Ichthyosaurs

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Ichthyosaurs
Life picture of Shastasaurus, a representative of giant ichthyosaurs from the Triassic

Life picture of Shastasaurus , a representative of giant ichthyosaurs from the Triassic

Temporal occurrence
Lower Triassic ( Olenekian ) to Upper Cretaceous ( Cenomanian )
251.2 to 93.9 million years
Locations
  • Worldwide
Systematics
Land vertebrates (Tetrapoda)
Amniotes (Amniota)
Sauropsida
Eureptiles (Eureptilia)
Diapsida
Ichthyosaurs
Scientific name
Ichthyopterygia
Owen , 1840

The ichthyosaur ( Ichthyopterygia from gr. Ἰχθῦς ICHTYS or ἰχθύς ICHTYS "fish"; colloquially ichthyosaurs ) are a group of extinct reptiles of the Mesozoic (Mesozoic). They were fully adapted to aquatic life and lived exclusively in the sea. A total of about eighty species have been described. They lived for a period of more than 150 million years ago and died before 93 million years ago in the early Cretaceous out about 30 million years before the extinction of the dinosaurs . The ichthyosaurs underwent major radiations in the late Triassic and twice during the Jurassic , from which the Neoichthyosauria with, among others, the Ophthalmosauridae and the Platypterygiinae emerged .

The first complete skeleton of an ichthyosaur was found in 1811 by twelve-year-old Mary Anning in Lyme Regis , England , when dinosaurs were still unknown. The fossils confused people because the body was reminiscent of that of terrestrial vertebrates in some respects . Even so, some researchers initially mistook them for fish. Others saw them as amphibians or even marine mammals.

etymology

Ichthyosauria comes from the Greek and means fish lizard (ἰχθύς ichthys ' fish ' and σαῦρος sauros ' lizard '). The taxon was established by de Blainville in 1835 . In order to integrate the basal forms, Owen set up the taxon Ichthyopterygia in 1840 ("ichthyos" and "pteryx" = wings). Both are called ichthyosaurs in German and are also described here together. The Ichthyosauria are defined as a subgroup of the Ichthyopterygia and include all forms that are more closely related to Ichthyosaurus than to Grippia .

Evolution and stratigraphy

Ichthyosaurs appeared in the Lower Triassic . An early representative of the ichthyosaur tribe was Cartorhynchus . The first forms like Grippia , Utatsusaurus and Chaohusaurus still had a lizard- like elongated body and probably moved close to the coast in shallow water by an anguilliform meandering of the whole body. They had a large number of elongated vertebrae . Mixosaurus , Parvinatator and the almost ten meter long Cymbospondylus lived in the Middle Triassic . At the end of this time, all elongated ichthyosaurs disappeared and were replaced in the Upper Triassic by the Shastasaurids, forms with a more spindle-like physique. They are the sister group of all ichthyosaurs living after the Triassic. Shonisaurus , Toretocnemus, and Californosaurus lived in the early, Macgowania and Hudsonelpidia in the late, and Shastasaurus in the entire Upper Triassic. In the end, the last three genera also died out.

The ichthyosaurs of the Middle Triassic show the greatest variety of forms, when there were both purely fish-eating forms and those with heterodontic or cracked teeth ( durophagia ). In the Jurassic fossil record , the species richness is highest in the Aalen and Kimmeridgian , in the Cretaceous it is reduced to the group of Platypterygiinae and the genus Malawania .

The ichthyosaurs reached their greatest biodiversity in the Lower Jurassic. All Jurassic and later ichthyosaurs form a monophyletic taxon , the Neoichthyosauria . An important find from this time is the Posidonia slate near the municipality of Holzmaden in southern Germany. So far, the fossil remains of around 3000 specimens from the genera Eurhinosaurus , Stenopterygius and Temnodontosaurus have been excavated. Many specimens of the Ichthyosaurus type genus have been found in Great Britain . Other ichthyosaurs from this period are suevoleviatan , as well as the long-snouted eurhinosaurs Leptonectes and Excalibosaurus . While Chacaicosaurus , Mollesaurus and Ophthalmosaurus are known from the Middle Jurassic, Brachypterygius and Caypullisaurus as well as Ophthalmosaurus can be found in the Upper Jurassic . All three genera died out at the transition from the Jura to the Cretaceous period. Both the genus Malawania, which is closely related to Ichthyosaurus , and various representatives of the Baracromia can be identified in the chalk . Of these, the Platypterygius , which occurs worldwide, survived until the end of the Cenomanium , when the last representative of the ichthyosaurs died out with him.

