Biochronology

Last updated August 07, 2024

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 (in contrast to biostratigraphy, where they are). 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.

Comparison with biostratigraphy

In sedimentary rocks, fossils are the only widely applicable tool for time correlation.^[1]^: 229 Evolution leaves a record of progressive change, sequential and nonrepeating.^[1]^: 230 A rock unit has a characteristic assemblage of fossils, independent of its lithology.^[1]^: 229 Thus, the fossils can be used to compare the ages of different rock units.

The basic unit of biochronology is the biostratigraphic zone, or biozone, a collection of fossils found together in a rock unit. This is used as the basis of a biochron, "a unit of time in which an association of taxa is interpreted to have lived."^[1]^: 229 However, a biozone may vary in age from one location or another. For example, a given taxon may migrate, so its first appearance varies from place to place. In particular, facies-controlled organisms (organisms that lived in a particular sedimentary environment) are not well suited for biochronology because they move with their environment and may change little over long periods of time.^[1]^{: 230–231} Thus, biostratigraphers search for species that are particularly widespread, abundant, and not tied to particular sedimentary environments. This is particularly true of free-swimming animals such as benthic foraminifera, which readily spread throughout the world's oceans.^[1]^: 230

Another challenge for stratigraphy is that there are often large gaps in the fossil record at a given location. To counter this, biostratigraphers search for a particularly well-preserved section that can be used as the type section for a particular biostratographic unit. As an example, the boundary between the Silurian and Devonian periods is marked by the first appearance of the graptolite Mongraptus uniformus uniformus in a section in Klonk, Czech Republic.^[1]^: 237

In terrestrial deposits, fossils of land mammals and other vertebrates are used as stratigraphic tools, but they have some disadvantages relative to marine fossils. They are seldom evenly distributed through a section, and they tend to occur in isolated pockets with few overlaps between biozones. Thus, correlations between biozones is often indirect, inferred using a knowledge of their sequence of evolution.^[1]^: 240 This practice was first proposed by H. S. Williams in 1941.

In the United States, biochronology is widely used as a synonym for biostratigraphy, but in Canada and Europe the term is reserved for biochronology that is not tied to a particular stratigraphic section.^[2] This form of biochronology is not recognized by the International Stratigraphic Guide, but it is "really what a great many paleontologists and stratigraphers are after ... an optimum network of fossil correlations, thought to embody a reliable and high-resolution isochronous time (lines) framework."^[3]

Land mammal ages

A Cenozoic chronology based on mammal taxa has been defined on all the continents except Antarctica.^[4]^: 939 Because the continents have been separated through most of the Cenozoic, each continent has its own system.^[5] Most of the units are based on assemblage zones, layers of strata that contain three or more distinctive fossils.^[6]^: 4, 15

North America

In 1941, a committee chaired by Horace E. Wood II compiled a list of 19 "provincial ages" for North America, later called North American Land Mammal Ages (NMLAs). An example of an NMLA is the Rancholabrean, named after the Rancho La Brea fossil site. One of its characteristic fossils is the bison, which first appears in the Rancholabrean.^[7] The committee tried to make the definitions unambiguous by providing multiple criteria such as index fossils, first and last occurrences, and the relation to a particular formation. Some of these criteria have turned out to be inconsistent, leading to conflict. For example, the Chadronian Land Mammal Age in the late Eocene was defined by the boundaries of the Chadron Formation in Nebraska as well as the co-occurrence of Mesohippus, an early horse, and titanotheres, a family of rhinoceros-like animals. Titanotheres have since been found above the Chadron Formation, leaving the definition of the age uncertain.^[1]^: 240 Since NAMLs are not tied to stratigraphic sections, they are not true chronostratigraphic stages, so some authors place quotes around "Ages".^[1]^: 240^[4]^: 943^[8]

South America

The development of South American land mammal ages is largely due to two brothers, Florentino Ameghino and Carlos Ameghino. As of 1983, there were 19 ages, all but one of which were based on sections in Argentina.^[9] Since then three more ages have been added for the Paleocene.^[10]^: 16

Europe

The first European European land mammal age (ELMA), the Villafranchian, was defined in 1865. It was based on sedimentary units near Villafranca d'Asti in Italy.^[11] Several more were proposed between 1950 and 1975; and in 1975 Mein introduced a finer division called Mammal Neogene (MN) zones.^[11] A total of 30 Mammal Paleogene zones have also been defined.^[10]^: 15

