Tetrapod Zoology

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Time for more borhyaenoids. Finally, we get round to the taxa that you might have seen or read about in prehistoric animal books: the sabre-toothed thylacosmilids, the supposedly bear-like borhyaenids, and the gigantic and even more bear-like proborhyaenids. We previously looked at basal borhyaenoids here, and at the mostly scansorial, mustelid-like hathlyacinids and prothylacinids here. Here we go…

We begin with the borhyaenids (yes, borhyaenid borhyaenoids), a group of about ten genera of superficially dog- or thylacine-like borhyaenoids. The oldest (Nemolestes) is from the Early Eocene or possibly Late Palaeocene while the youngest (Eutemnodus and Parahyaenodon) are from the Early Pliocene (Marshall 1978). Easily the best known member of the group is Borhyaena tuberata from the Santacrucian (= Early Miocene), and it’s like its contemporary Cladosictis in being frequently depicted in the popular and semi-technical literature. As was also the case with Cladosictis, its ‘conventional’ image is – so it turns out – pretty far off the mark.

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The best known life restoration of this animal (that produced by John Long for Mammal Evolution: An Illustrated Guide) depicts it as something like a long-tailed bear, and I had always thought that Borhyaena was giant, and perhaps similar in size to a brown bear. In fact, weight estimates (Argot 2003) put it at 19-29 kg, which is about equivalent to a small hyaena or wolf, or a large thylacine. However, its robust skull, with its particularly broad zygomatic arches, indicate a disproportionately large amount of skull and neck musculature, and mass estimates for the whole animal based on skull proportions alone (and assuming body proportions resembling those of extant carnivorous mammals) give Borhyaena an inflated mass of 74 kg (vividly illustrating why knowing the overall proportions of an animal are important when estimating its weight: Van Valkenburgh 1985, 1987). The substantial neck musculature indicates an ability to carry heavy loads.

A semi- or fully digitigrade manus, short, blunt claws, and forelimbs that were restricted to parasagittal movement and exhibit reduced distal musculature indicate that Borhyaena was terrestrial and cursorial – and, in fact, the most cursorial of all borhyaenoids – but its limbs weren’t as proportionally elongate as those of extant cursorial predators. However, that might not have been such a problem, because virtually all the potential large-bodied prey (an incredible assortment of xenarthrans, astrapotheres, notoungulates and big rodents) were not cursorial either (in the Santacrucian fauna, only proterotheriid and macraucheniid litopterns can be considered cursorial) (Argot 2004a). While previously depicted as being plantigrade, what is known of ankle morphology and forelimb proportions show that Borhyaena was more likely digitigrade in the hindlimb (Argot 2003: life restoration and skeletal reconstruction above © C. Argot). Whether the other borhyaenids were like ‘new-look Borhyaena‘ remains to be shown.

Proborhyaenids, the ‘giant marsupial bears’, and their kin the sabre-toothed thylacosmilids

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Proborhyaenids have usually been thought of as hyaena-like or bear-like, while thylacosmilids are well known for being strongly convergent with sabre-toothed cats. While Marshall (1977) thought that proborhyaenids might be the most basal of borhyaenoids (while at the same time the most specialised), it has more recently been argued that proborhyaenids and thylacosmilids share a number of derived characters and are hence sister-taxa (Muizon 1994, 1999, Babot et al. 2002). One of the most interesting characters present in both proborhyaenids and thylacosmilids is the presence of ever-growing, open-rooted upper canines. Both groups also exhibit strongly projecting occipital condyles, indicating that they were capable of greater rotation and movement at the head-neck joint than other borhyaenoids. Babot et al. (2002) suggested that the presence of fine ridges and grooves on the canine roots might be diagnostic for proborhyaenids, but the fact that thylacosmilids have such strongly modified canines raises the possibility that thylacosmilids had this character ancestrally but later reversed it.

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Proborhyaenids are unique to the Eocene and Oligocene: there are only four recognised genera (Callistoe, Arminiheringia*, Paraborhyaena and Proborhyaena), and Proborhyaena in particular has often been referred to as huge and bear-like, with there being estimates here and there of skulls perhaps 60 cm long [P. gigantea holotype lower jaw shown here, from Patterson & Marshall (1978). From top to bottom, the specimen is shown in labial, occlusal and lingual views. Scale bar = 50 mm]. However, as has turned out to be the case for other archaic carnivorous mammals (like the hyaenodontids), big, bear-sized skulls do not necessarily mean big, bear-sized bodies, and an articulated proborhyaenid skeleton (read on) shows that these animals had big heads for their size.

