[Author's Note: I'm out in the field at Dinosaur National Monument this week, but when I come back next Tuesday I'll be hosting the paleo blog carnival I started way back when - The Boneyard. I've picked sabertooths as the theme for this edition, but feel free to send me any paleo posts you would like featured when the link-fest goes up next week. In the meantime, here's a repost of one of my recent sabercat essays.]

How does one go about selling a sabercat skeleton? This was the question the Argentinean naturalist Francisco Javier Muñiz asked Charles Darwin in a letter sent on August 30, 1846.

Almost one year previously, in the pages of the Gaceta Mercantil, Muñiz published a detailed description of a nearly-complete saber-toothed cat skeleton. The article’s title proclaimed it as the “Muñi-felis bonaerensis”, and Muñiz believed that the creature was unlike any fossil mammal found in South America before. “I am the first, in the account that follows,” Muñiz wrote, “to recommend [the skeleton] to the attention of savants dedicated to examining these witnesses and victims of terrible, devastating catastrophes.”

Muñiz wasn’t entirely right about the uniqueness of his find – a few pieces of South American sabercat erroneously attributed to the genus Machairodus had found their way into European collections by the time of his letter to Darwin – but nothing as complete as the new fossil had been found before. Muñiz hoped that Darwin, a scientific celebrity in Argentina after his earlier visits on the HMS Beagle, might help find the fossil a home.

The English naturalist did not offer Muñiz much assistance. In a reply to Muñiz thdated February 26th, 1847, Darwin wrote:

I conceive the only feasible plan would be to send your fossils here to some agent to dispose of them.^^No society will purchase anything of the kind without having them inspected, and most societies only receive presents. Your specimen of the Muñi-felis must be a noble one; I suspect it will turn out to be a Machairodus, of which there are some fragments in the British Museum from the Pampas. I will endeavour to get your paper translated and inserted in some scientific periodical.

This isn’t to say that Darwin didn’t try. Two weeks earlier he had written to Richard Owen, the influential but cantankerous anatomist, hoping that the College of Surgeons might purchase the sabercat or, at the least, cover the expenses required for Muñiz to send the fossils. “If S. Muniz is encouraged,” Darwin prodded, “he will probably send other things”, thus establishing a valuable connection between the English academics and a promising naturalist working in a far-off field.

But nothing happened. Though Darwin sent a translation of Muñiz’s original description on to Owen, the paper never saw publication. Nor was Owen or anyone else willing to pay for the “Muñi-felis.” The skeleton was effectively forgotten, at least until the German zoologist Hermann Burmeister moved to Argentina two decades later and met Muñiz. Given charge of the disorganized Museo Público in Buenos Aires, Hermann negotiated to purchase the neglected specimen, which he described under the name “Machaerodus neogaeus” in 1866.

Little has been said of this great cat since the time of Hermann’s update of the original work by Muñiz. Adriana Novoa and Alex Levine’s recent book From Man to Ape – from which the above account was drawn – dug up the tale of this historically-significant fossil, and we now know it was only one of the first finds of sabercat species that once stalked the Pleistocene grasslands of South America.

Up until now, only two sabercat species could be confirmed from the fossil deposits of South America. They were the species Smilodon fatalis and Smilodon populator, which both lived on the continent between 1 million to 11,000 years ago. Muñiz’s skeleton was one of the first Smilodon skeletons found anywhere.

Both Smilodon species appeared on the southern continent after the Panamanian land bridge was established around three million years ago. This small connection opened up a highway for the animals of the Americas to move across. South American forms such as terror birds, glyptodonts, and giant sloths moved north, while bears, elephants, and other northern species moved south, with Smilodon being the only genus of sabercats known to make the jump. (Other cats - such as pumas, jaguars, and ocelots - also moved into South America during the interchange, where they persist to this day.)

