Eight, temporally successive assemblage zones of tetrapod (amphibian and reptile) fossils provide the basis for dividing Triassic time into eight land-vertebrate faunachrons (LVF). The beginning of each LVF is defined by the first appearance datum (FAD) of a widespread tetrapod genus. These LVFs, the taxa whose FADs define their beginnings, and their approximate correlation to the standard global chronostratigraphic scale (SGCS) are (ascending order): 1. Lootsbergian, FAD Lystrosaurus = late Dorashamian-Induan; 2. Nonesian, FAD Cynognathus = Olenekian; 3. Perovkan, FAD Shansiodon = Anisian; 4. Berdyankian, FAD Mastodonsaurus = Ladinian-early Carnian; 5. Otischalkian, FAD Paleorhinus = late early-early late Carnian; 6. Adamanian, FAD Rutiodon = latest Carnian; 7. Revueltian, FAD Pseudopalatus = Norian; 8. Apachean, FAD Redondasaurus = Rhaetian. These Triassic LVFs provide a framework for the correlation of Triassic nonmarine deposits with a temporal resolution comparable to the seven Triassic Stages/Ages of the SGCS.
Romer (1975; also see Cox, 1973) presented
the first global Triassic tetrapod biochronology when he identified three
successive types of land-vertebrate "faunas:" A (Early Triassic), B (Middle
Triassic) and C (Late Triassic) (Fig. 2). Cosgriff (1984) divided Romer's
division A into A1 (= Lystrosaurus biochron) and A2 (Cynognathus
biochron). Ochev & Shishkin (1989; also see Anderson & Cruickshank,
1978) recognized the same intervals as Romer, but chose to name them the
proterosuchian epoch (= A), kannemeyerioidean epoch (= B) and dinosaurian
epoch (= C).
Cooper (1982) proposed a more detailed global tetrapod biostratigraphy of the Triassic than did Romer (Fig. 2). He recognized a succession of six Triassic zones based largely on a perceived stratigraphic succession of dicynodonts (see Lucas & Wild, 1995 for a revised dicynodont bio zonation; also, note that Cooper  considered the Lystrosaurus zone to be Permian). However, Cooper's zonation has not been used by subsequent workers. The status of global Triassic tetrapod biostratigraphy and biochronology thus has not progressed much beyond that of Romer (1975), as a recently published synthesis (Ochev & Shishkin, 1989) indicates.
More detailed subdivision of Triassic time has been made in provincial biochronologies proposed for Argentina, North America and China. Bonaparte (1966, 1967, 1982) introduced a set of "provincial ages" for the Triassic of Argentina, but he never defined these terms (Fig. 2). (Lucas & Harris  did define the Chanarian as a LVF). Lucas (1993) proposed a succession of LVFs for the Chinese Early-Middle Triassic tetrapod record. Lucas & Hunt (1993) proposed Late Triassic LVFs based on the Chinle Group tetrapod record from the western United States, and Huber et al. (1993; Lucas and Huber, 1998) proposed Middle-Late Triassic LVFs based on the Newark Supergroup record of eastern North America (Fig. 2).
Lucas & Huber (1998) reviewed global
Late Triassic tetrapod biochronology and demonstrated the broad utility
of the Chinle Group tetrapod biochronology proposed by Lucas & Hunt
(1993; also see Lucas, 1997). The status of "provincial" tetrapod biochronology
of the Triassic is that schemes exist for the Argentinian and Chinese record
and for the Middle-Late Triassic record from North America. Although
I advocate a global tetrapod biochronology, this does not obviate the need
for some provincial biochronologies, whose utility as a secondary standard
(Cope, 1996) is noted below.
The terms Lystrosaurus zone, beds or fauna have been applied to a wide geographic range of strata/fossils of Lootsbergian age. The most significant vertebrate fossil assemblages of Lootsbergian age are from the upper Guodikeng and lower Jiucaiyuan formations, Junggur basin, China; Heshanggou Formation, Ordos basin, China; lower part of Fremouw Formation, Antarctica; Panchet Formation, India; Vokhmian horizon of Vetluga Series, Russian Urals; and Wordy Creek Formation, eastern Greenland.
Direct cross-correlation of the Lootsbergian
to part of the Induan is provided by the occurrence of characteristic Lootsbergian
temnospondyls in ammonite-bearing Induan strata of the Wordy Creek Formation
in eastern Greenland (Trümpy, 1961). Apparently, the beginning of
the Lootsbergian does not correspond to the beginning of the Triassic.
Indeed, the FAD of Lystrosaurus has long been assumed to equate
to the beginning of the Triassic, but a close correlation has not been
documented. Whether or not the end of the Lootsbergian correlates to the
end of the Induan also is uncertain.