Asia and Africa

Asian land mammal ages are more recently named and more tentative than the ages for the above continents, with poor geochronological constraints. There is no consensus for the names of some of the ages.^[10]^: 17 However, the picture is rapidly improving, since Central Asia has some of the world's best records of Neogene mammals.^[5]^: 11 In Africa, sequences of fossils (including those of primates) have been determined and some land mammal ages designated, but not yet formally defined.^[10]^: 11

Other tetrapod-based biochronologies

Land-mammal ages mostly represent intervals in the Cenozoic; they have not been proposed for the Mesozoic. However, related systems have been proposed for other periods of prehistory. Land-vertebrate "ages" (LVAs) based primarily on dinosaur faunas have been proposed for the late Cretaceous in western North America.^[12]

Land vertebrate faunachrons

The most widely utilized pre-Cenozoic tetrapod biochronology system involves Land vertebrate faunachrons (LVFs). The LVF system was originally designed by Spencer G. Lucas to correlate terrestrial faunal assemblages of the Triassic period.^[13] LVFs have also been used in Permian biochronology.^[14] Although LVFs are a common method used to date Triassic terrestrial sediments, their reliability is more heavily debated than that of Land Mammal Ages.^[15]^[16]

Geochronology

The order of evolutionary events that have been used to sequence land mammal records have been verified using geochronological methods.^[1]^: 241 Although first and last occurrences of taxa can vary with location, assemblages show little variation.^[1]^: 240 Fossils of mammals also have the advantage that the mammals have evolved rapidly.

The resolution of terrestrial fossil records have improved as the methods have improved. Although K–Ar dating has largely yielded correct results, some needed revision after the advent of Argon–argon dating.^[17]^: 10 Magnetic stratigraphy allows synchronization with the global magnetic polarity record resulting from reversals of the Earth's magnetic field.^[17]^: 10 This has made it possible to correlate terrestrial sediments with the time scale from marine sediments, and compare them directly with global climate change and mass extinctions.^[17]^: 10

Paleontologists have moved towards finer zonation of terrestrial fossils, with the potential to divide the Cenozoic into time intervals of 300,000 years or less.^[17]^: 10 They have also attempted to convert some of the intervals, including the Wasatchian age/stage and Clarkforkian age/stage, into biostratigraphic units.^[6]^: 16 However, the fossil record remains discontinuous even in North America, and Woodburne speculates that "mammal age correlations provide results that are satisfactory to their users."^[6]^: 18

Related Research Articles

Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. The primary objective of biostratigraphy is correlation, demonstrating that a particular horizon in one geological section represents the same period of time as another horizon at a different section. Fossils within these strata are useful because sediments of the same age can look completely different, due to local variations in the sedimentary environment. For example, one section might have been made up of clays and marls, while another has more chalky limestones. However, if the fossil species recorded are similar, the two sediments are likely to have been laid down around the same time. Ideally these fossils are used to help identify biozones, as they make up the basic biostratigraphy units, and define geological time periods based upon the fossil species found within each section.

In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 247.2 million years ago until 242 million years ago. The Anisian Age succeeds the Olenekian Age and precedes the Ladinian Age.

The Messinian is in the geologic timescale the last age or uppermost stage of the Miocene. It spans the time between 7.246 ± 0.005 Ma and 5.333 ± 0.005 Ma. It follows the Tortonian and is followed by the Zanclean, the first age of the Pliocene.

<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.

The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between 242 Ma and ~237 Ma. The Ladinian was preceded by the Anisian and succeeded by the Carnian.

The Cistecephalus Assemblage Zone is a tetrapod assemblage zone or biozone found in the Adelaide Subgroup of the Beaufort Group, a majorly fossiliferous and geologically important geological group of the Karoo Supergroup in South Africa. This biozone has outcrops located in the Teekloof Formation north-west of Beaufort West in the Western Cape, in the upper Middleton and lower Balfour Formations respectively from Colesberg of the Northern Cape to east of Graaff-Reinet in the Eastern Cape. The Cistecephalus Assemblage Zone is one of eight biozones found in the Beaufort Group, and is considered to be Late Permian in age.

The Daptocephalus Assemblage Zone is a tetrapod assemblage zone or biozone found in the Adelaide Subgroup of the Beaufort Group, a majorly fossiliferous and geologically important Group of the Karoo Supergroup in South Africa. This biozone has outcrops located in the upper Teekloof Formation west of 24°E, the majority of the Balfour Formation east of 24°E, and the Normandien Formation in the north. It has numerous localities which are spread out from Colesberg in the Northern Cape, Graaff-Reniet to Mthatha in the Eastern Cape, and from Bloemfontein to Harrismith in the Free State. The Daptocephalus Assemblage Zone is one of eight biozones found in the Beaufort Group and is considered Late Permian (Lopingian) in age. Its contact with the overlying Lystrosaurus Assemblage Zone marks the Permian-Triassic boundary.

