SINCE I STARTED this blog I have received an increasing number of hits from search engines. Unsurprisingly, one of the topics funneling people this way is the Nimravidae. My entry on the Dinictis skull replica found at Bone Clones has received the most hits overall since I started this blog. Unfortunately, there is not really much information about nimravids available without some digging, and very little on the open web. So here I will pull together everything I can currently get my hands on!
The nimravids appeared in the Eocene, with the oldest fossils about 37 million years old, but probably the lineage originated between 40 and 50 million years ago. After their first appearance they spread rapidly throughout the northern hemisphere before finally becoming extinct about 23 million years ago. In the past the barbourofelids, which showed up several million years after the nimravids died out, were also included in the nimravids, but recent studies have placed these organisms in their own group closer to the felids.1 For about the past 80 years taxonomists have placed nimravids in their own clade outside Felidae, but that has not kept less taxonomically scrupulous scientists from lumping them into Felidae frequently. A key differentiating character is the auditory bulla, which is a bony chamber in felids, but in nimravids only partially encased by bone, with a floor of cartilagenous tissue.2 Since recent studies have clarified the phylogenetic relationships of these carnivores I hope that in the future their status as an independent clade will be more widely recognized. This phylogenetic tree3 shows the relationships between nimravids and other carnivores.
Now for a ‘sloppy taxonomy’ mini-rant: See who’s sitting right next to Felis? Hyaena. The hyenas are thought to be vastly more closely related to cats than to dogs, and you can see here, much more closely related to cats than the nimravids were. Nimravids are equally closely related to both the cats and the hyenas, so it would really make just as much sense to lump the nimravids in with the hyenas as it does to lump them in with the felids. Indeed, there might be a better rationale for this type of lumping, as some scientists want to move both Nimravidae and Hyaenidae outside the Feliformia/Caniformia split, placing them as related sister clades to the rest of the carnivores. This, however, is a minority opinion at this time.
For another side-track in sloppy taxonomy, see the groups with ‘Miacidae’ written across their stems? The family Miacidae was previously thought to consist of a group of generalized carnivores that branched off before the appearance of Carnivora. This paper demonstrates that ‘Miacidae’ is a paraphyletic group, containing organisms from many different evolutionary branches. Further research will be required to sort ‘Miacidae’ into monophyletic clades.
Peigné has done some great work in nimravid phylogenetics (you’ll see her name on many papers related to nimravids) and produced this phylogenetic tree showing groups appearance over different time periods.4 It is a simplified version of the diagram found in the original paper, which included detailed breakdowns of geological time periods that I am not familiar with and probably will not be of interest to most readers, but if you are interested I have uploaded the original.
Peigné points out that in order to be Nimravidae’s sister clade, the Barborifelidae would have needed a ghost lineage (existing members but no fossil record) extending back almost 25 million years. This would not be unlikely for a group in the Triassic, but it is much less likely for a major group living in the Eocene, which is fairly recent on a geological time scale.
In spite of their relative recency, the nimravids unfortunately do not have a great fossil record. The earliest nimravids known already have the characteristic saber-teeth, although it is thought that the nimravids evolved from a smallish, non-saber-toothed, less cat-like carnivore. The recent description of a nimravid skull found in France provides support for this, since this skull lacks saber teeth but has many other nimravidine traits.5 Unfortunately this skull is too badly damaged for a complete description and of unknown age, since it was recovered fortuitously by miners. A skull more representative of later nimravids6 is shown below.
The nimravids had two body styles. The later nimravids Hoplophoneus and Eusmilus were dirk-toothed, with long, finely serrated canines and short, powerful legs. Most earlier nimravids were scimitar-toothed, with comparatively shorter canines and longer legs. Based upon jaw buttressing, Therrien concludes that the two different types of dentition produced two different killing bites, and different hunting strategies as well.7
These results suggest that dirk-toothed taxa delivered sabre bites on better-restrained prey than scimitar-toothed taxa, which can be explained by the postcranial differences between the two ecomorphs. Dirk-toothed sabretooths could have immobilized prey with their powerful forelimbs prior to delivering a powerful sabre bite while scimitar-toothed ecomorphs would have delivered shallow, slashing bites during pursuit to weaken their prey, pulled it down with the aid of their robust incisor battery and immobilized it prior to delivering a sabre bite.
The dirk-toothed nimravids probably hunted by ambush at close quarters, while the scimitar-toothed nimravids pursued prey over short distances, similar to modern cats. In both groups the bite was driven by both jaw and neck muscles, but the dirk-toothed nimravids were more adapted for a single powerful stabbing bite, similar to that of the true cat Smilodon.
A recent study suggests that juvenile nimravids were dependent upon adults for food for an extended time.8 Juvenile nimravids’ saber teeth erupted late after the loss of the deciduous canines, and their jaw musculature was insufficient for killing prey. However, they had strong neck musculature that was probably used in conjunction with the large, curved incisors (feature 2 on the skull above) in pulling and twisting meat away from carcasses. Nimravids probably had a prolonged juvenile stage similar to modern large cats. Otherwise it is hard to say much about their social lives. They may have been solitary or cooperative hunters, or perhaps behavior varied among different genera.
Two other blogs have covered the Nimravidae, Laelaps in Just what is a Nimravid, anyway? and in passing at “What big teeth you have. . .” (his blog has now moved to Science Blogs) and Olduvai George in “Not Quite A Cat? Wasn’t This Supposed to be About Whales?” at his sadly now-inactive blog. Olduvai George’s entry is actually half about nimravids and half about barbourofelids, the news of their promotion to Barbourofelidae not having spread widely at that time.
- Morlo, M.; Peigné, S.; Nagel, D. “A new species of Prosansanosmilus: implications for systematic relationships of the family Barbourofelidae new rank (Carnivora, Mammalia).” Zoological Journal of the Linnean Society 2004, 140, 43-61. DOI:10.1111/j.1096-3642.2004.00087.x
- Hunt, R. M. “Evolution of the Aeluroid Carnivora: Significance of Auditory Structure in the Nimravid Cat Dinictis.” American Museum Novitates 1987, 2886, 1-74.
- Wesley-Hunt, G. D.; Flynn, J. J. “Phylogeny of the Carnivora: basal relationships among the Carnivoramorphans, and assessment of the position of ‘Miacoidea’ relative to Carnivora.” Journal of Systematic Palaeontology 2005, 3, 1-28. DOI:10.1017/S1477201904001518
- Peigné, S. “Systematic review of European Nimravidae (Mammalia, Carnivora, Nimravidae) and the phylogenetic relationships of Paleocene Nimravidae.” Zoologica Scripta 2003, 32, 199-229. DOI:10.1046/j.1463-6409.2003.00116.x
- Peigné, S. “A primitive nimravine skull from the Quercy fissures, France: implications for the origin and evolution of Nimravidae (Carnivora).” Zoological Journal of the Linnaean Society 2001, 132, 401-410. DOI:10.1006/zjls.2000.0276
- Barycka, E. “Evolution and systematics of the feliform Carnivora.” Mammalian Biology 2007, 72, 257-282. DOI:10.1016/j.mambio.2006.10.011
- Therrien, F. “Feeding behavior and bite force of sabretoothed predators.” Zoological Journal of the Linnean Society 2005, 145, 393-426. DOI:10.1111/j.1096-3642.2005.00194.x
- Peigné, S.; Bonis, L. “Juvenile cranial anatomy of Nimravidae (Mammalia, Carnivora): biological and phylogenetic implications.” Zoological Journal of the Linnean Society 2003, 138, 477-493. DOI:10.1046/j.1096-3642.2003.00066.x