Tuesday, November 3, 2015

Steulett's Terror Bird (Andalgalornis steuletti)

The dorsal (A), ventral (B), and lateral (C)
view of the skull of Andalgalornis steuletti.
Figure 1 from Degrange et al., 2010. (Wiki)
Steulett’s Terror Bird (Andalgalornis steuletti) is a mid-sized terror bird (Phorusrhacidae) from the late Miocene and early Pliocene. It ranks as one of the deadliest predators of its time, armed with speed, agility, and a guillotine-like beak.

Habitat & Distribution
Steulett’s Terror Bird lived during the upper Miocene to lower Pliocene of South America. Its remains are currently known only from Argentina, which was covered primarily by grassland and open woodland at the time.

Physical Attributes
This species is known from a partial skeleton as well as isolated bones. Steulett’s Terror Bird was roughly the size of a Greater Rhea (Rhea americana) but was more robust, weighing perhaps 40 to 50kg compared to 35kg for the average adult male rhea. It stood 90 to 100cm high at the level of the back and could raise its head to about 140cm above the ground, or about the height of the average 12 year-old. Overall, Steulett’s Terror Bird was more powerfully built in proportion to other terror birds. Its 37cm skull in particular had a viciously hooked beak which was very tall, somewhat blade-like, and capable of withstanding considerable forces. This suggests that these animals were able to handle relatively large prey items, perhaps even larger than themselves. Detailed studies of the neck vertebrae have been performed which suggest that the neck of Steulett’s Terror Bird would have been held in an S-shaped position while at rest and was adapted for rapid and powerful movements in the sagittal plane*, an ideal motion for striking prey.
Ecology & Behavior
Although it has traditionally been thought of as a hunter of small prey, the reinforced skull and blade-like beak of Steulett’s Terror Bird was built to withstand the considerable stresses involved in bringing down animals of considerable sizes. Potential prey items included a broad range of small to relatively large mammalian herbivores like hegetotheres* and cavimorph rodents, as well as many of the smaller toxodonts*, machraucheniids*, and ground sloths with which it coexisted. Whether it hunted singly or in small social groups is unknown, but regardless of its hunting method Steulett’s Terror Bird was undoubtedly one of the top predators of its time. Competing predators included several sparassodonts*, including the Marsupial Sabertooth (Thylacosmilus atrox), and at least four other species of terror bird, including smaller Scaglia’s Terror Bird (Llallawavis scagliai).
Hegetothere: an extinct family of small, rabbit-like ungulates endemic to South America.
Macrauucheniid: an extinct family of small to large, long-necked ungulates endemic to South America.
Sagittal plane: the vertical plane which separates the body into right and left halves.
Sparassodonta: an extinct order of predatory mammals endemic to South America from the Paleocene to the Pliocene.
Toxodont: an extinct family of sheep to bison-sized ungulates endemic to South America until the Pleistocene.

References & Further Reading
Tambussi CP, de Mendoza R, Degrange FJ, Picasso MB (2012). “Flexibility along the neck of the Neogene terror bird Andalgalornis steuletti (Aves Phorusrhacidae)”. PLoS ONE 7(5): e37701 <Full Article>

Degrange FJ, Tambussi CP, Moreno K, Witmer LM, Wroe S (2010). “Mechanical analysis of feeding behavior in the extinct “terror bird” Andalgalornis steulleti (Gruiformes: Phorusrhacidae)”. PLoS ONE 5(8): e11856 <Full Article>

Alvarenga HMF, Höfling E (2003). "Systematic revision of the Phorusrhacidae (Aves: Ralliformes)". Papéis Avulsos de Zoologia 43(4): 55–91 <Full Article>

Monday, November 2, 2015

Dire Wolf (Canis dirus)

The Dire Wolf (Canis dirus) is one of the most well-known predators of Pleistocene North America and recently made famous by the television series Game of Thrones (although the animals depicted in the series are much larger than their real-life counterparts). These were mid-sized predators closely related to the modern Coyote (C. latrans) and Gray Wolf (C. lupus), both of which coexisted with it during the Pleistocene.
Reconstructed and restored Dire Wolf skeleton from Rancho La Brea,
on display at the Perot Museum, Texas. Wiki.
The genus name Canis is the Greek word for “dog”. The species name dirus is derived from the Latin word dira, which means “ominous”, “fearful”, or “dreadful”.

