The first vertebrates to evolve jaws (gnathostomes) are the
acanthodians (class Acanthodii "spines") or spiny sharks.
fish have a shark-shaped body with paired fins and
an upturned tail (heterocercal),
they are not sharks. There is good reason
to believe that the jaws of acanthodians evolved
found in their ancestral jawless fish (Dixon, D., 1988, p
Acanthodians were typically small fish
around 20 cm. Spiny sharks had a streamlined body with
a relatively large head and eyes. Acanthodians had
skeletons made of cartilage, close fitting scales in
their skin made of bone, bone protecting
their head and girdle, and fins with a broad bony base that
extended along the anterior edge as a dentine spine. The
close fitting scales grew by addition of bone with dentine at the
margins forming concentric lines that recorded the animal's
growth. All of the fins had a reinforcing spine except for the
tail. Some early
pairs of spines
belly. Later forms, like Acanthodes,
may have been able to erect their pectoral spines as
(Benton, 2005, p. 60). Some acanthodians developed
a bony operculum covering their
gill openings. Many acanthodians lacked teeth and instead
used gill-rakers for suspension feeding. Acanthodians
first appear in the Late Ordovician as marine fish,
into many species including freshwater forms. The class
goes extinct in the Permian.
Science Olympiad Fossil Event
The 2016 Science Olympiad Fossil List does not include the
M.J. (2005) Vertebrate Palaeontology [3rd Edition].
Blackwell Publishing: Main, USA.|
D., Cox, B., Savage, R.J.G., & Gardiner, B. (1988). The
Macmillan Illustrated Encyclopedia of Dinosaurs and Prehistoric
Animals: A Visual Who’s Who of Prehistoric Life.
New York: Macmillan Publishing Company.
Teleostomi Page: http://www.palaeos.com/Vertebrates/
Perkins, R. (2001-2008). The Virtual Fossil Museum Acanthodes