Need help with which animal appeared during mesozoic era

Small mammals and aquatic life.

Explanation:

Copied from Britannica:

The first true mammals, which were small, shrewlike omnivores, also appeared in the Late Triassic, as did the lizards, turtles, and flying pterosaurs. In the oceans, mollusks—including ammonites, bivalves, and gastropods—became a dominant group. Fishes, sharks, and marine reptiles such as plesiosaurs, nothosaurs, and ichthyosaurs also swam the Mesozoic seas.

The dominant terrestrial vertebrates were dinosaurs, which exhibited great diversity during the Jurassic and Cretaceous. Birds are believed to have evolved from dinosaur ancestors during the Late Jurassic. Ancestors of living vertebrates, such as frogs, toads, and salamanders, appeared on land along with the two important modern mammal groups, the placentals and the marsupials. Plant life also exhibited a gradual change toward more-modern forms during the course of the Mesozoic. Whereas seed ferns had predominated in the Triassic, forests of palm like gymnosperms known as cycads and conifers proliferated under the tropical and temperate conditions that prevailed during the Jurassic. The first flowering plants, or angiosperms, had appeared by the Cretaceous. They radiated rapidly and supplanted many of the primitive plant groups to become the dominant form of vegetation by the end of the Mesozoic.

Genomic imprinting is an epigenetic phenomenon that causes genes to be expressed in a parent-of-origin-specific manner. ... These epigenetic marks are established ("imprinted") in the germline (sperm or egg cells) of the parents and are maintained through mitotic cell divisions in the somatic cells of an organism.

Explanation:

Genomic imprinting affects a subset of genes in mammals and results in a ... In contrast, nonimprinted genes will be expressed from both parental gene ... Surprisingly, mice carrying the mutant nonfunctional allele showed a ... In contrast, embryos that develop within eggs are unable to directly influence maternal resources.