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Alvarezsauridae
Patagonykus puertai
1996 - Argentina
The largest of the Alvarezasaurids

Shuvuuia deserti
1998 - Mongolia
   This is the best known alvarezsaurid, because it is the only one to have fossils of complete and well-preserved skulls.
Alvarezsaurus calvoi
1991 - Argentina
   When Alvarezsaurus was discovered in 1991, it was obvious that it appeared to be a theropods. But it had characteristics distinctively different from other North American carnivorous dinosaurs. This led to it being placed in its own family.

No Image Available

Parvicursor remotus
1996 - Mongolia
   A little smaller than a chicken, it is currently the smallest known dinosaur.
Mononykus olecranus
1923, 1993 - Mongolia
   Discovered in 1923, but reexamined and reclassified in 1993.
  Other Possible Alvarezsaurids
  Rapator ornitholestoides
This is
a large Australian dinosaur from the middle Cretaceous known only from a single finger bone. It has puzzled researchers since it was described by von Huene in 1932. It so closely resembled that of the coelurosaur Ornitholestes hermani from North America that it was given the species name ornitholestoides, meaning 'like Ornitholestes'.
So far, nothing definitive has been reached as to it's identity. The size of the bone suggests that it was over 20 feet long.
  Heptasteornis andrewsi (Harrison and Walker, 1975)
This is known only from distal tibiotarsi and was originally classified as a large owl, later as a troodontid. It may have reached 8 feet in length
     Alvarezsaurus calvoi  was discovered in Argentina in 1991. It was a small, lightly-built, bird-like, bipedal theropod. The incomplete fossil skeleton revealed that it was unique in that it had a single large claw on each of its forelimbs. It was discovered and described by José Bonaparte as the anchor taxon of a new family, the Alvarezsauridae and its containing taxon (clade), Alvarezsauria. This first species was loosely classified as a ceratosaurian. It was named for the historian Don Gregorio Alvarez, not the more familiar physicist Luis Alvarez, who proposed that the Cretaceous-Tertiary extinction event was caused by an impact event.
    Actually it was not the first of these strange dinosaurs to be discovered. In 1923, a partial skeleton of a strange dinosaur was found in the Gobi Desert, but there was not enough material to get a good idea of its appearance. A group of scientists reexamined it and found that it was also an Alvarezsaurid. The fossil remains were more complete than Alvarezsaurus calvoi, so they helped to fill out the picture of what these animals looked like. They named it
Mononykus olecranus.
   
 In 1987 a joint Soviet-Mongolian expedition found a few remains of a bipedal dinosaur.  It was similar to Velociraptor, who lived at the same time and was also found in the Gobi  Desert. This newly discovered dinosaur appeared to be related, but was much smaller - about the size of a turkey. In 1992, an expedition team from the American Museum of Natural History and the Mongolian Academy of Sciences discovered more fossilized remains of this fossil, which  they named Shuvuuia deserti . It had a single claw on each forelimb established that it was also an Alvarezsaurid. More important was the discovery of two complete skulls. Although Shuvuuia looked like a dinosaur, examination of the skulls showed that it had a pointed beak filled with tiny teeth. The most amazing thing is that it could raise its upper jaw, with respect to the braincase. This is a characteristic of modern birds. The group was reclassified as flightless birds.
     The subsequent discoveries of Patagonykus puertai and Parvicursor remotus provided even more information. Novas & Pol (2002) and other authors consider them a gorup of non-conforming theropods. The Alvarezsaurids are now considered to belong to a group of dinosaurs known as the Maniraptorids , which includes Deinonychosaurs, Therizinosaurs and Oviraptorids, as well as true birds, which are now considered to be specialized flying dinosaurs.
   While its exact position is uncertain, Alvarezsauridae is placed just a step or two away from Archaeopteryx. Alvarezsaurid material has also been reassigned to Ornithomimus, and there may be a relationship between the alvarezsaurids and the Ornithomimosauria. Classification is difficult because the known specimens are all very derived forms from the late Cretaceous, which provides little information on what early forms they evolved from.
    All five species had very similar skeletons. All had long legs, suggesting they were fast runners.  All also had long tails and many bird-like features in the backbone, pelvis and hindlimbs. In fact, Mononykus looked even more birdlike than Archaeopteryx. On the other side of the coin, The Shuvuuia deserti skulls show that it was more closely related to modern birds than is the famous first bird, Archaeopteryx. Plus their forelimbs were short and stubby. Shuvuuia’s forelimbs were much like that of an  ostrich and emu. They were very strong, but certainly unsuitable for flight.
   The primary distinguishing characteristics of these dinosaurs is that they were believed to have had but one big claw on each of their forelimbs. This is different from all other theropods as they have three. New evidence has shown that  Alvarezsaurids probably never lost the two other fingers, but they had shrunk to almost nothing.
   They did vary in size. Parvicursor remotus is now the smallest known dinosaur. It was a little smaller than a chicken. Patagonykus puertai was the largest. At six feet in length, it was close in size to its contemporary, Velociraptor. It is possible that
Rapator ornitholestoides and Heptasteornis andrewsi (see above) could be members of this family. If so, then Alvarezsaurids could have been over 20 feet in length. Unfortunately the fossil records of these species is so scant that no classification is possible.
   Although these animals are extremely bird-like, no fossilized feathers have been found.  If it had feathers, then they were not preserved.  Mary Schweitzer has made an important study of the "dino fuzz" fossilized integument found with Shuvuuia desertit and arrived to the conclusion that the main chemical component is Beta-Keratin: Important demonstration that "dino fuzz" is in reality feathers.

 

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