Optical properties, ecological differences, and Virtual Ophthalmoscopy: Morphometry of optical parameters in diapsids and a case study in restoring visual fields in terror birds (Aves: Phorusrhacidae).

CERIO DG; RIDGELY RC; DEGRANGE FJ; WITMER LM; TAMBUSSI CP

Praga

Congreso; 12 International Congress of Vertebrate Morphology; 2019

Visual fields provide inroads to quantitatively study selection pressures at the intersection of anatomy, ecology, and optics. The visual fields and optical properties of living vertebrates are commonly studied using ophthalmoscopy, which cannot be applied to extinct species. A literature search was performed to collate optical data?radius of curvature, refractive index, and visual fields?across diapsids, supplemented by new data collected from diceCT, spiceCT, and other microCT datasets of an additional 30 diapsids. Significant correlations were recovered between radii of curvature and orbit and scleral-ring dimensions, as well as between the orientations of optic axis and orbit?thus, these bony metrics constitute osteological correlates for the quantitative optical traits. An intriguing case-study for reconstructing the visual abilities of an extinct species is Llallawavis scagliai, an exceptionally well-preserved phorusrhacid that preserves scleral rings and exemplifies the uniquely narrow bill morphology typical of phorusrhacids. Here, we present estimates of eye size and shape for L. scagliai, and we make quantitative predictions of the optical properties and performance of its visual system. Phylogenetically-informed regression equations for eyeball and lens dimensions for L. scagliai were calculated, and an eyeball was virtually modeled and optically tested using Virtual Ophthalmoscopy (VO), our recently-validated modeling technique for estimating visual properties of extinct species. When its eyes were converged, L. scagliai would have had a binocular field of view between 18º and 38º wide. In addition, the tip of the bird?s bill would have fallen squarely within this binocular field, consistent with an animal that was using its beak to acquire food, a key perceptual challenge for birds. Funding: NSF IOS-1050154, 1456503 to LMW; Jurassic Foundation grant to DGC.