9 results
Palate and braincase of Whatcheeria deltae Lombard & Bolt, 1995
- John R. BOLT, R. Eric LOMBARD
-
- Journal:
- Earth and Environmental Science Transactions of The Royal Society of Edinburgh / Volume 109 / Issue 1-2 / March 2018
- Published online by Cambridge University Press:
- 18 December 2018, pp. 177-200
- Print publication:
- March 2018
-
- Article
- Export citation
-
The reconstructed palate of Whatcheeria deltae indicates a skull that was unusually narrow: at least 2.2 times longer than wide if the pterygoids are conservatively placed in the horizontal plane. This maximum width is narrower than any other early tetrapod reconstructed so far. Rotating the pterygoids to produce a vaulted palate would produce an even narrower skull. Primitive palatal features include very narrow interpterygoid vacuities and a vomer, palatine, and ectopterygoid with fang-sized replacement pairs. It is derived in that there is no anterior palatal fenestra and the premaxilla has a substantial palatal shelf – a combination of characters shared only with Proterogyrinus among early tetrapods. There is a possible septomaxilla in one specimen. Whatcheeria differs from and is more derived than Pederpes, its likely sister taxon, in that only the pterygoid is covered with denticles, the vomer, palatine, and ectopterygoid containing labyrinthine teeth only. Reconstructed dental occlusion indicates that the large choana apparently accommodated the large dentary fangs; this would be a unique feature among early tetrapods. The palatal ramus of the pterygoid is longer than the quadrate ramus, which does not have a descending flange. Like Meckel's cartilage in the lower jaw, the palatoquadrate is fully ossified in larger specimens, such that in a posterior view of the skull the pterygoid is mostly hidden from sight by the epipterygoid. The ossified neurocranium consists of the basiparasphenoid and basioccipital; no ossified sphenethmoid has been found. Remains of otic capsules are partial, crushed, and smeared, so no useful morphology is available. The stapes appears to be more columnar and less plate-like than in many other primitive, early tetrapods.
Sigournea multidentata, a new stem tetrapod from the Upper Mississippian of Iowa, USA
- John R. Bolt, R. Eric Lombard
-
- Journal:
- Journal of Paleontology / Volume 80 / Issue 4 / July 2006
- Published online by Cambridge University Press:
- 11 August 2017, pp. 717-725
-
- Article
- Export citation
-
Sigournea multidentata n. gen. and sp., an early tetrapod, is described from the Late Mississippian Delta locality of southern Iowa, USA. The holotype and only known specimen, a right mandible, is unique in the structure of the symphysial region, and in addition has a unique combination of characters that are shared with other tetrapods. The free ventral border of the single exomeckelian fenestra is formed by infradentary bones. Its visible portion shows several arch bases, separated by notched or straight intervals. This morphology is interpreted as indicating that the arch bases and intervals between them reflected a series of Meckelian fenestrae that were partly exo- and partly endoskeletal, due to the fact that the exoskeletal arch bases continued dorsally in Meckelian cartilage. We suggest that this may exemplify a stage in the evolution of exomeckelian fenestrae, in at least some lineages of early tetrapods. The relations of Sigournea are indeterminate. That it is a tetrapod is indicated by the presence of pit and ridge ornamentation, an open lateral line sulcus, a dorsally directed glenoid, a single elongate exomeckelian fenestra, absence of intercoronoid fossae, absence of coronoid fangs, a single row of marginal teeth on the dentary, and an absence of dentition on the prearticular. It is at present impossible to determine its relationship with other early tetrapods, and we conclude that Sigournea is best considered as an early tetrapod incertae sedis.
