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Omphalosaurus

Omphalosaurus
Temporal range: Middle Triassic - Late Triassic, 250–235 Ma
Omphalosaurus10DB.jpg
Restoration of Omphalosaurus nevadanus
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Ichthyosauria
Family: Omphalosauridae
Genus: Omphalosaurus
Merriam, 1906
Species
  • O. nevadanus Merriam, 1906 (type)
  • O. merriami Maisch, 2010
  • O. nettarhynchus Mazin and Bucher, 1987
  • O. peyeri Maisch and Lehmann, 2002
  • O. wolfi Tichy, 1995

Omphalosaurus (from the Greek root "Button Lizard", for their button-like teeth) is an extinct genus of marine reptile from the Middle Triassic, thought to be in the order of Ichthyosauria. Most of what is known about Omphalosaurus is based on multiple jaw fragments, ribs, and vertebrae. Specimens of Omphalosaurus have been described from the western United States, Germany, and the island of Spitsbergen off the northern coast of Norway.

Omphalosaurus are moderately large and plump marine reptiles and are best known for their highly specialized dentition compared to other Ichthyosaurs. The teeth are button-like, with a dome shape when viewed laterally and almost circular crowns that have an irregular enamel surface akin to the texture of an orange peel. Individual teeth do not exceed 12mm in diameter and are arranged in tooth plates exclusively on the premaxilla, which sit at 90º from each other, and dentary. Based on O. nevadanus’ well preserved and smooth palatine, it’s unlikely that Omphalosaurus had palatine teeth akin to Placodonts. Nonetheless, Omphalosaurus teeth could potentially number in the hundreds, and are concentrated along the skull midline. Each species has varying degrees of tooth organization, but O. nevadanus has the most neatly organized teeth, which most closely resemble distinct rows despite some unevenness. Attempts have been made to count the number of rows of teeth for the other species, but they are mostly irregularly patterned on the occlusal surface.

The upper tooth plates form a convex surface, while the lower plate is concave. They were previously thought to have short, broad jaws and powerful bite forces, but recent reconstruction indicate that the dentary symphesis is elongated and connects at an approximately 15º angle, giving the jaw a long “V” shape. If reconstructed, the lower jaw of O. nevadanus could potentially exceed 50 cm in length.

Jaw fragments have revealed that Omphalosaurus had a dental batteries that were optimized for constant wear, with high tooth replacement rates.Omphalosaurus is unusual in that their immature replacement teeth and mature teeth had different enamel microstructure. Like other Ichthyosaurs, Omphalosaurus have a microunit enamel in their mature teeth, while replacement teeth have columnar enamel. It is currently unknown how this transformation occurs.


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Wikipedia

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