The first endocast of the extinct dodo (Raphus cucullatus) and an anatomical comparison amongst close relatives (Aves, Columbiformes)

Abstract

The dodo (Raphus cucullatus) became extinct only 100 years after humans first arrived on the Indian Ocean island of Mauritius. Even though it has become an example of oddity, obsolescence, stupidity, and extinction, most aspects of its biology are still unknown. We used high-resolution X-ray computed tomography (CT) scanning to examine the endocranial morphology of the dodo and compare this virtual endocast to eight close relatives. Enlarged olfactory bulbs are a shared characteristic of the Raphinae and posteriorly angled semicircular canals are particular to the dodo compared with the other eight species sampled here. A regression of log endocranial volume against log body size shows that the dodo has an endocranial volume on par with other pigeons. Aspects of the dodo's biology are discussed in relation to these endocranial features.

Beyond Endocasts: Using Predicted Brain-Structure Volumes of Extinct Birds to Assess Neuroanatomical and Behavioral Inferences

“…The correlation between the surface area of the Wulst and the volume of the hyperpallium supports the tendency of other authors to equate the two structures when making functional inferences [18][19][20][21][23][24][25]48]. Similarly, the correlation between the surface area of the optic lobe and the volume of the optic tectum lends credence to the inferences of potential functional capabilities made in previous publications that were based on the size of the optic lobe [18,22,26,50].…”

“…The trend in Wulst size observed in extinct and extant penguins fits the general avian pattern of Wulst expansion throughout evolution of the clade [21,23,25]. Counter to this trend, the Wulst seems to have been larger in extinct columbiforms than their extant relatives [24]. Another endocast structure that has been a major focus of attention is the optic lobe, which overlies the bilateral expansion of the midbrain that serves as a relay point for sensory information heading toward the forebrain for higher-level processing ( Figure 1).…”

“…Similar to the optic lobe, the expansion of the Wulst (and presumably, its underlying brain structure) is a characteristic trait of avian brain evolution [7,10,34]. Many studies on the endocasts of extinct taxa have found Wulsts that fall within the range of variation seen in extant birds and thus have ascribed them similar visual capabilities [11,[18][19][20][21][22][23][24][25][26]. The trend in Wulst size observed in extinct and extant penguins fits the general avian pattern of Wulst expansion throughout evolution of the clade [21,23,25].…”

“…Its expansion and ventrolateral displacement by the expanded telencephalic hemispheres is one of the hallmark traits of brain evolution on the lineage from non-avian theropods to birds [7,46,47]. This trend is supported by the many fossil endocasts whose optic lobes appear similar in size to those of their extant relatives [11,[16][17][18][19][20][21]23,24,48]. There are cases in which the optic lobes of some extinct birds appear to be relatively smaller than those of their extant relatives, which has been interpreted as a possible indication of reduction in visual abilities [9,22,26,[49][50][51].…”

“…The overall shape of the endocast and how that shape correlates with behavioral and life-history traits have become more available for analysis with the advent of 3D geometric morphometric techniques [11][12][13][14]. The most common approach in endocast studies has been to describe a fossil endocast in comparison with its living relatives, both in terms of general morphology and relative size of discrete structures [7,9,11,[15][16][17][18][19][20][21][22][23][24][25][26]. These studies have allowed researchers to document trends in avian brain evolution by using endocast morphology as a proxy for neuroanatomy.…”