Limusaurus, INEXTRICABILIS

Guinard, Geoffrey, 2016, Limusaurus inextricabilis (Theropoda: Ceratosauria) gives a hand to evolutionary teratology: a complementary view on avian manual digits identities, Zoological Journal of the Linnean Society 176 (3), pp. 674-685 : 676

LIMUSAURUS INEXTRICABILIS : FOCUS ON FORELIMB

ANATOMICAL TRAITS

Compared with Ceratosaurus nasicornis (155.7–150.8 Ma) ( Marsh, 1884), forelimbs of L. inextricabilis ( Xu et al., 2009) are proportionally shorter with a notable variation of manus proportion ( Figs 3 , 4 ). Carpals are not ossified. The manus shows four digital rays, not all completely developed. Digit I is represented by a small metacarpal while metacarpal II is robust with three phalanges. Digit III bears three phalanges instead of the four expected. Finally, digit IV consists of a metacarpal with a joint for a phalanx. It is highly likely there is no more than one phalanx on the fourth digit, given the manual configuration of theropods predating Ceratosauria such as Coelophyis bauri (205.6– 201.6 Ma) ( Cope, 1889).

Figures

Figure 3. Forelimb of Limusaurus inextricabilis (modified from Xu et al., 2009). MTC, metacarpal.

Figure 4. Comparison of proportions of forelimb segments – humerus, radius and median metacarpal (MTC II) – in some theropod dinosaurs. Data used are from Gilmore (1920) and Alroy & Garcia Selles (2014) for Ceratosaurus nasicornis; Middleton & Gatesy (2000) and Bonaparte et al. (1990) for Carnotaurus sastrei; Middleton & Gatesy (2000) for Allosaurus fragilis and Coelophysis bauri; Brochu (2003) for Tyrannosaurus rex; Xu et al. (2009) for Limusaurus inextricabilis; and Burch & Carrano (2012) for Majungasaurus crenatissimus.