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Details on Protoavis :-) Part 2: Skull



At last I've found some time...

I'll skip the cranial arterial system as I can't comment it anyway. For
answering any questions I can send Fig. 5.

Superficially at least, the skull as reconstructed doesn't look like what I
know of *Megalancosaurus*. However, it was found in the form of many
fragments in the 2 different individuals.
        "The skull is relatively small and lightly built. It is 74 mm long,
38 mm wide, and 32 mm deep, as restored in the holotype (9200). It has a
relatively short snout, an enormous orbit (27 % of the skull length) to
accomodate large eyes, and an inflated temporals region for a large brain
(Table 1). The teeth are retained at the tip of the jaws, but the posterior
teeth are lost (Fig. 2a). The premaxilla bears three and the dentary has two
teeth that are small and compressed sidewise. The naris is bounded by the
premaxilla and nasal. The nasal-frontal hinge is narrow and flexible. [...]
The temporal configuration is a "fully modified diapsid" condition
(CHATTERJEE 1991) where the orbit is confluent with the upper and lower
temporal openings because of the breakdown of the postorbital-jugal and the
sqamosal-quadratojugal bars. [Better explained in the book.] The postorbital
bone is lost, and its place [sic] a postorbital process, formed jointly by
the frontal and the laterosphenoid."
        Considering the facts that *Archaeopteryx* and lots of basal birds
still have postorbitals, I'd say it is more parsimonious to assume that
*Protoavis* had a partly modified diapsid condition, with the "postorbital
process" bearing a postorbital bone and the upper temporal fenestra still
intact. From the figures I can't say whether this is possible, though.
        "The squamosal has a long, forwardly directing [sic] zygomatic
process [that may or may not have contacted a postorbital] and a separate
ventral cotyle for the reception of the quadrate head.
        In the palate, the choana has been shifted considerably backward so
that the palatal components of the maxillae and the intervening vomers
contribute to an extensive secondary palate (Fig. 3b; Pl. 4g), conforming to
the primitive avian condition (WITMER & MARTIN 1987). The vomers are long,
fused and expanded anteriorly to contact the premaxillae. Posteriorly they
are separated and meet the pterygoids. The palatine is a large and complex
bone, while the pterygoid is considerably reduced and forms the posterior
margin of the choana. The ectopterygoid is unknown and probably is absent.
The quadrate (Fig. 2b, 2c; Pls. 3h, 3i, 4d, 4e) has a single, spherical
head, a free orbital process, a ventral condylar articulation with the
pterygoid, and a lateral cotylus for the quadratojugal. It is streptostylic
to execute the prokinetic movement of the upper jaw."
        Looks persuasive in his drawings.
        "The braincase (Figs. 3c, 4a, 4b, 5a, 5b, 5c; Pls. 3f, 3g, 4a, 4b)
is inflated and shows neurosensory specialization[s] possibly associated
with balance, coordination, flight, and endothermy."
        The braincase has, if correctly identified (what I can't possibly
comment), one exit for the cranial nerve V.
        "The skull is highly pneumatized in the tympanic region where all
the middle air sinuses of birds -- anterior ( = rostral), posterior ( =
caudal), superior ( = dorsal), quadrate, and articular tympanic recesses are
present (see WITMER 1990). The basioccipital-basisphenoid complex is
extensively permeated by pneumatic cavities."
        Any pneumatization in drepanosaurids???
        "The endocast reveals a relatively large brain where the
encephalization quotient (0.41) compares well within the range of living
birds (CHATTERJEE 1991). The olfactory lobes are short and reduced, partly
because of emphasis on vision; the cerebral hemispheres are large and
expanded and show the sagittal eminence (Wulst), bordered by the vallecula.
The cerebrum contacts cerebellum dorsally to displace the large optic lobe
ventrolaterally.
        The lower jaw (Fig. 2a; Pls. 3e, 4h) is slender, tapers slightly
forward, and is very shallow for most of its length. The mandibular
symphysis is ossified, and the postdentary bones are fused. [Odd...] The
quadrate articulates with the mandible by means of three condyles [a
character of birds according to the explanation of the character matrix --
see a forthcoming post]. The external mandibular fenestra is small and
elongated and is bordered by a fossa anteriorly. The retroarticular process
is well developed. The surangular shows a lateral process for the attachment
of the postorbital ligament [for prokinesis].

4.2 Postcranial skeleton

        The postcranial elements are fairly well preserved in *Protoavis*.
In my previous paper, most of the postcranial bones from the Post quarry
were briefly mentioned (CHATTERJEE 1991, Figs. 3, 4). Since long bones were
extremely hollow and thin-walled, many of their shafts were broken and
separated, lacking exact matching ends. An attempt is made here to fit these
shafts to the corresponding bones guided by their general contour and
cross-section. In addition, excellent postcranial elements of *Protoavis*
from the Kirkpatrick quarry provide additional anatomical information. Many
of my previous [1991] identifications of postcranial elements were tentative
and require modifications with the evidence of new material."

More probably tomorrow... it's 22:52 here.

Again, I can send:

Figures are drawings, plates are photos. I'll send the abbreviations
(inhumanely placed in the appendix) with all drawings except Fig. 1.

