Capybaras and Hippos Take II

(Note: I tried publishing this post yesterday but due to undetermined technical difficulties the text disappeared.  Hopefully, this entry will have text.)

I planned on writing a blog article about Pleistocene capybaras of southeastern North America, but when I began researching the topic on google I discovered I’d already written a pretty good essay 2 years ago.  (See: https://markgelbart.wordpress.com/2015/12/07/megafauna-habitat-modification-and-pleistocene-capybaras-in-southeastern-north-america/https://markgelbart.wordpress.com/2015/12/07/megafauna-habitat-modification-and-pleistocene-capybaras-in-southeastern-north-america/ ) I’ve written 601 articles for my blog, and it’s hard for me to remember everything I’ve already covered.  Much to my disappointment, there has been little recent academic research about the extinct species of capybaras.  There were 2 species that lived in Florida, Georgia, South Carolina, and probably the Gulf States during the Pleistocene–Neochoerus pinkneyi  and Hydrochoerus holmesi.  Both were more than twice as large as the 2 extant species of capybaras that are presently confined to Central and South America near the equator.  I hypothesize the extinct species could endure somewhat colder air temperatures than their modern day kin due to their larger size.  Nevertheless, they probably extended their range during warmer wetter climate cycles. In my previous blog entry linked above  I think I mentioned how capybaras occupy an ecological niche similar to that occupied by African hippos.  Both are aquatic species that graze adjacent water’s edge marshes into lawn-like environments.  But I didn’t note the remarkable evolutionary convergence in the physical appearance between the 2 unrelated animals.

Capybara and young.

Convergent evolution is when 2 unrelated organisms evolve similar characteristics to adapt to similar environments.  Capybaras and hippos have similar height to weight ratios.  They also share other characteristics such as small round ears, short necks, square faces, and thick hides.

Hippos remind me of ancient extinct animals from earlier ages…like the kind of monstrous beasts of the Miocene or Eocene.  They should be appreciated for their resemblance to primitive extinct evolutionary dead-ends and ancestral species.  Hippos are most closely related to whales, having shared a common ancestor 28 million years ago known as Epirigenys lokonensis. Hippos resemble the primitive ancestors of whales.

Several extinct species of hippos were widespread in Europe during the Pleistocene but disappeared during the Last Glacial Maximum when available habitat shrank into small refugia where they were more easily hunted into extinction by man. Several species of hippos were also driven into extinction when man colonized Madagascar.  Dwarf species of hippos lived on the Mediterranean Islands of Crete, Cyprus, Sicily, and Malta until man discovered those places.  Just 2 extant species of hippo remain —Hippopotamus amphibious and Hexaprotodon lieberiensis. 

Hippos are the most dangerous non-human vertebrate in Africa.  They are responsible for an average of 2900 deaths every year.  However, mosquitoes and flies spread tropical diseases that kill about 655,000 people annually.  Paradoxically, these tiny pests are a greater hazard than a 2 ton hippo.

 

 

The Extended Pleistocene Range of the porcupine (Erethizon dorsatum)

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.

Specimen # F: AM 95737

Photo of a Glyptodont skull with puncture holes made by the bite of a species of fanged cat, probably a western dirktooth.  This fossil is at least 1.8 million years old.

The Frick Collection in the American Museum of Natural History includes a remarkable specimen catalogued as F: AM 95737.  One lucky fossil hunter found this skull of a juvenile glyptodont at the 111 Ranch in Graham County, Arizona.  It’s a complete skull minus a few missing lower molars.  This alone makes it unusual because most excavated fossils consist of disarticulated pieces.  Holes in the skull inflicted by a fanged cat make this discovery all the more fascinating.  This species of glyptodont is Glyptotherium texanus, a species which dates to the Blancan Land Mammal Age, a stage that ended early in the Pleistocene 1.8 million years ago.  G. texanus is believed to be ancestral to G. floridanus, the species of glyptodont that lived in southeastern North America from 300,000-11,000 years BP.  The species of cat that apparently killed this baby glyptodont can’t be determined with certainty, but it was probably a western dirktooth (Megantereon hesperus), a species ancestral to the Rancholabrean era species’ Smilodon fatalis and Dinobastis serum (the scimitar-toothed cat).

The dirktooth evidentally attacked this young glyptodont from the front.  Scientists consider this unusual because most cats assault their prey from the rear.  In addition to their armored skull adult glyptodonts had a tough cephalic shield protecting their skull, but the cephalic shield was undeveloped in the young, explaining how a western dirktooth’s bite was able to penetrate through to the brain.

The glyptodont skull was found associated with other fossils, including those of one and three-toed horses (Equus and Nannihippus), hares, and more tellingly capybaras and giant tortoises.  The latter two species indicate a subtropical to tropical climate.  Climatic patterns were quite different during the Pliocene and throughout much of the Pleistocene.  Southwestern North American enjoyed a wet lush environment then, unlike the desert of today.  Lots of lakes and marshes dotted the landscape.

Illustration of a glyptodont.  More than one description in the literature compares the size and shape of this beast to a Volkswagon.  They weighed up to a ton.  Note the stiff turtle-like shell and wide spreading feet.

The glyptodont was a bizarre mammal resembling a turtle.  It’s closest living relatives are the other edentates–armadilloes, anteaters, and sloths.  Armadilloes also have armor, but theirs is flexible.  Glyptodont armor was stiff and turtle-like.  Scientists don’t know if it could withdraw its head inside when threatened.  They were adapted for living in flat, marshy terrain.  Their feet spread wide enabling them to stand on and traverse muddy marshy ground, but they were unable to climb up hills.  The range map below suggests they inhabited coastal lowlands and flat river valleys.  They expanded their range during warm interglacials and interstadials, and conversely their range contracted during cold arid stadials.  They inhabited dense vegetation in marshes and swamps which predators avoided because of difficulty in gaining traction and perhaps mosquitoes.  Mosquitoes may not have been able to penetrate glyptodont armor.

Map of fossil sites where remains of G. floridanus have been found.  This is from the below referenced paper.  This map was drawn in 1981 before a glyptodont fossil was discovered in Louisiana.  I added that locality to the map.  Note the latitude of some of the inland sites.  This suggests that during warm interglacials glyptodonts colonized wetlands in upper river valleys.  They may have periodically occurred as far north as what’s now Augusta.

Glyptodont fossils are often found associated with fossils of capybaras and giant tortoises, indicating they occupied the same kinds of habitat.  Glyptodont teeth even resemble capybara teeth, though the former lack enamel.  Glyptodonts are in the edentate family.  Edentate translates to toothless, but they aren’t actually toothless–their teeth simply have no enamel.  Of the three only giant tortoises could occupy drier habitat.  Glyptodonts and capybaras required subtropical or tropical climate because they both fed upon succulent green vegetation, and they couldn’t survive on winter-killed or dormant plants.

Photo of capybaras by a lake shore.  Extinct species of capybaras shared the same habitat with glyptodonts.  Capybaras are the world’s largest rodent, but during the Pleistocene in North America they were second to the giant beaver.

The authors of the below referenced paper suspect a commensal species of bird, like an oxpecker, existed during the Pleistocene and it fed on external parasites formerly found on glyptodonts.

Reference

Gillette, David; and Clayton Ray

“Glyptodonts of North America”

Smithsonian Contributions to Paleobiology #40 1981

Note: I mentioned this specimen in my book but couldn’t remember where I read about it and didn’t include it in my bibliography.  I was happy when I finally find this paper which is available online as a pdf download.