Altacreodus is a genus of basal, placental eutherians. The time of appearance of the earliest eutherians has been a matter of controversy. "Notostylops" was a very generalized animal, very similar to first eutherians and ungulates. Zalambdalestidae is a clade of Asian eutherians occurring during the Late Cretaceous. Tooth enamel evolved differently in marsupials and eutherians. Groups represented include multituberculates, metatherians, and eutherians. Theria includes the eutherians (including the placental mammals) and the metatherians (including the marsupials). UCP1 is expressed in brown adipose tissue, which is functionally found only in eutherians. A variety of early mammals were present including multituberculates, metatherians, and eutherians. RBP3 orthologs have been identified in most eutherians except tenrecs and armadillos. Bustylus is an extinct genus of eutherians in the family Adapisoriculidae. Even non-placental eutherians probably reproduced this way. Taeniodonts are unambiguously Eutherians, and part of Cimolesta; "Cimolestes" is the immediate outgroup to Taeniodonta. Most recent studies show them to be non-placental eutherians, however. These early eutherians were small, nocturnal insect eaters, with adaptations for life in trees.