Habitat & Distribution
Dire Wolves were geographically widespread throughout North and South America during the Pleistocene, reported from 136 localities in North America and 3 localities in South America. Whether or not this species originated in North or South America is a matter of much debate. Its range extended from Alberta, Canada to Tarija, Bolivia north-to-south. Its habitat included forested mountains to open grasslands and plains up to 2255m (7400ft). Compared to Pleistocene Gray Wolves, Dire Wolves appears to have favored somewhat wetter environments and their fossils are often found in association with ancient marshes, rivers, and lakes. Most famously, the highly productive site of Rancho La Brea, California has yielded the remains of over 4,000 individual Dire Wolves, which had become mired in the asphalt trap most likely after attempting to hunt or scavenge other animals that died there. These wolves are frequently found at the same localities as the Saber-toothed Cat (Smilodon fatalis).
Physical Attributes
Dire Wolves were comparable to Gray Wolves in terms of linear measurements. However, the Dire Wolf was physically more robust and heavily built than the Gray and could have weighed as much as 20% more than a comparably sized Gray Wolf. The skull in particular is proportionally larger and broader with a more prominent sagittal crest*. The canines and carnassials* are also larger. Measurements of the skull suggest that Dire Wolves had a bite force that was about 20% greater than that of the Gray Wolf. Dire Wolves also had sturdier limbs with shortened metapodials and a longer tail. Although undoubtedly a swift runner, Dire Wolves were not built to pursue fast-moving herbivores over great distances the way that Gray Wolves do. Instead, they may have relied more on ambushing prey, taking turns chasing it, or even by chasing animals into the water where its movements are hindered, all of which are tactics still employed by modern pack-hunting canids.
Ecology & Behavior
Because of their greater biting capacity, Dire Wolves have often been suspected of being bone-cracking specialists similar to modern hyenas of the genus Hyaena and extinct “hyena-dogs” of the genus Borophagus. However, studies of their overall dentition and bite damage of fossil bones have demonstrated that their teeth were no better at breaking bones than its modern relative the Gray Wolf, although it must be noted that these wolves can (and do) damage and ingest considerable amounts of bone during feeding. Furthermore, the crushing aspect of the Dire Wolf dentition is not any more developed than that of its modern relative while the slicing aspect is enhanced. Thus, it may be inferred that the robust skull, stronger bite, and larger teeth of the Dire Wolf, coupled with its sturdier frame, was more of an adaptation for seizing and pulling down and rapidly consuming larger herbivores rather than an adaptation for bone cracking. In this way, the hunting and feeding style of the Dire Wolf was likely more akin to that of modern canids like Dholes (Cuon alpinus) or Bush Dogs (Speothos venaticus) which frequently and efficiently hunt prey that is considerably larger than themselves.
Skeletal comparison of Gray Wolf (left) and Dire Wolf (right). Wiki
This, in turn, hints at the potential niche stratification between the Dire Wolf and the Gray Wolf during the Pleistocene. Gray Wolves were more commonly found in drier and more well-drained environments and can exist at higher altitudes than what the Dire Wolf appears to have tolerated. Pleistocene Gray Wolves would probably have focused more on ungulates weighing 50 to 300kg (110 to 660lbs) as its primary prey base. Modern Gray Wolves struggle to bring down ungulates weighing more than 500kg (1,102lbs), even in winter when such animals are easier to overwhelm, with hunts often lasting hours and with a high incidence of injury. Dire Wolves, on the other hand, were potentially hunting prey as much as 10 times their own weight, with a prey menu that included horses, tapir, large deer, camels, and bison, although they would also have opportunistically hunted smaller animals in their environment such as capybaras, giant beavers, and peccaries as encountered. Given that larger prey animals were a more prominent element of the Dire Wolf diet, it is also likely that these animals occurred in relatively larger packs numbering as many as 20 individuals, as opposed to modern Gray Wolves whose packs average 10 members in most areas.
Display of some of the thousands of Dire Wolf skulls recovered from Rancho La Brea
on display at the Page Museum, California. Wiki.
Carnassial: specialized shearing cheek teeth found in terrestrial mammalian predators.
Sagittal crest: the ridge of bone that runs down the midline of the skull in many mammals.

References & Further Reading
Pardi MI & Smith FA (2015). "Biotic responses of canids to the terminal Pleistocene megafauna extinction". Ecography 38: 1-11 <Abstract>

Anyonage W & Baker A (2006). “Craniodental morphology and feeding behavior in Canis dirus, the extinct Pleistocene dire wolf”. Journal of Zoology 269: 309-316 <Abstract>

Dundas RG (1999). “Quaternary records of the dire wolf, Canis dirus, in North and South America”. Boreas 28: 375-385 <Abstract>

Dire Wolf, Canis dirus (Mammalia; Carnivora; Canidae), from the Late Pleistocene (Rancholabrean) of East-Central Sonora, Mexico <Abstract>

Kurten B & Anderson E. “Pleistocene Mammals of North America”. New York City, New York: Columbia University Press, 1980. 171-172 <Book>

Monday, September 28, 2015

Scaglia’s Terror Bird (Llallawavis scagliai)

Scaglia’s Terror Bird (Llallawavis scagliai) is the most recently discovered member of the terror bird family (Phorusrhacidae). This species known for a single near-complete, fully-articulated skeleton which even includes a preserved windpipe.
Drawing showing the skeletal anatomy of Llallawavis scagliai.
Figure 2 from Degrange et al., 2015.
The name Llallawa means “magnificent” in Quechua, in reference to the well-preserved nature of the remains. Avis is the Latin word for “bird”. The species name is after Galileo Juan Scalia, a naturalist and director of the Museo Municipal de Ciencias Naturales in Mar del Plata, Argentina. Fully translated, the binomial name therefore means “Scaglia’s Magnificent Bird”.

