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Re: possible FAQs



Comments on a list of possible FAQ's (thanks to everyone who told me what
they were):
>
> From: Neil Taylor <neil@arc.ug.eds.com>
> > 
> > * Were dinosaurs reptiles?
>
>This is a matter of definitions and of the rules used for creating
>classifications.
>
>By one set of definitions and rules, yes they are.
>
>By another set of definitions and rules (the ones used by a
>group called cladists), "reptiles" either do not exist as a
>recognized group, or are restricted to lepidosauromorphs
>(the living forms of which are lizards, snakes and tuataras).

Actually, many cladists (including myself) restrict the term "Reptilia" to
the most recent common ancestor of turtles, crocodiles, and lepidosaurs and
all of its descendants.  This keeps dinosaurs (including birds),
pterosaurs, ichthyosaurs, plesiosaurs, mesosaurs, etc. as reptiles, but
excludes the synapsids (mammals and "mammal-like reptiles").


> > * How big were they?
>
>The largest were Brachiosaurus and its close relatives, which
>got to be around 50-60 tons.  The longest was probably Seismosaurus,
>at well over a hundred feet.

Actually, brachiosaurids are now just middling sauropods.  The record
holders are the andesaurid titanosaurian Argentinosaurus (at about 90
tonnes) and the diplodocid Amphicoelias (which some people estimate might
be as much as 150 tonnes!).  Argentinosaurus is based on some good
material, and includes vertebrae which are over 1.6 meters from the bottom
of the centrum to the top of the neural spine (about twice the height of
the equivalent in Brachiosaurus).  

The most complete specimen of Amphicoelias (a North American form) is
bigger than any mounted Apatosaurus skeleton, but not as big as
Brachiosaurus.  There was a specimen of Amphicoelias, now lost but well
figured, which was simply half of a neural arch over 1.5 meters long.  If
scaled to the smaller Amphicoelias, it indicates a vertebra about 2.5 to 3
meters tall!  This summer there has been renewed interest in Amphicoelias,
and it is known that bones are still weathering out of the original
quarry...


> > * How small did they come?
>
>The smallest certain dinosaur known is Compsognathus, at less than
>2 feet in length, and less than 1 kilogram in weight.  If Protoavis
>is a dinosaur it is even smaller.

Actually, that specimen of Compsognathus is a juvenile.  The adult specimen
from France is about 1.1 meters long.


> > * Did some (Stegosaurs,...) really have two brains?
>
>No.  All dinosaurs had a sacral ganglion, that is an enlargement
>of the spinal cord in the pelvis.  This is not a brain, no matter
>how large it is. In Stegosaurus the cavity for this ganglion was
>larger than the skull.  However there is reason to believe alot
>of the volume of this cavity was filled with fatty tissue, not
>nerve tissue.
>

Indeed.  Emily Giffen (one of the best paleoneurologists around) thinks
that the sacral enlargements are not only ganglia.  Instead, she thinks
they housed a glycogen body, as is found in many modern tetrapods.


> > * How big were Deinonychus and Velociraptor?
>
>I do not have the figures at hand for this.

Velociraptor massed about the same as a jackal (about 20 kg) and was around
2 to 2.5 meters long.  Deinonychus massed about the same as a grey wolf
(big individuals around 70 kg) and got up to 3.5 to 4 meters long.  There
are other, much larger dromaeosaurids (Utahraptor and a couple of
undescribed albertosaur-sized Asian forms).

>
> > * Did Dilophosaurs have frills and spit poison?
>
>No.  And it was about 10 feet long as well.

Actually, more like 20 to 25 feet long.  Dilophosaurus and its relatives
were the first large theropods.

> > * Have we really extracted DNA, blood,... from Dinosaur remains?
>
>Not yet, but there are people working on extracting DNA from
>dinosaur bones.
>

Actually, what looks for all the world like dessicated red blood cells have
been reported from the marrow cavity of the femur of a VERY well preserved
Tyrannosaurus.

Hope these comments help.

                                     

                                
Thomas R. Holtz, Jr.
Vertebrate Paleontologist in Exile
U.S. Geological Survey
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092

email:  tholtz@geochange.er.usgs.gov 
Phone:  703-648-5280
FAX:            703-648-5420