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67-631: 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. Regardless, Late Triassic phytosaurs are considered to have strong biostratigraphic utility even among detractors of Lucas's system. Tetrapod biostratigraphy has been used for

134-407: A faunal assemblage , rather than an individual species — this allows greater precision as the time span in which all of the species in the assemblage existed together is narrower than the time spans of any of the members. Furthermore, if only one species is present in a sample, it can mean either that (1) the strata were formed in the known fossil range of that organism; or (2) that the fossil range of

201-594: A fossiliferous geological formation . Together, the defining index fossil and assemblage could be used to correlate fossil assemblages worldwide. Updates to this system have been published continuously for Triassic LVFs, which remain a heavily-discussed topic in the study of Triassic chronology. Lucas has also defined LVFs for the Permian , Jurassic , and Carboniferous , 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

268-686: 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. Lucas's approach to correlating LVFs with global marine stages has been met with criticism. The Triassic timescale

335-472: A large number of skulls and assorted postcranial fossils discovered in the Cumnock Formation of North Carolina . Fossils referable to the species are also known from Pennsylvania , New Jersey , and Virginia . Rutiodon carolinensis is the most well-described species of phytosaur in eastern North America, though its validity as a natural taxon has been questioned. Some paleontologists also recognize

402-496: 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. Martz and Parker argued that the term "faunachron" was misleading and redundant, as each "faunachron"

469-413: A larger and more robust species, Rutiodon manhattanensis , which is known from teeth and postcranial fossils from New Jersey and Pennsylvania. Like other phytosaurs , Rutiodon strongly resembled a crocodile , but its nostrils were positioned far back on the head, close to the eyes, instead of at the tip of the snout. It had enlarged front teeth, and a relatively narrow jaw, somewhat resembling that of

536-470: 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%. Biostratigraphy Biostratigraphy

603-443: A modern gharial . This suggests that this carnivore probably caught fish and it may also have snatched land animals from the waterside. Also, like modern crocodiles, its back, flanks, and tail were covered with bony armored plates . Rutiodon was among the largest carnivorous animals of its environment, measuring up to 8 metres (26 ft) long and weighing about 1 metric ton (1.1 short tons). The type species of Rutiodon

670-399: A particular span of geologic time or environment, and can be used to identify and date the containing rocks. To be practical, index fossils must have a limited vertical time range, wide geographic distribution, and rapid evolutionary trends. Rock formations separated by great distances but containing the same index fossil species are thereby known to have both formed during the limited time that

737-552: 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. Although the utility of a global LVF system is questionable, LVF-derived biostratigraphy may be useful in limited circumstances. Phytosaurs in particular have played

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804-562: A phytosaur skull from Chatham County, North Carolina . This was the second phytosaur skull found in the area, after that of Emmons (1860). Marsh named his phytosaur skull Rhytidodon rostratus . Belodon validus is considered dubious and undiagnostic, while "Rhytidodon rostratus " (specimen USNM 5373) has been referred to R. carolinensis . Phytosaur fossils tentatively referred to R. carolinensis were unearthed in 1959 in Fairfax County, Virginia , near Dulles International Airport which

871-512: A segment of time (and strata) between two paleobiological events: the first appearance datum (FAD) of one index taxon and the FAD of another. 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

938-666: A single continent, and have no relevance to a global biostratigraphy system. These include Doswellia , Longosuchus , Typothorax , “ Pseudopalatus ” ( Machaeroprosopus ), Redondasaurus , and Redondasuchus , among others. 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. Index taxa for

1005-681: 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. While certainly large enough to momentarily devastate areas near the impact point in Quebec , broader environmental effects of the Manicouagan impact are mostly conjectural. Besides

1072-436: A tier of the phytosaur family tree more derived than Paleorhinus and less derived than Leptosuchus . In other words, Rutiodon lies within the large clade Phytosauridae (alternatively known as Mystriosuchinae ) and outside the less inclusive clade Leptosuchomorpha . A 2001 conference abstract argued that Rutiodon carolinensis was a synonym of Angistorhinus , mirroring older suggestions that Angistorhinus

1139-693: A time-constrained index taxon. 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 . A similar situation occurs in Paleorhinus/Parasuchus , which has historically been used as

