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TINY DINOSAURS



Jeff Hecht wrote:
<<That also raises another question: were all small dinosaurs members
 of the theropod/bird lineage?>>
 
Then Jaime Headden wrote: 
<<*Drinker* - around 2 ft (LJ)
   *Laeallynasaurua* - same (EC?)
   *Microceratops* - about 3 ft (LC?)
   *Comsognathus*, of course - about 3 ft (LJ/EC, one of the two)>>

Indeed.  Some of the smallest, but also rarest and most ignored dinosaurs are
basal ornithischians, and basal ornitthopods in general.  They were tiny.

In the Middle Jurassic, the Chinese Agilisaurus louderbacki and "Yandusaurus"
multidens were both under 2 metres.  Agilisaurus was also almost 1/2 tail, so
it was comparitively smaller than your average 2 metre dinosaur :-)  The
fragmentary Yandusaurus hongheensis and Xiaosaurus are also small, less than 2
metres.

The Late Jurassic Drinker, Othnielia and Nanosaurus are tiny, tiny, tiny.
Othnielia is less than 1.5 metres long, and the others are smaller.  By the
by...  Bakker has told me that he has a lot more info on Drinker than has been
published, so we should all look forward to a nice monograph on a basal
ornithopod :-)

The Early Cretaceous saw yet more small basal ornithopods.  Hypsilophodon is
little, less than 1.5 metres, Zephyrosaurus is too, although only known from a
partial skull that was maybe 12 cm long, which would make a whole animal of
about 1.5 metres.  The yet-to-be-described Proctor Lake ornithopod was between
1.2 and 1.5 metres in length based on published drawings.  The basal
iguanodontian Gaspirinisaura was extremely small, and may just take the cake
for the smallest dinosaur ever: about 80 cm in length.  A soon to be described
ornithopod from Spain (Ruiz-Omenyaca pers com) that seems to be closest to
Othnielia is around 1 - 1.5 metres.

The Australian ornithopods Laealynasaura (or however you spell that...),
Atlascopcosaurus, and Fulgurotherium are less than 1.5 metres, the first two
being even smaller, perhaps less than 1 metre.

The Campanian/Early Maastrichtian ornithopods Orodromeus and Parksosaurus were
slightly larger than the average, about 2 metres, which is still pretty small.

The Maastrichtian ornithopods included in Thescelosaurus (my count is between
2 and 5 animals AT LEAST) were the only ones that seemed to get big, but still
it was less than 3 metres.  This was only in the last couple of million years
ago before the KT boundry.

Bugenasaura from the same time and place, remained small however, around 1.5
- 2 metres.  Again, since it is only known from a skull, we have to guess :-)

The point I am trying to make is that small ornithopods and ornithischians are
known from throughout the Mesozoic right up and to the KT boundry.  There are
probably a lot more tiny ornithischians, even thescelosaurs from the latest
Cretaceous: they tend to be ignored, overlooked, or not described since they
are not specifically diagnostic because they are isolated teeth.

So the small dinosaurs aren't just theropods and they were not kept out of the
Maastrichtian.  Extinction hypotheses based on "only tiny animals survived, ie
birds and mammals" will have to explain why there aren't flocks of ornithopods
running around because they were consistantly just as small as many birds and
mammals throughout the Mesozoic right up til the end.

Peter Buchholz
Tetanurae@aol.com