Our Upcoming Speaker

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MONDAY, May 3, 2021 AT 7:00 PM Central Time USA

Title: "An Ichnological Perspective on Some Major Events of Paleozoic Tetrapod Evolution"

Speaker: Dr. Spencer Lucas, Curator of Paleontology at the New Mexico Museum of Natural History and Science

Abstract: Tetrapod trace fossils (primarily footprints) provide significant insight into some major events of the Paleozoic evolution of tetrapods. The oldest fossils of tetrapods are Middle Devonian footprints from Ireland. Bona fide Devonian tetrapod footprints indicate lateral sequence walking by quadrupedal tetrapods with a smaller manus than pes. These trackways indicate that tetrapods other than “ichthyostegalians” remain to be discovered in the Devonian body-fossil record. Devonian tetrapod footprints are from nonmarine paleoenvironments, so they do not support a marginal marine/marine origin of tetrapods. Nevertheless, the Devonian tetrapod footprint record is too sparse to be of paleobiogeographic significance and to evaluate unsubstantiated claims of Late Devonian tetrapod mass extinctions. “Romer’s gap”, a supposed paucity of Early Mississippian terrestrial fossils, has largely been filled by sampling and description of already known fossils. It includes the first substantial assemblage of tetrapod footprints, from Blue Beach, Nova Scotia, Canada. This assemblage consists of footprints of small and large temnospondyls and reptiliomorphs, which supports the concept that the Carboniferous diversification of terrestrial tetrapods had begun during (or before) Tournaisian time. No definite pre-Pennsylvanian amniote footprints are known, so the Early Pennsylvanian age of the oldest amniote footprints and body fossils is the same. The Kasimovian revolution was a prolonged and complex change across the Middle-Late Pennsylvanian boundary from the “coal forests” to a more xerophytic vegetation accompanied by changes and “sluggish evolution” in the marine biota and the appearance of new tetrapod taxa in the body-fossil record, notably the oldest high fiber herbivores, the diadectomorphs and the edaphosaurid eupelycosaurs. However, the tetrapod footprint record changes little during the Kasimovian and documents much older records of diadectomorph and eupelycosaur (possible edaphosaurs) footprints in the Bashkirian, thus diminishing the extent of tetrapod originations during the Kasimovian revolution. The Permian tetrapod footprint record is much more extensive and better understood than the Carboniferous footprint record. Tetrapod footprints confirm the body-fossil record in demonstrating no significant changes in tetrapod evolution took place across the Carboniferous- Permian boundary. The late early Permian sauropsid radiation is best documented by a change in the tetrapod footprints from synapsid- and non-amniote-dominated assemblages to those dominated by the footprints of captorhinomorphs and parareptiles. Early Permian tetrapod footprints from eolian sediments demonstrate the colonisation of deserts by tetrapods. Olson’s gap is a global hiatus in the tetrapod body-fossil record during which eupelycosaur-dominated assemblages of the early Permian were replaced by therapsid-dominated assemblages of the middle-late Permian. The gap in the body fossil record corresponds to most of Kungurian time, and the tetrapod footprint record indicates an abundance of captorhinomorph footprints and very few eupelycosaur footprints just before and during Olson’s gap, suggesting that the extinction of the eupelycosaurs had already begun well before the first appearance of therapsids. The substantial extinction of dinocephalian therapsids and other tetrapods at approximately the end of the middle Permian, the dinocephalian extinction event, is well documented by the tetrapod footprint record in paleoequatorial Pangea, where there is a paucity of tetrapod body fossils during this interval. The lack of an end-Permian tetrapod mass extinction finds support in the tetrapod footprint record because most late Permian tetrapod footprint ichnogenera continue into the Triassic. Late Permian archosauriform footprints add evidence that their diversification, and the upright gait, began during the Permian. Most Paleozoic tetrapod trackways indicate quadrupedal lateral sequence walking with a sprawling gait, but relatively narrow gauge tetrapod trackways as old as Carboniferous may indicate some semi-upright to upright walking. Definite upright walking is demonstrated by late Permian therapsid and archosauriform footprints, and no know footprints of bipedal tetrapods are known from Paleozoic strata, although a few Permian tetrapod taxa known from skeletons may have been bipeds. Besides footprints, other Paleozoic tetrapod trace fossils (bromalites, burrows and dentalites) are too poorly known and too little studied to provide much insight into Paleozoic tetrapod evolution. Nevertheless, the tetrapod footprint record documents key events in Devonian-Permian tetrapod evolution and needs to be part of a complete understanding of Paleozoic tetrapod evolutionary history.  


