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the Nyctosaurus problem(s)
One of the characters of Nyctosaurus is the presence of three wing
phalanges, not four as in all other pterosaurs. A Nebraskas specimen
worked on by Greg Brown in 1986, UNSM 93000, clearly shows this. The
terminal phalanx, number three in this ?unique case, is curved, as is
traditional in almost all other pterosaurs for phalanx four.
So what happened to the intervening phalanges? Did a phalanx get lost?
Or did two fuse?
The Kansas specimen (SMM or FHSM 11311), the infamous pseudo-crested'
specimen worked on by Bonner in 1964 and revisisted in 1972 (both prior
to Brown's work) seemed to show four distinct wing phalanges, the
Brown's text for his poster session reports: "The element reported to be
an intermediate (Bonner and Miller's 'phalanx three' of SMM 11311) is,
in actuality, the distal portion of phalanx 2 of the right wing."
If so, this would be the only distal element of the right wing
preserved. It also assumes that all nyctosaurs are Nyctosaurus.
Earlier, working on this paradigm, I reported to the DML that I thought
I saw a possible fusion of m4.2 and 4.3 in the KS nycto. This was an
error caused by impressions of underlying bones. A bit more work helped
me see all four wing phalanges as Miller reported, and yes, they all
seem to be from the same wing. Phalanx three does not taper distally.
It's more cylinder-ish, as it is in Pteranodon and other sister taxa
among the dsungaripterids and germanodactylids.
So, now it begins to become clear that the NE Nycto is more derived than
the KS Nycto in having
1. lost its rostral crest (I'm a believer in the KS rostral crest)
2. more obliquely oriented scapulae
3. a relativlely shorter wingspan/torso ratio
2. a relatively shorter forearm
2. increased the relative length of m4.1 relative to the metacarpus
3. fused m4.2 and 4.3 (both shorter relatively)
4. having a relatively longer tibia than femur ( > 8/7 )
Nyctosaurs are derived from dsungaripterids. A loss of the rostral crest
is expected. The wing phalanx proportions of the KS nycto are similar to
known dsungaripterids. However, the hind limbs are much reduced
comparatively, no doubt via neotony.
With the recognition of four wing phalanges among basal nyctosaurs, they
are no longer "virtually eliminated" from possible ancestry to
Pteranodon, as G. Brown reported.
Manual digits I-III of the dsungaripterid Noripterus are among the
smallest known, relative to the metacarpus, of all pterosaurs. They
become smaller still in nyctosaurs.
The Field Museum specimen, FMNH P 25026, appears to be intermediate in
form. The distal wing phalanges are not preserved, but the rostrum is
crestless and the tibia is relatively elongated. M4.1+4.2 extends far
beyond the elbow, much further than the KS nyctosaur but not quite as
far as the NE nyctosaur or KJ2, the super-crested nyctosaur.
In KJ2, there is a break in m4.2 (or 4.2+4.3) about halfway down the
shaft. Chris Bennett interpreted this as a mid-shaft break, but I wonder
if the break occurred near the point of fusion? To make matters a bit
more confusing, KJ2 appears to have a rather short tibia/femur ratio.
Regarding the sudden appearance of crests:
As some of you who have been following my work know, I have been a
proponent of the hypothesis that pterosaurs never dispensed with their
Longisquama-derived cranial and dorsal plumes, but incorporated these
decorations into their regime in various fashions. Some pterosaur
specimens preserve impressions of these plumes and others do not,
depending on geology. Among nyctosaurs, the Field Museum specimen
preserves impressions, and interestingly, a single soft plume rises from
the skull and divides midway forming a posterior plume. I wonder if,
like deer velvet, these soft plumes were structural precursors to the
ossified crests described for KJ1 and KJ2 by Chris Bennett. He thought
ossified crests might have developed in the second year of growth, or
might only be found in old individuals. My guess, given these prior
hypotheses, is that the ossified crests of the new nyctos represent an
ossification of something that was already present in roughly the same
visual form. Seems to be broadly similar to the situation in the sister
taxa, germanodactylids and tapejarids.