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Re: Riddle of the "Smallest": Quantifying "Small"



Jaime Headden wrote-

>   To answer this final question, least mass and all
> that, in theropods excluding Aves, one first must
> consider whether alvarezsaurs are within Aves or not;
> assume they are not, then *Parvicursor*, at an
> estimated 1.7-2ft, with an estimated total hindlimb
> length of about 7.5in., may be the smallest non-avian
> dinosaur _period_.

The femur of Parvicursor is 52.6 mm long.  Saltopus has a femur 47 mm long.
Then again, it has a longer tail than would be expected for a mononykine, so
it was probably longer and it may not be a dinosaur (scapula looks very
Marasuchus-like to me).  Protoavis has a femur 58 mm long and has a short
tail, but the long arms might make it heavier and, of course, it could be a
chimeara and is extremely controversial.  Ligabueino has a femur 62 mm,
although the proportions of noasaurids are not well known.  I estimate
Caenagnathasia at about .3 m, which would give it a femur length of about 40
mm.  Also, "Ornithomimus" minutus, a mononykine (or avimimid), is similar to
Parvicursor in size.  And even if Rahonavis and Yandangornis are not avians
(both are in my analyses), they would be larger than those taxa listed above
(femoral lengths of 88 and 106 mm respectively).  These are the smallest
described non-avian theropods (tooth taxa not included).

> *Tianchisaurus*, the animal almost named after
> "Jurassic Park" and whose species name is virtually
> un-pronouncable, may be smaller as well -- I have yet
> to read the paper or see any of the material. [see
> below for a possibly smaller animal]

According to Glut's encyclopedia, the sacrum (of seven vertebrae) is ~287 mm
long, a dorsal vertebrae is ~67 mm long and a proximal caudal vertebra is
~53 mm long.  This scales to 2.44 m when Sauropelta is used as a guide.

>   The smallest "prosauropod": probably
> *Thecodontosaurus*, the most complete of the basal
> forms, and probably a basal sauropodomorph, outside of
> the *Plateosaurus* + *Saltasaurus* node. Around 4ft?.

2.5 m for adults according to Benton et al. (2000).  Saturnalia is smaller,
at 1.5 m long.

Mickey Mortimer