A little while back we looked at the claws, bony knobs and other structures present on the hands of certain palaeognaths, waterfowl and other birds. Time to look at more of this sort of stuff – I kind of got distracted by lapwing taxonomy, so this is all going on for a bit longer than expected, sorry. Anyway…
Charadriiformes – waders, gulls and relatives – are also notable in including species that possess spurs and other peculiar forelimb structures. At least three jacanas have spurs: the Northern jacana [shown in the adjacent image, from wikipedia] is named for this feature, being known scientifically as Jacana spinosa. In this species, the Wattled jacana J. jacana and Pheasant-tailed jacana Hydrophasianus chirurges, the spurs are sharp-tipped, conical structures located on the extensor process of the carpometacarpus. In Northern jacanas these spurs are between 7 and 10 mm long.
Other jacanas lack spurs, but have a peculiar radius that is flattened and heavy relative to the ulna, and possesses a long blade-like ridge along its leading edge. In life, this possesses a cornified covering. It’s present in the African jacana Actophilornis africana, Madagascan jacana A. albinucha, Bronze-winged jacana Metopidius indicus and Comb-crested jacana Irediparra gallinacea. Both the spurs and radial blades are used in combat [the diagram below, from Rand (1954), shows (F) the radial blade of an African jacana and (in both G1 and G2) the carpal spur of a Northern jacana].
Jacanas are weird birds – not just because of their incredible toes and reversed sexual dimorphism, but also because they indulge in some very neat bits of behaviour. Northern, Wattled and Pheasant-tailed jacana chicks, for example, hide beneath the water surface when scared by predators, and use their short bills as snorkels (their nostrils are placed further anteriorly on the bill than is usual for charadriiforms. This is also true of some gallinules, inviting speculation that they indulge in this behaviour too). Bosque & Herrera (1999) report that they were surprised to discover some weird yellow flowers sticking out of the water on a Venezuelan floodplain: on examination, these proved to be the bills of juvenile jacanas.
Spurs are particularly common in plovers, especially in the members of Vanellinae (the lapwings and wattled plovers*). Rand (1954) reported prominent carpal spurs in the Southern lapwing Belonopterus chilensis, White-headed lapwing Vanellus albiceps, Javan lapwing V. macropterus, Masked lapwing V. miles, African wattled lapwing V. senegallus, Pied lapwing V. cayanus and, of course, in the Spur-winged lapwing V. spinosus, River lapwing (also called Spur-winged lapwing, confusingly) V. duvauceli and Blacksmith lapwing V. armatus.
* Having referred to these birds as plovers, I should note that they do not form a clade with other plovers (Charadriinae) in all studies (e.g., Strauch 1978, Chu 1995, Ericson et al. 2003), and consequently have sometimes been given ‘family’ status (as Vanellidae). Pluvialis never groups with other plovers, so Charadriidae of tradition is not monophyletic… (there’s more to say here, because some workers have noted that a monophyletic Charadriidae – i.e., one that includes Pluvialis, lapwings and true plovers – can be retained, but only if haematopodids (oystercatchers) and recurvirostrids (stilts and avocets) are included within it. That seems weird and not particularly useful) [image below shows hand – with spur – of a Masked lapwing].
In most of these lapwing species, the spurs are between 8 and 12 mm long (up to 22 mm in female White-headed lapwings) and clearly visible in life. Do remember that the bony processes you’re seeing in the diagrams and photos used here are enlarged in life by keratinous extensions.
Incidentally, lapwing taxonomy has been substantially revised since Austin Rand wrote his paper on avian carpal spurs (Rand 1954: consulted extensively in the preparation of these articles). The majority of modern authors include all lapwings in the genus Vanellus but Rand and his contemporaries recognised many lapwing genera: the species mentioned above were listed in Xiphidiopterus, Rogibyx, Lobibyx, Afribyx, Hoplopterus and Hoploxypterus by Rand (1954). Phylogenies that incorporate a good sampling of lapwing species tend to recover little resolution within the group (Thomas et al. 2004), but a few clades have emerged, including four that seem to correspond to Belonopterus, Hoplopterus, Lobibyx and Lobivanellus. Given that we’re now using unranked nomenclatures, any clades can be named, so it’s conceivable that these old names could come back into use if they’re deemed useful (I’m currently reading Jonathan Losos’s Lizards in an Evolutionary Tree: Ecology and Adaptive Radiation of Anoles, and he makes the same argument therein for anole clades contained within the ‘genus’ Anolis) [hand skeleton of Southern lapwing shown below, from Rand (1954)].
