Alvarezsauridae

    One of the most bizarre groups of dinosaurs, the alvarezsaurids may be flightless avialans, or close relatives of the ornithomimosaurians, or pretty much anywhere in Maniraptora before you hit Aves.  The derived members, the mononykines, are very birdlike and have shrunk their arms to almost nothing, retaining only one useful finger per hand in the form of a large stubby clawed thumb, with two other minute fingers hanging off fetchingly, while ironically making the arms very strong.  Some sort of digging is implied, but of what is not known, although some evidence suggests that they dug into termite mounds, anthills, and the like.  They had big heads with tiny teeth, long skinny running legs, and long thin tails, and are among the smallest known classic dinosaurs.

<--Alvarezsauridae
      |--Haplocheirus
      `--+--Alvarezsaurus
           |--Patagonykus
           `--Parvicursorinae
                |--Mononykus
                |--Parvicursor
                |--Shuvuuia
                `--Xixianykus

Alvarezsauridae:

Taxon or Taxa: Time/Place: Comments:
Haplocheirus sollers Choiniere, Xu X., Clark, J. M., Forster, Guo Y., and Han F., 2010 Oxfordian (LJ) of China Haplocheirus gets pride of place for both earliest known alvarezsaurid and most basal, from a time when alvarezsaurids still had a few large teeth to go with the little pointy ones, and their hands were not yet completely bizarre (from the standpoint of other theropods).  In gross morphology, it looks something like a short-tailed compsognathid, which just goes to show that if you go down any coelurosaurian lineage, the basal members all begin to take on that compsognathid-Coelurus-Ornitholestes look.
You may have noted, if you are in the habit of perusing other dinosaur information sources, that Haplocheirus was described as an alvarezsauroid, not an -id.  This was done to recognize alvarezsaur diversity and the basal nature of this genus (back in the day, of course, it would have gotten its own family, like Harypmimidae or Garudimimidae).  I tend to favor less sprawl, so I'm keeping everything as Alvarezsauridae for the moment.
Haplocheirus is known from the Shishugou Formation, which is accumulating more than its fair share of odd theropods, including this, the herbivorous alvarezsaur-mimicking ceratosaurian Limusaurus, the extravagantly crested tetanuran Monolophosaurus, and the extravagantly crested tyrannosauroid Guanlong (and the extravagantly plain Sinraptor, but we can't all be unusual).  Now if they could only get around to "Gongbusaurus" wucaiwanensis...
Alvarezsaurus calvoi Bonaparte, 1991 Santonian (LK) of Argentina Based on a partial skeleton, this animal was at first considered to a "ceratosaurian", making its current classification somewhat ironic.
Patagonykus puertai Novas, 1997 Coniacian (LK) of Argentina This animal is apparently transitional between Alvarezsaurus and the rest of Parvicursorinae.  It is known from vertebrae, coracoids, a forelimb, partial hips (weakly opisthopubic [pointing backwards, like in dromaeosaurids and birds]), and hindlimbs.

Alvarezsauridae i.s.:

Taxon or Taxa: Time/Place: Comments:
Achillesaurus manazzonei Martinelli and Vera, 2007 Santonian (LK) of Argentina Achillesaurus was a large alvarezsaurid.  It is known from partial remains including pelvic and hindlimb bones and caudal verts, and is basal to the parvicursorines.
Albertonykus borealis Longrich and Currie, 2008 early Maastrichtian (LK) of Alberta Surprisingly from Alberta, Albertonykus gets the honor of being the first genus recognized and named as an alvarezsaurid from North America ("Ornithomimus" minutus could conceivably be an alvarezsaurid, but it wasn't named as its own genus and predated the recognition of alvarezsaurids by a century, so there).  It's known from forelimb and hindlimb elements from several individuals, mostly from the well-known Albertosaurus bonebed.  Longrich and Currie proposed that it was eating wood-nesting termites.
Ceratonykus oculatus Alifanov and Barsbold, 2009 ?mid Campanian (LK) of Mongolia Ceratonykus is known from a fragmentary skeleton including a partial skull, a few cervicals and caudals, partial pectoral and pelvic girdles, a partial humerus, wrist elements with "spurs," and most of the hindlimbs.  The brain is described as nonavian in form.
Heptasteornis andrewsi (N.D.) Harrison and Walker, 1975 early-mid Maastrichtian (LK) of Romania Heptasteornis, often lumped with Bradycneme (see under Maniraptora i.s.), is apparently actually an alvarezsaurid (possibly a parvicursorine), Europe's first.  It is based on a partial tibiotarsus that, as with Bradycneme, were first described as belonging to an extinct owl. 
Kol ghuva Turner, Nesbitt, and Norell, 2009 late Campanian (LK) of Mongolia Kol is a rare, exceptionally large (well, twice the size of Shuvuuia, so big for its group) alvarezsaurid.  A contemporary of Shuvuuia, it is known from a foot.

Parvicursorinae:

Taxon or Taxa: Time/Place: Comments:
Mononykus olecranus Perle, Norell, Chiappe, and Clark 1993 (originally Mononychus Perle et al., 1993) late Campanian-early Maastrichtian (LK) of Mongolia Interestingly, remains of this animal (or Shuvuuia; it can get hard to keep track of these little devils) were discovered back in the 1920s by the American Museum of Natural History's Mongolia expeditions, but went unrecognized until the 1990s, when Mononykus was named from other material.  It was based on precaudal verts, limbs, parts of both limb girdles, and bones from the back of the skull.  Several other individuals are now known.
Parvicursor remotus Karhu and Rautian 1996 ?mid Campanian (LK) of Mongolia This is a very derived (and tiny; femur length shy of 5 cm) parvicursorine, known from verts, a partial pelvis, and hindlimb material.
Shuvuuia deserti Chiappe, Norell, and Clark, 1998 late Campanian (LK) of Mongolia Known from remains including skull material, this animal is very close to Mononykus.  The skull contains numerous tiny teeth.  The tail is longer than expected, and the hand had, in addition to the big finger, tiny digits II and III.  Skeletally, it may be the best known alvarezsaurid, although its material has at times been confused with contemporaneous Mononykus. 
Xixianykus zhangi Xu X., Wang D. Y., Sullivan, Hone, Han F. L., Yan R. H., and Du. F. M., 2010 Coniacian-Santonian (LK) of China Xixianykus is an early parvicursorine, perhaps a half meter (twenty inches) long but with legs twenty cm (eight inches) long, suggesting that it could move in a hurry if the mood struck it.  It is known from a partial postcranial skeleton. 

 

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