Habitat & Distribution
Scaglia’s Terror Bird lived during the late Pliocene in what is now Argentina. Its habitat was likely grassland and open woodland.

Physical Attributes
This species is known from a single, nearly complete articulated skeleton, the most complete of any terror bird known to date. Discovered in 2010 and described in 2015, the skeleton (shown above) was missing only some of the forelimb bones, toe bones, and the pygostyle*. This specimen is particularly valuable in that it includes the only complete trachea known for any terror bird, as well as intact sclerotic rings*.

Scaglia’s Terror Bird was one of the smaller members of its family, with an estimated body mass of 18kg (40lbs) and a hip height of about 90cm (3ft). When fully erect, it could have stood 120cm (4ft) tall at the top of its head. The body was lightly-built with long, slender legs for fast running. The skull was about 27cm (0.9ft) long with a beak that was relatively shallower and with a less prominent hook than that of other terror birds. Another notable feature of the bird’s head was its narial knob or bump just above its nostrils.

Ecology & Behavior
The structure of the inner ear suggests that Scaglia’s Terror Bird was adapted for very rapid and precise movements of the head and neck in response to visual and audio cues. Its low, narrow beak and lightweight body suggests that its diet consisted of relatively small prey items such as cavimorph rodents and other small mammals, as well as smaller birds and reptiles. It probably hunted in a manner similar to modern seriemas; after a short dash the prey would be pinned down before being picked up and violently slammed into the ground repeatedly. This action not only kills the victim, but also makes it easier to swallow due to the breaking of its bones.
Although it is currently impossible to reproduce the types of sounds Scaglia’s Terror Bird could produce, detailed analysis of its hearing capacity has shown that it could detect frequencies ranging from 380 to 4230 Hz, with a mean sensitivity of 2300 Hz. The bird’s own vocalizations, as well as those of its prey would have fallen within this range.

Hertz (Hz): a unit of frequency
Pygostyle: in birds, the fusion of several caudal (tail) vertebrae into a single bone.
Sclerotic ring: rings of interlocking bones which support the eyeball in several vertebrate groups.

References & Further Reading
Degrange FJ, Tambussi CP, Taglioretti ML, Dondas A, Scaglia F (2015). “A new Mesembriornithinae (Aves, Phorusrhacidae) provides new insights into the phylogeny and sensory capabilities of terror birds”. Journal of Vertebrate Paleontology 35(2): e912656 <Abstract>

Wednesday, September 2, 2015

Phorusrhacidae: the Terror Birds

The phorusrhacids, known commonly as the “terror birds”, were a diverse group of predatory flightless birds that inhabited South America from the early Paleocene to the late Pleistocene. The family Phorusrhacidae belongs to a larger order of birds known as the Cariamiformes or Cariamae, which originated during the late Cretaceous and appear to have become specialized for a primarily terrestrial lifestyle very early in their evolutionary history. In addition to South America, close relatives of terror birds were also distributed through Europe, Africa, and Antarctica during the Paleocene and Eocene. By the Oligocene, however, they had become extinct on all other continents except South America where they remained diverse.
Life restoration of Phorusrhacos longissimus
by Charles R. Knight, 1901. Wiki
The terror birds themselves were prominent components of the carnivore-omnivore guild in South America throughout the Cenozoic together with sebecid* crocodylians and sparassodont* marsupials. At least one species, Titanis walleri, managed to colonize the southern United States after the Isthmus of Panama connected the two Americas during the middle Pliocene. Species within this family range in mass from 5kg to about 400kg (10 to 880lbs). Terror birds continued to thrive in South America until they became extinct at the end of the Pleistocene together with many other types of large birds and mammals. The closest living relatives of the terror birds, and the only surviving representatives of the Cariamae, are the two species of seriema (Cariamidae) from South America. These modern birds are still capable of flight but prefer to hunt on the ground.
Red-legged Seriema (Cariama cristata), one
of two surviving representatives of the
Cariamae. Wiki
Anatomy & Action
Terror birds had proportionally large heads with deep, laterally flattened beaks with a hooked tip for tearing flesh. The inner structure of the beak was reinforced by bony struts and the skull bones were tightly fused together for strength. The pelvis was especially large to act as a counterbalance. They had long, powerful necks which would have been held in an S-shaped position when at rest. Detailed studies of the neck vertebrae shows that they were particularly well-adapted at making swift movements in the sagittal* plane, which is an ideal motion for striking prey. The caudal* vertebrae also appear to be somewhat more developed than those of modern flightless birds, implying that the tail, though highly reduced, may have been functional as a rudder of sorts during the pursuit of prey. As with all flightless birds, the bones of the forelimbs are greatly reduced in terror birds and were possibly involved in stability and maneuverability while running. The overall skeleton is much heavier and sturdier than what would be expected for a flying bird of the same size.

