Alaskacephale

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Alaskacephale
Temporal range: early Maastrichtian, 70–69  Ma
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Alaskacephale gangloffi copia.jpg
Life restoration of Alaskacephale gangloffi
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade:† Ornithischia
Clade:† Neornithischia
Clade:† Pachycephalosauria
Family:† Pachycephalosauridae
Genus:† Alaskacephale
Sullivan, 2006
Species:
†A. gangloffi
Binomial name
†Alaskacephale gangloffi
Sullivan, 2006

Alaskacephale is an extinct genus of pachycephalosaurid, a group of dome-headed, herbivorous ornithischian dinosaurs, that lived during the Maastrichtian stage of the Late Cretaceous period in what is now northern Alaska [1] The genus is one of the few known Arctic dinosaurs and was found in the Prince Creek Formation, which preserves a menagerie of fossils. The only known specimen, a squamosal bone, was found in 1999 and later described in 2005. However, Alaskacephale was not formally named until the next year.

Contents

Alaskacephale, due to the lack of fossil remains, is poorly known. Despite this, the presence of bony protuberances from the skull prove that it was a pachycephalosaur. Later phylogenetic analyses suggest it was a close relative of Pachycephalosaurus . However, Alaskacephale is distinguished from other genera by the two rows of nodules found along the squamosal.

The Prince Creek Formation bears a variety of fossils, many of them similar to other previously known Laramidian taxa. Alaskacephale coexisted with dinosaurs like the ceratopsian Pachyrhinosaurus , ornithopod Edmontosaurus , and tyrannosaurid Nanuqsaurus in addition to mammals like Unnuakomys.

Discovery and naming

In 1999 during an expedition by the University of Alaska, an isolated pachycephalosaur squamosal was unearthed from bluffs on the bank of the Colville River in North Slope Borough, Alaska. Strata (rock layers) deriving from this area come from the latest Campanian-aged (72-71 mya) Prince Creek Formation. [2] [3] The fossil was then deposited in the University of Alaska Museum and described in 2005 by Roland Gangloff and colleagues as belonging to a pachycephalosaurine closely related to, and possibly, Pachycephalosaurus . [3] However, the next year paleontologist Robert Sullivan described it as a new genus and species, Alaskacephale gangloffi. The genus name comes from Alaska, the state the holotype (name-bearing specimen) was found in, and cephale, from the Greek kephale meaning "head". Its species name is in honor of Gangloff, who published the earlier 2005 description. [4]

Description

The dimensions of the holotype suggest that A. gangloffi was about half the size of Pachycephalosaurus wyomingensis or three-quarters the size of Prenocephale , and about the same size as Sphaerotholus and Foraminacephale . [3] The latter measured 1.5 metres (4.9 ft) long and 10 kilograms (22 lb) in weight. [5] This would make Alaskacephale one of the smaller known pachycephalosaurs. [3] [4] No postcranial fossils belonging to Alaskacephale have been found, though there are well-preserved skeletons of the related Stegoceras, Homalocephale, and Prenocephale. Based on these taxa, Alaskacephale had a short neck, tiny forelimbs, long hindlimbs, and a thick, rodlike tail for balance. The neck was slender and U-shaped, and held in a curved posture, attaching at the occipital condyle on the back of the skull. Its spinal column bore firm connections between the vertebrae that were reinforced by ossified tendons. Its arms were lightly-built and slender ending in a hand with five fingers. The limbs terminated in a pes with three toes, the middle being the longest, all of which had unguals. [6] [5]

Life restoration of the close relative Pachycephalosaurus Pachycephalosaurus Reconstruction.jpg
Life restoration of the close relative Pachycephalosaurus

The only known specimen consists of a skull fragment containing a nearly complete left squamosal, much of the left posterior supraorbital, a fragment of the quadrate, and sections of the postorbital. Alaskacephale is distinguished from other pachycephalosaurs by the presence of two divergent rows of bony nodes along the squamosal. All of these nodes have polygonal bases, unlike the rounded nodules in Pachycephalosaurus, with distinct grooves separating them. The squamosal has twelve of these nodes, the largest of which is at the base of the parietal. Along the quadrate-squamosal articulation, a cluster of nodes is present on the squamosal, with one large center node and three smaller ones surrounding it. [4] [3] The holotype was described as having an interdigitated suture at the base of the quadrate, as in Pachycephalosaurus, by Gangloff and colleague's description. However, Sullivan opined that this "suture" is instead a breakage point in quadrates of both Alaskacephale and Pachycephalosaurus, so it could not be used to unite the two taxa. Part of the dome is preserved, with the thickest point being 4.05 centimetres (1.59 in) thick, whereas the nuccal shelf (a curved shelf at the back of the skull) is only 1.50 centimetres (0.59 in) thick. The back of the dome bears several (pits in bone), as in other pachycephalosaurs. [3] [4]

