Laccognathus embryi
Encyclopedia
Laccognathus embryi is an extinct species of porolepiform
lobe-finned fish recovered from Ellesmere Island
, Canada
. It existed during the Frasnian
age of the Late Devonian epoch (around 385.3 to 374.5 mya).
of Ellesmere Island, Nunavut
, Canada from 2000 to 2008 in the Nunavut Paleontological Expeditions. The expeditions were led by Jason P. Downs, Edward Daeschler, Farish Jenkins, Jr., and Neil Shubin
, and previously resulted in the discovery of the tetrapodomorph
Tiktaalik roseae from the same locality.
Ellesmere Island was also the site of previous Norwegian scientific expeditions by the ship Fram
in 1893-1896
by Fridtjof Nansen
and in 1898–1902 by Otto Sverdrup
. In the second expedition, a few vertebrate fossils were collected from Ellesmere Island by a member of Sverdrup's crew, the geologist Per Schei. The collection included a few porolepiform
scales attributed to Glyptolepis
and Holoptychius
.
Prior to its discovery, the genus Laccognathus
was known only from Latvia
and Russia
. L. embryi is the first member of the genus discovered in North America
.
of modern fishes and sharks, an analog to our ear
s. It had a distinctly dorsoventrally flattened short and wide head, less than one-fifth of the length of the body and with a width-to-length ratio of approximately 2:1. The eyes are very small, even smaller than those of L. panderi
. The jaws possessed coronoid fangs
up to 3.8 cm (1.5 in) in length. These are bordered with marginal teeth, with the exception of coronoids 1 and 2. Much of the external surface of the lower jaw is oriented downwards, suggesting that the animal spent a considerable amount of time resting on the substrate
.
L. embryi is estimated to have been 1.8 m (6 ft) long with a wide flattened body. Though only two partial specimens of the postcranial body have been recovered, L. embryi are believed to have the same body form as other species of Laccognathus. L. grossi
, for example, had wide and relatively short pectoral and pelvic fins arising from fleshy lobes. The caudal (tail) fin was heterocercal, with a long low upper (epichordal) blade and a rounded lower (hypochordal) blade three times as wide as the upper blade. The dorsal
and anal fins were positioned close to the caudal fin. The body was also covered in broadly overlapping thick scales, each roughly 2.5 cm (1 in) in diameter and ornamented at the exposed ends with small radially arranged tubercles, ridges, or both.
. The formation, which consists of alternating layers of siltstone
and sandstone
, is dated to the Frasnian
age of the Late Devonian epoch (around 385.3 ± 2.6 to 374.5 ± 2.6 mya). Specific palynological examination reveals that the NV2K17 locality itself is from the early to middle Frasnian. The area is believed to have been the floodplain
of a meandering river system.
The variety of fossils found in Ellesmere Island is similar to those found in the Gauja Formation
s of Latvia
and Estonia
, from whence other species of Laccognathus were recovered. North America
and western Eurasia
were once part of the ancient supercontinent
of Euramerica
(also known as Laurussia) located at the equator
during the Devonian
period.
. There are fossils of at least eight other vertebrate
taxa found within the same fossiliferous zone as L. embryi, including Asterolepis
, several large tetrapodomorphs, dipnoans, and another small undescribed holoptychiid. Though the locality in Ellesmere island is from freshwater
siltstone
alluvial deposits, the existence of other members of the genus in marine
and estuarine deposits in Europe
suggest that Laccognathus species could tolerate a wide range of environmental conditions and salinity
levels.
. This family, in turn, belongs to the extinct order
Porolepiformes
, of the class Sarcopterygii
(lobe-finned fishes). Together with their closest living relatives, subclass Dipnoi (lungfish
es), Laccognathus are members of the clade
Dipnomorpha. Unlike its sister group, the Tetrapodomorpha
, dipnomorphs were not direct ancestors of land vertebrates
.
The generic name
Laccognathus is derived from Greek λάκκος (lakkos, 'pit') and γνάθος (gnathos, 'jaw') in reference to the three wide pits along the labial surface of the lower jaw. The specific name is in honour of Ashton Embry
of the Geological Survey of Canada.