* Arminiheringia was originally given its own ‘family’, Arminiheringiidae Amegino, 1902.

As is the case with most borhyaenoid genera, proborhyaenids are mostly known from fragmentary jaws and other parts of skulls, but in 2002 a near-complete proborhyaenid skeleton [shown above: from Babot et al. (2002). Scale bar = 100 mm], representing the new taxon Callistoe vincei, was described from the Casamayoran (= Early Eocene) Lumbrera Formation of Salta, Argentina (Babot et al. 2002). The generic name comes from Callisto, the Arcadian nymph loved by Zeus and changed by him into a bear to protect her from Hera’s wrath (Jupiter has a moon called Callisto). In contrast to the other proborhyaenids, Callistoe has a gracile, narrow snout and might have superficially resembled a thylacine in facial shape.

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Arminiheringia had unusual procumbent lower canines: there has actually been some disagreement as to whether this is natural or not (Bond & Pascual 1983), but it does appear to be according to Babot et al. (2002) (A. auceta shown here, from Simpson 1932). Paraborhyaena also had somewhat procumbent lower canines. After Thylacosmilus, Simpson (1932) regarded Arminiheringia auceta (one of three species in the genus) as the most specialised borhyaenoid, and also one of the largest, ‘about the size of the great Pharsophorus lacerans‘ (Pharsophorus is a borhyaenid). Exactly how big Pharsophorus was, however, I have no idea – and was it supposed to be bigger than, say, Proborhyaena?

The marsupial sabre-tooths

Finally, we come to the superficially cat-like thylacosmilids, the only borhyaenoid group that are at all familiar, and all thanks to the incredible Thylacosmilus atrox Riggs, 1933 of the Late Miocene and Early Pliocene of Catamarca, north-western Argentina. In contrast to all other borhyaenoids, thylacosmilids were short-faced and had a complete bony postorbital bar (although not all did – read on). T. atrox is the only thylacosmilid we ever hear about, but it isn’t the only one.

Achlysictis Ameghino, 1891, known only from mandibular fragments and teeth (three species have been named), was smaller than T. atrox and differed from it in tooth cusp characters. Similar comments can be made about Hyaenodonops Ameghino, 1908, known only from teeth (though postcrania has been referred to it). Notosmilus Kraglievich, 1960, named for a maxilla and canine, was only about half the size of T. atrox. Marshall (1976) regarded all of these taxa as distinct, but Goin & Pascual (1987) and McKenna & Bell (1997) regarded them all as synonyms of Thylacosmilus. Of course, if that’s true, then the generic name Thylacosmilus is predated by both Achlysictis and Notosmilus and the ICZN would have to be petitioned if we want to preserve Thylacosmilus (which we do). Incidentally, Riggs (1933) named a second species of Thylacosmilus, T. lentis, but it was argued by Marshall (1976) to be synonymous with T. atrox. Most recently, Goin (1997) named the Middle Miocene species Anachlysictis gracilis from the La Venta site in Colombia. This animal differed from the other thylacosmilids in smaller size, in possessing a flattened skull roof, and in lacking a postorbital bar.

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You might think you know Thylacosmilus, but it’s rather stranger than usually thought. It has no upper incisors at all (though this is not completely certain: see Churcher 1985) and only one pair of lower incisors. The laterally compressed, ever-growing upper canines were not just rooted in maxillary sockets as they are in sabre-toothed cats, but arced up and over the orbits, forming a notably convex skull roof. The premolars and molars were narrow lineal blades, specialised for slicing. Huge, laterally flattened flanges grew downwards from the lower jaw, and the sabre teeth would have rested against their sides when the jaws were closed. Protuberances, rugosities and excrescenses at the back and base of the skull show that a substantial amount of powerful musculature allowed both great power and fine control to be exerted over the head, and large muscle attachment sites on the neck vertebrae also show that the neck was very strong and flexible. Several studies have looked at these features and should be referred to if you want more information. Marshall (1976) discussed skull function and its possible role in behaviour, Turnbull (1976) reconstructed the cranial musculature, and Turner & Antón (1997) and Argot (2004b) analysed postcranial morphology.

