Piksi

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Piksi
Fossil range: Campanian (Late Cretaceous)
Conservation status
Fossil
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Subclass: Ornithothoraces
Genus: Piksi
Varricchio, 2002
Species: P. barbarulna
Binomial name
Piksi barbarulna
Varricchio 2002

Piksi barbarulna[1] is a prehistoric bird. It lived roughly 75-76 million years ago in what is now Montana, USA. Known from parts of a right wing - the humerus, ulna and radius bones - the only specimens found so far are housed in the Museum of the Rockies (collection number MOR 1113). The genus Piksi is monotypic at present.

The fossils were found in 1991 by Gloria Siebrecht in the Blackfeet Indian Reservation, namely at Bob's Vacation Site locality TM-088, Glacier County. Recovered from an old stratum of the upper Two Medicine Formation, they are probably from an individual that died in or near a small pool. It was described in 2002 by David J. Varricchio.

Contents

[edit] Description and systematics

The bones are fragmentary and represent roughly the elbow area. They show a mix of characters known since very primitive birds (such as Confuciusornis[2]) and others known from living taxa such as chickens. In addition, there are autapomorphies hitherto unknown in other birds, in accordance with which the specific name was chosen: both the dorsal epicondyle of the humerus and the dorsal cotyla of the ulna are consicuously large and well-developed.

Comparing the fossils' size to the wing bones of other ground birds, P. barbarulna seems to have been about as large as a Common Pheasant, i.e. some 15 in (35-40 cm) long excluding tail, and with a wingspan of perhaps 30 in (80 cm) or somewhat less. It would thus have weighed maybe 1 - 2 pounds (some 500 g - 1 kg).[3]

The cladistic analysis - essentially limited to characters of the elbow joint - found these to be phylogenetically quite uninformative; it was not even possible to distinguish Neornithes from Enantiornithes. Still, it provided a valuable hint, not for the phylogeny but for the morphology of P. barbarulna: apart from the autapomorphies, the elbow joint of the prehistoric bird is very similar to that of such little-related birds as the Little Chachalaca, the Dusky Grouse and the prehistoric Palaeortyx gallica (all galliforms), the Little Tinamou (a tinamou), and the Western Crowned Pigeon (a columbiform) - but not the Wood Pigeon (another columbiform). Despite belonging to very different lineages, the living species that grouped close to it are all united by a largely terrestrial lifestyle and a heavy body with rounded wings, making for a rather weak flying ability. Thus, while P. barbarulna was almost certainly not flightless[4], it is most likely that it was a heavyset bird with comparatively small, rounded wings, in general body shape rather similar to a tinamou or galliform.

Nonetheless, the original description found its affinities unresolvable except that it was probably ornithothoracine - a bird with a modern flight apparatus that permitted deep wingbeats, as opposed to the shallow, mainly downward wingbeats of Confuciusornis or Archaeopteryx[5] and a well-developed sternum serving as attachment for the main flight muscles.

A later analysis by Mortimer (2004, 2007) found Piksi to be indeed an ornithothoracine incertae sedis. Any attempt to resolve its relationship further is at present hampered by the facts that only its wing bones can be compared to other taxa, and that, as shown by the initial analysis, it would tend to group according to ecomorphology rather than according to its phylogenetic relationship. This problem is exacerbated by the scarcity of Mesozoic landbird remains in general and non-Enantiornithes landbirds specifically, for if there is one thing that the new analysis indicated with any certainty, it is that P. barbarulna was not a member of that group. Still, it did neither group with the paleognaths and galliforms, for which wing skeletons were available.

In conclusion, Piksi barbarulna may represent a distinct lineage of ornithothoracines without any known relatives (as of now), a basal ornithuran[6], or even - though rather unlikely - an early modern bird - a paleognath or even a member of the Galloanseres, the "fowl" clade which includes, among others, chicken. As indicated by its autapomorphies and Mortimer's analysis, even in the latter case it was not particularly close to any known bird lineage living or extinct.

[edit] Ecology

The deposit in which the bones were found was a silty claystone. This was formed from sediments deposited during what seems to have been a rather cool phase of the Late Cretaceous[7]: sea levels of the Western Interior Seaway at least were apparently very low for Mesozoic standards, though this may also have been due to strong tectonic uplift in the Cordilleran Overthrust Belt. The location was inland, with the Western Interior Seaway's coast at least 220 miles (350 km) away.

