Skulls from the University of Canterbury (UC) collection (n = 9) were used without additional preparation.

Cranial volume of clean, dry skulls (n = 21) was determined in triplicate using spherical plastic beads with a mean diameter of 5.6 ± 0.03 mm. The density of packed beads was first determined from the mass of beads that could be packed into the spherical (i.e., cranium-like) portion of volumetric flasks (100, 250, 500, mTOR inhibitor and 1,000 mL capacity); the volume of the spherical portion was measured by weighing distilled water at 20°C and dividing the resulting mass by the density of water at this temperature (0.998203 g/cm3). The relationship of bead bulk volume (y, cm3) to bead mass (x, g) was (1) Skulls sectioned for brain mass (Fig. 1) were reassembled using masking tape, and in all skulls foramina were plugged with foam ear plugs and/or masking tape to prevent loss of beads. Prepared skulls were

weighed empty to determine the tare mass before filling the cranial CHIR-99021 chemical structure cavity with beads through the foramen magnum. Care was taken to shake skulls during filling to ensure close packing of beads (Donev et al. 2004) and reduce interference by the bony tentorium (tentorium cerebelli osseum) present in Weddell seals. The net mass of the beads was determined as the difference between the mass of empty (tare) and filled skulls (tare + beads), and cranial capacity was calculated from net bead mass according to the relationship between bead mass and bead volume derived previously in vitro (Eq. (1) above).

The relationship between measured brM (x, g) and measured CC (y, cm3) was used to estimate brM from CC for adult (n = 9; UC collection) and neonatal (n = 3) skulls for which brM could not be directly determined (Fig. 2, Table 1). Unless otherwise indicated, results are expressed as mean ± SEM. BL, body length; BM, body mass; brM, brain mass; CC, cranial capacity (intracranial volume); CMR, cerebral metabolic rate; DGB, daily glucose demand of the brain; f. dom., forma domestica; MF, multiplication factor; RCMR, relative cerebral metabolic rate; medchemexpress UC, University of Canterbury, New Zealand. The relationship of measured brain mass (brM: x, g) and cranial capacity measured using plastic beads (CC: y, cm3) for pups and adults is shown in Fig. 2. Mean CC and brM of the two adult females measured directly (181, 5028; Table 1) were 574.7 cm3 and 563.4 g, respectively. Mean CC of skulls from the UC collection (n = 9) was 624.4 ± 16 cm3 (range 539–709 cm3), corresponding to a mean estimated brM of 626.9 ± 21 g. There was no significant difference in CC between the two sets of adult seals (t-test, P = 0.21). One stillborn pup (7547; Table 1) appeared to be premature on the basis of low body mass and small size, and was therefore omitted from analysis of brain size (but not from the comparison of brM and CC shown in Fig. 2, n = 7). Only skulls were available for pups 7639 and 7949, and brM for pup 7524 was not determined due to a taring error.