Reconstruction of the Cortical Maps of the Tasmanian Tiger and Comparison to the Tasmanian Devil

Abstract

ABSTRACTThe last known Tasmanian tiger (Thylacinus cynocephalus) – aka the thylacine – died in 1936. Because its natural behavior was never documented, we are left to infer aspects of its behavior from museum specimens and unreliable historical recollections. Recent advances in brain imaging have made it possible to scan postmortem specimens of a wide range of animals, even more than a decade old. Any thylacine brain, however, would be more than 100 years old. Here, we show that it is possible to reconstruct white matter tracts in two thylacine brains. For functional interpretation, we compare to the white matter reconstructions of the brains of two Tasmanian devils (Sarcophilus harrisii). We reconstructed the cortical projection zones of the basal ganglia and major thalamic nuclei. The basal ganglia reconstruction showed a more modularized pattern in the cortex of the thylacine, while the devil cortex was dominated by the putamen. Similarly, the thalamic projections had a more orderly topography in the thylacine than the devil. These results are consistent with theories of brain evolution suggesting that larger brains are more modularized. Functionally, the thylacine’s brain may have had relatively more cortex devoted to planning and decision-making, which would be consistent with a predatory ecological niche versus the scavenging niche of the devil.SIGNIFICANCEThe Tasmanian tiger – aka the thylacine – was a carnivorous marsupial and apex predator in Tasmania until the last one died in 1936. Very little is known about its natural behavior. Only four intact brain specimens are known to have survived. We used diffusion-weighted MRI to reconstruct the white matter pathways in two of these specimens, and for comparison, the brains of two Tasmanian devils. By comparing the maps of these projections in the cortex, we show that the thylacine’s brain is consistent with a more complex predatory strategy than the scavenging strategy of the Tasmanian devil.