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Mesozoic Birds Above the Heads of Dinosaurs



Mesozoic Birds Above the Heads of Dinosaurs

Witmer, 2002. The debate on avian ancestry: Phylogeny, function and fossils.
Larry starts off this book well, with a good summary of the bird origins
debate.  Perhaps the most interesting part is his opinion of Protoavis.  He
feels the braincase is "indeed (that) of a coelurosaur", which would be
notable given its Triassic age.  Reasons include the caudal tympanic recess,
large cerebellar auricular fossa, metotic strut and vagal canal opening
leading into the occiput.  Recall Paul (2002) felt it was drepanosaurid,
though Witmer doesn't seem to consider this possibility for either the
braincase or the cervicals.  Also interesting are Witmer's observations of
Protarchaeopteryx.  He could not confirm a short frontal process of the
premaxilla, nor could he identify serrations on the teeth.  The presence of
a reversed hallux was also ambiguous, though Middleton's (2002) SVP
presentation may have implications for this.  He reaffirms Caudipteryx's
lack of a pygostyle, and says Nomingia's "is certainly not homologous" with
those in pygostylians, which I find premature.  An interesting paper he
cites is Zweers and Vanden Berge (1998), who advocated an odd avian
phylogeny.  Archaeopteryx, alvarezsaurids and enantiornithines were in one
clade, ornithomimids, Hesperornis, Ichthyornis and palaeognaths were in
another, and troodontids, Confuciusornis and neognaths were in the last.

Clark, Norell and Makovicky, 2002. Cladistic approaches to the relationships
of birds to other theropod dinosaurs.
This is very similar to Norell et al. (2001), but with a bit more
discussion.  Norell et al. (in prep.) have a troodontid nest from Ukhaa
Tolgod with small posthatchlings associated with an adult tooth.  Oddly,
they put Archaeornithoides in quotes in the heading to their section on it.
Their results are similar to others using their matrix (Norell et al., 2001;
Xu et al., 2002; Hwang et al., 2002; Hwang et al., 2002- this last is the
SVP 2002 poster).
|--+--Gorgosaurus
|  `--Tyrannosaurus
`--+--+--Harpymimus
   |  |--Pelecanimimus
   |  |--Garudimimus
   |  `--+--Struthiomimus
   |     `--Gallimimus
   `--+--Ornitholestes
      `--+--+--Alvarezsaurus
         |  `--+--Patagonykus
         |     `--+--Shuvuuia
         |        `--Mononykus
         `--+--+--+--Alxasaurus
            |  |  |--Segnosaurus
            |  |  `--Erlikosaurus
            |  `--+--+--Avimimus
            |     |  `--Chirostenotes
            |     `--+--Microvenator
            |        `--+--Caudipteryx
            |           `--+--Oviraptor
            |              |--"Rinchenia"
            |              |--Citipati sp.
            |              |--Conchoraptor
            |              `--Ingenia
            `--+--+--+--Sinovenator
               |  |  `--+--Sinornithoides
               |  |     |--Byronosaurus
               |  |     `--+--Troodon
               |  |        `--+--Saurornithoides mongoliensis
               |  |           `--Saurornithoides junior
               |  `--+--Sinornithosaurus
               |     `--+--Microraptor
               |        `--+--Unenlagia
               |           |--Velociraptor
               |           |--IGM 100/1015
               |           |--Saurornithoides
               |           |--Deinonychus
               |           |--Dromaeosaurus
               |           |--Adasaurus
               |           |--Utahraptor
               |           `--Achillobator
               `--+--Rahonavis
                  `--+--Archaeopteryx
                     `--Confuciusornis
This is credited to the then in press Hwang et al. 2002 Microraptor paper,
but the latter differs in placing Sinornithosaurus closer to Dromaeosauridae
than Microraptor.  They use proper nomenclature, except for their stem-based
Dromaeosauridae (not explicitely defined), and it's nice to see
tyrannosaurids are called coelurosaurs (contra Norell et al. 2001).  The
authors dismiss neoflightlessness rather unfairly, and do not reference
Rauhut's (1997, 2000) work when discussing affinities of Shuvosaurus.
Oddly, several key taxa are lacking in their appendix 2.1 that are among the
earliest of their lineages (eg. Beipiaosaurus, Caudipteryx, Sinovenator).
Interestingly, they have a different cladogram as figure 2.2C, which is not
explained or commented on-
|--Tyrannosauridae
`--+--+--Ornithomimosauria
   |  `--Ornitholestes
   `--+--Therizinosauroidea
      `--+--+--Protarchaeopteryx
         |  `--+--Caudipteryx
         |     `--"Oviraptorosauria"
         `--+--Dromaeosauridae (incl. Unenlagia)
            `--+--Troodontidae
               `--+--Rahonavis
                  |--Archaeopteryx
                  `--Alvarezsauridae (incl. Confuciusornis)
I'm quite intrigued by this topology, placing Ornitholestes in the
Arctometatarsalia, segnosaurs outside Oviraptorosauria+Paraves, troodontids
as avialans, and Confuciusornis inside Alvarezsauridae(?!).
Protarchaeopteryx was not an OTU in the AMNH analysis, but I've never seen
this topology anywhere else.  I wonder what it is from...