features

Fossil of Stenopterygius quadriscissus in the Aquazoo - Löbbecke Museum

Ichthyosaurs were reptiles and thus belonged to the land vertebrates . Secondarily they returned to life in the water. Their shoulder girdle is not firmly attached to the skull as it is in fish, and in their fins one can distinguish between the upper and lower arm bones, carpal bones and finger bones. Like other diapside reptiles , they have skull windows , the upper temporal windows. The lower temporal windows present in other diapsids were closed again secondarily.

Like the plesiosaurs and mosasaurs , the ichthyosaurs are said to have been able to keep their body temperature at a constantly high, constant level of 35 to 39 ° C ( endothermia ). The taphonomy of ichthyosaurs suggests that this group of animals - like most recent whale species - had a higher specific weight than seawater. Dark traces ( eumelanin ) in the fossilized soft tissue of ichthyosaur fossils show that they were dark in color and that some ichthyosaurs - similar to the deep-diving sperm whales - were monochrome dark and showed no counter-shading with a light underside.

Ichthyosaurs could be one meter ( Mixosaurus ), but also up to twenty meters ( Shonisaurus ) long. A bone fragment found in 2016 in the Upper Triassic of Lilstock, England, was identified as part of the lower jaw of a large ichthyosaur. The total length of the animal to which this bone belonged was carefully estimated in a publication from 2018 using various comparison methods to be around 20 to 25 meters, with which the largest ichthyosaurs reached the length of blue whales .

extremities

The fossil fin of an ichthyosaur

All ichthyosaurs, including the earliest, had fin-like limbs. These are homologous to those of the other vertebrates , but they have changed drastically in the course of time in adaptation to the water habitat. The bones of the forelimbs shortened and widened as a result of evolutionary changes. At the same time the finger bones increased ( hyperphalangia ). Then the first of the five fingers (which corresponded to the human thumb) disappeared. After that there was an increase in the number of fingers ( polydactyly ) themselves on both sides of the remaining fingers . The forelimbs were probably only used for steering and changing direction, while propulsion in primitive forms by the eel-like meandering of the body, in advanced forms by blows the caudal fin was generated. Some paleontologists also suspect propulsion through the forelimbs, but the ichthyosaurs' shoulder girdle is not very strong, rather weaker than that of vertebrates that move in this way.

eyes

The Temnodontosaurus scleral ring

The eyes of the ichthyosaurs were very large in relation to their body length and surrounded by a ring-shaped, bony reinforcement, the scleral ring , which occurs in many vertebrates. The scleral ring was probably used to keep the ichthyosaurs' flat, non-round eyeballs in shape, as their large eyes were exposed to varying water pressures while swimming. The part of the eyes that is closer to the muzzle was exposed to greater water pressure than the one further back.

The largest eye found in an ichthyosaur is also the largest eye of all vertebrates. It was 26.4 cm in diameter and belonged to Temnodontosaurus platyodon . In relation to the body length, however , Ophthalmosaurus had even larger eyes.

The eyes were very bright. Compared to the aperture setting of a photo lens, the ichthyosaurus eye had an f-number of 1 / 1.1 to 1 / 1.3, that of the Ophthalmosaurus reached 1 / 0.8 to 1 / 1.1. It is known that the eyes of nocturnal animals have low f-numbers. It is 1 / 1.1 for an owl and 1 / 0.9 for a cat. The human eye has an f-number of 1 / 2.1.

nutrition

The ichthyosaurs could see in low light. But that doesn't mean they were nocturnal. Rather, they looked for their food in the depths of the ocean.

The diet of some advanced ichthyosaurs is known from what remains of the prey in the stomach region. Above all, the hooks on the belemnite tentacles and fish scales have been preserved. The rostrums of Belemnites may have been spewed. Very large forms like the Temnodontosaurus, which can reach ten meters in length, probably also ate other vertebrates. Numerous young sea turtles of the Protostegidae family and a bird from the Enantiornithes group have been found in the epigastric region of a fossil from the Upper Cretaceous Australia . Later forms, such as Ophthalmosaurus , had short, strong jaws, blunted teeth, and probably ate hard-shelled animals such as mussels or ammonites . The ammonites were bitten into pieces before being swallowed and the casings were thrown away.

