''Phyllolepis'' (from the Greek roots for ‘leaf’ and ‘scale’)Murphy, Dennis C. 4..20.2016. “Phyllolepis rossimontia (placoderm).” ''Devonian'' Times. <http://www.devoniantimes.org/who/pages/phyllolepis.html#credits> is the type genus of

Phyllolepida Phyllolepida ("leaf scales") is an extinct taxon of flattened placoderms found throughout the world, with fossils being found in Devonian strata. Like other flattened placoderms, the phyllolepids were bottom-dwelling predators that ambushed prey. ...

, an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

taxon of arthrodire placoderm fish from the middle to late

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

.“The life and times of Phyllolepis.” ''Phyllolepida''. Palaeos.com. 2005 <http://palaeos.com/vertebrates/placodermi/phyllolepida.html> The species of ''Phyllolepis'', themselves, are restricted to the Famennian-aged freshwater strata of the Late Devonian, around 360 million years ago. Fossils of this genus have been found primarily in Europe and

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

. The end of the Devonian saw them disappear in a mass extinction. ''Phyllolepis'' lived in

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

environments, possibly rivers and

stream A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a stream ...

s. As with all other known

phyllolepids Phyllolepida ("leaf scales") is an extinct taxon of flattened placoderms found throughout the world, with fossils being found in Devonian strata. Like other flattened placoderms, the phyllolepids were bottom-dwelling predators that ambushed prey. ...

, ''Phyllolepis'' were presumed to have been blind, bottom-dwelling predators that detected prey through

sensory organs A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of stimuli. (For example, in the human body, the brain which is part of the central nervous system rec ...

in the surface grooves of their

armor plates Military vehicles are commonly armoured (or armored; see spelling differences) to withstand the impact of shrapnel, bullets, shells, rockets, and missiles, protecting the personnel inside from enemy fire. Such vehicles include armoured fighting ...

(which gave their plates a distinctive "wooden surface" appearance).

Description and paleobiology

''Phyllolepis'', as was typical of Phyllolepida, tended to be 30 to 40 cm in length and very flat. ''Phyllolepis'' have extensive armor made of full, flat plates, rather than scales, with both a wide jaw and

mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...

. They are characterized by a broad, enlarged

nuchal The nape is the back of the neck. In technical anatomical/medical terminology, the nape is also called the nucha (from the Medieval Latin rendering of the Arabic , "spinal marrow"). The corresponding adjective is ''nuchal'', as in the term ''nu ...

plate paired with four small plates around the upper jaw. They have short and broad

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

ventrolateral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

plates, as well as paranuchal plates with postnuchal process. They also feature long, narrow anterior

dorsolateral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

plates and a dermal ornamentation of smooth, concentric rings upon their plates. As a placoderm, ''Phyllolepis'' was a primitive jawed fish, with their jaws likely having been evolved from the first set of their

gill arches Branchial arches, or gill arches, are a series of bony "loops" present in fish, which support the gills. As gills are the primitive condition of vertebrates, all vertebrate embryos develop pharyngeal arches, though the eventual fate of these arc ...

. Elongated basiptergia have been found on some phyllolepid placoderms, such as ''

Austrophyllolepis ''Austrophyllolepis ''is an extinct genus of phyllolepid arthrodire placoderm from Middle to Late Devonian freshwater strata of Australia. The type species, ''A. ritchiei'' is found in Givetian to early Frasnian-aged freshwater strata near what ...

'' and ''

Cowralepis ''Cowralepis'' is an extinct genus of phyllolepid placoderm of Givetian The Givetian is one of two faunal stages in the Middle Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Eifelian Stage an ...

'', suggesting ''Phyllolepis'' may have had them as well.Long, J.A. 1984. New phyllolepids from Victoria and the relationships of the group. ''Proceedings of the Linnean Society of New South Wales'' 107: 263–308. As with other members of Phyllolepida, ''Phyllolepis'' have

eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...

s on either side of their heads, unlike modern

flounder Flounders are a group of flatfish species. They are demersal fish, found at the bottom of oceans around the world; some species will also enter estuaries. Taxonomy The name "flounder" is used for several only distantly related species, thou ...

s, as well as an absent sclerotic ring. This suggests that the eyes of ''Phyllolepis'' may have been much reduced, vestigial, or completely absent. The pattern of raised ridges on its

head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals may ...

and trunk plates are a defining trait, setting them apart from other placoderms. The highly developed system of lateral ridges are suggested to have been used for electroreception, in order to sense their surroundings in absence of functional eyes.

Synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

of ''Phyllolepis'' include the sub triangular dermal portion of the marginal plate. This genus can be distinguished from ''Cowralepis'' because of their deeply concave

margin, where it meets the postorbital plate, as well as the exit of the main lateral line canal in the middle of the plate (rather than in its posterior third division). ''Cowralepis'' also features a distinct posterior

plate, which ''Phyllolepis'' lack entirely. However, because many defining traits for ''Phyllolepis'' must be used in conjunction with other traits (for example, the genera ''Phyllolepis'', ''

Placolepis ''Placolepis'' is an extinct genus of phyllolepid placoderm first discovered in New South Wales. ''Placolepis'' was the most widespread phyllolepid genus, with fossils found in Australia, Turkey, Venezuela and Antarctica Antarctica () is ...