CT scan of the skull of the mid-sized terror
bird Andalgalornis steulleti. Wiki
Terror birds were primarily carnivorous, as evidenced by their large heads and massive, hooked beaks. Recent studies have shown that the sense of hearing in terror birds was well-developed and particularly sensitive to low-frequency sounds, suggesting that these birds utilized deep, resonant vocalizations to communicate with one another. CT scans of the brain cavities have shown that the areas of the brain that deal with visual information and problem-solving are also well-developed, while the sense of smell was relatively less so. It seems likely that terror birds hunted using vision and hearing as their primary senses. Once captured and dispatched, smaller prey items would have simply been swallowed whole, while larger meals were torn apart by the birds’ massive beak. Studies of terror bird limb muscular and proportions suggests that they were capable of exceptional feats of speed and agility.

Restored skeleton of Titanis walleri at the Florida Museum of
Natual History. Wiki
Terror Bird Groups
The family Phorusrhacidae is divided into five subfamilies; Psilopterinae, Brontornithinae, Patagornithinae, Mesembriornithinae, and Phorusrhacinae.
Restored skulls and heads of five terror bird species belonging to each of the subfamilies. 
A. Psilopterus lemoinei (Psilopterinae), B. Paraphysornis brasiliensis (Brontornithinae),
C. Andalgalornis steuletti (Patagornithinae), D. Llawllavis scagliai (Mesembriornithinae),
E. Kelenken guillermoi (Phorusrhacinae).
The longest-lived terror bird lineage, the Psilopterinae have a temporal range spanning from the late Paleocene to the early Pliocene. They are characterized by relatively slender, lightweight bodies, proportionally thin hindlimbs, and small overall size. Members of this subfamily range from 5 to 15kg in body mass. Known species include Paleopsilopterus itaboraiensis (early Paleocene), Psilopterus affinis (late Oligocene), P. bachmanni (late Miocene), P. lemoinei (late Miocene), and P. cozecus (late Miocene).

The brontornithines were large-bodied terror birds that existed during the Oligocene through to the early Miocene. Over time they appear to have been replaced by the Phorusrhacinae (see below) by the middle Miocene. Known species include Physornis fortis (late Oligocene), Paraphysornis brasiliensis (middle Oligocene to early Miocene), Brontornis burmeisteri (late Oligocene to middle Miocene).

Patagornithines were mid-sized terror birds with lean bodies and slender limb proportions. Known species include Andalgalornis steulleti (late Miocene to Pliocene), Andrewsornis abbotti (middle to late Oligocene), Patagornis marshi (middle Miocene).

The Mesembriornithinae are the shortest-lived and most diverse phorusrhacid subfamily, with a fossil record dating back to the late Miocene to the late Pliocene. Most are relatively small at around 10kg, while a few grew considerably large achieving estimated body weights of up to 70kg. It contains three genera and four species; Procariama simplex (late Miocene to late Pliocene), Llallawavis scagliai (Pliocene), Mesembriornis incertus (late Miocene to Pliocene), and M. milineedwardsi (late Miocene to Pliocene).

The Phorusrhacinae, together with the Brontornithinae, include some of the largest of the terror birds, with species ranging in mass from 100 to 400kg. This subfamily first appeared during the middle Miocene and persisted to the end of the Pleistocene. Known species include Phorusrhacos longissimus (middle Miocene), Kelenken guillermoi (middle Miocene), Devincenzia pozzi (late Miocene to early Pliocene), Titanis walleri (late Pliocene to early Pleistocene).

Caudal: of or referring to the tail of an animal.
Sagittal: a vertical plane that divides the body into right and left halves.
Sebecidae: an extinct group of terrestrial crocodilians endemic to South America until the late Miocene.
Sparassodonta: an extinct order of predatory mammals endemic to South America until the Pliocene.

References & Further Reading
Degrange FJ, Tambussi CP, Taglioretti ML, Dondas A, Scaglia F (2015). “A new Mesembriornithinae (Aves, Phorusrhacidae) provides new insights into the phylogeny and sensory capabilities of terror birds”. Journal of Vertebrate Paleontology 35(2): e912656 <Abstract>

Blanco RE & Jones WW (2013). “Terror birds on the run: a mechanical model to estimate its maximum running speed”. Proceedings of the Royal Society B 272: 1769-1773 <Full Article>

Angst D, Buffetaut E, Lecuyer C, Amiot R (2013). “Terror birds (Phorusrhacidae) from the Eocene of Europe imply trans-Tethys dispersal”. PLoS ONE 8(11): e80357 <Full Article>

