Metabolic Expenditures of Lunge Feeding Rorquals Across Scale: Implications for the Evolution of Filter Feeding and the Limits to Maximum Body Size

Bulk-filter feeding is an energetically efficient strategy for resource acquisition and assimilation, and facilitates the maintenance of extreme body size as exemplified by baleen whales (Mysticeti) and multiple lineages of bony and cartilaginous fishes. Among mysticetes, rorqual whales (Balaenopteridae) exhibit an intermittent ram filter feeding mode, lunge feeding, which requires the abandonment of body-streamlining in favor of a high-drag, mouth-open configuration aimed at engulfing a very large amount of prey-laden water. Particularly while lunge feeding on krill (the most widespread prey preference among rorquals), the effort required during engulfment involve short bouts of high-intensity muscle activity that demand high metabolic output. We used computational modeling together with morphological and kinematic data on humpback (Megaptera noveaangliae), fin (Balaenoptera physalus), blue (Balaenoptera musculus) and minke (Balaenoptera acutorostrata) whales to estimate engulfment power output in comparison with standard metrics of metabolic rate. The simulations reveal that engulfment metabolism increases across the full body size of the larger rorqual species to nearly 50 times the basal metabolic rate of terrestrial mammals of the same body mass. Moreover, they suggest that the metabolism of the largest body sizes runs with significant oxygen deficits during mouth opening, namely, 20% over maximum at the size of the largest blue whales, thus requiring significant contributions from anaerobic catabolism during a lunge and significant recovery after a lunge. Our analyses show that engulfment metabolism is also significantly lower for smaller adults, typically one-tenth to one-half . These results not only point to a physiological limit on maximum body size in this lineage, but also have major implications for the ontogeny of extant rorquals as well as the evolutionary pathways used by ancestral toothed whales to transition from hunting individual prey items to filter feeding on prey aggregations.     

Underwater acrobatics by the world's largest predator: 360° rolling manoeuvres by lunge-feeding blue whales

The extreme body size of blue whales requires a high energy intake and therefore demands efficient foraging strategies. As an obligate lunge feeder on aggregations of small zooplankton, blue whales engulf a large volume of prey-laden water in a single, rapid gulp. The efficiency of this feeding mechanism is strongly dependent on the amount of prey that can be captured during each lunge, yet food resources tend to be patchily distributed in both space and time. Here, we measured the three-dimensional kinematics and foraging behaviour of blue whales feeding on krill, using suction-cup attached multi-sensor tags. Our analyses revealed 360° rolling lunge-feeding manoeuvres that reorient the body and position the lower jaws so that a krill patch can be engulfed with the whale''s body inverted. We also recorded these rolling behaviours when whales were in a searching mode in between lunges, suggesting that this behaviour also enables the whale to visually process the prey field and maximize foraging efficiency by surveying for the densest prey aggregations. These results reveal the complex manoeuvrability that is required for large rorqual whales to exploit prey patches and highlight the need to fully understand the three-dimensional interactions between predator and prey in the natural environment.     

Mandible allometry in extant and fossil Balaenopteridae (Cetacea: Mammalia): the largest vertebrate skeletal element and its role in rorqual lunge feeding

Rorqual whales (crown Balaenopteridae) are unique among aquatic vertebrates in their ability to lunge feed. During a single lunge, rorquals rapidly engulf a large volume of prey‐laden water at high speed, which they then filter to capture suspended prey. Engulfment biomechanics are mostly governed by the coordinated opening and closing of the mandibles at large gape angles, which differentially exposes the floor of the oral cavity to oncoming flow. The mouth area in rorquals is delimited by unfused bony mandibles that form kinetic linkages to each other and with the skull. The relative scale and morphology of these skeletal elements have profound consequences for the energetic efficiency of foraging in these gigantic predators. Here, we performed a morphometric study of rorqual mandibles using a data set derived from a survey of museum specimens. Across adult specimens of extant balaenopterids, mandibles range in size from ～1–6 m in length, and at their upper limit they represent the single largest osteological element of any vertebrate, living or extinct. Our analyses determined that rorqual mandibles exhibit positive allometry, whereby the relative size of these mandibles becomes greater with increasing body size. These robust scaling relationships allowed us to predict mandible length for fragmentary remains (e.g. incomplete and/or fossil specimens), as we demonstrated for two partial mandibles from the latest Miocene of California, USA, and for mandibles from previously described fossil balaenopterids. Furthermore, we showed the allometry of mandible length to body size in extant mysticetes, which hints at fundamental developmental constraints in mysticetes despite their ecomorphological differences in feeding styles. Lastly, we outlined how our findings can be used to test hypotheses about the antiquity and evolution of lunge feeding. © 2012 The Linnean Society of London     