Classification

Alaskacephale was a member of the group Pachycephalosauria, a family of thick-skulled, herbivorous, bipedal dinosaurs that lived during the Cretaceous period in Asia and North America. [7] The last pachycephalosaurs went extinct during the Cretaceous-Paleogene extinction event, the last surviving genus being Pachycephalosaurus itself. [6] [8] However, a 2020 cladistic analysis recovered the heterodontosaurids as an early branch of the group, which extend the age of pachycephalosaurs as far back as the Early Jurassic. [9] Currently, pachycephalosaurs are recognized as being part of the larger group Marginocephalia which encompasses it and the gigantic, horned ceratopsians. [10] [11]

Within Pachycephalosaurinae, Alaskacephale belongs to the tribe Pachycephalosaurini, which contains Alaskacephale, Pachycephalosaurus, and, according to some phylogenetic analyses, Stygimoloch , Dracorex , and Sphaerotholus . Pachycephalosauria originated in Asia but later colonized North America. The Asian members of this clade are more basal compared to the North American genera, which bear more derived characteristics. [12] Pachycephalosaurini is the most advanced group in Pachycephalosauria and is made up of North American members. [13]

Below is a cladogram from Evans et al., 2021. [14]

Paleoenvironment

A herd of Pachyrhinosaurus resting next to contemporaneous paleofauna from the Prince Creek Formation Prince Creek Formation fauna.png
A herd of Pachyrhinosaurus resting next to contemporaneous paleofauna from the Prince Creek Formation

Alaskacephale lived alongside many other dinosaurs during latest interval of the Campanian stage. Having resided at an estimated 80°–85°N paleolatitude, the area Alaskacephale thrived in experienced climatic extremes unlike that experienced by most other dinosaurs. The temperature of this Northern environment would've ranged from around 10 to 12 °C during the warmer months and about -2 °C ± 3.9 °C during the colder months. As well as this, the environment would have faced 120 days of continuous low-light conditions during the Winter. In contrast to the contemporary large herbivores Edmontosaurus and Pachyrhinosaurus , which preferred coastal lowland and upland environments respectively, Nanuqsaurus appears to have been fairly ubiquitous throughout the Prince Creek landscape. [15] [3]

Other animals that lived alongside Alaskacephale include the following: unnamed leptoceratopsid, the hadrosaurid Edmontosaurus (similar to E. regalis), [16] an unnamed lambeosaurine, an unnamed thescelosaurine (mentioned to be similar to Parkosaurus and Thescelosaurus ), an unnamed orodromine (mentioned to be similar to Orodromeus ), the ceratopsid Pachyrhinosaurus perotorum, the tyrannosaurid Nanuqsaurus , a large troodontid referred to the dubious genus Troodon, the dromaeosaurid Dromaeosaurus , the dromaeosaurid Richardoestesia (similar to R. isosceles), an unnamed saurornitholestine, an unnamed ornithomimosaur, and multiple avialans. [17] As well as this, several mammals, including the metatherian Unnuakomys , [18] the eutherian Gypsonictops , both an unnamed and named multituberculate, the latter being Cimolodon , and finally an indeterminate marsupial. Interestingly, due to the cooler conditions of this habitat, many otherwise common ectothermic clades lack representation entirely in the Prince Creek Formation, suggesting that all the animals that did thrive in these extreme latitudes were indeed endotherms to some degree. [15] [19]

See also

Related Research Articles

<span class="mw-page-title-main">Marginocephalia</span> Extinct clade of dinosaurs

