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Re: tiny dinosaurs

At 17:30 2000-02-03 -0800, you wrote:
>>>>>Somebody was asking about teeny-tiny dinosaurs.  There's some very small
>dinosaur specimens known only from teeth.. . . But who's to say these teeth
>didn't come from
>juveniles (even hatchlings)?<<
>As  long as we're talking about _any_ small dinosaur, I know of an extinct
>that is only slightly larger than the (extant) bee hummingbird.  Liaoxiornis
>delicatus was a toothed bird from China during the Early Cretaceous (or
was it
>Late Jurassic?) and measured about 6 cm long (taking into account an
>long tail).  The body may well be about the same size as the bee hummingbird,
>but L. delicatus was probably an insectivore (it having a short bill and
>not being many flowers around at the time).
>Speaking of which, what advantage would such tiny size be to an insectivore?
>I've looked at the skeletal reconstruction and L. delicatus did not have the
>giant sternum of a hummingbird so it probably didn't hover.  No modern insect
>eaters (that we know of anyway) are that small, well, kinglets come close,
>they are still 10 cm long.  So why be so tiny?
Actually there are extant avian insectivores that almost match L. delicatus
in size the Rifleman Acanthisitta chloris, one of the two surviving New
Zealad "wrens" are about 8 cm and the Pygmy Antwren Myrmotherula brachyura
ignota of Colombia is slightly less than 7 cm long and several other
antwrens are only slightly larger. The Bee Hummingbird is about 6,5 cm and
the closely related Vervain about 7 cm. However, generally speaking birds
<9 cm in length as adults are rare, and the Kinglets are probably about the
minimum size that can survive a northern winter, they can be almost wiped
out by a bad season.

Being small has some obvious advantages for insectivores that live in dense
forests and thickets. The main drawback is the difficulty of obtaining
enough food to keep a high-powered avian metabolism going (particularily
overnight) in a body with so large a surface/volume quotient (hummingbirds
go torpid at night). This may have been less of a problem in early birds
which were probably not fully endothermic. A equable tropical climate would
also have helped. It is interesting to note that even back in the
Cretaceaous birds panned more or less the same size-range as today
(Liaoningornis - Gargantuavis vs. Mellisuga - Struthio (or Dinornis)).

By the way if You want to see a REALLY tiny dinosaur then juvenile Bee
Hummingbirds is the thing to go for. I´ve only seen adult Bee's (it's a
rather rare species), but (newly fledged) juveniles of the slightly larger
Vervain of Hispaniola are literally bumble-bee size!

Tommy Tyrberg