Reproduction

Ichthyosaur birth

Ichthyosaurs could no longer crawl ashore and lay eggs there. They were viviparous and probably descended from viviparous ancestors. More than 50 fossils were found in which some, at most ten to eleven young animals of the same species are in the body of the mother within the rib cage . As with dolphins, the cubs were born tail first ( but head first in the basal Chaohusaurus ), so they could quickly get to the surface of the water to take their first breath. With some of the fossils, the animals are said to have died at the moment of birth, the young is still with head or snout in the womb. It is more likely, however, that in these cases an embryo was driven out by putrefactive gases after the death of the mother.

External system

The ichthyosaurs have completely adapted to a life in water, and their original characteristics ( plesiomorphies ) have changed significantly. Basal forms that still show these features have only seldom been passed down in fossil form. That is why it has long been controversial how the ichthyosaurs are related to other amniotes . Finally, the primitive Ichthyopterygian Utatsusaurus hataii was found in the Lower Triassic of Japan . Through him the relationship of the ichthyosaurs became clearer.

Phylogenetic analyzes show that the ichthyosaurs belong to the diapsid reptiles , but not like the second large group of marine reptiles in the Mesozoic Era, the Sauropterygia, to their crown group , which includes today's scaled crawfish, the bridge lizards, the crocodiles and the birds. Probably the line of ichthyosaurs split off before the division of the Diapsida into Archosauromorpha and Lepidosauromorpha . So they are not closely related to the other large marine reptiles of the Mesozoic, the plesiosaurs and the mosasaurs , both of which belong to the lepidosauromorpha.

An ichthyosaur fossil at the Charmouth Heritage Coast Center in Charmouth England

The position of the ichthyosaurs within the reptiles is illustrated by the following cladogram :

The internal systematics of the ichthyosaurs is shown in the following cladogram:

Internal system

More than 50 valid genera had been described by September 2013.

Grippia
Omphalosaurus
Mixosaurus fossil
Contectopalatus
Cymbospondylus
Besanosaurus leptorhynchus fossil
Shonisaurus popularis
Temnodontosaurus eats Stenopterygius
A 6.4 meter long fossil of Eurhinosaurus made from Holzmaden
Fossil of a narrow-finned ichthyosaur ( Stenopterygius megalorhinus ) from the Posidonia schist
Platypterygius kiprjanov

die out

The ichthyosaurs died out 93 million years ago, at the end of the Cenomanian . The last genus that can be clearly identified is the Platypterygius , which is found worldwide . The reasons for the extinction are unknown. So far it has been suspected that the emergence of the mosasaurs , gigantic marine reptiles from the group of scaled reptiles , has to do with it. But they did not develop large forms until the ichthyosaurs were already extinct.

Another possible reason is the oceanic anoxic event at the end of the Cenomanium. It caused the oceans below the surface layer to become depleted in oxygen, which resulted in the extinction of marine invertebrates and also of cephalopods . According to this theory, the ichthyosaurs perished because their food sources disappeared. Some scientists point to the reproduction strategy of the ichthyosaurs. An ichthyosaur had only a few relatively large, well-developed young animals. For them the new, large predatory fish in the Upper Cretaceous, like Xiphactinus from the order of the Ichthyodectiformes, were dangerous .

literature

  • Michael W. Maisch, Andreas T. Matzke: The Ichthyosauria. Stuttgart Contributions to Natural History, Series B. No. 298 ( PDF 2.1 MB)
  • Richard Ellis : Sea Dragons. Predators of the Prehistoric Oceans. University Press of Kansas, Lawrence KS 2003, ISBN 0-7006-1269-6 .
  • Martin Sander: † Ichthyosauria, fish lizards . (ex: p. 371-272) p. 271 f. or 371 f. In: Wilfried Westheide & Reinhard Rieger (Hrsg.): Special Zoology Part 2: Vertebrate or skull animals. 2nd edition, Gustav Fischer, Jena 2010, ISBN 3-8274-0900-4
  • Robert L. Carroll : Paleontology and Evolution of the Vertebrates. Thieme, Stuttgart 1993, ISBN 3-13-774401-6
  • Michael J. Benton : Paleontology of the vertebrates. 3rd edition (translation of the 3rd English-language edition by Hans-Ulrich Pfretzschner), Verlag Dr. Friedrich Pfeil, Munich 2007, ISBN 3-89937-072-4

