New Moa Studies (J. Morph, Nature, and PNAS)

["Jaime A. Headden" <qilongia@yahoo.com>]

  Turvey, S. T., O. R. Green, and R. N. Holdaway. 2005. _Nature_ 435:940-943.

Abstract:
  "Cyclical growth marks in cortical bone, deposited before attainment of adult
   body size, reflect osteogenetic changes caused by annual rhythms and are a
   general phenomenon in non-avian ectothermic and endothermic tetrapods.
   However, the growth periods of ornithurines (the theropod group including
all
   modern birds) are usually apomorphically shortened to less than a year so
   annual growth marks are almost unknown in this group. Here we show that
   cortical growth marks are frequent in long bones of New Zealand's moa (Aves:
   Dinornithiformes), a recently extinct ratite order. Moa showed the
   exaggerated K-selected life-history strategy formerly common in the New
   Zealand avifauna, and in some instances took almost a decade to attain
   skeletal maturity. This indicates that reproductive maturity in moa was
   extremely delayed relative to all extant birds. The two presently recognized
   moa families (Dinornithidae and Emeidae) also showed different postnatal
   growth rates, which were associated with their relative differences in body
   size. Both species of giant *Dinornis* moa attained their massive stature
(up
   to 240 kg live mass) by accelerating their juvenile growth rate compared to
   the smaller emeid moa species, rather than by extending the skeletal growth
   period."

  The authors cite *Diatryma* as a gruiform, referencing de Ricqlés, Padian and
Horner (2001, Ostrom Symposium volume) and Starck and Chinsamy (2002, _Journal
of Morphology_ 254) in connection with the cortical bone growth patterns.

  While one specimen of *Pachyornis* shows a divergent cortical bone structure,
emeid and dinornithids acheived different strategies for attaining adult
growth, one by accelerating, the other by arresting juvenile growth. A previous
paper (Baker et al., 2005) used nuclear DNA amplification to determine species
integrity in specimen referral, but the sampling of specimens here does not
seem to be impacted by that study.

  Baker, A. J., L. J. Huynen, O. Haddrath, C. D. Millar, and D. M. Lambert.
    2005. Reconstructing the tempo and mode of evolution in an extinct clade of
    birds with ancient DNA: The giant moas of New Zealand. _Proceeding of the
    National Academy of Sciences_ 102(23):8257-8262.

Abstract:
  "The tempo and mode of evolution of the extinct giant moas of New Zealand
   remain obscure because the number of lineages and their divergence times
   cannot be estimated reliably by using fossil bone characters only. We
   therefore extracted ancient DNA from 125 specimens and genetically typed
them
   for a 658-bp mtDNA control region sequence. The sequences detected 14
   monophyletic lineages, 9 of which correspond to currently recognized
species.
   One of the newly detected lineages was a genetically divergent form of
   *Megalapteryx* originally described as a separate species, two more were
   lineages of *Pachyornis* in southern and northeastern New Zealand, and two
   were basal lineages of South Island *Dinornis*. When results from genetic
   typing and previous molecular sexing were combined, at least 33.6% of the
   specimens were incorrectly classified. We used longer sequences of the
   control region and nine other mtDNA genes totaling 2,814 base pairs to
derive
   a strongly supported phylogeny of the 14 moa lineages. Molecular dating
   estimated the most recent common ancestor of moas existed after the
Oligocene
   drowning of New Zealand. However, a cycle of lineage-splitting occurred
   {approx}4?10 million years ago, when the landmass was fragmented by tectonic
   and mountain-building events and general cooling of the climate. These
events
   resulted in the geographic isolation of lineages and ecological
   specialization. The spectacular radiation of moa lineages involved
   significant changes in body size, shape, and mass and provides another
   example of the general influence of large-scale paleoenvironmental changes
on
   vertebrate evolutionary history."

  The phylogenetic results from that study is graphically represented here:
 
http://masseynews.massey.ac.nz/2005/Massey_News/issue-09/images/moa-graphic-2.jpg

  Turvey, S. T. and R. N. Holdaway. 2005. Postnatal ontogeny, population
structure, and extinction of the giant moa Dinornis. _Journal of Morphology_
265(1):70-86.

  "Recent reinterpretation of the giant moa *Dinornis* as consisting of two
   sexually dimorphic allospecies permits thorough site-by-site investigation
of
   the ontogeny and population biology of this genus. Analysis of subadult
   skeletal material from natural swamp sites in the North and South Islands of
   New Zealand forms the basis for recognition of growth series for each long
   bone element, characterized by sequential formation of fossulae in the femur
   and fusion of bones in the tibiotarsus and tarsometatarsus. Femora reached
   progressive developmental stages more rapidly than the other long bones, but
   all three elements reached maturity at about the same time. Patterns of bone
   fusion in *Dinornis* are more similar to those in Apteryx than in
*Struthio*,
   and kiwi are recognized as a suitable developmental analog for interpreting
   moa ontogeny. Samples from Bell Hill Vineyard Swamp (South Island) and
   Makirikiri swamp (North Island) are interpreted as representing
autochthonous
   moa populations; comparison with stages of kiwi long bone development
   suggests that Dinornis at these sites had high adult survivorship in
strongly
   K-selected populations, with 72.5-87.3% of individuals having achieved adult
   body mass, and 55.9-78.2% being sexually mature. The pattern of low
fecundity
   and probable high longevity in both Dinornis species suggests that
   populations were vulnerable to loss of adults, primarily through hunting,
   rather than as a result of habitat destruction."

  Cheers,

Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

"Human beings, who are almost unique in having the ability to learn from the 
experience of others, are also remarkable for their apparent disinclination to 
do so." --- Douglas Adams

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