Re: Good mother dinos

[Tom Holtz <tholtz@geochange.er.usgs.gov>]

>>> 1) How can you tell from fossilized bones whether any particular
>>> species of dinosaur was a "good mother" or cared for its young?

>In the case of Maiasaura, there is evidence that when the young
>hatched, their long bones weren't fully ossified, so the animals
>couldn't support their own weight.  The obvious inference is that food
>had to be brought to them until they outgrew that condition.

One complication of this bit was the presentation of Dave Unwin (U. of
Bristol, UK) at the 1993 SVP.  He showed that, based on embryo-to-egg ratio
found in modern birds and reptiles, the Maiasaura "hatchlings" are actually
the proper size for a late-stage non-hatched embryo.  He did go on to point
out that this doesn't disprove parental care in the Dinosauria, but it does
take a way one previously important piece of evidence.

Another piece of evidence for parental care in dinosaurs comes from their
position in the vertebrate family tree.  Since both crocodilians and birds
have some amount of parental care (and lizards, turtles, etc., don't), it's
reasonable to assume that that is the primitive condition for Archosauria.
As archosaurs, dinosaurs should have had some parental care, at least
primitively, although certain species may have lost that character state
through evolution.

                                
Thomas R. Holtz, Jr.                                   
tholtz@geochange.er.usgs.gov
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092
U.S.A.