Allosaur baby faces

[Christopher Taylor <ck.taylor@auckland.ac.nz>]

New paper:

Rauhut, O. W. M., & R. Fechner. 2005. Early development of the facial region
in a non-avian theropod dinosaur. Proceedings of the Royal Society of London
Series B Biological Sciences 272(1568): 1179-1183.

"An isolated maxilla of the theropod dinosaur Allosaurus from the Late
Jurassic (the Kimmeridgian, 153 million years ago) of Portugal is the first
cranial remain of a non-coelurosaurian theropod hatchling reported so far,
and sheds new light on the early cranial development of non-avian theropods.
Allosaurus hatchlings seem to have been one-seventh or less of the adult
length and are thus comparable in relative size to hatchlings of large
extant crocodile species, but are unlike the relatively larger hatchlings in
coelurosaurs. The snout experienced considerable positive allometry and an
increase in tooth count during early development. The element is especially
noteworthy for the abundant and well-developed features associated with the
paranasal pneumatic system. Pneumatic structures present include all those
found in adult allosaurids and most are even more developed than in adult
skulls. Together with evidence on the ontogeny of the tympanic pneumatic
system in allosaurids, these findings demonstrate that cranial pneumaticity
developed early in theropod ontogeny. The strong development of pneumatic
features in early ontogenetic stages of non-avian theropods supports the
hypothesis that pneumatization of cranial bones was opportunistic and
indicates that heterochrony played an important role in the evolution of
craniofacial pneumaticity in this group."


    Which reminds me of another question I was thinking of asking - does
anyone know if coelurosaurs laid hard-shelled eggs like modern birds, or
leathery-shelled eggs like other reptiles? What is the earliest branch on
the avian stem that we can be sure laid a hard egg? I ask because I was
wondering if well-known stem birds such as Hesperornithiformes and
_Ichthyornis_, which are commonly (albeit perhaps mistakenly) assumed to be
biologically much the same as modern birds, can be assumed to lay a hard
egg. Considering how difficult it is to imagine _Hesperornis_ moving at all
on land, could it have even produced live young? (That last is rampant
speculation, which I don't support in any way)