''Gemuendina stuertzi'' (named for Gemünden from where it was discovered) is a placoderm of the order

Rhenanida Rhenanida ("Rhine (fish)") is an Order (biology), order of scaly placoderms. Unlike most other placoderms, the rhenanids' armor was made up of a mosaic of unfused scales and tubercles. The patterns and components of this "mosaic" correspond to t ...

, of the seas of Early Devonian Germany. In life, ''Gemuendina'' resembled a scaly ray with an upturned head, or a large-finned stargazer. ''G. stuertzi'' is often invoked as an example of

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

- with its flat body and huge,

wing A wing is a type of fin that produces lift while moving through air or some other fluid. Accordingly, wings have streamlined cross-sections that are subject to aerodynamic forces and act as airfoils. A wing's aerodynamic efficiency is e ...

-like

pectoral fin 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 it has a strong, albeit superficial similarity to

rays Ray may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), a bony or horny spine on a fin Science and mathematics * Ray (geometry), half of a line proceeding from an initial point * Ray (gra ...

. Unlike rays, however, both ''Gemuendina''`s eyes and

nostril A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...

s were placed atop the head, facing upward. Furthermore, ''G. stuertzis upturned mouth would have enabled it to suction prey that swam overhead, rather than swallow sediment or suction prey out of the substrate like modern rays. Gemuendina_stuertzi_by_avancna

Unlike most other placoderm orders, such as the

Antiarch Antiarchi ("opposite anus") is an order of heavily armored placoderms. The antiarchs form the second-most successful group of placoderms after the arthrodires in terms of numbers of species and range of environments. The order's name was coi ...

s, or the

Arthrodire Arthrodira (Greek for "jointed neck") is an order of extinct armored, jawed fishes of the class Placodermi that flourished in the Devonian period before their sudden extinction, surviving for about 50 million years and penetrating most marine eco ...

s, ''Gemuendina'' and its four other known relatives (or seven, if the three species of the

ichthyolith An ichthyolith (from Greek, “fish“ and ”stone”, “rock“, literally "fish- rock") is any disarticulated remains of a fish found in the fossil record, most often a scale, denticle or tooth A tooth ( : teeth) is a hard, calcified ...

genus '' Ohioaspis'' are confirmed to be rhenanids) had armor made up of a mosaic of unfused bony plates and scales. Because their armor was so fragile, few intact examples of rhenanids have survived in the

fossil record 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 ...

. Because several regions of the Hunsruck

lagerstätte A Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These f ...

were anoxic, thus free of scavenging organisms, intact, nearly pristine (albeit flattened) specimens of ''G. stuertzi'' have been found as a result. Also unlike other placoderms, it did not have the characteristic tooth plates of placoderms. Instead, it had star-shaped tubercle scales that allowed it to seize, then swallow fish and other animals that swam too close with its mouth. Specimens of ''G. stuertzi'' ranged in size from 30 to 100 centimeters in length. In 1971,

Erik Stensiö Prof Erik Helge Osvald Stensiö HFRSE (2 October 1891 – 11 January 1984) was a Swedish paleozoologist. He later took his new surname from his place of origin and is occasionally referred to with both names (as Erik Andersson Stensiö, Erik ...

described a metre long specimen as a new species, "''Broilina heroldi''," which was later synonymized with ''Gemuendina''.

References

* Janvier, Philippe. ''Early Vertebrates'' Oxford, New York: Oxford University Press, 1998. * Long, John A. ''The Rise of Fishes: 500 Million Years of Evolution'' Baltimore: The Johns Hopkins University Press, 1996.

External links

''Paleos Rhenanida''
Rhenanida Placoderms of Europe Placoderm genera {{Placoderm-stub Hunsrück Slate fossils