Selective foraging behaviour of basking sharks on zooplankton in a small-scale front

Abstract

A silty matrix still adheres to the external left half of the specimen.For logistic reasons it has not yet been possible to clean, reconstruct and fully study the cranium, so here we offer only a preliminary assessment. For similar reasons the pelvic fragments and incisors are not described here.A remarkable feature of UA 31 is its great anteroposterior length (204 mm) in relation to its maximum cranial breadth (130 mm). The greatest cranial breadth is located at the level of the supramastoid crests and with the length gives a cranial index of 63.7. Although the skull has not yet been restored and cleaned, tentative estimates suggest an endocranial capacity of 750-800 cm 3 .The neurocranium is low compared to its maximum length, but high relative to its transverse diameter. The upper-middle facial skeleton is slightly concave and marked prognathism is evident in the subnasal region. The face is narrow and short. The palate is shallow, wide and short, with its length reaching less than one-third of the total cranial length as seen in basal view. The very heavily built, forwardly projecting supraorbital torus is arched and thickened medially and over the middle of each orbit (17 mm). The minimum frontal breadth is 84.0 mm. Substantial elevation of the forehead and absence of sagittal keeling are evident in frontal view.The frontal squame is well curved to bregma and the vault outline becomes gradually flatter on the parietals. The temporal lines originate in the form of a raised crest at the posterolateral margin of the supraorbital torus, but disappear early on the parietals. A slightly thickened angular torus is present. There is no nuchal torus, but a modest external protuberance is detectable where opisthocranion coincides with inion.The specimen also shows a modest protrusion of the mastoidsupramastoid-auriculare complex lateral to the temporal squame. The mastoid process is short and broad. In coronal section, the parietal walls converge slightly inferiorly (Fig. 3); there is a high positioning of the maximum biparietal breadth (125.0 mm); the parietal thickness progressively decreases up to the midline (from 7.4 to 6.0 mm); the thickness at bregma is 6.3 mm.The cranium from Buia shows the following combination of features, which are characteristic of the African specimens referred to Homo erectus and Homo ergaster 11,12 : long ovoid braincase with low endocranial capacity; greatest cranial breadth across the supramastoid crests; massive supraorbital torus; opisthocranion coincident with inion. One trait typical of H. sapiens is the high position of the greatest biparietal breadth with parietal walls converging slightly inferiorly. This mosaic of primitive and progressive features increases the known morphological variation reported for earlymiddle Pleistocene Homo crania and urges caution in the specific assessment of UA 31. Until we have conducted a full comparative study, we prefer to leave open its specific allocation.Given its chronological position, in the middle of the time interval 1.4-0.6 Myr, from w...

Behaviour and kinematics of continuous ram filtration in bowhead whales (Balaena mysticetus)

“…For example, basking sharks decrease locomotion in low food concentrations to save energy when food concentrations are low (Sims & Quayle 1998;Sims 1999). Herring switch from ram filtering to particulate feeding when food densities drop and the increased food uptake of filter feeding no longer compensates the increased energetic cost of ram filter feeding (Gibson & Ezzi 2006).…”

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Movements and habitat use of reef manta rays off eastern Australia: offshore excursions, deep diving and eddy affinity revealed by satellite telemetry

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“…As a result, bottom-up processes, whereby physical oceanographic features act to concentrate prey items in specific water bodies, are likely to influence predator distributions and their behavioural decisions. For instance, basking sharks Ceto rhinus maximus congregate and feed on zooplankton blooms in frontal areas of the northeastern Atlantic (Sims & Quayle 1998, Sims et al 2003. However, the dispersal capabilities, behavioural ecology and ha bitat use patterns of other planktivorous elasmobranchs, such as manta rays (Manta spp.…”

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