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Session Schedule & Abstracts

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Friday 1st July, 2016

Feeding 1

Room: Salon A   2:30 pm–4:00 pm

Moderator(s): Hernandez LP, O'Keefe FR
FED1-1  2:30 pm  Assessing the role of the rostrum in skull variation and feeding performance among billfishes: a 3-D Geometric Morphometric approach. Habegger M.L.*, University of South Florida; Motta P.J., University of South Florida; Lajeunesse M.J., University of South Florida; Ford J., University of South Florida; Decker S., University of South Florida
Abstract: Feeding is perhaps one of the major drivers of skull diversification and the acquisition of novel structures can amplify this diversity. However, new structures can be costly, limiting structural space and sometimes jeopardizing organismal performance. Billfish are a group of fishes characterized by the elongation of their upper jaw. This structure utilized as a feeding weapon is morphologically diverse within the group, offering a good opportunity to investigate how changes in rostrum morphology could influence skull variation. In this study we investigated the role of the rostrum and potential trade-offs in cranial architecture by the use of 3-D geometric morphometrics. Subsequent implications of rostral morphology in billfish feeding performance were also evaluated. A total of 55 digital landmarks were positioned along the skulls of five billfish species and wahoo. Warping analysis showed most of the variation to occur between swordfish and istiophorids. Swordfish had an abrupt reduction in skull dimensions and an elongation of the rostrum. Within istiophorids, most of the variation was found between blue marlin and shortbill spearfish, not only in rostrum length, but also in relative lower jaw length. Billfish species with relatively long rostrums showed relatively short lower jaws. No trade-offs were found between eye size and muscle size suggesting that the eye may be under selective pressure to remain the same. The possible implications of these results are discussed within an ecological context.

FED1-2  2:45 pm  Evolution of mysticete-like filter feeding in plesiosaurs of the austral Late Cretaceous. O'Keefe FR*, Marshall University, Huntington, WV, USA; Otero RA, Museo Nacional de Historia Natural, Santiago, Chile; Soto-Acuna S, Museo Nacional de Historia Natural, Santiago, Chile
Abstract: The marine reptiles of the Cretaceous of the southern hemisphere have puzzled paleontologists for decades. Despite abundant fossil material, basic questions of morphology and taxonomy of the austral elasmosaurs (Plesiosauria) have defied repeated analysis, largely due to the bizarre anatomy of the animals involved. Here we report a new synthesis of cranial fossils from Antarctica, Chile, and New Zealand, allowing the first confident cranial reconstruction of the entire skull of a derived member of the Aristonectinae. The cranial anatomy of Morturneria seymourensis is radically derived relative to all other plesiosaurs, possessing an unprecedented suite of dental and oral cavity adaptions. Both the upper and lower dentition form a sieving oral battery that is unique among vertebrates, yet probably functioned like baleen in straining food particles from water ejected from the oral cavity. The volume of the oral cavity is increased enormously by a posteriorly displaced jaw articulation and broad, hooped mandible. The palate is also highly vaulted, a condition unique among plesiosaurs. Several osteological correlates demonstrate the presence of a large, distensible gular pouch. This highly derived suite of adaptations is shared by extant mysticete cetaceans, and we hypothesize that it functioned in a similar manner. This is the first identification of whale-like sieve feeding in any marine reptile, a condition once claimed to be anatomically impossible. Further review of southern hemisphere elasmosaurs suggests significant taxic and trophic diversity, revealing a Late Cretaceous circumpolar marine ecosystem populated with filter-feeding plesiosaurs highly reminiscent of the mysticete whales living there today.

FED1-3  3:00 pm  Bioinspired design: A novel mechanism of filtration based on manta ray feeding . Paig-Tran EWM*, CSU Fullerton; Bolla V, CSU Fullerton; Summers AP, U Washington
Abstract: Filtering particles from fluids is ubiquitous, both in nature and in engineered systems. In particular, filter-feeding is used to capture small (20-2000 micron) food particles in a wide variety of aquatic organisms from sub-millimeter bryozoans to 12 m whale sharks. Intriguingly, mobulid fishes (mantas and devil rays) appear to use a particle filtration mechanism that is distinct from previously described systems. Mobulids are obligate ram suspension feeders who can filter particles without any noticeable clogging along their filters. We have created bioinspired physical models of manta ray filters to identify the basic hydrodynamic principles of filtration in three biologically relevant variations: smooth lobe filters, denticulate lobes, and lobes with finger-like projections. The location and form of these morphological structures suggest that they play an important role in controlling turbulence and boundary layer separation at the filter pore. We have documented a new modality of filtration in a vertebrate system, cyclonic filtration, that works in conjunction with cross-flow filtration to filter particles both larger and smaller than the filter pore size while also eliminating clogging at the filter surface.