Some authors, I note, have already taken to using some of these ‘old’ generic names: Campbell (1979, 2002) and Cenizo & Agnolin (2007), for example, argued that Belonopterus is highly distinct compared to Vanellus and they hence reinstated the use of this name. While relatively big carpal spikes are present in the Southern lapwing, as mentioned above, they’re present in other members of the Belonopterus lapwing group and are very evident in such fossil species as B. downsi from the Pleistocene of La Brea (Campbell 2002) [carpometacarpi of some Belonopterus species shown below, from Campbell (2002). The fossil species B. downsi is shown in D-F].
Going back (just briefly) to those old lapwing names, you’ll note that some of them incorporate specific references to the wing armament. Both Hoplopterus and Hoploxypterus, for example, mean something like ‘shield wing’.
Really short spurs (just a few mm long) are present in various others lapwings, including Long-toed lapwing V. crassirostris, Grey-headed lapwing V. cinereus, Red-wattled lapwing V. indicus and Andean lapwing B. resplendens (again, note that – when Rand was writing – these species were all given their own genera separate from Vanellus [Hemiparra, Microsarcops, Lobivanellus and Ptiloscelys, respectively], thereby artificially raising the count of spur-handed plover genera).
Besides jacanas and lapwings (and the waterfowl looked at in the previous article), spurs are also said to be present in the Antarctic sheathbills. I’d love to know what these look like, but I’ve been unable to find any illustrations depicting these organs in the literature [Snowy sheathbill Chionis alba shown here; photo by David M. Jensen, from wikipedia].
Finally for now, spurs are also present on the hands of a peculiar and poorly known group of fossil birds best known from the Eocene and Oligocene of Query in France: the archaeotrogonids (Eocene British specimens are also known). Archaeotrogonids were originally described as trogons but it now seems more likely that these short-legged, superficially nightjar-like insectivores are members (or close allies) of Strisores (the clade that includes ‘caprimulgiforms’ and apodiforms). As is the case in most other bird carpal spurs, the archaeotrogonid spur is a stout, pointed conical process that seems to be a modified extensor process. The function of these spurs is unknown, but – like the spurs of spur-winged waterfowl, jacanas and lapwings – they were probably used in combat and/or defence.
And that’s still not all on this subject. Pigeons and ibises next.
Bird hand anatomy has been mentioned or discussed a few times previously on Tet Zoo. See…
- Raven, the claw-handed bird, last of the phorusrhacids
- Yes, it was a kiwi
- Dissecting an emu
- Dissecting Ozbert the ostrich
- Clubs, spurs, spikes and claws on the hands of birds (part I)
Refs – –
Bosque, C. & Herrera, E. A. 1999. “Snorkeling” by the chicks of the Wattled jacana. The Wilson Bulletin 111, 262-265.
Campbell, K. E. 1979. The non-passerine Pleistocene avifauna of Talara Tar Seep, northwestern Perú. Life Science Contributions, Royal Ontario Museum 118, 1-203.
– . 2002. A new species of Late Pleistocene lapwing from Rancho La Brea, California. The Condor 104, 170-174.
Cenizo, M. M. & Agnolin, F. 2007. La presencia del género Belonopterus Reichenbach, 1852 (Aves, Charadriidae) en el Pleistoceno de Argentina, con la descripción de Belonopterus lilloi nov. sp. Rev. Mus. Argentino Cienc. Nat., n.s. 9, 41-47.
Chu, P. C. 1995. Phylogenetic reanalysis of Strauch’s osteological data set for the Charadriiformes. The Condor 97, 174-196.
Ericson PG, Envall I, Irestedt M, & Norman JA (2003). Inter-familial relationships of the shorebirds (Aves: Charadriiformes) based on nuclear DNA sequence data. BMC evolutionary biology, 3 PMID: 12875664
Rand, A. L. 1954. On the spurs on birds’ wings. The Wilson Bulletin 66, 127-134.
Strauch, J. G. 1978. The phylogeny of the Charadriiformes (Aves): a new estimate using the method of character compatibility analysis. Transaction of the Zoological Society of London 34, 263-345.
Thomas, G. H., Wills, M. A. & Székely, T. 2004. A supertree approach to shorebird phylogeny. BMC Evolutionary Biology 4: 28 doi:10.1186/1471-2148-4-28