The atlas-axis complex in the late Paleozoic genus Diadectes and the characteristics of the atlas-axis complex across the amphibian to amniote transition
- Stuart S. Sumida, R. Eric Lombard
-
- Journal:
- Journal of Paleontology / Volume 65 / Issue 6 / November 1991
- Published online by Cambridge University Press:
- 20 May 2016, pp. 973-983
-
- Article
- Export citation
-
The atlas-axis complex in the Early Permian diadectomorph Diadectes is shown to be similar to those of a variety of primitive amniotes. Diadectes does not possess elements in addition to the standard complement seen in advanced batrachosaurs and primitive amniotes as previously thought. Characteristics of the complex include: paired, well-developed proatlases and atlantal neural arches, lack of atlantal neural spines, an extremely robust atlantal intercentrum, fusion of the atlantal pleurocentrum and axial intercentrum, a large anterior projection of the axial intercentrum, exclusion of the atlantal pleurocentrum from ventral exposure, fusion of axial neural arch and pleurocentrum, and a robustly developed axial neural spine. An analysis of the transformations of the atlas-axis complex in advanced anthracosaurs and primitive amniotes indicates that many of the characteristics of the complex previously thought to be definitive of amniotes or reptiles appear to be conditions common to Diadectes plus Amniota.
The mandible of the primitive tetrapod Greererpeton, and the early evolution of the tetrapod lower jaw
- John R. Bolt, R. Eric Lombard
-
- Journal:
- Journal of Paleontology / Volume 75 / Issue 5 / September 2001
- Published online by Cambridge University Press:
- 20 May 2016, pp. 1016-1042
-
- Article
- Export citation
-
Exceptionally well-preserved Late Mississippian colosteid amphibian specimens occur in southern Illinois; the mandible is described here. Unexpectedly primitive features include toothed adsymphysial and intercoronoid fossa with fenestrate floor. The large adsymphysial bears teeth, forms 50 percent of the symphysis, and meets its antimere in a very coarsely rugose suture. These and other characters are shown to occur also in Greererpeton burkemorani, to which we refer the Illinois specimens. Colosteid mandibles from a Late Mississippian locality in southern Iowa resemble G. burkemorani closely, although they are not conspecific. Our findings are summarized in a PRESERVE-format data table containing 226 characters. G. burkemorani's adsymphysial suture morphology is shared with the baphetid Megalocephalus pachycephalus. However, the relationship of colosteids to other Paleozoic amphibian groups remains unclear, beyond their position as stem tetrapods. The single elongate Meckelian fenestra of colosteids is likely primitive for tetrapods. A three-stage model is proposed for the evolution of Meckelian fenestrae in tetrapods. Based on sutural morphology, G. burkemorani is considered to have a kinetic joint between skull table and cheek. A functional hypothesis is outlined in which movements at this joint are accommodated at the symphysis. A phylogenetically based test of this hypothesis is proposed.
Reinterpretation of the temporal and occipital regions in Diadectes and the relationships of diadectomorphs
- David S Berman, Stuart S. Sumida, R. Eric Lombard
-
- Journal:
- Journal of Paleontology / Volume 66 / Issue 3 / May 1992
- Published online by Cambridge University Press:
- 14 July 2015, pp. 481-499
-
- Article
- Export citation
-
New materials from the Permo-Pennsylvanian of north-central New Mexico permit a new description of the temporal and occipital regions of the diadectomorph Diadectes. The important issue of the fate of the intertemporal bone is resolved by demonstrating its absence and apparent incorporation into the parietal as a lateral lappet. Four cranial autapomorphies of Diadectes are recognized: 1) loss of contact between postparietal and tabular; 2) supratemporal greatly enlarged with well-developed occipital process; 3) tabular no longer exposed on skull roof, but greatly reduced and incorporated into occipital plate, with a coarse, posteromedially facing surface; and 4) skull roofing bones thick and porous, with a consistent network of U-shaped grooves. The temporal–occipital region of Diadectes is compared with those of holotypic and recently collected specimens of Limnoscelis and Tseajaia, the type genera of the other two recognized diadectomorph families, Limnoscelidae and Tseajaiidae. On the basis of the literature the comparisons are extended to include certain late Paleozoic amniotes: synapsid Pelycosauria, Captorhinomorpha, and the primitive diapsid Petrolacosaurus. The results are subjected to a cladistic analysis, which supports the following hypotheses of relationships: 1) Diadectidae, Tseajaiidae, and Limnoscelidae form a natural group, the Diadectomorpha; 2) Diadectes and Tseajaia share a more recent common ancestor than either does with Limnoscelis; 3) Diadectomorpha, Pelycosauria, and their descendants form an unnamed, primitive sister clade to that consisting of Captorhinomorpha, Petrolacosaurus, and their descendants; and 4) the taxon Cotylosauria (sensu Heaton, 1980), consisting of Diadectomorpha and Seymouriamorpha, is paraphyletic and invalid. The third hypothesis dictates the assignment of Diadectomorpha to Amniota.
