The Hesperornithiformes were flightless, … Flora. Flowering plants first appeared, although they did not become predominant until near the end of the period ( Campanian age). b) Enantiornithe birds were the most diverse clade of Mesozoic birds and the most common Mesozoic birds c) Enantiornithe birds survived until the terminal Cretaceous mass extinction (1 genus from Hell Creek Formation), but > 60% of the 70+ genera are Early Cretaceous in age with > 1/2 from Early Cretaceous strata of Liaoning Province in NE China First came the Precambrian period, which stretched from the earth’s formation to about 542 million years ago. Climates were warm, and even polar regions had no permanent ice. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Start studying Age of Dinosaurs: Final Exam Practice Questions. In the area that is now India, massive lava beds called the Deccan Traps were laid down in the very late Cretaceous and early Paleocene. The living Aves are in this group, as well as the Hesperornithiformes, and the Ichthyornithiformes, (both Cretaceous in age) the closest fossil relatives to living birds. To put these geologic periods in the proper context, bear in mind that the Triassic, Jurassic, and Cretaceous don't cover all of prehistory, not by a long shot. Marine reptiles included ichthyosaurs in the early and middle of the Cretaceous, plesiosaurs throughout the entire period, and mosasaurs in the Late Cretaceous. And in fact, paleontologists have only one decent example of a Cretaceous crown bird, a creature known as Vegavis iaai, plus a jumble of incomplete fossils that could come from crown birds. Curiously, the same mechanism apparently evolved independently in the extinct Cretaceous-age Hesperornithiformes, which are totally unrelated birds. Grebes have unusual plumage. There at least 15 unambiguous characters which unite all the members of the Ornithurae. It is dense and waterproof, and on the underside the feathers are at right-angles to the skin, sticking straight out to begin with and curling at the tip. Also in this group are all the remaining birds in a clade known as Ornithurae. Birds had diversified by the Early Cretaceous, evolving into a number of groups of varying anatomy and ecology (Figure 1; example fossils in Figure 5). Baculites, a straight-shelled form of ammonite, flourished in the seas.