Why armadillos have a horny carapace

Why Armadillos Have a Horny Carapace

Perhaps the most conspicuous feature of armadillos is the horny shell (carapace) that surrounds their bodies. Throughout their evolution, this shell has helped them survive attacks from other species (but not the automobile attacks of modern humans).

A study of the evolutionary consequences of the carapace has been published in 2011 by Mariella Superina and W. J. Loughry.* These consequences go beyond that of protective armor, which the authors contend is a logical interpretation but one that has never been experimentally tested

For example, there are obvious constraints on reproduction. These include:

1. Slower locomotion due to physical constraints. However, armadillos can run fast for short distances when they need to.

2. A lowered aerobic capacity and metabolic rate. Actually, their metabolic rate is among the lowest for any mammalian species. Thus, they can tolerate low levels of oxygen when they grub deeply in dirt for food and when they hole up in their burrows.

3. A lowered requirement for high-quality diets. Thus armadillos do well just eating bugs and worms.

4. Excessive body heat loss. There is no insulating fur and not much subcutaneous insulation from fat.  There is high thermal conductance, causing excessive heat loss in the cold and minimization of body heat accumulation in hot weather. This limits their geographical range but actually promotes their adaptability in the hot climates where they originated and live today. Al Prudom and I showed that soon after they go to sleep, they start to shiver violently, even at laboratory room temperature.

5. Mating performance. The carapace makes mounting difficult. One apparent adaptation is a long penis, amounting to as much as 50-60% of body length.

6. Birthing. A rigid carapace would make difficult the delivery of offspring through the birth canal. Thus, fetal carapace is soft and flexible. Ossification of dermal scutes occurs after birth.

7. Limited social interactions. Armadillos don’t have the time. For metabolic reasons, they can’t be very active, and during the limited time when they are active they have to spend 80-90% of their time in food acquisition.

*Superina, M., and Loughry, W. J. 2011. Life on the half-shell: consequencies of a carapace in the evolution of armadillos (Xenarthra: Cingulata). J. Mammal. Evol. DOI 10.1007/s10914-011-9166-x

Updated: August 18, 2014 — 8:32 pm
thinkbrain © 2014 Frontier Theme