''Psarolepis'' (; ''psārolepis'', from Greek ψαρός 'speckled' and λεπίς 'scale') is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of extinct
bony fish which lived around 397 to 418
million years ago
The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds.
Usage
Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago) ...
(
Pridoli to
Lochkovian
The Lochkovian is one of three faunal stages in the Early Devonian Epoch. It lasted from 419.2 ± 3.2 million years ago to 410.8 ± 2.8 million years ago. It marked the beginning of the Devonian Period, and was followed by the Pragian Stage. It is ...
stages). Fossils of ''Psarolepis'' have been found mainly in South
China and described by
paleontologist
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
Xiaobo Yu in 1998. It is not known certainly in which group ''Psarolepis'' belongs, but paleontologists agree that it probably is a
basal genus and seems to be close to the common ancestor of
lobe-finned and
ray-finned fish
Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species.
The ray-finned fishes are so called because their fins are webs of skin supported by bony or h ...
es.
[Benton, M. J. (2005): ''Vertebrate Palaeontology'', page 65.] In 2001, paleontologist
John A. Long compared ''Psarolepis'' with
onychodontiform fishes and refer to their relationships.
Description
''Psarolepis'' had a pair of 'parasymphysical tooth whorls', teeth which extend up at the front of the
lower jaw
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
. The head was made of several thick dermal plates and covered with deep pock-marks and large pores. Another trait is a large
pectoral spine, just in front of the pectoral fin, extending back from the
shoulder girdle, and a
dorsal spine located in front of a median fin behind the head, which gives the fish a
shark
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachi ...
-like form.
The pock-marked head of ''Psarolepis'' was made of plates containing a layer of
porcelain
Porcelain () is a ceramic material made by heating substances, generally including materials such as kaolinite, in a kiln to temperatures between . The strength and translucence of porcelain, relative to other types of pottery, arises main ...
-like
cosmine
Cosmine is a spongy, bony material that makes up the dentine-like layers in the scales of the lobe-finned fishes of the class Sarcopterygii. Fish scales that include layers of cosmine are known as cosmoid scales.
Description
As traditionally d ...
. Because the cosmine layer obscures the suture lines of the skull, it is difficult to study the exact bone structure. The snout was strangely humped and the
nostrils
A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...
were located above the eyes, which were just above the
upper jaw
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...
.
The most spectacular findings were the fin spines. Two are known: one extending back from the
shoulder girdle and another which is associated with the
dorsal fin
A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...
. These fin spines are found only in primitive jawed fishes and are apparently absent from the most primitive sharks, but present in abundance in more derived forms.
''Psarolepis'' had teeth at the very front of the snout with large fangs on the tooth plate. Outstanding feature are the 'parasymphysical tooth whorls' which place the fish in the
order of
Onychodontida.
[Zhu; Yu; Janvier, 1999.] The
premaxilla
The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...
and the
dentary
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...
had large inner teeth and irregular array of tiny outer teeth.
Discovery
Most of the fossils of ''Psarolepis'' were discovered at the same locality of the
Yulongsi,
Xishancun and
Xitun Formations,
about northwest of the city of
Qujing,
Yunnan, China. With this discovery other prehistoric lobe-finned fishes came to light such as ''
Youngolepis'' and ''
Diabolepis
''Diabolepis'' (or ''Diabolichthys'') is an extinct genus of very primitive lungfish which lived about 400 million years ago, in the Early Devonian period of South China. ''Diabolepis'' is the most basal known dipnoan.
A rather small fish, the ...
''. The remains of ''Psarolepis'' were collected in 1981 and 1984 by paleontologist Min Zhu and colleagues and dated from
Early Devonian
The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonian series. It lasted from and began with the Lochkovian Stage , which was followed by the Pragian from and then by the Emsian, ...
and Late
Silurian periods.
[Ahlberg, 1999.] Other fossils, also dated from Late Silurian, have been found in
Vietnam
Vietnam or Viet Nam ( vi, Việt Nam, ), officially the Socialist Republic of Vietnam,., group="n" is a country in Southeast Asia, at the eastern edge of mainland Southeast Asia, with an area of and population of 96 million, making i ...
but the description of the fish was based on the materials from China because they were better preserved.
History and classification
When ''Psarolepis'' was described for the first time in 1998, it was placed in the group of sarcopterygians (lobe-finned fishes) because the skull and jaws resemble those of primitive
lungfish
Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...
es. In 1999 Zhu et al. were unable to locate ''Psarolepis'' in the
cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
because they did not know if it was the most primitive lobed-finned fish or the most primitive bony fish.
There are some characteristics that bony fish do not have, such as the median spine located behind the head, which is known in
sharks
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorp ...
and
acanthodians, and the pectoral spine extending back from the shoulder girdle which is found in some
placoderms and acanthodians.
Later, in 2001, Zhu and Schultze gave more basis to the theory that ''Psarolepis'' was probably a basal bony fish.
The same year Long re-examined the phylogenetic position of the fish and pointed out several similarities between ''Psarolepis'' and Onychodontiform fishes.
[Long, 2001.] He also noted that the presence of a rotational tooth whorl combined with the other characteristics in the skull, and possibly in the shoulder girdle, show that ''Psarolepis'' is better placed as a sister taxon to ''
Onychodus'' as the most basal member of the group of Onychodontiforms. Moreover, Long, referring to new fossils collected from
Gogo Formation
The Gogo Formation in the Kimberley region of Western Australia is a Lagerstätte that exhibits exceptional preservation of a Devonian reef community. The formation is named after Gogo Station, a cattle station where outcrops appear and fossil ...
,
Western Australia
Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...
, said that ''Psarolepis'' and ''Onychodus'' are both basal bony fish and are more primitive than other lobe-finned groups.
References
*
*
*
*
*
*
Notes
External links
''Psarolepis'' at Palaeos
{{Taxonbar, from=Q291624
Prehistoric bony fish genera
Fish enigmatic taxa
Transitional fossils
Pridoli life
Silurian bony fish
Devonian bony fish
Early Devonian fish
Devonian fish of Asia
Silurian fish of Asia
Silurian China
Fossils of China
Fossil taxa described in 1998
Taxa named by Xiaobo Yu