Acanthodes (meaning spiny base or thorny base) is an extinct genus of
spiny shark. Fossils have been found in Europe, North America, and
5 External links
Compared with other spiny sharks,
Acanthodes was relatively large, at
30 centimetres (12 in) long. The genus had no teeth, instead
gills. Because of this, it is presumed to have been a filter feeder,
filtering plankton from the water. The
Acanthodes has been found to
have only a couple of skull bones. It was covered in scales that were
cubical in shape.
It also had fewer spines than many of its relatives. Each of the
paired pectoral and pelvic fins had a spine, as did the single anal
and dorsal fins, giving it a total of just six, less than half that of
many other species.+ A fossil discovered near
Hamilton, Kansas in
Carboniferous Hamilton Formation, and published in 2014 as
Acanthodes bridgei was so well-preserved that traces of its eye tissue
were sufficient to establish that
Acanthodes had both rod and cone
photoreceptor cells, and thus profited from color vision.
Several specimens of
Acanthodes were recovered from an abandoned
quarry (Hamilton Quarry) which contained individuals ranging in total
length from 54 nm to 410 nm. A. bridgei was one of the
species found there. A. bridgei has large orbits, a shorter
pre-pectoral region, and shallower insertions of the fin spines.
The scientific classification of acanthodians is still a subject of
great dispute, due to the fact that they share qualities of both bony
fish (osteichthyes) and cartilaginous fish (chondrichthyes). A recent
study has suggested that
Acanthodes may have been, or closely related
to an early common ancestor to all cartilaginous and bony fish,
Acanthodian internal anatomy is primarily
Acanthodes bronni because it remains the only example
preserved in substantial detail, central to which is an ostensible
osteichthyan braincase. For this reason,
Acanthodes has become an
indispensable component in early gnathostome phylogenies.
Acanthodes is quantifiably closer to chondrichthyans than to
osteichthyans. However, phylogenetic analysis places
Acanthodes on the
osteichthyan stem, as part of a well-resolved tree that also recovers
acanthodians as stem chondrichthyans and stem gnathostomes. As such,
perceived chondrichthyan features of the
Acanthodes cranium represent
shared primitive conditions for crown group gnathostomes. There has
been increasingly detailed findings of early gnathostome evolution
highlights ongoing and profound anatomical reorganization of
vertebrate crania after the origin of jaws but before the divergence
of living clades.
As mentioned earlier, A. bronni is an acanthodian, a group of stem
gnathostomes more derived than placoderms, but fairly close to the
origins of chondrichthyans and osteichthyans. A. bronni lived about
290 million years ago during the
Carboniferous period. Researchers
took 138 characteristics of various skulls of A. bronni and compared
these with skulls of both chondrichthyans and osteichthyans, and
determined that acanthodians are closer to cartilaginous fishes.
^ Royal Physical Society of Edinburgh (1880). "Proceedings of the
Royal Physical Society of Edinburgh". V: 115.
^ Nicholson, Henry Alleyne; Richard Lydekker (1889). A Manual of
Palaeontology. p. 966.
^ a b Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of
Dinosaurs and Prehistoric Animals. London: Marshall Editions.
pp. 30–31. ISBN 1-84028-152-9.
^ NewsScienceMag, "Three hundred million year old fossil fish still
has traces of eye tissue", 23 December 2014: accessed 23 December
^ Zidek, Jiri (1976). "Kansas Hamilton Quarry (Upper Pennsylvanian)
Acanthodes, with remarks on the previously reported North American
occurrences of the genus". The University of Kansas Paleontological
^ Article on
Acanthodes as ancestor of Man,
http://www.sci-news.com/paleontology/article00396.html, accessed 15
^ Journal article on Acanthodes,
accessed 15 June 2012
^ a b c d Davis, S; Finarelli, J; Coates, M (2012). "
shark-like conditions in the last common ancestor of modern
gnathostomes". Nature. 486: 247–250. doi:10.1038/nature11080.
Parker, Steve. Dinosaurus: the complete guide to dinosaurs. Firefly
Books Inc, 2003. Pg. 60
entry at the Fossil Museum
entry at Saint Joseph's University