Posts Tagged ‘caviomorph’

The Extended Pleistocene Range of the porcupine (Erethizon dorsatum)

November 7, 2012

The North American porcupine has an odd biogeographical history.   It evolved from a tropical family of rodents originating in South America.  This family includes 15 species of porcupines found only in warm frost-free climates.  But as the present day range map shows, the North American porcupine is restricted to regions with cooler climates and is conspicuously absent from the southeast.

North American porcupine with young.  They mostly eat wood–the cambium layer just under the bark.

Present day range map of the porcupine.  Note that it is absent from regions with long hot summers, despite evolving from a tropical family of rodents.

During the Pleistocene, porcupines did inhabit the southeast.  Fossil hunters have unearthed porcupine specimens from several sites in Florida, and a porcupine jaw with teeth washed up on Edisto Beach, South Carolina where late Pleistocene fossils are commonly found.  Fossil porcupine teeth have been found in at least 2 other sites in that state as well.  Ice Age Florida had a similar composition of tree species as present day Florida, so it seems strange that this tree-dwelling rodent no longer lives in the region.  Porcupines mostly eat tree cambium as well as pine needles, tree leaves, and other arboreal vegetation.  There’s no shortage of suitable porcupine food in the southeast.  I think the best explanation for their present day absence in the south is the extreme summertime heat.  The high summer temperatures either directly stress porcupine physiology or make them susceptible to some types of diseases carried by insects or parasites that need longer summers.  Average summer temperatures in the southeast during Ice Ages were significantly cooler than those of today, though winter temperatures were only slightly cooler.  Porcupines are less common in the southern parts of their range, suggesting they thrive better in cooler temperatures–the opposite of their closest relatives which can’t survive freezing tempertures.  Perhaps, the loss of the capability to live in warmer climates is a recent ecological development that occurred with the proliferation of some kind of parasite.

The North American porcupine probably evolved from a poorly known extinct species–Coendou intermedia.  Fossils of Coendou intermedia were excavated from caves in West Virginia and date to ~500,000 BP.  It has characteristics intermediate between the North American porcupine (Erethizon dorsatum) and the Brazilian prehensile-tailed procupine (Coendou prehensilis).

The Brazilian prehensile-tailed porcupine.  It’s the closest living relative to the North American porcupine.  It’s entirely adapted for living in trees, unlike the North American porcupine which spends part of its time on the ground as well as in trees.  The pictured species can hang from a tree with just its tail.

North and South American porcupines are not closely related to African and Asian porcupines.  It’s an example of convergent evolution that both families evolved defensive quill-like hairs.  New World species of porcupines are arboreal; old world porcupines are terrestrial and dig deep burrows in the ground–a big difference in general behavior.

American porcupines belong to a family of South American rodents known as the caviomorphs which also includes capybaras, agoutis, pacas, chinchillas, and nutrias.  Genetic and fossil evidence suggests the caviomorphs and New World monkeys accidentally rafted on storm-created debris from Africa approximately 41 million years ago during the Ecoene era when the 2 continents were much closer than they are today.  The great diversity of caviomorph and monkey species in South America today probably are descendent from just a handful of species that somehow survived a transatlantic journey on a mass of driftwood.

Map of earth during the Eocene.  Africa and South America were much closer together then, allowing the ancestors of today’s species of South American rodents and monkeys to accidentally raft across from the former continent and establish new populations and species.  The North American porcupine and the nutria are the only species descendent from this colonization now present north of the Rio Grande, but capybaras formerly lived in southeastern North America too.

In addition to porcupines, 2 species of capybaras inhabited southeastern North America during the Pleistocene.  After porcupines became extirpated here following the end of the Ice Age, and capybaras were driven to extinction (probably from human overhunting) caviomorphs were absent from the region.  But thanks to the introduction of the nutria, a caviomorph once again resides in the south.