ostracoderm การใช้

• Ostracoderms existed in two major groups, the more primitive cephalaspids.
• This allowed placoderms to lift their heads, unlike ostracoderms.
• The first fossil fishes that were discovered were ostracoderms.
• Ostracoderms have heads covered with a bony shield.
• Other ostracoderms, such as the Galeaspida are now known to have a paired olfactory organ.
• Later, about 420 million years ago, the jawed fish evolved from one of the ostracoderms.
• Early fish from the fossil record are represented by a group of small, jawless, armored fish known as ostracoderms.
• Like other ostracoderms, " Ateleaspis " had a head shield similar to that of " Cephalaspis ".
• Current phylogenetic analysis using a large number of characteristics now place pteraspidomorphs as the sister-group of all other ostracoderms and the gnathostomes.
• One of the earliest known armoured agnathan ( " ostracoderm " ) vertebrate, " Arandaspis ", dates from the Middle Ordovician.
• This sea remained in place during the early Paleozoic era and would come to be inhabited by creatures like brachiopods, ostracoderms, and trilobites.
• It was long assumed that pteraspidomorphs and thelodonts were the only ostracoderms with paired nostrils, while the other groups have just a single median nostril.
• In 1890 paleontologist Charles D . Walcott found broken pieces of the bony plates embedded in the skin of Middle Ordovician jawless fish known as ostracoderms.
• The ostracoderm armour consisted of 3 5 mm polygonal plates that shielded the head and gills, and then overlapped further down the body like scales.
• The evidence of phylogeny, however, suggests the lamprey lineage diverged much earlier from other vertebrates, rather than arising from among the " ostracoderms ".
• It is now accepted that the precursors of the jawed vertebrates are the long extinct bony ( armoured ) jawless fish, the so-called ostracoderms.
• After the appearance of jawed fish, most ostracoderm species underwent a decline, and the last ostracoderms became extinct at the end of the Devonian period.
• After the appearance of jawed fish, most ostracoderm species underwent a decline, and the last ostracoderms became extinct at the end of the Devonian period.
• Other fossils found alongside the ostracoderms lived articulated brachiopods, conodonts, gastropods, ostracods, pelecypods, sponges, trilobites, and trace fossils left by worms.
• These characteristics are, however, likely to be general for either the vertebrates or, at any rate, for the ensemble of all ostracoderms and the gnathostomes.