Encephalization of Australian and New Guinean Marsupials

Ashwell, Ken W.S.

doi:10.1159/000114406

Cited by 43 publications

(45 citation statements)

References 24 publications

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“…Species with small craniums have brains that occupy over 25% of the cranial volume, and species with large cranium have relatively small brains that occupy only 5% of the total cranial volume (table 2). The volumes determined for extant taxa are within the range measured by Ashwell (2008) for wombats, and Taylor et al (2006) for koalas, so it is assumed that the estimated volumes for the extinct taxa are also realistic. …”

Section: Volume Comparisonmentioning

confidence: 99%

“…A disadvantage is that it might overestimate the brain volume depending on what proportion of the cranial cavity is occupied by the brain. The majority of Australian marsupials have brains almost completely occupying the endocranium (Ashwell, 2008;Taylor et al, 2006;Tyndale-Biscoe, 2005), so it was assumed that endocast volume is a reasonable proxy for brain size. To avoid as much error as possible, the volume of the endocast for each species was segmented so that the meninges, cranial nerves, blood vessels and the pituitary occupied similar proportions of the endocranial volume across the data set.…”

Section: Introductionmentioning

confidence: 99%

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A quantitative comparative analysis of the size of the frontoparietal sinuses and brain in vombatiform marsupials

Sharp¹

2016

MMV

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Sharp, A.C. 2016. A quantitative comparative analysis of the size of the frontoparietal sinuses and brain in vombatiform marsupials. Memoirs of Museum Victoria 74: 331-342.Cranial sinuses result from the resorption and deposition of bone in response to biomechanical stress during a process known as pneumatisation. The morphology of a pneumatic bone represents an optimisation between strength and being light weight. The presence of very large sinuses has been described in a number of extinct marsupial megafauna, the size of which no longer exist in extant marsupials. With advances in digital visualisation, and the discovery of a number of exceptionally preserved fossil crania, a unique opportunity exists to investigate hypotheses regarding the structure and evolution of the atypically voluminous sinuses. Sinus function is difficult to test without first obtaining data on sinus variation within and between species. Therefore, the crania of seven species of extinct and extant vombatiform marsupials were studied using CT scans to provide a volumetric assessment of the endocast and cranial sinuses. Sinus volume strongly correlates with skull size and brain size. In the extinct, large bodied palorchestids and diprotodontids the sinuses expand around the dorsal and lateral parts of the braincase. Brain size scales negatively with skull size in vombatiform marsupials. In large species the brain typically fills less than one quarter of the total volume of the endocranial space, and in very large species, it can be less than 10%. Sinus expansion may have developed in order to increase the surface area for attachment of the temporalis muscle and to lighten the skull. The braincase itself would have provided insufficient surface area for the predicted muscle masses.

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Section: Volume Comparisonmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A quantitative comparative analysis of the size of the frontoparietal sinuses and brain in vombatiform marsupials

Sharp¹

2016

MMV

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“…At less inclusive clades, however, empirical encephalization allometries often scale significantly lower than 0.75 (e.g. Ashwell 2008;Finarelli 2008b;Finarelli & Flynn 2009). However, BMR is only one potential proxy for maternal energetic investment (Martin 1981); increased encephalization through increased total maternal energy investment in the embryo could also be achieved by lengthening the gestational period (Martin 1996).…”

Section: Introductionmentioning

confidence: 99%

Does encephalization correlate with life history or metabolic rate in Carnivora?

Finarelli

2009

Biol. Lett.

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A recent analysis of brain size evolution reconstructed the plesiomorphic brain-body size allometry for the mammalian order Carnivora, providing an important reference frame for comparative analyses of encephalization (brain volume scaled to body mass). I performed phylogenetically corrected regressions to remove the effects of body mass, calculating correlations between residual values of encephalization with basal metabolic rate (BMR) and six life-history variables (gestation time, neonatal mass, weaning time, weaning mass, litter size, litters per year). No significant correlations were recovered between encephalization and any life-history variable or BMR, arguing against hypotheses relating encephalization to maternal energetic investment. However, after correcting for clade-specific adaptations, I recovered significant correlations for several variables, and further analysis revealed a conserved carnivoran reproductive strategy, linking degree of encephalization to the welldocumented mammalian life-history trade-off between neonatal mass and litter size. This strategy of fewer, larger offspring correlating with increased encephalization remains intact even after independent changes in encephalization allometries in the evolutionary history of this clade.

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“…46 and 47) have been collected. This lack of interest might be related to the persistent notion that marsupials are small-brained (1,45,48), despite evidence to the contrary (46,49,50).…”

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Brain size, life history, and metabolism at the marsupial/placental dichotomy

Weisbecker

Goswami²

2010

Proc. Natl. Acad. Sci. U.S.A.

114

118

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The evolution of mammalian brain size is directly linked with the evolution of the brain's unique structure and performance. Both maternal life history investment traits and basal metabolic rate (BMR) correlate with relative brain size, but current hypotheses regarding the details of these relationships are based largely on placental mammals. Using encephalization quotients, partial correlation analyses, and bivariate regressions relating brain size to maternal investment times and BMR, we provide a direct quantitative comparison of brain size evolution in marsupials and placentals, whose reproduction and metabolism differ extensively. Our results show that the misconception that marsupials are systematically smaller-brained than placentals is driven by the inclusion of one large-brained placental clade, Primates. Marsupial and placental brain size partial correlations differ in that marsupials lack a partial correlation of BMR with brain size. This contradicts hypotheses stating that the maintenance of relatively larger brains requires higher BMRs. We suggest that a positive BMRbrain size correlation is a placental trait related to the intimate physiological contact between mother and offspring during gestation. Marsupials instead achieve brain sizes comparable to placentals through extended lactation. Comparison with avian brain evolution suggests that placental brain size should be constrained due to placentals' relative precociality, as has been hypothesized for precocial bird hatchlings. We propose that placentals circumvent this constraint because of their focus on gestation, as opposed to the marsupial emphasis on lactation. Marsupials represent a less constrained condition, demonstrating that hypotheses regarding placental brain size evolution cannot be generalized to all mammals.encephalization | maternal energy hypothesis | altricial | basal metabolic rate M ammalian brain size is widely relevant to neuroscience. Aside from the classical interpretation of brain size as a proxy for cognitive or sensorimotor capacity (1-3), brain size corresponds to the macroscopic, microstructural, and connective composition of the mammalian brain with remarkable accuracy (4, 5). However, despite decades of research, the factors underlying the evolution of brain size relative to body size (referred to as "brain size" hereafter), particularly relative brain enlargement, remain a matter of debate (6). Maternal life history investment traits, such as gestation and litter size, are generally accepted as mammalian brain size correlates (7-13) and are considered to reflect a female's ability to energetically provision her offspring's brain growth (14,(15)(16)(17). A more controversial potential brain size correlate is basal metabolic rate (BMR) (18,19). Recent studies have confirmed a consistent correlation between increased brain size and BMR across placentals (20, 21), although this does not apply to all placental clades (8,22).Interpretations as to why BMR should influence mammalian brain size vary. It has been suggested t...

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Encephalization of Australian and New Guinean Marsupials

Cited by 43 publications

References 24 publications

A quantitative comparative analysis of the size of the frontoparietal sinuses and brain in vombatiform marsupials

A quantitative comparative analysis of the size of the frontoparietal sinuses and brain in vombatiform marsupials

Does encephalization correlate with life history or metabolic rate in Carnivora?

Brain size, life history, and metabolism at the marsupial/placental dichotomy

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