Vickers-Rich, Chiappe and Kurzanov, 2002. The enigmatic birdlike dinosaur
Avimimus portentosus: Comments and a pictorial atlas.
This is basically a collection of photographs of the specimen PIN 3907/1,
with less than three pages of text, less than one of which is new
information.  One point I have an issue with is their quoting of Norman's
(1990) statement that the retention of metatarsal V is "unusual for Late
Cretaceous theropods" when only ornithothoracines (except Vorona) and some
other pygostylians lack the element.  It's present in tyrannosaurids,
ornithomimids, alvarezsaurids, segnosaurs, oviraptorosaurs, troodontids,
dromaeosaurs, you name it.  The scapulacoracoid "appears to be from another
taxon".  Chiappe says Avimimus has no premaxillary teeth, from examination
of the specimen.  Thus, it seems Watabe et al.'s new Avimimus specimen with
them may be more primitive in that regard.  The quadrate has only two
condyles (contra Chatterjee 1995).  The small axis and single distal humeral
condyle are said to be similar to alvarezsaurids.  Open neurocentral sutures
show it was subadult.  Chiappe confirms the presence of posterior ulnar
bumps.  There is no capital ligament fossa, but the distal femoral condyles
are connected below the popliteal fossa by a transverse ridge, which is
known in ornithothoracines, but not in Rahonavis or other non-avian
dinosaurs.

Chiappe, Norell and Clark, 2002. The Cretaceous, short-armed
Alvarezsauridae: Mononykus and its kin.
This is a much needed paper, as descriptions of Shuvuuia have been very
brief up to this point.  Apparently only the holotype is known for Mononykus
(Maastrichtian Nemegt Formation), the others all being referred to Shuvuuia
(Campanian? Djadochta Formation equivalents).  The previous report of
Mononykus having one quadrate head is probably incorrect, the preserved head
being the medial one.  The braincase of Shuvuuia is said to be
"proportionately very small".  Chiappe et al. do not consider the cervical
described by Novas (1997) to be referrable to an alvarezsaurid because it
"does not show diagnostic features of other alvarezsaurids" and is "quite
different".  Shuvuuia does indeed have seven sacral vertebrae, and the
authors believe the ilial length makes this a valid estimate for
Alvarezsaurus as well.  Only the first two preserved caudals of Shuvuuia
have a ventral keel, the others are grooved.  The glenoid faced
posterolaterally in Shuvuuia.  In Shuvuuia, the metacarpus is unfused,
though the semilunate is still fused to metacarpal I.  Chiappe et al. report
that contra Sereno 2001, the ischia of Shuvuuia do not form a symphysis.
They compare the "prominent cone-shaped surface" of the lateral femoral
condyle to Bagaraatan.  An alvarezsaurid fibula from the Iren Dabasu
Formation is figured.  Mass estimates are given for Alvarezsaurus (3.507
kg), Patagonykus (4.270 kg), Mononykus (2.944 kg) and Shuvuuia (IGM 100/99;
659 g) based on femoral shaft circumference.  The last is a juvenile.  The
holotype is about the same size as Mononykus, but lacks well preserved
femora.  It's unfortunate a new skeletal reconstruction wasn't made, leaving
Sereno's (2001) and Paul's (2002) as the best available.

Novas and Pol, 2002. Alvarezsaurid relationships reconsidered.
A new phylogeny is presented based on an unpublished data matrix (including
an unknown amount of characters dating from 1998 or prior, specifically not
including Sereno's ornithomimosaur data) is presented.  Two most
parsimonious trees (309 steps; CI 0.48; RI .54) give the consensus topology
of-
|--Allosaurus
`--+--Ornitholestes
   `--+--Tyrannosauridae
      `--+--Ornithomimidae
         `--+--+--Alvarezsaurus
            |  `--+--Patagonykus
            |     `--+--Mononykus
            |        `--Parvicursor
            `--+--Therizinosauridae
               `--+--Oviraptorosauria
                  `--+--Troodontidae
                     |--Dromaeosauridae
                     `--+--Unenlagia
                        `--+--Archaeopteryx
                           `--Ornithothoraces
Only one additional step is needed to make Enigmosauria, and only two to
make alvarezsaurids arctometatarsalian.  Characters excluding alvarezsaurids
from the segnosaur + oviraptorosaur + paravian clade are- kidney-shaped
anterior articular surface of cervical centra; pronounced proximodorsal lip
on manual unguals; no supracetabular crest; postacetabular process
subvertically oriented; medial flange of ilium (brevis shelf?) strongly
reduced; pedal unguals III and IV deep with enlarged flexor tubercles.
Metornithes is supported by- caudal neural spines confined to vertebrae
1-12; semilunate carpal; posterodorsal margin of ilium ventrally curved;
pubis caudoventrally oriented compared to pubic peduncle of ilium;
proximomedial fibular fossa reduced or absent; proximal ulna with cranially
oriented notch for reception of radius and reduced ulnar proximal articular
processes; pubic peduncle of ilium anteroposteriorly narrow; short midcaudal
prezygopophyses; dorsal fossa on posterior coracoid process absent;
prominent cervicodorsal hypapophyses.
One problem is that Dromaeosauridae + Avialae is termed Maniraptora, when it
it actually Eumaniraptora.

Part 2 coming..... sometime.  Maybe this week.  I've had virtually no time
for dinosaur-related things as of late, largely due to college.

Mickey Mortimer