''Laccognathus embryi'' is an extinct species of porolepiform

lobe-finned fish Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includ ...

recovered from Ellesmere Island,

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

. It existed during the

Frasnian The Frasnian is one of two faunal stages in the Late Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Givetian Stage and followed by the Famennian Stage. Major reef-building was under way during th ...

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 Formation The Fram Formation is an Upper Devonian (Frasnian) 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-finn ...

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 Neil Shubin (born December 22, 1960) 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 ...

, and previously resulted in the discovery of the

tetrapodomorph The Tetrapodomorpha (also known as Choanata) are a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advance ...

Tiktaalik roseae ''Tiktaalik'' (; Inuktitut ) is a monospecific genus of extinct sarcopterygian (lobe-finned fish) from the Late Devonian Period, about 375 Mya (million years ago), having many features akin to those of tetrapods (four-legged animals). It may hav ...

'' from the same locality. Ellesmere Island was also the site of previous

Norwegian Norwegian, Norwayan, or Norsk may refer to: *Something of, from, or related to Norway, a country in northwestern Europe * Norwegians, both a nation and an ethnic group native to Norway * Demographics of Norway *The Norwegian language, including ...

scientific expeditions by the ship '' Fram'' in 1893-1896 by Fridtjof Nansen and in 1898–1902 by

Otto Sverdrup Otto Neumann Knoph Sverdrup (31 October 1854, in Bindal, Helgeland – 26 November 1930) was a Norwegian sailor and Arctic explorer. Early and personal life He was born in Bindal as a son of farmer Ulrik Frederik Suhm Sverdrup (1833–1914) ...

. In the second expedition, a few vertebrate fossils were collected from Ellesmere Island by a member of Sverdrup's crew with the geologist Per Schei. The collection included a few porolepiform scales attributed to '' Glyptolepis'' and ''

Holoptychius ''Holoptychius'' (from el, όλος , 'whole' and el, πτυχή 'fold') is an extinct genus of porolepiform lobe-finned fish from the Middle Devonian to Carboniferous ( Mississippian) periods. It is known from fossils worldwide. The genus ...

''. Prior to its discovery, the genus '' Laccognathus'' was known only from Latvia and

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...

. ''L. embryi'' is the first member of the genus discovered in North America. The fossil

sarcopterygian Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includ ...

fish ''Laccognathus embryi'' of the Devonian was named in honour of

Geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althoug ...

Ashton F. Embry.

Description

Like other members of the genus, ''Laccognathus embryi'' possessed three deep longitudinal pits (fossae) on the external surface 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 ...

. They are believed to have functioned as sensory pits able to detect changes in surrounding

water pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...

, similar to the lateral line of modern fishes and sharks, an analogous to our

ear An ear is the organ that enables hearing and, in mammals, body balance using the vestibular system. In mammals, the ear is usually described as having three parts—the outer ear, the middle ear and the inner ear. The outer ear consists of ...

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 were very small, even smaller than those of '' L. panderi''. The jaws possessed coronoid fangs up to in length. These were 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 Pectoral may refer to: * The chest region and anything relating to it. * Pectoral cross, a cross worn on the chest * a decorative, usually jeweled version of a gorget * Pectoral (Ancient Egypt), a type of jewelry worn in ancient Egypt * Pectorali ...

and pelvic fins arising from fleshy lobes. The caudal (tail) fin was

heterocercal Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as s ...

, with a long low upper (epichordal) blade and a rounded lower (hypochordal) blade three times as wide as the upper blade. The

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal c ...

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

locality Locality may refer to: * Locality (association), an association of community regeneration organizations in England * Locality (linguistics) * Locality (settlement) * Suburbs and localities (Australia), in which a locality is a geographic subdivis ...

. The formation, which consists of alternating layers of siltstone and

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

, is dated to the

age of the Late Devonian epoch (around 385.3 ± 2.6 to 374.5 ± 2.6 mya). Specific

palynological Palynology is the "study of dust" (from grc-gre, παλύνω, palynō, "strew, sprinkle" and ''-logy'') or of "particles that are strewn". A classic palynologist analyses particulate samples collected from the air, from water, or from deposit ...

examination reveals that the NV2K17 locality itself is from the early to middle Frasnian. The area is believed to have been the

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

of a meandering river system. The variety of fossils found in Ellesmere Island is similar to those found in the

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. Description The Gauja Formation has a maximum thickness of . It is composed of weakly to ...

s of Latvia and

Estonia Estonia, formally the Republic of Estonia, is a country by the Baltic Sea in Northern Europe. It is bordered to the north by the Gulf of Finland across from Finland, to the west by the sea across from Sweden, to the south by Latvia, a ...

, from whence other species of ''Laccognathus'' were recovered. North America and western

Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago ...

were once part of the ancient

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leav ...

of Euramerica (also known as

Laurussia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pan ...

) located at the equator during the Devonian period.

Paleoecology

The flattened head of ''Laccognathus embryi'' indicates that it was a benthic sit-and-wait

ambush predator Ambush predators or sit-and-wait predators are carnivorous animals that capture or trap prey via stealth, luring or by (typically instinctive) strategies utilizing an element of surprise. Unlike pursuit predators, who chase to capture prey ...

. There are fossils of at least eight other

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

found within the same

fossiliferous A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

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 deposit Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluv ...

s, the existence of other members of the genus in marine and estuarine deposits in

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...

suggest that ''Laccognathus'' species could tolerate a wide range of environmental conditions and salinity levels.

Taxonomy

''Laccognathus embryi'' belongs to the genus ''Laccognathus,'' of the family Holoptychiidae. This family, in turn, belongs to the extinct order Porolepiformes, of the class

Sarcopterygii Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includi ...

(lobe-finned fishes). Together with their closest living relatives, subclass Dipnoi (

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), ''Laccognathus'' are members of the clade

Dipnomorpha 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 ...

. Unlike its sister group, the

Tetrapodomorpha The Tetrapodomorpha (also known as Choanata) are a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advance ...

, dipnomorphs were not direct ancestors of land vertebrates. The generic name ''Laccognathus'' is derived from

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

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 The Geological Survey of Canada (GSC; french: Commission géologique du Canada (CGC)) is a Canadian federal government agency responsible for performing geological surveys of the country, developing Canada's natural resources and protecting the e ...

References