What are some characteristics of ostracoderms?
The ostracoderms were primitive vertebrates, small to medium in size. Their body form was fish-like, usually flattened dorsoventrally, with a huge head and gill region, a tapering but muscular trunk and some sort of tail fin. They had no jaws and no pectoral or pelvic fins but had only median fins.
What are the characteristics of jawless fish?
Features of the jawless fish include a notochord, paired gill pouches, a pineal eye, and a two-chambered heart.
What are the characteristics of Agnatha?
Key Features of Agnatha
- Jaws are absent.
- Paired fins are generally absent.
- Early species had heavy bony scales and plates in their skin, but these are not present in living species.
- In most cases the skeleton is cartilaginous.
- The embryonic notochord persists in the adult.
- Seven or more paired gill pouches are present.
Are there any living ostracoderms?
After the appearance of jawed fish (placoderms, acanthodians, sharks, etc.) about 420 million years ago, most ostracoderm species underwent a decline, and the last ostracoderms became extinct at the end of the Devonian period.
Are ostracoderms Marine?
Ostracoderms and bony fishes are represented in both marine and freshwater deposits of the Devonian period. A marine origin for the vertebrates is supported by the fact that the three protochordate groups, Hemichordata, Urochordata, and Cephalochordata, are marine.
How did the ostracoderms feed without jaws?
The absence of jaws doesn’t mean they lacked a mouth. Their lips were movable to some degree, although they were unable to bite or create a strong enough suction to inhale prey like today’s fishes. The more active ostracoderms likely swam through the water with their mouth open similar to whale shark or manta ray.
What term best describes jawless fish?
Scientific definitions for jawless fish Any of various primitive fish of the class Agnatha that lack jaws. Living jawless fish (lampreys and hagfish) have a long, cylindrical body and a cartilaginous skeleton. The numerous extinct species were often heavily armored and are among the earliest vertebrate fossils known.
What are two major features of Chondrichthyans?
Chondrichthyes characteristics
- They are mostly marine fishes.
- They contain a pair of jaws.
- Whale sharks are the second largest vertebrate and the largest fish.
- The mouth is present ventrally.
- They contain cartilaginous endoskeleton, the deposits of calcium salts provide strength to it.
What is ostracoderm?
Ostracoderm, an archaic and informal term for a member of the group of armoured, jawless, fishlike vertebrates that emerged during the early part of the Paleozoic Era (542–251 million years ago).
How did ostracoderms make their armor?
According to evolutionary biologists, their peculiar armor had a structure like our teeth. When viewed under a microscope, it was formed by layers of dentin and enamel, as if ostracoderms crafted a wearable headpiece out of thousands of fused tiny teeth.
What happened to ostracoderms in the Devonian period?
Ostracoderm diversity peaked at the end of the Silurian Period roughly 419 million years ago, when they outnumbered any other kind of fishes. Although the following Devonian Period is also known as “The Age of Fishes,” the ostracoderms went through a steady decline while another group of fishes diversified more rapidly.
What does ostracoderm Cephalaspis look like?
In fact, the ostracoderm Cephalaspis resembled an armored catfish at first glance. With its big, armored head, this trout-sized fish could have stirred the bottom sediment to reveal prey animals hidden in the mud.