Triassic land vertebrate faunachrons

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Land vertebrate faunachrons (LVFs) are biochronological units used to correlate and date terrestrial sediments and fossils based on their tetrapod faunas. [1] First formulated on a global scale by Spencer G. Lucas in 1998, LVFs are primarily used within the Triassic Period (252 - 201 Ma), [1] though Lucas later designated LVFs for other periods as well. [2] Eight worldwide LVFs are defined for the Triassic. The first two earliest Triassic LVFs, the Lootsbergian and Nonesian, are based on South African synapsids and faunal assemblage zones estimated to correspond to the Early Triassic. These are followed by the Perovkan and Berdyankian, based on temnospondyl amphibians and Russian assemblages estimated to be from the Middle Triassic. The youngest four Triassic LVFs, the Otischalkian, Adamanian, Revueltian, and Apachean, are based on aetosaur and phytosaur reptiles common in the Late Triassic of the southwestern United States. [1] [3] [4]

Contents

The LVF system, though widely used, is also a controversial application of biostratigraphy, as many Triassic tetrapods are rife with complications which endanger their utility as index fossils. Limited occurrences, inaccurate age estimates, overlapping LVF faunas, or taxonomic disagreement may jeopardize global correlations between Triassic tetrapods. This could render some LVFs as misleading assessments of Triassic faunal change through time. [5] [6] [7] [8] Regardless, Late Triassic phytosaurs are considered to have strong biostratigraphic utility even among detractors of Lucas's system. [9]

Lucas's LVFs

Tetrapod biostratigraphy has been used for the Triassic of South Africa since 1906 and Argentina since 1966, [6] but without much connection to global faunas. [1] Starting in 1993, New Mexico Museum of Natural History and Science paleontologist Spencer G. Lucas and his colleagues began to define tetrapod biostratigraphy intervals in the Triassic of China [10] and eastern [11] and western [12] North America. These named biostratigraphic intervals were inspired by the Land Mammal Age (LMA) system already in use for Cenozoic faunal assemblages.

Triassic tetrapod biozones, under the term "land vertebrate faunachrons" (LVFs) were formalized on a global level by Lucas in 1998. They were diagnosed by a primary index fossil (a particular genus of widespread time-constrained tetrapod) and characterized by a faunal type assemblage (distinguishing collection of taxa) from a fossiliferous geological formation. Together, the defining index fossil and assemblage could be used to correlate fossil assemblages worldwide. [1] Updates to this system have been published continuously for Triassic LVFs, which remain a heavily-discussed topic in the study of Triassic chronology. [13] [3] [14] [4] Lucas has also defined LVFs for the Permian, [2] [15] [16] Jurassic, [17] and Carboniferous, [18] though these are not as widely used as his Triassic LVFs.

Later authors characterized Lucas's LVFs as "interval eubiochrons". This means that they correspond to a segment of time (and strata) between two paleobiological events: the first appearance datum (FAD) of one index taxon and the FAD of another. [9] A first appearance datum is a point in the geological record with the earliest known fossil of a given animal, which can estimate when that animal speciates or evolves into existence. As an example, the Lootsbergian LVF is defined as the period of time between the FAD (estimated speciation) of Lystrosaurus and the FAD (estimated speciation) of Cynognathus . Some taxa which are index fossils for one stage may persist into a later stage. [1]

List of Triassic LVFs

LVFs of the Triassic Period from youngest to oldest:

LVF nameNamesakePrimary index fossilOther index fossilsProposed age estimate
(but see below)		Type assemblageOther correlated assemblages
ApacheanApache Canyon, New Mexico, USA [12]
Redondasaurus bermani at CMNH 04.jpg

Redondasuchus , Riojasaurus late Norian to Rhaetian Redonda Formation, New Mexico, USA Rock Point Formation (Chinle Group, New Mexico, USA), Wingate Sandstone (Utah, USA), upper "Cliftonian" strata of the Newark Supergroup (eastern USA), Trossingen Formation (Germany / Switzerland), [3] upper Arnstadt Formation (Germany), [3] Los Colorados Formation? (Argentina), Quebrada del Barro Formation? (Argentina), [3] Lower Elliot Formation? (South Africa), upper Mercia Mudstone Group? (UK), lower Penarth Group? (UK), Rhaetian fissure fills? (UK)
RevueltianRevuelto Creek, New Mexico, USA [12]
Typothorax coccinarum cropped.jpg

Revueltosaurus, [3] Aetosaurus, Rioarribasuchus, [3] Pseudopalatus-grade phytosaurs, Eudimorphodon [3] early to middle Norian

(but see below)

 Bull Canyon Formation, New Mexico, USA Painted Desert Member / Petrified Forest Formation (Chinle Group, Arizona / New Mexico, USA), Owl Rock Member (Chinle Formation, Arizona, USA), [3] "Neshanician" and lower "Cliftonian" strata of the Newark Supergroup (eastern USA), Fleming Fjord Formation (Greenland), Stubensandstein (Germany), Lisowice (Poland), [19] [20] Calcare di Zorzino (Italy), Dolomia di Forni (Italy), lower Dharmaran Formation (India), Los Colorados Formation? (Argentina), [4] Quebrada del Barro Formation? (Argentina), [4] Lower Elliot Formation? (South Africa) [4]
Adamanian Adamana, Arizona, USA [12]
Smilosuchus adamanensis flipped.jpg

