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The appendages of opisthosomal segments 1 and 2 (the seventh and eighth segments overall) were fused into a structure termed the genital operculum, occupying most of the underside of the opisthosomal segment 2. Near the anterior margin of this structure, the genital appendage (also called the Zipfel or the median abdominal appendage) protruded ...
Like the extinct and related acanthothoracids, and the living and unrelated holocephalians, most of the ptyctodontids are thought to have lived near the sea bottom and preyed on shellfish. On account of their lack of armour, some paleontologists have suggested that the Ptyctodontida were not placoderms, but holocephalians or the ancestors of ...
Animals are multicellular eukaryotes, [note 1] and are distinguished from plants, algae, and fungi by lacking cell walls. [1] Marine invertebrates are animals that inhabit a marine environment apart from the vertebrate members of the chordate phylum; invertebrates lack a vertebral column. Some have evolved a shell or a hard exoskeleton.
A deep-diving robot that chiseled into the rocky Pacific seabed at a spot where two of the immense plates comprising Earth's outer shell meet has unearthed a previously unknown realm of animal ...
Surface-living animals (such as sea otters) need the opposite, and free-swimming animals living in open waters (such as dolphins) need to be neutrally buoyant in order to be able to swim up and down the water column. Typically, thick and dense bone is found in bottom feeders and low bone density is associated with mammals living in deep water.
The majority of siphonophores live in the deep sea and can be found in all of the oceans. [11] Siphonophore species rarely only inhabit one location. [ 11 ] Some species, however, can be confined to a specific range of depths and/or an area of the ocean.
The footprints, found at several sites in southern Africa, were recently identified as the oldest birdlike tracks ever found, preceding the earliest known skeletal fossils of avians by about 60 ...
This is an accepted version of this page This is the latest accepted revision, reviewed on 7 January 2025. Taxonomic group of semi-aquatic mammals Pinnipeds Temporal range: Latest Oligocene – Holocene, 24–0 Ma Pre๊ ๊ O S D C P T J K Pg N Clockwise from top left: Grey seal (Halichoerus grypus), Steller sea lion (Eumetopias jubatus), New Zealand fur seal (Arctocephalus forsteri), walrus ...