Marginocephalia is a clade of ornithischian dinosaurs that is characterized by a bony shelf or margin at the back of the skull. These fringes were likely used for display. This clade was officially defined in the PhyloCode by Daniel Madzia and colleagues in 2021 as "the smallest clade containing Ceratops montanus, Pachycephalosaurus wyomingensis, and Triceratops horridus". There are two clades included in Marginocephalia: the thick-skulled Pachycephalosauria and the horned Ceratopsia. All members of Marginocephalia were primarily herbivores. They basally used gastroliths to aid in digestion of tough plant matter until they convergently evolved tooth batteries in Neoceratopsia and Pachycephalosauria. Marginocephalia first evolved in the Jurassic Period and became more common in the Cretaceous. They are basally small facultative quadrupeds while derived members of the group are large obligate quadrupeds. Primitive marginocephalians are found in Asia, but the group migrated upwards into North America.

<span class="mw-page-title-main">Pachycephalosauria</span> Extinct clade of dinosaurs

Pachycephalosauria is a clade of ornithischian dinosaurs. Along with Ceratopsia, it makes up the clade Marginocephalia. With the exception of two species, most pachycephalosaurs lived during the Late Cretaceous Period, dating between about 85.8 and 66 million years ago. They are exclusive to the Northern Hemisphere, all of them being found in North America and Asia. They were all bipedal, herbivorous/omnivorous animals with thick skulls. Skulls can be domed, flat, or wedge-shaped depending on the species, and are all heavily ossified. The domes were often surrounded by nodes and/or spikes. Partial skeletons have been found of several pachycephalosaur species, but to date no complete skeletons have been discovered. Often isolated skull fragments are the only bones that are found.

<i>Pachycephalosaurus</i> Genus of pachycephalosaurid dinosaurs

Pachycephalosaurus is a genus of pachycephalosaurid ornithischian dinosaur. The type species, P. wyomingensis, is the only known species, but some researchers argue that Stygimoloch might be a second species, P. spinifer, or a juvenile specimen of P. wyomingensis. It lived during the Maastrichtian age of the Late Cretaceous period in what is now western North America. Remains have been excavated in Montana, South Dakota, Wyoming, and Alberta. The species is known mainly from a single skull, plus a few extremely thick skull roofs. More complete fossils would come to be found in the following years.

<i>Stegoceras</i> Genus of pachycephalosaurid dinosaurs

Stegoceras is a genus of pachycephalosaurid (dome-headed) dinosaur that lived in what is now North America during the Late Cretaceous period, about 77.5 to 74 million years ago (mya). The first specimens from Alberta, Canada, were described in 1902, and the type species Stegoceras validum was based on these remains. The generic name means "horn roof", and the specific name means "strong". Several other species have been placed in the genus over the years, but these have since been moved to other genera or deemed junior synonyms. Currently only S. validum and S. novomexicanum, named in 2011 from fossils found in New Mexico, remain. The validity of the latter species has also been debated, and it may not even belong to the genus Stegoceras.

<i>Homalocephale</i> Extinct genus of dinosaurs

Homalocephale is a genus of pachycephalosaurid dinosaur that lived during the Late Cretaceous period of what is now the Nemegt Formation, Mongolia, about 70 million years ago. The genus was described in 1974 by Halszka Osmólska and Teresa Maryańska, and consists of a single species, H. calathocercos. Though Homalocephale has been regarded as a synonym of Prenocephale, juvenile specimens of the latter indicate that they were distinct. Homalocephale was 1.8 m (5.9 ft) long and possibly a omnivore.

<i>Prenocephale</i> Extinct genus of dinosaurs

Prenocephale is a genus of small pachycephalosaurid dinosaur from the Late Cretaceous Nemegt Formation of Mongolia. It was similar in many ways to its close relative, Homalocephale.

<i>Micropachycephalosaurus</i> Extinct genus of dinosaurs

Micropachycephalosaurus is an extinct genus of basal marginocephalian dinosaur containing only the type species, Micropachycephalosaurus hongtuyanensis. It lived in China during the Late Cretaceous (Campanian) and was found in the Jiangjunding Formation.

<i>Yaverlandia</i> Extinct genus of dinosaurs

Yaverlandia is a genus of maniraptoran dinosaur. Known from a partial fossil skull found in Lower Cretaceous strata of the Wessex Formation on the Isle of Wight. it was described as the earliest known member of the pachycephalosaurid family, but research by Darren Naish shows it to have actually been a theropod, seemingly a maniraptoran. The type species is Y. bitholus.