1206-404: A unique association of three or more taxa within it. Abundance biozones are strata in which the abundance of a particular taxon or group of taxa is significantly greater than in the adjacent part of the section. Index fossils (also known as guide fossils , indicator fossils , or dating fossils ) are the fossilized remains or traces of particular plants or animals that are characteristic of

1273-456: Is R. carolinensis . It was originally named by Ebenezer Emmons in 1856, based on fossils from the Deep River coal field ( Cumnock Formation ) of North Carolina. The original fossils include five striated teeth and associated vertebrae, ribs, and interclavicle fragments. Later, Emmons (1860) mentioned that he had discovered a nearly complete skull of R. carolinensis from North Carolina, at

1340-528: Is a debatable, as many species assigned to the genus may not be closely related (see below). 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

1407-465: 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. 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

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1474-485: 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

1541-617: 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

1608-430: 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

1675-490: 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 . 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

1742-619: The American Museum of Natural History (AMNH). In 1963, a small partial phytosaur skull (AMNH 5500) was discovered at the Granton Quarry of North Bergen, New Jersey . This skull, recovered from grey argillite of the Lockatong Formation , was described by Colbert in 1965. He identified the skull as a probable juvenile specimen of R. carolinensis . Doyle and Sues (1995) described a well-preserved phytosaur skull ( SMP VP-45) from

1809-710: 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. 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

1876-473: 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

1943-601: The New Oxford Formation in York County, Pennsylvania . This skull was very similar to skulls previously referred to R. carolinesis . They considered R. carolinensis to be an undiagnostic species, as it was originally diagnosed based on teeth. According to these authors, " Rutiodon " is a metataxon of eastern phytosaurs for which monophyly cannot be established. Since its original description, R. carolinensis has been conflated with various other phytosaur species from

2010-539: The 18th century it began to be accepted that fossils were remains left by species that had become extinct, but were then preserved within the rock record. The method was well-established before Charles Darwin explained the mechanism behind it— evolution . Scientists William Smith , George Cuvier , and Alexandre Brongniart came to the conclusion that fossils then indicated a series of chronological events, establishing layers of rock strata as some type of unit, later termed biozone . From here on, scientists began relating

2077-531: The Adamanian are fraught with uncertain time estimates brought on by weak correlations on a global scale. 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

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2144-492: The Adamanian-Revueltian turnover, the impact has also been linked to a minor marine extinction in eastern Panthalassa . Alternatively, the Adamanian-Revueltian turnover may be a consequence of the gradual aridification of western Pangea as it drifted north into arid latitudes. Comparative estimates of extinction rates and occurrences find little support for a synchronized Adamanian-Revueltian turnover, and instead support

2211-638: 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

2278-567: 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. LVFs of the Triassic Period from youngest to oldest: (but see below) (but see below) Several paleontologists have independently questioned the validity of Lucas’s system, criticizing its inconsistent and often contradictory approach to taxonomy and faunal correlations. Many index taxa are very rare or endemic to

2345-400: 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. Conversely, other "Adamanian" strata, such as fossiliferous layers in the lower Ischigualasto Formation of Argentina, can be assigned to the late Carnian (~231 Ma). This supports the conclusion that LVFs such as

2412-676: 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 . 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,

2479-412: The Triassic of South Africa since 1906 and Argentina since 1966, but without much connection to global faunas. 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 and eastern and western North America . These named biostratigraphic intervals were inspired by

2546-436: The area around this time, while metoposaurs and allokotosaurs 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. The cause and relevance of this turnover is debatable, as it may indicate only

2613-498: The basic biostratigraphy units, and define geological time periods based upon the fossil species found within each section. Basic concepts of biostratigraphic principles were introduced centuries ago, going as far back as the early 1800s. A Danish scientist and bishop by the name of Nicolas Steno was one of the first geologists to recognize that rock layers correlate to the Law of Superposition . With advancements in science and technology, by

2680-451: The boundaries of the different eras ( Paleozoic , Mesozoic , Cenozoic ), as well as Periods ( Cambrian , Ordovician , Silurian ) through the isotopes found within fossils via radioactive decay. Current 21st century uses of biostratigraphy involve interpretations of age for rock layers, which are primarily used by oil and gas industries for drilling workflows and resource allocations. Fossil assemblages were traditionally used to designate

