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| マカエロプロソプス | ||||||||||||||||||||||||||||||
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 ニューメキシコ自然史科学博物館にて、マカエロプロソプスの頭蓋骨
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| 地質時代 | ||||||||||||||||||||||||||||||
| 後期三畳紀 | ||||||||||||||||||||||||||||||
| 分類 | ||||||||||||||||||||||||||||||
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| 学名 | ||||||||||||||||||||||||||||||
| Machaeroprosopus Cope, 1881 | ||||||||||||||||||||||||||||||
| タイプ種 | ||||||||||||||||||||||||||||||
| Belodon buceros Cope, 1881 | ||||||||||||||||||||||||||||||
| 種 | ||||||||||||||||||||||||||||||
マカエロプロソプス[5]（Machaeroprosopus）は、アメリカ合衆国南部から化石が発見されている植竜類の属[5]。他の植竜類と同様に後期三畳紀に生息した大型爬虫類であり、現在のワニにも類似した半水棲の生活に適応した動物食性動物であったと見られる[5]。本属の下位分類については複数の見解があるが、5種以上の種が報告されており、属内でも吻部の形態に多様性がある[5]。また属レベルの分類も変遷した過去があり、例としてプセウドパラトゥスが本属のジュニアシノニムとされている[5][6]。
分類の変遷[編集]
かつてマカエロプロソプス属のタイプ種と考えられていたM. validusはアリゾナ州のチンリ層から産出した3個の完全な頭蓋骨に基づいて命名されたが、これらの頭蓋骨が1950年代以降紛失しているため、本種の視覚的記録は1916年の原記載に描かれた線画を残すのみとなっている[7]。他の種にはニューメキシコ州から産出して1922年に命名されたM. andersoni、1930年に命名されたM. adamanensis、M. gregorii、M. lithodendrorum、M. tenuis、M. zuniiがいたが、これらの種の大半はスミロスクス属[8]やルーティオドン属あるいはフィトサウルス属に再分類されている[9]。この状況でM. validusが他の属に再分類されていない唯一の種と考えられていたため、マカエロプロソプス属は他の植竜類との区別を支持する標徴的標本を欠くことから疑問名とみなされていた。その後Parker et al. (2013)によるマカエロプロソプス属の分類学的再評価により、M. validusのホロタイプ標本UW 3807がマカエロプロソプス属のホロタイプ標本として否定され、種Machaeroprosopus bucerosがマカエロプロソプスの置換名として提唱された。Machaeroprosopusが置換名として提唱された。本種の学名はBelodon bucerosのコンビナティオ・ノヴァである。そのため、プセウドパラトゥスという名前はマカエロプロソプスのジュニアシノニムであり、プセウドパラトゥス属の全ての種はマカエロプロソプス属に再分類される[10]。この更新された分類はStocker and Butler (2013)をはじめとする複数の研究に受け入れられている[11]。Stocker and Butler (2013)はまたM. andersoniを有効な種として扱っており[11]、かつてLing and Murry (1995)が提唱したようにMachaeroprosopus bucerosのジュニアシノニムとしていない[12]。
種[編集]
M. andersoni[編集]
M. andersoni was first described and named by Maurice G. Mehl in 1922, on the basis of the holotype FMNH UC 396, partial skull.[11] It was probably collected from the Bull Canyon Formation of the Chinle Group or Dockum Group, probably at the Bull Canyon, in the Guadalupe County of New Mexico.[12] This taxon was considered to be a junior synonym of M. buceros by Long and Murry (1995) and later authors,[12][13][1] although Stocker and Butler (2013) treated M. andersoni as a valid species.[11]
The holotype is the only known specimen of this species, although there are other specimens from the Bull Canyon Formation that were referred to Arribasuchus buceros by Long and Murry (1995),[12] but not by Stocker and Butler (2013).[11]
M. buceros[編集]
M. buceros was first described and named by Edward Drinker Cope in 1881 as Belodon buceros, on the basis of the holotype AMNH 2318, partial skull. It was collected from the Norian-aged Petrified Forest Member of the Chinle Formation, at the Arroyo Seco drainage, Orphan Mesa in the Rio Arriba County of New Mexico.[14] Later, the skull was occasionally referred to Phytosaurus buceros. Jaekel (1910) erected a new genus for the species, creating Metarhinus buceros, however this generic name was preoccupied by Metarhinus Osborn, 1908, a brontotheriid mammal. Mehl (1915) referred this species to Lophoprosopus, as Lophoprosopus buceros, but as the type species of this genus is considered to be synonymous with Nicrosaurus kapffi, Mehl (1916) erected a new genus for B. buceros, creating Machaeroprosopus buceros, but also explicitly indicated M. validus as the type. Subsequent studies accordingly considered M. validus to be the type species of Machaeroprosopus. Later, the skull was referred to as Rutiodon buceros, Machaeroprosopus buceros or Pseudopalatus buceros. Long and Murry (1995) erected a new genus for the species, not knowing that M. validus was not in fact the type species of Machaeroprosopus, creating Arribasuchus buceros.[12] Subsequent studies, including Hungerbühler (2002), Lucas et al. (2002),[14] Zeigler et al. (2002), Irmis (2005)[13] and Parker and Irmis (2006),[1] referred the species back to Pseudopalatus buceros, and considered Arribasuchus to be a junior synonym of Pseudopalatus. A taxonomic revision of Machaeroprosopus, conducted by Parker et al. in 2013, revealed that Machaeroprosopus buceros is the combinatio nova of the type species of the genus because Article 67-8 ICZN rules that with replacement names the original type species (i.c. Cope's Beladon buceros) is maintained. Therefore, the name Pseudopalatus was considered a junior synonym of Machaeroprosopus, and all species of the former were reassigned to the later, including P. buceros.