<i>Tylocephale</i> Extinct genus of dinosaurs

Tylocephale is a genus of pachycephalosaurid dinosaur, a group of dome-headed, herbivorous ornithischians, that lived during the Late Campanian stage of the Late Cretaceous in what is now Mongolia. It is known from a partial skull and associated mandible that were unearthed in 1971 by a Polish-Mongolian Expedition to the Barun Goyot Formation of the Gobi Desert. The specimen was described in 1974 by Polish paleontologists Teresa Maryańska and Halszka Osmólska as a new genus and species.

<i>Goyocephale</i> Extinct genus of dinosaurs

Goyocephale is an extinct genus of pachycephalosaurian ornithischian that lived in Mongolia during the Late Cretaceous about 76 million years ago. It was first described in 1982 by Altangerel Perle, Teresa Maryańska and Halszka Osmólska for a disarticulated skeleton with most of a skull, part of the forelimb and hindlimb, some of the pelvic girdle, and some vertebrae. Perle et al. named the remains Goyocephale lattimorei, from the Mongolian гоё (goyo), meaning "decorated", and the Ancient Greek κεφαλή (kephale), for head. The species name honours Owen Lattimore.

<i>Sphaerotholus</i> Extinct genus of pachycephalosaur dinosaurs

Sphaerotholus is a genus of pachycephalosaurid dinosaur from the Upper Cretaceous of the western United States and Canada. To date, five species have been described: the type species, S. goodwini, from the Den-na-zin Member of the Kirtland Formation and possibly the Fossil Forest Member of the Fruitland Formation of San Juan County, New Mexico, USA; S. buchholtzae, from the Hell Creek Formation of western Carter County, Montana, USA and the Frenchman Formation of Saskatchewan, Canada; S. edmontonensis, from the Horseshoe Canyon Formation of Alberta, Canada; S. lyonsi, from the Dinosaur Park Formation (Campanian) of Alberta, Canada; and S. triregnum from the Hell Creek Formation of Garfield County, Montana, USA.

<span class="mw-page-title-main">Centrosaurinae</span> Extinct subfamily of dinosaurs

Centrosaurinae is a subfamily of ceratopsid, a group of large quadrupedal ornithischian dinosaur. Centrosaurine fossil remains are known primarily from the northern region of Laramidia but isolated taxa have been found in China and Utah as well.

<span class="mw-page-title-main">Prince Creek Formation</span> Geological formation

The Prince Creek Formation is a geological formation in Alaska with strata dating to the Early Maastrichtian stage of the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.

<i>Foraminacephale</i> Extinct genus of dinosaurs

Foraminacephale is a genus of pachycephalosaurid dinosaur from Late Cretaceous deposits of Canada.

<i>Acrotholus</i> Extinct genus of dinosaurs

Acrotholus is an extinct genus of pachycephalosaur dinosaur that lived during the Santonian of the late Cretaceous, in the Milk River Formation of Canada. The type species, A. audeti, was named after Roy Audet allowing access to his ranch leading to the discovery of the species. The discovery of this specimen lead to several new revelations in the fossil records questioning the preservation of small-bodied organisms along with the evolution of early pachycephalosaurs. The iconic cranial dome found on Acrotholus makes it one of the earliest indisputable known members of the pachycephalosaur family.

<i>Nanuqsaurus</i> Extinct genus of dinosaurs

Nanuqsaurus is a genus of tyrannosaurine theropod dinosaur known from the Late Cretaceous period Prince Creek Formation of the North Slope of Alaska, having lived roughly 70-68 million years ago. It contains a single species, Nanuqsaurus hoglundi, known only from a partial skull and multiple undescribed postcranial and teeth elements.

