Dipnoi fish
The Dipnoi are a group of fish,
are sarcopterygiian are commonly known as the lungfish. Their "lung" is a modified swim
bladder, which in most fish is used
for buoyancy in swimming, but in the lungfish also absorbs oxygen and removes
wastes.
Modern lungfish in Africa and South America are able to survive
when their pools dry up by
burrowing into the mud and sealing themselves within a mucous-lined burrow.
During this time, they breathe air through their swim bladder instead of
through their gills, and reduce their metabolic rate dramatically.
These
fish will even drown if they are kept underwater and not allowed to
breathe air!
Fossilized lungfish burrows of Gnathorhiza have been found in rocks as old as the permian with the lungfish still inside, and older burrows are known from the Carboniferous and Devonian. The oldest fossil dipnoan is Diabolichthyes, from the Lower devonain of Yunnan, China. It is not clear whether this particular fish was marine or lived in freshwater like modern lungfish, but both marine and freshwater fossils of other groups are known
While there are seven families of fossil lungfish known, only two
survived into the Triassic (and still exist today). There are
only three genera of lungfish alive today and each is found on a
single continent. The Australian lungfish is Neoceratodus; in
South America lives Leipdosiren; and Protopterus lives in
Africa. The largest of these is the Australian species, which may grow
to as long as 1.8 meters. Though Neoceratodus today is found only
in Australia, fossils of that genus and the related Ceratodus have
been found almost worldwide in mosozoic strata, indicating that this group once had a much wider distribution.
There were no premaxillae and maxillae. The jaw suspension resembles the autostylic condition. The broad, ridged tooth plates were developed on prevomers and palatopterygoids. Throughout the dipnoan evolution, the durophagous condition has persisted, an adaptation for feeding on hard foods like mollusces and other invertebrates with the help of broad tooth plates.
This habit of aestivation is adopted by the group since the Permian period. This fact is attested by the remains of cylindrical burrows associated with fossilized dipnoan bones. Lepidosiren has also the property of aestivation to escape death during summer. It lives in rivers which become shallow and stagnant in summer, but never dry up completely.
Fossilized lungfish burrows of Gnathorhiza have been found in rocks as old as the permian with the lungfish still inside, and older burrows are known from the Carboniferous and Devonian. The oldest fossil dipnoan is Diabolichthyes, from the Lower devonain of Yunnan, China. It is not clear whether this particular fish was marine or lived in freshwater like modern lungfish, but both marine and freshwater fossils of other groups are known
There were no premaxillae and maxillae. The jaw suspension resembles the autostylic condition. The broad, ridged tooth plates were developed on prevomers and palatopterygoids. Throughout the dipnoan evolution, the durophagous condition has persisted, an adaptation for feeding on hard foods like mollusces and other invertebrates with the help of broad tooth plates.
This habit of aestivation is adopted by the group since the Permian period. This fact is attested by the remains of cylindrical burrows associated with fossilized dipnoan bones. Lepidosiren has also the property of aestivation to escape death during summer. It lives in rivers which become shallow and stagnant in summer, but never dry up completely.
Comments
Post a Comment