MODELING VISUAL ABILITIES IN EXTINCT SPECIES USING VIRTUAL OPHTHALMOSCOPY, WITH A CASE STUDY IN PREDICTING EYE SIZE, OPTICAL PARAMETERS, AND VISUAL FIELDS IN TERROR BIRDS (AVES: PHORUSRHACIDAE)

TAMBUSSI, C.P.; CERIO, D.G; RIDGELY, R.; DEGRANGE, F.J.; WITMER, L.

Albuquerque

Congreso; 78th Society of Vertebrate Paleontology Annual Meeting 2018v; 2018

c78th SVP Annual Meeting 2018

All animals face competing visual perceptual challenges including food-acquisition andvigilance against predation. There has been much recent work to shed light on the visualabilities of extant species and to correlate bony dimensions of the orbit with the soft tissuesof the visual system. However, few studies have made quantitative predictions of visualabilities in extinct animals, and most of these have focused on diel activity patterns (e.g.,diurnal vs. nocturnal). Behavioral studies have commonly employed ophthalmoscopy andgeometrical optics to measure visual fields of living animals. A new method for modelingvisual fields, called Virtual Ophthalmoscopy (VO), was devised to allow the study ofattributes of the visual system in fossil birds and other dinosaurs. Eyeballs for 10 extantbird species were virtually modeled using optical schematics from the literature, and theiroptical properties and visual fields were generated in raytracing and animation software.The resulting in silico models of visual fields were validated by comparison to in vivo andex vivo measurements taken from the literature and the modeled values fell within theranges of literature values. An intriguing case-study for reconstructing the visual abilitiesof an extinct species is Llallawavis scagliai, an exceptionally well-preserved phorusrhacidthat preserves scleral rings and exemplifies the uniquely narrow bill morphology typical ofphorusrhacids. Here, we present estimates of eye size and shape for L. scagliai, and wemake quantitative predictions of the optical properties and performance of its visualsystem. A broad taxonomic survey of cadaveric birds was undertaken to identify bonycorrelates for the orientation of the eyeball within the orbit. Measurements of eyeball,scleral ring, and skull dimensions were also taken for 113 extant bird species and on L.scagliai. Phylogenetically-informed regression equations for eyeball and lens dimensionsfor L. scagliai were calculated, and an eyeball was virtually modeled and optically testedusing VO. When its eyes were converged, L. scagliai would have had a binocular field ofview between 18° and 38° wide. In addition, the tip of the bird?s bill would have fallensquarely within this binocular field, consistent with an animal that was using its beak toacquire food, a key perceptual challenge for birds. Moving forward, the success of VOpresents an opportunity to expand our ability to reconstruct the visual apparatus and makeinferences about the visual ecology of extinct organisms in deep time.