How exactly did the thylacosmilids live? Again, Argot’s (2004b) detailed functional analysis gives us a huge amount of information. With its semi-plantigrade hindfeet, stout fibulae and curved tibiae, Thylacosmilus looks poorly suited for fast running, and a massively powerful upper arm and a reinforced and relatively inflexible lumbar region imply that it was an ambush predator that attacked prey after a short dash. It is now widely thought that sabre-toothed predatory mammals used their elongate and delicate weapons for precise attacks inflicted on the ventral surface of the neck, and for this to work the predator has to be able to physically manipulate and restrain the prey, and use coordinated and precise neck and head movements to attack in the right place. A semi-opposable thumb and tremendous forelimb strength suggest that Thylacosmilus could pin down and restrain prey, and its elongate, powerful neck demonstrates the presence of a ‘neck-driven’ precision biting style. In their study of bite forces seen in various mammalian predators, Wroe et al. (2005) found bite forces of Thylacosmilus to be very low. This is also the case for sabre-toothed cats like Smilodon and indicates that these animals were not ‘power biting’ like short-toothed predators, but driving their unusual killing style with their neck musculature [image of Thylacosmilus model below from Link & Pin Hobbies. Most thylacosmilid reconstructions make the animals look far too cat-like, and also give them completely incorrect limb details].

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Another thing to consider about thylacosmilids: given that sabre-toothed biting appears to have been so specialised and difficult, it is inferred that sabre-toothed predators had to go through a very dangerous apprenticeship in which they learnt how to successfully inflict a bite without getting smacked in the head or breaking a tooth. But, for this to occur, juveniles and adults must stay together for an extended post-weaning period. In marsupials* in general, this is very rare, with juveniles rarely staying with their parents for more than a few weeks once weaning is finished. Were thylacosmilids a major exception? Unfortunately we just don’t know.

* Remember that borhyaenoids may not actually be marsupials, but members of the more inclusive group Metatheria. This was all explained in the first borhyaenoid article.

What were thylacosmilids preying on anyhow? Argot (2004a) proposed that mesotheriid notoungulates, litopterns and big rodents like capybaras were among the prey of Thylacosmilus. And it’s also interesting to note that thylacosmilids were living alongside other borhyaenoids: in the Huayquerian, Thylacosmilus was sharing its habitat with late-surviving hathlyacinids, the probably omnivorous prothylacinid Stylocynus, and the borhyaenid Eutemnodus. Phorusrhacids were around too: did they compete with borhyaenoids, or did the groups occupy different niches and avoid competition? So many animals, so many questions.

While that’s hardly everything, I think that’ll do on borhyaenoids for now.

Refs – –

Argot, C. 2003. Functional adaptations of the postcranial skeleton of two Miocene borhyaenoids (Mammalia, Metatheria), Borhyaena and Prothylacinus, from South America. Palaeontology 46, 1213-1267.

– . 2004a. Evolution of South American mammalian predators (Borhyaenoidea): anatomical and palaeobiological implications. Zoological Journal of the Linnean Society 140, 487-521.

– . 2004b. Functional-adaptive features and palaeobiologic implications of the postcranial skeleton of the late Miocene sabretooth borhyaenoid Thylacosmilus atrox (Metatheria). Alcheringa 28, 229-266.

Babot, M. J., Powell, J. E. & de Muizon, C. 2002. Callistoe vincei, a new Proborhyaenidae (Borhyaenoidea, Metatheria, Mammalia) from the Early Eocene of Argentina. Geobios 35, 615-629.

Bond, M. & Pascual, R. 1983. Nuevos y elocuentes restos craneanos de Proborhyaena gigantea Ameghino, 1897 (Marsupialia, Borhyaenidae, Proborhyaeninae) de la Edad Deseadense. Un ejemplo de coevolución. Ameghiniana 20, 47-60.

Churcher, C. S. 1985. Dental functional morphology in the marsupial sabre-tooth Thylacosmilus atrox (Thylacosmilidae) compared to that of felid sabre-tooths. Australian Mammalogy 8, 201-220.

Goin, F. J. 1997. New clues for understanding Neogene marsupial radiations. In Kay, R. F., Madden, R. H., Cifelli, R. L. & Flynn, J. J. (eds) Vertebrate Paleontology in the Neotropics: The Miocene fauna of La Venta, Colombia. Smithsonian Institution Press (Washington, D.C.), pp. 187-206.

– . & Pascual, R. 1987. New on the biology and taxonomy of the marsupials Thylacosmilidae (late Tertiary of Argentina). Anales de la Academia Nacional de Ciencias Exactas, Físicas y Naturales 39, 219-246.

Marshall, L. G. 1976. Evolution of the Thylacosmilidae, extinct saber-tooth marsupials of South America. PaleoBios 23, 1-30.

– . 1977. Cladistic analysis of borhyaneoid, dasyuroid, didelphoid, and thylacinid (Marsupialia: Mammalia) affinity. Systematic Zoology 26, 410-425.

– . 1978. Evolution of the Borhyaenidae, extinct South American predaceous marsupials. University of California Publications in Geological Sciences 117, 1-89.