Porolepiformes
Porolepiformes is an order of prehistoric lobe-finned fish which lived during the Devonian period . The group contains two families: Holoptychiidae and Porolepididae....
lobe-finned fish recovered from Ellesmere Island
Ellesmere Island
Ellesmere Island is part of the Qikiqtaaluk Region of the Canadian territory of Nunavut. Lying within the Canadian Arctic Archipelago, it is considered part of the Queen Elizabeth Islands, with Cape Columbia being the most northerly point of land in Canada...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. It existed during the Frasnian
Frasnian
The Frasnian is one of two faunal stages in the Late Devonian epoch. It lasted from 385.3 ± 2.6 million years ago to 374.5 ± 2.6 million years ago. It was preceded by the Givetian stage and followed by the Famennian stage...
age of the Late Devonian epoch (around 385.3 to 374.5 mya).
Discovery
Specimens from at least 22 individuals of Laccognathus embryi were recovered from the Fram FormationFram Formation
The Fram Formation is a Late Devonian sequence of rock strata on Ellesmere Island that came into prominence in 2006 with the discovery in its rocks of examples of the transitional fossil, Tiktaalik, a sarcopterygian or lobe-finned fish showing many tetrapod characteristics...
of Ellesmere Island, Nunavut
Nunavut
Nunavut is the largest and newest federal territory of Canada; it was separated officially from the Northwest Territories on April 1, 1999, via the Nunavut Act and the Nunavut Land Claims Agreement Act, though the actual boundaries had been established in 1993...
, Canada from 2000 to 2008 in the Nunavut Paleontological Expeditions. The expeditions were led by Jason P. Downs, Edward Daeschler, Farish Jenkins, Jr., and Neil Shubin
Neil Shubin
Neil Shubin is an American paleontologist, evolutionary biologist and popular science writer. He is the Robert R. Bensley Professor of Organismal Biology and Anatomy, Associate Dean of Organismal Biology and Anatomy and Professor on the Committee of Evolutionary Biology at the University of...
, and previously resulted in the discovery of the tetrapodomorph
Tetrapodomorpha
Tetrapodomorpha is a clade of vertebrates, consisting of tetrapods and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish...
Tiktaalik roseae from the same locality.
Ellesmere Island was also the site of previous Norwegian scientific expeditions by the ship Fram
Fram
Fram is a ship that was used in expeditions of the Arctic and Antarctic regions by the Norwegian explorers Fridtjof Nansen, Otto Sverdrup, Oscar Wisting, and Roald Amundsen between 1893 and 1912...
in 1893-1896
Nansen's Fram expedition
Nansen's Fram expedition, 1893–1896, was an attempt by the Norwegian explorer Fridtjof Nansen to reach the geographical North Pole by harnessing the natural east–west current of the Arctic Ocean...
by Fridtjof Nansen
Fridtjof Nansen
Fridtjof Wedel-Jarlsberg Nansen was a Norwegian explorer, scientist, diplomat, humanitarian and Nobel Peace Prize laureate. In his youth a champion skier and ice skater, he led the team that made the first crossing of the Greenland interior in 1888, and won international fame after reaching a...
and in 1898–1902 by Otto Sverdrup
Otto Sverdrup
Otto Neumann Knoph Sverdrup was a Norwegian sailor and Arctic explorer.-Early and personal life:...
. In the second expedition, a few vertebrate fossils were collected from Ellesmere Island by a member of Sverdrup's crew, the geologist Per Schei. The collection included a few porolepiform
Porolepiformes
Porolepiformes is an order of prehistoric lobe-finned fish which lived during the Devonian period . The group contains two families: Holoptychiidae and Porolepididae....
scales attributed to Glyptolepis
Glyptolepis
Glyptolepis is an extinct genus of porolepiform lobe-finned fish which lived during Devonian period....
and Holoptychius
Holoptychius
Holoptychius is an extinct genus of porolepiform lobe-finned fish from the Devonian period. It is known from fossils worldwide.Holoptychius was streamlined predator about long, which fed on other bony fish. Its rounded scales and body form indicate that it could have swum quickly through the water...
.
