''Megalophthalma'' (meaning "large eye" from the

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 ...

''megale'' large"and ''ophthalmós'' eye" is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphi ...

amphibian belonging to the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Plagiosauridae Plagiosauridae is a clade of temnospondyl amphibians of the Middle to Late Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ...

. It is represented by the single

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

''Megalophthalma ockerti'' from the

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...

Erfurt Formation The Erfurt Formation, also known as the Lower Keuper (German: ''Untere Keuper'', ''Lettenkeuper'', ''Lettenkohle'' or ''Lettenkohlenkeuper''), is a stratigraphic formation of the Keuper group and the Germanic Trias supergroup. It was deposited du ...

in southern Germany, which is itself based on a single partial skull and a fragment of the lower jaw. ''Megalophthalma'' is distinguished from other temnospondyls by its very large

orbits In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

or eye sockets, which occupy most of the skull and are bordered by thin struts of bone. Like those of most plagiosaurids, the skull flat, wide, and roughly triangular. The orbits are pentagon-shaped. The bones at the back of the skull (the

occiput The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the cereb ...

) are highly modified and show similarities with those of the plagiosaurid ''

Plagiosternum ''Plagiosternum'' (plae-jee-oh-ster-num, meaning "sideways breastbone") was a middle Triassic temnospondyl Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order o ...

''. Both ''Megalophthalma'' and ''Plagiosternum'' lack prefrontal and

postfrontal bone The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

s. In fact, ''Megalophthalma'' and ''Plagiosternum'' are thought to form their own

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

or evolutionary grouping within Plagiosauridae called Plagiosterninae. In overall form ''Megalophthalma'' and ''Plagiosternum'' are intermediate between the basal plagiosaurid '' Plagiosuchus'' (which more closely resembles non-plagiosaurid temnospondyls) and the

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

Gerrothorax ''Gerrothorax'' ("wicker chest") is an extinct genus of temnospondyl amphibian from the Triassic period of Greenland, Germany, Poland, Sweden, and possibly Thailand. It is known from a single species, ''G. pulcherrimus'', although several other s ...

'' (which has an even more highly modified skull than plagiosternines).

The authors who originally described ''Megalophthalma'' hypothesized that it and other plagiosaurids had eyes that were much smaller than the orbits. Most reconstructions of plagiosaurids, particularly those of ''Gerrothorax'', show them having flattened eyes that fill up most of the orbits. However, a flattened eye is extremely unlikely because the lens would be too close to the

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...

to focus an image. ''Megalophthalma'' and other plagiosaurids more likely had spherical eyes like those of modern amphibians. The skull of ''Megalophthalma'' is too shallow for a spherical eye the width of the orbit to fit within it, so the eye was probably much smaller, perhaps less than in diameter. The eye was probably positioned near the front of the orbit as in modern small-eyed amphibians like cryptobranchid salamanders and pipid frogs. Another possibility, although far less likely, is that ''Megalophthalma'' and other plagiosaurids had eyes similar to those of the living deep-sea fish ''

Ipnops ''Ipnops'' is a genus of deep-sea fish in the family Ipnopidae, which also includes the better-known tripodfish (''Bathypterois grallator''). ''Ipnops'' are small, slender fish that live close to the ocean floor in the bathyal and abyssal zones. ...

'', which are reduced to sheet-like retina that cover the upper surface of the skull and are only able to detect movement from shadows. Like ''Ipnops'', plagiosaurids are hypothesized to have rested on the bottom of bodies of water and ambushed prey that swam above them. However, ''Ipnops'' and plagiosaurids are very distantly related, making it unlikely that lensless eyes evolved in ''Megalophthalma''.

References

{{Taxonbar, from=Q16985278 Triassic temnospondyls Triassic temnospondyls of Europe Plagiosauridae