McKenna, M. C. & Bell, S. K. 1997. Classification of Mammals: Above the Species Level. Columbia University Press.

Muizon, C. 1994. A new carnivorous marsupial from the Palaeocene of Bolivia and the problem of marsupial monophyly. Nature 370, 208-211.

– . 1999. Marsupial skulls from the Deseadan (late Oligocene) of Bolivia and phylogenetic analysis of the Borhyaenoidea (Marsupialia, Mammalia). Geobios 32, 483-509.

Patterson, B. & Marshall, L. G. 1978. The Deseadan, Early Oligocene, Marsupialia of South America. Fieldiana Geology 41, 37-100.

Riggs, E. S. 1933. Preliminary description of a new marsupial sabertooth from the Pliocene of Argentina. Geological Series of Field Museum of Natural History 6, 61-66.

Simpson, G. G. 1932. Skulls and brains of some mammals from the Notostylops beds of Patagonia. American Museum Novitates 578, 1-11.

Turnbull, W. D. 1976. Restoration of masticatory musculature of Thylacosmilus. In Churcher, C. S. (ed) Athlon, Essays in Palaeontology in Honour of Loris Shano Russell. Royal Ontario Museum (Toronto), pp. 169-185.

Turner, A. & Antón, M. 1997. The Big Cats and Their Fossil Relatives. Columbia University Press, New York.

Van Valkenburgh, B. 1985. Locomotor diversity within past and present guilds of large predatory mammals. Paleobiology 11, 406-428.

– . 1987. Skeletal indicators of locomotor behaviour in living and extinct carnivores. Journal of Vertebrate Paleontology 7, 162-182.

Wroe, S., McHenry, C. & Thomason, J. 2005. Bite club: comparative bite force in big biting mammals and the prediction of predatory behaviour in fossil taxa. Proceedings of the Royal Society B 272, 619-625.


  1. #1 Mark Lees
    July 4, 2008

    Fascinating. You note that the reconstructions of Thylacosmilus tend to be too cat-like. The picture you post seems to have elements of thylacine and cat and all with a very ?inflated? forehead. I guess that makes good sense.

    I noticed a statement made recently that they suckled their young in pouches. Is there any evidence (not sure what form this would take) to suggest they was the case, or was it, as I assumed an assumption based on them being viewed as masupials. Of course not all marsupial species have pouches.

    The use of the teeth has me puzzled, and more so since I recently was given a life-sized museum quality reproduction of a Smilodon skull (an anniversary present from my wife) and it is very obvious how flattened the teeth are. I understand now why it is claimed that care would have be taken not to break the teeth when hunting. Indeed their flattened cross-section would seem highly vulnerable to being shattered it subjected to twisting or sideways motion. I assume the same applies to Thylacosmilus.

    While the powerful forelimb build is consistent with overcoming prey and holding it still (relatively) so as to be able to slash the throat with the teeth, I am not convinced this is really a viable option. Remember this strategy would have to work every time, as breaking teeth could well prove fatal. To be able to guarantee that the prey was remaining still enough every time for that to work seems to be asking a bit much. Its not simply hitting bone that would be a problem, it is specifically the twisting or sideways motions caused by prey struggling.
    You refer to ?a very dangerous apprenticeship in which they learnt how to successfully inflict a bite without getting smacked in the head or breaking a tooth? ? I think that ?very dangerous? understates the case ? the losses would surely have been appalling. One mistake, and starvation or infections become a real possibility.

    Of course most large cats scavenge when they can, and it seems to me that the role of first rank scavenger of megafauna is worth at least considering for both Smilodon and Thylacosmilus. The powerful, indeed superficially hyaena-like, build would serve to secure first place at large carcasses, and possibly even to drive away not only other scavengers, but also perhaps even the predators that brought the carcass down (predators that may well have been lighter build, but not having vulnerable canines). The blade-like teeth would then allow short work to be made of the flesh, before surrendering the carcass to the next guild of scavengers.

    I know that this idea is no where near as appealing as sabretooth as awesome predator, but I really have difficulty accepting that they would survive their “dangerous apprenticeship” and thereafter consistently be able to hold prey sufficiently still so as not to endanger their teeth.

    Just some thoughts for discussion.

  2. #2 johannes
    July 4, 2008

    I wonder about the long apprenticeship. This requires tightly knit social structures, and long-lasting family relations. This is quite easy to imagine in nimravids or cats. It is somewhat more idiosyncrasic in metatherians. And what about the saber-toothed non-mammalian synapsids, like gorgonopsians or therocephalians – or those crocs that were approaching the saber-toothed condition, too?