<span class="mw-page-title-main">Timeline of pachycephalosaur research</span> The progression of pachycephalosaur research over time

This timeline of pachycephalosaur research is a chronological listing of events in the history of paleontology focused on the pachycephalosaurs, a group of dome-skulled herbivorous marginocephalian dinosaurs. One of the first major events related to the history of pachycephalosaur research actually regards the discovery of an unrelated dinosaur called Troodon, reported from the western United States by Joseph Leidy in 1856. The type specimen of Troodon was simply an unusual tooth, but the close resemblance between Troodon teeth and pachycephalosaur teeth would cause taxonomic confusion for over a century. This was resolved by Phil Currie in 1987, who realized that Troodon belonged to a group of bird-like carnivores then known as saurornithoidids, but since renamed Troodontidae after Troodon itself. The first scientifically documented true pachycephalosaur remains were discovered in Early Cretaceous rocks from England and named Stenopelix not long after Troodon was named in America. Other notable early finds include the well-known pachycephalosaur Stegoceras validum.

Sinocephale is a genus of pachycephalosaurid dinosaur that lived in Inner Mongolia, China during the Cretaceous period. The only species, Sinocephale bexelli, was originally named as a species of the genus Troodon in 1953, and later transferred to the genus Stegoceras. After decades of being considered dubious, it was re-evaluated in 2021 and recognized as a valid taxon, being given a unique generic name. The original holotype was lost, with modern research conducted using rediscovered plaster casts. Scant material makes for limited knowledge of its life appearance, but it is distinguished by an embayment on the back of the domed skull, which would give it a heart shape as seen from above. It is potentially the oldest known pachycephalosaurid and falls within the subset of the family called Pachycephalosaurinae, related to animals such as Pachycephalosaurus and Prenocephale. The geologic context of the species has been historically unclear but it is currently thought to originate in rocks belonging to the Ulansuhai Formation.

