Wednesday, July 18, 2007

Vulture Mimics: An Introduction to Cathartids

I'll level with you, cathartids actually aren't vulture mimics, vulture originators would technically be more appropriate. Technicalities such as earlier fossil/implied genetic age aside, the "Old World" vultures were known to the West much earlier (obviously) and still remain the by far the most popular conception of what a "vulture" is*. Why is this important do you ask? For instance, ostrich-mimics (ornithomimosaurids) are older than ostriches, but unfortunately they were discovered later and are less familiar. There is even a non-dinosaurian ostrich-mimic-mimic (Effigia) that is even older and less familiar still. While cathartids are often called "New World" vultures, as we'll see that is a very poor name indeed. I won't call them vulture mimics either, that was just a scam to initiate discussion, I'll call them cathartids**. But as we'll see...

*Actually the genus Gyps (Griffin vultures) seems to be the long-necked "vulture" archetype. Ever notice how in cartoons taking place in the American West the vultures are all Griffins? Vultures most certainly are not limited to deserts either, by the way. Aegypiine vultures have some interesting forms and classification controversies, they might get discussed later.

**According to Amadon 1977, at least one authority called the whole group "condors".


Some sources such as Mikko's phylogeny put cathartidae and vulturidae as synonyms. Curiously I've noticed that papers on condors (e.g. Vultur) classify them as vulturids but just about everything else calls them cathartids (e.g. Cathartes aura, the turkey vulture). I suspect vulturidae may be a functional sub-family in most classifications, but I have yet to find a source specifically stating this [Edit: "Vulturid" is a synonym with priority nonetheless. However, it likely that it was named with "old world" vultures in mind. See comments]. The big-picture classification of cathartids is more confusing still. Traditionally they were classified as falconiformes along with the familiar birds of prey. Their overall appearance is similar, although cathartids have odd features such as weak feet and perforate nostrils. The oft-cited Sibley-Ahlquist taxonomy upheaval placed them in the order ciconiiformes along with storks and relatives. To cite something, why not the Turkey Vulture Society page, yep, turkey vultures are more popular than what I'd previously thought. A stork/vulture association isn't as nonsensical as it seems; the shockingly hideous marabou stork is a bald-headed (occasional) scavenger with the same self-urination (the white stuff in bird poop isn't poop) habit of keeping cool. Interestingly, the stork/vulture connection has been suspected as early as 1967 (Fedduccia, 1974). However, it most certainly is yet another vulture-mimic of sorts.

But here's the problem: cathartids aren't ciconiiformes either. Popular literature is often outdated and/or a simplification of controversial issues. As a layman, the world of bird phylogeny seems ludicrously confusing and unsettled. A 2006 paper by Ericson et al places them closer to falconiformes (and near-passerines, apparently) than ciconiiformes, although their split apparently took place slightly before the K/T event. Slack et al in a 2007 paper places them in a super-group called the Cracrafti/Conglomerati, although they are positioned in an unstable area in between the falcon/buzzard, gull/oystercatcher, and albatross/loon/stork/penguin lineages. Another paper by Gibb et al in 2007 again with more species included it the synonymous "water-carnivore" super-group and interestingly placed cathartids closer to the seabirds/shorebirds than anything. However, they are still clearly quite isolated. The phylogenetic trees also demonstrates a surprising distance between falcons and buzzards making falconiformes apparently paraphyletic; and demonstrated storks and pelicans grouping rather than with herons, making the traditional ciconiiformes polyphyletic. With more species getting studied, it seems like birds phylogeny is going to need a radical overhaul. Cathartids are now apparently an incertae sedis, although I have seen a proposal for the creation of the order cathartiformes. I've seen this used in a recent Spanish-language publication (here), although widespread acceptance is lacking.

Despite taxonomic upheavals galore the extinct family teratornithidae is still attached to cathartids in recent publications (e.g. Chatterjee 2007). Mikko's phylogeny page places both groups in an encompassing group called vulturides. Usage of that group appears exceedingly rare in publications and I am not certain if it could be synonymous with cathartiformes or not. Despite traditionally being portrayed as super-condors (such as here) tetatorns are now believed to be predatory and distinctive. Given their size (bigger than even super-marabous) they might just be present in the final post of some trilogy.