Rutiodon -grade phytosaurs (including Leptosuchus and Smilosuchus )
 Stagonolepis, Spinosuchus , [3] Colognathus , [3] Tecovasaurus , [3] Crosbysaurus [3] late Carnian

(but see below)

 Blue Mesa Member, Chinle Formation, Arizona, USA Bluewater Creek Formation (Chinle Group, New Mexico, USA), Santa Rosa Formation (New Mexico, USA), Garita Creek Formation (New Mexico, USA), Tecovas Formation (Texas, USA), "Conewagian" strata of the Newark Supergroup (eastern USA), Lossiemouth Sandstone (Scotland, UK), Krasiejów (Poland), [3] Lehrberg Schichten / Blasensandstein / Kieselsandstein (Germany), [3] DeGeerdalen Formation (Svalbard), [4] Ischigualasto Formation (Argentina), upper Santa Maria Formation (Brazil), Caturrita Formation (Brazil), [3] upper Maleri Formation (India), Isalo II (Madagascar) [3]
Otischalkian Otis Chalk, Texas, USA [12]
Paleorhinus cropped.png

Metoposaurus, Placerias, [3] Hyperodapedon, [3] Doswellia, Angistorhinus, Longosuchus middle Carnian Colorado City Formation, Texas, USA Popo Agie Formation (Wyoming, USA), Salitral Formation (New Mexico, USA), "Sanfordian" strata of the Newark Supergroup (eastern USA and Canada), Stuttgart Formation (Germany), Timezgadiouine Formation (Irohalene Member, Morocco), lower Maleri Formation (India), Tiki Formation (India), [4] Madygen Formation? (Kyrgyzstan)
Berdyankian Berdyanka River, Russia
Mastodonsaurus DB.jpg

Massetognathus, Dinodontosaurus, Stahleckeria late Anisian to early Carnian [4] Bukobay Formation, Russia Lower Keuper (Germany), Chañares Formation (Argentina), lower Santa Maria Formation (Brazil), upper Omingonde Formation (Namibia) [4]
Perovkan Perovka, Russia
Eocyclotosaurus wellesi1DB.jpg

Eryosuchus , Paracyclotosaurus , [3] Scalenodon , Shansiodon , Parakannemeyeria , Sinokannemeyeria , " Kannemeyeria cristarhynchus ", [3] Arizonasaurus [3] Anisian Donguz Formation, Russia Moenkopi Formation (Holbrook and Anton Chico members, USA), lower Wolfville Formation (Nova Scotia, Canada), Otter Sandstone (UK), Upper Buntsandstein (Germany / France), lower Kelamayi Formation (China), upper Ermaying Formation (China), Yerrapalli Formation (India), [3] Cynognathus Assemblage Zone (Subzone C, South Africa), [3] Omingonde Formation (Namibia), [3] Manda Beds (Tanzania)
Nonesian Nonesi's Nek Pass, South Africa
Cynognathus NT small.jpg

Parotosuchus, Odenwaldia, [3] Trematosaurus, [3] Trematosuchus, Diademodon, Trirachodon, Kannemeyeria simocephalus, Erythrosuchus [3] Olenekian Cynognathus Assemblage Zone (Subzones A-B), South Africa Moenkopi Formation (Torrey and Wupatki members, USA), Sticky Keep Formation (Svalbard), Middle Buntsandstein (Germany), [3] Yarenskian Gorizont (Russia), lower Ermaying Formation (China), Puesto Viejo Group (Argentina), Rio Mendoza Formation (Argentina), lower Zarzaïtine Formation (Algeria), lower Ntawere Formation (Zambia), Kingori Sandstone (Tanzania), upper Fremouw Formation (Antarctica)
Lootsbergian Lootsberg Pass, South Africa
Lystr georg1DB.jpg

Wetlugasaurus , Tupilakosaurus , Luzocephalus , Lydekkerina , Scaloposaurus , Thrinaxodon , Procolophon , Prolacerta , Proterosuchus latest Permian (Changxingian) to Induan Lystrosaurus Assemblage Zone, South Africaupper Guodikeng Formation (China), lower Jiucaiyuan Formation (China), Heshanggou Formation (China), lower Fremouw Formation (Antarctica), Panchet Formation (India), Wordie Creek Formation (Greenland), Vokhmian Gorizont (Russia), [3] Sludkian Gorizont (Russia), [3] Ustmylian Gorizont (Russia), [3] Sanga do Cabral Formation (Brazil), [3] Rewan Formation (Australia), [3] Arcadia Formation (Australia) [3]

Criticism

Several paleontologists have independently questioned the validity of Lucas’s system, criticizing its inconsistent and often contradictory approach to taxonomy and faunal correlations. [5] [6] [7] [8]

Endemic index taxa

Many index taxa are very rare or endemic to a single continent, and have no relevance to a global biostratigraphy system. These include Doswellia , Longosuchus , Typothorax , “ Pseudopalatus ” ( Machaeroprosopus ), Redondasaurus , and Redondasuchus , among others. [5] [6] [7] [21] For the Berdyankian LVF, very few species are shared between the index assemblage (the Bukobay Formation of Russia) and other correlated assemblages. Direct relationships between Russian, German, and South American dicynodonts are conjectural and based on undiagnostic European fragments. [5] [7]

