Eurhinosaurus

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Eurhinosaurus
Temporal range:
Ma
A 6.4 m (21 ft) Eurhinosaurus specimen
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: †Ichthyosauria
Family: †Leptonectidae
Genus: †Eurhinosaurus
Abel, 1909
Species
  • E. longirostris (Mantell 1851) (type) (dubious)
  • E. huenei Swinton, 1930
  • E. quenstedti Maisch 2022

Eurhinosaurus (Greek for 'well-nosed lizard'- eu meaning 'well or good', rhino meaning 'nose' and sauros meaning 'lizard') is an extinct genus of

ichthyosaurs. An adult individual could reach up to 7 metres (23 ft) in length.[6]

Eurhinosaurus followed the regular body morphology, with a fish-like fusiform body including well developed dorsal fin, hypocercal caudal fin,[7] paired pectoral and pelvic fins, and remarkably large eyes.[3] Like other ichthyosaurs, Eurhinosaurus did not have gills and used lungs for breathing.[5] Eurhinosaurus had one distinct feature different from other ichthyosaurs: the upper jaw was twice as long as the lower jaw and covered with up and downwards-pointing teeth.[5][8]

History and discovery

Skeleton and skull of Eurhinosaurus, along with a Stenopterygius skeleton, London

The name Ichthyosaurus longirostris was first published by Mantell in 1851 in a guide to the paleontological galleries of the old British Museum, where one of the ichthyosaurian specimens was displayed as Ichthyosaurus longirostris.[9] That specimen had exceedingly slender and elongated muzzle, but the skull was crushed. No characteristic preserved. The specific name, longirostris, was just affixed to the specimen. Since the features were so unclear, scientists at that time were not able to name this specimen.[9] The first skull of Eurhinosaurus longirostris was found by Owen and Jaeger in Switzerland in 1856, which showed clearly shortened mandibles.[4] The genus Eurhinosaurus was erected in 1909 in a paper describing the Miocene cetacean Eurhinodelphis cocheteuxi. Abel noted that it was not certain whether the cetacean's mandible extended to the tip of the snout or whether it was abbreviated, which was like the case in Ichthyosaurus longirostris in 1851.[9] He considered that the weak, attenuated mandible and some other distinguishing features of Ichthyosaurus longirostris and decided to erect a separate genus and names as Eurhinosaurus.[9] The type species by monotype, was Eurhinosaurus longirostris.[9] In 2022, a second species, E. quenstedti was described from Germany. The original species, E. longirostris was considered dubious due to the poor preservation of the type specimen, with the species E. huenei, based on a complate skeleteon described in 1930 resurrected to replace it.[10]

Description

Size compared to a human

Eurhinosaurus was a large-bodied, small-toothed, slender

Xiphias.[12][3] The upper jaw was more than twice as long as the lower jaw. The orbits of Eurhinosaurus were very large and directed anterolaterally.[3] Their huge orbits were combined with an extremely short cheek region and reduced upper temporal openings.[12] The external naris was large and retracted.[3]

Eurhinosaurus had elongated, slender and straight teeth without distinct surface ornamentation of the crown.

ichthyosaurs, the parietal foramen was located on the connection point between parietal and frontal.[12] The temporal fenestra was extremely small.[3]

Skull

The supratemporal of Eurhinosaurus was very large and wide in the dorsal view, reaching the orbital margin.

caudal fin of Eurhinosaurus was in hypocercal shape (the notochord extended into the lower lobe) with cartilaginous chevrons which could be used for swimming in a high speed.[3]

Life restoration

In the vertebral column, the neural spins of the dorsal vertebrae were remarkably short, less than the height of the centrum, which was also found in other lower Jurassic large-bodied ichthyosaur such as Temnodontosaurus and Platypterygius.[12] The forefins of Eurhinosaurus offered a peculiarity: the radius was much larger than the ulna.[12] Besides, the fins were very long and slender with four primary digits, no accessory digits and strong hyperphalangy.[11][13] Their hindfins were about two thirds the length of forefins.[5][13]

In the shoulder girdle, the interclavicle was small and T-shaped.[3] The scapula was elongated with a narrow, expanded dorsal blade.[12] The postglenoidal portion of the coracoid was larger than the much reduced anterior extension.[12] The coracoid was rounded with a notch in the anterolateral margin.[3] The humerus had a constricted, very thickened head and expanded, flattened distal end.[12]

The pelvic girdle was moderately reduced and also showed the fusion of pubis and ilium seen Stenopterygius.[12] The plate-like bones of the pelvis (pubis and ischium) had modified to the elongate and waisted bones. The pubis in this form lacked an obturator foramen. [clarification needed][12]

Classification

Skulls of Eurhinosaurus and the related Temnodontosaurus

The cladogram below is based on Sander (2000),[12] Maisch and Matzke (2000),[3] Maisch (2010)[14] and an analysis by Marek et al (2015).[15]

Parvipelvia 

Palaeobiology

Feeding mechanisms and diet

The postcranial morphology of Eurhinosaurus was intermediate between those super fast swimmers and slower, more flexible predators.