Multiaxial movements at the minke whale temporomandibular joint

Mandibular mobility accompanying gape change in Northern and Antarctic minke whales was investigated by manipulating jaws of carcasses, recording jaw movements via digital instruments (inclinometers, accelerometers, and goniometers), and examining osteological and soft tissue movements via computed tomography (CT)-scans. We investigated longitudinal (α) rotation of the mandible and mediolateral displacement at the symphysis (Ω₁) and temporomandibular joint (Ω₂) as the mouth opened (Δ). Results indicated three phases of jaw opening. In the first phase, as gape increased from zero to 8°, there was slight (<1°) α and Ω rotation. As gape increased between 20 and 30°, the mandibles rotated slightly laterally (Mean 3°), the posterior condyles were slightly medially displaced (Mean 4°), and the anterior ends at the symphysis were laterally displaced (Mean 3°). In the third phase of jaw opening, from 30° to full (≥90°) gape, these motions reversed: mandibles rotated medially (Mean 29°), condyles were laterally displaced (Mean 14°), and symphyseal ends were medially displaced (Mean 1°). Movements were observed during jaw manipulation and analyzed with CT-images that confirmed quantitative inclinometer/accelerometer data, including the unstable intermediate (Phase 2) position. Together these shifting movements maintain a constant distance for adductor muscles stretched between the skull's temporal fossa and mandible's coronoid process. Mandibular rotation enlarges the buccal cavity's volume as much as 36%, likely to improve prey capture in rorqual lunge feeding; it may strengthen and stabilize jaw opening or closure, perhaps via a simple locking or unlocking mechanism. Rotated lips may brace baleen racks during filtration. Mandibular movements may serve a proprioceptive mechanosensory function, perhaps via the symphyseal organ, to guide prey engulfment and water expulsion for filtration.     

New views of humpback whale flow dynamics and oral morphology during prey engulfment

The rise of inexpensive, user‐friendly cameras and editing software promises to revolutionize data collection with minimal disturbance to marine mammals. Video sequences recorded by aerial drones and GoPro cameras provided close‐up views and unique perspectives of humpback whales engulfing juvenile salmon at or just below the water surface in Southeast Alaska and Prince William Sound. Although humpback feeding is famous for its flexibility, several stereotyped events were noted in the 47 lunges we analyzed. Engulfment was rapid (mean 2.07 s), and the entrance through which the tongue inverts into the ventral pouch was seen as water rushes in. Cranial elevation was a major contributor to gape, and pouch contraction sometimes began before full gape closure, with reverberating waves indicating rebounding flow of water within the expanded pouch. Expulsion of filtered water began with a small splash at the anterior of the mouth, followed by sustained excurrent flow in the mouth's central or posterior regions. Apart from a splash of rebounding water, water within the mouth was surprisingly turbulence‐free during engulfment, but submersion of the whale's head created visible surface whirlpools and vortices which may aggregate prey for subsequent engulfment.     

Rorqual whale (Balaenopteridae) surface lunge‐feeding behaviors: Standardized classification,repertoire diversity,and evolutionary analyses

Rorqual whales (Family: Balaenopteridae) are the world's largest predators and sometimes feed near or at the sea surface on small schooling prey. Most rorquals capture prey using a behavioral process known as lunge‐feeding that, when occurring at the surface, often exposes the mouth and head above the water. New technology has recently improved historical misconceptions about the natural variation in rorqual lunge‐feeding behavior yet missing from the literature is a dedicated study of the identification, use, and evolution of these behaviors when used to capture prey at the surface. Here we present results from a long‐term investigation of three rorqual whale species (minke whale, Balaenoptera acutorostrata; fin whale, B. physalus; and blue whale, B. musculus) that helped us develop a standardized classification system of surface lunge‐feeding (SLF) behaviors. We then tested for differences in frequency of these behaviors among the three species and across all rorqual species. Our results: (1) propose a unified classification system of six homologous SLF behaviors used by all living rorqual whale species; (2) demonstrate statistically significant differences in the frequency of each behavior by minke, fin, and blue whales; and (3) provide new information regarding the evolution of lunge‐feeding behaviors among rorqual whales.     

