Facts About a Chordate Fossil

Characteristics

• A chordate is identified by its segmented muscle blocks, dorsal, hollow nerve cord, pharyngeal gill slits, post-anal tail and notochord. Notochords, which are made of cartilage not bone, provide support for the nerve cord. In some chordates, the notochord is lost at some stage in the organism's adult life, as shown in the fossils. More complex chordates have vertebrae that surround the notochord.

Origins

• Scientists seek to understand chordates to understand the origins of the vertebrates, but the fossils hold scant evidence. Some of the fossil records look like nothing more than smudges on a rock. By studying fossil records, some researchers speculate that the chordates emerged from cephalochordate larvae that did not metamorphose, leading to organisms that eventually evolved into chordates.

Earliest Discovery

• The earliest proven fossil record of the chordates traces back to the Lower Cambrian period, with a fossilized organism that was not a vertebrate. The earliest vertebrate fossils came from tiny fragments of bone found in the Late Cambrian Deadwood Formation of Wyoming.

Time Frame

• The Cambrian period saw the largest explosion of species variety in the history of the planet, with most of today's phyla appearing. The fossil discovery of a jawless chordate in China, traced back to the early Cambrian period, revealed to scientists that chordates existed during this period. The previous theory held that chordates evolved from echinoderms, but the echinoderms that the chordates were originally hypothesized to evolve from actually coexisted with the earliest chordates.

Related Species

• Researchers have struggled to figure out which species the chordates are the most related to. Possibilities include arthropods, graptolites, frond-like organisms and cephalochordates. The chordate fossils Yunnanozoon and Pikaia from the Cambrian period are likely related to the cephalochordates. Fossils from the main species of fish-like vertebrates have been linked to the Devonian Period. Archaeologists have discovered one species called the calcichordata, which might be from the chordates because it has gills. However, it also has a mineralized skeleton, which suggests that it is related more to echinoderms.