laid by them. However, considering the strong thumb claw of alvarezsaurid dinosaurs, we prefer to the third interpretation. Alvarezsaurid dinosaurs perhaps use their special claw to break eggs, and they are perhaps egg-eaters (Fig. 4).
The skeleton of Qiupanykus is associated with oviraptorid egg shell fragments suggesting that at least the derived alvarezsaurid dinosaurs may be an egg-eaters, which use their special arms (the strong thumb claws) to pierce the hard eggshell. Qiupanykus is a relatively small sized alvarezsaurid and it represents the youngest alvarezsaurid dinosaur from China so far.
Jun-Chang Lü, Li Xu, Hua-Li Chang, Song-Hai Jia, Ji-Ming Zhang, Dian-Song Gao, Yi-Yang Zhang, Cheng-Jun Zhang and Fang Ding. 2018. A New Alvarezsaurid Dinosaur from the Late Cretaceous Qiupa Formation of Luanchuan, Henan Province, central China. China Geology. 1(1): 28–35. DOI: 10.31035/cg2018005