Imprecise or inaccurate time scales

Index taxa for a given LVF often range into the succeeding LVF, blurring the distinction between the two time periods. Angistorhinus , Hyperodapedon , Paleorhinus / Parasuchus (all Otischalkian index taxa) range into the Adamanian, fossils referred to Rutiodon (an Adamanian index taxon) range into the Revueltian, and Metoposaurus can be found throughout the Otischalkian, Apachian, and Revueltian LVFs. [5] [6] [7] [21]

Lucas's approach to correlating LVFs with global marine stages has been met with criticism. The Triassic timescale is under constant revision from a series of age dating methods, including magnetostratigraphy, cyclostratigraphy, radiometric dating, and biozones of marine invertebrates such as conodonts and ammonoids. [8] [21] However, there are only a few areas where fossils of Triassic land tetrapods and marine organisms overlap, mostly restricted to coastal sediments in central Europe. Palynomorph and conchostracan biozones can help correlate terrestrial strata to an extent. One complication is that Lucas's view of the Late Triassic time scale contradicts the consensus established by other biostratigraphers. Most paleontologists estimate that the three stages of the Late Triassic (Carnian, Norian, and Revueltian) are strongly unequal in size, with the Norian far longer than the Carnian. Under this consensus "long-Norian" hypothesis, the Carnian-Norian boundary is close to 228 Ma. Lucas, on the other hand, prefers a "short-Norian" perspective, with a lengthier Carnian stage and a Carnian-Norian boundary at around 220 Ma. [8]

For example, Lucas has maintained that the lower part of the Chinle Formation (the Blue Mesa Member and equivalent units) is Carnian (>220 Ma) in age. This was justified by the assumption that fossils of Stagonolepis , a European aetosaur, can be found in North and South America, allowing correlation between these regions. However, this proposed widespread occurrence of Stagonolepis is a debatable, as many species assigned to the genus may not be closely related (see below). [1] [3] [6] [21]

According to the "short-Norian" interpretation, these lower Chinle Formation, and other strata of the Adamanian LVF, would be firmly pre-Norian in age, suggesting that any taxonomic change between the Adamanian and Revueltian represents a Carnian-Norian extinction event. However, the consensus "long-Norian" interpretation firmly places Adamanian strata of North America into the Norian stage (<228 Ma). The Norian age of the lower Chinle Formation has been independently confirmed by U-Pb dating and magnetostratigraphic correlations to global time scales. [8] [27] [28] Conversely, other "Adamanian" strata, such as fossiliferous layers in the lower Ischigualasto Formation of Argentina, can be assigned to the late Carnian (~231 Ma). [6] [29] This supports the conclusion that LVFs such as the Adamanian are fraught with uncertain time estimates brought on by weak correlations on a global scale. [6] [8]

Some authors have elected to ignore LVFs in favor of older and more localized biostratigraphic units. Named tetrapod assemblages zones (AZs) were well-established for the Triassic of Gondwana prior to the LVF, and recent updates have helped to constrain these units with greater clarity and agreement than global correlations. In Argentina, Bonaparte (1966) established the Chanarian (named after the Chañares Formation) and the Ischigualastian (named after the Ischigualasto Formation). Equivalents faunas are easily traced across Brazil, Africa, and India. These two biostratigraphic zones correlate with Lucas's Berdyankian, Otischalkian, and Apachean LVFs, but do not precisely overlap in time with those LVFs. Moreover, aetosaurs and phytosaurs, which are common in the Northern Hemisphere, are rarer and more scattered in the Southern Hemisphere. As a result, Gondwanan assemblage zones are defined by more common Southern taxa. For example, the Ischigualastian zone is defined by the rhynchosaur Hyperodapedon and the cynodont Exaeretodon, as well as the aetosaur Aetosauroides and herrerasaurid dinosaurs. [6]

Taxonomic uncertainty and dubious correlations

Mastodonsaurus, a purported index fossil of the Berdyankian LVF Mastodonsaurus giganteus.JPG
Mastodonsaurus , a purported index fossil of the Berdyankian LVF

Some correlations are based on connections between fragmentary or poorly-constrained taxa rather than direct correlations between type assemblages or LVF-defining index taxa. For example, the Ermaying Formation of China is correlated with the Moenkopi Formation of the United States via a tenuous (and likely unjustifiable) comparison between proposed erythrosuchid fossils. The primary index fossil of the Perovkan LVF, Eocyclotosaurus , is absent from China. [5] [7]

One particularly contradictory index fossil is Mastodonsaurus , the defining index fossil of the Berdyankian LVF. Fossils referable to this genus can be found across Ladinian-age Europe, but the proposed Russian species (M. torvus) may be unrelated to the endemic German type species (M. giganteus). Moreover, if one approaches Mastodonsaurus from a broader taxonomic perspective (as expected if M. torvus is included), they must also incorporate Anisian and Carnian material referred to the genus, including the small species “Heptasaurus” cappelensis . This precludes any reason to use Mastodonsaurus as a time-constrained index taxon. [5] [7]

Some LVFs are based on evolutionary grades as index taxa. This ignores the potential for high diversity and long temporal ranges within a given grade, and may lead to arbitrary and subjective inclusion or exclusion of descendant taxa. “ Stagonolepis ”, in its broadest form, is a wastebasket taxon of basal aetosaurs ranging through the Otischalkian and Apachean. Lucas’s usage of Stagonolepis lumps in many genera separated by other authors, such as Aetosauroides and Calyptosuchus . [6] [7] A similar situation occurs in Paleorhinus/Parasuchus, which has historically been used as a persistent grade of early phytosaurs. On the other hand, the characteristic phytosaur (Redondasaurus) and aetosaur (Redondasaurus) genera of the Apachean LVF are very similar to, and perhaps synonymous with, index taxa of the underlying Revueltian LVF: “Pseudopalatus” (Machaeroprosopus) and Typothorax, respectively. [5] [7]

