Chatterjee, Sankar. (The Museum, Texas Tech University, Lubbock, TX 79409) Skull of Protoa
Chatterjee, Sankar. (The Museum, Texas Tech
University, Lubbock, TX 79409) Skull of Protoavis
and Early Evolution of Birds. Journal of
Vertebrate Paleontology, 7 (Supplement to no. 3),
16 September l987: Abstracts of Papers, 47th Annual
Meeting, Society of Vertebrate Paleontology,
October 22-24, l987.
Protoavis, the oldest known bird from the Triassic
of Texas is united with the ornithurine birds by 30
postulated cranial synapomorphies which are grouped
as follows: 1) loss of diapsid arch and postorbital
bar resulting in confluence of supra- and
infratemporal fenestrae and orbit; 2) formation of
postorbital and zygomatic processes; 3) external
naris bounded by premaxilla and nasal; 4)
streptostylic quadrate with developments of orbital
process, condylar articulation with pterygoid, and
lateral cotylus for quadratojugal; 5) loss of
postorbital and ectopterygoid, formation of jugal
bar and prokinesis; 6) highly enlarged brain,
cerebrum contacts cerebellum dorsally, displacing
optic lobes ventrally; 7) presence of all five
tympanic diverticula with the formation of
squamosal roof over the superior tympanic recess;
both ATR and STR developed contralateral
communications; 8) bony eustachian tubes; 9) bony
mandibular symphysis; mandibular elements fused
posteriorly and compressed laterally, obliterating
Meckelian canal; 10) horizontal braincase with
well-developed metotic process and cochlear recess.
Most of these ornithurine apomorphies are absent or
unknown in Archaeopteryx, indicating a basal
dichotomy in the early lineages of birds.
Archaeopteryx seems to be on a separate line from
modern birds. Protoavis is the ancestor of the
Ornithurae to which all modern birds belong.
The architectures of the brain and inner ear of
Protoavis indicate neurosensory specializations
associated with flight.
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