The Jurassic period is considered the era of undivided domination of gigantic lizards, and it is customary to think about mammals that they eked out a miserable existence in the shadow of giant reptiles. In fact, in the Mesozoic, mammals were quite a thriving group.
As Russian paleontologist and popularizer of science Kirill Eskov noted: “The number of currently known species of Mesozoic mammals simply exceeds the number of dinosaur species; however, they were all small creatures, and therefore not so loved by popularizers of science and science fiction writers. Dinosaurs and mammals appeared on Earth at the same time - at the end of the Triassic period and then shared the Earth for 120 million years. Large animals were represented by dinosaurs, and the small size class was dominated by mammals, which achieved considerable diversity.
This point of view is supported by the fossil remains of two mammals found in the Middle and Late Jurassic deposits of northeastern China. One of the species discovered by scientists was named Docofossor brachydactylus, which means “pre-codont burrowing broad-fingered” - this animal was a burrowing animal and distantly resembled a mole. The second ancient mammal was named Agilodocodon scansorius ("agile climbing precodont"). Judging by the structure of the limbs and spine, agilodocodon was a tree-climbing animal, resembling a squirrel or a small lemur.
The incisors of agilodocodon have an unusual shape: they look like wide, pointed at the end of the scapula, curved in a special way. Similar incisors are found in some American monkeys, which use incisors to gnaw through tree bark (in order to get to the plant sap). Apparently, Agilodocodon also got his food in this way. Both newly discovered species belong to the precodonts - an extinct branch of ancient mammals. The amazing waterfowl "beaver tail" Castorocauda, a mammal of the Jurassic period, which simultaneously resembled a beaver and an otter, belongs to the same group of precodonts.
New finds have shown that early mammals were already a successful and plastic group, whose representatives successfully occupied the ecological niches of lemurs and moles in the era of the highest flowering of giant dinosaurs.