Heteronectes
| Heteronectes | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Temporal occurrence | ||||||||||||
| Ypresium (= Lower Eocene ) | ||||||||||||
| 47 million years | ||||||||||||
| Locations | ||||||||||||
|
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Heteronectes | ||||||||||||
| Friedmann , 2008 | ||||||||||||
| species | ||||||||||||
|
Heteronectes is a 47 million year old, extinct genus from the order of flatfish , whose type species , Heteronectes chaneti , wascalled "the most primitive known flatfish" when it was first described. One eye of the animal is in the lateral position that is usual for fish, while the other eye is on the opposite side of the head, far above the position that is usual for fish, immediately next to the dorsal line (center of the back). As a mosaic form , this species - together with comparable old representatives of the genus Amphistium -occupiesa mediating position between the bilaterally symmetrical fish and the flat fish.
Naming
Heteronectes is an artificial word . The name of the genus is derived from the Greek words heteros (= different, different) and netri (= swimmer). The epithet of the only scientifically described species so far, Heteronectes chaneti , was chosen in honor of Bruno Chanet, who did a great job of researching fossil flatfish. Heteronectes chaneti therefore means "Chanets different swimmers".
The holotype of the genus and at the same time the type species Heteronectes chaneti are the plate and counter plate with the archive numbers NHMW 1974.1639.24 and NHMW 1974.1639.25, which are kept in the Natural History Museum Vienna .
features
Heteronectes had a very narrow body with a high body disc in relation to its length and a rather long fin edge on the belly and back. The most noticeable anatomical peculiarity of the approx. 11 cm long fossil was emphasized in the first description of the pronounced asymmetry of the head, especially in the area of the bony eye sockets , which is of natural origin and not a result of deformation in the course of fossilization . The positional relationship of the front to the back of the fish's head - apart from the position of one eye - and of the head to the rest of the body correspond to the usual proportions of fish. It can also be deduced from the degree of ossification of the skull that the position of the eyes corresponds to that of an adult fish of its kind; Recent young, only approx. 1 cm long flatfish still have symmetrically arranged eyes on both sides, one of which "migrates" over the middle of the back to the other side before the final ossification of the skull bones. At the same time, the fins - especially the dorsal and anal fin - of the holotype differ from the two known fossil species of the genus Amphistium in terms of strength, number and arrangement of the rays ; This is the same old fossil Amphistium paradoxum (place of discovery: Bolca) and the somewhat younger fossil Amphistium altum (from the Lutetium ; place of discovery: Paris basin ). In these fossils, however, the side of the body with the eyes offset towards the middle of the back was not preserved. For this reason, these finds were only re-examined after the discovery of Heteronectes chaneti and their significance as mosaic forms was recognized in the same publication as its first description due to similar anatomical features.
Importance of the find
According to a comment in New Scientist , Heteronectes fills "a gap in the sequence of documented fossil finds that has plagued the theory of evolution since Darwin's day ." Critics of evolution have repeatedly objected to both an upright swimming fish with symmetrically arranged eyes on both sides a flatfish is built purposefully because one variant has advantages when swimming in open water, while the other has advantages when staying on the ground. An intermediate form, however, has no recognizable advantage, which is why a natural selection that could develop a “normal” fish into a flat fish is unlikely. Only the fossils described in 2008 finally refuted this objection. The journal Nature commented that the discovery of the fossil "shows that the evolution of flatfish has indeed been gradual, and it helps an example popular among creationists to be laid to rest."
According to Matt Friedmann from the University of Chicago , who first described it, Heteronectes chaneti presumably - leaning on the pectoral fin on the side of the body with the eye turned towards the back - lay diagonally on the sea floor and ambushed potential prey there.
Web links
- Original drawings and family tree of Heteronectes chaneti On: nature.com from July 10, 2008
- Photos of the head of Heteronectes chaneti found on: eurekalert.org , accessed on May 2, 2018
Individual evidence
- ↑ In: Nature . Volume 454, No. 7201, 2008, p. IX
- ↑ Flatfish fossils fill in a missing link. (with images) On: uchicago.edu from July 9, 2008
- ^ Matt Friedmann: The evolutionary origin of flatfish asymmetry. In: Nature . Volume 454, No. 7201, 2008, pp. 209-212, doi: 10.1038 / nature07108
- ↑ Jeff Hecht: Flatfish caught evolving, thanks to its roving eye. In: New Scientist, July 13, 2008, p. 16
- ^ Philippe Janvier: Squint of the fossil flatfish. In: Nature. Volume 454, 2008, p. 169, doi: 10.1038 / 454169a