[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Somebody call it heads or tails, and were any dinosaurs born with their eyes still closed?

"Andy Farke" <andyfarke@hotmail.com> wrote of what might be called the
pushme-pullyou-saurus model of Ankylosaur defense:

> The picture that was posted makes me think of the tail being used as
> a decoy for the head--or at least drawing attention away from
> it. This is somewhat similar to those snakes (I can't remember the
> species) that have coloration on their "tail" that resembles the
> head. Could a similar thing be going on in ankylosaurs?

In case Honored Person Ralph Chapman hasn't already told you, you
might want to look through the dinosaur list archives.  You can start
with Ralph's own summary of a relevant paper:


> Again, this is totally speculation!

That's kind of what we said back in 1995.  In any case, I fear you've
been scooped by a good five years :-)

In totally other news, Larry Dunn <majestic_cheese@yahoo.com> asked
about altricial vs. precocial dinosaurs:

> Can we tell from fossilized eggs and fossilized hatchlings how
> dinosaurs were born?  Would this have varied among the dinosaur
> species as it does with birds?

This is actually an old topic for Jack Horner.  He's got a new review
on the subject which contains (among other statements):

   Skeletal Development 

   The degree of epiphyseal development and ossification in embryonic
   and neonatal dinosaurs has been used to hypothesize stages of
   overall development and to speculate on altricial and precocial
   post-hatching behaviors (Horner & Weishampel 1988, 1996). It was
   observed that the epiphyseal ends of the embryonic femora of the
   coelurosaur Troodon, originally misidentified as the
   hypsilophodontid Orodromeus (Horner & Weishampel 1996), consisted
   of a thick pad of calcified cartilage penetrated by an opening that
   appeared to contain a cartilage cone. In contrast, the epiphyseal
   ends of an embryonic femur hypothesized to belong to the
   hadrosaurid Maiasaura was described as having a thin calcified
   cartilage pad overlying a very spongy endochondral metaphysis. The
   ends of the Maiasaura femur were described as spongy and
   incomplete, and incapable of withstanding the rigor of locomotor
   activity. Maiasaura was hypothesized to have been altricial, or
   nest-bound, and in need of parental assistance for acquiring food
   (Horner & Weishampel 1988).  Troodon was regarded as capable of
   locomotor activities and precocial. Later discoveries of other
   non-avian dinosaur skeletons that had limb bones with incomplete
   condyles were interpreted as representing altricial young (Jacobs
   et al 1994, Chure et al 1994), and those with well-formed limbs
   were regarded as precocial (Coombs 1980, Winkler & Murry 1989). A
   compilation of data and cladistic analysis (Weishampel & Horner
   1994) of the evolution of dinosaur life histories with regard to
   mode of development suggested that several hadrosaurid taxa were

   Geist & Jones (1996) challenged the interpretation of the epiphyses
   by correctly pointing out that the reason that the neonate
   Maiasaura femora appeared incomplete was that they were missing
   their articular fibro-cartilage caps (Reid 1997). Geist & Jones
   suggested that the Maiasaura neonates (perinates) and various other
   embryonic and neonatal individuals all possessed well-ossified
   skeletons, and showed no characteristics suggestive of altricial
   behaviors. The Geist and Jones study, however, was based on
   morphological observation rather than histology. Horner (1996; see
   also Horner et al 2000a) re-examined the bones using histological
   techniques, and showed that there were major differences in
   metaphyseal development separating Maiasaura from Orodromeus and
   Troodon. Maiasaura possessed massive calcified cartilage
   pads. However, a thin calcified pad overlying endochondral bone was
   evident in both Troodon and Orodromeus. Horner (1996) and his
   colleagues (Horner et al 2000a, b) showed that the epiphyseal ends
   of the limbs of hadrosaurs possessed calcified cartilage structures
   that would have severely limited active locomotion during the time
   between hatching and when the hatchling doubled in size. Within the
   avian altricial-precocial spectrum (Stark & Ricklefs 1998b), the
   maiasaurs appear to have been semi-altricial, requiring adult care
   until they at least doubled in linear dimensions from hatching
   (Horner et al 2000a, b).

Hope that helps,

Mickey Rowe     (rowe@psych.ucsb.edu)

Ref: John R. Horner, (2000). "Dinosaur Reproduction and Parenting",
     Annu. Rev. Earth Planet. Sci. 28:19-45.

(I don't think you'll be able to read the full text on-line unless
you're at an institution like UCSB that has a subscription.)