Deltaherpeton hiemstrae, a new colosteid tetrapod from the Mississippian of Iowa
- John R. Bolt, R. Eric Lombard
-
- Journal:
- Journal of Paleontology / Volume 84 / Issue 6 / November 2010
- Published online by Cambridge University Press:
- 14 July 2015, pp. 1135-1151
-
- Article
- Export citation
-
A new colosteid, Deltaherpeton hiemstrae gen. et sp. nov., is described from the Mississippian Upper Viséan site at Delta, Iowa. Deltaherpeton is represented by a skull roof and both jaws. The new taxon is unique among colosteids in having an internasal and single midline postparietal. An additional midline pair of cf. ‘interfrontonasals’ may be present. Characters previously used to define the colosteids are reviewed and a refined diagnosis for the family Colosteidae is presented. Synapomorphies which unite Deltaherpeton, Colosteus, Greererpeton, and Pholidogaster as Colosteidae are: premaxilla with fang pair; dentary with notch for receipt of premaxillary fang; mandible with single elongate exomeckelian fenestra; pre-narial infraorbital lateral line terminating at ventral margin of premaxilla just anterior to external naris; and post-narial infraorbital lateral line terminating at the ventral margin of the maxilla just posterior to the external naris. Our review of dermal bones in the colosteid snout concludes that no specimen is sufficiently free of distortions or breakage to indicate clearly whether or not the prefrontal borders the external naris, or that an anterior tectal is present. The morphology of Deltaherpeton and the revised data presented for colosteids do not clarify the relationship of colosteids to other early tetrapods.
A microsaur from the Mississippian of illinois and a standard format for morphological characters
- R. Eric Lombard, John R. Bolt
-
- Journal:
- Journal of Paleontology / Volume 73 / Issue 5 / September 1999
- Published online by Cambridge University Press:
- 14 July 2015, pp. 908-923
-
- Article
- Export citation
-
The oldest known microsaur is preserved in a nodule from the Kinkaid Formation (Mississippian; Elvirian) collected near Goreville, Illinois. At least eight individuals are represented: three by partial skulls plus vertebral column segments with associated limb elements, and five by postcrania only. Skulls are crushed, incomplete, and exposed mainly in palatal view. Palatal bones are denticulate and the palatine has in addition a single large tooth. The basipterygoid process is laterally directed and the basipterygoid joint is open. The atlas carries large articulating facets for proatlantes, a pair of which are identifiable in one specimen. These features have not been found previously in a microsaur. All vertebral segments are dominated by a biconcave pleurocentrum; sutures between the pleurocentrum and neural arch are visible in presacral vertebrae. Distinctive microsaurian intercentra occur between all presacral pleurocentra. Their presence reinforces the hypothesis that microsaur intercentra are homologous with those of other early tetrapods. Caudal vertebrae retain separate haemal arches and some have ribs.
Observed microsaur synapomorphies include: atlas with large median odontoid; atlas with concave lateral facets for occipital condyle; paired occipital condyles that are broad and concave; and thin, straplike intercentra. No observed features support a sister-group relationship with any other microsaur species, or placement within any higher level microsaur group. Because significant portions of the skeleton are missing or inaccessible, the Goreville microsaur is not formally named. A standardized, hierarchical format for skeletal characters is introduced that facilitates data sharing and comparison and fosters rapid archiving and retrieval.