Vezzosi RI (2012). “First record of Procariama simplex Rovereto, 1914 (Phorusrhacidae, Psilopterinae) in the Cerro Azul Formation (upper Miocene) of La Pampa Province; remarks on its anatomy, palaeogeography and chronological range”. Alcheringa: an Australasian Journal of Palaeontology 36(2): 157-169 <Full Article>

Tambussi CP, de Mendoza R, Degrange FJ, Picasso MB (2012). “Flexibility along the neck of the Neogene terror bird Andalgalornis steuletti (Aves Phorusrhacidae)”. PLoS ONE 7(5): e37701 <Full Article>

Degrange FJ & Tambussi CP (2011). “Re-examination of Psilopterus lemoinei (Aves, Phorusrhacidae), a late early Miocene little terror bird from Patagonia (Argentina)”. Journal of Vertebrate Paleontology 31(5): 1080-1092 <Abstract>

Mourer-Chauvire C, Tabuce R, Mahboubi M, Adaci M, Bensalah M (2011). “A Phororhacoid bird from the Eocene of Africa”. Naturwissenschaften 98: 815-823 <Full Article>

Degrange FJ, Tambussi CP, Moreno K, Witmer LM, Wroe S (2010). “Mechanical analysis of feeding behavior in the extinct “terror bird” Andalgalornis steulleti (Gruiformes: Phorusrhacidae)”. PLoS ONE 5(8): e11856 <Full Article>

Alvarenga H, Jones W, Rinderknecht A (2010). “The youngest record of phorusrhacid birds (Aves, Phorusrhacidae) from the late Pleistocene of Uruguay”. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 256(2): 229-234 <Full Article>

Bertelli S, Chiappe LM, Tambussi C (2007). “A new phorusrhacid (Aves: Cariamae) from the middle Miocene of Patagonia, Argentina”. Journal of Vertebrate Paleontology 27(2): 409-419 <Full Article>

Chiappe LM & Bertelli S (2006). "Skull morphology of giant terror birds". Nature 443: 929 <Full Article>

Alvarenga HMF, Höfling E (2003). "Systematic revision of the Phorusrhacidae (Aves: Ralliformes)". Papéis Avulsos de Zoologia 43(4): 55–91 <Full Article>

Baskin JA (1995). "The giant flightless bird Titanis walleri (Aves: Phorusrhacidae) from the Pleistocene coastal plain of south Texas". Journal of Vertebrate Paleontology 15(4): 842-844 <>

Brodkorb P (1963). "A giant flightless bird from the Pleistocene of Florida". The Auk 80(2): 111-115 <Full Article>

Patterson B (1941). "A new phororhacoid bird from the Deseado formation of Patagonia". Geological Series of Field Museum of Natural History 8(8): 49-54 <Full Article>

Thursday, June 11, 2015

Saber-toothed Cat (Smilodon fatalis)

Saber-toothed Cat skeleton at the National Museum of Nature
and Science in Tokyo, Japan. Wiki
One of the most iconic animals of the Pleistocene, the Saber-toothed Cat (Smilodon fatalis) was abundant throughout North and South America for over 1 million years. We know more about this animal than any other extinct cat thanks to the wealth of material recovered from the La Brea tar pits in Los Angeles, California from which over 2,000 individuals representing nearly every demographic have been identified. It was the last known of North America's giant predators, with the youngest material coming from Nashville, Tennessee just over 9,000 years ago.

The name Smilodon is derived from the Greek words smilē, knife, and odous, tooth. The species name fatalis mean “fatal” or “deadly. Thus, the full binomial name of this species translates as “Deadly Knife-tooth”. The name “saber tooth” refers to the extreme length of the upper canines, which in this species may reach lengths of up to 20cm (8in). Other names have been assigned to North American Smilodon specimens mostly based on geographic location, including S. californicus, S. floridanus, and S. mercerii. However, these now defunct classifications are now recognized as being synonymous with S. fatalis.

Habitat & Distribution
Saber-toothed Cats appear to have favored open or lightly wooded lowland environments in association with permanent water sources like swamps, marshes, bogs, wetlands, floodplains, rivers, and lakes. Their range is known to have included Canada and much of the United States in the north, and through Central and South America in the south. There is no record of them ever living in the Great Plains and Rocky Mountain regions. This cat could have potentially lived further north as far as present day Alaska during interglacial periods. However, the periodic advancing of the northern ice sheets would have destroyed most evidence of these animals' existence in these northern latitudes. The oldest record of this species dates to about 1.6mya. It was the last known of North America's giant predators, with the youngest material coming from Nashville, Tennessee just over 9,000 years ago.

