Psarolepis
Encyclopedia
Psarolepis is a genus
of extinct lobe-finned fish which lived around 397 to 418 million years ago (Pridoli
to Lochkovian stages
). Fossils of Psarolepis have been found mainly in South China
and described by paleontologist 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 fishes. In 2001, paleontologist John A. Long compared Psarolepis with Onychodontiform fishes and refer to their relationships.
located in front of a median fin behind the head, which gives the fish a shark
-like form.
The pock-marked head of Psarolepis was made of plates containing a layer of porcelain
-like cosmine. 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 were located above the eyes, which were just above the upper jaw.
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
. 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
. The premaxilla
and the dentary had large inner teeth and irregular array of tiny outer teeth.
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Most of the fossils of Psarolepis were discovered at the same locality of the Yulongsi
, Xishancun
and Xitun
formations, about 10 km northwest of the city of Qujing
, Yunnan, China. With this discovery other prehistoric lobe-finned fishes came to light such as Youngolepis
and Diabolepis
. The remains of Psarolepis were collected in 1981 and 1984 by paleontologist Min Zhu and colleagues and dated from Early Devonian and Late Silurian
periods. Other fossils, also dated from Late Silurian, have been found in Vietnam
but the description of the fish was based on the materials from China because they were better preserved.
es. In 1999 Zhu et al. were unable to locate Psarolepis in the cladogram
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 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. 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
, Western Australia
, said that Psarolepis and Onychodus are both basal bony fish and are more primitive than other lobe-finned groups.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of extinct lobe-finned fish which lived around 397 to 418 million years ago (Pridoli
Prídolí
Přídolí is a small town in Český Krumlov District in the South Bohemian Region of the Czech Republic.The town covers an area of , and has a population of 583 ....
to Lochkovian stages
Faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.Rock...
). Fossils of Psarolepis have been found mainly in South China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
and described by paleontologist Xiaobo Yu
Xiaobo Yu
Dr. Xiaobo Yu is a Chinese palaeontologist and professor on biological sciences. Yu is credited with first describing the lobe-finned fish Psarolepis romeri, a transitional species between fish and amphibians. Yu is currently a professor at Kean University in Union, New Jersey.-References:* 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 fishes. 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. 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 spineDorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
located in front of a median fin behind the head, which gives the fish a shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
-like form.
The pock-marked head of Psarolepis was made of plates containing a layer of porcelain
Porcelain
Porcelain is a ceramic material made by heating raw materials, generally including clay in the form of kaolin, in a kiln to temperatures between and...
-like cosmine. 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 were located above the eyes, which were just above the upper jaw.
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
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
. 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
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of onychodontida
Onychodontida
Onychodontida is a group of prehistoric fish. This order was it represents a small group of sarcopterygian fishes that lived between Late Silurian to Late Devonian period...
. The premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
and the dentary had large inner teeth and irregular array of tiny outer teeth.
Discovery
Yulongsi Formation
The Yulongsi Formation is a palaeontological formation located at Qujing, Yunnan, South China. The formation represents the Late Silurian period of China....
, Xishancun
Xishancun Formation
The Xishancun Formation is a geological formation located at Qujing, Yunnan, South China. Xishancun Formation has remains of petalichthyid and galeaspid fish and it represents the Early Devonian period of China....
and Xitun
Xitun Formation
The Xitun Formation is a palaeontological formation which named after the Xitun, a location in South China. This formation it includes many remains of fossilized fish of Early Devonian period ....
formations, about 10 km northwest of the city of Qujing
Qujing
Qujing is a prefecture-level city in eastern Yunnan province of Southwest China. It is an important industrial city, and is Yunnan's second largest city by population, after Kunming....
, Yunnan, China. With this discovery other prehistoric lobe-finned fishes came to light such as Youngolepis
Youngolepis
Youngolepis is a genus of prehistoric lobe-finned fish which lived during the Early Devonian period . Fossils have been found in China....
and Diabolepis
Diabolepis
Diabolepis is an extinct genus of sarcopterygian fish related to lungfishes which lived in the Early Devonian period of South China...
. The remains of Psarolepis were collected in 1981 and 1984 by paleontologist Min Zhu and colleagues and dated from Early Devonian and Late Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
periods. Other fossils, also dated from Late Silurian, have been found in Vietnam
Vietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...
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 lungfishLungfish
Lungfish are freshwater fish belonging to the Subclass Dipnoi. Lungfish are best known for retaining characteristics primitive within the Osteichthyes, including the ability to breathe air, and structures primitive within Sarcopterygii, including the presence of lobed fins with a well-developed...
es. In 1999 Zhu et al. were unable to locate Psarolepis in the cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
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 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. 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
Onychodus
Onychodus is a genus of prehistoric lobe-finned fish which lived during the Devonian period . It is one of the best known of the group of onychodontiform fishes. Scattered fossil bones of Onychodus were first discovered in 1857, in North America, and described by John Strong Newberry...
as the most basal member of the group of Onychodontiforms. Moreover, Long, referring to new fossils collected from Gogo Formation
Gogo Formation
The Gogo Formation in the Kimberley region of Western Australia is a Lagerstätte that exhibits exceptional preservation of a Devonian reef community.- Sedimentology :...
, Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
, said that Psarolepis and Onychodus are both basal bony fish and are more primitive than other lobe-finned groups.