''Laccognathus'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus of amphibious

lobe-finned fish Sarcopterygii (; )—sometimes considered synonymous with Crossopterygii ()—is a clade (traditionally a class or subclass) of vertebrate animals which includes a group of bony fish commonly referred to as lobe-finned fish. These vertebrates ar ...

from

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

and

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. They existed from the

Middle Devonian In the geological timescale, the Middle Devonian epoch (from 393.3 ± 1.2 million years ago to 382.7 ± 1.6 million years ago) occurred during the Devonian period, after the end of the Emsian age. The Middle Devonian epoch is subdivided into two ...

to the

Late Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at million years ago ( Ma), to the beginning of the succeeding ...

(around 397.5 to 360 mya). The name comes from Greek for 'pitted jaw'.

Description

Species of ''Laccognathus'' were characterized by the presence of three large pits (fossae) on the external surface of the lower jaw, which may have had sensory functions. It is the origin of the genus name, from

Greek Greek may refer to: 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 of all kno ...

λάκκος ('pit') and γνάθος ('jaw'). ''Laccognathus'' grew to approximately in length. They had very short dorsoventrally flattened heads, less than one-fifth the length of the body. Like other

sarcopterygian Sarcopterygii (; )—sometimes considered synonymous with Crossopterygii ()—is a clade (traditionally a class or subclass) of vertebrate animals which includes a group of bony fish commonly referred to as lobe-finned fish. These vertebrates ar ...

s, their fins arise from pairs of fleshy lobes. The

skeleton A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal fra ...

of ''Laccognathus'' was structured such that large areas of the skin were stretched out over solid plates of bone. This bone was composed of particularly dense fibers—so dense that

cutaneous respiration Cutaneous respiration, or cutaneous gas exchange (sometimes called skin breathing), is a form of respiration in which gas exchange occurs across the skin or outer integument of an organism rather than gills or lungs. Cutaneous respiration may be ...

(exchange of

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

through the skin) was not a likely trait exhibited by ''Laccognathus''. Rather, the dense

ossification Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in t ...

s may have served to retain water inside the body as ''Laccognathus'' traveled on land between bodies of water.

Taxonomy

''Laccognathus'' are classified under the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Holoptychiidae Porolepiformes is an Order (biology), order of prehistoric lobe-finned fish which lived during the Devonian geological period, period (about 416 to 359 million years ago). They are thought to represent the sister group to lungfish (class Dipnoi). ...

in the extinct

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

Porolepiformes Porolepiformes is an order of prehistoric lobe-finned fish which lived during the Devonian period (about 416 to 359 million years ago). They are thought to represent the sister group to lungfish (class Dipnoi). The group contains two families: ...

. They are not direct ancestors of

tetrapods A tetrapod (; from Ancient Greek τετρα- ''(tetra-)'' 'four' and πούς ''(poús)'' 'foot') is any four- limbed vertebrate animal of the clade Tetrapoda (). Tetrapods include all extant and extinct amphibians and amniotes, with the lat ...

like the

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

Tetrapodomorpha Tetrapodomorpha (also known as Choanata) is 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. Advanced f ...

, but instead belong to the clade

Dipnomorpha Rhipidistia, also known as Dipnotetrapodomorpha, is a clade of lobe-finned fishes which includes the tetrapods and lungfishes. Rhipidistia formerly referred to a subgroup of Sarcopterygii consisting of the Porolepiformes and Osteolepiformes, a ...

. Their closest living relatives are the members of the subclass

Dipnoi Lungfish are freshwater vertebrates belonging to the class Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, inc ...

(lungfish).

Species

The following are the species classified under ''Laccognathus''. A fourth undescribed species recovered from the Middle Devonian of Latvia may exist. *†'' Laccognathus panderi'' Gross, 1941 ::Recovered from the

and

formations of various parts of

eastern Europe Eastern Europe is a subregion of the Europe, European continent. As a largely ambiguous term, it has a wide range of geopolitical, geographical, ethnic, cultural and socio-economic connotations. Its eastern boundary is marked by the Ural Mountain ...

. *†'' Laccognathus grossi'' Vorobyeva, 2006 ::Recovered from the Middle Devonian

Gauja Formation The Gauja Formation is a Middle Devonian fossil locality in Estonia and Latvia. It is named after the Gauja, Gauja River, where it is exposed along the banks. Description The Gauja Formation has a maximum thickness of . It is composed of weakl ...

Latvia Latvia, officially the Republic of Latvia, is a country in the Baltic region of Northern Europe. It is one of the three Baltic states, along with Estonia to the north and Lithuania to the south. It borders Russia to the east and Belarus to t ...

. *†'' Laccognathus embryi'' Downs ''et al.'', 2011 ::Recovered from Late Devonian

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 ...

Ellesmere Island Ellesmere Island (; ) is Canada's northernmost and List of Canadian islands by area, third largest island, and the List of islands by area, tenth largest in the world. It comprises an area of , slightly smaller than Great Britain, and the total ...

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

, the same locality from which ''

Tiktaalik ''Tiktaalik'' (; ) 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). ''Tiktaalik'' is est ...

'' was found.

References

{{Taxonbar, from=Q1940255 Porolepiformes Prehistoric lobe-finned fish genera Middle Devonian sarcopterygians Late Devonian sarcopterygians Devonian sarcopterygians of Europe Devonian sarcopterygians of North America Fossil taxa described in 1941

Description

Taxonomy

Species

See also

References