Effects of ram speed on prey capture kinematics of juvenile Indo-Pacific tarpon,Megalops cyprinoides

We examined the effects of variation in swimming speed, or ‘ram speed’, on the feeding kinematics of juvenile Indo-Pacific tarpon, Megalops cyprinoides. Tarpon were filmed feeding on non-elusive prey at 500 images s^?1. Prey items were offered at one end of the filming tank, the opposite end where tarpon grouped, to encourage them to use a ram strategy to capture their prey. We describe tarpon as ram-suction feeders. Ram speed varied among strikes from 0.19 to 1.38 m/s and each individual produced speeds that spanned at least 0.9 m/s across trials. Although suction distances were much less variable, prey movement towards the predator was present in all feeding trials. There was a strong positive relationship between initial predator – prey distance and ram speed (r²=0.72, P<0.001). When tarpon initiated their strike from further away, they achieved higher ram speeds, but also took longer to capture their prey. All other timing variables were unaffected by ram speed whereas at higher ram speeds tarpon exhibited greater expansion of the mouth and buccal cavity. Greater buccal expansion accomplished in the same period of time implies that both the total volume of water captured and the water flow rate entering the mouth was greater in strikes at higher ram speeds. Our results demonstrate how feeding kinematics may vary as a function of ram speed, and how fish predators that lack jaw protrusion and have a large gape capacity can maximize their feeding success by altering their swimming speed.     

Osteology,myology and feeding mechanism of Astronotus ocellatus (Pisces,Perciformes)

Summary Astronotus ocellatus captures its prey by creating a negative pressure in the buccal cavity which is caused by its quick expansion. Once the prey has been accommodated, the buccal cavity undergoes a compression which may propel the prey towards the pharyngeal jaws for mastication. The motion picture recordings indicate retracted premaxillae at the beginning of food intake followed by a maximum attainment of mouth gape and then mastication. During the maximum opening of the mouth the premaxillae are protruded and dentaries are at maximum depression. These events are followed by activities such as buccopharyngeal cavity expansion, bulging on the ventral surface of the head, and prominent curvature on the ventral surface anterior to the urohyal, caused by the upward movement of the glossohyal. Based on the cinematographic results, it may be inferred that the maximum mouth gape is caused by the sternohyoid-hyoid-interopercular-mandible coupling, and not by the opercular apparatus-mandible coupling, as the latter acts after the full descent of the lower jaw. Impression of the expanded buccopharyngeal cavity has been made by a paraffin mold technique, which confirms the displacement of the buccopharyngeal elements during expansion of the cavity.     

A KINEMATIC STUDY OF SUCTION FEEDING AND ASSOCIATED BEHAVIOR IN THE LONG-FINNED PILOT WHALE, GLOBICEPHALA MELAS (TRAILL)

Analysis of videotaped feeding sequences provides novel documentation of suction feeding in captive juvenile long-finned pilot whales ( Globicephala melas ). Swimming and stationary whales were videotaped while feeding at the surface, mid-water, and bottom. The ingestion sequence includes a preparatory phase with partial gape followed by jaw opening and rapid hyoid depression to suck in prey at a mean distance of 14 cm (duration 90 msec), although prey were taken from much greater distances. Depression and retraction of the large, piston-like tongue generate negative intraoral pressures for prey capture and ingestion. Food was normally ingested without grasping by teeth yet was manipulated with lingual, hyoid, and mandibular movement for realignment; suction was then used to transport prey into the oropharynx. Whales frequently rolled or inverted before taking prey, presumably to avoid grasping and repositioning. Prey were sucked off the bottom or sides of the pool without direct contact; lateral suction was used to ingest items from the sides of the mouth.     

Morphology and function of the feeding apparatus of the lungfish, Lepidosiren paradoxa (Dipnoi)

