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Nautilus (from Latin nautilus 'paper nautilus', from Ancient Greek ναυτίλος nautílos 'little sailor') [3] are the ancient pelagic marine mollusc species of the cephalopod family Nautilidae. This is the sole extant family of the superfamily Nautilaceae and the suborder Nautilina .
Nautiloids are first known from the late Cambrian Fengshan Formation of northeastern China, where they seem to have been quite diverse (at the time this was a warm shallow sea rich in marine life). However, although four orders have been proposed from the 131 species named, there is no certainty that all of these are valid, and indeed it is ...
The Oncocerids also appear during this time; they are restricted to shallow water and have short exogastric conchs. [2] The mid Ordovician saw the first cephalopods with septa strong enough to cope with the pressures associated with deeper water, and could inhabit depths greater than 100–200 m. [2]
The classification of species within Nautilus has been contentious for decades, and the genus has been reconfigured and redefined several times throughout its history. Nautilus is the type genus of the family Nautilidae , originally defined as any coiled- shell species with simple sutures , or walls, between shell compartments. [ 7 ]
However, the Helcionellids, which first appear over in Early Cambrian rocks from Siberia and China, [11] [12] are thought to be early molluscs with rather snail-like shells. Shelled molluscs therefore predate the earliest trilobites. [1]
Unlike most modern cephalopods, most ancient varieties had protective shells. These shells at first were conical but later developed into curved nautiloid shapes seen in modern nautilus species. Competitive pressure from fish is thought to have forced the shelled forms into deeper water, which provided an evolutionary pressure towards shell ...
Only a single genus, Cenoceras, with a shell similar to that of the modern nautilus, survived the less severe Triassic extinction, at which time the entire Nautiloidea almost became extinct. For the remainder of the Mesozoic , nautilids once again flourished, although never at the level of their Paleozoic glory, and 24 genera are known from the ...
Many modern mammal groups begin to appear: first glyptodonts, ground sloths, canids, peccaries, and the first eagles and hawks. Diversity in toothed and baleen whales. 33 Ma Evolution of the thylacinid marsupials . 30 Ma First balanids and eucalypts, extinction of embrithopod and brontothere mammals, earliest pigs and cats. 28 Ma