Prior to its discovery, the genus Laccognathus
Laccognathus
Laccognathus is an extinct genus of amphibious lobe-finned fish from Europe and North America. They existed from the Middle Devonian to the Late Devonian...
was known only from Latvia
Latvia
Latvia , officially the Republic of Latvia , is a country in the Baltic region of Northern Europe. It is bordered to the north by Estonia , to the south by Lithuania , to the east by the Russian Federation , to the southeast by Belarus and shares maritime borders to the west with Sweden...
and Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
. L. embryi is the first member of the genus discovered in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.
Description
Like other members of the genus, Laccognathus embryi possessed three deep longitudinal pits (fossae) on the external surface of the lower jaw. They are believed to have functioned as sensory pits able to detect changes in surrounding water pressure, similar to the lateral lineLateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
of modern fishes and sharks, an analog to our ear
Ear
The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
s. It had a distinctly dorsoventrally flattened short and wide head, less than one-fifth of the length of the body and with a width-to-length ratio of approximately 2:1. The eyes are very small, even smaller than those of L. panderi
Laccognathus panderi
Laccognathus panderi is an extinct lobe-finned fish from eastern Europe. They existed from the Middle Devonian to the Late Devonian .L...
. The jaws possessed coronoid fangs
Coronoid process of the mandible
The mandible's coronoid process is a thin, triangular eminence, which is flattened from side to side and varies in shape and size....
up to 3.8 cm (1.5 in) in length. These are bordered with marginal teeth, with the exception of coronoids 1 and 2. Much of the external surface of the lower jaw is oriented downwards, suggesting that the animal spent a considerable amount of time resting on the substrate
Substrate (marine biology)
Stream substrate is the material that rests at the bottom of a stream. There are several classification guides. One is:*Mud – silt and clay.*Sand – Particles between 0.06 and 2 mm in diameter.*Granule – Between 2 and 4 mm in diameter....
.
L. embryi is estimated to have been 1.8 m (6 ft) long with a wide flattened body. Though only two partial specimens of the postcranial body have been recovered, L. embryi are believed to have the same body form as other species of Laccognathus. L. grossi
Laccognathus grossi
Laccognathus grossi is an extinct lobe-finned fish from eastern Europe. They existed during the Middle Devonian. The species is named after Walter Gross, who collected the first Laccognathus fossils belonging to L. panderi.L...
, for example, had wide and relatively short pectoral and pelvic fins arising from fleshy lobes. The caudal (tail) fin was heterocercal, with a long low upper (epichordal) blade and a rounded lower (hypochordal) blade three times as wide as the upper blade. The dorsal
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...
and anal fins were positioned close to the caudal fin. The body was also covered in broadly overlapping thick scales, each roughly 2.5 cm (1 in) in diameter and ornamented at the exposed ends with small radially arranged tubercles, ridges, or both.
Distribution and geologic time range
Laccognathus embryi was recovered in the middle part of the Fram Formation, designated as the NV2K17 localityType locality (geology)
Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....
. The formation, which consists of alternating layers of siltstone
Siltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
and sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
, is dated to the Frasnian
Frasnian
The Frasnian is one of two faunal stages in the Late Devonian epoch. It lasted from 385.3 ± 2.6 million years ago to 374.5 ± 2.6 million years ago. It was preceded by the Givetian stage and followed by the Famennian stage...
age of the Late Devonian epoch (around 385.3 ± 2.6 to 374.5 ± 2.6 mya). Specific palynological examination reveals that the NV2K17 locality itself is from the early to middle Frasnian. The area is believed to have been the floodplain
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...
of a meandering river system.
The variety of fossils found in Ellesmere Island is similar to those found in the Gauja Formation
Gauja Formation
The Gauja Formation is a Middle Devonian fossil locality in Estonia and Latvia. It is named after the Gauja River, where it is exposed along the banks....
s of Latvia
Latvia
Latvia , officially the Republic of Latvia , is a country in the Baltic region of Northern Europe. It is bordered to the north by Estonia , to the south by Lithuania , to the east by the Russian Federation , to the southeast by Belarus and shares maritime borders to the west with Sweden...
and Estonia
Estonia
Estonia , officially the Republic of Estonia , is a state in the Baltic region of Northern Europe. It is bordered to the north by the Gulf of Finland, to the west by the Baltic Sea, to the south by Latvia , and to the east by Lake Peipsi and the Russian Federation . Across the Baltic Sea lies...
