Dissecting lions and tigers (& snow leopards): Inside Nature’s Giants series 2, part III

Dissecting lions and tigers: Inside Nature’s Giants series 2, part III
Category: community • mammalogy
Posted on: September 6, 2010 9:37 AM, by Darren Naish

Given that big cats are more popular (among the general populace) than are either sharks or snakes, it’s predictable that this was the most discussed, most anticipated episode. Like the others, it was excellent [adjacent image © Windfall Films/Channel 4].

And let me say again how good the whole of ING series 2 was: well done to everyone involved, you left us wanting more. And to those who haven’t seen the series (yet), I hope these articles serve as useful promotional tools – it’s certainly not my intention to steal proverbial thunder. WARNING: total, epic spoiler ahead…

So, to work. Episode 3 featured dissections of both a Lion Panthera leo and Tiger P. tigris* [Panthera taxa shown above (from wikipedia)… but no Snow leopard**]. Mark Evans noted at the start that one of the aims was to see whether lions and tigers are essentially the same under their skins, or whether any differences would become apparent. Most of the filming was done at the Royal Veterinary College: Tecumseh Fitch, a cognitive biologist who you might know best for his publications on mammalian vocal tracts, worked on the dissections with Joy Reidenberg and Andrew Kitchener. Penny Hudson, who works on cheetah locomotion at the RVC, also appeared. Members of the team travelled to Africa to see lions in the wild, while Richard Dawkins discussed the general principles behind predator/prey ‘arms races’.

* Obligatory mention here of the fact that some workers regard P. tigris of tradition as consisting of three phylogenetic species. Under this proposal, the Sumatran tiger P. sumatrae and Javan tiger P. sondaica warrant separation (Cracraft et al. 1998, Mazák & Groves 2006).

** Molecular data indicates firm inclusion of the Snow leopard within Panthera. However, because it differs in throat anatomy, skull shape, tooth shape and limb proportions from definite Panthera species (in some respects it’s rather cheetah-like), some anatomists argue that the Snow leopard warrants placement outside of Panthera and still use the name Uncia uncia for the species [adjacent Snow leopard photo by Bernard Landgraf, from wikipedia].

I know that some viewers were a little disappointed to see that the matter of how lions and tigers can be differentiated wasn’t really elucidated. But perhaps that’s because the two are extremely similar, and it’s this similarity that was concentrated on, rather than the differences. The fact that lions and tigers can produce hybrids was looked at (but this doesn’t mean much about lions and tigers specifically, given that hybrids between just about any and all similar-sized cats are possible and have been produced in captivity) [lion skeleton below, courtesy Windfall Films. Photographed at the University Museum of Zoology, Cambridge, I think].

Indeed, something that couldn’t be covered in the episode is that, yes, lions and tigers are similar, but they’re not especially similar among the big cats; rather, all the big cats (indeed, all cats) are highly similar, and I would say that people only think of lions and tigers as being similar because both are similar in size. Most studies show that tigers and lions aren’t even that close within Panthera: lions are part of a ‘spotted clade’ that also includes leopards and jaguars, while tigers lie elsewhere, possibly being the sister-taxon to the Snow leopard (Bininda-Emonds et al. 2001, Burger et al. 2004, Yu & Zhang 2005, Johnson et al. 2006).

The possible function of the lion’s mane was looked at. As has been discussed on Tet Zoo before [see book cover below], there are several competing hypotheses that hope to explain mane evolution: these explanations may well be overlapping and compatible, and it may also be that different factors take precedence in different parts of the lion’s range. So, while the mane is conventionally regarded as a visual signal of maturity and fitness in some lion populations (Yamaguchi et al. 2004), its development seems to be delayed in some populations (Kays & Patterson 2002) because having a large mane interferes with thermoregulation (Gnoske et al. 2006, Patterson et al. 2006).

Something of incidental interest is the observation that zoo lions typically have larger manes than wild ones (Patterson et al. 2006, pp. 196-197), presumably because their nutrition is better and their manes are subjected to less abrasion than that experienced by wild lions (hmmm… does this explain why there are so many claims of Barbary lions being ‘discovered’ in captivity?). Captive lion cubs are sometimes larger than their wild counterparts, and one study reported that captive tigers have deeper occipital regions than wild animals (Duckler 1998), apparently because captive animals engage in excessive grooming and thereby over-exercise their head and neck musculature. O’Regan (2001) found that the skulls of captive big cats were broader across the zygomatic arches than wild animals, but it wasn’t clear why this was so. Anyway, I digress.

