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INCISIVOSAURUS

an oviratorosaurian theropod dinosaur from the Early Cretaceous of China.
incisivosaurus-skull.png
Pronunciation: IN-si-SEE-vo-SOR-us
Meaning: Incisor lizard
Author/s: Xu, Cheng, et al. (2002)
Synonyms: None known
First Discovery: Liaoning, China
Chart Position: 424

Incisivosaurus gautheri

The path of paleontology often chucks up a few surprises. For example, the freaky therizinosaurs; huge hand-clawed, pot-bellied theropods trying their damnedest to become vegetarians and oviraptorosaurs; the so-called egg snatchers that maybe weren't. Incisivosaurus has features typical of both therizinosaurs and oviraptorosaurs but falls into the latter camp as its most basal member. However, a lack of advanced family features was offset by some rather unique features of its own.

The specialist oviraptorosaurs — known as oviraptorids — were toothless, barring two tooth-like "prongs" on the roof of their mouth, and are thought of as omnivores because their short, deep skulls anchor a robust beak that seems as suited to dispatching small vertebrates as it is to cracking Ginkgo nuts and Araucarian cones. By comparison, Incisivosaurus was primitive in having a shallow snout accounting for half of its total skull length with just the faintest whiff of a beak at the tip of its lower jaw and a beakless upper jaw packed with small, leaf-shaped, cheek teeth. But its most stand-out feature, literally, is a pair of large, flat, incisor teeth, much like those of a beaver.

Given the impracticality of blunt buck teeth for dealing with meat and the signs of severe tooth wear and tear associated with tough foliage processing, it seems likely that Incisivosaurus was a herbivore. And this theory is backed up by the presence of gastroliths -- common stones that are swallowed to pulverize food and extract maximum nutrients by critters who lack grinding teeth, such as some herbivorous dinosaurs and, perhaps surprisingly, modern birds. Incisivosaurus, though, was lacking any of the bird-like features typical of advanced oviraptorids despite the fact that it lived alongside birds, which proved that its descendants gained their bird-like characteristics via convergent evolution and weren't merely birds that had lost the ability to fly, as once thought.

3D imaging after CT scans showed that Incisivosaurus had fewer air spaces in its skull bones than oviraptorids, which was another primitive trait. But it was also the lineage trailblazer. It had set the trend for larger eye sockets and expanded optic lobes (the part of the brain used for seeing) at the expense of reduced olfactory lobes (the part of the brain that deals with smelling) which would culminate in oviraptorids proper, suggesting sight was more important than scent. Its teeth were important too, and although rodentine they weren't ever-growing like those of mammals, as replacement teeth were found hidden just behind the visible teeth, ready to take their place if lost or damaged in the typical dinosaurian manner.

Unfortunately, the body-less head of Incisivosaurus may well belong to the skull-less body of Protarchaeopteryx, and the latter will have priority name-wise if they turn out to be synonymous because Xu et al. coined it five years earlier.
(Gauthier’s Incisor Lizard)Etymology
Incisivosaurus is derived from the Latin "incisivi" (incisor), for its large front teeth, and the Greek "sauros" (lizard). The species epithet, gautheri, honors Dr. Jacques Gauthier, a pioneer of the phylogenetic method of classification.
Discovery
The first remains of Incisivosaurus were recovered from the fluvial Lujiatun beds in the Yixian Formation, Sihetun area, near Beipiao City, western Liaoning Province, China.
The holotype (IVPP V13326) is an almost complete skull (approx. 100 mm long) and a partial neck (cervical) vertebra.
Isolated teeth from Aptian-Albian rocks in Fuxin (western Liaoning Province, northeastern China) have also been assigned to Incisivosaurus, which suggests at least some critters from the Jehol Biota lived beyond the Berremian period of the Early Cretaceous.
Estimations
Timeline:
Era: Barremian
Epoch: Early Cretaceous
Stage: Mesozoic
Age range: 128-125 mya
Stats:
Est. max. length: 0.9 meters
Est. max. hip height: 0.3 meters
Est. max. weight: 6 Kg
Diet: Herbivore
References
Xu X., Cheng Y.-N., Wang X.-L. and Chang C.-H. (2002) "An unusual oviraptorosaurian dinosaur from China". Nature, Vol. 419, September 2002. [skull image credit]
• Osmolska H., Currie P. J., and Barsbold R. (2004) "Oviraptorosauria" in Weishampel, Dodson and Osmólska (eds.) "The Dinosauria: Second Edition".
• Balanoff AM, Xu X, Kobayashi Y, et al. (2009) "Cranial Osteology of the Theropod Dinosaur Incisivosaurus gauthieri (Theropoda: Oviraptorosauria)". American Museum novitates, no. 3651. [3d image at digimorph]
• Paul G.S. (2010) "The Princeton Field Guide to Dinosaurs".
• Amiot R., Kusuhashi N., Xu X., and Wang Y. (2010) "Isolated dinosaur teeth from the Lower Cretaceous Shahai and Fuxin formations of northeastern China". Journal of Asian Earth Sciences 39(5):347-358.
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To cite this page:
Atkinson, L. "INCISIVOSAURUS :: from DinoChecker's dinosaur archive".
›. Web access: 21st Oct 2017.
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