Martz & Parker (2017) revision

Although the utility of a global LVF system is questionable, LVF-derived biostratigraphy may be useful in limited circumstances. Phytosaurs in particular have played a large role in the tetrapod biostratigraphy of the Chinle and Dockum Group of the southwest United States. A revision of the LVF system in this narrow context was undertaken by Jeff Martz and Bill Parker (2017), retaining several names and concepts previously used by Lucas and colleagues. [9]

Martz and Parker argued that the term "faunachron" was misleading and redundant, as each "faunachron" is bound by a single taxon rather than an assemblage (fauna) of multiple taxa. They preferred using a specific type of interval biozone known as a teilzone, referring to a local interval of strata equivalent to an interval of time. [9] [30] The base of each teilzone was marked by the Lowest known Occurrence (LOk) of a particular category of phytosaur, i.e. the oldest layer where fossils of that category are found in the study area. LOks are local points in time and stratigraphy, disregarding occurrences in other regions or the estimated time of speciation. For the Otischalkian, Adamanian, and Revueltian, the top of each teilzone is marked by the LOk of a more exclusive subgroup of phytosaurs. The top of the Apachean is marked by the LOk of Protosuchus , an Early Jurassic crocodylomorph, as with Lucas's system. [9]

"Faunachrons" could also be defined beyond the constraints of teilzones; other biozonation categories include holochronozones (a stratigraphic interval, involving multiple study areas) and holochrons (an estimated time interval, involving the time of speciation or immigration into the region). Each phytosaur-based "faunachron" could be considered a teilzone (in local biostratigraphy), an estimated holochronozone (in regional chronostratigraphy), or an estimated holochron (in regional biochronology). [9]

One complication in defining biozones based on phytosaurs is instability in phytosaur systematics. Many proposed phytosaur taxa are dubious, paraphyletic (such as Leptosuchus and Machaeroprosopus) or have unclear relationships to each other. Nevertheless, a series of nested clades is apparent in most recent overviews. Rather than relying on a single index taxon per biozone, Martz and Parker allowed multiple representatives per a given stage of phytosaur evolution. These representatives were chosen based on their occurrence in the southwest United States, commonness, and relatively stable phylogenetic position despite paraphyly in some circumstances. [9]

NameBase-defining eventRepresentative phytosaursEstimated ageIncluded Chinle unitsIncluded Dockum units
ApacheanLOk of " Redondasaurus ""Redondasaurus" (subgenus of Machaeroprosopus?) Rhaetian (207-202 Ma)
RevueltianLOk of Pseudopalatinae (= Mystriosuchini) Machaeroprosopus ( sensu lato )middle to late Norian (Alaunian to Sevatian, 215-207 Ma)
AdamanianLOk of Leptosuchomorpha Smilosuchus , Leptosuchus , "Phytosaurus" doughtyiearly to middle Norian (Lacian to early Alaunian, 224-215 Ma)
OtischalkianLOk of Phytosauria Wannia , Parasuchus (Paleorhinus) bransoni earliest Norian (earliest Lacian, 227-224 Ma)

Adamanian-Revueltian turnover

Although most LVFs or equivalent concepts are not marked by major biotic changes, one exception is apparent in the southwest United States. The boundary between the Adamanian and Revueltian zones is marked by a faunal turnover, an event where several tetrapod species quickly disappear from the fossil record as others appear for the first time. At Petrified Forest National Park, the event occurs in the Jim Camp Wash beds. This sediment layer is positioned in the middle of the Chinle Formation's Sonsela Member, and would have been deposited around 215 million years ago. Trilophosaurus , Poposaurus , Desmatosuchus , dicynodonts, and non-mystriosuchin phytosaurs are extirpated from the area around this time, while metoposaurs and allokotosaurs [31] as a whole decline in abundance. New species of aetosaurs and phytosaurs replaced losses across the purported boundary event. Palynomorph assemblages overturn to more dry adapted species, and a higher concentration of pedogenic carbonate nodules may also support increasing aridity. [21] [31]

The cause and relevance of this turnover is debatable, as it may indicate only a small localized extinction. The Manicouagan Impact, the second-largest bolide impact of the Mesozoic Era (besides the Chicxulub Impact which caused the K-Pg Mass Extinction at 66 Ma), is dated to around 215.4 Ma. [32] [33] While certainly large enough to momentarily devastate areas near the impact point in Quebec, broader environmental effects of the Manicouagan impact are mostly conjectural. [8] Besides the Adamanian-Revueltian turnover, the impact has also been linked to a minor marine extinction in eastern Panthalassa. [34]

Alternatively, the Adamanian-Revueltian turnover may be a consequence of the gradual aridification of western Pangea as it drifted north into arid latitudes. [31] Comparative estimates of extinction rates and occurrences find little support for a synchronized Adamanian-Revueltian turnover, and instead support a model where extinctions are stretched out over several million years. For most species, extinction probabilities are "decoupled" in time from other species, as well as geological or climatological drivers. The only plausible correlation is between the Manicouagan Impact and palynomorph turnover, and even then the probability of synchronicity is only about 34%. [35]