The Cynognathus Assemblage Zone is a tetrapod biozone utilized in the Karoo Basin of South Africa. It is equivalent to the Burgersdorp Formation, the youngest lithostratigraphic formation in the Beaufort Group, which is part of the fossiliferous and geologically important Karoo Supergroup. The Cynognathus Assemblage Zone is the youngest of the eight biozones found in the Beaufort Group, and is considered to be late Early Triassic (Olenekian) to early Middle Triassic (Anisian) in age. The name of the biozone refers to Cynognathus crateronotus, a large and carnivorous cynodont therapsid which occurs throughout the entire biozone.

The Pristerognathus Assemblage Zone is a tetrapod assemblage zone or biozone which correlates to the upper Abrahamskraal Formation and lowermost Teekloof Formation, Adelaide Subgroup of the Beaufort Group, a fossiliferous and geologically important geological Group of the Karoo Supergroup in South Africa. The thickest outcrops, reaching not more than 300 metres (980 ft), occur just east of Sutherland through to Beaufort West in the south and Victoria West in the north. Exposures are also found west of Colesberg and south of Graaff-Reinet. The Pristerognathus Assemblage Zone is the third biozone of the Beaufort Group.

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.

The Blancan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 4,750,000 to 1,806,000 years BP, a period of 2.944 million years. It is usually considered to start in the early-mid Pliocene Epoch and end by the early Pleistocene. The Blancan is preceded by the Hemphillian and followed by the Irvingtonian NALMA stages.

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 North American land mammal ages (NALMA) establishes a geologic timescale for North American fauna beginning during the Late Cretaceous and continuing through to the present. These periods are referred to as ages or intervals and were established using geographic place names where fossil materials were obtained.

The Irvingtonian North American Land Mammal Age on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), spanning from 1.8 million – 250,000 years BP. Named after an assemblage of fossils from the Irvington District of Fremont, California, the Irvingtonian is usually considered to overlap the Lower Pleistocene and Middle Pleistocene epochs. The Irvingtonian is preceded by the Blancan and followed by the Rancholabrean NALMA stages.

The European Land Mammal Mega Zones are zones in rock layers that have a specific assemblage of fossils (biozones) based on occurrences of fossil assemblages of European land mammals. These biozones cover most of the Cenozoic, with particular focus having been paid to the Neogene and Paleogene systems, the Quaternary has several competing systems. In cases when fossils of mammals are abundant, stratigraphers and paleontologists can use these biozones as a more practical regional alternative to the stages of the official ICS geologic timescale. European Land Mammal Mega Zones are often also confusingly referred to as ages, stages, or intervals.

The Williams Fork Formation is a Campanian to Maastrichtian (Edmontonian) geologic formation of the Mesaverde Group in Colorado. Dinosaur remains are among the fossils that have been recovered from the formation, most notably Pentaceratops sternbergii,. Other fossils found in the formation are the ammonite Lewyites, tyrannosaurids, dromaeosaurids, troodontids, nodosaurids, ankylosaurids, hadrosaurids, hybodonts, neosuchian crocodylomorphs, and the mammals Glasbius and Meniscoessus collomensis.

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.

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 Bone Valley Formation is a geologic formation in Florida. It is sometimes classified as the upper member of the Peace River Formation of the Hawthorn Group. It contains economically important phosphorite deposits that are mined in west-central Florida, as well as rich assemblages of vertebrate fossils.

Land vertebrate faunachrons (LVFs) are biochronological units used to correlate and date terrestrial sediments and fossils based on their tetrapod faunas. First formulated on a global scale by Spencer G. Lucas in 1998, LVFs are primarily used within the Triassic Period, though Lucas later designated LVFs for other periods as well. 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.

