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 : 679-681

Limusaurus inextricabilis

including digits ( Delpretti, Zákány & Duboule, 2012). The size and number of digits are dependent of Hoxa- 11, Hoxd-12, Hoxd-13 and Hoxa-13, which are major determinants of digital morphogenesis ( Zákány et al., 1997; Zákány & Duboule, 2007; Young, Wagner & Hallgrimsson, 2010). The region producing digit I is identified as positive Hoxd-13 and negative Hoxd-11 / 12, but Shh signalling is involved in the identity of the other digits ( Seki et al., 2012). Factors and signalling pathways such as Fgf8, Bmp and Shh are implicated in determining the length and the number of phalanges ( Seki et al., 2012), their relative size being determined at the time of the initial cell condensation ( Kavanagh et al., 2013).

In addition to the characterization of Limusaurus , a ‘pollex’ aspect of digit II is of note ( Vargas, Wagner & Gauthier, 2009). Such clinodactyly may well be a morphological consequence of the manual teratology itself. Note that a clinodactyly with radial deflection can be observed in cases of brachydactyly ( Temtamy & Aglan, 2008) and more generally in the case of acromelia ( Al-Qattan, Yan & Kozin, 2009). In addition, experimentation on Hoxd-13 and Hoxa-13 can produce a radial deflection of digit II ( Zákány et al., 1997) or the deviation of digit II and III phalanges towards digit I ( Delpretti et al., 2012).