Early Cretaceous mammals from Bol’shoi Kemchug 3 locality in West Siberia, Russia

A new mammal skull from the Lower Cretaceous of China with implications for the evolution of obtuse-angled molars and ‘amphilestid’ eutriconodonts

“…The Amphilestidae have molars with one dominant central cusp, and two smaller subequal cusps on either side; molars that occlude at the embrasure of opposing molars; lower molars that lack a tongue-in-groove interlock; and premolars that tend to be symmetrical (Simpson 1928;Ji et al 1999). They are known from the Middle Jurassic of Europe, the Late Jurassic of Asia, Africa and North America, the Early Cretaceous of Asia, and possibly the EarlyMiddle Jurassic of India and Middle Jurassic of South America (Kielan-Jaworowska et al 2004;Averianov et al 2005;Rougier et al 2007a,b). In contrast, the Triconodontidae, from the Early Cretaceous of Europe and the Late Jurassic-Late Cretaceous of North America, have molars with three main cusps of subequal height.…”

“…That Hakusanodon and Juchilestes are nested together to the exclusion of more ancient 'amphilestid' taxa is also consistent with the hypothesis that East Asia was a refugium for late surviving taxa. 'Amphilestids' that persisted into the Early Cretaceous are otherwise only known by an indeterminate 'amphilestid' taxon from western Siberia (Averianov et al 2005). Intriguingly, its lower molar cusp pattern is similar to that of Juchilestes and Hakusanodon in having cusp b higher than c (Averianov et al 2005).…”

“…(b) Palaeobiogeography The geographical distribution of Early Cretaceous mammals from East Asia has expanded in the last 20 years with new findings from Russia (Averianov et al 2005;Lopatin et al 2005), Japan (e.g. Tsubamoto et al 2004;Kusuhashi 2008), Korea and China (e.g.…”

“…'Amphilestids' that persisted into the Early Cretaceous are otherwise only known by an indeterminate 'amphilestid' taxon from western Siberia (Averianov et al 2005). Intriguingly, its lower molar cusp pattern is similar to that of Juchilestes and Hakusanodon in having cusp b higher than c (Averianov et al 2005). Clearly, however, East Asia had a complex palaeogeographic history that included prolonged isolation and intermittent connections, of which the exact timing and pattern is still uncertain (Enkin et al 1992;Haggart et al 2006).…”

An amphilestid-grade eutriconodontan from the Middle Jurassic of Russia

“…The upper dentition is not known for the Klameliidae, but lack of enamel striation safely removes PIN 5087/4 from that group. The upper dentition of Amphilestidae is known from only two isolated molariforms referred to the Middle Jurassic Amphilestes broderipii (Owen, 1845) (Freeman, 1979: pl.16, figs.12;Averianov et al, 2005b: 4) and to the Early Cretaceous Kemchugia magna Averianov et al, 2005(Averianov et al, 2005b fig.2AC). Both teeth have strong cingulum around the whole crown and therefore lack of a labial cingulum in PIN 5087/4 precludes its attribution to the Amphilestidae.…”