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RE: they keep on growing despite early fusion
Thanks for your thoughts, John.
re: squamates. Anybody can discover what I did, just by plugging in taxa. In
fact, Benton 1985 nested pterosaurs next to lepidosaurs and far from archosaurs
in the only published cladogram that had all three taxa included.
So, I'm not the first. But I don't think Benton realized his coup because he
dropped lepidosaurs from all subsequent studies.
>From: John Scanlon <email@example.com>
>Sent: Jan 24, 2008 6:46 PM
>To: 'David Peters' <firstname.lastname@example.org>, 'Dinosaur Mailing List'
>Subject: RE: they keep on growing despite early fusion
>It isn't all that surprising that this happens in the limbs, considering
>that vertebral arches also fuse to each other and the centrum in early
>ontogeny of (at least) all squamates. Growth occurs through remodeling at
>the bone surface (external and internal), and snakes lack separate epiphyses
>at all stages of ontogeny. Of course, David is the only person in the world
>who thinks that squamates are especially relevant to pterosaurs, but they do
>show that caution is indeed required more generally.
>Dr John D. Scanlon, FCD
>Riversleigh Fossil Centre, Outback at Isa
>From: David Peters [mailto:email@example.com]
>Sent: 24 January, 2008 4:44 AM
>To: Dinosaur Mailing List
>Subject: they keep on growing despite early fusion
>Was wondering if anyone has any thoughts on this?
>In a nutshell, Jessica Maisano found early fusion of many skeletal
>elements, yet major growth continued in certain squamates.
>It has the potential to put a cautionary note on putative size-
>independent criteria for determining maturity in fossil squamates
>(including pterosaurs & their kin).
>JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 22, NO. 2, 2002
>TERMINAL FUSIONS OF SKELETAL ELEMENTS AS INDICATORS OF
>MATURITY IN SQUAMATES
>JESSICA ANDERSON MAISANO*
>Department of Geology and Geophysics, Yale University, New Haven,
>ABSTRACT-Terminal fusions-fusions of skeletal elements thought to
>mark the cessation of significant growth-
>can be used to estimate the relative maturity of fossilized
>individuals. Little is known of how the absolute timing of
>terminal fusions relates to sexual and skeletal maturity in
>squamates. Examination of postnatal ontogenetic series of
>extant representatives of 14 crown squamate clades reveals that no
>terminal fusion universally coincides with the
>achievement of either sexually or skeletally mature size; however,
>certain fusions may serve as benchmarks of maturity
>within particular crown clades. Complete fusion of the braincase is a
>reliable benchmark for skeletal maturity in
>scleroglossans, but not iguanians. Complete fusion of long bone
>epiphyses will indicate that a squamate individual is
>within roughly 20% of maximum size, whereas complete fusion of the
>scapula and coracoid, the pelvis, and the
>astragalus and calcaneum can be taken as evidence only that an
>individual has achieved at least half of the maximum
>size of its species.
>and from near the end of the text:
>Because terminal fusions are thought to mark the cessation
>of significant growth, it is difficult to understand how individuals
>could continue to grow after such fusions are complete.
>This is especially true of the fusion of the long bone epiphyses,
>which may reach completion in individuals that are only 63%
>of the maximum reported size for their species (Callisaurus).
>It may very well be that these individuals have achieved their
>personal maximum size, and this could be tested via longitudinal
>allometric studies employing X-radiography. However,
>even a considerable range in individual maximum size cannot
>account for the extreme case presented by Bipes. In neonates
>of this fossorial species, the braincase, scapulocoracoid, and
>vertebral elements are already fused, yet Bipes almost triples in
>length-from 90 to 240 mm SVL-during postnatal ontogeny.
>How Bipes accomplishes this is unknown, but clearly, ''terminal''
>fusions cannot be taken as de facto evidence that an individual
>squamate has stopped growing. Only by continuing to
>examine the timing of terminal fusions in extant taxa-especially
>via more longitudinal studies of individual ontogenies-
>will we gain a better understanding of their relationship to
>growth, and thus be able to more rigorously utilize them in the
>interpretation of fossil individuals.