[10][11] Following the revision, M. andersoni was treated as a valid species by Stocker and Butler (2013),[11] and not a junior synonym of Machaeroprosopus buceros as was previously suggested by Long and Murry (1995). Other specimens were referred to P. buceros by Long and Murry (1995),[12] although all specimens from Arizona and Texas was later reassigned to other species (namely M. lottorum, M. mccauleyi and M. validus), and as M. andersoni from the Dockum Group was re-validated, M. buceros is currently known only from Chinle Formation of New Mexico.[11][2]
M. jablonskiae[編集]
M. jablonskiae was first described and named by William G. Parker and Randall B. Irmis in 2006, on the basis of the holotype PEFO 31207, posterior skull roof and braincase missing the rostrum and palate. This specimen was initially referred to Pseudopalatus cf. mccauleyi by Parker and Irmis (2004) based on the morphology of the squamosals and the opisthotic, then to Pseudopalatus sp. by Parker and Irmis (2005) and finally to Pseudopalatus jablonskiae by Parker and Irmis (2006). It was collected in September 2002 from the lower Jim Camp Wash beds, Sonsela Member of the Chinle Formation, at locality PFV 295, near Mountain Lion Mesa in Petrified Forest National Park, Arizona. The specific name honors Pat Jablonsky, who discovered the holotype and only known specimen.[1] Following the taxonomic revision of Machaeroprosopus by Parker et al. (in press), all species of Pseudopalatus, including P. jablonskiae, were reassigned to Machaeroprosopus.[10] This was already accepted by Stocker and Butler (2013).[11]
Although M. jablonskiae is known from an incomplete specimen, it can be diagnosed by at least one autapomorphy and a unique suite of traits, and it includes a well-preserved braincase, which is rarely preserved or described in detail for most phytosaur specimens. A phylogenetic analysis of mystriosuchin phytosaurs performed by Parker and Irmis (2006) found the species to be the most basal species of "Pseudopalatus".[1]
M. lottorum[編集]
M. lottorum was first described and named by Axel Hungerbühler, Bill Mueller, Sankar Chatterjee and Douglas P. Cunningham in 2013. The specific name honors John Lott and Patricia Lott Kirkpatrick, for their support during the work at the TTU VPL 3870. It is known from two complete skulls, the holotype TTU-P10076 and the paratype TTU-P10077 housed at Texas Tech University. The skulls were collected at Patricia Site (TTU Vertebrate Paleontology Locality 3870), 13 km South of Post, Garza County of west Texas, from the upper unit of the Norian Cooper Canyon Formation, Dockum Group. Other vertebrates known from this site include TTU-P10074, a partial skull referred to Machaeroprosopus sp., a phytosaur postcranial skeleton, fish, a temnospondyl amphibian, Typothorax, Postosuchus, Shuvosaurus and a theropod dinosaur.[2]
A phylogenetic analysis of mystriosuchin phytosaurs performed by Hungerbühler et al. (2013) found the species to be a derived Machaeroprosopus species, most closely related to the type species of Redondasaurus, "R." gregorii. This clade in addition to Machaeroprosopus sp. (TTU-P10074) was recovered as the sister taxon of the clade formed by M. pristinus and M. buceros. M. jablonskiae, M. mccauleyi and "Redondasaurus" bermani were found to be basal species of Machaeroprosopus.[2]
M. mccauleyi[編集]
M. mccauleyi was first described and named by Karen A. Ballew in 1989 as a species of Pseudopalatus, on the basis of the holotype UCMP 126999, an incomplete skull, lacking the anterior half of the rostrum, and probably associated lower jaws. The specific name honors John D. McCauley and Mrs. Molly McCauley McLean from Winslow, Arizona, the owners of the land at "Billings Gap" from which the holotype was found.[3] The specimen was originally informally designated as Pseudopalatus "bilingsensis" by Ballew (1986).[8] It was collected at Dry Creek Tank SE (also known as UCMP V82040, UCMP 7043 and PFV 55), Apache County of Arizona, from the Norian-aged Upper Petrified Forest Member / Formation according to most authors,[8][11][12] or possibly Sonsela Member of the Chinle Formation according to Parker & Irmis (2005). Ballew (1989) also referred to this species USNM 15839, another incomplete skull lacking the anterior half of the rostrum from Arizona.