[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Big = Old = Advanced?
At 05:39 PM 8/31/97 -0400, John Bois wrote:
>I think we can make informed guesses from extant species. Emus, and
>ostriches would seem to be germane at something like 7 weeks. Bigger
>species would take longer of course. And then there is the laying period
>which also can take time.
Most birds lay one egg a day; of course this differs from reptiles such as
sea turtles which lay the entire clutch at once. Perhaps one advantage of
having a nest to which one returns regularly is that more time can be taken
in the laying process, allowing for larger eggs in the oviduct (yes, you
could turn this around too and say that such a laying process requires
According to the Handbook of the Birds of the World, an ostrich egg is only
1.5% of its body mass (as opposed to 25% in some hummingbirds). I suspect
the ratio is still smaller for many dinosaurs. Most birds, by the way, can
replace an entire clutch if the first is destroyed.
Ostrich eggs hatch some six weeks after the first egg is laid, all hatching
simultaneously (so some delay hatching, apparently until stimulated by
calls from the mother and other hatchlings). They reach adult size within
IHorner goes even farther saying that it is
>practically suicidal for hatchlings to be untended. If this is true, I
>have not too much of an idea why turtles (as untended as they are) don't
>seem to have a problem with this.
I think Horner's comment overlooks crypticity. Turtles, of course, bury
their eggs, and many hatchling birds (and eggs) are cryptically-coloured
and can be extremely difficult to spot. Of course larger animals have more
trouble with this - but many deer habitually leave their fawns untended for
long periods, while the fawns "lie up" concealed in vegetation and relying,
probably, to some degree on their spotted coats to make them harder to
spot. It would not surprise me if young dinosaurs, or some species at
least, may have also had patterns of spots or stripes that aided in their
concealment (as, say, ostrich chicks do today).
>W.P. Coombs Jr. in _Modern Analogues for dinosaur nesting and parental
>behavior_ Geological Society of America, Special Paper 238 1989, says that
>there is a hole-nesting megapode in which both parents are completely
>absent--you may well have more recent information.
You are correct, except that burrows, not "holes", are used and there are
several such species. Relying on the Handbook of the Birds of the World
again: megapodes use five breeding systems depending on species:
mound-building, mound parasitism, and burrow-nesting using geothermal
sites, solar-heated beaches or decaying tree roots. In mound-builders
males invest a great deal of time in tending the mound prior to hatching.
Burrow-nesters are unable to regulate the temperature of the brood chamber,
and indeed abandon the site after the egg is laid. The mound-builders
include the Mallee Fowl of Australia; burrow-nesters include the Maleo of
Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2 mailto:email@example.com