    Perhaps the fact that the canines in thylacosmilids were open-rooted and continously growing meant that a “wrong” bite was less fatal for them than it would have been for a nimravid, barbourofelid or cat?

  3. #3 Dave Godfrey
    July 4, 2008

    Similarly the crocs and gorgonopsids continually replaced their teeth, (and therocephalians? I don’t know enough about them) so loss of a tooth (or even two) wouldn’t be a problem either. Its only when mammaliforms stopped this that there would be the need for an apprenticeship.

  4. #4 Zach Miller
    July 4, 2008

    Those canines seem bigger (proportionatelly) than anything in felids, sabertooth or otherwise. The fact that the roots are so deep suggests that the teeth were more powerful. The giant mandibular flanges are very strange–are they known in felids?

    And thank you for providing a wonderful skull reconstruction, Darren. I’m SO using that.

  5. #5 Alan Kellogg
    July 4, 2008


    I was going to post a comment in this thread about the borhyaenids of Ærth, but my copy of the Ærth Bestiary is hidden in the paleontology dig I call my apartment. When I find the tome folks reading this will get a look at how the beasties were once seen.

  6. #6 David Marjanovi?
    July 5, 2008

    It has no upper incisors at all

    That does not make sense. Nothing with ziphodont teeth lacks front teeth.

    I refuse to believe it without a picture of a premaxilla.

    Of course most large cats scavenge when they can, and it seems to me that the role of first rank scavenger of megafauna is worth at least considering for both Smilodon and Thylacosmilus.

    There are way too many of them per ecosystem. Who should kill all those herbivores for them? That makes no more sense than thinking Tyrannosaurus was a scavenger, I’m afraid.

  7. #7 Lars Dietz
    July 5, 2008

    “That does not make sense. Nothing with ziphodont teeth lacks front teeth.

    I refuse to believe it without a picture of a premaxilla.”

    I’ve found this on Google Books:

    Apparently the preservation isn’t complete enough to say whether it had upper incisors or not. The paper is from 1985, so maybe new specimens have been found since then.

  8. #8 johannes
    July 5, 2008

    > and therocephalians? I don’t know enough about them

    Many died during the process of canine replacement, the resulting fossils show two sets of canines, the old and the new one. This led to the idea that at least some therocephalians had double canines. You can still see this impressive but biomechanically useless double-fang setup in older reconstructions of therocephalians.
    So the answer should be, yes, there was canine replacement in therocephalians, but it was a dangerous, probably painful and often deadly process.

    > The giant mandibular flanges are very strange–are they
    > known in felids?

    Flanges are known in nimravids and barbourofelids, but not in felids.

  9. #9 Hai~Ren
    July 5, 2008

    Wow, this is the most I have ever read about the borhyaenoids. I’ve learned so much more about this group, and I really wonder just how long it took for you to read and compile all the information for this series of posts.

  10. #10 Dave Godfrey
    July 5, 2008

    >Flanges are known in nimravids and barbourofelids, but not in

    Not true. Both Machairodus and Megantereon had a mandibular flanges. Neither’s canines were as large as thoes of Thylacosmilus and Barbourofelis, (which had flanges) or Smilodon– which lacked a flange, despite being a close relative of Megantereon.

  11. #11 DDeden
    July 5, 2008

    IMO ‘Saber cats’ of various forms most likely often attacked prey by pushing them into water/mud/tar, leaping/climbing onto the back, then either piercing the eyes or the exposed throat while firmly anchored on the prey’s shoulders. The prey would have to keep the head above water, allowing a safe easy target to a ‘cat’ with powerful gripping forelimbs and opposable thumbs. I cannot imagine any equivalent ‘dry’ attack method where sabers would be advantageous.

  12. #12 Darren Naish
    July 5, 2008

    Thanks to all for comments. I’ll try and respond to all of the above in one go, rather than address everything point by point. Obviously people are mostly up in arms about the ‘apprenticeship’ and killing style of thylacosmilids.

    What we know of sabre-tooth morphology (this goes for machairodonts, nimravids, barbourofelids and thylacosmilids) suggests powerful manipulative abilities and precision biting in which the power, fine control and flexibility of the neck was important. It seems most reasonable to interpret all of these features as evidence showing that these predators were attacking the ventral surface of the prey’s neck: for full discussion see Turner & Antón (1997) and Antón & Galobart (1999).

