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Troodontid skulls in other nests: the answer
There was a recent feature on Mark Norell in the Wall Street Journal:
http://online.wsj.com/article/SB10001424052702304447804576411911713825824.html
It includes a photograph (the second photograph, halfway down the page) of a
troodontid nest and one nearly complete hatchling, minus skull. The hatchling
is IGM 100/1003, and it is assigned to Byronosaurus jaffei. This same material
was displayed at the AMNH in 2000:
http://www.amnh.org/exhibitions/fightingdinos/ex4.html#
I asked Mark about these specimens and he told me some amazing facts, some of
which were already published in the 2009 Bever paper on the Byronosaurus
skulls. He blew away our whole debate on DML about how the Byronosaurus skulls
IGM 100/972 and IGM 100/974 could have gotten into the nest of Citipati,
IGM/979.
It turns out that the Byronosaurus nest was collected two years after the
Citipati nest, and just two meters uphill and laterally from the famous
Citipati nest at the Xanadu sublocality of Ukhaa Tolgod. The Citipati nest was
at the end of a drainage course from the Byronosaurus one, so the troodontid
material must have tumbled down and come to rest in the depression of the lower
nest.
When we had our debate about this on DML I entertained several scenarios but at
one point I suggested that we need not resort to any explanations that included
biological interaction. By biological interaction I meant scenarios where the
Citipati fed on perinate Byronosaurus, or vice versa, nor nest parasitism. I
thought that sheer proximity of nests in a perennially occupied nesting ground
could explain how debris from one nest lands in another.
Dr. Norell is preparing to publish this information, including more important
details, but he is a darned busy guy. I thank him for sharing this preliminary
information with those of us who were dying to know.
Jason Brougham
Senior Principal Preparator
American Museum of Natural History
jaseb@amnh.org
(212) 496 3544