Chatterjee, Sankar. (The Museum, Texas Tech University, Lubbock, TX 79409) Skull of Protoa

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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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