    If this was the case, could they learn this technique without training from adults? We’re never going to know, but I still think that this must be the answer. Support for this idea is provided by the fact that juvenile barbourofelids – while nearly adult in size – did not have erupted canines and hence are inferred to have relied on parental care despite their large size. In other words, here is evidence both for extended parental care, and for the inability of juveniles to kill large prey. Extending this to thylacosmilids does, yes, seem difficult in view of extant marsupial behaviour but – while this is very speculative – I am tempted to think that thylacosmilids broke the rules and evolved a level of parental care above and beyond what occurs today. Having said that, extant marsupials are not so consistent as to make such a possibility totally unlikely. Yes, most marsupial parents part with post-weaning juveniles after a few weeks, but extended care of juveniles does take place in some species (one of the best examples being the Rock-haunting ringtail Petropseudes dahli).

    Were sabre-toothed gorgonopsians, therocephalians and crocodilians also having these periods of parental training? While these animals had big caniniform teeth like sabre-toothed cats and thylacosmilids, I don’t think they were behaving in the same way (viz, physically restraining prey and then performing precise bites) as they just weren’t built the same. Don’t be fooled by the teeth: ‘sabre teeth’ do not mean ‘sabre-tooth lifestyle’. In other words I think those animals are irrelevant to this debate.

    Finally, I agree, incidentally, that the alleged lack of upper incisors in thylacosmilids is bizarre, but until reading Churcher (1985) – which I was previously unaware of (thanks Lars) – I hadn’t realised that there is evidence for the presence of upper incisors. I’ve altered the text accordingly.

    Refs – –

    Antón, M. & Galobart, À. 1999. Neck function and predatory behavior in the scimitar toothed cat Homotherium latidens (Owen). Journal of Vertebrate Paleontology 19, 771-784.

    Turner, A. & Antón, M. 1997. The Big Cats and Their Fossil Relatives. Columbia University Press, New York.

  13. #13 Alan Kellogg
    July 5, 2008

    For You Amusement

    Here are a few write ups from the world of Ærth, Gary Gygax’s setting for his Dangerous Journeys: Mythus roleplaying game. The information here is from the Ærth Bestiary book.

    (Nota Bene: Gary wrote these animals up around 1992 and was relying in information from before then. That aside, he did have a habit of beefing creatures up if he thought they weren’t challenge enough for his players.)

    Bear, Long-tailed (borhyaenid, Magmur)
    5-7 feet long, 4 feet tall, 400 to 600 pounds

    A marsupial predator of bear like appearance. Aggressive disposition, omnivorous diet.

    Bear, Long-tailed Polar (borrhyaenid, Magmur)
    6 to 7 feet long, 5 feet tall, 850 to 1,000 pounds

    Close cousin to the long-tailed bear of Magmur. Found on islands south of Magmur leading to the southern opening to the interior world. Hunts seals, penguins, and the southern walrus.

    Lion, Pike-toothed (Thylacosamiliid, Amazonia)
    4 to 6 feet long, 250 to 450 pounds

    Limited to the southern third of the Amazonian continent, these predators hunt herd animals, flightless birds, and the herds of the Onaxeresians who colonized the area some 200 years ago.

    Tiger, Pike-toothed (Thylacosamiliid, Amazonia)
    8 to 10 feet long, 650 pounds

    A more successful cousin of the pike-toothed lion, found throughout Amazonia from the Andes to the coast of the Lantic Ocean

    There are more along this line, but this should give you some idea of what Gygax was into, and how he like to mess with official statistics. Should you feel like working out habits, diet, behavior and the like, be my guest.

  14. #14 Zach Miller
    July 5, 2008

    Has anyone considered that giant saber-teeth are perhaps sexually dimorphic, and may have to do with display? Just a thought. Slitting throats is great, but there’s gotta be an easier way to kill your quarry. Also, the fact that juveniles do NOT have sabers seems like evidence for display functionality. I don’t know enough about how often saber-tooth “cats” are found with or without sabers, so I don’t pretend to know anything about dimorphism in those animals. It’s just a thought.

    But yeah. Display?

  15. #15 David Marjanovi?
    July 6, 2008

    then either piercing the eyes

    A very important fact that lots of people don’t seem to get is that saber teeth are not circular in cross-section. They are flat from side to side and even have serrated cutting edges. They are like theropod teeth. They are not stabbing instruments, they are cutting instruments. Slitting throats sounds about right!

    I don’t know enough about how often saber-tooth “cats” are found with or without sabers

    They are never found without sabers. Also see above — why go to the trouble of evolving serrated edges on display organs? Why not just get bigger canines, baboon-style?

  16. #16 Dave Godfrey
    July 6, 2008

    Any predator dependant on typical predator traps to catch prey isn’t going to be terribly successful. The sabre-toothed cats, nimravids, etc, are better muscled than equivalent sized bears. Holding prey still while cutting the throat is not going to be a problem.

