Posts Tagged ‘Friesenhahn Cave’

The Friesenhahn Cave Fossil Site in Bexar County, Texas

November 14, 2017

Rob Nelson stood next to a wall of fossils on 1 episode of Secrets of the Underground, a Science channel tv series.  He was visiting Friesenhahn Cave in Bexar County, Texas about 20 miles north of San Antonio during the taping of the series he hosts.  The tusk of a mammoth or mastodon, a baby mammoth tooth, and many small fossils were visible; and they were cemented together.  It’s remarkable that such an undisturbed matrix could still exist here because people have been excavating fossils from this site off and on for about 100 years.  Specimens collected by local amateurs were first described from this site in a paper published during 1920.  For awhile the landowner stopped permitting people to collect fossils in the cave, but then in 1949 Mr. Friesenhahn himself invited some professors to excavate fossils in the cave. They found the complete skeletons of scimitar-toothed cats and a long-nosed peccary plus the bones of 30 other species of mammals and the remains of reptiles and amphibians. The discovery of the complete scimitar-toothed cat skeletons was important because before this the species was known from an incomplete skull, a few teeth, and some isolated bones.  Large numbers of juvenile mammoth and mastodon bones were found associated with the scimitar-toothed cat skeletons, and the paleontologists came to the conclusion the big cats used the cave as a den and dragged their prey inside.

A flurry of papers about the cave were published, but access was again restricted until Concordia University purchased the property in 1998.  Apparently, since the purchase, some scientists have been working with the disturbed sediments, but they are waiting for a private or government grant before tackling the remaining undisturbed strata.  I suppose they want to use the most modern techniques when going through this material.  During the original dig 68 years ago, scientists mention fossils that were in such poor condition “they weren’t worth preserving.”  (I was appalled when I read this.)  There are modern methods that can preserve fossils that are in poor condition, but they can be costly.  Scientists have also developed better ways of excavating fossils.  Nevertheless, nothing has been published in the scientific literature about this cave since Concordia University purchased the property.  It has been nearly 20 years, and they still haven’t been able to obtain funding for new excavations, though they do have a corporate grant to study the disturbed sediments.  Still, it seems as if someone currently studying the cave would have at least published a paper by now entitled “Additional fossils recovered from Friesenhahn Cave.”  To be honest, I am not impressed with their academic efforts here.

Brief excerpt of an episode of Secrets of the Underground, featuring Friesenhahn Cave.

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A grate protects the cave from looters and keeps trespassers from falling inside.

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The paleontologist, Grayson Mead, with the complete skeleton of a scimitar-toothed cat discovered in Friesenhahn Cave during 1949.

So far, 13 adult and 5 juvenile scimitar-toothed cat remains have been found in the cave.  It’s unclear which of these were recovered in 1949 and which were discovered more recently.  The cave has also yielded 1 bone of a saber-toothed cat, hundreds of baby mammoth and mastodon teeth, the bone of 1 ground sloth; and the remains of bison, deer, camel, tapir, long-nosed peccary, black bear, dire wolf, and coyote.  The latter was especially abundant.  Smaller animals that inhabited the area during the late Pleistocene, based on the bone accumulation in the cave, were jack rabbit, cottontail, desert cottontail, pocket mouse, and 4 species of mice in the Peromyscus genus.  Some of these species are listed in the paleobiology database, and others are mentioned in the below referenced bulletin or on the Texas University website.  The lists don’t match up.  Someone needs to do a more thorough review of the specimens to determine exactly which species were found by whom and during which excavation.

Evidence suggests a pond periodically existed in the cave, depending upon rain and drought cycles. The basin filled during rainy years but dried out during droughts. No fossil evidence of pond turtles exists here.  Instead paleontologists report remains of 2 terrestrial species–a large extinct subspecies of box turtle and an extinct tortoise (Geochelone wilsonirelated to the extinct giant tortoises that ranged throughout the south during the Pleistocene.  G. wilsoni is known from just a few sites in North America but was first discovered in Frisenhahn Cave.  Pond turtles never found the ephemeral water hole in the cave, but northern leopard and barking frogs did. Diamondback rattlesnakes used the cave as a den as well.

The species composition suggests the region around the cave was an arid grassland with some scrub.  Woodlands existed alongside local rivers.  The mammoth, bison, camel, coyote, and jackrabbit indicate dry grassland environments.  However, the presence of deer, tapir, long-nosed peccary, and black bear suggest some woodlands or forest edge habitat existed nearby.

The cave formed when rainwater dissolved limestone rock underground.  The initial entrance was small, and the oldest levels contain small vertebrates deposited in the form of owl pellets.  Gradually, the entrance enlarged so that larger vertebrates began to use it as a den.  Some of the fossil remains are from animals that died in the cave, but others were brought in by predators.  Periodic flash floods may have added small bones to the collection.  Eventually, the cave entrance collapsed, and the chamber was sealed for thousands of years until recent times when a sinkhole formed on top of the cave, allowing modern day access.  The remains are estimated to be 19,000 years old, but it’s unclear where this estimate originated.  I’m unaware of any carbon-dating of the objects in this cave.  It was originally discovered before carbon-dating was invented.  The site is badly in need of a more modern review, and I’m not sure Concordia University is up to the task.

References:

Evans, Glen; and Grayson Meade

“The Friesenhahn Cave” and “The Saber-toothed Cat, Dinobastis serus

Bulletin of the Texas Memorial Museum  September 1961

Secrets of the Underground  Season 1 Episode 5

Why did Fanged Cats have Long Forelimbs and Sloping Backs?

October 8, 2010

Until about 13,000 calender years ago, two species of large, powerful, fanged cats stalked the beautiful forests and plains of southeastern North America.

