Qianosuchus mixtus Li et al., 2006

Nesbitt, Sterling J., 2011, The Early Evolution Of Archosaurs: Relationships And The Origin Of Major Clades, Bulletin of the American Museum of Natural History 2011 (352), pp. 1-292 : 26-27

Qianosuchus mixtus Li et al., 2006

AGE: Anisian, Middle Triassic ( Li et al., 2006).

OCCURRENCE: Guanling Formation, Xinmin, Panxian County, southwestern Guizhou Province, China.

HOLOTYPE: IVPP V13899 , a skeleton with distal part of forelimbs and posterior end of the tail missing.

REFERRED MATERIAL: IVPP V14300 , an incomplete skeleton with nearly complete skull ; NMNS 000408/F003877, an incomplete skull.

REMARKS: Li et al. (2006) described Qianosuchus from marine sediments from the Anisian of southern China. The taxon is the most completely known early archosaur and one of the most completely documented basal archosaurs to date given that it is represented by two nearly complete skeletons and a crushed skull in ventral view. Even though the specimens are essentially ‘‘slabspecimens,’’ the bones are nearly threedimensionally preserved. Qianosuchus awaits a full anatomical description.

Li et al. (2006) hypothesized that Qianosuchus was semiaquatic based on tall neural spines of the caudal series, a thinned platelike scapula and coracoid, an elongate neck (the nine cervical vertebrae reaching 75% of the trunk length and, together with the skull, over 120% of the latter) with long and slender cervical ribs, and small-sized dorsal osteoderms in the neck and trunk regions, but absent in the tail region. The authors rightly pointed out that characters one and four are common in marine tetrapods. However, an elongated neck is also present in fully terrestrial archosaurs (e.g., Arizonasaurus, MSM 4590; Effigia, AMNH FR 30587; Hesperosuchus agilis, AMNH FR 6758), and a thinned plate-like scapula and coracoid seem to be an autapomorphy of the taxon with no clear ecological significance. As the authors noted, other features of the skeleton are typical of terrestrial archosaurs. The ecology of this important taxon is unclear because of the ambiguous mix of potentially semiaquatic and terrestrial features and that there are multiple skeletons of Qianosuchus from marine deposits.

Qianosuchus possesses an intriguing mix of character states commonly listed as ‘‘rauisuchian’’ and poposauroid apomorphies. Qianosuchus clearly bears a crocodylian-normal ankle similar to that of aetosaurs, ‘‘rauisuchians,’’ poposauroids, and crocodylomorphs. The taxon has a short pubis and ischium relative to the femur, at least four leaf-shaped osteoderms per vertebra in the presacral series, and typically carnivorous teeth, features found in Prestosuchus (UFRGS 0156-T; UFRGS 0152-T; BSP XXV 1-3/5-11/ 28-41/49), Ticinosuchus (PIZ T2817) , and Saurosuchus (PVSJ 32). The elongated cervicals with elongated cervical ribs, the enlarged narial opening, a slot on the anterolateral surface of the maxilla for the posterior process of the maxilla, and the presence of three sacral vertebrae support a close relationship to poposauroids (Nesbitt, 2005). The age, mix of ‘‘rauisuchian’’ and poposauroid character states, and mixed ecological signal makes Qianosuchus important to the early radiation of the crocodylianline archosaurs.

Li et al. (2006) provided the following diagnosis: A medium-sized archosaurian, over 3 m in length, differing from all other archosaurians in having the following combination of derived features: low premaxilla bearing nine daggerlike teeth; posteriorly positioned external naris longer than any other skull opening and mainly enclosed by nasal dorsally and maxilla ventrally; external mandibular fenestra half oval in outline; neural spines in cervical vertebrae 2 to 9 longitudinally very broad, each with five pairs of small osteoderms on its top; neural spines of caudal vertebrae very tall, at least four times the height of the centra and longer than chevrons in midtail region; cervical ribs elongate, most of them over four times length of corresponding centra; scapula plate-like, hatchet shaped in outline.

KEY REFERENCES: Li et al., 2006.