Sturgeons – contemporaries of dinosaurs
97
in the northern Caspian and stay on the ice until they are taught to swim and
forage. The seals were intensively killed for their valuable fur. Until recently,
they were under the threat of extinction. Now the number of seals is being
restored.
The third group of species is the Mediterranean species that came (either
independently or with the humans’ help) to the Caspian from the Black
Sea. These are: two types of mollusks – M ytilaster and Abra; crustaceans –
amphipods (small, side-swimming crayfi sh); shrimps, Atlantic crab from the
Black Sea, and the following fi sh – golden mullet and litt le mullet from the
gray mullet family, the pipefi sh and the Black Sea turbot.
Finally, the fourth group includes the freshwater fi sh species. Having
entered the Caspian Sea, they turned into seawater or diadromous (migrating
upstream) fi sh. This group also comprises typical freshwater fi sh that enters
saline waters. These species include catfi sh, sea sander, and fi sh of the carp
family – Caspian barbel, Asp Caspian and Caspian vimba.
This group also includes Russian and Persian sturgeon, beluga and starred
sturgeon. It should be noted that the Caspian Sea contains approximately 80%
of the world’s sturgeon populations. Caspian barbels (reaching 1m in length
and 20 kg in weight) and vimba (50 m, 3 kg) are valuable commercial fi sh.
They feed on benthic organisms – mollusks, larvae, crustaceans and small
fi sh.
Sturgeons are undoubtedly the main treasure of the Caspian Sea. Our
book is dedicated to them.
G.M.Palatnikov, R.U.Qasimov
98
CONTEMPORARIES OF DINOSAURS
Sturgeon-like fi sh are the most ancient among the currently living
vertebrates. Their ancestors swam in the seas as early as the Jurassic period.
Their traces are found in the Cretaceous deposits. The most ancient of the
known sturgeons is Chondrosteus of the early Jurassic period. Remains of
this fi sh demonstrate that sturgeons did not change for millions of years.
Regardless of their ancient origin and primitive morphology, until recently
sturgeons have occupied a vast habitat area covering almost the whole
Northern hemisphere of the Earth.
Areas of sturgeon distribution
Sturgeons – contemporaries of dinosaurs
99
Position of sturgeons in zootaxy:
Type:
Chordata
(Chordates)
Sub-type:
Vertebrata
(Vertebrates)
Group:
Pices
(Fish)
Sub-group:
Actytoperygii
(Actinopterygian
fi sh)
Superorder:
Chondrostei (Cartilaginous ganoids).
Order:
Acipenseriformes
(Sturgeon-like)
Family:
Acipenseridae
(Sturgeons);
Genuses:
Huso (Belugas) – 2 species; Acipenser (Sturgeons) –
18 species; Scaphirhynchus (Shovelnose sturgeons)
– 2 species; Pseudoscaphirhynchus (False shovelnose
sturgeons) – 3 species.
Family of Copepoda: (Polyodontidae)
Two
species:
Paddlefi sh (Polyodon spathula); Chinese paddlefi sh
(Psephurus gladius).
STURGEON FAMILY (ACIPENSERIDAE)
Sturgeons are diadromous, fl uvial anadromous and freshwater fi sh;
inhabit the waters of the Northern hemisphere – Europe, North Asia and
North America. Four genera are distinguished: beluga, sturgeon, shovelnose
and false shovelnose.
Sturgeon-like fi shes have a number of features that are common with
Head of sturgeon
(ventral view)
those of cartilaginous fi shes, and they are slightly
similar to squaloids in appearance.
Sturgeons have a long fusiform body covered with
fi ve rows of bony scutes: one dorsal, two lateral, and two
ventral rows. Scatt ered between the rows of scutes are
small bony granules and plates. The snout is elongated,
conical or spatulate. The mouth is located on the lower
part of the head and is edged by fl eshy lips; some have
a mouth that projects to the sides of the head. There
are 4 barbels in a transverse row on the lower part of
the snout. The mouth is protractile, toothless; however,
juveniles do have weak teeth.
G.M.Palatnikov, R.U.Qasimov
100
The forward pectoral fi n ray is strongly hardened and turned into a
spine. The dorsal fi n is set back. The swim bladder is usually well developed
(some sturgeons, like shovelnoses, have a rudimentary swim bladder) and
connected to the stomach or esophagus. The internal skeleton is cartilaginous,
and the notochord, which is covered by a thick joined sheath, remains for the
life of the fi sh. Vertebral centra do not develop, although lower and upper
vertebral curves do exist.
As with sharks, the sturgeon’s caudal fi n is heterocercal.
The common feature that unites bony fi shes and sturgeons is the presence
of dermal bones in the neurocranium, which is covered with fi ve rows of big
plates (scutes). Sturgeons have a bony operculum and swim bladder, which
is connected to the intestines.
Among other ray-fi nned fi shes, sturgeons have the most archaic
structural features, which are not observed in bony fi shes. The sturgeons’
axial skeleton is based on a permanent notochord, the internal skeleton
is made of cartilage, the internal cranium to a great degree remains
cartilaginous, and the tail fi n is heterocercal with large upper peduncle.
The body has fi ve longitudinal bony scales - “scutes,” which are vestiges
of denticles. As with cartilaginous fi shes, sturgeons retain a spiracle – a
special aperture on the edge of the operculum, which leads to the branchial
aperture. The heart has a conus arteriosus, and the intestine has a spiral
valve – just like in squaloids.
Sturgeon family representative – Kaluga (
Huso dauricus
)
Based on these characteristics, some authors considered sturgeons to
be a very primitive group, similar to cartilaginous fi sh. In other words, they
thought that the sturgeons originated not from the ancestors common with
bony fi sh, but from primitive cartilaginous fi sh, ancestors of squaloids.
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