LATE TRIASSIC TETRAPOD BIOCHRONOLOGY OF PANGAEA
LUCAS, Spencer G., New Mexico Museum of Natural History
and Science, 1801 Mountain Rd. NW, Albuquerque,
HUNT, Adrian P., Mesalands Dinosaur Museum, Mesa
Technical College, Tucumcari, NM 88401
HUBER, Philip, Dept. of Education, University of Bridgeport,
Bridgeport, CT 06601
Tetrapods provide a concise means by which Late Triassic
nonmarine strata across much of Pangaea can be correlated. Early
Carnian (Julian) faunas are poorly represented, and include Laurasian
assemblages dominated by labyrinthodonts with relatively few
thecodonts (Schilfsandstein, T-4 Morocco) and a Gondwanan
assemblage (Caturrita Fm.) marked by an abundance of
rhynchosaurids. Late Carnian (early Tuvalian) faunas are widespread,
and defined by a diverse association that includes numerous
labyrinthodonts, the last rhynchosaurs, the first definite phytosaurs,
aetosaurs and dinosaurs, dicynodonts and sphenodontids. Of
importance are the near-cosmopolitan distribution of Paleorhinus on
four continents, and it's occurrance in marine (dilleri zone) strata,
thus providing a critical tiepoint to the standard Alpine stage
chronology. Well-documented early Tuvalian faunas include those
from the basal Chinle Group, Pekin and Wolfville Fms. (Newark),
Lossiemouth Fm. (Scotland), interval T-5 (Morocco), Maleri (India)
and Ischigualasto (Argentina) Fms. and Blasensandstein. Late
Tuvalian faunas are largely restricted to North America and are
dominated by an association of metoposaurids, rutiodontid phytosaurs
and aetosaurs from the lower Chinle Group and type Pekin, Cumnock,
New Oxford, upper Stockton Fms of the Newark. Other Newark
faunas of this age include aquatic lepidosaur-dominated assemblages
from the Cow Branch and Lockatong Fms. and a terrestrial therapsid
assemblage from the Turkey Branch Fm. Late Tuvalian faunas from
other regions of Pangaea may occur in the Tiki (India) and basal Los
Colorados (Argentina) Fms., but these have not been described.
Early to middle Norian faunas are well-represented in the
middle Chinle Group, Newark Supergroup, Fleming Fjord Fm.
(Greenland), German Keuper and lower Elliot Fm. (S. Africa).
Laurasian faunas show a certain degree of provinciality, as illustrated
by the abundance of prosauropods and turtles in the Stubensandstein-
Knollenmergel and Fleming Fjord Fm. compared to the metoposaur-
phytosaur-aetosaur fauna from the middle Chinle Group.
Nonetheless, the middle Keuper and middle Chinle share a number of
taxa (pseudopalatine phytosaurs, Paratypothorax) that support their
correlation, while the Newark contains a transitional fauna that
includes indet. metoposaurs, phytosaurs and the aetosaur Aetosaurus,
a taxon common to the Stubenstandstein, Fleming Fjord Fms. and
marine (columbianus zone) strata in Italy. Laurasian late Norian-
Rhaetain faunas are characterized by a high relative abundance of
theropod dinosaurs and/or their footprints in the upper Chinle and
Newark, while coeval European faunas include a variety of
sphenodontids and mammals, in addition to dinosaurs,
crocodilomorphs and a depauperate record of largely indet.
labyrinthodonts and thecodonts. The upper Elliott and Los Colorados
faunas are marginally similar to European assemblages in terms of
composition, but lack independent age control and are tentatively
assigned a Rhaetian age.
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