Brain size in palm cockatoo

Although the palm cockatoo (Probosciger aterrimus) is only a bit more than one kilogram in body mass, it has a brain of 20.5 ml volume, equivalent to approx. 20.5 grams mass. This is an astonishingly large brain considering that the domestic cat, which weighs more than three-fold more, has a brain mass of approx. 30 g. The short-beaked echidna and bat-eared fox both weigh about 4 kg, and their brain masses are respectively 25 g and 28.5 g. So, if one compares palm cockatoo with echidna, the body masses are about four-fold different but the brain masses are not much different: about 20 g in the bird and about 25 g in the monotreme.

Subject: from antoni: most recent paper by iwaniuk et al. on braininess in australian birds

Subject: from antoni: valuable information on encephalisation quotients in many mammals
This is my commentary on the data shown below, for encephalisation in various mammals.
The following species fall below the threshold EQ of 0.5. All these species have brains less than half as massive/voluminous as predicted for the average mammal of their body mass:
armadillo Dasypus novemcinctus 0.44: this species is as decephalised as bandicoots, but I think this is largely for a different reason, i.e. the heavy armour of armadillos
hedgehog Erinaceus frontalis 0.36: conforms to the generalisation that armoured mammals are decephalised
Hippopotamus amphibius 0.37: the decephalisation of the larger of the two extant spp. of hippos is noteworthy, but difficult to make sense of, partly because all mammals > 1 tonne in body mass tend to show a kind of breakdown in the allometric relationship applying to smaller mammals
guinea pig Cavia porcellus 0.4: all caviomorph rodents tend to be brainy compared with non-caviomorph rodents other than tree squirrels, but even the caviomorph rodents show a general pattern in which rodents and lagomorphs are small-brained relative to e.g. primates of similar body mass; I also suspect that the domestic guinea pig is decephalised relative to its wild ancestor
beaver Castor canadensis 0.4: my interpretation here is similar to that above for cavies
Sus scrofa (domestic) 0.44: pigs (Suidae) are oddly decephalised, not only by domestication but even in the wild ancestral species
The following species fall only slightly above the threshold of 0.5:
anteater Tamandua 0.52: South American anteaters are decephalised, which is unsurprising for termite- and ant-eaters with slow metabolism; however, the ant-eaters are not as decephalised as the armadillos
eland 0.56: I suspect that decephalisation in large ruminants is rather misleading, reflecting the fact that males continue to grow brawn to full maturity while their brains remain at the size of the adult female
domestic rabbit 0.51: my interpretation here is similar to that for rodents and cavies, above; it is interesting that the feral rabbit in Australia is almost as decephalised as the native bandicoots while reproducing far more rapidly than the bandicoots
Rats and mice about 0.5: these rodents are more intelligent than their values for EQ might indicate; I don’t know why rodents differ from primates in having a different ratio of intelligence to encephalisation, but that seems to be the case
Sus scrofa (wild) 0.54: see my remarks for the domestic descendents of this wild species; it is odd that the wild boar is so decephalised relative to other cloven-hoofed mammals
Other noteworthy species:
Note that the porcupines Hystrix cristata has similar EQ to the capybara, the values being respectively 0.63 and 0.67. Porcupines seem not to conform to the rule that armoured mammals are decephalised; this porcupine actually beats the guinea pig in EQ
tree sloths 0.63-0.71: rather surprisingly, sloths are not as decephalised as other Xenarthra despite having extremely slow metabolism
bat-eared fox Otocyon megalotis 1.16: although this insect-eating species is decephalised relative to typical foxes in the genus Vulpes, it remains brainy relative to the average mammal of its body size; this is testimony to the fact that Canidae are one of the brainiest families of Carnivora

Posted on Σεπτέμβριος 04, 2022 0917 ΠΜ by milewski milewski


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