Smilodon depicted in top illustration; Dinobastis on the bottom.

The more famous saber-tooth (Smilodon fatalis) is well known from the thousands of specimens found in the La brae tar pits in California, but many have also been discovered in Florida, and some fossils of them have turned up in Alabama, Tennessee, and South Carolina.  Fossils of the scimitar-tooth (Dinobastis serus) are less common–nearly complete skeletons in North America only being discovered in Friesenhahn Cave, Bexar County, Texas, though individual specimens have been found in Oklahoma, Tennessee, Florida, and some western states, such as Alaska.  This latter species had a worldwide distribution, leaving fossils in what today is England as well as Africa.

Sketch of skull found in Friesenhahn Cave from The Bulletin of the Texas Memorial Museum number 2 September 1961.

The skulls of both species of fanged cats are similar, but the two differ greatly in dentition.  The scimitar-tooth had larger incisors, but its fangs or canines were shorter and smaller.  Smilodon’s fangs were serrated in front; Dinobastis’s were serrated on both sides. When Smilodon closed its mouth, the fangs extended lower than the jaw, while Dinobastis’s fangs only reached the bottom of the jaw.

Both species had longer forelimbs than hindlimbs.  The scimitar-tooths had even longer forelimbs than the saber-tooth’s, but they weren’t quite as heavily built.

Based on anatomical characteristics, scientists believed saber-tooths and scimitar-tooths were closely related, and a recent study of DNA supports this hypothesis.  They are considered a sub-family within the Felidae.  The fanged cats are in the Machairodontinae, while all other cats, including every extant species, are considered to be in the Felinae.  See: http://www.adelaide.edu.au/acad/publications/papers/SmilodonFinal.pdf

The fanged cats had a sloping back, much like modern day hyenas (Crocuta crocuta), and likely ran about in a gait that would have resembled that of a hyena.  I’ve often wondered why they were built like this.  Some scientists speculate the longer forelimbs gave them an advantage when hunting juvenile proboscideans.  But it occurred to me after watching videos of a hyena fighting off a pack of wild African hunting dogs, that perhaps this build made it easier for them to do battle with packs of wild canids, such as their most important ecological competitor, the dire wolf, though dholes or red Indian dogs also occurred in the central part of North America during the Pleistocene, and were probably an important competitor there as well.

http://www.youtube.com/watch?v=YiqAxa1tJ5g

Perhaps with a sloping back, it was easier for the fanged cats to sit on their haunches and use their paws and fangs to defend themselves against packs of wolves that would’ve tried to nip them from behind and even bite their hamstrings.

Cats are distantly related to hyenas.  The cat branch on the evolutionary tree is placed next to the hyena branch, and the machairodontinae sub-family is the closest cat related to the hyenas.  The trait of a sloping back and longer forelimbs evolved millions of years before the Pleistocene, perhaps originating with some common ancestor of hyenas and cats.

Friesenhahn Cave in Bexar County, Texas

This is a really nice sketch of Friesenhahn Cave from the previously mentioned periodical.  The artist’s name isn’t given.

A sinkhole on a cattle ranch in south central Texas opens to an ancient cave where thousands of Pleistocene age fossils have been preserved.  Two nearly complete skeletons of the scimitar cat were discovered here about fifty years ago, along with the skeletons of two scimitar cat kittens.  This species periodically must have used the cave as a den for millennia.  The Pleistocene-age fossils are dated from between 19,000-17,000 years BP.  Some other fossils in the cave date to 9,000 BP, and some are even more recent, dating to less than 300 years BP.   Scientists believe the surrounding environment was mostly arid grassland, but occasional heavy rains (due to the drastically fluctuating Ice Age climate) caused flash floods that washed sediment into the cave, burying the bones of dead animals.  Later, the cave entrance collapsed, sealing the bones from the atmosphere.  Moreover, the limestone in the soil contributed to the preservation of the fossil material.  The sinkhole formed recently, providing the opportunity for people to discover the cave.

Thousands of baby mammoth teeth were recovered here–evidence that scimitar cats ambushed them and dragged them in the cave.  Though a pond that existed in the cave may have attracted herbivores seeking drinking water, the sheer number of individual baby mammoth specimens that accumulated here must have been the result of scimitar-tooth cat predation.  Scimitar-tooth cats must have specialized in preying on juvenile proboscideans–baby mastodon teeth were found here too.  How they successfully hunted baby mammoths, guarded by adults, is a mystery.  I assume they ambushed ones that wondered too far from the herd.

In addition to the scimitar cat fossils, the cave was the final resting place for many other Pleistocene animals.  One tooth of the other fanged cat, Smilodon fatalis, was found here along with many coyote fossils, and some of black bear.  Other remains include mammoth, mastodon, ground sloth, deer, bison, horse, camel, tapir, long-nosed peccary (a nearly complete skeleton), flat-headed peccary, black-tailed jack rabbit, cottontail rabbit, eastern chipmunk, pocket gopher, bog lemming, pine vole, eastern mole, short-tailed shrew, desert shrew, giant tortoise, box turtle, aquatic turtles, toads, snakes, and lizards.  There may be some human artificats, but nothing definite because it’s sometimes difficult to distinguish natural artifacts from manmade ones.

Scientists think the Pleistocene environment that existed at the time the specimens were deposed is one that no longer occurs anywhere.  They believe that what was to become Bexar County was mostly an arid grassland interspersed with riparian woodlands consisting of deciduous trees.  It is strange that the desert shrew, a species of the southwest desert, lived near the eastern chipmunk which lives in moist woodlands.  And indeed grassland species (bison, horse, camel, mammoth) and woodland species (mastodon, deer, long-nosed peccary, tapir) both found suitable habitat near the cave.