Xenicibis xympithecus

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Xenicibis xympithecus

Absract

Birds have frequently evolved to exploit insular environments by becoming adapted to a terrestrial lifestyle and losing the ability to fly, usually via reducing the wings and pectoral girdle. The enigmatic flightless ibis Xenicibis xympithecus (Threskiornithidae) from the Quaternary of Jamaica provides a rare example of flight loss in ibises. We report on previously undescribed fossils of Xenicibis, and show that the wing differed radically from that of all other birds, flightless or volant. The metacarpus is elongate, grotesquely inflated and has extremely thick walls; phalanges are short and block-like; the radius is distally expanded; and the humerus is elongate. The furcula, coracoid and sternum are all well developed. We propose that the elongate forelimb and massive hand functioned in combat as a jointed club or flail. This hypothesis is supported by the morphology of the carpometacarpus, by features permitting rapid extension of the wing and by the presence of fractures in wing bones. Although other birds use the wings as weapons, none resemble Xenicibis, which represents a unique and extraordinary morphological solution to this functional problem. Xenicibis strikingly illustrates how similar selective pressures, acting on a similar starting point, can result in novel outcomes.
Source

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Description paper:

Holotype.—Proximal half of left tarsometatarsus, vertebrate paleon- tological collections AMNH 11006. Collected 16 or 17 January 1920 by H. E. Anthony at Long Mile Cave, Windsor, Trelawny Parish, Jamaica. Late Quaternary.
Measurements of holotype.—Proximal width 18.6 mm, proximal depth through hypotarsus 17.5, width and depth of shaft 30 mm from apex of intercotylar knob 9.6, 6.4.
Paratypes.—Eight other specimens, all of which, with the possible excep- tion of the humeras noted above, have the same data as the holotype and are in the AMNH vertebrate paleontological collections. Nearly complete right coracoid, AMNH 11008; left coracoid lacking sternal end, AMNH 11013; shaft of right humerus, AMNH 11031; proximal end of left femur, AMNH 11005; imperfect proximal end of left tibiotarsus, AMNH 11009; distal % of left tibiotarsus, AMNH 11007; distal % of right tibiotarsus, AMNH 11004; pedal phalanx 1 of left digit IV, AMNH 11011.
Measurements of paratypes.—Coracoid AMNH 11008—greatest length 50.0 mm, length from internal distal angle 47.8, least width of shaft 7.9, least depth of shaft 3.3; humerus—width and depth of shaft at distal end of attachment of latissimus dorsi posteriori* 6.2, 6.4; femur—proximal width 22.6, transverse diameter of head 10.1, proximal depth 17.5, width and depth of shaft 40 mm from proximal end 8.0, 8.7; tibiotarsus AMNH 11004—distal width 15.6, distal depth 15.6, least width of shaft 8.4, least depth of shaft 5.6, length of internal condyle 9.4; tibiotarsus AMNH 11009—proximal width through outer cnemial crest 28.2; phalanx 1 of digit IV—length 21.7, proximal width 7.6, least width 4.2, distal width 5.7.
Diagnosis.—As for the genus.

Diagnosis of the genus:

A large, heavy-legged ibis with wing and pectoral girdle proportionately quite small. Differs from the other genera of Threski- ornithidae examined as follows: tarsometatarsus with hypotarsus simple, consisting of 2 calcaneal ridges separated by a deep groove, the internal ridge being much shorter than the external one; tibiotarsus with very wide anterior intercondylar fossa, reduced supratendinal bridge, very large outer cnemial crest extending far laterally, inner cnemial crest displaced much farther laterally than in other ibises; femur with head larger and more proximally oriented, antero-proximal portion of shaft greatly exca- vated and flattened; phalanx 1 of digit IV very stout; coracoid with sternal end thin and weak, area of sterno-coracoidal impression nearly convex and lacking thin diagonal ridges, internal distal angle slender and exca- vated on ventral surface.
Etymology.—Gr. xenikos, strange, and ibis, f. a wading bird, an ibis.

si-pddr.si.edu/bitstream/handle/10088/12829/VZ_80_Xenicibis.pdf?sequence=1&isAllowed=y

Short version:
Holotype: AMNH 11006
Collected: In 1920
Described by: Storrs L. Olson and David W. Steadman (1977)
Holotype: AMNH 11006
Paratypes: AMNH 11007-11014
Habitat: Late Quaternary of Jamaica (not far ago)
Description: Large, heavy-legged and flightless ibis

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Here's what Darren Naish said about it a while ago.

"We finish it all by looking at another extinct bird that also possessed distinctive wing armament: I’m referring to the flightless ibis Xenicibis xympithecus from Jamaica, sometimes called the Club-winged ibis. I started writing the article you’re reading now in July 2010 and had no idea at all that a paper describing the club-winged condition of Xenicibis in definitive fashion was in the works (though I was familiar with this research, having heard about it all off Nick Longrich some years ago). Yes, as you’ll likely now know, Nick Longrich and Storrs Olson published their description and interpretation of this remarkable bird’s wings in January of this year (to date, only the online version is out). The paper (Longrich & Olson 2011) got a lot of press coverage. I was even asked to do a radio interview on it (after all, I did play a crucial role in the research [massive joke]). It was pretty weird as the radio host asked me to describe what kind of ‘dino’ Xenicibis was. I proceeded to explain what ibises were and how they were actually pretty familiar birds. Anyway…



The weird wing bones of this bird have resulted in previous suggestions that it was possibly quadrupedal and that it used its hands as props, like crutches (I used to have a cartoon depicting this idea but can’t find it anymore. UPDATE: FOUND IT!). I’ve also heard informal (and very much unpublished) suggestions that these clubs were used for bashing snakes. As Longrich & Olson (2011) argue, the wing structure seen in Xenicibis indicates that it used these limbs as flail-like combative organs, probably against other members of its own species. However, because it lived alongside various snakes, raptors and other predators it’s certainly plausible that these bizarre wings were also used to fight off or even kill such animals. And good evidence for use of the wings in combat comes from healed fractures in the upper arm and hand."

Source

And the thing he said at the end.

"Many people who regularly get close to, or handle, birds know that (as we’ve discussed on Tet Zoo quite a bit before) they’re frequently pretty formidable animals for their size. Angry waterfowl, chickens, raptors and gulls can be real nasty: powerful and gutsy enough to fight off and injure (even kill) mammals bigger than they are. Should you encounter a specialised, weapon-bearing bird of any sort (either here or in the past, should you go time travelling) my advice is to be very, very careful and to try not to piss it off. Should you be attacked, be sure that someone is taking photos – - – that kind of stuff is blogging gold!!!"