Tetrapod Zoology

Better late than never, I’ve only recently gotten hold of Zhou et al.’s paper on the enantiornithine bird Pengornis houi, published online in Journal of Anatomy back in January but now available in hard-copy. I must say that I really dislike the new trend of publishing things in special, online versions prior to their ‘proper’ publication. Anyway… Pengornis (which is from the Lower Cretaceous Jiufotang Formation of Dapingfang, Liaoning, China) is particularly interesting for several reasons…

i-688cfa1cec6d6deb9c37342261b3e190-Pengornis houi Zhou et al.jpg

It’s very well preserved, with one of the best-preserved skulls of any Mesozoic bird [skull shown below, from Zhou et al. (2008)]. Most of the teeth are small with conical, uncurved crowns, but those toward the back are globular and blunt with wear facets. I’d love to know what Pengornis was doing with these weird teeth (stomach contents from other enantiornithines show that they were feeding on such things as small crustaceans and fishes, so perhaps it was crushing arthropods or little gastropods). Secondly, it’s large for a Lower Cretaceous enantiornithine, and as a basal member of the group (Zhou et al. 2008) it suggests that relatively large size was primitive for the clade: most other basal enantiornithines can be loosely described as finch-sized, whereas (with a skull about 55 mm long and a wing skeleton [humerus + ulna + carpemetacarpus] about 170 mm long) Pengornis was perhaps closer in size to a small corvid (warning: this was a guesstimate and I haven’t done any proper size comparisons).

i-af8a51778b8c18de344ec549181a04d2-Pengornis houi Zhou et al. skull.jpg

Pengornis is of further interest because it possesses several characters that were previously thought limited to ornithurines*, including a globular humeral head, a hooked acromion on the scapula and heterocoelous cervical vertebrae. Did these characters therefore evolve earlier in bird phylogeny than hitherto thought, or were they convergently acquired by both enantiornithines and ornithurines? First recognised by Cyril Walker in 1981 from incomplete remains from Upper Cretaceous Argentina (Walker 1981), enantiornithines – sometimes called ‘opposite birds’ – have proved to be the most abundant, diverse and widespread group of Mesozoic birds, and over 35 genera are presently recognised.

* The name Ornithurae has a complex history and it’s been used in different ways by different authors. Here I follow the majority of bird workers in using it for the node-based clade that includes hesperornithines, crown-group birds, and all descendants of their most recent common ancestor [for help, here's a bird phylogeny. From one of Tom Holtz's lectures: full-size version here].

i-e739d6024d965bc896f1d32910ccebb3-Holtz Eumaniraptora cladogram.jpg

Pengornis is one of several recently described Cretaceous birds which have shown that body size, limb proportions, flight specialisations, and ecology overlapped among the several bird clades that existed during the Early Cretaceous (confuciusornithids, enantiornithines and basal ornithurines like the yanornithids). We can still find characters that allow these groups to be reliably distinguished, but it is becoming increasingly difficult to maintain claims that they were occupying different ecological niches.

For more on Mesozoic birds, there’s the recent article on the Crato enantiornithine here, and a brief look at archaeopterygids here.

Refs – -

Walker, C. 1981. New subclass of birds from the Cretaceous of South America. Nature 292, 51-53.

Zhou, Z., Clarke, J. & Zhang, F. 2008. Insight into diversity, body size and morphological evolution from the largest Early Cretaceous enantiornithine bird. Journal of Anatomy 212, 565-577.

Comments

  1. #1 J-Dog
    July 15, 2008

    Beautiful clade chart – thanks for thaking the time to psot about it.

  2. #2 Thomas R. Holtz, Jr.
    July 15, 2008

    Thanks! I have an even newer one here, and a phylogeny scaled against time here.

  3. #3 pough
    July 15, 2008

    It kinda looks like it’s doing a tango.

  4. #4 Zach Miller
    July 15, 2008

    I can’t click on the tree to make it bigger. Doesn’t the fact that Archaeopteryx could occupy a more basal Paravian position suggest that Aves should be restricted to Enantiornithines + Ornithurines? How much more advanced is Jeholornis with respect to the urvogal?

    Aaaand you knew I was going to ask this: Can I get a copy of the paper? :-D

  5. #5 Thomas R. Holtz, Jr.
    July 15, 2008

    Zach: I have newer version of this cladogram up here, and a temporally-scaled phylogeny
    here
    .

    The enat + ornithurine (or euornithine) clade is Ornithothoraces. Personally, although I was once against it, I’m actually comfortable for restricting Aves to the crown group.

  6. #6 Darren Naish
    July 15, 2008

    I can’t click on the tree to make it bigger.

    Did you click on the link?

    Doesn’t the fact that Archaeopteryx could occupy a more basal Paravian position suggest that Aves should be restricted to Enantiornithines + Ornithurines

    Aves is one of the most problematical terms in maniraptoran nomenclature, as some people (e.g., Gauthier, and thereby PhyloCode) argue that it should be restricted to the crown while others (e.g., Padian, Chiappe) use it for the Archaeopteryx + Neornithes clade. Under current recommendations, we can’t just ignore Archaeopteryx if it were found to be outside a deinonychosaur + neornithine clade, and in such a topology deinonychosaurs would be part of Avialae/Aves. The enantiornithine + ornithurine clade, incidentally, is Ornithothoraces Chiappe & Calvo, 1994 (though Ornithopectae has been used for the same clade).

    How much more advanced is Jeholornis with respect to the urvogal?

    Jeholornis and its presumed relatives (we are informally calling these the jeholornithids, but a full study of their morphology and affinities has yet to be published) have several characters, including a reduced dentition and a fused dentary symphysis, which indicate that they are closer to pygostylians than are archaeopterygids. At the same time they don’t exhibit the synapomorphies of Pygostylia.