Laryngeal anatomy: why lions are like people

I’m a big fan of laryngeal and tracheal anatomy, and one of the main stories focused on in this episode concerned the structure and function of the big cat larynx and its role in vocalising. Well known (and oft-mentioned) is that big cats differ from little ones in having a ligamentous (rather than ossified) epihyoideum component in the throat skeleton, thereby allowing them to roar (though it is not this component alone that allows roaring (see Hast 1989); as usual, things have turned out to be more complicated). Less well known is that the big cat larynx is positioned well posterior in the throat. Weissengruber et al. (2002) inferred the thyroid cartilage (the largest component of the larynx: the part often called the ‘Adam’s apple’) to be about level with the axis vertebra in Panthera (in contrast, it’s only just behind the rear margin of the lower jaw in a domestic cat and most other ‘ordinarily’ mammals). However, they suggested that, in life, its normal resting position was much lower (as in, level with the 5th-7th cervical vertebra) (see Pérez et al. (2006) for data on tigers) [adjacent picture shows (l ro r) Penny Hudson, Mark Evans and Tecumseh Fitch dissecting the lion’s throat. Image © Windfall Films/Channel 4].

In having such a low-set larynx, Panthera cats resemble us humans, a point made during the episode. Big cats also resemble humans in that the larynx is bigger in males than in females, and it migrates posteriorly as an animal approaches sexual maturity. Worth noting here is that a descended larynx is not unique to big cats and humans*: some deer also have a permanently descended larynx, and koalas, some bats and possibly elephants have one too (Fitch & Reby 2001, Weissengruber et al . 2002, McElligott et al. 2006). I’ve mentioned some of this before when discussing Fallow deer Dama dama (and this reminds me, there’s a near-finished article on the subject of mammal throats and vocalisation waiting in the wings) [lion palate and teeth shown below, image © Windfall Films/Channel 4].

* Seriously, humans are nice and everything, but they’re not all that special. All those old claims about humans being “the only animals capable of [insert behavioural or cognitive trait]”, or “the only animals possessing [insert anatomical component or configuration]” stem from lack of knowledge or data on non-humans.

During the dissection, it was discovered that the lion’s sternohyoid – one of the muscles involved in pulling the larynx down toward the chest during vocalising – attached deeper in the chest than previously thought. This means that the larynx can actually be pulled even further ventrally than hypothesised, hence helping to explain how lions can produce such low fundamental frequencies and low formant frequencies in their roars. The deep-set larynx, combined with the length of the pharynx, very large, fleshy vocal folds and cavernous mouth, has led some workers to propose that the big cat mouth and throat functions in analogous fashion to a brass trumpet (Hast 1989). Even in death, bodies can be made to vocalise: all you have to do is force air from the lungs out through the larynx. In series 1, a dead Nile crocodile was made to vocalise when its trachea was connected to a hose, and the same neat trick was used here on the lion. Nice!

Claws, paws and jaws

The forelimb anatomy of big cats got some coverage. Cat wrists and hands are more flexible that those of carnivorans – like hyaenids and dogs – that don’t use their hands in grappling with prey. We were shown how cat claws only become unsheathed when both the dorsal and ventral tendons on the digits are flexed (the extensor digitorum lateralis and communis tendons dorsally, and the flexor digitorum profundus tendons ventrally). Cat claws are hyper-retracted when not in use, and are actually ‘stored’ in special concavities located on the lateral sides of the penultimate phalanges. Accordingly, those phalanges are strongly asymmetrical. The fore- and hindlimb claws of cats are different in shape and function, with the strongly hooked manual claws acting in prehension and combat, and the more blade-like pedal claws acting in raking (Bryant et al. 1996). Note to dinosaur fans: dromaeosaur pedal digit II claws look similar to cat pedal claws, and this is why I think that a raking/disembowelment role for these claws remains viable (and, in part, why the climbing crampon idea is not). Someone should look into this properly, hint hint [adjacent image: Panthera ligaments involved in claw retraction being manipulated. Image © Windfall Films/Channel 4].

Incidentally, the claw retraction mechanism present in cats isn’t as unique as tradition would have it: Nandinia (the African palm civet) and various viverrids have the same mechanism, and a less elaborate but very similar system is present in some mustelids and procyonids. In fact, retractile claws might be a synapomorphy for the whole of Carnivora (since lost or reduced in many lineages).

ING also covered biting styles and the function of the teeth, and they included a bit of comparison between Panthera and Smilodon [replica skull shown here © Windfall Films]. However, I don’t think that what was said was really up-to-date in terms of current ideas on sabretooth behaviour. Recent studies on the predatory behaviour of these cats indicate that they practised a conventional felid throat bite (aiming for the windpipe and blood vessels) after restraining the prey with massive forelimb and pectoral musculature (Antón & Galobart 1999, Antón et al. 2004).

Final thoughts!

So there we have it. ING ep 3 was great, but (in my opinion), the White shark and giant python articles were better. But that sounds a bit unfair, as all the episodes of series 2 were great. In no way did this second series seem at all ‘samey’ or tired in view of series 1; each episode focused on entirely novel material of the sort not really shown on TV before [image below © Windfall Films/Channel 4].

