Northern sportive lemur have large bacteria-filled ceca, which helps them to digest plant matter such as cellulose and break it down into sugars and starches. The northern sportive lemur is preyed on by the native Malagasy tree boa, which hunts the lemurs while they are sleeping in tree holes. Large birds of prey, Falconiformes and Strigiformes, are also natural predators of the lemurs. Along with these ecological threats, the arboreal lemur species are also highly threatened by human charcoal production, which still continues to remove the only remaining forest habitat of the lemurs, greatly restricting their range. "L. septentrionalis" is also illegally hunted
The Origin of Birds exquisite detail the fossil remains of several extinct birds, including "Hesperornis", "Ichthyornis", "Archaeopteryx", and ""Archaeornis"", the name used commonly at the time for the Berlin specimen, which was then thought to represent a separate genus. Throughout this section are many finely detailed and labeled renderings of different parts of the skeletal anatomy of these birds, as well as other groups of extinct reptiles and some modern birds. Heilmann's attention to detail in his artwork is inspired at least in part by his dissatisfaction with anatomical renderings of these animals in scholarly works of the time, which he deemed as "unsatisfactory"