Re: tiny dinosaurs

[Tommy Tyrberg <tommy.tyrberg@norrkoping.mail.telia.com>]

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
one
>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
unusually
>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
there
>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,
but
>they are still 10 cm long.  So why be so tiny?
>
>Dan
>
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