And the episodes were pretty comprehensive: it occurred to me as I wrote up the python episode that it had covered pretty much everything you would want to touch on when providing an introductory overview to snake anatomy and biology. I also think that the episodes did a good job of finding the right balance in terms of showing both ‘sciencey’ bits (the dissections and discussions of anatomy), and more standard natural history-themed bits. There was more than enough to keep a hard-core nerd interested yet, at the same time, many people with only a passing interest in science, natural history or animals also remained transfixed. The people involved in the series represent a good mix. All came across well: as likeable, knowledgeable and never as arrogant. At the risk of pissing off some of my friends in TV-land, I have to say that at least a few of the people who feature on science-based TV programmes come across as extremely annoying, or extremely arrogant, or both, so it’s nice to walk away from a TV series without a feeling of rage or frustration. So, I am totally happy with ING series 2, I loved it.

As mentioned earlier, a special episode of ING, focusing on giant squid, will be featured some time later this year. I also hear inklings that work on series 3 is underway – I really hope so, and I hope that ING becomes a regular thing on our TV sets. Well done to Windfall Films, to Channel 4, and to everyone involved. You served us well, showed us so much, and did not let us down.

Special thanks to Zach Buchan for his help with this series of articles, to Joy Reidenberg, Penny Hudson, and to Tom Mustill at Windfall Films. If you’re on facebook be sure to ‘like’ Joy’s page.

For other Tet Zoo articles on ING, see…

Inside Nature’s Giants: a major television event worthy of praise and accolade. Part I!
Inside Nature’s Giants part II: whale guts and hindlimbs ahoy
Enough mammals for the time being: crocodiles on Inside Nature’s Giants (part III)
Inside Nature’s Giants part IV: the incredible anatomy of the giraffe
Inside Nature’s Giants, series 2: does Carcharodon bite?
Monster pythons of the Everglades: Inside Nature’s Giants series 2, part II
For previous Tet Zoo articles on cats see…

Belated welcome to a ‘new’ clouded leopard.. named in 1823
Peter Hocking’s big cats: where are you now?
Homage to The Velvet Claw (part I)
Homage to The Velvet Claw (part II)
Europe, where the sabre-tooths, lions and leopards are
Pumas of South Africa, cheetahs of France, jaguars of England
Britain’s lost lynxes and wildcats
Super-size cougars
The Pogeyan, a new mystery cat
The Hayling Island Jungle cat
‘Revising’ the Siberian tiger
And, if you liked the discussion above of laryngeal anatomy and what it might mean for vocalisation, be sure to check out…

Deer oh deer, this joke gets worse every time I use it
Dissecting an emu
Ridiculous super-elongate, coiled windpipes allow some birds to function like trombones – – or is it violins?
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.

– ., Salesa, M. J., Pastor, J. F., Sánchez, I. M., Fraile, S. & Morales, J. 2004. Implications for the mastoid anatomy of larger extant felids for the evolution and predatory behaviour of sabretoothed cats (Mammalia, Carnivora, Felidae). Zoological Journal of the Linnean Society 140, 207-221.

Bininda-Emonds, O. R. P., Decker-Flum, D. M. & Gittleman, J. L. 2001. The utility of chemical signals as phylogenetic characters: an example from the Felidae. Biological Journal of the Linnean Society 72, 1-15.

Bryant, H. N., Russell, A. P., Laroiya, R. & Powell, G. L. 1996. Claw retraction and protraction in the Carnivora: skeletal microvariation in the phalanges of the Felidae. Journal of Morphology 229, 289-308.

Burger, J., Rosendahl, W., Loreille, O., Hemmer, H., Eriksson, T., Götherstrom, A., Hiller, J., Collins, M. J., Wess, T. & Alt, K. W. 2004. Molecular phylogeny of the extinct cave lion Panthera leo spelaea. Molecular Phylogenetics and Evolution 30, 841-849.

Cracraft, J., Feinstein, J., Vaughn, J. & Helm-Bychowski, K. 1998. Sorting out tigers (Panthera tigris): mitochondrial sequences, nuclear inserts, systematics and conservation genetics. Animal Conservation 1, 139-150.

Duckler, G. L. 1998. An unusual osteological formation in the posterior skulls of captive tigers (Panthera tigris). Zoo Biology 17, 135-142.

Fitch, W. T. & Reby, D. 2001. The descended larynx is not uniquely human. Proceedings of the Royal Society of London B 268, 1669-1675.

Gnoske, T. P., Celesia, G. G. & Kerbis Peterhans, J. C. 2006. Dissociation between mane development and sexual maturity in lions (Panthera leo): solution to the Tsavo riddle? Journal of Zoology 270, 551-560.

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Johnson, W. E., Eizirik, E., Pecon-Slattery, J., Murphy, W. J., Antunes, A., Teeling, E. & O’Brien, S. J. 2006. The Late Miocene radiation of modern Felidae: a genetic assessment. Science 311, 73-77.

Kays, R. W. & Patterson, B. D. 2002. Mane variation in African lions and its social correlates. Canadian Journal of Zoology 80, 471-478.

Mazák, J. H. & Groves, C. P. 2006. A taxonomic revision of the tigers (Panthera tigris) of southeast Asia. Mammalian Biology 71, 268-287.

McElligott, A. G., Birrer, M. & Vannoni, E. 2006. Retraction of the mobile descended larynx during groaning enables fallow bucks (Dama dama) to lower their formant frequencies. Journal of Zoology 270, 340-345.

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