The Non-Precambrian Rabbit

In one of the more interesting stories of scientific history it is said that J. B. S. Haldane, a British geneticist and evolutionary biologist, once wrote (or said) that the only thing that could shake his confidence in the theory of evolution would be the discovery of rabbit fossils in Precambrian rocks. He also wrote a poem about rectal cancer shortly before his death, so he was likely trying to be funny with his rabbit crack as well as a little flippant toward people questioning his life's work and confidence in it. Haldane was an interesting figure regardless of negatives one might find reading about him (he was a vocal supporter of Communism and Joseph Stalin, for example). Anyhow, the question of "how old are rabbits exactly?" has really piqued my interest this week.

The oldest ancestor of rabbits is a 53 million year old fossil consisting of two recognizably lagomorphine (rabbits, hares, and pikas are lagomorphs) feet. These feet belonged to an animal the size of a hamster. However, I do not want to focus on two small feet this week. Instead, let us look at the opposite end of the size spectrum. We have all seen enormous rabbits, but have any of you seen the largest fossil rabbit? I got trapped in a Wikipedia loop of bunnies looking up the Minorcan King of the Hares, Nuralagus rex. Discovered and described in 2011, Nuralagus was approximately 0.5 m  (1.64 ft) tall and may have weighed around 12 kg (26 lbs). For comparison, the largest breed of domesticated rabbits, the Flemish Giant, has an average weight of 6.80 kg (15 lbs).

Nuralagus fossils have been recovered exclusively from the scrubland areas of Minorca, a small island of Spain approximately 402 km (250 miles) south of Barcelona. The discovery of the rabbit fossils in the scrublands indicates that the diet of these rabbits was most likely centered on roots and tubers of the small scrub plants. Some might wonder how an animal like a rabbit, surviving on roots and tubers might become so large. Foster's Rule, also called the "Island Rule" states that large animals with scarce resources tend to evolve to smaller sizes and small animals continue to be small except in the absence of predators which allows lineages to evolve to larger sizes.

Figure 3 from Quintana et al., 2011.