Individual evidence

  1. ↑ a b Ryosuke Motani: Robbers in the Jurassic Sea . Spectrum of Science Dossier 1/05: Ancient Animals. Pp. 24-31, ISSN  0947-7934
  2. ↑ a b Ryosuke Motanis Ichthyosaur Page Notes
  3. ↑ a b c Martin Sander: Ichthyosauria: their diversity, distribution, and phylogeny. Paleontological Journal. Vol. 74, No. 1-2, 2000, pp. 1-35, doi : 10.1007 / BF02987949
  4. ↑ Richard Ellis, 2003, p. 81
  5. ↑ A. Bernard, C. Lecuyer, P. Vincent, R. Amiot, N. Bardet, E. Buffetaut, G. Cuny, F. Fourel, F. Martineau, J.-M. Mazin, A. Prieur: Regulation of Body Temperature by Some Mesozoic Marine Reptiles. Science. Vol. 328 (No. 5984), 2010, pp. 1379-1382, doi : 10.1126 / science.1187443
  6. ^ AG Reisdorf, R. Bux, D. Wyler, M. Benecke, C. Klug, MW Maisch, P. Fornaro, A. Wetzel: Float, explode or sink: post-mortem fate of lung-breathing marine vertebrates. Palaeobiodiversity and Palaeoenvironments. Vol. 92, No. 1, 2012, pp. 67-81, doi : 10.1007 / s12549-011-0067-z
  7. ↑ Johan Lindgren, Peter Sjövall, Ryan M. Carney, Per Uvdal, Johan A. Gren, Gareth Dyke, Bo Pagh Schultz, Matthew D. Shawkey, Kenneth R. Barnes, Michael J. Polcyn: Skin pigmentation Provides evidence of convergent melanism in extinct marine reptiles. Nature. Vol. 506, 2014, pp. 484-488, doi : 10.1038 / nature12899
  8. ↑ Dean R. Lomax, Paul De la Salle, Judy A. Massare, Ramues Gallois: A giant Late Triassic ichthyosaur from the UK and a reinterpretation of the Aust Cliff 'dinosaurian' bones . In: PLOS ONE . tape 13 , no. 4 , 2018, p. e0194742 , doi : 10.1371 / journal.pone.0194742 .
  9. ↑ Ryosuke Motanis Ichthyosaur Page Forefin of Ichthyosaurs
  10. ↑ Ryosuke Motanis Ichthyosaur Page Eyes of Ichthyosaurs ( Memento of the original from June 22, 2007 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . @1@ 2Template: Webachiv / IABot / www.ucmp.berkeley.edu
  11. ↑ Ryosuke Motanis Ichthyosaur Page Diving ( Memento of the original from May 27, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . @1@ 2Template: Webachiv / IABot / www.ucmp.berkeley.edu
  12. ↑ Ryosuke Motanis Ichthyosaur Page Diets ( Memento of the original from May 27, 2009 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.ucmp.berkeley.edu
  13. ↑ a b c Michael J. Benton: Paleontology of the vertebrates. 3rd edition, 2007 (see literature ), p. 263 f.
  14. ↑ Richard Ellis: Sea Dragons. 2003 (see literature ), p. 87.
  15. ↑ a b Ryosuke Motani, Da-Yong Jiang, Andrea Tintori, Olivier Rieppel, Guan-Bao Chen: Terrestrial Origin of Viviparity in Mesozoic Marine Reptiles Indicated by Early Triassic Embryonic Fossils. PLoS ONE. Vol. 9, No. 2, 2014, e88640, doi : 10.1371 / journal.pone.0088640
  16. ↑ Ryosuke Motani, Nachio Minoura, Tatsuro Ando: Ichthyosaurian relationships illuminated by new primitive skeletons from Japan. Nature. Vol. 393, 1998, pp. 255-257, doi : 10.1038 / 30473
  17. ^ Jacques A. Gauthier, Arnold G. Kluge, Timothy Rowe: The early evolution of the Amniota. Pp. 103–155 in: Michael J. Benton (Ed.) The phylogeny and classification of the tetrapods, Volume 1: amphibians, reptiles, birds. Clarendon Press, Oxford 1988
  18. ↑ Ryosuke Motanis Ichthyosaur Page Phylogeny of Ichthyosaurs ( Memento of the original from January 1, 2009 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.ucmp.berkeley.edu