About the Speaker (from the New Mexico Museum of Natural History and Science website: http://www.nmnaturalhistory.org/paleontology-curators/spencer-g-lucas-ph-d): Spencer G. Lucas received a B. A. from the University of New Mexico (1976) and a M. S. (1979) and Ph. D. (1984) from Yale University. As a paleontologist and stratigrapher, he specializes in the study of late Paleozoic, Mesozoic and early Cenozoic vertebrate fossils and continental deposits, particularly in the American Southwest. Lucas has extensive field experience in the western United States as well as in northern Mexico, Costa Rica, Kazakhstan, Nicaragua, Soviet Georgia and the People's Republic of China. He has published more than 1000 scientific articles, co-edited 14 books and authored three books.
Lucas’s scientific career began with research on Paleocene-Eocene mammals, particularly from the San Juan Basin, New Mexico. Field research by Lucas and his collaborators in the San Juan Basin during the last 35 years resulted in the collection of thousands of Late Cretaceous, Paleocene and Eocene vertebrate fossils and led to major revisions of the lithostratigraphy and correlation of the Upper Cretaceous-Eocene strata in this region. Diverse research by Lucas on Paleocene-Eocene mammals resulted in major contributions to the taxonomy, evolution and biostratigraphy of several groups, including condylarths, pantodonts, uintatheres, pyrotheres, taeniodonts, tillodonts, entelodonts, brontotheres and rhinocerotoids.
Beginning in the 1980s, Lucas worked extensively on nonmarine Triassic stratigraphy and biostratigraphy, especially in the western United States. In the 1990s, this became the basis for developing a global Triassic timescale based on tetrapod evolution that provides a framework for ordering and correlating tetrapod evolution during the Triassic. Lucas has also developed a similar tetrapod-based timescale for the Permian Period, and made diverse contributions to Jurassic, Cretaceous and Cenozoic vertebrate biostratigraphy and biochronology.Lucas also worked on diverse aspects of Triassic biostratigraphy, magnetostratigraphy and correlation in North America, Europe, Asia and South America. He has been a Voting Member of the Subcommission on Triassic Stratigraphy (International Commission on Stratigraphy) since 1992. He has been a corresponding member of both the Permian and the Carboniferous Subcommissions for about a decade.
Beginning in 1985, Lucas took an active role in the New Mexico Geological Society (to which he was elected an Honorary Member in 1994). He served as managing editor of the New Mexico Geological Society Guidebooks from 1987 through 1991, has co-organized 11 field conferences of the society and contributed extensively to its guidebooks and other publications. Lucas also worked extensively to develop a fossil collection at the New Mexico Museum of Natural History and Science. The Museum now boasts a collection of more than 70,000 catalogued fossils, including world class collections of nonmarine Triassic, Cretaceous, Paleocene and Eocene vertebrates, as well as the largest and most significant Permian footprint collection.
As an exhibit curator, Lucas has been responsible for most of the scientific content of the three Mesozoic exhibit halls at the New Mexico Museum of Natural History and Science: “Dawn of the Dinosaurs: Triassic New Mexico,” “Jurassic: Age of Super Giants,” and “Cretaceous: New Mexico’s Seacoast.” In 1991, Lucas launched the new journal “Bulletin of the New Mexico Museum of Natural History and Science” to publish research on natural history, especially related to New Mexico. As of 2015, 67 separate bulletins have been published in this series, mostly on paleontology, with contributions from hundreds of scientist worldwide.Lucas’s research on fossils has included original contributions to many groups, including palynomorphs, charophytes, late Paleozoic-Mesozoic megafloras, conodonts, fusulinids, brachiopods, mollusks (especially Triassic and Cretaceous ammonites), fishes and many different kinds of amphibians, reptiles and mammals. His recent research objectives have focused on Upper Paleozoic stratigraphy and biostratigraphy, particularly the placement and correlation of the Carboniferous-Permian boundary.

Recent publications:

  1. Joyce, W.G., Lucas, S.G., Scheyer, T.M., Heckert, A.B., and Hunt, A.P. 2009, A thin-shelled reptile from the Late Triassic of North America and the origin of the turtle shell: Proc. R. Soc. B. vol. 276 pp. 507–513. PDF (590K)
    Lucas, S.G. 2009, Global Jurassic tetrapod biochronology; in Volumina Jurassica, vol. 6 pp. 99–108. PDF (396K)
    Renesto, S.C., Spielmann, J.A., and Lucas, S.G. 2009, The oldest record of drepanosaurids (Reptilia, Diapsida) from the Late Triassic (Adamanian PlaceriasQuarry, Arizona, USA) and the stratigraphic range of the Drepanosauridae: N. Jb. Geol. Paläont. Abh. vol.252 pp. 315–325. PDF (1.8M)
    Heckert, A.B., Lucas, S.G., Rinehart, L.F. and Hunt, A.P. 2008, A new genus and species of sphenodontian from the Ghost Ranch Coelophysis Quarry (Upper Triassic: Apachean), Rock Point Formation, New Mexico, USA: Palaeontology, vol.51/4, pp. 827–845. PDF (1.6M)
    Minter, N.J., Lucas, S.G., Lerner, A.J and Braddy, S. J. 2008, Augerinoichnus helicoidalis, a new helical trace fossil from the nonmarine Permian of New Mexico: Journal of Paleontology, vol.82, pp.1201–1206. PDF (4.7M)

MONDAY, May 3, 2021 AT 7:00 PM Central Time, USA
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