2747-498: The changes in strata and biozones to different geological eras, establishing boundaries and time periods within major faunal changes. By the late 18th century the Cambrian and Carboniferous periods were internationally recognized due to these findings. During the early 20th century, advancements in technology gave scientists the ability to study radioactive decay . Using this methodology, scientists were able to establish geological time,

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2814-525: 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 ). One complication in defining biozones based on phytosaurs

2881-413: The duration of periods. Since a large change in fauna was required to make early stratigraphers create a new period, most of the periods we recognize today are terminated by a major extinction event or faunal turnover. A stage is a major subdivision of strata, each systematically following the other each bearing a unique assemblage of fossils. Therefore, stages can be defined as a group of strata containing

2948-442: The eastern United States. Isaac Lea named several phytosaur species from Pennsylvania shortly before Emmons' description: Clepsysaurus pennsylvanicus (in 1851) and Centemodon sulcatus (in 1856). Both species were compared favorably with R. carolinensis by Emmons, and some authors have noted that either could be considered a senior synonym of Rutiodon . Nevertheless, fossils of R. carolinensis are much more complete, so

3015-529: 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

3082-466: The genera Leptosuchus , Machaeroprosopus , and Pseudopalatus . A 1995 paper, and most subsequent studies on phytosaurs, disagreed with the idea that Rutiodon encompassed western phytosaur species. The authors re-instated the validity of Machaeroprosopus (with Pseudopalatus as a junior synonym ) and Leptosuchus . They also created the new genus Smilosuchus for " Machaeroprosopus" gregorii . Recent papers agree that Rutiodon occupies

3149-451: The holotype has the largest femur he had ever observed in phytosaurs, at a length of 43-44 cm (17 inches). Some authors have referred R. manhattanensis to "Clepsysaurus" or Phytosaurus , but its referral to Rutiodon was upheld by Colbert (1965). Very large phytosaur teeth, osteoderms, and hindlimb fossils (specimen YPM - PU 11544) from York, Pennsylvania have also been referred to R. manhattanensis . A few authors have doubted

3216-481: The known stratigraphic and geographic range of occurrence of a single taxon. Concurrent range biozone includes the concurrent, coincident, or overlapping part of the range of two specified taxa. Interval biozones include the strata between two specific biostratigraphic surfaces and can be based on lowest or highest occurrences. Lineage biozones are strata containing species representing a specific segment of an evolutionary lineage. Assemblage biozones are strata that contain

3283-663: The most fundamental unit of measurement. The thickness and range of these zones can be a few meters, up to hundreds of meters. They can also range from local to worldwide, as the extent of which they can reach in the horizontal plane relies on tectonic plates and tectonic activity. Two of the tectonic processes that run the risk of changing these zones' ranges are metamorphic folding and subduction . Furthermore, biostratigraphic units are divided into six principal kinds of biozones: Taxon range biozone , Concurrent range biozone, Interval biozone, Lineage biozone, Assemblage biozone, and Abundance biozone . The Taxon range biozone represents

3350-461: The organism was incompletely known, and the strata extend the known fossil range. For instance, the presence of the trace fossil Treptichnus pedum was used to define the base of the Cambrian period, but it has since been found in older strata. If the fossil is easy to preserve and easy to identify, more precise time estimating of the stratigraphic layers is possible. The concept of faunal succession

3417-635: The other hand, prefers a "short-Norian" perspective, with a lengthier Carnian stage and a Carnian-Norian boundary at around 220 Ma. 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

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3484-430: The overlapping range of fossils. They represent the time between the appearance of species chosen at the base of the zone and the appearance of other species chosen at the base of the next succeeding zone. Oppel's zones are named after a particular distinctive fossil species, called an index fossil. Index fossils are one of the species from the assemblage of species that characterize the zone. Biostratigraphy uses zones for

3551-481: The principle of faunal succession, where fossil organisms succeed one another in a definite and determinable order, and therefore any time period can be categorized by its fossil extent. Rutiodon Rutiodon ("Wrinkle tooth") is an extinct genus of mystriosuchine phytosaurs from the Late Triassic of the eastern United States . The type species of Rutiodon , Rutiodon carolinensis , encompasses

3618-433: 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

3685-423: 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

3752-443: The same major fossil assemblages. French palaeontologist Alcide d'Orbigny is credited for the invention of this concept. He named stages after geographic localities with particularly good sections of rock strata that bear the characteristic fossils on which the stages are based. In 1856 German palaeontologist Albert Oppel introduced the concept of zone (also known as biozones or Oppel zone). A zone includes strata characterized by