Xiphias.[12] The elongated, densely toothed upper jaw was used as weapon to penetrate or make damage to small soft prey from the back.[12][2] Eurhinosaurus belongs to the "Pierce I" predatory guild, so its dietary habits were consisted of small and soft, very delicate prey, such as small fishes, oysters and squids.[2]

Swimming style and movement

Like other

peduncle, moved through the water in a sinuous curve by the powerful muscles of the posterior trunk and the anterior tail region. From this motion, a strong force would be generated to pull Eurhinosaurus forward.[12]

Like other

sclerotic ring, a circular shaped bone that was embedded in their eye.[5] The sclerotic ring was probably used to maintain the shape of their eyes against the high pressure in the deep sea while they were diving.[5] Ichthyosaurs had the biggest eyes of any animal ever known.[citation needed] The big eye of Eurhinosaurus suggested that they had very good visual capacity, which helped them see clearly in the dark environment of the deep sea.[5]

Palaeoenvironment

Eurhinosaurus lived in open ocean, which was far away from the coastline.

ammonites.[4] This was also the evidence could show Eurhinosaurus was a creature from the marine environment.[4]

See also

References

  1. ^ Maisch MW. 2010: Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art. Palaeodiversity 3: 151-214
  2. ^ a b c d e Fischer V, Guiomar M & Godefroit P. 2011: New data on the palaeobiogeography of Early Jurassic marine reptiles: the Toarcian ichthyosaur fauna of the Vocontian Basin (SE France). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 261(1): 111-127
  3. ^ a b c d e f g h i j k l m n Maisch MW, Matzke AT. 2000. The Ichthyosauria. Stuttgarter Beiträge zur Naturkunde, Serie B (Geologie und Paläontologie) 298: 1-159
  4. ^ a b c d e f g h i Reisdorf AG, Maisch MW & Wetzel A. 2011. First record of the leptonectid ichthyosaur Eurhinosaurus longirostris from the Early Jurassic of Switzerland and its stratigraphic framework. Swiss Journal of Geosciences 104(2): 211-224
  5. ^ a b c d e f g h Motani R. 2000. “Rulers of the Jurassic seas”. Scientific American. 283 (6): 52-59
  6. doi:10.1080/02724634.2015.1025956
    .
  7. ^ Crofts S. B., Shehata R. and Flammang B. E. 2019. Flexibility of Heterocercal Tails: What Can the Functional Morphology of Shark Tails Tell Us about Ichthyosaur Swimming?. Integrative Organismal Biology 1(1): obz002 1-10
  8. ^ McGowan. 1986. A Putative Ancestor For The Swordfish-like Ichthyosaur Eurhinosaurus. Nature. 322(31): 454-456
  9. ^ a b c d e McGowan C. 1995. The Taxonomic Status of the Upper Liassic Ichthyosaur Eurhinosaurus longirostris. Palaeontology. 37: 747-753
  10. doi:10.26251/JHGFN.178.2022.117-148
    .
  11. ^ a b c d e f g Emily A. Buchholtz 2000. Swimming styles in Jurassic Ichthyosaurs. Journal of Vertebrate Paleontology 21, 63-71
  12. ^ a b c d e f g h i j k l m n o p Sander,P.M.(2000). "Ichthyosauria: their diversity, distribution, and phylogeny", Paläontologische Zeitschrift 74: 1–35
  13. ^ a b McGowan C. 2003. A New Specimen Of Excalibosaurus From The English Lower Jurassic. Journal of Vertebrate Paleontology 23(4): 950-956
  14. ^ Maisch M. 2010. Phylogeny, Systematics, and Origin of The Ichthyosauria-The State of the Art. Palaeodiversity. 3: 151-214
  15. ^ R. D. Marek, B. C. Moon, M. Williams, M. J. Benton: The skull and endocranium of a Lower Jurassic Ichthyosaur based on digital reconstructions. In: Palaeontology 58, 2015, S. 723–742.
  16. ^ “The lithostratigraphy of the Blue Lias Formation (Late Rhaetian–Early Sinemurian) in the southern part of the English Midlands”. Proceedings of the Geologists' Association. 112(2): 97-110
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