The feeding mechanism of the South American lungfish, Lepidosiren paradoxa retains many primitive teleostome characteristics. In particular, the process of initial prey capture shares four salient functional features with other primitive vertebrates: 1) prey capture by suction feeding, 2) cranial elevation at the cranio-vertebral joint during the mouth opening phase of the strike, 3) the hyoid apparatus plays a major role in mediating expansion of the oral cavity and is one biomechanical pathway involved in depressing the mandible, and 4) peak hyoid excursion occurs after maximum gape is achieved. Lepidosiren also possesses four key morphological and functional specializations of the feeding mechanism: 1) tooth plates, 2) an enlarged cranial rib serving as a site for the origin of muscles depressing the hyoid apparatus, 3) a depressor mandibulae muscle, apparently not homologous to that of amphibians, and 4) a complex sequence of manipulation and chewing of prey in the oral cavity prior to swallowing. The depressor mandibulae is always active during mouth opening, in contrast to some previous suggestions. Chewing cycles include alternating adduction and transport phases. Between each adduction, food may be transported in or out of the buccal cavity to position it between the tooth plates. The depressor mandibulae muscle is active in a double-burst pattern during chewing, with the larger second burst serving to open the mouth during prey transport. Swallowing is characterized by prolonged activity in the hyoid constrictor musculature and the geniothoracicus. Lepidosiren uses hydraulic transport achieved by movements of the hyoid apparatus to position prey within the oral cavity. This function is analogous to that of the tongue in many tetrapods.     

Feeding strategy of the megamouth shark Megachasma pelagios (Lamniformes: Megachasmidae)

The feeding biology of the planktivorous megamouth shark Megachasma pelagios was investigated. Morphological examination disclosed that the megamouth has a suite of unique characteristics among sharks, such as large mouth, large bucco-pharyngeal cavity, elongate jaw cartilages, long palatoquadrate levator and preorbital muscles, long ethmopalatine ligament and elastic skin around the pharynx. The combination of these characters suggests that the megamouth shark performs engulfment feeding that is typically seen in the rorqual and humpback whales. Engulfment is a new feeding method for sharks, and the detailed mechanism of the engulfment feeding is discussed.     

The scaling of locomotor performance in predator-prey encounters: from fish to killer whales.

During predator-prey encounters, a high locomotor performance in unsteady manoeuvres (i.e. acceleration, turning) is desirable for both predators and prey. While speed increases with size in fish and other aquatic vertebrates in continuous swimming, the speed achieved within a given time, a relevant parameter in predator-prey encounters, is size independent. In addition, most parameters indicating high performance in unsteady swimming decrease with size. Both theoretical considerations and data on acceleration suggest a decrease with body size. Small turning radii and high turning rates are indices of maneuverability in space and in time, respectively. Maneuverability decreases with body length, as minimum turning radii and maximum turning rates increase and decrease with body length, respectively. In addition, the scaling of linear performance in fish locomotion may be modulated by turning behaviour, which is an essential component of the escape response. In angelfish, for example, the speed of large fish is inversely related to their turning angle, i.e. fish escaping at large turning angles show lower speed than fish escaping at small turning angles. The scaling of unsteady locomotor performance makes it difficult for large aquatic vertebrates to capture elusive prey by using whole-body attacks, since the overall maneuverability and acceleration of small prey is likely to be superior to that of large predators. Feeding strategies in vertebrate predators can be related to the predator-prey length ratios. At prey-predator ratios higher than approximately 10(-2), vertebrate predators are particulate feeders, while at smaller ratios, they tend to be filter feeders. At intermediate ratios, large aquatic predators may use a variety of feeding methods that aid, or do not involve, whole body attacks. Among these are bubble curtains used by humpback whales to trap fish schools, and tail-slapping of fish by delphinids. Tail slapping by killer whales is discussed as an example of these strategies. The speed and acceleration achieved by the flukes of killer whales during tail slaps are higher and comparable, respectively, to those that can be expected in their prey, making tail-slapping an effective predator behaviour.     

Feeding with speed: prey capture evolution in cichilds

The diversity of both the locomotor and feeding systems in fish is extensive, although little is known about the integrated evolution of the two systems. Virtually, all fish swim to ingest prey and all open their buccal cavity during prey capture, but the relationship between these two ubiquitous components of fish feeding strikes is unknown. We predicted that there should be a positive correlation between ram speed (RS) and maximum gape (MG) because the accuracy of a predatory strike goes down with an increase in RS and fish with larger mouths eat larger, more evasive prey. For 18 species of neotropical cichlids, we used phylogenetic-independent contrasts to study the relationship between the predator closing speed (RS) and mouth size (MG) during prey capture. To provide a robust comparative framework, we augmented existing phylogenetic information available from the mitochondrial cytochrome b gene with sequences from the S7 nuclear ribosomal intron for these species. Then, we captured high-speed (500 images per second), lateral view feeding sequences of each species by using a digital video camera and measured both RS and MG. Uncorrected species values of MG and RS were positively and significantly correlated. When accounting for any of the set of phylogenetic relationships recovered, the independent contrasts of RS and MG remained significantly, and positively, correlated. This tight evolutionary coupling highlights what is likely a common relationship between locomotor behaviour and feeding kinematics in many organisms.     