Physical Attributes
In linear measurements, Saber-toothed Cats were noticeably smaller than Lions (Panthera leo). However, the Saber-tooth was a much more powerfully built animal with particularly robust limbs and a compact body. Though differing in size, the two would have been closely matched in weight with the Saber-toothed Cat averaging 50kg heavier than a Lion of the same head-and-body length. Saber-toothed Cats also differ from Lions in having a much longer and stronger neck, a shortened lower back, and a stubby tail no more than a foot long. The carnassials* were longer and more blade-like, and the upper canines were elongated, laterally flattened, and could grow up to 20cm (8 inch) in length. These were also lined with fine serrations for cutting through flesh. Isotope analyses reveal these specialized killing tools would begin to erupt at 8 to 12 months of age, and reached their full adult length by the time the cats reached sexual maturity at around 2 years. To employ these teeth in a killing bite, Saber-toothed Cats had a maximum gape of around 120°. 
Juvenile Saber-toothed Cat skulls showing tooth replacement. Wiki
The overall skeletal anatomy of the Saber-toothed Cat suggests an animal adapted to more actively grapple with the prey animals that were considerably larger than themselves. In comparison, Lions tend to more frequently target prey species that more closely match them in size, only taking to larger prey when smaller animals are scarce or when a particularly large hunting group is involved. Because this species seems to have had an affinity for wet habitats, it is likely to have had a rather dense coat to repel water, especially in winter. Sexual dimorphism* appears to have been less pronounced than it is in modern cats, however, past studies have suggested that males did indeed grow slightly larger than females and possessed more robust skulls.

Ecology & Behavior
Saber-toothed Cats are famously one of most abundant predator recovered from the Rancho La Brea site in California with over 2,000 individuals identified, second only to the Dire Wolf (Canis dirus) which is represented by over 4,000 individuals. The sheer number of individuals, the frequency and severity of bone injuries, mixed age demographic, and the rate of tooth replacement known from Saber-toothed Cat from this site all strongly suggest that this species was a social predator that lived in family groups perhaps numbering 2 to 6 adults. As with modern cats, it is likely that male and female groupings lived separately from each other most of the time and selected differently sized prey to minimize intraspecific* competition. Both sexes would have occasionally intermingled at larger kills or when the females came into estrus. Male and female groups may have also been compelled to gather in the same locality and sometimes hunt together in response to prey migrations and the tendency of herbivores to congregate in particular areas due to seasonal changes in food and water availability. Like most social animals, Saber-toothed Cats were likely to have been highly vocal with a broad range of short-range and long-range communications, including roars. 

Saber-toothed Cats appear to have had a preference for the more common, larger herbivores of the Pleistocene such as bison, horses, and large camels. They were also capable of bringing down young mammoths, mastodons, and some of the smaller ground sloths and could have occasionally tackling smaller prey such as deer and capybara. A favorite hunting technique of the Saber-toothed Cat may have been to ambush large herbivores as they came near the water to either drink or wallow. Group members would have strategically positioned themselves in different locations in order to trap prey; for example, one cat may chase the prey within range of two or three nearby partners. They may have also chased their prey into shallow water where their broad paws, powerful limbs, and leaping ability would have afforded them greater mobility over softer substrates than many of their hoofed victims. These hunting strategies are still employed by large cats today. Captured prey would be very swiftly immobilized by the cats’ powerful limbs and dispatched with a single bite to the neck, with the large upper canines severing the major arteries resulting in a very rapid and efficient kill.

Dire Wolves are frequently found in the same fossil localities as Saber-toothed Cats, implying that they had the same habitat preferences and likely hunted many of the same prey animals. The smaller size of the wolves, however, means that they were obligated to focus on smaller prey than what the larger cats were hunting. This behavior reduces interspecific* competition, and a similar relationship may be seen among modern African Lions and Spotted Hyenas (Crocuta crocuta). The other large, contemporaneous social predators included the Lion and the Scimitar Cat (Homotherium serum). However, these competitors would have preferred to hunt in higher, drier areas, thus reducing the frequency of encounters.
Two Saber-toothed Cats approach a Harlan's Ground Sloth (Paramylodon harlani)
that has become mired in the La Brea Tar Pits. Artwork by Charles R. Knight, 1921.

Carnassial: specialized shearing cheek teeth found in terrestrial mammalian predators.
Interspecific: referring to members of different species.
Intraspecific: referring to members of the same species.
Sexual dimorphism: differences in appearance between males and females of a given species.

References & Further Reading
Christiansen P, Harris JM (2012) “Variation in Craniomandibular Morphology and Sexual Dimorphism in Pantherines and the Sabercat Smilodon fatalis”. PLoS ONE 7(10): e48352. doi:10.1371/journal.pone.0048352 <Full article>

P. David Polly (2011), Fossils: Saber-toothed Cats, Indiana Geological Survey, retrieved 15 March 2013 from <Full article>

Carbone C, et al. (2009) “Parallels between playbacks and Pleistocene tar seeps suggest sociality in an extinct sabretooth cat, Smilodon”. Biol Lett 5:81–85. <Full article>