Related Research Articles

Phytosaurs are an extinct group of large, mostly semiaquatic Late Triassic archosauriform reptiles. Phytosaurs belong to the order Phytosauria. and are sometimes referred to as parasuchians. Phytosauria, Parasuchia, Parasuchidae, and Phytosauridae have often been considered equivalent groupings containing the same species. Some recent studies have offered a more nuanced approach, defining Parasuchidae and Phytosauridae as nested clades within Phytosauria as a whole. Phytosaurs were long-snouted and heavily armoured, bearing a remarkable resemblance to modern crocodilians in size, appearance, and lifestyle, as an example of convergence or parallel evolution. The name "phytosaur" means "plant reptile", as the first fossils of phytosaurs were mistakenly thought to belong to plant eaters.

<span class="mw-page-title-main">Carnian</span> First age of the Late Triassic epoch

The Carnian is the lowermost stage of the Upper Triassic Series. It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by the Norian. Its boundaries are not characterized by major extinctions or biotic turnovers, but a climatic event occurred during the Carnian and seems to be associated with important extinctions or biotic radiations. Another extinction occurred at the Carnian-Norian boundary, ending the Carnian age.

<span class="mw-page-title-main">Aetosaur</span> Extinct order of heavily armoured reptiles

Aetosaurs are heavily armored reptiles belonging to the extinct order Aetosauria. They were medium- to large-sized omnivorous or herbivorous pseudosuchians, part of the branch of archosaurs more closely related to crocodilians than to birds and other dinosaurs. All known aetosaurs are restricted to the Late Triassic, and in some strata from this time they are among the most abundant fossil vertebrates. They have small heads, upturned snouts, erect limbs, and a body ornamented with four rows of plate-like osteoderms. Aetosaur fossil remains are known from Europe, North and South America, parts of Africa, and India. Since their armoured plates are often preserved and are abundant in certain localities, aetosaurs serve as important Late Triassic tetrapod index fossils. Many aetosaurs had wide geographic ranges, but their stratigraphic ranges were relatively short. Therefore, the presence of particular aetosaurs can accurately date a site in which they are found.

<span class="mw-page-title-main">Chinle Formation</span> Geological formation in the western US

The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In New Mexico, it is often raised to the status of a geological group, the Chinle Group. Some authors have controversially considered the Chinle to be synonymous to the Dockum Group of eastern Colorado and New Mexico, western Texas, the Oklahoma panhandle, and southwestern Kansas. The Chinle Formation is part of the Colorado Plateau, Basin and Range, and the southern section of the Interior Plains. A probable separate depositional basin within the Chinle is found in northwestern Colorado and northeastern Utah. The southern portion of the Chinle reaches a maximum thickness of a little over 520 meters (1,710 ft). Typically, the Chinle rests unconformably on the Moenkopi Formation.

<i>Acaenasuchus</i> Genus of reptiles

Acaenasuchus is an extinct genus of pseudosuchian, endemic to what would be presently be known as Arizona during the Late Triassic, specifically during the Carnian and Norian stages of the Triassic. Acaenasuchus had a stratigraphic range of approximately 11.5 million years. Acaenasuchus is further categorized as one of the type fauna that belong to the Adamanian LVF, based on the fauna of the Blue Mesa Member of the Chinle Petrified Forest Formation of Arizona, where Acaenasuchus was initially discovered.

<span class="mw-page-title-main">Dockum Group</span> Geologic group of western Texas and eastern New Mexico

The Dockum is a Late Triassic geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle. The Dockum reaches a maximum thickness of slightly over 650 m but is usually much thinner. The Dockum rests on an unconformity over the Anisian aged Anton Chico Formation.

In paleontology, biochronology is the correlation in time of biological events using fossils. In its strict sense, it refers to the use of assemblages of fossils that are not tied to stratigraphic sections. Collections of land mammal ages have been defined for every continent except Antarctica, and most are correlated with each other indirectly through known evolutionary lineages. A combination of argon–argon dating and magnetic stratigraphy allows a direct temporal comparison of terrestrial events with climate variations and mass extinctions.

Redondasaurus is an extinct genus or subgenus of phytosaur from the Late Triassic of the southwestern United States. It was named by Hunt & Lucas in 1993, and contains two species, R. gregorii and R. bermani. It is the youngest and most evolutionarily-advanced of the phytosaurs.

The Cooper Canyon Formation is a geological formation of Norian age in Texas and New Mexico. It is one of several formations encompassed by the Dockum Group.

Ebrachosaurus is an extinct genus of aetosaur. It was named after the town of Ebrach, Germany, near an outcrop of the Blasensandstein Formation where the original fossils have been found. Other Blasensandstein fauna include the temnospondyl Metoposaurus and the phytosaur Francosuchus. The genus has often been considered synonymous with the closely related Stagonolepis. The holotype specimen was lost during World War II, so its relationships within Stagonolepididae remain indeterminant.

Adamanasuchus is an extinct genus of aetosaur. Fossils have been found from several localities from the Chinle Group in Arizona and date back to the late Carnian stage of the Late Triassic. The locality from which it was named after also lends its name to the Adamanian LVF.

