Dryolestoid
| Dryolestoidea Temporal range: Jurassic-Neogene Bathonian–Miocene |
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| Four meridiolestidan taxa: Leonardus, Mesungulatum, Barberenia and Austrotriconodon. | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Clade: | Cladotheria |
| Superorder: |
†Dryolestoidea Butler 1939 |
| Orders | |
Dryolestoidea is an extinct clade of Mesozoic mammals that only contains two orders. It has been suggested that this group is closely related to modern therian mammals.
Dryolestids are mostly represented by teeth, fragmented dentaries and parts of the rostrum. The Jurassic forms retained a coronoid and splenial, but the Cretaceous forms lack these. Another primitive feature is the presence of a Meckelian groove (Meridiolestidans lost it altogether). A fundamentally modern ear is known in at least Dryolestes and mesungulatids.
Tooth enamel evolved differently in marsupials and eutherians. In a first phase, during the late Triassic and Jurassic, prisms separated from the interprismatic matrix, probably independently in several Mesozoic mammal lineages. More derived enamel types evolved in a second phase, during the Tertiary and Quaternary, but without replacing the old prismatic enamel, instead forming various combinations of three-dimensional structures (called schmelzmuster). Dryolestid dentition is thought to resemble the primitive mammalian dentition before the marsupial-eutherian differentiation and dryolestids are candidates to be the last common ancestor of the two mammalian subclasses.
Dryolestoids are known from the Jurassic through Early Cretaceous of the northern hemisphere (North America, Eurasia, and North Africa) and from the Late Cretaceous through to the Miocene of South America. Drylestoids are very rarely found in the Cenozoic, as are the few other Mesozoic mammals with later descendants, such as multituberculates, monotremes, and gondwanatheres.
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