Predicting patterns of prey use from morphology of fishes

Synopsis Ecomorphological analyses that search for patterns of association between morphological and prey-use data sets will have a greater chance of understanding the causal relationships between form and diet if the morphological variables used have known consequences for feeding performance. We explore the utility of fish body size, mouth gape and jaw-lever mechanics in predicting patterns of prey use in two very different communities of fishes, Caribbean coral reef fishes, and species of the Centrarchidae that live in Lake Opinicon, Ontario. In spite of major differences in the spectrum of potential prey available, the centrarchids of Lake Opinicon show dietary transitions during ontogeny that are very similar to those seen among and within species of Caribbean groupers (Serranidae). The transition from small zooplankton to intermediate sized invertebrates and ultimately to fishes appears to be very general in ram-suction feeding fishes and is probably driven largely by the constraints of mouth size on prey capture ability. The jaw-lever systems for mouth opening and closing represent direct trade-offs for speed and force of jaw movement. The ratio of in-lever to out-lever in the opening system changes during ontogeny in bluegill, indicating that the mechanics and kinematics of jaw movement may change as well. Among 34 species of Caribbean reef fishes, biting species had jaw-closing ratios that favored force translation, while species that employ rapid-strike ram-suction had closing ratios that enhanced speed of closing and mouth opening ratios that favored a more rapid expansion of the mouth during the strike. We suggest that when prey are categorized into functional groups, reflecting the specific performance features that are important in capturing and handling them, and the differences among habitats in the available prey resource are taken into account, general patterns can be found in morphology-diet relations that cross phylogenetic boundaries.     

Functional analysis of a specialized prey processing behavior: winnowing by surfperches (Teleostei: Embiotocidae).

Several surfperches (Embiotocidae), including the black surfperch, Embiotoca jacksoni, exhibit a specialized prey handling behavior known as winnowing, in which ingested food and non-nutritive debris are separated within the oropharyngeal cavity. Prey items are swallowed, and unpalatable material is ejected from the mouth. Winnowing is believed to play an important role in the partitioning of food resources among sympatric embiotocids. We present a mechanistic model for this separative prey processing based on high-speed video analysis, cineradiography, electromyography, and buccal and opercular cavity pressure transducer recording. Winnowing by embiotocids is characterized by premaxillary protrusions repeated cyclically with reduced oral gape. Protrusion is accompanied by depression of the hyoid apparatus and adduction of the opercula. Alternating expansion and contraction of the buccal and opercular cavities generate regular pressure waveforms that indicate bidirectional water flow during processing. Separation of food from debris by Embiotoca jacksoni occurs in three phases. The prey-debris bolus is transported anteriorly and posteriorly within the oropharyngeal cavity and is then sheared by the pharyngeal jaws. Mechanical processing is complemented by the rinsing action of water currents during hydraulic prey transport. The feeding apparatus of Embiotoca jacksoni is functionally versatile, although not obviously specialized relative to that of nonwinnowing surfperches. Protrusion of the premaxillae and depression of the hyoid apparatus are critical to both prey capture and subsequent prey processing. The pharyngeal jaws exhibit kinematic patterns during separation of food from debris distinct from those observed during mastication of uncontaminated prey. This behavioral flexibility facilitates resource partitioning and the coexistence of E. jacksoni in sympatric embiotocid assemblages.     

Intraspecific variation in Gape–prey size Relationships and Feeding Success During Early Ontogeny in Red Drum, Sciaenops Ocellatus