Coltrain JB, Harris JM,  Cerling TE, Ehleringer JR, Dearing MD, Ward J, Allen J (2003). "Rancho La Brea stable isotope biogeochemistry and its implications for the palaeoecology of late Pleistocene, coastal southern California". Science Direct: Palaeogeography, Palaeoclimatology, Palaeoecology 205 (2004) 199 – 219 <Full article>

Feranec RS. (2002) “Isotopic evidence of saber-tooth development, growth rate, and diet from the adult canine of Smilodon fatalis from Rancho la Brea”. Science Direct: Paleogeography, Paleoclimatology, Paleoecology 206 (2004) 303-310 <Full article>

Morgan, GS & Lucas, SG (2001), “The sabertooth cat Smilodon fatalis (Mammalia: Felidae) from a Pleistocene (Rancholabrean) site in the Pecos River valley of southeastern New Mexico/southwestern Texas”, New Mexico Geology <Full article>

A. Turner: The big cats and their fossil relatives. Columbia University Press, 1997.ISBN 0-231-10229-1 <Book>

Tejada-Flores AE & Shaw CA (1984). "Tooth replacement and skull growth in Smilodon from Rancho la Brea". Journal of Vertebrate Paleontology 4(1): 114-121 <Full Article>

B. Kurten. Pleistocene Mammals of North America. Columbia University Press, 1980. ISBN 978-0231037334 <Book>

Wednesday, April 15, 2015

Scimitar Cat (Homotherium serum)

The Scimitar Cat (Homotherium serum) was a smaller and lesser known cousin of the more famous Saber-toothed Cat (Smilodon fatalis). This species lived from the early Pliocene to the late Pleistocene and enjoyed one of the largest geographic distributions of any known cat living or extinct.

Scimitar Cat skeleton on display at the Texas Memorial
Museum in Austin. Wiki
The genus name Homotherium is derived from the Greek words homo, meaning “same”, and therion, meaning “beast”. The common name “Scimitar-toothed Cat” or “Scimitar Cat” is in reference to this cat’s blade-like canines, named after the curved sword from southwest Asia. Numerous species have been attributed to the genus based on body size, the shape of the canines, and geographic location. However, these supposed differences are minor and may be attributed to sexual and geographic variation. It must be noted that such fluctuations may easily be observed among modern cats which have particularly broad distributions. Here, I will be focusing on the North American variant of this genus, Homotherium serum.

Habitat & Distribution
Scimitar Cats had an extremely wide distribution that encompassed Africa, Eurasia, North America, and South America. This nearly global distribution was matched only by the Lion (Panthera leo) among contemporary felids. The Scimitar Cat’s preferred habitat would have been grassland, open woodland, and semi-desert. This species seems to have originated in Eurasia about 5mya during the early Pliocene, is recorded in Africa by 3mya, North America by the start of the Pleistocene, and reached South American pampas by at least 1.8mya. The extinction of Scimitar Cats around the world seems to coincide with the disappearance of many of the larger herbivores within its range. The youngest evidence for the species in North America is about 11,000 years old.

Physical Attributes
Compared to comparably-sized cats of the Pleistocene, Scimitar Cats were much more lightly built and rangy in their overall body proportions. They were particularly well-adapted for covering great distances of open terrain at considerable speeds. Cursorial* adaptations include; long slender limbs to increase its stride, a deep thoracic cavity that housed a large heart and lungs, large nasal passages for high oxygen intake, a short lower back to save energy when running, and non-retractile claws for traction. The forelimbs were slightly longer than the hindlimbs. Scimitar Cats were built for long-distance pursuit rather than power, likely adopting a tireless cantering gait when running. As a cat of the open plains, its coat is likely to have been either mostly plain or spotted, the background color varying with region. In temperate zones, a light summer coat would likely have given way to a thicker, darker-colored winter coat. 

The cats’ most impressive feature was its highly sectoral* dentition. All the teeth were lined with fine serrations on their front and back edges. The upper canines were up to 15cm (6in) long and blade-shaped. These killing teeth were well-suited for slicing through thick hide and severing blood vessels of large prey items. Large incisors were adept at gripping prey and dismembering carcasses. The carnassials* were extremely well-developed relative to contemporary cats and would have enabled Scimitar Cats to cut away steak-sized chunks of flesh with every bite. Among living cats only the Cheetah (Acinonyx jubatus) has such efficient meat slicing teeth, which are adapted for speedily devouring their prey on the competitor-rich plains in which they live.

Ecology & Behavior
Much of what we know about the Scimitar Cat comes from the wealth of fossil materials unearthed from Friesenhahn Cave, Texas. Prior to the discovery of this site, Scimitar Cats were known only from very fragmentary remains elsewhere in the world. Once an active den site for these animals, this famous locality has yielded the remains of at least 32 individuals (19 adults and 13 cubs), providing unparalleled insight into the ontology, ecology, and behavior of these cats. The following description will be based on inferences made by the Friesenhahn sample.