References

1 2 3 4 5 6 7 8 9 10 11 12 Prothero, Donald R. (1989). Interpreting the stratigraphic record. New York: W.H. Freeman. ISBN 0716718545.
↑ Lucas, Spencer G. (1997). "Biostratigraphy". In Padian, Kevin; Currie, Philip J. (eds.). Encyclopedia of Dinosaurs. Burlington: Elsevier. pp. 65–68. ISBN 9780080494746.
↑ Gradstein, Felix M (2012). "Biochronology". In Gradstein, Felix M; Ogg, J G; Schmitz, Mark; Ogg, Gabi (eds.). The geologic time scale 2012. Amsterdam: Elsevier. pp. 43–62. ISBN 9780444594488.
1 2 Hilgen, F J; Jourens, L J; Van Dam, J A (2012). "The Neogene Period". In Gradstein, Felix M; Ogg, J G; Schmitz, Mark; Ogg, Gabi (eds.). The geologic time scale 2012. Amsterdam: Elsevier. pp. 923–978. ISBN 9780444594488.
1 2 Lindsay, Everett H; Tedford, Richard H (1989). "Development and Application of Land Mammal Ages in North America and Europe, a Comparison". In Lindsay, Everett H; Fahlbusch, Volker; Mein, Pierre (eds.). European Neogene mammal chronology. NATO ASI Series. Vol. 180. New York: Plenum Press. pp. 601–624. doi:10.1007/978-1-4899-2513-8_36. ISBN 978-1-4899-2513-8.
1 2 3 Woodburne, Michael O. (2004). "Principles and procedures". In Woodburne, Michael O. (ed.). Late Cretaceous and Cenozoic Mammals of North America : biostratigraphy and geochronology. New York: Columbia university press. ISBN 978-0231130400.
↑ Bell, Christopher J; Lundelius Jr, Ernest L; Barnosky, Anthony D; Graham, Russell W; Lindsay, Everett H; Ruez, Dennis R; Semken Jr, Holmes A; Webb, S David; Zakrewski, Richard J (2004). "The Blancan, Irvingtonian, and Rancholabrean Mammal Ages". In Woodburne, Michael O (ed.). Late Cretaceous and Cenozoic Mammals of North America : biostratigraphy and geochronology. New York: Columbia university press. ISBN 978-0231130400.
↑ Wood, H. E.; Chaney, R. W.; Clark, J.; Colbert, E. H.; Jepsen, G. L.; Reeside, J. B.; Stock, C. (1 January 1941). "Nomenclature and correlation of the North American continental Tertiary". Geological Society of America Bulletin. 52 (1): 1–48. Bibcode:1941GSAB...52....1W. doi:10.1130/GSAB-52-1.
↑ Larry G., Marshall; Hoffster, Robert; Pascual, Rosendo (1983). "Mammals and stratigraphy: geochronology of the continental mammal-bearing Tertiary of South America". Palaeovertebrata. Retrieved 6 August 2024.
1 2 3 4 Rose, Kenneth D. (2006). The beginning of the age of mammals. Baltimore, Md.: Johns Hopkins Univ. Press. ISBN 9780801884726.
1 2 Lindsay, Everett (October 1997). "Eurasian mammal biochronology: an overview". Palaeogeography, Palaeoclimatology, Palaeoecology. 133 (3–4): 117–128. Bibcode:1997PPP...133..117L. doi:10.1016/S0031-0182(97)00083-7.
↑ Lucas, Spencer G. (1997). "Land-mammal ages". In Padian, Kevin; Currie, Philip J. (eds.). Encyclopedia of Dinosaurs. Burlington: Elsevier. pp. 395–397. ISBN 9780080494746.
↑ Lucas, Spencer G (1998-11-01). "Global Triassic tetrapod biostratigraphy and biochronology" (PDF). Palaeogeography, Palaeoclimatology, Palaeoecology. 143 (4): 347–384. Bibcode:1998PPP...143..347L. doi:10.1016/S0031-0182(98)00117-5. ISSN 0031-0182.
↑ Lucas, Spencer G. (2005). "Permian Tetrapod Faunachrons". New Mexico Museum of Natural History and Science Bulletin. 30: 197–201.
↑ 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. Bibcode:2009JVPal..29...80R. doi:10.1671/039.029.0132. ISSN 0272-4634. S2CID 86502146.
↑ 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.
1 2 3 4 Prothero, Donald R (1998). "The chronological, climatic, and paleogeographic background to North American mammalian evolution". In Janis, Christine M; Scott, Kathleen M; Jacobs, Louise L (eds.). Evolution of Tertiary mammals of North America. Cambridge: Cambridge Univ. Pr. ISBN 9780521355193.

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[ProtheroBook-1] 1 2 3 4 5 6 7 8 9 10 11 12 Prothero, Donald R. (1989). Interpreting the stratigraphic record. New York: W.H. Freeman. ISBN 0716718545.

[lucasBiostrat-2] Lucas, Spencer G. (1997). "Biostratigraphy". In Padian, Kevin; Currie, Philip J. (eds.). Encyclopedia of Dinosaurs. Burlington: Elsevier. pp. 65–68. ISBN 9780080494746.