FED1-4  3:15 pm  Ontogeny of a cypriniform filter-feeding novelty. Hernandez LP*, George Washington University; McCalley M, George Washington University; Cohen K, George Washington University
Abstract: Silver carp, as well as a number of other Asian carp, have garnered recent interest as invasive species well-established within several American rivers and threatening to enter the Great Lakes. Part of the reason for their success has been their capacity to feed so efficiently within eutrophic environments. While previous research has described the structure and function of the epibranchial organ (a snail-shaped structure comprised of highly modified branchial arches used to concentrate material filtered from the water column) other aspects of their feeding anatomy have been ignored. Although concentration of phytoplankton is important for efficient feeding, the actual filtration mechanism at the level of the gill rakers has not been investigated within a functional context. This is a particularly glaring omission given that silver carp possess highly derived gill rakers that interdigitate with extended ventral folds of the palatal organ. The palatal organ is an important structure located on the dorsal pharyngeal roof. Previous work has shown that it is important in a specialized type of feeding that characterizes goldfish and carp, in which particulate matter is captured by localized protrusion of this muscular structure. Recent work in our lab has revealed that the overwhelming majority of cypriniform species examined have a muscular palatal organ, however the specialized nature of the palatal organ of the silver carp rivals anything previously described. It has been suggested that the large palatal organ is simply used as a piston pump to drive water through the gill rakers. Given the complex muscular architecture of each palatal fold this proposed mechanism seems overly simplistic.

FED1-5  3:30 pm  Forelimb morphology determines prey processing style in pinnipeds (Mammalia, Carnivora). Hocking D.P.*, Monash University; Fitzgerald E.M.G., Museum Victoria; Evans A.R., Monash University
Abstract: Living pinnipeds show a range of forelimb morphologies that reflect their method of aquatic locomotion. Otariids (fur seals and sea lions) have hydrofoil-shaped forelimbs used to propel themselves underwater, whereas many phocids (true seals) have less aquatic-specialised forelimbs with dexterous digits and robust claws, and accordingly rely on their hind limbs to generate propulsion. In terrestrial and semi-aquatic mammals, the forelimbs frequently play an important role in feeding behaviour. We aimed to discover whether, and to what degree, pinnipeds use forelimbs to deal with prey. We investigated skeletal and muscular forelimb anatomy using skeletal specimens, dissections and MRI/CT scans. We then related morphology to foraging behaviours observed during field observations and captive feeding trials, as well as data from the literature. We found marked differences in prey processing behaviour that correlate with forelimb anatomy. Phocine seals, which have the least modification of forelimbs relative to their ancestral (i.e. terrestrial) condition, resemble smaller, semi-aquatic mammals in securing prey in their clawed forelimbs while tearing off pieces using their teeth. By contrast, most otariids do not use their forelimbs and instead process large prey by holding it in their teeth and shaking it at the surface, breaking it into swallowable pieces. There is also a trend among monachine phocids away from clawed forelimbs and towards more “otariid-like” flippers (including leopard seals), apparently with similar functional limitations. Overall, living pinnipeds demonstrate the morphological transition from clawed, dexterous forelimbs to the more derived, flipper-like anatomy considered typical of marine mammals. The link between pinniped forelimb morphology and other aspects of their biology may plausibly extend to fossil species, and thus provide new insights into how and when their ancestors adapted to life in the sea.

FED1-6  3:45 pm  Independent transitions to a more goose-like beak in waterfowl (Aves: Anseriformes) correlate with a performance trade-off between terrestrial and aquatic feeding. Olsen A.M.*, University of Chicago
Abstract: The evolution of beak shapes in birds to match a particular diet is a classic example of adaptation. Yet, the correlation between beak shape and diet has been tested in relatively few groups. Additionally, in most cases the precise relationship between beak morphology and feeding function remains unclear. The bird order Anseriformes, which includes ducks and geese, is an ideal group in which to test the relationship between beak structure and function: waterfowl exhibit diverse beak shapes and their diets are among the best documented of any bird order. I collected data on 3D beak curvature from museum specimens representing 49 species in Anseriformes (including two extinct forms) and 13 species in Galliformes, the sister group to Anseriformes, using a recently published stereo camera method. For 43 of these species I also compiled diet data from the literature, classifying each dietary entry to create several continuous characters representing dietary composition (proportion animal, seeds, herbivory, terrestrial, etc.). Geometric morphometric analysis reveals that the major axis of shape variation describes convex ("goose"-like) versus concave ("duck"-like) curvature of both the culmen (upper ridge) and tomium (biting edge) of the beak. Additionally, models of trait evolution show independent transitions toward a more goose-like beak from a more duck-like beak. Of all the dietary characters, the major axis of shape variation correlates most strongly with whether food items are acquired in an aquatic or terrestrial environment. This parallels a previously described performance trade-off in waterfowl between filter-feeding (aquatic) and grazing (terrestrial), strengthening the argument that a more convex culmen and tomium represent adaptations to grazing. The results of this study additionally raise the possibility that performance trade-offs may be a principal driver of major axes of shape variation in functional systems more generally.

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