Sinornithoides

*Sinornithoides youngi*

***Sinornithoides*** (meaning "Chinese birdlike") is a Troodontid from early Cretaceous China. It was about 3.9 feet (1.2 meters) long and weighed about as much as a chicken. Like *Mei* known from a fossil in "sleeping" position. It lived in Inner Mongolia, China, and probably ate invertebrates and other small prey.

## Discovery

In 1988, a Chinese-Canadian expedition discovered the remains of a small theropod near Huamuxiao, in the Ordos Basin of Inner Mongolia. *Sinornithoides youngi*, the type species, was named and described in 1993/1994 by Dale Russell and Dong Zhiming based on this fossil specimen from the Lower Cretaceous Ejinhoro Formation. The generic name is derived from Latin Sinae, "Chinese", and Greek ὄρνις, ornis, "bird", en ~ειδής, ~eides, a suffix meaning "~like", in reference to the bird-like build. The specific name honours Yang Zhongjian.

It is represented by a holotype, IVPP V9612, an almost complete skeleton with skull, which is articulated and nearly complete except for the roof of the skull, some cervical and many dorsal vertebrae, along with some other referred skeletal elements. The holotype is preserved in much the same roosting position as another troodontid fossil, that of *Mei long*, with its snout tucked under its left hand. It represents a subadult individual.

*Sinornithoides youngi*, the type species, was described in 1993 by Dale Russell and Dong Zhiming based on a fossil specimen from the Ejinhoro Formation. It is represented by a holotype which is articulated and nearly complete except for the roof of the skull and the cervical and dorsal vertebrae, along with some other referred skeletal elements. The holotype is preserved in much the same roosting position as another troodontid fossil, that of *Mei long*, with its snout tucked under its left hand.

## Description

*Sinornithoides* is a troodontid, a group of small, bird-like, gracile maniraptorans. All troodontids have many unique features of the skull, such as closely spaced teeth in the lower jaw, and large numbers of teeth. Troodontids have sickle-claws and raptorial hands, and some of the highest non-avian encephalization quotients, meaning they were behaviorally advanced and had keen senses.[4] In 2010, Gregory S. Paul estimated its body length at 1.1 metres, its weight at 2.5 kilogrammes.

In 1994, *Sinornithoides* was one of the most completely known troodontids, especially as regarded the palate, but the lack of sufficient fossil material to compare it with induced Russell and Dong not to indicate any diagnostic traits.

The skull of *Sinornithoides* is elongated and pointed. However, the head is relatively short compared to the body as a whole. The praemaxilla is short. There is a fenestra promaxillaris, a small opening in the front of the maxilla side, which is rare among troodontids. There are four premaxillary and about twenty-three maxillary teeth. The maxillary teeth have no serrations on their front edge; the denticles on the concavely curved rear edge are small. The maxillary teeth are rather recurved. The lacrimal bone lacks a pneumatic channel. In the braincase the subotic recess is large. The tips of the lower jaws do not curve towards each other but touch at their inner sides. The external mandibular fenestra is large. The dentary, lower jaw, teeth are quite pointed and have no front edge denticles; their rear edge is very straight. The holotype preserves a furcula and a basket of fifteen pairs of gastralia. The arms are weakly developed, with a slender humerus and ulna. The front top of the third metatarsal is not fully overgrown by the second and fourth metatarsals. The sickle claw of the second toe is relatively large and long for a troodontid.

## Phylogeny

*Sinornithoides* was in 1994 assigned to the Troodontidae.

A possible position of *Sinornithoides* in the evolutionary tree of the Paraves is shown by the cladogram below, following a 2012 analysis by Turner, Makovicky and Norell.

## Dinosaur Field Guide Description

Sinornithoides ("Chinese bird form") is one of the oldest known troodonts, or "wounding tooth" dinosaurs. Troodonts were meat-eating dinosaurs with extremely long hind legs. They were very bird-like in the details of their braincases, their backbones, and other features. They were also probably among the fastest of the smaller dinosaurs. Before Sinornithoides was discovered, troodonts were only known from incomplete fossils. Then, in 1988, the skeleton of this little dinosaur was found in the region of China called Inner Mongolia. This dinosaur had been buried by a sandstorm while lying on its belly. Its head and neck were tucked under its arm, and its tail was wrapped around its body. Because it was covered over so quickly and so completely, nearly the entire skeleton was preserved in fine detail. Sinornithoides was about the size of a wild turkey. It could easily chase down mammals, lizards, smaller dinosaurs (including babies), and similar creatures for their meat. Because the teeth of troodonts are similar to those of plant-eating dinosaurs, some scientists think that troodonts like Sinornithoides also ate insects and plants. Many small carnivorous mammals (foxes and raccoons, for instance) are actually omnivores: They eat meat, plants, and other food.

### Fun Facts

Sinornithoides is not the only Asian troodont. There are several other kinds, including one called Borogovia after the borogoves in Lewis Carroll' poem \*Jabberwocky.

### Trivia

Until Sinornitholdes was found, many paleontologists thought that troodonts had long arms like raptors.

## References

1. ↑ Russell, D. and Dong, Z. (1993). "A nearly complete skeleton of a new troodontid dinosaur from the Early Cretaceous of the Ordos Basin, Inner Mongolia, People's Republic of China." *Canadian Journal of Earth Sciences*, **30**: 2163-2173.
2. ↑ Currie, P. and Dong, Z. (2001). "New information on Cretaceous troodontids from the People's Republic of China." *Canadian Journal of Earth Sciences*, **38**: 1753–1766. DOI: 10.1139/cjes-38-12-1753