Contributors
-
- By Mitchell Aboulafia, Frederick Adams, Marilyn McCord Adams, Robert M. Adams, Laird Addis, James W. Allard, David Allison, William P. Alston, Karl Ameriks, C. Anthony Anderson, David Leech Anderson, Lanier Anderson, Roger Ariew, David Armstrong, Denis G. Arnold, E. J. Ashworth, Margaret Atherton, Robin Attfield, Bruce Aune, Edward Wilson Averill, Jody Azzouni, Kent Bach, Andrew Bailey, Lynne Rudder Baker, Thomas R. Baldwin, Jon Barwise, George Bealer, William Bechtel, Lawrence C. Becker, Mark A. Bedau, Ernst Behler, José A. Benardete, Ermanno Bencivenga, Jan Berg, Michael Bergmann, Robert L. Bernasconi, Sven Bernecker, Bernard Berofsky, Rod Bertolet, Charles J. Beyer, Christian Beyer, Joseph Bien, Joseph Bien, Peg Birmingham, Ivan Boh, James Bohman, Daniel Bonevac, Laurence BonJour, William J. Bouwsma, Raymond D. Bradley, Myles Brand, Richard B. Brandt, Michael E. Bratman, Stephen E. Braude, Daniel Breazeale, Angela Breitenbach, Jason Bridges, David O. Brink, Gordon G. Brittan, Justin Broackes, Dan W. Brock, Aaron Bronfman, Jeffrey E. Brower, Bartosz Brozek, Anthony Brueckner, Jeffrey Bub, Lara Buchak, Otavio Bueno, Ann E. Bumpus, Robert W. Burch, John Burgess, Arthur W. Burks, Panayot Butchvarov, Robert E. Butts, Marina Bykova, Patrick Byrne, David Carr, Noël Carroll, Edward S. Casey, Victor Caston, Victor Caston, Albert Casullo, Robert L. Causey, Alan K. L. Chan, Ruth Chang, Deen K. Chatterjee, Andrew Chignell, Roderick M. Chisholm, Kelly J. Clark, E. J. Coffman, Robin Collins, Brian P. Copenhaver, John Corcoran, John Cottingham, Roger Crisp, Frederick J. Crosson, Antonio S. Cua, Phillip D. Cummins, Martin Curd, Adam Cureton, Andrew Cutrofello, Stephen Darwall, Paul Sheldon Davies, Wayne A. Davis, Timothy Joseph Day, Claudio de Almeida, Mario De Caro, Mario De Caro, John Deigh, C. F. Delaney, Daniel C. Dennett, Michael R. DePaul, Michael Detlefsen, Daniel Trent Devereux, Philip E. Devine, John M. Dillon, Martin C. Dillon, Robert DiSalle, Mary Domski, Alan Donagan, Paul Draper, Fred Dretske, Mircea Dumitru, Wilhelm Dupré, Gerald Dworkin, John Earman, Ellery Eells, Catherine Z. Elgin, Berent Enç, Ronald P. Endicott, Edward Erwin, John Etchemendy, C. Stephen Evans, Susan L. Feagin, Solomon Feferman, Richard Feldman, Arthur Fine, Maurice A. Finocchiaro, William FitzPatrick, Richard E. Flathman, Gvozden Flego, Richard Foley, Graeme Forbes, Rainer Forst, Malcolm R. Forster, Daniel Fouke, Patrick Francken, Samuel Freeman, Elizabeth Fricker, Miranda Fricker, Michael Friedman, Michael Fuerstein, Richard A. Fumerton, Alan Gabbey, Pieranna Garavaso, Daniel Garber, Jorge L. A. Garcia, Robert K. Garcia, Don Garrett, Philip Gasper, Gerald Gaus, Berys Gaut, Bernard Gert, Roger F. Gibson, Cody Gilmore, Carl Ginet, Alan H. Goldman, Alvin I. Goldman, Alfonso Gömez-Lobo, Lenn E. Goodman, Robert M. Gordon, Stefan Gosepath, Jorge J. E. Gracia, Daniel W. Graham, George A. Graham, Peter J. Graham, Richard E. Grandy, I. Grattan-Guinness, John Greco, Philip T. Grier, Nicholas Griffin, Nicholas Griffin, David A. Griffiths, Paul J. Griffiths, Stephen R. Grimm, Charles L. Griswold, Charles B. Guignon, Pete A. Y. Gunter, Dimitri Gutas, Gary Gutting, Paul Guyer, Kwame Gyekye, Oscar A. Haac, Raul Hakli, Raul Hakli, Michael Hallett, Edward C. Halper, Jean Hampton, R. James