Judging from the stratigraphical, sedimentological and faunal data, environment was thus probably semi-humid, possibly (seasonally?) semi-arid grassland or shrubland in a tropical or subtropical climate. The claystone apparently formed from sediment of a small floodplain, such as an ephemeral pool.

Plentiful fauna utilized the location as habitat. Theropods were plentiful, such as Troodon of which a nest was found, tyrannosaurids and dromaeosaurids. Orodromeus had an abundant presence; herds might have come the pool to to drink or breed, as adults, juveniles and hatchlings were found together. Early mammals - marsupials and multituberculates - occurred in the area, as well as lizards. That there was a temporary though not permanent body of water is indicated by the presence of articulated frog skeletons and the absence of fish and other aquatic animals.

The lifestyle of Piksi barbarulna thus probably resembled most - among living birds[8] - that of a mid-sized galliform or a tinamou from similar habitat. It probably fed on seeds, tubers and other plantstuffs, as well as invertebrates such as the land snails with planispiral shells found in the same rocks; as its beak is not known, this is conjectural however. It probably flew only when threatened or to cover longer distances. The Common Pheasant, Chukar or Yellow-necked Spurfowl which share a similar size and habitat seem to be as close an ecological analogue among living birds as can be expected for a prehistoric species with an undetermined place in the trophic web of its time.

The taphonomy of the remains are peculiar. While not found in articulation - as if they would have been positioned in the living bird - it is likely that these three bones, which are adjacent in life, come from the same individual bird; they were catalogued as a single specimen. Also, they were found in a rather well-worked deposit, from which both fossils smaller than the Piksi bone pieces - the mammalian teeth - and more delicate - the snail shells - were recovered. The wings of birds, especially weak-flying species, provide little sustenance but much inedible material to predators from the mid-humerus distad. At least by terrestrial predators today, they are often torn off and discarded essentially whole after eating the muscles off the proximal humerus. Thus, though it can of course not be verified anymore[9], the taphonomy of the type specimen is suggestive of the wing of a bird discarded by a predator and ending up, already isolated from the rest of the body, in or by the shallow pool to decompose there.

[edit] Footnotes

  1. ^ Etymology: "Big bird with strange elbow". From Blackfoot piksi, "big bird" or, specifically, "chicken" and Latin barbarus "strange, outlandish" (cf. "barbarian") + ulna, elbow.(Varricchio 2002)
  2. ^ Though they also occur in more advanced forms.
  3. ^ Based on the data in Snow et al. (1998).
  4. ^ The ulna lacks quill knobs; this might be due to flightlessness, abrasion in the fossil, or fairly weak secondary remiges. However, flamingos which fly well and have normally-developed secondaries also lack ulnar quill knobs (Varricchio 2002).
  5. ^ See Senter (2006) for a thorough discussion.
  6. ^ The "short-tailed" birds, a clade with a stubby pygostyle, including living birds and extinct "semi-modern" lineages such as the Hesperornithes and Ichthyornithes
  7. ^ Though still much warmer than today: see Cretaceous for contemporary climate.
  8. ^ Bear in mind that these have to deal with different predators and prey items. As opposed to, say, a francolin, Piksi barbarulna would have had to avoid getting eaten by smaller "raptor" theropods and similar dinosaurian carnivores.
  9. ^ Though it could still be falsified.

[edit] References

  • Mortimer, Michael (2007): Our current understanding of Mesozoic bird phylogeny. Analysis posted on Dinosaur Mailing List 2007-MAR-11. Retrieved 2007-AUG-21.
  • Senter, Phil (2006): Scapular orientation in theropods and basal birds, and the origin of flapping flight. Acta Palaeontologica Polonica 51(2): 305–313. PDF fulltext
  • Snow, David W.; Perrins, Christopher M.; Doherty, Paul & Cramp, Stanley (1998): The complete birds of the western Palaearctic on CD-ROM. Oxford University Press. ISBN 0192685791
  • Varricchio, David J. (2002): A new bird from the Upper Cretaceous Two Medicine Formation of Montana. Canadian Journal of Earth Sciences 39(1): 19-26. HTML abstract

[edit] External links