Illustration of the transition of upper jaw bones in the Mammaliaformes, an evolutionary grouping that includes living and extinct mammal species. (IMAGE)
Caption
Mammals with flexible, motile noses that can “sniff” are in the group Theria (right side of pink dot). As species’ ancestors accumulated more physical and genetic differences (increasingly younger species are shown from left to right), the jaw tip bone, the premaxilla (green), became smaller and migrated upwards and the bone that was behind it, the septomaxilla (yellow), became larger and moved forwards to become therian mammals’ jaw tip.
Credit
Image by Hiroki Higashiyama, CC BY-SA 4.0, first published in PNAS
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License
CC BY-SA