References

  1. ↑ Flaig, Peter P; Mccarthy, Paul J.; Fiorillo, Anthony R. (January 2011), A Tidally Influenced, High-Latitude Coastal-Plain: The Upper Cretaceous (Maastrichtian) Prince Creek Formation, North Slope, Alaska, doi:10.2110/sepmsp.097.233
  2. ↑ Fiorillo, Anthony R.; Tykoski, Ronald S. (2014-03-12). "A Diminutive New Tyrannosaur from the Top of the World". PLOS ONE. 9 (3): e91287. Bibcode:2014PLoSO...991287F. doi: 10.1371/journal.pone.0091287 . ISSN   1932-6203. PMC   3951350 . PMID   24621577.
  3. 1 2 3 4 5 6 7 Gangloff, R.A.; A.R. Fiorillo; D.W. Norton (2005). "The first pachycephalosaurine (Dinosauria) from the Paleo-Arctic of Alaska and its paleogeographic implications". Journal of Paleontology. 79 (5): 997–1001. doi:10.1666/0022-3360(2005)079[0997:tfpdft]2.0.co;2. S2CID   130669713.
  4. 1 2 3 4 Sullivan, RM (2006). "A taxonomic review of the Pachycephalosauridae (Dinosauria: Ornithischia)". New Mexico Museum of Natural History and Science Bulletin (35): 347–365.
  5. 1 2 Paul, Gregory S. (2016). The Princeton Field Guide to Dinosaurs: Second Edition. Princeton, New Jersey: Princeton University Press. p. 268. ISBN   978-0-691-16766-4.
  6. 1 2 Galton, Peter M.; Sues, Hans-Dieter (1983-03-01). "New data on pachycephalosaurid dinosaurs (Reptilia: Ornithischia) from North America". Canadian Journal of Earth Sciences. 20 (3): 462–472. Bibcode:1983CaJES..20..462G. doi:10.1139/e83-043. ISSN   0008-4077.
  7. ↑ Maryańska, T.; Osmólska, H. (1974). "Pachycephalosauria, a new suborder of ornithischian dinosaurs" (PDF). Palaeontologica Polonica (30): 45−102.
  8. ↑ Boyd, Clint A. (2015-12-22). "The systematic relationships and biogeographic history of ornithischian dinosaurs". PeerJ. 3: e1523. doi: 10.7717/peerj.1523 . ISSN   2167-8359. PMC   4690359 . PMID   26713260.
  9. ↑ Dieudonné, P. -E.; Cruzado-Caballero, P.; Godefroit, P.; Tortosa, T. (2021-10-03). "A new phylogeny of cerapodan dinosaurs". Historical Biology. 33 (10): 2335–2355. Bibcode:2021HBio...33.2335D. doi:10.1080/08912963.2020.1793979. ISSN   0891-2963. S2CID   221854017.
  10. ↑ Butler, R. J., Upchurch, P., & Norman, D. B. (2008). "The phylogeny of the ornithischian dinosaurs." Journal of Systematic Palaeontology, 6(1), 1-40.
  11. ↑ Hailu, You; Xing, Xu; Xiaolin, Wang (2010-09-07). "A New Genus of Psittacosauridae (Dinosauria: Ornithopoda) and the Origin and Early Evolution of Marginocephalian Dinosaurs". Acta Geologica Sinica. 77 (1) (English ed.): 15–20. Bibcode:2003AcGlS..77...15Y. doi:10.1111/j.1755-6724.2003.tb00105.x. S2CID   89051352.
  12. ↑ Longrich, N. R., Sankey, J., & Tanke, D. (2010). "Texacephale langstoni, a new genus of pachycephalosaurid (Dinosauria: Ornithischia) from the upper Campanian Aguja Formation, southern Texas, USA." Cretaceous Research, 31(2), 274-284.
  13. ↑ Schott, Ryan K.; Evans, David C. (2016). "Cranial variation and systematics of Foraminacephale brevis gen. nov. and the diversity of pachycephalosaurid dinosaurs (Ornithischia: Cerapoda) in the Belly River Group of Alberta, Canada". Zoological Journal of the Linnean Society. doi:10.1111/zoj.12465.
  14. ↑ Evans, David; Brown, Caleb M.; You, Hailu; Campione, Nicolás E. (2021). "Description and revised diagnosis of Asia's first recorded pachycephalosaurid, Sinocephale bexelli gen. nov., from the Upper Cretaceous of Inner Mongolia, China". Canadian Journal of Earth Sciences. 58 (10): 981–992. Bibcode:2021CaJES..58..981E. doi:10.1139/cjes-2020-0190. S2CID   244227050.
  15. 1 2 Herman, Alexei B.; Spicer, Robert A.; Spicer, Teresa E. V. (2016-01-01). "Environmental constraints on terrestrial vertebrate behaviour and reproduction in the high Arctic of the Late Cretaceous". Palaeogeography, Palaeoclimatology, Palaeoecology. Selected papers based on Geological Society of America, Annual Meeting, Theme Session 241, Ancient Polar Ecosystems and Climate History in Deep Time, Denver, Colorado, USA, 30 October 2013. 441: 317–338. Bibcode:2016PPP...441..317H. doi: 10.1016/j.palaeo.2015.09.041 . ISSN   0031-0182.
  16. ↑ Takasaki, Ryuji; Fiorillo, Anthony R.; Tykoski, Ronald S.; Kobayashi, Yoshitsugu (2020-05-06). "Re-examination of the cranial osteology of the Arctic Alaskan hadrosaurine with implications for its taxonomic status". PLOS ONE. 15 (5): e0232410. Bibcode:2020PLoSO..1532410T. doi: 10.1371/journal.pone.0232410 . ISSN   1932-6203. PMC   7202651 . PMID   32374777.
  17. ↑ Druckenmiller, Patrick S.; Erickson, Gregory M.; Brinkman, Donald; Brown, Caleb M.; Eberle, Jaelyn J. (2021). "Nesting at extreme polar latitudes by non-avian dinosaurs". Current Biology. 31 (16): 3469–3478.e5. Bibcode:2021CBio...31E3469D. doi: 10.1016/j.cub.2021.05.041 . ISSN   0960-9822. PMID   34171301.
  18. ↑ Eberle, Jaelyn J.; Clemens, William A.; McCarthy, Paul J.; Fiorillo, Anthony R.; Erickson, Gregory M.; Druckenmiller, Patrick S. (2019-11-02). "Northernmost record of the Metatheria: a new Late Cretaceous pediomyid from the North Slope of Alaska". Journal of Systematic Palaeontology. 17 (21): 1805–1824. Bibcode:2019JSPal..17.1805E. doi:10.1080/14772019.2018.1560369. ISSN   1477-2019. S2CID   92613824.
  19. ↑ Fiorillo, Anthony R. (2004). "The Dinosaurs of Arctic Alaska". Scientific American. 291 (6): 84–91. Bibcode:2004SciAm.291f..84F. doi:10.1038/scientificamerican1204-84. ISSN   0036-8733. JSTOR   26060803. PMID   15597984.
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