In a paper just published in the Journal of Vertebrate Paleontology, scientists Ascanio Rincón, Francisco Prevosti, and Gilberto Parra have now added two other sabercat species to the roll of South America’s prehistoric fauna. The finds come from El Breal de Orocual in the northeastern Venezuelan state of Monagas. Dating between 1 million and 500,000 years ago, this site is a fossil tar seep – think of the well-known La Brea Tar Pits – that was once surrounded by a prehistoric grassland supported patches of forest and fringed by rivers. Giant sloths, glyptodonts, huge armadillos, tapirs, llamas, and horses lived there, and at least some of them were preyed upon by a pair of sabercat species that were previously unknown in South America.

Of the two sabercat species reported by Rincón and co-authors, one is a new species and the other is a North American migrant. They represent the two major subgroups of sabercats. Even though one saber-toothed felid might look the same as another, paleontologists have broken down sabercats into the “scimitar-tooths” and the “dirk-tooths.” The scimitar-tooths, such as Homotherium, had relatively short, coarsely-serrated fangs and long-limbed bodies adapted for speed. Dirk-tooths such as Smilodon, by comparison, had longer, more recurved canine teeth and stockier bodies well-suited to literally tackling large prey.

(Not every sabercat falls neatly into one category or another, though. In 2000, Larry Martin and colleagues wrote a short note on Xenosmilus from the Pleistocene of Florida – a close cousin of Homotherium that had scimitar teeth but a bulky body more like that of Smilodon.)

The new species from Venezuela was a scimitar cat given the name Homotherium venezuelensis. Known from a distorted skull, most of a lower jawbone, and some isolated teeth, this sabercat was similar to other Homotherium species found in Africa, Europe, Asia, and North America, but was distinguished by having a relatively broad front portion of the skull in which the upper palate was about as wide as it was long. Though the partial jaw of an unidentifiable scimitar cat of an uncertain age had recently been reported from Uruguay, the new identification of Homotherium venezuelensis has left no doubt that the scimitar cats made the crossing into South America.

Smilodon gracilis – a small, dirk-toothed species – was the other sabercat found in the tar seep. Only a fractured canine and a few other isolated teeth were found.

Often considered as a potential ancestor to later, larger Smilodon species, Smilodon gracilis has previously been found in North America. The fossils from El Breal de Orocual confirm that this species extended its range into prehistoric Venezuela, too. A southern population of Smilodon gracilis may have even been ancestral to the larger Smilodon populator of South America, Rincón and colleagues suggest, though large samples of sabercat fossils will be needed to test this idea about ancestry.

Why these cats disappeared is unknown. At this point, the scimitar cats are just a blip in South America’s fossil record – disappearing soon after they arrived – although further sampling may turn up additional bones from other sites. What happened to Smilodon gracilis is also unclear – did it speciate into Smilodon populator, or was it out-competed by other, bigger Smilodon species? A deeper knowledge of Pleistocene South America than we presently have is needed to find out. Though these fossils were found in the northern part of the continent, most other sabercat finds have been made further south, and paleontologists will have to fill in the geographic and stratigraphic gaps if these mysteries are to be solved. There is much left to learn about southern Smilodon and their scimitar-toothed cousins.

Top image: A restoration of the North American scimitar cat Homotherium serum on display in the "Mammoths and Mastodons" exhibit during its stop at the Liberty Science Center. Photo by author.

References:

Martin, L., Babiarz, J., Naples, V., & Hearst, J. (2000). Three Ways To Be a Saber-Toothed Cat Naturwissenschaften, 87 (1), 41-44 DOI: 10.1007/s001140050007

Novoa, A., and Levine, A. 2010. From Man to Ape: Darwinism in Argentina 1870-1920. Chicago: University of Chicago Press. pp. 33-36, 52, 64

Rincon, A., Prevosti, F., & Parra, G. (2011). New saber-toothed cat records (Felidae: Machairodontinae) for the Pleistocene of Venezuela, and the Great American Biotic Interchange Journal of Vertebrate Paleontology, 31 (2), 468-478 DOI: 10.1080/02724634.2011.550366