[3] Long and Murry (1995) restricted this species to its holotype, although recent studies suggest that USNM 15839 is referable to it.[15] Long and Murry (1995) also considered M. mccauleyi to be a species of their Arribasuchus, probably synonymous with A. buceros,[12] although most subsequent studies, like Hungerbühler (2002), Parker and Irmis (2006),[1] Stocker (2010)[8] and Stocker and Butler (2013)[11] treated M. mccauleyi as a valid species. Other specimens that are currently referred to M. mccauleyi include PEFO 31219,[8] complete skull, lower jaws and articulated postcranial skeleton, from Petroglyph phytosaur site (also known as PFV 42) collected by UCMP in 1985, and possibly UCMP 27149, a large skull, from Cowboy (UCMP A257), both from the Petrified Forest Member, Arizona. Both specimen were originally referred to A. buceros by Long and Murry (1995).[12]
M. pristinus[編集]
M. pristinus was first described and named by Maurice G. Mehl in 1928 as the type species of Pseudopalatus, Pseudopalatus pristinus, on the basis of the holotype MU 525, nearly complete skull. It was collected, from the Norian-aged Upper Petrified Forest Member of the Chinle Formation, near Adamana, Arizona. Additional skulls and postcranial material, some articulated skeletons, from the same member were referred to this species by Colbert (1946) and Long and Murry (1995) from Arizona, and by Lawler (1979), Ballew (1986) and Long and Murry (1995) from New Mexico.[12] Charles Camp (1930) described and named Machaeroprosopus tenuis on the basis of UCMP 27018, a nearly complete skull, lower jaws, and some complete postcranial material, from the Billings Gap locality (UCMP 7043, Upper Petrified Forest Member), Apache County of Arizona. This specimen was occasionally referred to as Rutiodon tenuis, although since Long and Murry (1995) it is considered to be a junior synonym of M. pristinus.[12] Long and Murry (1995) also suggested that Redondasaurus gregorii from the Redonda Formation of New Mexico is a junior synonym of M. pristinus,[12] although this was not accepted by subsequent authors.[1] Other, then unnumbered, specimens from the upper Church Rock Member (Chinle Formation, Utah), Bull Canyon Formation and Travesser Formation (New Mexico) and Cooper Canyon Formation (Texas), were referred to M. pristinus by Long and Murry (1995),[12] although recent studies suggest that M. pristinus is currently known only from the Upper Petrified Forest Member of Arizona and New Mexico.[11]
M. validus[編集]
M. validus was first described and named by Maurice G. Mehl in Mehl et al., in 1916 on the basis of the holotype UW 3807, a complete skull, and the two paratypes UW 3808 and UW 3809, partial skulls,[7] from Norian-aged Upper Petrified Forest Member of the Chinle Formation, Coconino County of Arizona.[12] The skulls have been lost since the 1950s, and a line drawing in the original 1916 description is the only visual record of the specimen. M. validus, once thought to be the type species of Machaeroprosopus, was suggested by some authors to represent the same species as Pseudopalatus pristinus. If this is the case, the name Machaeroprosopus would have precedence over Pseudopalatus because Pseudopalatus was named in 1928, twelve years after Machaeroprosopus was named.[7] Long and Murry (1995) erected a new genus for Belodon buceros, not knowing that it was in fact the type species of Machaeroprosopus (and not M. validus), creating Arribasuchus buceros. They also suggested that M. validus might be a junior synonym of A. buceros.[12]
Until recently, M. validus was considered to be the only species of Machaeroprosopus that has not been reassigned. Thus, Machaeroprosopus was considered to be a nomen dubium or "doubtful name" because of the lack of diagnostic specimens that can support its distinction from other phytosaur genera. However, a taxonomic revision of Machaeroprosopus, conducted by Parker et al. (in press), revealed that UW 3807 is not the holotype of Machaeroprosopus, while the species Machaeroprosopus buceros is in fact the correct new combination for the type species of the genus.