Kitching (1977) reviewed the Cynognathus
Assemblage Zone localities, and Kitching (1995) provided a recent synopsis
of the stratigraphic ranges of the genera. Watson (1942) and Kitching (1977)
subdivided the Cynognathus Assemblage Zone into two subzones. Hancox
and Rubidge (1994), Hancox et al. (1995) and Shishkin et al. (1995a) divided
the Cynognathus Assemblage Zone into three successive zones: (1)
Kestrosaurus acme zone; (2) "Parotosuchus" africanus acme
zone; and (3) advanced capitosauroid zone. Kitching (1995), however,
made no attempt at subdivision, and no formal subdivisions are advocated
here, pending publication of research in progress by P.J. Hancox and his
Principal vertebrate fossil assemblages of Nonesian age come from the upper Fremouw Formation, Antarctica; Petropavlovsk Formation ("Yarenskiy horizon") in the Russian Urals; Wupatki and Torrey formations of the Moenkopi Group, Arizona-Utah, USA; Puesto Viejo andRio Mendoza formations, Argentina; lower part of Ermaying Formation, Ordos basin, China; Omingonde Formation, Namibia; lower N'tawere Formation, Zambia; K7 horizon of the Kingori Sandstone, Tanzania; and Sticky Keep Formation of Svalbard.
The occurrence of Parotosuchus in
marine Olenekian strata of the Mangyshlak Peninsula in western Kazakstan
(Lozovsky & Shishkin, 1974) is the most direct cross-correlation of
the Nonesian to the SGCS. Aphanerama or Parotosuchus records
in Svalbard, Germany and/or North America also support correlation of the
Nonesian with at least part of the Olenekian.
The beginning of the Otischalkian is the
FAD of the phytosaur Paleorhinus. The end of the Otischalkian is
the beginning of the Adamanian, which is defined by the FAD of the phytosaur
Rutiodon. The vertebrate fossil assemblage of the Colorado City
Member of the Dockum Formation, Chinle Group near the defunct town of Otis
Chalk, Howard County, Texas, USA characterizes the Otischalkian.
The following tetrapod genera are restricted to Otischalkian time and are widespread and/or common enough to be useful as index fossils: Paleorhinus, Angistorhinus, Longosuchus (= Lucasuchus), Metoposaurus, Doswellia. Besides Chinle Group correlatives, principal Otischalkian- age vertebrate assemblages are from the Sanfordian interval of the Newark Supergroup basins of eastern North America; Schilfsandstein, Kieselsandstein, Lehrbergschichten and Blasensandstein of the German Keuper; Irohalene Member (T4) of the Timesgadiouine Formation, Argana Group, Morocco; and basal part of Maleri Formation, Pranhita-Godavari Valley, India. The Otischalkian is of Carnian (late Julian-early Tuvalian) age on the SGCS based on Paleorhinus and Metoposaurusrecords in marine strata in Austria (Hunt and Lucas, 1991), palynostratigraphy (Litwin et al., 1991, 1993; Cornet, 1993) and magnetostratigraphy (Kent et al., 1995; Molina-Garza et al., 1996).
The beginning of the Adamanian is defined
as the FAD of the phytosaur Rutiodon. The end of the Adamanian is
the beginning of the Revueltian, which is defined by the FAD of the phytosaur
Pseudopalatus. The Adamanian LVF is characterized by the vertebrate
fauna of the Blue Mesa Member of the Petrified Forest Formation in the
Petrified Forest National Park, Arizona, USA. The following tetrapod taxa
are restricted to Adamanian time and are widespread and/or common enough
to be useful as index fossils: Scaphonyx, Stagonolepis and Rutiodon-grade
phytosaurs, including Leptosuchus and Smilosuchus.
Besides the Chinle Group correlatives, major Adamanian-age vertebrate faunas are those of the Conewagian interval of the Newark Supergroup basins of eastern North America; Lossiemouth Sandstone Formation, Scotland; Ischigualasto Formation, Argentina; and upper Santa Maria Formation, Brazil.
The Adamanian is of latest Carnian age based mostly on palynostratigraphy and magnetostratigraphy (see references cited above under marine cross-correlation of the Otischalkian). In West Texas, Otischalkian and Adamanian tetrapod assemblages are stratigraphically superposed. Therefore, Adamanian time is a younger portion of the Tuvalian than the Otischalkian. Norian (Revueltian LVF) vertebrates are stratigraphically above Adamanian vertebrates in Arizona, New Mexico and Texas. Therefore, Adamanian vertebrates are the youngest Carnian vertebrates known. Like the Otischalkian, the Adamanian is relatively short, easily recognized over a broad area and relatively precisely correlated to the SGCS.