<i>Leptosuchus</i> Extinct genus of reptiles

Leptosuchus is an extinct genus of leptosuchomorph phytosaur with a complex taxonomical history. Fossils have been found from the Dockum Group and lower Chinle Formation outcropping in Texas, New Mexico, and Arizona, USA, and date back to the Carnian stage of the Late Triassic.

Lucasuchus is an extinct genus of aetosaur. Fossils have been found from the Bull Canyon Formation of the Dockum Group outcropping in the Revuelto Creek locality in Quay County, New Mexico. All specimens date back to the Norian stage of the Late Triassic. The genus was named in 1995 after the American paleontologist Spencer G. Lucas.

Tecovasuchus is an extinct genus of aetosaur. It is known primarily from osteoderms found from the Tecovas Formation in Texas, which is Late Triassic in age, dating back to the lower Norian. Material is also known from several other localities of the Chinle Group in New Mexico and Arizona, such as older Carnian outcrops and younger Rhaetian outcrops. Specimens of Tecovasuchus have been collected from the Tecovas Formation, the Bluewater Creek Formation, and the Los Esteros Member of the Santa Rosa Formation.

The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to 208.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.

<span class="mw-page-title-main">Manda Formation</span>

The Manda Formation is a Middle Triassic (Anisian?) or possibly Late Triassic (Carnian?) geologic formation in Tanzania. It preserves fossils of many terrestrial vertebrates from the Triassic, including some of the earliest dinosauromorph archosaurs. The formation is often considered to be Anisian in age according to general tetrapod biochronology hypotheses and correlations to the Cynognathus Assemblage Zone of South Africa. However, some recent studies cast doubt to this age, suggesting that parts deposits may actually be younger (Carnian) in age.

The Colorado City Formation is a Late Triassic geologic formation in the Dockum Group of Texas, United States. It has previously been known as the Iatan Member, Colorado City Member or 'Pre-Tecovas Horizon'.

The Bluewater Creek Formation is a geologic formation in west-central New Mexico. It preserves fossils dating back to the late Triassic period.

<i>Vivaron</i> Extinct genus of reptiles

Vivaron is a genus of rauisuchid known from the Late Triassic Chinle Formation in New Mexico. It is the second rauisuchid known from the southwestern United States, and it highlights the wide biogeographic range similar rauisuchid taxa occupied during the Late Triassic across Pangaea, despite the varied faunal assemblages at different latitudes.