  19. ↑ Ryosuke Motanis Ichthyosaur Page Classification
  20. ↑ Ryosuke Motanis Ichthyosaur Page Stratigraphic occurrences
  21. ↑ Michael W. Maisch: Phylogeny, systematics, and origin of the Ichthyosauria - the state of the art. Paleodiversity. Vol. 3, 2010, pp. 151–214 ( PDF )
  22. ↑ Robin S. Cuthbertson, Anthony P. Russell, Jason S. Anderson: Cranial Morphology and Relationships of a New Grippidian (Ichthyopterygia) from the Vega-Phroso Siltstone Member (Lower Triassic) of British Columbia, Canada. Journal of Vertebrate Paleontology. Vol. 3, No. 4, 2013, pp. 831-847, doi : 10.1080 / 02724634.2013.755989
  23. ↑ NB Fröbisch, JR Fröbisch, PM Sander, L. Schmitz and O. Rieppel: Macropredatory ichthyosaur from the Middle Triassic and the origin of modern trophic networks. Proceedings of the National Academy of Sciences. Vol. 110 (4): 1393-1397, 2013, doi : 10.1073 / pnas.1216750110
  24. ↑ Stephen L. Brusatte et al. Ichthyosaurs from the Jurassic of Skye, Scotland. Scottish Journal of Geology, January, 2015; doi: 10.1144 / sjg2014-018
  25. ↑ Dean R. Lomax. A new leptonectid ichthyosaur from the Lower Jurassic (Hettangian) of Nottinghamshire, England, UK, and the taxonomic usefulness of the ichthyosaurian coracoid. Journal of Systematic Palaeontology, June 13, 2016; doi: 10.1080 / 14772019.2016.1183149
  26. ↑ Valentin Fischer, Robert M. Appleby, Darren Naish, Jeff Liston, James B. Riding, Stephen Brindley, Pascal Godefroit: A basal thunnosaurian from Iraq reveals disparate phylogenetic origins for Cretaceous ichthyosaurs. Biology Letters. Vol. 9, No. 4, 2013, pp. 1-6, doi: 10.1098 / rsbl.2013.0021
  27. ↑ EE Maxwell: Generic reassignment of an ichthyosaur from the Queen Elizabeth Islands, Northwest Territories, Canada. Journal of Vertebrate Paleontology. Vol. 30, No. 2, 2010, pp. 403-415, doi : 10.1080 / 02724631003617944
  28. ↑ Lene Liebe Delsett, Aubrey J. Roberts, Patrick S. Druckermiller and Jørn H. Hurum. 2017. A New Ophthalmosaurid (Ichthyosauria) from Svalbard, Norway, and Evolution of the Ichthyopterygian Pelvic Girdle. PLoS ONE. 12 (1): e0169971. DOI: 10.1371 / journal.pone.0169971
  29. ↑ a b c Valentin Fischer, Michael W. Maisch, Darren Naish, Ralf Kosma, Jeff Liston, Ulrich Joger , Fritz J. Krüger , Judith Pardo Pérez, Jessica Tainsh, Robert M. Appleby: New Ophthalmosaurid Ichthyosaurs from the European Lower Cretaceous Demonstrate Extensive Ichthyosaur Survival across the Jurassic – Cretaceous Boundary . PLOS ONE. Vol. 7, No. 1, 2012, doi : 10.1371 / journal.pone.0029234
  30. ^ A b V. Fischer, MS Arkhangelsky, GN Uspensky, IM Stenshin, P. Godefroit: A new Lower Cretaceous ichthyosaur from Russia reveals skull shape conservatism within Ophthalmosaurinae. Geological Magazine. Vol. 151, No. 1, 2013, pp. 60-70, doi : 10.1017 / S0016756812000994
  31. ↑ Patrick S. Druckermiller, Erin E. Maxwell: A new Lower Cretaceous (lower Albian) ichthyosaur genus from the Clearwater Formation, Alberta, Canada. Canadian Journal of Earth Sciences. Vol. 47, No. 8, 2010, pp. 1037-1053, doi : 10.1139 / E10-028
  32. ↑ Richard Ellis: Sea Dragons. 2003 (see literature ), pp. 113-116, 200

Web links

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