出典[編集]
- ^ a b c d e f g Parker, W. G.; Irmis, R. B. (2006). “A new species of the Late Triassic phytosaur Pseudopalatus (Archosauria: Pseudosuchia) from Petrified Forest National Park, Arizona”. Museum of Northern Arizona Bulletin 62: 126–143.
- ^ a b c d Hungerbühler, A.; Mueller, B.; Chatterjee, S.; Cunningham, D. P. (2013). “Cranial anatomy of the Late Triassic phytosaur Machaeroprosopus, with the description of a new species from West Texas”. Earth and Environmental Science Transactions of the Royal Society of Edinburgh 103 (3–4): 269. doi:10.1017/S1755691013000364.
- ^ a b c Ballew, K. L. (1989). “A phylogenetic analysis of Phytosauria from the Late Triassic of the western United States”. In Lucas, S. G.; Hunt, A. P.. Dawn of the age of dinosaurs in the American Southwest. Albuquerque: New Mexico Museum of Natural History. pp. 309–339
- ^ a b Mehl, Maurice; Toepelmann, W. C.; Schwartz, G. M. (1916). “New or little known reptiles from the Trias of Arizona and New Mexico with notes from the fossil bearing horizons near Wingate, New Mexico”. University of Oklahoma Bulletin 103: 1–44.
- ^ a b c d e 柴田正輝 編『ギガ恐竜展2017 地球の絶対王者の謎』東洋一 総合監修、柴田正輝 監修、読売新聞社、2017年、12-14頁。
- ^ 『世界の巨大恐竜博2006 生命と環境─進化のふしぎ』長谷川善和、ケネス・カーペンター、董枝明、徐星 監修、日本経済新聞社、NHK、NHKプロモーション、日経ナショナルジオグラフィック社、24頁。
- ^ a b c Parker, Bill (2007年2月7日). “The Tragic Tale of Machaeroprosopus and Acompsosaurus”. Chinleana. Field of Science. 2012年4月15日時点のオリジナルよりアーカイブ。2012年5月11日閲覧。
- ^ a b c d e Stocker, Michelle R. (2010). “A new taxon of phytosaur (Archosauria: Pseudosuchia) from the Late Triassic (Norian) Sonsela Member (Chinle Formation) in Arizona, and a critical reevaluation of Leptosuchus Case, 1922”. Palaeontology 53 (5): 997–1022. doi:10.1111/j.1475-4983.2010.00983.x.
- ^ Gregory, J.T. (1962). “The relationships of the American phytosaur Rutiodon”. American Museum Novitates (2095): 1–22.
- ^ a b c Parker, W. G.; Hungerbühler, A.; Martz, J. W. (2013). “The taxonomic status of the phytosaurs (Archosauriformes) Machaeroprosopus and Pseudopalatus from the Late Triassic of the western United States”. Earth and Environmental Science Transactions of the Royal Society of Edinburgh 103 (3–4): 265–268. doi:10.1017/S1755691013000339.
- ^ a b c d e f g h i j k l Stocker, M. R.; Butler, R. J. (2013). “Phytosauria”. Geological Society, London, Special Publications 379 (1): 91–117. Bibcode: 2013GSLSP.379...91S. doi:10.1144/SP379.5.
- ^ a b c d e f g h i j k l m n o Long, R. A.; Murry, P. A. (1995). “Late Triassic (Carnian and Norian) tetrapods from the southwestern United States”. New Mexico Museum of Natural History and Science Bulletin 4: 1–254.
- ^ a b Irmis, R. B. (2005). Nesbitt, S. J.; Parker, W. G.; Irmis, R. B.. eds. “The vertebrate fauna of the Upper Triassic Chinle Formation in northern Arizona”. Guidebook to the Triassic Formations of the Colorado Plateau in Northern Arizona: Geology, Paleontology, and History. Mesa Southwest Museum Bulletin 9: 63–88.
- ^ a b Lucas, S. G.; Heckert, A. B.; Zeigler, K. E.; Hunt, A. P. (2002). Heckert, A. B.; Lucas, S. G.. eds. “The type locality of Belodon buceros Cope, 1881, a phytosaur (Archosauria: Parasuchidae) from the Upper Triassic of north-central New Mexico”. Upper Triassic Stratigraphy and Paleontology, New Mexico Museum of Natural History and Science Bulletin 21: 189–192.
- ^ Holloway, W. L.; Claeson, K. M.; O’Keefe, F. R. (2013). “A virtual phytosaur endocast and its implications for sensory system evolution in archosaurs”. Journal of Vertebrate Paleontology 33 (4): 848. doi:10.1080/02724634.2013.747532.