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Comparative studies of enamel and functional morphology in selected mammals with tribosphenic molar teeth : = Phylogenetic applications.

紀錄類型:	書目-語言資料,手稿 : Monograph/item
正題名/作者:	Comparative studies of enamel and functional morphology in selected mammals with tribosphenic molar teeth :/
其他題名:	Phylogenetic applications.
作者:	Wood, Craig Breckinridge.
面頁冊數:	1 online resource (239 pages)
附註:	Source: Dissertations Abstracts International, Volume: 54-10, Section: B.
Contained By:	Dissertations Abstracts International54-10B.
標題:	Paleontology. -
電子資源:	click for full text (PQDT)
ISBN:	9798643157021

Comparative studies of enamel and functional morphology in selected mammals with tribosphenic molar teeth : = Phylogenetic applications.
Wood, Craig Breckinridge.

Comparative studies of enamel and functional morphology in selected mammals with tribosphenic molar teeth :Phylogenetic applications. - 1 online resource (239 pages)

Source: Dissertations Abstracts International, Volume: 54-10, Section: B.

Thesis (Ph.D.)--Harvard University, 1992.

Includes bibliographical references

Tribosphenic molar teeth are plesiomorphic for both placental and marsupial mammals. Late Cretaceous tribosphenic mammals are known almost exclusively from dental remains. This study adds new characters for phylogenetic analysis of Cretaceous therians and their Cenozoic descendants. An SEM (scanning electronic microscope) survey of enamel structure, in molars of representative extant New World opossum genera (Didelphimorphia), reveals that Dromiciops has the most plesiomorphic pattern and Philander the most derived pattern, with intermediate Caluromys, Marmosa, and Didelphis in a sequence consistent with cladograms from other studies of comparative morphology, karyology, and serology. Contrary to previous reports, enamel indicates that, after Alphadon, Glasbius and Pediomys are the most derived Cretaceous marsupials (comparable to Dromiciops), and that stagodontids including Didelphodon vorax have the most plesiomorphic enamel yet observed in any tribosphenic molars. Enamel in stagodontids is quite similar to that in a Jurassic, "pre-tribosphenic" pantothere. Quite derived enamel in two Late Cretaceous pantotheres, Groebertherium and Mesungulatum, demonstrates potential for convergence (and mosaicism) in all therians. A more detailed documentation of enamel in stagodontids demonstrates the need for extended views of enamel, in several specimens, to be sure of patterns in relatively plesiomorphic (i.e., "non-complex") states; and also extends the hypothesis for the Family Stagodontidae as the first sister group to all other members of the marsupial clade. The hypothesis predicts that a common ancestor to placetal and marsupial mammals will have structure no more derived than that of stagodontids. Tests of Spurr's and Araldite 6005 resins show that Spurr's stands up especially well to the brighter LaB6 filament beam in the SEM at an operating voltage (20 KV) used for actual specimens. Because of its low viscosity (60 cps) Spurr's makes bubble-free, three dimensional casts which are excellent for teaching and research collections but which also display original surface details as small as 1 μm wide. G.E. RTV 700 silicone rubber (with Beta 5 curing agent) is an excellent molding compound for Spurr's resin because it resists high curing temperatures and produces multiple, high-fidelity casts. Functional studies of occlusion in a new specimen of Batodon tenuis support the association of isolated upper and lower molars referred to the species by earlier workers. This rarest of tiny Cretaceous placental mammals has had controversial assignment within Eutheria. Its true relationships await further analysis, but complete M³, M², and probably M¹ are described here for the first time in complete series.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798643157021Subjects--Topical Terms:

668656
Paleontology.
Subjects--Index Terms:

CretaceousIndex Terms--Genre/Form:

554714
Electronic books.

Comparative studies of enamel and functional morphology in selected mammals with tribosphenic molar teeth : = Phylogenetic applications.
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520 $a Tribosphenic molar teeth are plesiomorphic for both placental and marsupial mammals. Late Cretaceous tribosphenic mammals are known almost exclusively from dental remains. This study adds new characters for phylogenetic analysis of Cretaceous therians and their Cenozoic descendants. An SEM (scanning electronic microscope) survey of enamel structure, in molars of representative extant New World opossum genera (Didelphimorphia), reveals that Dromiciops has the most plesiomorphic pattern and Philander the most derived pattern, with intermediate Caluromys, Marmosa, and Didelphis in a sequence consistent with cladograms from other studies of comparative morphology, karyology, and serology. Contrary to previous reports, enamel indicates that, after Alphadon, Glasbius and Pediomys are the most derived Cretaceous marsupials (comparable to Dromiciops), and that stagodontids including Didelphodon vorax have the most plesiomorphic enamel yet observed in any tribosphenic molars. Enamel in stagodontids is quite similar to that in a Jurassic, "pre-tribosphenic" pantothere. Quite derived enamel in two Late Cretaceous pantotheres, Groebertherium and Mesungulatum, demonstrates potential for convergence (and mosaicism) in all therians. A more detailed documentation of enamel in stagodontids demonstrates the need for extended views of enamel, in several specimens, to be sure of patterns in relatively plesiomorphic (i.e., "non-complex") states; and also extends the hypothesis for the Family Stagodontidae as the first sister group to all other members of the marsupial clade. The hypothesis predicts that a common ancestor to placetal and marsupial mammals will have structure no more derived than that of stagodontids. Tests of Spurr's and Araldite 6005 resins show that Spurr's stands up especially well to the brighter LaB6 filament beam in the SEM at an operating voltage (20 KV) used for actual specimens. Because of its low viscosity (60 cps) Spurr's makes bubble-free, three dimensional casts which are excellent for teaching and research collections but which also display original surface details as small as 1 μm wide. G.E. RTV 700 silicone rubber (with Beta 5 curing agent) is an excellent molding compound for Spurr's resin because it resists high curing temperatures and produces multiple, high-fidelity casts. Functional studies of occlusion in a new specimen of Batodon tenuis support the association of isolated upper and lower molars referred to the species by earlier workers. This rarest of tiny Cretaceous placental mammals has had controversial assignment within Eutheria. Its true relationships await further analysis, but complete M³, M², and probably M¹ are described here for the first time in complete series.
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