Predator and Prey in the Early Pleistocene of Florida

Pleistocene ecosystems supported a great variety of large predators.  During the early Pleistocene the saber-toothed cat (Smilodon gracilis, ancestor of S. fatalis) and Edward’s wolf (Canis edwardii, possible ancestor of C. dirus) were 2 important carnivores that kept herbivore populations in check.  A study analyzed the chemistry of megafauna bones from 2 early Pleistocene-aged sites in Florida to determine what these 2 predators chose to prey upon.  The study included data from 110 specimens of 12 species excavated from Leisey Shell Pit, and 51 specimens of 9 species found at Inglis 1A.  Species used from Leisey Shell Pit in addition to the 2 carnivores mentioned above included mammoth, mastodon, gompothere, horse, 2 kinds of llama, 2 kinds of peccaries, white tail deer, and tapir.  Subfossil remains from this site date to between 1.5 million years BP-1.1 million years BP during an interglacial climate phase when the environment is thought to have been lowland forest and swamp, though there must have been some grassland.  Species used from Inglis 1A were mastodon, white-tail deer, peccary, tapir, horse, llama, and an extinct species of pronghorn along with Smilodon and Edward’s wolf.  Subfossil remains from Inglis 1A date to between 1.9 million years BP-1.6 million years BP during a glacial climate phase when the environment is thought to have been a mix of longleaf pine savannah, oak scrub, and forest.

Jaw bone of the extinct Edward’s wolf, 1 of the oldest wolf species known to have lived in North America.

Photoshopped Smilodon gracilis, the evolutionary ancestor of the late Pleistocene Smilodon fatalis.

The results of the study indicate Edward’s wolf ate a greater variety of prey than Smilodon, but both species were adaptable to changing environments.  During the interglacial period Smilodon ate herbivores that fed in forest environments (mastodon, deer, tapir, paleollama), while wolves mostly ate grassland herbivores (mammoth, horse).  However, during glacial periods when grasslands predominated Smilodon adapted by eating more grassland herbivores.  Choice of prey among individual saber-toothed cats varied.  Some individual cats ate nothing but forest herbivores, while others ate just grassland herbivores.  I think this shows saber-tooths were territorial animals that stayed in the same home range their entire life.  They ate whatever prey occurred within their established territory.  Herbivores that fed in both forest and grassland (large-headed llamas, gompotheres, peccaries) likely fell prey to both carnivores.

Reference:

Feranec, Robert; and L. Desantis

“Understanding Specifics in Generalist Diets of Carnivores by Analyzing Stable Carbon Isotope Values in Pleistocene Mammals of Florida”

Paleobiology 40 (3) 2014

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New Species of Early Pliocene Saber-tooth (Rhizosmilodon fiteae) Discovered in Florida

Phosphate mining requires the removal of 50 feet of soil, resulting in severe environmental degradation.  By law, mining companies must restore the land following completion of mineral extraction, but it will be centuries before anyone can honestly say the eyesore has been returned to a pristine condition.  Strip mining operations are bad for the environment, but they often expose fossiliferous strata, much to the delight of paleontologists.  Fossil hunters prospecting the spoil piles of the Fort Meade phosphate mine in Polk County, Florida found the remains of 70 species of vertebrates (from thousands of specimens)  dating to the early Pliocene (~4-5 million years BP).

Polk County, Florida–the location of the Fort Meade Mine where many early Pliocene fossils were found.

Fort Meade Mine in Florida.  Scientists discovered an early Pliocene fauna of fossils here in the excavated spoil piles.  

Periodic sea level transgressions explain why marine fossils were found mixed with fossils of land mammals at this site.  Shark’s teeth, including those of the extinct Hemipristis, along with gar and barracuda remains, turtle shells, and fossils of alligators, seals, and whales were found next to the bones of many species of mammals known to have lived in North America during the early Pliocene, just before Ice Ages began occurring.  This was the final age of the hippo-like rhino (Teleoceras), a beast that was about to become extinct after being the most common large mammal here for millions of years.  Several species of 3-toed horses, as well as long-necked camels and llamas browsed the subtropical vegetation.  Eocoileus, the earliest known ancestor to the modern white tail deer and probably the first deer species to live in North America, was part of the fauna then.  Two elephant-like animals–a gompothere and Matthew’s Mastodon–trudged through the forests.  There were 2 types of short-faced bears, a flat-headed peccary, a ground sloth, and a bobcat (Lynx rexroadensis) that were all probable ancestors to the more recent and better known Pleistocene forms.  However, it was the last stand for the extinct bone-eating dog (Borophagus).  This carnivore left no descendents.  Altogether, this list of species is known as the Whidden Creek Local Fauna which corresponds to the regional Palmetto Fauna.

Perhaps the most interesting fossils from the Whidden Creek Local Fauna were the 2 species of saber-tooth cat.  Machairodus colorodensis was a lion-sized saber-tooth that may have been top predator here then.  Scientists at first misidentified the smaller jaguar-sized saber-tooth.  All they found was 1 jaw and based on that specimen it was thought to belong to a Megantereon hesperus, a species known to have ranged well to the north and west of Florida.  However, scientists later found a few more jaws and leg bones assumed to originate from the same species.  Based on this material, they determined the fossils were from a previously unknown species.  They named this new species Rhizosmilodon fiteae.  They believe this new species was ancestral the the early Pleistocene species Smilodon gracilis which was in turn ancestral to 2 late Pleistocene species–Smilodon fatalis and Smilodon populator. The former ranged across North America, while the latter lived in South America.

Jaw and leg bones of Rhizosmilodon fiteae–a probable ancestor to Pleistocene species of Smilodon.

There are several anatomical characteristics that differentiate Rhizosmilodon from its later descendents: It has more minor serrations on its canines, a less developed mandibular flange, larger lower canines, and a lower premolar that is absent or reduced in Pleistocene species of Smilodons.  The mandibular flange is the recess in the lower jaw that acted as a space for the large upper canines when the jaw was shut.

The scientists who identified Rhizosmilodon believe it is a related sister species to Megantereon hesperus.  Rhizosmilodon and Megantereon likely co-occurred temporally but in different geographical ranges.  Rhizosmilodon’s ancestors spread throughout North America, while Megantereon’s ancestors dispersed to Asia, Europe, and Africa.  Rhizosmilodon is the oldest known ancestor to Smilodon and suggests a North American origin of the genus.

Refererence:

Wallace, Steven; and Richard Hulbert

“A New Machairodont from the Palmetto Fauna (Early Pliocene) of Florida, with comments on the origin of the Smilodontii (Mammalia, Carnivora, Felidae)

Plos One March 2013

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0056173