Let us now discuss cathartids proper, the extinct ones. The reason I don't call cathartids "New World vultures" is that they were certainly present in the Eocene-Oligocene of Europe. To make matters worse, aegypiine vultures are known from both Old and New Worlds from the lower Miocene to Pleistocene, obscuring their "world" of origin (Fedduccia 1974). That's a tale for another day though. Cracraft & Rich in their 1972 paper discuss how for years possible remains of Old World cathartids were discounted or ignored due to their problematic nature (the vice versa was true as well interestingly). Despite their outwards similarity to aegypiines, cathartids are very distinctive from a skeletal standpoint, particularly the shape of the tarsometatarsus and to a lesser degree the tibiotarsus. They named four genera, one of which (Amphiserpentarius) was apparently re-classified as a secretary bird, but according to Mikko's the rest still stand up. [[Edit: Peer editing has revealed to me that the alleged smallest crow-sized cathartid, Plesiocathartes, is a leptosomid. The paper is unfortunately unavailable to me, but see comments]]. The authors raise the remarkable possibility that cathartids in fact originated in Europe in between the late Cretaceous and Eocene and branched out to the New World in the Early Eocene. This was presented as an alternate hypothesis and not a replacement. I haven't seen much more discussion on this, but it should be noted that they used the non-cathartid Neocathartes in their theory. This was alleged to be a "walking turkey vulture" of sorts, but turned out not to be. Sorry for not being able to find the actual paper for that one.

I hope that this was an adequate prelude to the cathartids. There are still some fossil forms that I'll probably cover some time in the future, but I'd like to talk more about extant species. Perhaps I can do a cathartid-of-the-random-time-interval sort of feature. Or maybe not, I like to focus on obscurity...


Oh, I'm not done just yet.


-Cameron


References:
Some free, some not.


Amadon, Dean. 1977. Note on the Taxonomy of Vultures. The Condor. 79: 413-416. Available: Here

Chatterjee, Sankar & Templin, R. Jack & Campbell, Kenneth E. 2007. The aerodynamics of Argentavis, the world's largest flying bird from the Miocene of Argentina. Proceedings of the National Academy of Sciences. Published online (for free) Here

Cracraft, Joel & Rich, Pat Vickers. 1972. The Systematics and Evolution of the Cathartidae in the Old World Tertiary. The Condor. 74: 272-283. Available: Here

Ericson, G.P. et al. 2006. Diversification of Neoaves: integration of molecular sequence data and fossils. Biology Letters. 2: 543-547. Available: Here

Fedduccia, A. 1974. Another Old World vulture from the New World. Wilson Bull. 86: 251-255. Available online Here (for free)

Gibb, Gillian C. et al. 2007. Mitochondrial Genomes and Avian Phylogeny: Complex Characters and Resolvability without Explosive Radiations. Mol Biol Evol. 24: 269-280. Available: Here

Slack, Kerryn E. et al. 2007. Resolving the root of the avian mitogenomic tree by breaking up long branches. Molecular Phylogenetics and Evolution. 42: 1-14. Available: Here

8 comments:

Caitling said...

One day we're going to find out that we're really human-mimics, the real humans died out a long time ago, we're all aliens pretending to be them, of course none of us know this yet.

More on the topic of the blog, what's so great about vultures that other things want to be like them?

As for the french, it's easy to understand really, it's all about this bird.

Anonymous Coward said...

Wow that was an epic post. thanks!

I see you're a fan of both Kevin Z and Lim (or perhaps the other way around?).

Would you like to exchange blog links?

bayblab.blogspot.com

Lars Dietz said...

Interesting!
By the way, Plesiocathartes is not a cathartid. It appears to be a probable leptosomid (cuckoo-roller). See the following reference:
Gerald Mayr: A new species of Plesiocathartes (Aves: ?Leptosomidae) from the Middle Eocene of Messel, Germany. PaleoBios, 22 (1): 10-20.

Cameron McCormick said...

Thank you Lars for demonstrating the value of peer review! I'll spread the word on to Mikko.

Christopher Taylor said...

Cathartidae and Vulturidae are the same taxon, independently named after different genera. The name "Vulturidae" has priority, but for reasons I don't know about (a large proportion of bird family names date from before concepts such as priority became well established in biology, and besides there are far too many cases were priority is a bitch to establish) was almost universally ignored in favour of the later Cathartidae until Bridkorb (IIRC) revived it in his catalogue of fossil birds. Apparently Brodkorb replaced a number of familiar family names with less-known but technically accurate names in this way. While palaeontologists have tended to follow Brodkorb's lead, most neontologists feel that the use of Cathartidae has become so ingrained that insisting on Vulturidae is more confusing than its worth. The reference I read about this in (Bock, 1994) proposed that an application be made to the ICZN for conserving Cathartidae (among others), but I don't know if such a proposal was ever passed.

Bock, W. J. 1994. History and nomenclature of avian family-group names. Bulletin of the American Museum of Natural History 222: 1-281.

Christopher Taylor said...

Also there's the problem that Vultur was originally used for both New World and Old World vultures. Even when they were recognised as different, some authors used Vultur for Old World vultures, and some used it for New World vultures. It seems likely that the original author of Vulturidae was thinking of Old World vultures, not New World.

Cameron McCormick said...

Ah, so you're the Christopher Taylor from the "Catalogue of Organisms"...I was wondering if my friend on the Brown basketball team of the same moniker was unusually knowledgeable on nomenclature :)

Thank you for the corrections and insights

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