Conferencias

 

INTERPRETING THE ANATOMY OF THE CAUDAL CRANIUM IN FOSSIL MAMMALS USING COMPUTED TOMOGRAPHY: TRIGONOSTYLOPS AND OTHER SOUTH AMERICAN NATIVE UNGULATES

 

ROSS D. E. MACPHEE
American Museum of Natural History
New York NY USA
macphee at amnh.org

The use of CT (computed tomography) is now a common investigatory tool in vertebrate paleontology, but maximizing what can be learned from segmental data and 3D reconstructions requires experience with interpreting morphology in different planes (transverse, sagittal, horizontal), and not only in adult specimens but across the ontogenetic spectrum. This point particularly applies to the study of anatomically complex regions such as the caudal cranium. In this talk I will discuss our recent investigation of the cranial anatomy of the late M. Eocene astrapothere Trigonostylops, with regard to 3 areas of interest using new insights developed from segmental data: (1) the effects of pneumatization on cranial morphology, and how to interpret it ontogenetically; (2) arterial and venous anatomy, with particular reference to the existence of the internal carotid artery and lateral head vein in SANUs; and (3) possible physiological implications of patterns of vasculature revealed with CT. These topics will be discussed within a broad comparative framework emphasizing traditional as well as CT-based morphological treatments of extant perissodactyls, phenacodontid “condylarths”, and other relevant placental groups. CT opens new sources of morphological characters to include in phylogenetic studies, while offering new ways of understanding functional features.

 

 

 

THE IMPORTANCE OF GEOCHRONOLOGY FOR UNDERSTANDING EARLY MESOZOIC GONDWANAN VERTEBRATE EVOLUTION

RANDALL B. IRMIS
Natural History Museum of Utah and Department of Geology & Geophysics
Salt Lake City, UT, USA
irmis at umnh.utah.edu

Determining the tempo of evolution in the fossil record requires precise and accurate geochronologic constraints. In non-marine settings, these data are also critical for correlating to the geologic timescale defined using marine biostratigraphic markers. Triassic non-marine sequences in Gondwana preserve a rich record of biotic and paleoenvironmental change that spans two mass extinctions, a number of sudden climate change events, and witness the origin of several modern vertebrate clades.  Until recently, these strata were dated using predominantly biostratigraphic means, so their absolute age and duration were unclear, as well as their precise correlation to each other and the geologic timescale. Recent geochronologic data, particularly U-Pb zircon ages, have significantly changed the age assignments for these sediments and their fossil assemblages. These dates demonstrate that some “Middle Triassic” and “Late Triassic” fossil assemblages are several million years older or younger than previously thought, changing their stage-level assignment. These data suggest that South America preserves one of the most complete records of Triassic non-marine vertebrate evolution, including the recovery from the end-Permian mass extinction as well as the origin and diversification of key clades such as dinosaurs. The new dates also suggest that the ages of other non-marine vertebrate assemblages throughout Gondwana may be less well-constrained than previously thought. This hypothesis is being tested by additional dating of other Gondwanan strata (e.g., Karoo Basin in southern Africa). Complimentary efforts in Laurasia, such as in western North America, help provide a chronostratigraphic framework that allows global correlation of key Triassic fossil archives.

 

 

 

 

34° Jornadas Argentinas de Paleontología de Vertebrados - Mendoza 2020

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