'', and ''

Cobandrahlepis ''Cobandrahlepis'' is an extinct genus of phyllolepid placoderm found in New South Wales, Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (c ...

'' all lack a posterior median ventral plate), it is difficult to identify phyllolepid placoderms unless a full fossil assemblage is known. Due to the isolated phyllolepid plates found for species such as ''P. concentrica, konicki, undulata'', and ''

delicatula ''Delicatula'' is a genus of fungi in the family Tricholomataceae. It was first described by Swiss mycologist Victor Fayod in 1889. The genus contains two widely distributed species. See also *List of Agaricales genera *List of Tricholomataceae ...

'', it has been suggested by J. Long and E. Daeschler that they be recategorized as

e gen. et sp. Indeterminate. ''P.'' ''woodwardi'''', orvini, neilseni'', and '' rossimontina'' are all species with complete and valid sets of plates.

Ecology

These fishes were likely ambush predators, lying in wait in the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

as bottom-dwellers. Their long tails would be used for rapid propulsion to catch their prey. This is typical of many flattened placoderms. One of the sites where various ''Phyllolepis''

specimen Specimen may refer to: Science and technology * Sample (material), a limited quantity of something which is intended to be similar to and represent a larger amount * Biological specimen or biospecimen, an organic specimen held by a biorepository ...

s have been discovered, Red Hill in Clinton County, Pennsylvania, shows signs of having been a freshwater subhabitat, similar to current Midwestern lakes. However, dig sites in EuropeLane, J. A. and R.J. Cuffey. (2005) .Phyllolepis rossimontina sp. nov. (Placodermi) from the Uppermost Devonian at Red Hill, North-Central Pennsylvania. Revista Brasileira de Paleontologia 8(2): 117-126- and even locations still in the Pennsylvania Catskill formationLong, J., & Daeschler, E. (2013). First articulated phyllolepid placoderm from North America, with comments on phyllolepid systematics. ''Proceedings of the Academy of Natural Sciences of Philadelphia,'' ''162'': 33-46. Retrieved from http://www.jstor.org/stable/42751947- may have been home to coastal-

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

''Phyllolepis'' species, based on the composition of

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

s and sediment deposits. At least one phyllolepid specimen has been found surrounded by plant material and greenish siltstones, suggesting a low energy environment, such as a floodplain pond. This divide raises some questions about how the genus lived in both places. It is possible there were land connections intercontinentally, or the fishes were

euryhaline Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the molly (''Poecilia sphenops'') which can live in fresh water, brackish water, or salt water. The green crab (''Carcinus maenas'') is an e ...

-tolerant. The fish may have even evolved a freshwater habit after arriving in North America by marine waterways. All of the phyllolepids found in the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

have been found in

rock Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wales ...

dated to the later Devonian Period (Famennian), however

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

n and

Antarctic The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other ...

samples date earlier, from the late middle Devonian up through the late Famennian. The oldest confirmed Phyllolepid is from the middle Devonian. The genus ''Phyllolepis'' has so far only been found in Famennian age

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

Species

History of categorization

''Phyllolepis'' was the first genus to be recognized in the order Phyllolepidae until 1984. ''Phyllolepis concentrica'' was the first species discovered of the genus, by Louis Agassiz in 1844 at Clashbennie, Scotland. This specimen caused Woodward to incorrectly classify them as a distinct group belonging to the jawless fishes in 1915, along with '' Drepanaspidae''. Sensiö continued, with several publications in the 1930s, to show that phyllolepids had jaws, and belonged with placoderms. He also proclaimed them part of Phyllolepida, based on his studies of ''P. orvini, P. soederberghi,'' and ''P. neilseni''. From the 1930s to 50s, there were several isolated dermal plates of phyllolepids found in Australia, attributed by Hills to be ''Phyllolepis'' but specific species left undefined. In the 1970s many complete, articulated Phyllolepid specimens were found from the middle Devonian at the Mt. Howitt site in Australia. This material was gradually defined as genus ''Austrophyllolepis'', based on plate proportions, but also solidified the assignment of the group to Placodermi and as a clade inside Arthrodira. The more recent introduction of ''P. rossimontina'' as a species in 2005 demonstrated, in part, a wide range of variability within the genus ''Phyllolepis'', causing some scientists to begin a revision of the genus. The low number of complete ''Phyllolepis'' specimens found combined with key identifying features only visible on specific plates has made it difficult to confidently identify species, causing some paleontologists to call for redesignations of the current named species of ''Phyllolepis''.

References

* ''Wildlife of Gondwana: Dinosaurs and Other Vertebrates from the Ancient Supercontinent'' (Life of the Past) by Pat Vickers Rich, Thomas Hewitt Rich, Francesco Coffa, and Steven Morton * ''The Rise of Fishes: 500 Million Years of Evolution'' by John A. Long

External links

Phyllolepida
at Palaeos.com {{Taxonbar, from=Q7188831 Phyllolepids Placoderms of Europe Placoderms of North America Fossil taxa described in 1844 Famennian life Famennian genus first appearances Famennian genus extinctions