Picture of the Day: long tailed widow bird

Just a quick post while I'm on leave - I'll be revealing the mystery orifice soon, so keep guessing - one of you is very close. We took a family outing to the rhino and lion park in ‘The cradle of humankind’ a world heritage area that includes the famous Sterkfontein and Swartkrans caves where several australopithecines have been found. While there I managed to get this shot of a breeding male long-tailed widow bird (Euplectes progne), the epitome of an elaborate sexual display that is a major handicap to its owner. Non-breeding males are drab, brownish, sparrow-like birds with tails of normal length.

Lookin' out my back door

Well out my back window actually. We've been watching this industrious little guy for almost three years now. He is a masked weaver (Ploceus velatus), and in order to attract a mate he has to construct a nest of sufficient quality to encourage a female to lay her eggs in it. Sadly he's a bit of a loser. Although several females have checked him out he has never been able to seal the deal. After every rejection he would demolish the nest and start again. Now however it appears he is so riddled with frustration and self-doubt that he just builds and destroys nest after nest without even getting it looked at first. I kind of empathize with him, my early years (15 through to 26) weren't too dissimilar.

Jumping the gun: Similicaudipteryx

Hagfish from www.itsnature.org

Hi folks, Yes its been quiet here on Dracovenator. School is back on, and I have a hectic 16 hours of teaching a week which coupled with a newborn in the house is leaving me kind of exhausted. In anycase I'm going to give voice to a few thoughts that flashed through my mind when I read the abstract for the latest dinosaur taxon to be named from the Jehol Group of Liaoning. I haven't seen the paper yet, someone want to forward the pdf?, So this should all be read as speculative thoughts and nothing more. Firstly I'm sure you are are wondering why the hell I've put up a picture of a hagfish, of all things, to illustrate a post about a dinosaur, well read on....
Similicaudipteryx yixianensis He et al. 2008 is described as a caudipterygiid oviraptorosaur in the latest Vertebrata Palasiatica. For those who may need reminding, Caudipteryx was one of the first non-avian theropods discovered with a plumage of undeniable pennaceous feathers. As one could have expected the 'BAND' didn't take to kindly to the idea of fully plumed non-avian theropod dinosaur and they fairly quickly responded with claims that Caudipteryx was actually a true bird that had become secondarily flightless and ground-dwelling. Indeed there is something terribly birdy about the incredibly stump-tailed Caudipteryx and its wing-like hand with a highly reduced third digit.

A very nice model skeleton of Caudipteryx. From www.dinocasts.com

These observations have occurred to many and even Stephen Gould wrote an essay about how blurry the bird-dino distinction had become and in this case he thought us dino palaeontologists had got it wrong. In anycase it didn't take long for people to see that Caudipteryx shared much with the mid to late Cretaceous Oviraptorosaurs. It has always been puzzling how many bird-like features Oviraptorosaurs display that are not present in the Deinonychosauria which is the currently accepted sister group of birds. These have been largely thought of as convergences because comprehensive cladistic analyses routinely place them outside the clade of Deinonychosauria + Birds. Why is this? Well for all their birdiness oviraptorosaurs have a suite of plesiomorphies including (but not limited to) a straight(versus bowed) metacarpal three , a deep ilium with a post-acetabular process that exceeds in length the pre-acetabular process, and a forwardly directed pubis with an anteriorly and posteriorly expanded boot. Now along comes Similicaudipteryx and adds a couple more bird-like features that are not seen in deinonychosaurs. One is the presence of deep hypapophyses on the anterior dorsal vertebrae and a pygostyle on the end of the tail. The latter had been previously reported in the oviraptorosaur Nomingia but had been dissmissed as convergence since other oviraptorosaurs apparently didn't have one. Similicaudipteryx raises the spectre that pygostyles may have been primitive for oviraptorosaurs and lost in later taxa (or simply not present because the material was not mature enough in the case of Caudipteryx). One more little observation before we can finally get to slime-hags: The undoubted volant pygostylian bird, Sapeornis, also from Liaoning, has a remarkably caudipterygiid-like skull as noted by Stephen Czerkas when he briefly described a specimen (under the name Omnivoropteryx).
Now to hagfish. Although the dust (slime?) hasn't settled on the controversy over their systematic position, it seems that the evidence for cyclostome monophyly (that is lampreys + hagfish) is growing. Now that is deeply uncomfortable to those used to working with morphology, since everything about hagfish seems to shout that they are basal to lampreys + jawed vertebrates. For instance they lack extrinsic eye muscles, innervation of the heart, vertebrae of any sort and muscles in the caudal fin. Nonetheless it looks like hagfish really are an example of pervasive, wholesale reversion to a more primitive condition. There are other less extreme examples of this phenomenon. For instance gavials are now firmly placed as the sister-group to tomistomines (false gavials) within Crocodylidae (based on combined, morphological and molecular analyses, including fossils) they have a suite of plesiomorphies throughout the skeleton that initially confounded morphological cladistic analyses by place gavials at the base of modern Crocodylia.