The relationship between predator gape and prey consumption in laboratory-reared larva and field-caught early juvenile red drum, Sciaenops ocellatus, was investigated in light of the hypothesis that feeding success varies throughout the early life history intervals of marine fishes. We expected the feeding ability of red drum to be more strongly constrained by mouth gape in smaller fish and expected this ability to improve with gape size. To test this hypothesis, field-caught, early juvenile red drum were examined to determine the relationship between gape size and prey size consumed. In field-caught early juveniles, gape (height and width) and prey size consumed (length and width) increased linearly with standard length (SL); however, mean width of prey consumed was only 20–47% of gape width. Furthermore, when regressed on SL, gape width yielded a higher slope than prey width. To further test this hypothesis on less developed, pre-metamorphic fish, age-specific differences in gape, number of prey and size of prey consumed prior to metamorphosis were determined from laboratory-reared red drum larvae. Similar patterns were observed for gape height– and gape width–SL relationships in laboratory-reared red drum larvae. Size of consumed prey increased from three days from hatching (dfh) to 18dfh. The percentage of feeding larvae also increased from 3% at 3dfh to 97% at 18dfh. In both field-caught, early juvenile red drum and laboratory-reared larvae, there was little evidence that the size of prey consumed was constrained by mouth gape. It is hypothesized that besides gape size, the development of other features of the feeding mechanism (e.g., hyoid and opercular series) influences prey-capture performance prior to settlement in marine fishes.     

Surface tension prey transport in shorebirds: how widespread is it?

Surface tension prey transport is a feeding mechanism employing the surface tension of water surrounding prey to transport prey from bill tip to mouth. Previously, it has been demonstrated only in the Red-necked Phalarope Phalaropus lobatus. On the basis of a model of the bill morphology necessary for this method of prey transport, I suggest that many species of shorebird should be capable of surface tension feeding. Laboratory investigations of the feeding mechanics of Wilson's Phalarope Phalaropus tricolor , Western Sandpiper Calidris mauri and Least Sandpiper Calidris minutilla demonstrated that all three use surface tension transport of prey when feeding in water. I examined interspecific variation in the performance of this feeding mechanism with a high-speed video system and a customized motion analysis system. Exploratory analyses indicated significant interspecific variation in distance the prey is transported per cycle of mandibular spreading, gape increase per unit transport, speed of transport, total number of cycles necessary to complete transport and total time to complete transport. The calidrid sandpipers also occasionally used other feeding mechanisms in conjunction with surface tension transport of prey. The discovery that these sandpipers, which normally obtain prey by probing, are capable of surface tension transport of prey implies that the capacity to employ this feeding mechanism may be widespread in the Scolopacidae and may have been a significant factor in the evolutionary radiation of phalaropes into aquatic environments.     

A Southern Ocean archipelago enhances feeding opportunities for a krill predator

Productivity in the oceans is heightened around oceanographic and bathymetric features such as fronts and islands. This can have a flow-on effect, providing increased food availability for higher trophic level species. Using data from a 5-day combined visual and acoustic survey, we examined the hypothesis that higher Antarctic krill (Euphausia superba) density provides a lucrative resource for humpback whales (Megaptera novaeangliae) at a remote Antarctic feeding area, the Balleny Islands (67^oS, 164°E). We assessed whale presence at the feeding area in relation to prey (krill), productivity and environmental variables using density surface modeling. We found stark differences between krill swarms near the islands and those in adjacent open water. Swarms were twice as dense and three times more numerous near the Balleny Islands compared to an open water pelagic environment, suggesting that the islands offered a profitable feeding opportunity. At the feeding area, whales were found in deeper and more productive waters with medium krill densities. These relationships, along with the high krill availability around the islands, may be the result of the Island Mass Effect.     

Odontocete suction feeding: Experimental analysis of water flow and head shape

The role of cranial morphology in the generation of intraoral and oropharyngeal suction pressures in odontocetes was investigated by manipulating the jaw and hyolingual apparatus of submerged heads of three species presenting varied shapes. Hyoid and gular muscles were manually employed to depress and retract the tongue. Pressures were recorded at three locations in the oral cavity, as gape and site, speed, and force of pull were varied. A biomechanical model was also developed to evaluate pressure data. The species with the shortest, bluntest head and smallest mouth opening generated greater negative pressures. Suction generation diminished sharply as gape increased. Greatest negative pressures attained were around -45 mmHg (-6,000 Pa), a magnitude deemed suitable for capture of small live prey. Odontocetes utilizing this bidirectional flow system should profit by evolution of a rounder mouth opening through progressive shortening and widening of the rostrum and jaws, a trend evident in cranial measurements from fossil and recent odontocetes. Blunt heads correlate with anatomical, ecological, and behavioral traits associated with suction feeding. Small-gape suction (with minimally opened jaws) could be used by odontocetes of all head and oral shapes to draw prey sufficiently close to the mouth for suction ingestion or grasping via dentition. Principal limitations of the experimental and mathematical simulations include assumption of a stationary odontocete with static (open or closed) jaws and potential scaling issues with differently sized heads and gapes.