References

  1. 1 2 3 4 5 6 7 Lucas, Spencer G (1998-11-01). "Global Triassic tetrapod biostratigraphy and biochronology". Palaeogeography, Palaeoclimatology, Palaeoecology. 143 (4): 347–384. Bibcode:1998PPP...143..347L. doi:10.1016/S0031-0182(98)00117-5. ISSN   0031-0182.
  2. 1 2 Lucas, Spencer G. (2005). "Permian Tetrapod Faunachrons". New Mexico Museum of Natural History and Science Bulletin. 30: 197–201.
  3. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 Lucas, Spencer G. (2010-01-01). "The Triassic timescale based on nonmarine tetrapod biostratigraphy and biochronology". Geological Society, London, Special Publications. 334 (1): 447–500. Bibcode:2010GSLSP.334..447L. doi:10.1144/SP334.15. ISSN   0305-8719. S2CID   128911449.
  4. 1 2 3 4 5 6 7 8 9 Lucas, Spencer G. (2018), Tanner, Lawrence H. (ed.), "Late Triassic Terrestrial Tetrapods: Biostratigraphy, Biochronology and Biotic Events", The Late Triassic World: Earth in a Time of Transition, Topics in Geobiology, Springer International Publishing, vol. 46, pp. 351–405, doi:10.1007/978-3-319-68009-5_10, ISBN   978-3-319-68009-5 , retrieved 2020-05-31
  5. 1 2 3 4 5 6 7 8 Rayfield, E. J.; Barrett, P. M.; McDonnell, R. A.; Willis, K. J. (2005-07-01). "A Geographical Information System (GIS) study of Triassic vertebrate biochronology" (PDF). Geological Magazine. 142 (4): 327–354. Bibcode:2005GeoM..142..327R. doi:10.1017/S001675680500083X. ISSN   0016-7568. S2CID   129914103.
  6. 1 2 3 4 5 6 7 8 9 10 Langer, Max Cardoso (2005-06-01). "Studies on continental Late Triassic tetrapod biochronology. II. The Ischigualastian and a Carnian global correlation". Journal of South American Earth Sciences. 19 (2): 219–239. Bibcode:2005JSAES..19..219L. doi:10.1016/j.jsames.2005.04.002. ISSN   0895-9811.
  7. 1 2 3 4 5 6 7 8 9 Rayfield, Emily J.; Barrett, Paul M.; Milner, Andrew R. (2009-03-12). "Utility and validity of Middle and Late Triassic 'land vertebrate faunachrons'". Journal of Vertebrate Paleontology. 29 (1): 80–87. doi:10.1671/039.029.0132. ISSN   0272-4634. S2CID   86502146.
  8. 1 2 3 4 5 6 7 Irmis, Randall B.; Martz, Jeffrey W.; Parker, William G.; Nesbitt, Sterling J. (March 2010). "Re-evaluating the correlation between Late Triassic terrestrial vertebrate biostratigraphy and the GSSP-defined marine stages" (PDF). Albertiana. 38: 40–53.
  9. 1 2 3 4 5 6 7 Martz, J. W.; Parker, W. G. (2017-01-01), Zeigler, Kate E.; Parker, William G. (eds.), "Revised Formulation of the Late Triassic Land Vertebrate "Faunachrons" of Western North America: Recommendations for Codifying Nascent Systems of Vertebrate Biochronology", Terrestrial Depositional Systems, Elsevier, pp. 39–125, ISBN   978-0-12-803243-5 , retrieved 2022-08-28
  10. ↑ Lucas, Spencer G. (1993). "Vertebrate biochronology of the Triassic of China". New Mexico Museum of Natural History & Science Bulletin. 3: 301–306.
  11. ↑ Huber, Phillip; Lucas, Spencer G.; Hunt, Adrian P. (1993). "Vertebrate biochronology of the Newark Supergroup Triassic, eastern North America". New Mexico Museum of Natural History & Science Bulletin. 3: 179–186.
  12. 1 2 3 4 5 Lucas, Spencer G.; Hunt, Adrian P. (1993). "Tetrapod biochronology of the Chinle Group (Upper Triassic), western United States". New Mexico Museum of Natural History & Science Bulletin. 3: 327–329.
  13. ↑ Lucas, S.G.; Hunt, A.P.; Heckert, A.B.; Spielmann, J.A. (2007). "Global Triassic tetrapod biostratigraphy and biochronology: 2007 status" (PDF). In Lucas, S.G.; Spielmann, J.A. (eds.). The Global Triassic. New Mexico Museum of Natural History and Science Bulletin. Vol. 41. pp. 229–240. Archived from the original (PDF) on 2011-09-27. Retrieved 2010-07-17.
  14. ↑ Lucas, Spencer G.; Tanner, Lawrence H. (2014). Rocha, Rogério; Pais, João; Kullberg, José Carlos; Finney, Stanley (eds.). "Triassic Timescale Based on Tetrapod Biostratigraphy and Biochronology". Strati 2013. Springer Geology. Cham: Springer International Publishing: 1013–1016. doi:10.1007/978-3-319-04364-7_192. ISBN   978-3-319-04364-7.
  15. ↑ Lucas, Spencer G. (2006). "Global Permian tetrapod biostratigraphy and biochronology". Geological Society, London, Special Publications. 265 (1): 65–93. Bibcode:2006GSLSP.265...65L. doi:10.1144/GSL.SP.2006.265.01.04. ISSN   0305-8719. S2CID   129613959.
  16. ↑ Lucas, Spencer G. (2018). "Permian tetrapod biochronology, correlation and evolutionary events". Geological Society, London, Special Publications. 450 (1): 405–444. Bibcode:2018GSLSP.450..405L. doi:10.1144/SP450.12. ISSN   0305-8719. S2CID   134768451.
  17. ↑ Lucas, S. (2008). "Global Jurassic tetrapod biochronology". Volumina Jurassica. 6 (1): 99–108.
  18. ↑ Lucas, Spencer G. (2022). "Carboniferous tetrapod biostratigraphy, biochronology and evolutionary events". Geological Society, London, Special Publications. 512 (1): 965–1001. Bibcode:2022GSLSP.512..965L. doi:10.1144/SP512-2021-5. ISSN   0305-8719. S2CID   235528136.
  19. ↑ Lucas, Spencer (2015). "Age and correlation of Late Triassic tetrapods from southern Poland". Annales Societatis Geologorum Poloniae. doi: 10.14241/asgp.2015.024 .
  20. ↑ Racki, Grzegorz; Lucas, Spencer G. (2020-04-20). "Timing of dicynodont extinction in light of an unusual Late Triassic Polish fauna and Cuvier's approach to extinction". Historical Biology. 32 (4): 452–461. doi:10.1080/08912963.2018.1499734. ISSN   0891-2963. S2CID   91926999.