"Fig. 1. C: composite geologic section of the Dockum Group showing the two
stratigraphic levels of *Protoavis*."
Fig. 2, 3, 4 and 5: composite restoration of skull, 2 showing the skull in
lateral view and the quadrate, 3 showing the skull in dorsal, ventral and
occipital views, 4 and 5 showing the braincase.
"Table 1. Estimated skull and jaw dimensions (in mm) of *Protoavis texensis*
(based on TTU P 9200)."
"Table 2. Vertebral counts in various theropod species". Includes lots of
birds.
"Table 3. Measurements (in mm) of vertebrae of *Protoavis texensis*."
Fig. 6: Anterior cervical vertebrae of *Protoavis texensis* and *Aquila
chrysaetos*.
Fig. 7: Posterior cervical vertebrae of *P.*.
Fig. 8: Dorsal vertebrae of *P.*.
Fig. 9: Sacral and caudal vertebrae of *P.*.
"Fig. 10. Neural canal indices of various theropod genera. Note *Protoavis*
and modern birds have much higher NCI values (>60) than the condition in
nonavian theropods."
"Table 4. Measurements (in mm) of the elements of shoulder girdles of
*Protoavis texensis*."
Fig. 11: Scapula, coracoid, furcula and sternum of *P.*, with a comparison
to the furcula of a chicken.
Fig. 12: Composite restoration of the shoulder girdle plus comparison of the
sternum to that of a chicken.
Fig. 13: Shoulder girdles of *Archaeopteryx*, *Iberomesornis* and
"Enantiornithes".
Fig. 14: Humeri.
Table 5: Measurements of arm bones.
Fig. 15: Forearm elements.
Table 6 (incorrectly labeled as 2): Measurements of elements of the right
hand.
Fig. 16: The odd hand of *P.*.
Fig. 17: Pelvis.
"Table 7. Preacetabular elongation (PE) indices of some nonavian theropods
and birds."
Fig. 18: Composite restorations of pelvic girdles of *P.*, "Enantiornithes",
a turkey and *Archaeopteryx* (still wrong with pubis pointing, say, 30°
backward).
Table 8: Measurements of pelvic elements. + Table 9: Measurements of leg
elements.
Fig. 19: Femora.
Fig. 20: Tibia, fibula and astragalocalcaneum (low ascending process, as in
figured *Alwalkeria*).
Table 1[0]: Measurements of elements of the (only known) foot.
Fig. 21: A composite restoration of a foot that cries "perching bird", plus
claw measurement studies.

**The claws look much too big for the tiny toes they supposedly sat on.**

Fig. 22: Composite skeletal restoration.
Fig. 23: Life restoration.
"Fig. 24. Lines of actions of some principal muscles of the pelvis and femur
of *Protoavis*; right lateral view."
"Table 11. Femora[sic]/tibiotarsal (FT) indices in some theropods."
"Fig. 25. Stick diagram showing the running posture of *Protoavis* [...]
Note movements of the knee, rather than femoral retraction, accounts for
most of the foot displacement."
Fig. 26: The wing in flexion and extension.
Fig. 27: Restorations of flight muscles in frontal view.
"Fig. 28. Scansorial adaptation of a hypothetical proavian maniraptoran
(similar to *Velociraptor*)"; the book says "protodromaeosaur", and in the
illustration there the skeleton lacks the large opposed hallux it has in the
article.
"Fig. 29. Evolution of avian coracoid showing the progressive transformation
of origin for M. biceps brachii and M. supracoracoideus."
"Fig. 30. Hypothetical stages for evolution of major forms of avian flight
in arboreal mode." This figure and its caption are much more detailed in the
book.
Fig. 31: Tip vortices in a proavian protodromaeosaur and *P.*. This
illustration has a modern bird for comparison in the book.
Fig. 32: Uninteresting simple cladogram of Dinosauria.
Fig. 33: Various historical cladograms of birds and their relatives:
Thulborn 1984, Gauthier 1986, Cracraft 1986, Sanz & Bonaparte 1992, Martin
1987, Chiappe & Calvo 1994, Sereno & Rao 1992, Perle et al. 1993.
Fig. 34: Skulls and temporal regions of *Archaeopteryx* (wrong -- has been
shown to have an ascending process on the jugal, ~ corrected in the book),
*Avimimus*, *Protoavis*, *Hesperornis* and *Ichthyornis*.
Fig. 35: Holotype of *Ambiortus dementjevi* as found, plus interpretations.
Fig. 36: A few bones of *Patagopteryx*.
Fig. 37: Most parsimonious cladogram that results from Table 12, a data
matrix for 84 characters and 14 taxa.
Fig. 38: The cladogram of Fig. 37 plotted with a time scale.

I have managed to scan the plates in quite good quality, but the photocopies
I scanned are not exactly perfect, and even the quality of the originals is
limited. Some at least should be good enough to enable decisions on whether
the respective bones are drepanosaurid or whatever. (I still have too look
for that paper.)

For unknown reasons, nearly all bones are figured twice next to each other.

Warning: These are monster files (1 -- 4 MB or so). Outlook Express,
respectively the server, regularly needs several attempts for sending, and
people who have slow modems, restrictions on the size of emails they can get
or whatever may run
into problems.
No viruses! :-)

Plate 1: holotype.
Plate 2: paratype.
Plate 3: 3D photos of cranial elements of the holotype.
Plate 4: same for paratype.
Plate 5: 3D photos of vertebrae.
Plate 6: same of shoulder girdle elements.
Plate 7: same of humeri.
Plate 8: same of forearm and hand elements.
Plate 9: same of pelvic and leg elements.
Plate 10: comparisons of ascending processes. Includes foot of *P.*.