3819-418: The southwest United States, commonness, and relatively stable phylogenetic position despite paraphyly in some circumstances. 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

3886-832: The species lived. Index fossils were originally used to define and identify geologic units, then became a basis for defining geologic periods , and then for faunal stages and zones. Ammonites , graptolites , archeocyathids , inoceramids , and trilobites are groups of animals from which many species have been identified as index fossils that are widely used in biostratigraphy. Species of microfossils such as acritarchs , chitinozoans , conodonts , dinoflagellate cysts, ostracods , pollen , spores and foraminiferans are also frequently used. Different fossils work well for sediments of different ages; trilobites, for example, are particularly useful for sediments of Cambrian age. A long series of ammonite and inoceramid species are particularly useful for correlating environmental events around

3953-552: 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. "Faunachrons" could also be defined beyond

4020-665: The time the most complete phytosaur skull known from the United States. It is also the largest skull referred to Rutiodon , at a length of 77.3 cm (30.4 inches). This skull was described in more detail by Edwin H. Colbert in 1947. Emmons' phytosaur skull was originally stored in the Williams College geological museum, and was later transferred to the National Museum of Natural History (USNM). Many skulls and partial skeletons of R. carolinensis have been discovered near Egypt, North Carolina , and are now housed and displayed at

4087-492: The validity of R. manhattanensis , arguing that the differences between the two species may be due to sexual dimorphism . The exact relationship between Rutiodon and other phytosaurs has gone through much revision. Several papers in the late 20th century extended the scope of the genus Rutiodon , allowing it to encompass phytosaur species from both the eastern and western United States. Western species lumped into Rutiodon include nearly all species previously placed into

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4154-488: The validity of the genus is rarely questioned. Clepsysaurus and Centemodon are most commonly considered dubious and undiagnostic, and their fossils have variably been referred to Rutiodon , Phytosaurus , or Phytosauria incertae sedis by different authors. Othniel Charles Marsh (1893) named Belodon validus , based on a scapula from the New Haven Arkose near Simsbury, Connecticut . In 1896, Marsh mentioned

4221-635: The world during the super-greenhouse of the Late Cretaceous . To work well, the fossils used must be widespread geographically, so that they can be found in many different places. They must also be short-lived as a species, so that the period of time during which they could be incorporated in the sediment is relatively narrow. The longer lived the species, the poorer the stratigraphic precision, so fossils that evolve rapidly, such as ammonites, are favored over forms that evolve much more slowly, like nautiloids . Often biostratigraphic correlations are based on

4288-447: Was described by Friedrich von Huene , who provided a new species name in reference to its close proximity to Manhattan . The fossil is a partially articulated posterior torso, including the hip, hind limbs (missing the feet), and portions of the tail and scutes. It was differentiated from R. carolinensis based on a proportionally larger tibia and more robust hip. R. manhattanensis is also noticeably larger in size: Huene remarked that

4355-484: Was directly ancestral to Rutiodon . This interpretation of synonymy has not been formally published. A 2018 analysis of phytosaur relationships did support a placement for Rutiodon carolinensis as the sister taxon of Angistorhinus in a clade at the base of Mystriosuchinae. Later papers describing Volcanosuchus and Colossosuchus , two basal mystriosuchines from the Tiki Formation of India , did not support

4422-593: Was still under construction. These fossils, including vertebrae, ribs, and scutes, were recovered from red calcareous mudstones of the Ball's Bluff Siltstone . This extends the range of Rutiodon (and phytosaurs as a whole) into the Culpeper Basin . Fossils of a second species, R. manhattanensis , were discovered in 1910 from "red sandy marl" ( Stockton Formation ) below the Palisades near Fort Lee, New Jersey . In 1913, it

4489-619: Was theorized at the beginning of the 19th century by William Smith . When Smith was studying rock strata, he began to recognize that rock outcrops contained a unique collection of fossils. The idea that these distant rock outcrops contained similar fossils allowed for Smith to order rock formations throughout England. With Smith's work on these rock outcrops and mapping around England, he began to notice some beds of rock may contain mostly similar species, however there were also subtle differences within or between these fossil groups. This difference in assemblages that appeared identical at first, lead to

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