  21. 1 2 3 4 5 Parker, William G.; Martz, Jeffrey W. (2010). "The Late Triassic (Norian) Adamanian–Revueltian tetrapod faunal transition in the Chinle Formation of Petrified Forest National Park, Arizona". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 101 (3–4): 231–260. doi:10.1017/S1755691011020020. ISSN   1755-6910. S2CID   140536630.
  22. ↑ Widmann, Philipp; Bucher, Hugo; Leu, Marc; et al. (2020). "Dynamics of the Largest Carbon Isotope Excursion During the Early Triassic Biotic Recovery". Frontiers in Earth Science. 8 (196): 196. Bibcode:2020FrEaS...8..196W. doi: 10.3389/feart.2020.00196 .
  23. ↑ McElwain, J. C.; Punyasena, S. W. (2007). "Mass extinction events and the plant fossil record". Trends in Ecology & Evolution. 22 (10): 548–557. doi:10.1016/j.tree.2007.09.003. PMID   17919771.
  24. ↑ Retallack, G. J.; Veevers, J.; Morante, R. (1996). "Global coal gap between Permian–Triassic extinctions and middle Triassic recovery of peat forming plants". GSA Bulletin. 108 (2): 195–207. Bibcode:1996GSAB..108..195R. doi:10.1130/0016-7606(1996)108<0195:GCGBPT>2.3.CO;2 . Retrieved 2007-09-29.
  25. ↑ Payne, J. L.; Lehrmann, D. J.; Wei, J.; Orchard, M. J.; Schrag, D. P.; Knoll, A. H. (2004). "Large Perturbations of the Carbon Cycle During Recovery from the End-Permian Extinction". Science. 305 (5683): 506–9. Bibcode:2004Sci...305..506P. doi:10.1126/science.1097023. PMID   15273391. S2CID   35498132.
  26. ↑ Ogg, James G.; Ogg, Gabi M.; Gradstein, Felix M. (2016). "Triassic". A Concise Geologic Time Scale: 2016. Elsevier. pp. 133–149. ISBN   978-0-444-63771-0.
  27. ↑ Ramezani, Jahandar; Hoke, Gregory D.; Fastovsky, David E.; Bowring, Samuel A.; Therrien, François; Dworkin, Steven I.; Atchley, Stacy C.; Nordt, Lee C. (2011-11-01). "High-precision U-Pb zircon geochronology of the Late Triassic Chinle Formation, Petrified Forest National Park (Arizona, USA): Temporal constraints on the early evolution of dinosaurs". GSA Bulletin. 123 (11–12): 2142–2159. Bibcode:2011GSAB..123.2142R. doi:10.1130/B30433.1. ISSN   0016-7606.
  28. ↑ Rasmussen, Cornelia; Mundil, Roland; Irmis, Randall B.; Geisler, Dominique; Gehrels, George E.; Olsen, Paul E.; Kent, Dennis V.; Lepre, Christopher; Kinney, Sean T.; Geissman, John W.; Parker, William G. (2020-07-20). "U-Pb zircon geochronology and depositional age models for the Upper Triassic Chinle Formation (Petrified Forest National Park, Arizona, USA): Implications for Late Triassic paleoecological and paleoenvironmental change". GSA Bulletin. 133 (3–4): 539–558. doi:10.1130/B35485.1. ISSN   0016-7606.
  29. ↑ Martínez, R. N.; Apaldetti, C.; Alcober, O. A.; Colombi, C. E.; Sereno, P. C.; Fernandez, E.; Malnis, P. S.; Correa, G. A.; Abelin, D. (2013). "Vertebrate succession in the Ischigualasto Formation". Journal of Vertebrate Paleontology. 32: 10–30. Bibcode:2013JVPal..32S..10M. doi:10.1080/02724634.2013.818546. hdl: 11336/7771 . S2CID   37918101.
  30. ↑ Parker, W. G.; Martz, J. W. (2017-01-01), Zeigler, Kate E.; Parker, William G. (eds.), "Building Local Biostratigraphic Models for the Upper Triassic of Western North America: Methods and Considerations", Terrestrial Depositional Systems, Elsevier, pp. 1–38, ISBN   978-0-12-803243-5 , retrieved 2022-08-28
  31. 1 2 3 Kligman, Ben T.; Marsh, Adam D.; Nesbitt, Sterling J.; Parker, William G.; Stocker, Michelle R. (2020-03-26). "New trilophosaurid species demonstrates a decline in allokotosaur diversity across the Adamanian-Revueltian boundary in the Late Triassic of western North America". Palaeodiversity. 13 (1): 25. doi: 10.18476/pale.v13.a3 . ISSN   1867-6294. S2CID   216308379.
  32. ↑ Jaret, Steven J.; Hemming, Sidney R.; Rasbury, E. Troy; Thompson, Lucy M.; Glotch, Timothy D.; Ramezani, Jahandar; Spray, John G. (2018-11-01). "Context matters – Ar–Ar results from in and around the Manicouagan Impact Structure, Canada: Implications for martian meteorite chronology". Earth and Planetary Science Letters. 501: 78–89. Bibcode:2018E&PSL.501...78J. doi:10.1016/j.epsl.2018.08.016. ISSN   0012-821X. S2CID   134725972.
  33. ↑ Kent, Dennis V.; Olsen, Paul E.; Lepre, Christopher; Rasmussen, Cornelia; Mundil, Roland; Gehrels, George E.; Giesler, Dominique; Irmis, Randall B.; Geissman, John W.; Parker, William G. (16 October 2019). "Magnetochronology of the entire Chinle Formation (Norian age) in a scientific drill core from Petrified Forest National Park (Arizona, USA) and implications for regional and global correlations in the Late Triassic". Geochemistry, Geophysics, Geosystems. 20 (11): 4654–4664. Bibcode:2019GGG....20.4654K. doi:10.1029/2019GC008474. hdl: 10150/636323 . ISSN   1525-2027. S2CID   207980627.
  34. ↑ Onoue, Tetsuji; Sato, Honami; Yamashita, Daisuke; Ikehara, Minoru; Yasukawa, Kazutaka; Fujinaga, Koichiro; Kato, Yasuhiro; Matsuoka, Atsushi (8 July 2016). "Bolide impact triggered the Late Triassic extinction event in equatorial Panthalassa". Scientific Reports. 6: 29609. Bibcode:2016NatSR...629609O. doi:10.1038/srep29609. ISSN   2045-2322. PMC   4937377 . PMID   27387863.
  35. ↑ Hayes, Reilly F.; Puggioni, Gavino; Parker, William G.; Tiley, Catherine S.; Bednarick, Amanda L.; Fastovsky, David E. (2020-04-01). "Modeling the dynamics of a Late Triassic vertebrate extinction: The Adamanian/Revueltian faunal turnover, Petrified Forest National Park, Arizona, USA". Geology. 48 (4): 318–322. Bibcode:2020Geo....48..318H. doi:10.1130/G47037.1. ISSN   0091-7613. S2CID   213822986.
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