Skeleton of a 2 to 3 month old Scimitar Cat cub, one of 13
recovered from Friesenhahn Cave, Texas. Wiki
The disarticulated remains of large herbivores such as bison, horse, mammoth, mastodon, camel, deer, and tapir indicate that Scimitar Cats enjoyed a wide prey menu consisting of animals weighing 300 to 1,000kg. By far the most notable aspect of this cave fauna, however, are the bones and teeth of several hundred juvenile Columbian Mammoths (Mammuthus columbi) and some American Mastodon (Mammut americanum). The young elephants were determined to have been between 2 and 4 years of age around the time of death. This is the same age at which modern elephant calves become less dependent on their mothers and their curiosity occasionally compels them to stray dangerously far from the protective adults. Thus, this is the period during which they are most vulnerable to attack from predators. Lions today will take full advantage of this behavior and opportunistically hunt these stray calves. Scimitar Cats, it seems, were doing the same thing with the mammoth and mastodon calves from the Friesenhahn locality.

The great size of the animals that Scimitar Cats were hunting also tells us something about its social life. Averaging about the weight of a Lioness and more slender in build, Scimitar Cats would have found it rather difficult, if not impossible, to tackle such large prey single-handed, particularly the larger bison and elephant calves found at Friesenhahn. Thus, these cats most likely lived and hunted in groups. It can even be suggested that the Scimitar Cats at Friesenhahn represent a single family lineage that utilized the cave and surrounding area over successive generations as modern Lions are known to do. The cave would have been used as a shelter during the dry season and a safe environment in which to leave their cubs while hunting. It also offered a permanent supply of water. The cave would have been abandoned during the wetter periods of the year from May to October due to flooding. The home ranges of Scimitar Cats are likely to have been quite large and the cats would have been highly nomadic within this area. Seasonal movements depended on the migratory habits of local prey. As a result, the species had a relatively small population density compared to other large predators of the time.

Unlike other cats, Scimitar Cats were built for long-distance pursuit rather than ambush. Hunting techniques would have varied according to the type of prey, but in general these predators would have isolated and chased down intended victims, seizing them by the rump or hindquarters with enlarged dewclaws* in order to prevent escape. Other pack members would have then attacked the hindlimbs and throat of the immobilized prey, severing tendons and blood vessels with their blade-like teeth. The prey would have been killed rather quickly rapid blood loss. Kills would then be torn apart and eaten as rapidly as possible before competing predators could arrive on the scene. Powerful shoulders allowed Scimitar Cats to lift and carry away large pieces of surplus meat over long distances to a safe place to be consumed at a later date or fed to den-bound cubs.

Carnassial: specialized shearing cheek teeth found in terrestrial mammalian predators.
Cursorial: adapted specifically for running.
Dewclaw: any digit that is typically raised above the ground during regular locomotion.
Sectoral: adapted specifically for cutting.

References & Further Reading

“Friesenhahn Cave: Window on the Past”. CreationHistory.com. Robert E. Gentet and Edward C. Lain. Web. 15 December 2012. <

Anton M, Salesa MJ, Galobart A, Tseng ZJ (2014). "The Plio-Pleistocene scimtar-toothed felid genus Homotherium Fabrini, 1890 (Machairodontinae, Homotherini): diversity, palaeogeography and taxonomic implications". Quaternary Science Reviews 96: 259-268 <Full article>

Barnett R (2014). "An inventory of British remains of Homotherium (Mammalia, Carnivora, Felidae), with special reference to the material from Kent’s cavern". Geobios 47 (1-2): 19-29. <Full article>

McFarlane DA & Lundberg J (2013). “On the occurrence of the scimitar-toothed cat, Homotherium latidens (Carnivora: Felidae), at Kents Cavern, England”. Journal of Archaeological Science 40: 1629-1635 <
Full article>

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 <Abstract only>

Anton M, Salesa MJ, Turner A, Galobart A, Pastor JF (2009). "Soft tissue reconstruction of Homotherium latidens (Mammalia, Carnivora, Felidae). Implications for the possibility of representations in Palaeolothic art". Geobios 42: 541-551 <Full article>

Anton M, Galobart A, Turner A (2004). “Co-existence of scimitar-toothed cats, lions and hominins in the European Pleistocene. Implications of the post-cranial anatomy of Homotherium latidens (Owen) for comparative palaeoecology”. Quaternary Science Reviews 24: 1287-1301 <
Full article>

Reumer JWF, Rook L, Van Der Borg K, Post K, Mol D, De Vos J (2003). "Late Pleistocene survival of the saber-toothed cat Homotherium in northwestern Europe". Journal of Vertebrate Paleontology 23: 260. <
Full article>

Turner A (1997). The big cats and their fossil relatives. New York: Columbia University Press. ISBN 0-231-10229-1 <Book>

Kurten B & Anderson E. “Pleistocene Mammals of North America”. Ann Arbor, Michigan: University of Michigan Press, 1980. 190 <Book>