Hankinson, K. R. Hanley, Russell Hardin, Robert M. Harnish, William Harper, David Harrah, Kevin Hart, Ali Hasan, William Hasker, John Haugeland, Roger Hausheer, William Heald, Peter Heath, Richard Heck, John F. Heil, Vincent F. Hendricks, Stephen Hetherington, Francis Heylighen, Kathleen Marie Higgins, Risto Hilpinen, Harold T. Hodes, Joshua Hoffman, Alan Holland, Robert L. Holmes, Richard Holton, Brad W. Hooker, Terence E. Horgan, Tamara Horowitz, Paul Horwich, Vittorio Hösle, Paul Hoβfeld, Daniel Howard-Snyder, Frances Howard-Snyder, Anne Hudson, Deal W. Hudson, Carl A. Huffman, David L. Hull, Patricia Huntington, Thomas Hurka, Paul Hurley, Rosalind Hursthouse, Guillermo Hurtado, Ronald E. Hustwit, Sarah Hutton, Jonathan Jenkins Ichikawa, Harry A. Ide, David Ingram, Philip J. Ivanhoe, Alfred L. Ivry, Frank Jackson, Dale Jacquette, Joseph Jedwab, Richard Jeffrey, David Alan Johnson, Edward Johnson, Mark D. Jordan, Richard Joyce, Hwa Yol Jung, Robert Hillary Kane, Tomis Kapitan, Jacquelyn Ann K. Kegley, James A. Keller, Ralph Kennedy, Sergei Khoruzhii, Jaegwon Kim, Yersu Kim, Nathan L. King, Patricia Kitcher, Peter D. Klein, E. D. Klemke, Virginia Klenk, George L. Kline, Christian Klotz, Simo Knuuttila, Joseph J. Kockelmans, Konstantin Kolenda, Sebastian Tomasz Kołodziejczyk, Isaac Kramnick, Richard Kraut, Fred Kroon, Manfred Kuehn, Steven T. Kuhn, Henry E. Kyburg, John Lachs, Jennifer Lackey, Stephen E. Lahey, Andrea Lavazza, Thomas H. Leahey, Joo Heung Lee, Keith Lehrer, Dorothy Leland, Noah M. Lemos, Ernest LePore, Sarah-Jane Leslie, Isaac Levi, Andrew Levine, Alan E. Lewis, Daniel E. Little, Shu-hsien Liu, Shu-hsien Liu, Alan K. L. Chan, Brian Loar, Lawrence B. Lombard, John Longeway, Dominic McIver Lopes, Michael J. Loux, E. J. Lowe, Steven Luper, Eugene C. Luschei, William G. Lycan, David Lyons, David Macarthur, Danielle Macbeth, Scott MacDonald, Jacob L. Mackey, Louis H. Mackey, Penelope Mackie, Edward H. Madden, Penelope Maddy, G. B. Madison, Bernd Magnus, Pekka Mäkelä, Rudolf A. Makkreel, David Manley, William E. Mann (W.E.M.), Vladimir Marchenkov, Peter Markie, Jean-Pierre Marquis, Ausonio Marras, Mike W. Martin, A. P. Martinich, William L. McBride, David McCabe, Storrs McCall, Hugh J. McCann, Robert N. McCauley, John J. McDermott, Sarah McGrath, Ralph McInerny, Daniel J. McKaughan, Thomas McKay, Michael McKinsey, Brian P. McLaughlin, Ernan McMullin, Anthonie Meijers, Jack W. Meiland, William Jason Melanson, Alfred R. Mele, Joseph R. Mendola, Christopher Menzel, Michael J. Meyer, Christian B. Miller, David W. Miller, Peter Millican, Robert N. Minor, Phillip Mitsis, James A. Montmarquet, Michael S. Moore, Tim Moore, Benjamin Morison, Donald R. Morrison, Stephen J. Morse, Paul K. Moser, Alexander P. D. Mourelatos, Ian Mueller, James Bernard Murphy, Mark C. Murphy, Steven Nadler, Jan Narveson, Alan Nelson, Jerome Neu, Samuel Newlands, Kai Nielsen, Ilkka Niiniluoto, Carlos G. Noreña, Calvin G. Normore, David Fate Norton, Nikolaj Nottelmann, Donald Nute, David S. Oderberg, Steve Odin, Michael O’Rourke, Willard G. Oxtoby, Heinz Paetzold, George S. Pappas, Anthony J. Parel, Lydia Patton, R. P. Peerenboom, Francis Jeffry Pelletier, Adriaan T. Peperzak, Derk Pereboom, Jaroslav Peregrin, Glen Pettigrove, Philip Pettit, Edmund L. Pincoffs, Andrew Pinsent, Robert B. Pippin, Alvin