Variation in braininess among marsupials

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Marsupials (https://en.wikipedia.org/wiki/Marsupial) are generally less brainy than eutherian (https://en.wikipedia.org/wiki/Eutheria) mammals at body sizes approximately exceeding those of Rattus (https://search.informit.org/doi/10.3316/INFORMIT.585794741422012 and https://en.wikipedia.org/wiki/Brain_size and https://www.karger.com/Article/Fulltext/377666 and https://onlinelibrary.wiley.com/doi/10.1002/bies.201100013).

As an extreme example, the Virginia opossum (https://en.wikipedia.org/wiki/Virginia_opossum) is 5-fold less brainy than any cat (https://en.wikipedia.org/wiki/Felidae) of similar body mass. The brain volumes respectively are Didelphis virginiana 25 units of volume vs Felis catus 125 units of volume.

Dactylopsila (https://en.wikipedia.org/wiki/Striped_possum) is the brainiest marsupial, but falls short of cats - which themselves are about average for eutherians and only a little brainier than the general mammalian average.

Nonetheless, within marsupials there is 5-fold variation in braininess. The purpose of this series of Posts is to rank the various marsupials in order of braininess.

My sources are:

On the scale of braininess used by the first reference above,

This means that:

DATA

The following shows marsupials in order of decreasing braininess according to Nelson and Stephan (1982). A score of 100 equates approximately to Rattus (https://en.wikipedia.org/wiki/Rattus) among eutherians.

Scoring more than 180

Scoring 150-180

Scoring 140-170

Scoring 130-140

Scoring 110-130

Scoring 90-110 (approximately equivalent to Rattus among eutherians)

Scoring 80-90

Scoring less than 80

DISCUSSION

The common brush-tailed possum (Trichosurus vulpecula, https://en.wikipedia.org/wiki/Common_brushtail_possum) and the ring-tailed lemur (Lemur catta, https://en.wikipedia.org/wiki/Ring-tailed_lemur) both have body mass about 1.7 kilograms. However, the former (a phalangerid marsupial) is half as brainy as the latter (a prosimian primate). Their brains weigh 11 grams and 22 grams respectively.

The following mammals all weigh about 200 grams (slightly more massive than Rattus), but differ in braininess in decreasing order as follows:

As in the comparison of possum with lemur above, a petaurid marsupial has a smaller brain than that of an ecologically comparable, like-size prosimian primate.

The numbat (Myrmecobius fasciatus, https://en.wikipedia.org/wiki/Numbat) of southern Australia is comparable with a sengi (Rhynchocyon, https://en.wikipedia.org/wiki/Rhynchocyon) of Africa. However, the former scores lower (149) in braininess than the latter (180).

Along similar lines: kangaroos are less brainy than ruminants, and the thylacine is less brainy than canids despite its superficial evolutionary convergence. However, the relative braininess of potoroos, bettongs, and rat-kangaroos (e.g. https://en.wikipedia.org/wiki/Musky_rat-kangaroo) is puzzling, because in other respects these seem as primitive as other marsupials.

In general, many marsupials of diverse diets (burramyids, most dasyurids, peramelids, pseudocheirids, phalangerids) are about as brainy as the eutherians formerly called 'Insectivora' (https://en.wikipedia.org/wiki/Insectivora). The latter likewise range considerably in braininess, from 47 to 180.

The Virginia opossum is not only the most northerly of all marsupials but also one of the least brainy - which seems paradoxical given its success in the relatively intense predatory regime of North America.

Posted on 06 April, 2022 05:03 by milewski milewski

Comments

Posted by milewski almost 2 years ago

On the topic of braininess beyond marsupials, here is one of the most interesting papers I have seen in a long time: https://www.karger.com/Article/FullText/497268.

Also see https://www.nature.com/articles/s41598-022-07327-9

Posted by milewski almost 2 years ago

The Tasmanian devil Sarcophilus harrisii (https://en.wikipedia.org/wiki/Tasmanian_devil) is much less brainy than the largest-bodied species of mongoose, namely Ichneumia albicauda (https://en.wikipedia.org/wiki/White-tailed_mongoose). Body masses are 5.1 kg and 4.4 kg respectively, but brain masses are 14 grams or less, vs 28 grams.