Wholesale taxic atavism in gavials. A graphic representation of morphological characters that place gavials on a more basal branch of crocodylian phylogeny. From Gatesy et al. 2003.

Gatesy et al. 2003 called this pervasive reversal 'wholesale taxic atavism'. Note that it does not appear to be the result of sustained selection for any particular ecophenotype. False gavials are also longirostrine fish-eaters but lack the wholesale atavism seen in gavials. This to my mind is a very interesting and understudied aspect of evolution.
Whatever its cause I'd like to suggest that Oviraptorosauria might end up being yet another example. If this is so I will predict that as we get a better fossil record of maniraptorans from the latest Jurassic and the Earliest Cretaceous we will find earlier and earlier oviraptorosaurs that get more and more like pygostylians. Maybe we will find a volant or recently ex-volant sapeornithid-caudipterygiid intermediate. Of course I could just be jumping the gun....

references

Gatesy J, Amato G, Norell M, DeSalle R and Hayashi C (2003) Combined Support for Wholesale Taxic Atavism in Gavialine Crocodylians. Systematic Biology, 52(3): 403 — 422

He T, Wang X-L, and Zhou Z-H (2008). A new genus and species of
caudipterid dinosaur from the Lower Cretaceous Jiufotang Formation of
western Liaoning, China. Vertebrata PalAsiatica 46(3):178-189.

The most primitive short-tailed bird?

The latest issue of Palaeontology is choc-full of palaeo goodness. I might end up blogging quite a bit of it, then again time may elude me. For now I just want to say a few quick words about the paper by Gao Chunling et al. It describes yet another new bird from the Yixian Formation of Liaoning, China. Called Zhongornis haoae, Gao et al. bestow upon it a relatively high degree of importance because they believe it to be the sister group of all other short-tailed birds, a clade called Pygostylia. The image is from their paper (Gao et al. 2008). As the name would suggest pygostylians are characterised amongst other things by having a reduced number of tail vertebrae where the distal most ones are fused into a single element called the pygostyle. Although Zhongornis has various advanced pygostylian characters such as an elongate strut-like coracoid and a short tail (just 13 caudal vertebrae), it does not have a pygostyle. That is all 13 caudal vertebrae are unfused, separate bones. However, and this is a big however, it is clearly a juvenile specimen (based on small size, lack of fusion of wrist and manual elements and porous, grainy, bone texture). An therein lies the biggest problem with accepting Zhongornis to this privileged position. Other very juvenile early pygostylians also have unfused caudal vertebrae (e.g. ' Liaoxiornis'). Clearly like wrist fusion the formation of the pygostyle did not occur until quite late in ontogeny amongst early pygostylians. Gao et al try to side-step this problem by claiming the specimen was skeletally mature, or close to maturity because it had fledged, ie. it had grown long vaned feathers from its wings (remiges) and tail (retrices). This I think is the biggest fault with the authors' reasoning. Firstly fledging itself is a variable trait with variable timing of onset amongst modern birds (if I am not mistaken the modern mallee fowl, a kind of megapode, are hatched in a fully fledged state). Late fledging can be expected to be tied to altricial lifestyles. Altriciality is a derived trait in modern birds and should not be expected amongst the early pygostylians of the Cretaceous. Indeed the very same Liaxiornis I mentioned above is a very juvenile early pygostylian with well developed remiges. This more or less falsifies the argument of Gao et al.
So what is Zhongornis? Hard to say. It is toothless so there aren't that many contemporary taxa it could be a juvenile of (Bolouchia is a possibility). It has an unique configuration of phalanges in the third finger which could argue for its status as a valid taxon (although I would classify it as Pygostylia incertae sedis, rather than the pygostylian sister group). However I even wonder if it is possible for the digit three to be reduced as the bird matures, much in the same way that the juvenile claws of the hoatzin are lost as it matures.

GAO, C., CHIAPPE, L.M., MENG, Q., OCONNOR, J.K., WANG, X., CHENG, X., LIU, J. (2008). A NEW BASAL LINEAGE OF EARLY CRETACEOUS BIRDS FROM CHINA AND ITS IMPLICATIONS ON THE EVOLUTION OF THE AVIAN TAIL. Palaeontology, 51(4), 775-791. DOI: 10.1111/j.1475-4983.2008.00793.x