Plantinga, Louis P. Pojman, Richard H. Popkin, John F. Post, Carl J. Posy, William J. Prior, Richard Purtill, Michael Quante, Philip L. Quinn, Philip L. Quinn, Elizabeth S. Radcliffe, Diana Raffman, Gerard Raulet, Stephen L. Read, Andrews Reath, Andrew Reisner, Nicholas Rescher, Henry S. Richardson, Robert C. Richardson, Thomas Ricketts, Wayne D. Riggs, Mark Roberts, Robert C. Roberts, Luke Robinson, Alexander Rosenberg, Gary Rosenkranz, Bernice Glatzer Rosenthal, Adina L. Roskies, William L. Rowe, T. M. Rudavsky, Michael Ruse, Bruce Russell, Lilly-Marlene Russow, Dan Ryder, R. M. Sainsbury, Joseph Salerno, Nathan Salmon, Wesley C. Salmon, Constantine Sandis, David H. Sanford, Marco Santambrogio, David Sapire, Ruth A. Saunders, Geoffrey Sayre-McCord, Charles Sayward, James P. Scanlan, Richard Schacht, Tamar Schapiro, Frederick F. Schmitt, Jerome B. Schneewind, Calvin O. Schrag, Alan D. Schrift, George F. Schumm, Jean-Loup Seban, David N. Sedley, Kenneth Seeskin, Krister Segerberg, Charlene Haddock Seigfried, Dennis M. Senchuk, James F. Sennett, William Lad Sessions, Stewart Shapiro, Tommie Shelby, Donald W. Sherburne, Christopher Shields, Roger A. Shiner, Sydney Shoemaker, Robert K. Shope, Kwong-loi Shun, Wilfried Sieg, A. John Simmons, Robert L. Simon, Marcus G. Singer, Georgette Sinkler, Walter Sinnott-Armstrong, Matti T. Sintonen, Lawrence Sklar, Brian Skyrms, Robert C. Sleigh, Michael Anthony Slote, Hans Sluga, Barry Smith, Michael Smith, Robin Smith, Robert Sokolowski, Robert C. Solomon, Marta Soniewicka, Philip Soper, Ernest Sosa, Nicholas Southwood, Paul Vincent Spade, T. L. S. Sprigge, Eric O. Springsted, George J. Stack, Rebecca Stangl, Jason Stanley, Florian Steinberger, Sören Stenlund, Christopher Stephens, James P. Sterba, Josef Stern, Matthias Steup, M. A. Stewart, Leopold Stubenberg, Edith Dudley Sulla, Frederick Suppe, Jere Paul Surber, David George Sussman, Sigrún Svavarsdóttir, Zeno G. Swijtink, Richard Swinburne, Charles C. Taliaferro, Robert B. Talisse, John Tasioulas, Paul Teller, Larry S. Temkin, Mark Textor, H. S. Thayer, Peter Thielke, Alan Thomas, Amie L. Thomasson, Katherine Thomson-Jones, Joshua C. Thurow, Vzalerie Tiberius, Terrence N. Tice, Paul Tidman, Mark C. Timmons, William Tolhurst, James E. Tomberlin, Rosemarie Tong, Lawrence Torcello, Kelly Trogdon, J. D. Trout, Robert E. Tully, Raimo Tuomela, John Turri, Martin M. Tweedale, Thomas Uebel, Jennifer Uleman, James Van Cleve, Harry van der Linden, Peter van Inwagen, Bryan W. Van Norden, René van Woudenberg, Donald Phillip Verene, Samantha Vice, Thomas Vinci, Donald Wayne Viney, Barbara Von Eckardt, Peter B. M. Vranas, Steven J. Wagner, William J. Wainwright, Paul E. Walker, Robert E. Wall, Craig Walton, Douglas Walton, Eric Watkins, Richard A. Watson, Michael V. Wedin, Rudolph H. Weingartner, Paul Weirich, Paul J. Weithman, Carl Wellman, Howard Wettstein, Samuel C. Wheeler, Stephen A. White, Jennifer Whiting, Edward R. Wierenga, Michael Williams, Fred Wilson, W. Kent Wilson, Kenneth P. Winkler, John F. Wippel, Jan Woleński, Allan B. Wolter, Nicholas P. Wolterstorff, Rega Wood, W. Jay Wood, Paul Woodruff, Alison Wylie, Gideon Yaffe, Takashi Yagisawa, Yutaka Yamamoto, Keith E. Yandell, Xiaomei Yang, Dean Zimmerman, Günter Zoller, Catherine Zuckert, Michael Zuckert, Jack A. Zupko (J.A.Z.)