, from whence other species of Laccognathus were recovered. North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and western Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
were once part of the ancient supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
of Euramerica
Euramerica
Euramerica was a minor supercontinent created in the Devonian as the result of a collision between the Laurentian, Baltica, and Avalonia cratons .300 million years ago in the Late Carboniferous tropical rainforests lay over the equator of Euramerica...
(also known as Laurussia) located at the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....
during the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
period.
Paleoecology
The flattened head of Laccognathus embryi indicates that it was a benthic sit-and-wait ambush predatorAmbush predator
Ambush predators or sit-and-wait predators are carnivorous animals that capture prey by stealth or cunning, not by speed or necessarily by strength. These organisms usually hide motionless and wait for prey to come within striking distance. They are often camouflaged, and may be solitary...
. There are fossils of at least eight other vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
taxa found within the same fossiliferous zone as L. embryi, including Asterolepis
Asterolepis (fish)
Asterolepis is an extinct genus of placoderms from the Devonian of North America and Europe. They were heavily armored benthic detritivores with distinctive jointed limb-like pectoral fins.-See also:*Bothriolepis*List of placoderms...
, several large tetrapodomorphs, dipnoans, and another small undescribed holoptychiid. Though the locality in Ellesmere island is from freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
siltstone
Siltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
alluvial deposits, the existence of other members of the genus in marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
and estuarine deposits in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
suggest that Laccognathus species could tolerate a wide range of environmental conditions and salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
levels.
Taxonomy
Laccognathus embryi belongs to the genus Laccognathus, of the family HoloptychiidaeHoloptychiidae
Holoptychiidae is an extinct family of lobe-finned fishes which lived during the Devonian period. At least one genus, Laccognathus, is thought to have been amphibious....
. This family, in turn, belongs to the extinct 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...
Porolepiformes
Porolepiformes
Porolepiformes is an order of prehistoric lobe-finned fish which lived during the Devonian period . The group contains two families: Holoptychiidae and Porolepididae....
, of the class Sarcopterygii
Sarcopterygii
The Sarcopterygii or lobe-finned fishes – sometimes considered synonymous with Crossopterygii constitute a clade of the bony fishes, though a strict classification would include the terrestrial vertebrates...
(lobe-finned fishes). Together with their closest living relatives, subclass Dipnoi (lungfish
Lungfish
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), Laccognathus are members of the clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
Dipnomorpha. Unlike its sister group, the Tetrapodomorpha
Tetrapodomorpha
Tetrapodomorpha is a clade of vertebrates, consisting of tetrapods and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish...
, dipnomorphs were not direct ancestors of land vertebrates
Tetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
.
The generic name
Generic name
Generic name may be:*Generic name, name of a biological genus*Generic name, International Nonproprietary Name for a drug*A placeholder name, referring to nobody in particular, such as Joe Bloggs or John Q. Public...
Laccognathus is derived from Greek λάκκος (lakkos, 'pit') and γνάθος (gnathos, 'jaw') in reference to the three wide pits along the labial surface of the lower jaw. The specific name is in honour of Ashton Embry
Ashton F. Embry
Ashton F. Embry is a Canadian research scientist at the Geological Survey of Canada.Embry is a graduate of the University of Manitoba, who received a PhD in stratigraphy from the University of Calgary in 1976...
of the Geological Survey of Canada.
See also
- PanderichthysPanderichthysPanderichthys is a 90–130 cm long fish from the Devonian period 397 million years ago, of Latvia. It is named after the german-baltic palaeontologist Christian Heinrich Pander. It has a large tetrapod-like head...
- SarcopterygiiSarcopterygiiThe Sarcopterygii or lobe-finned fishes – sometimes considered synonymous with Crossopterygii constitute a clade of the bony fishes, though a strict classification would include the terrestrial vertebrates...
- List of sarcopterygians
- List of prehistoric bony fish