    Because the sabre-teeth are flat they are also relatively fragile. Stabbing with them is going to run the risk of hitting bone, which will break them, or drive them deep into flesh, and subject them to twisting forces which will probably also break them. Holding prey still and slicing through the blood vessels, windpipe, etc doesn’t have these problems.

  17. #17 Mark Lees
    July 6, 2008

    David M said “There are way too many of them per ecosystem. Who should kill all those herbivores for them? That makes no more sense than thinking Tyrannosaurus was a scavenger, I’m afraid.”

    Im not sure that the number per ecosystem argument works here. Firstly I dont know that there is any well established proof of what the correlation is. But any way just how many Thylacosmilus specimens are there? Are they adequate to give any idea of population size/density? I doubt it. For Smilodon many of the specimens come from La Brea. I think it is the best evidence for high population density, but this is clearly a site where Smilodons were scavenging either already dead, or at least dying animals trapped in the pits. In deed the relative high numbers of Smilodons as opposed to wolves and coyotes could suggest that Smilodon was more attracted to/ dependent on scavenging than the others.

    As for the question of who would provide the kills for them, well its important to remember that animals die of causes other than predation. In deed I recall a documentary of aseveral years ago where it was stated that over 70% of larger mammals dying on the Serengetti died of causes such as disease, accidents, even old age (probably rarely), with less than 30% being killed by a predator. Which is why even many predators opportunistically scavenge. On that basis in an ecosystem with large populations of megafauna there would be substantial food for large scavengers.

  18. #18 johannes
    July 7, 2008

    > Not true. Both Machairodus and Megantereon had a mandibular flanges.

    I checked the pictures of skulls available at the internet, and yes, you are right, *Megantereon* (and to a lesser degree *Machairodus*) had flanges of sorts, if not the imposing, sheath-like structures found in *Thylacosmilus* or *Barbourofelis*. What is interisting about *Megantereon* is that its canines seem to lack the serrations so typical for other sabre-tooths.

  19. #19 Mike Habib
    July 8, 2008

    Ah, Thylacosmilus, one of my all-time favorites! I’m hardly an expert on the animal, but I did have a couple of brief thoughts:

    – Do we really know that sabre-toothed biting was “difficult”? It seems to be pretty rare, and is rather specialized (in the sense of requiring extreme morphology), but it seems to be specialized and rare in the same way that the extreme of any continuum tends to be. There is a whole range of canine sizes represented in mammalian predators, might sabre-teeth be rare by virtue of being the tail of the distribution, as it were?

    – Laterally compressed teeth need not be for cutting; they will do just fine for piercing. Thick, rounded teeth are important for piercing if the target is armored, if the predator is breaking bone (essentially the same problem, mechanically), or if the piercing deformation itself is the primary source of damage and incapacitation. If penetration depth is the important aspect, then any shape that lessens resistence when interacting with soft tissue will work. A very thin, needle-like structure will be best from a pure penetration standpoint, but it may not be structurally viable – a blade is one of the viable compromises.

    And looking at how we might expect a neck-powered “stab” to interact with a target, some cutting power is probably important, as the tooth will have some aftward cutting action as it penetrates the target (the teeth are unlikely to enter with a pure piercing action – wish I had a figure handy to demonstrate).

    I had the recent pleasure of actually holding and examining the near-complete T. atrox skull. It’s truly awesome. Take care everyone.

  20. #20 Darren Naish
    July 8, 2008

    I had the recent pleasure of actually holding and examining the near-complete T. atrox skull. It’s truly awesome.

    !!! Did you get photos?

  21. #21 Vultur
    July 10, 2008

    This is very cool. I always thought the parallel evolution of saber-toothed pseudo-cats was completely incredible.

  22. #22 Christophe Thill
    July 10, 2008

    Darren, thanks for these articles. Now, a perhaps silly question. Where does our beloved thylacine fine among (or outside) all those flesh-eating marsupials? What are its ancestors? Actually I could ask the same question about kangaroos. There seem to be lots of information about extinct marsupials, but none of those remotely looks like the extant ones. Or is it just that I’m poorly informed?

  23. #23 Wilbert
    August 25, 2008

    About Parahyaenodon and some interesting notions about the competition between borhyaenids and eutherians.

