Gobiconodon (Mammalia) from the Early Cretaceous of Mongolia and Revision of Gobiconodontidae

There are two species of Gobiconodon in the Early Cretaceous Khoboor locality of Mongolia: G. borissiaki Trofimov, 1978, and G. hoburensis (Trofimov, 1978). The smaller G. hoburensis has i2 half the size of i1, double-rooted dp2, and two generations of molariforms (m1-5 and m1r-4r). In the larger G. borissiaki, i2 is about ¾ size of i1, dp2 is single-rooted, and there are three generations of molariforms (m1-5, m1r-5r, m1rr-2rr). In larger G. ostromi Jenkins and Schaff, 1988, there are three molariforms of the third generation (m1rr-3rr). The anterior lower dentition of Gobiconodon is interpreted as i1-3, c, and dp1-2. The replacement of dp1 by p1 is known only in G. hoburensis. The dp2 is not replaced and may be lost in some specimens (G. hoburensis, G. ostromi) with its alveolus plugged by bone. Gobiconodon includes five valid species: G. borissiaki, G. hoburensis, G. ostromi, G. hopsoni Rougier et al., 2001, and G. zofiae Li et al., 2001 (=G. luoianus Yuan et al., 2009, syn. nov.). The holotype upper maxilla of G. hopsoni is not diagnostic and a new diagnosis for this species is provided based on lower dentitions from the type locality. Repenomamus Li et al., 2001, and Meemannodon Meng et al., 2005, are the only other members of the Gobiconodontidae. The dental formula of Repenomamus is reinterpreted as I1-3, C, P1, M1-5/i1-2, c, p1-2, m1-5 and thus it differs from Gobiconodon by lack of i3 and P2. Meemannodon is different from Gobiconodon by lack of i3 (the upper dentition is unknown). The Early Cretaceous Jeholodens, Yanoconodon, and Liaoconodon are closer to the Gobiconodontidae than to the Amphilestidae by having only two premolars. Liaoconodon with modified anterior dentition is likely the closest relative to the Gobiconodontidae. The Gobiconodontidae is likely the sister taxon for the clade Amphilestidae + Trechnotheria.