Posted by milewski almost 2 years ago

INFORMATION ON BODY MASS, BRAIN MASS AND ENCEPHALISATION QUOTIENT (https://en.wikipedia.org/wiki/Encephalization_quotient) IN MARSUPIALS

Antechinus swainsoni 54 g 0.95 g EQ 0.55
Isoodon obesulus 925 g 4.95 g EQ 0.43
Dasyurus viverrinus 1.32 kg 6.10 g EQ 0.42
Dasyurus maculatus 3.0 kg 10.4 g EQ 0.42
Sarcophilus harrisii 5.1 kg 13.5 g EQ 0.38
Petaurus breviceps 116 g 2.95 g EQ 1.03
Trichosurus vulpecula 3.15 kg 13 g EQ 0.50
Phalanger maculatus 4.0 kg 17.1 g EQ 0.57
Vombatus ursinus 16.1 kg 48.1 g EQ 0.63
Potorous tridactylus 1.46 kg 12.0 g EQ 0.78
Thylogale billardieri 4.9 kg 22.5 g EQ 0.65
Macropus giganteus 34.53 kg 61.4 g EQ 0.48

Posted by milewski almost 2 years ago

The following is a list of marsupials, in decreasing order of braininess, from Haight J R and Nelson J E (1987) A brain that doesn't fit its skull: a comparative study of the brain and endocranium of the koala Phascolarctos cinereus (Marsupialia: Phascolarctidae). In: Possums and Opossums: Studies in Evolution, ed. by M Archer, pp. 331-352. Surrey Beatty and Sons and the Royal Society of New South Wales, Sydney.

https://www.semanticscholar.org/paper/A-brain-that-doesn%27t-fit-its-skull%3A-a-comparative-Haight-Nelson/2de97da5b994c9855007c3e0b0ad92758c0cc28c

Posted by milewski almost 2 years ago

Species, braininess score, body mass, and brain mass
Vombatus ursinus, 213, 15979 g, 55.7 g
Potorous tridactylus, 186, 1445 g, 12.1 g
Bettongia gaimardi, 179, 1640 g, 12.6 g
Petaurus breviceps, 170, 125 g, 2.69 g
Gymnobelideus leadbeateri, 169, 104 g, 2.39 g
Setonix brachyurus, 164, 2495 g, 14.7 g
Thylogale billardierii, 164, 5570 g, 23.3 g
Macropus giganteus, 162, 28650 g, 59.0 g
Macropus rufogriseus, 159, 12786 g, 36.6 g
Dendrolagus lumholtzii, 154, 5883 g, 22.6 g
Macropus eugenii, 153, 5655 g, 21.9 g
Trichosurus vulpecula, 147 & 125, 1630 g & 3231 g, 147 g & 125 g
Petaurus norfolcensis, 134, 237 g, 3.07 g
Cercartetus lepida, 133, 6.4 g, 0.376 g
Trichosurus caninus, 125, 2899 g, 12.2 g
Antechinus' swainsonii, 114, 41.7 g, 0.951 g
Perameles gunnii, 111, 828 g, 5.22 g
Antechinus stuartii, 110, 24.0 g, 0.627 g
Pseudocheirus peregrinus, 110, 844 g, 5.27 g
Dasyurus viverrinus, 107, 1217 g, 6.31 g
Sminthopsis leucopus, 106, 18.3 g, 0.550 g
Sarcophilus harrisii, 103, 5143 g, 14.0 g
Perameles nasuta, 96, 1272 g, 5.79 g
Dasyurus maculatus, 93, 2768 g, 8.85 g
Antechinus flavipes, 91, 40.6 g, 0.746 g
Isoodon obesulus, 91, 1072 g, 4.96 g
Sminthopsis murina, 88, 16.7 g, 0.434 g
Petauroides volans, 85, 1181 g, 4.91 g
Phascolarctos cinereus, 84, 9614 g, 16.7 g
Planigale maculata 62, 9.45 g, 0.219 g

Posted by milewski almost 2 years ago

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