Revueltian time begins with the FAD of
the phytosaur Pseudopalatus. The end of the Revueltian is the beginning
of the Apachean, which is defined by the FAD of the phytosaur Rendondasaurus
The Revueltian LVF is characterized by the vertebrate fossil assemblage
of the Bull Canyon Formation in east-central, New Mexico, USA. I term this
the Pseudopalatus Assemblage Zone.The following tetrapod taxa are restricted
to Revueltian time and are widespread and/or common enough to be useful
as index fossils: Typothorax, Aetosaurus and Pseudopalatus-grade
phytosaurs, including Nicrosaurus and Mystriosuchus.
Besides Chinle Group correlatives, the principal Revueltian-age tetrapod assemblages are those of the Newark Supergroup of eastern North America of Neshanician and Cliftonian (part) age; Ørsted Dal Member of the Fleming Fjord Formation, Greenland; Lower and Middle Stuben sandstein of the German Keuper; Zorzino Limestone and Forni Dolomite, northern Italy; and lower part of Dharmaran Formation, India.
Palynostratigraphy, magnetostratigraphy and sequence stratigraphy suggests the type Revueltian assemblage is of Norian age (Lucas, 1997). Based on stratigraphic position, magneto stratigraphy, and palynomorphs, the Neshanician LVF is of early to middle Norian age. Strati graphic position, magnetostratigraphy, and palynomorphs indicate the Cliftonian LVF is of late Norian-Rhaetian age. The Italian records of Aetosaurus provide direct evidence that at least part of the Revueltian = middle Norian (Alaunian). Revueltian correlates approximately with the entire Norian, which is consistent with the evidence cited above (Lucas, 1997). However, whether or not the beginning and end of the Revueltian and Norian are exact equivalents is unclear.
By any recent Triassic numerical timescale (e.g., Harland et al., 1990; Gradstein et al., 1995; Kent et al., 1995; Gradstein and Ogg, 1996), the duration of the Norian is at least 10 million years. This means the Revueltian is one of the longest Triassic LVFs recognized here. It merits subdivision, as Hunt and Lucas (1993) suggested, perhaps along the lines of the Cliftonian- Neshanician subdivision used in the Newark Supergroup, but no subdivision is attempted here.
Apachean time begins with the FAD of the
phytosaur Redondasaurus. The end of Apachean time is the FAD of
the crocodylomorph Protosuchus. The Apachean LVF is characterized
by the vertebrate fossil assemblage of the Redonda Formation (Chinle Group)
in east-central New Mexico, USA. The following tetrapod genera are restricted
to Apachean time and are widespread and/or common enough to be useful as
index fossils: Redondasaurus, Redondasuchus, Riojasaurus.
Principal vertebrate fossil assemblages of Apachean age are the Whitaker quarry in the Rock Point Formation of the Chinle Group at Ghost Ranch, New Mexico, the Cliftonian LVF assem blages, in part, of the Newark Supergroup and that of the Coloradan LVF of Argentina. Some of the fissure fill assemblages in the uppermost Mercia Mudstone Group and/or lowermost Penarth Group of the United Kingdom (Benton & Spencer, 1995) may be Apachean correlatives. However, their ages are problematic, in part, because they lack identifiable phytosaurs, aetosaurs or metoposaurs. Some of the so-called Rhaetian vertebrate sites in France, such as Saint-Nicolas-de-Port, may be Apachean correlatives as well (Lucas & Huber, 1998).
Correlation of the Apachean to the SGCS must be based on indirect lines of evidence. Apachean time is post-Revueltian (~ Norian) and pre-Jurassic, so I tentatively correlate it to the Rhaetian. However, whether or not it is in part of late Norian age is uncertain. Magnetostratigraphy of the uppermost Chinle Group in eastern New Mexico (Molina et al., 1996), correlated to the Newark Supergroup magnetostratigraphy (Kent et al., 1995), also suggests the Apachean is latest Triassic ("Norian-Rhaetian").
The Apachean is the most difficult Triassic LVF to correlate globally. This almost certainly reflects a provincialization of the global tetrapod fauna. Some of the apparent endemism of Apachean land vertebrate assemblages may also be due to facies, sampling and taphonomic biases. Rather than recognize a global Apachean LVF, it may be necessary to recognize two or more provincial LVFs during this time interval.
There is no evidence that the Apachean is in part of Jurassic age. The FAD of the crocodylo morph Protosuchus appears to correspond closely to the beginning of the Jurassic. Protosuchus occurs in the McCoy Brook Formation (Newark Supergroup), the upper Stormberg Group of South Africa and the Dinosaur Canyon Member of the Moenave Formation in Arizona (Colbert & Mook, 1951; Sues et al., 1996). The Moenave record of Protosuchus is stratigraphically super posed above Apachean-age body fossil assemblages of the uppermost Chinle Group (Lucas et al., 1997).
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