[Gradstein-3] Gradstein, Felix M (2012). "Biochronology". In Gradstein, Felix M; Ogg, J G; Schmitz, Mark; Ogg, Gabi (eds.). The geologic time scale 2012. Amsterdam: Elsevier. pp. 43–62. ISBN 9780444594488.

[Neogene-4] 1 2 Hilgen, F J; Jourens, L J; Van Dam, J A (2012). "The Neogene Period". In Gradstein, Felix M; Ogg, J G; Schmitz, Mark; Ogg, Gabi (eds.). The geologic time scale 2012. Amsterdam: Elsevier. pp. 923–978. ISBN 9780444594488.

[Lindsay-5] 1 2 Lindsay, Everett H; Tedford, Richard H (1989). "Development and Application of Land Mammal Ages in North America and Europe, a Comparison". In Lindsay, Everett H; Fahlbusch, Volker; Mein, Pierre (eds.). European Neogene mammal chronology. NATO ASI Series. Vol. 180. New York: Plenum Press. pp. 601–624. doi:10.1007/978-1-4899-2513-8_36. ISBN 978-1-4899-2513-8.

[Principles-6] 1 2 3 Woodburne, Michael O. (2004). "Principles and procedures". In Woodburne, Michael O. (ed.). Late Cretaceous and Cenozoic Mammals of North America : biostratigraphy and geochronology. New York: Columbia university press. ISBN 978-0231130400.

[Rancholabrean-7] Bell, Christopher J; Lundelius Jr, Ernest L; Barnosky, Anthony D; Graham, Russell W; Lindsay, Everett H; Ruez, Dennis R; Semken Jr, Holmes A; Webb, S David; Zakrewski, Richard J (2004). "The Blancan, Irvingtonian, and Rancholabrean Mammal Ages". In Woodburne, Michael O (ed.). Late Cretaceous and Cenozoic Mammals of North America : biostratigraphy and geochronology. New York: Columbia university press. ISBN 978-0231130400.

[8] Wood, H. E.; Chaney, R. W.; Clark, J.; Colbert, E. H.; Jepsen, G. L.; Reeside, J. B.; Stock, C. (1 January 1941). "Nomenclature and correlation of the North American continental Tertiary". Geological Society of America Bulletin. 52 (1): 1–48. Bibcode:1941GSAB...52....1W. doi:10.1130/GSAB-52-1.

[SouthAmerica-9] Larry G., Marshall; Hoffster, Robert; Pascual, Rosendo (1983). "Mammals and stratigraphy: geochronology of the continental mammal-bearing Tertiary of South America". Palaeovertebrata. Retrieved 6 August 2024.

[ageOfMammals-10] 1 2 3 4 Rose, Kenneth D. (2006). The beginning of the age of mammals. Baltimore, Md.: Johns Hopkins Univ. Press. ISBN 9780801884726.

[Eurasian-11] 1 2 Lindsay, Everett (October 1997). "Eurasian mammal biochronology: an overview". Palaeogeography, Palaeoclimatology, Palaeoecology. 133 (3–4): 117–128. Bibcode:1997PPP...133..117L. doi:10.1016/S0031-0182(97)00083-7.

[eod-12] Lucas, Spencer G. (1997). "Land-mammal ages". In Padian, Kevin; Currie, Philip J. (eds.). Encyclopedia of Dinosaurs. Burlington: Elsevier. pp. 395–397. ISBN 9780080494746.

[13] Lucas, Spencer G (1998-11-01). "Global Triassic tetrapod biostratigraphy and biochronology" (PDF). Palaeogeography, Palaeoclimatology, Palaeoecology. 143 (4): 347–384. Bibcode:1998PPP...143..347L. doi:10.1016/S0031-0182(98)00117-5. ISSN 0031-0182.

[14] Lucas, Spencer G. (2005). "Permian Tetrapod Faunachrons". New Mexico Museum of Natural History and Science Bulletin. 30: 197–201.

[15] 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. Bibcode:2009JVPal..29...80R. doi:10.1671/039.029.0132. ISSN 0272-4634. S2CID 86502146.

[16] 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.

[Prothero-17] 1 2 3 4 Prothero, Donald R (1998). "The chronological, climatic, and paleogeographic background to North American mammalian evolution". In Janis, Christine M; Scott, Kathleen M; Jacobs, Louise L (eds.). Evolution of Tertiary mammals of North America. Cambridge: Cambridge Univ. Pr. ISBN 9780521355193.

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