    Aaaand you knew I was going to ask this: Can I get a copy of the paper?

    It’s in the mail…

  7. #7 Zach Miller
    July 15, 2008

    Thanks. What side of the Archaeopteryx fence are you on, Darren?

  8. #8 Thomas R. Holtz, Jr.
    July 15, 2008

    Did either of my earlier two posts make it through?

  9. #9 Darren Naish
    July 15, 2008

    Hi Tom – they must have gotten spam-filtered, hold on a moment…

  10. #10 Nathan Myers
    July 15, 2008

    Thomas H: I think the rule is that two or more links in one post implies spam. Maybe the filter could be taught not to count links to “.edu” sites.

    So, what’s wrong with publishing an on-line copy of a paper before the journal comes out? Is it that the on-line one is less complete? Or that you don’t have proper bibliographic details until the regular publication?

  11. #11 jck
    July 15, 2008

    Nice post. The cladograms are a great picture of early bird evolution.

  12. #12 Christopher Taylor
    July 15, 2008

    So, what’s wrong with publishing an on-line copy of a paper before the journal comes out? Is it that the on-line one is less complete? Or that you don’t have proper bibliographic details until the regular publication?

    I don’t like early on-line versions either. Both Nathan’s points are potential issues. Articles can potentially change between the online and printed versions, and it’s not until the printed version comes out that things are “set in stone” (to coin a cliche). Most journals are pretty good about this, I’ll admit, but some are not – Molecular Phylogenetics and Evolution, I’m looking at you. In terms of nomenclature, they also muddy the waters significantly in terms of establishing publication date, as a taxonomic name is not officially published until the print version comes out. There is a proposal in the works to allow the release date for the online version to count as the publication date, which may make things easier, but that still suffers from the complication that the online version may not remain where it was. I can recall at least one case off the top of my head where the online version appeared about a year before the printed version. Also, try running a search on the taxonomic status of Epidendrosaurus vs. Scansoriopteryx (shudder).

  13. #13 David Marjanovi?
    July 16, 2008

    Gauthier, and thereby PhyloCode

    That’s not how it works. Read Article 10 and the like.

    Jeholornis and its presumed relatives [...] have several characters [...] which indicate that they are closer to pygostylians than are archaeopterygids. At the same time they don’t exhibit the synapomorphies of Pygostylia.

    True, though they also have several characters shared with only part of Pygostylia. For example, Archie, the confuciusornithids, and Sapeornis lack a joint between scapula and coracoid; Rahonavis, Shenzhouraptor/Jeholornis and the like have a joint, and it works the enanti- way (peg on coracoid, socket on scapula) rather than the eu- way (peg on scapula, socket on coracoid) or the Protopteryx way (flat surfaces).

  14. #14 David Marjanovi?
    July 16, 2008

    Also, try running a search on the taxonomic status of Epidendrosaurus vs. Scansoriopteryx (shudder).

    Did Naturwissenschaften have online prepublication back then? IIRC the problem was that the publication dates of the paper versions aren’t easy to pin down.

  15. #15 Darren Naish
    July 16, 2008

    That’s not how it works. Read Article 10 and the like.

    You know what I mean (surely).

  16. #16 David Marjanovi?
    July 16, 2008

    Well, there is less unanimity among the most prominent PN protagonists than Gauthier and friends sometimes make it look like… and the companion volume is progressing so slowly that it will be a major topic at the congress next week…

  17. #17 Christopher Taylor
    July 16, 2008

    Did Naturwissenschaften have online prepublication back then? IIRC the problem was that the publication dates of the paper versions aren’t easy to pin down.

    (Note: David probably knows a lot of this already, but I’ll give full details in case anyone else is twisted enough to care about the taxonomy of obscure paravians…)

    Naturwissenschaften did have preprints early enough for Epidendrosaurus to appear in one on 21 August 2002, though the printed journal did not appear until 30 September. The possibly synonymous Scansoriopteryx was published the same year in the Dinosaur Museum Journal (volume first and last). David is right in that the actual date of publication for the DMJ is a bit hazy – the book itself claims a date of 1 August, but there are grounds for doubting that it actually became available on that date. Certainly it was available by 2 September, which still predates the print version of Epidendrosaurus, giving Scansoriopteryx priority under the current rules of the ICZN. However, because Naturwissenschaften is such a well-known journal, the name Epidendrosaurus became well-known when the pre-print version appeared, which is before the DMJ probably became available. So the order of events is (1) claimed (but probably not valid) date of publication for Scansoriopteryx, (2) Epidendrosaurus appears as a pre-print, and achieves wide recognition despite being technically not yet valid, (3) probable actual date of effective publication for Scansoriopteryx, (4) technically valid publication for Epidendrosaurus.

    The text of Jerald Harris’ 2004 ICZN proposal detailing all this and proposing acceptance of pre-print release dates as publication is available on the ICZN website.

  18. #18 John Scanlon FCD
    July 17, 2008

    While on the topic of Mesozoic birds, somebody should mention Zhongornis haoae Gao et al. described in the current issue of Palaeontology. Rather neatly showing an intermediate state between long-tailed dino-birds and stumpy pygostylians – something that, based on consideration of modern reptiles and mammals, we do not expect to see very often. Many tetrapod groups have evolved stumpy tails or practically lost them, but usually have close relatives that are long-tailed, while intermediate-length tails are relatively rare and – my interpretation – much less likely to represent a local fitness peak.

  19. #19 Zach Miller
    July 17, 2008

    Ooh! Ooh! Must have! Please, please! :-)

  20. #20 cet
    March 26, 2009

    thanks. by Brooklyn

    [from Darren: yeah, thanks.]

  21. #21 Hai~Ren
    March 26, 2009

    Previous message left by a spammer… *sigh*