- Edited by Robert Audi, University of Notre Dame, Indiana
-
- Book:
- The Cambridge Dictionary of Philosophy
- Published online:
- 05 August 2015
- Print publication:
- 27 April 2015, pp ix-xxx
-
- Chapter
- Export citation
The atlas-axis complex of the Late Paleozoic Diadectomorpha and basal amniotes: defining the primitive condition of the atlas-axis complex of amniotes
- Stuart S. Sumida, R. Eric. Lombard, David S Berman
-
- Journal:
- The Paleontological Society Special Publications / Volume 6 / 1992
- Published online by Cambridge University Press:
- 26 July 2017, p. 283
- Print publication:
- 1992
-
- Article
-
- You have access Access
- Export citation
-
During the past decade, phylogenetic analyses of Late Paleozoic tetrapods have consistently demonstrated that the Permo-Pennsylvanian tetrapod suborder Diadectomorpha is closely related to more traditionally defined amniotes. Recent analyses provide two competing hypotheses of relationship: 1) the Diadectomoropha is the sister group of all amniotes, or 2) the Diadectomorpha and Synapsida comprise the most primitive clade within the Amniota. Subsequently more derived groups within the Amniota are: the reptilian family Captorhinidae, and the Protorothyrididae plus the Diapsida. The availability of well preserved atlas-axis complexes for all of the better known genera of diadectomorphs now allow a determination of the primitive condition of the atlas-axis complex for the Amniota. Further, accepted hypotheses of phylogenetic relationships among Late Paleozoic tetrapods allow mapping of features of the atlas-axis complex onto predefined topologies so that the transformations of the complex may be analyzed.
The diadectomorph atlas-axis complex may be characterized in the following manner: paired, well developed proatlases and atlantal neural arches; lack of proatlantal and atlantal neural spines with only posteriorly directed epipophyses present; an extremely robust atlantal intercentrum; tight articulation of the atlantal pleurocentrum with the dorsal aspect of the axial intercentrum preventing exposure of the former on the ventral surface of the vertebral column; a large, anteriorly directed midline projection of the axial intercentrum; a tall and well-developed axial neural spine, presumably for attachment of strong occipital muscles and ligaments. Except for the anterior projection of the axial intercentrum (which is an autapomorphic feature of diadectomorphs), basal amniotes share all of these features with diadectomorphs. Shared, derived features of the atlas-axis complex of diadectomorphs plus other basal amniotes include: 1) fusion of the axial centrum and neural arch, 2) small epipophyses of the atlantal neural arch and, with the exception of Tseajaia, 3) fusion of the atlantal pleurocentrum to the dorsal surface of the axial intercentrum.
The morphology of the atlas-axis complex alone is not sufficient to generate hypotheses of relationship between diadectomorphs and other basal amniotes. However, the atlas-axis complexes of diadectomorphs and other basal amniotes are clearly more similar to one-another than to those of other taxa.