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Troodon reference



        Authors:        DJ Varricchio, F Jackson, JJ Borkowski, JR Horner
        Title:  Nest and egg clutches of the dinosaur Troodon formosus and the
evolution of avian reproductive traits
        Full source:    Nature, 1997, Vol 385, Iss 6613, pp 247-250
        KeyWords Plus:  ORNITHISCHIAN DINOSAURS
        TGA/Book No.:   WC711
        Discipline:     Multidisciplinary
        Document type:  Article
        Language:       English
        Address:        Varricchio DJ,Old Trail Museum,POB 919,Choteau,MT 59422 
USA
        ISBN/ISSN:      0028-0836
        Publisher:      Macmillan Magazines Ltd,Porters South, 4 Crinan
St,London,England N1 9XW
        Abstract:       Living archosaurs (crocodilians and birds) share several
reproductive features, including hard-shelled eggs(1), parental care(2,3),
assembly-line oviducts(4) and luteal morphology(5). Nevertheless,
crocodilians produce many small eggs that they ovulate, shell and deposit en
masse, and incubate within sediments or vegetation mounds(2,4,6), whereas
birds produce fewer but larger eggs(7), usually from a single ovary and
oviduct(3). Further, birds ovulate, shell and lay one egg at a time and
incubate eggs directly with body heat(3). New discoveries from the Upper
Cretaceous of Montana allow re-evaluation of the transition from basal
archosaurian to avian reproductive behaviour in the Coelurosauria(8,9), the
theropod pod dinosaur dade that includes birds. Egg clutches and nests (Figs
1-3) suggest that the smalt coelurosaurian Troodon formosus (weight, about
50 kg) produced two eggs simultaneously at daily or longer intervals and
incubated eggs using a combination of soil and direct body contact.
Non-avian coelurosaurians thus possess several primitive features found in
crocodilians (two functional ovaries and oviducts, lack of egg rotation and
chalazae, partial burial of eggs, precocial young) and several derived
features shared with birds (relatively larger and potentially asymmetric
eggs, one egg produced per oviduct at a time, loss of egg retention, open
nests, brooding) (Fig. 4).

Graeme Worth