    Abstracts. Taxonomic revision of Parahyaenodon argentinus Ameghino and its implicances for the knowledge of the Mio-Pliocene large carnivorous mammals of South America. Parahyaenodon argentinus, from the Late Miocene-Early Pliocene of Monte Hermoso (Buenos Aires Province, Argentina), was recognized by Ameghino in 1904, who regarded it as Hyaenodontidae (Eutheria, Creodonta). Based on its dental features, later authors assigned P. argentinus to Borhyaeninae (Metatheria, Sparassodonta, Borhyaenidae). Thus, this taxon would have represented the last known borhyaenid. A new analysis of the type and only known specimen led us to reassign P. argentinus to Procyonidae (Eutheria, Carnivora). In this context, the biochron of Borhyaeninae extends up just to Late Miocene (Huayquerian Age), being cf. Borhyaena and possibly Eutemnodus the last known representatives of this subfamily. Based on these results and in the first records of carnivorous placental immigrants in South America, it is evident that there was no “competitive displacement” between metatherian and eutherian carnivores: there is a gap of no less than four Ma between the extinction of the last Borhyaeninae and the arrival of their alleged ecological counterparts, the Carnivora.

  24. #24 David Marjanovi?
    August 25, 2008

    Wilbert, that’s great, but where can I find the rest of the paper? You know, authors, title, journal, volume, page numbers?

  25. #25 Wilbert
    August 26, 2008

    Sorry (I am just someone who is interested in paleontology, so I rely heavily on the Net, marvelous blogs like these (or Eobasileus etc..) and on the myriade Amazons.coms and obscure antediluvian bookshops I can raid and pillage.
    (to be honest I think over here in the Netherlands noone seems to care about this subject and no books are available)

    But here it is
    Revisión taxonómica de Parahyaenodon argentinus Ameghino y sus implicancias en el conocimiento de los grandes mamíferos carnívoros del Mio-Plioceno de América de Sur
    Analía M. FORASIEPI, Agustín G. MARTINELLI y Francisco J. GOIN

    Ameghiniana 44: 143-159-426. Buenos Aires. ISSN 0002-7014 AMGHB2

    But I have to agree with Darren, The lack of enthousiasm of people concerning these highly interesting creatures suprises me.
    And a lot of questions remain. Where are the marsupial otters or the marsupial badgers ? How did they compete with the Phorusracidae ? Why didn’t they grow huge (like carnivora, Mesonychidae or creodonta ?)

    And about the social structure of some marsupials. I read somewhere that Thylacines often hunted in pairs and sometimes even with their young. That would require a larger brain. So who knows maybe Thylacosmilus was indeed a social animal and much smarter than the average possum.
    And be honest is a wallaby really dumber than their ecological equivalent the roe deer ?

    And about the thylacine, it was called a stupid animal for a long time but try to be ‘smart’ when you are wounded, starved, beaten, cold and locked in a tiny cage.

  26. #26 Christopher Taylor
    August 26, 2008

    And be honest is a wallaby really dumber than their ecological equivalent the roe deer?

    On the one hand, it was my understanding that modern Australian marsupials do have brains on average notably smaller compared to overall body size than placentals. However, modern Australian marsupials are also mostly adapted to life in an extremely arid environment, so large brains may simply be a luxury they can’t afford rather than something they are actually incapable of as such.

  27. #27 johannes
    August 26, 2008

    > On the one hand, it was my understanding that modern
    > Australian marsupials do have brains on average
    > notably smaller compared to overall body size than
    > placentals.

    Metatherian intelligence is limited – if it is limited at all – not so much by absolute or relative brain size, or lack thereof, but by lack of a corpus callosum.

  28. #28 David Marjanovi?
    August 26, 2008

    Thanks a lot for the reference. Ameghiniana is a sort of accessible journal… :-)

    How did they compete with the Phorusracidae ?

    Probably not at all. None of the sparassodonts was a dog-style pursuit-and-bite carnivore, right? That’s what the phorusrhacids seem to have been.

    I read somewhere that Thylacines often hunted in pairs and sometimes even with their young. That would require a larger brain.

    Nobody knows.

    In fact, nobody knows what a bloated brain like ours is actually good for in the first place. Compare us, mouse lemurs, and grey parrots…

  29. #29 Ronald Orenstein
    July 29, 2009

    I notice that everyone who restores Thylacosmilus does so with the sabre teeth visible when the mouth is closed. I have wondered about tis, though; is it possible that the jaw flange supported a soft-tissue sheath into which the canines fitted, rather than simply bracing them on the inner surface?

  30. #30 anavictoria
    December 19, 2009

    this is a ameazing animal its so pretty so i think

  31. #31 Ellen
    February 23, 2010

    I’m enjoying your posts about obscure mammals.

    I just found an amazing Thylacosmilus reconstruction online, one of the best I’ve seen.


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