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216 to 204 million years ago
The second of the three divisions that make up the Late Triassic , the term Norian was introduced by Mojsisovics in 1895 and Diener in 1926. The term Juvavic was at one time used. [Harland et al] The Norian stage was named after an ancient Roman province south of the Danube River in present-day Austria [Encyclopædia Britannica]. It is named after strata in the Eastern Alps in Europe [Harland et al]. . Geologically speaking, the Norian Stage underlies the Stage and overlies the Stage, these three make up the Upper Triassic . Chronologically, the Norian succeeds the Carnian and is in turned followed by the Rhaetian Age
The Norian was an important period in the history of life on Earth, for it saw the rise to prominence of a number of Mesozoic organisms that had previously played only a minor role in life's drama, and the decline and disappearance of others that had passed their heyday.
Among the successes were the (the and their immediate ancestors) in the seas, and the on land. Among the losers were the that, although still going strong, were experiencing a constant decline throughout the Late Triassic [Teichert 1988 p.59], including a minor extinction event at the Lower to Middle Norian substage boundary [Krystyn, 2003] in the sea; and the formerly ubiquitous herbivorous (the large and medium-sized ) on land. The success of dinosaurs over therapsids seems to be due to climatic factors; the increasing aridity meant that the moist biome that had enabled the therapsids to flourish had now become a narrow equatorial strip [Olsen et al 2001], bordered by deserts and semi-deserts to both north and south.
The Norian began as a world dominated by typically Carnian (and hence typically Triassic) forms on both land and in the sea. By the end of the age life, although retaining many earlier forms, was also well represented by clades that would continue to flourish and dominate for many tens or two hundreds of millions of years.
The Norian was originally introduced for the Pinacoceras metternichi and Cyrtopleurites bicrenatus fauna of the pelagic Hallstatt Limestone facies in the Hallstatt area (Mojsisovics, 1869 cited in Kozur 2003, and Encyclopædia Britannica]. The term Juvavic was at one time used. It is named after strata in the Eastern Alps. . In Europe there are three marine substages, which in ascending order are the Lacian, Alaunian, and Sevatian, which can be correlated worldwide with ammonoid and biozones. The (by Gradstein et al 2004) shows the various geological and magnetostratigraphy divisions, and ammonoid, conodont, palynological, and land vertebrate (Lucas 1998) biozones, that make up the Norian.
The following is an integrated and obviously somewhat speculative table combines Gradstein, Ogg, Smith et al 2004, Benton 1994, Lucas and Hunt 1994 (table) and Lucas 1998. We have given our own suggestion as well. However the more precise tetrapod stratigraphic correlations are tentative and will no doubt be refined and modified with future research and discoveries.
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During the Norian age, reefs are known from both the and the West / North American island-arc terranes. The two provinces followed somewhat different histories.
The Tethys-Panthalassan Reef Province:
Reefs were distributed throughout the vast shallow Tethys Seaway as well as around island outposts and terranes.
The Late Carnian-early Norian interval saw major reef extinctions here, with the loss of older and species (90% of species dying out), but diversity was maintained with reciprocal replacement by new taxa, with reefs were characterized by a diversification of and corals [Stanley 2001, with the emergence of the latter as reef builders [Stanley 2003]. These then in turn become extinct, possibly a result of a sudden global cooling, since the same period saw the extinction of tropical, low latitude ammonoids and their replacement by more cosmopolitan forms [Krystyn, 2003]. The early Norian Tethyan-Panthalassan reef systems are replaced by a much larger reef development during the latest Triassic (mid-Norian to Rhaetian), which extended up to 30°N and 35°S, coinciding with a major rise in global sea-level. At this time new higher taxa appear, sphinctozoid sponges diversify, and corals come to dominate; these two groups constituting a new reef building consortium. These are associated with a diverse selection of other reef organisms. This was a period of worldwide expansion of carbonate platforms (limestone laid down by reef organisms) and maximum reef diversity [Stanley 2003].
The West Pangean Reef Province:
The Triassic reef record for West Pangean / North American island-arc terranes is poor prior to the Norian. The Norian saw a great expansion here, with latitudes similar to those of the Tethys, but beginning even earlier, in the earliest Norian, and continuing through to the Rhaetian. Rare subtropical Carnian patch reefs are known from the western Canadian craton. Although these reefs lacked the development and carbonates deposits of their Tethyan equivalents, these were still high diversity communities, of which at least half were Tethyan species [Stanley 2003].
During the Mid Norian there is the appearance in the West Pangean reefs of more than in the [Stanley 2001]; presumably these forms had remained rare and geographically isolated (Panthalassan volcanic islands might have served as refuges during times of crisis when the Tethys was affected [Stanley 2003]), and possibly Middle Norian conditions were similar to those of the Permian.
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are important stratigraphic markers, because of their rapid evolutionary change. These shelled cephalopods (especially those of the ) were so common and diverse during the Triassic that it has been suggested that this period be called the "Age of Ceratites". But by the Norian, the Ammonoids were on the wane, following their maximum diversity during the Carnian. During this period, ammonoids experienced both gradual change and more dramatic turnovers and occasional extinction events. New discoveries have however shown some unexpected results.
It was previously thought that the Carnian-Norian stage boundaries showed extinctions of many Carnian genera and new Norian forms that replaced them. But new data show considerable overlapping ranges of many genera considered previously as distinct boundary markers, and no extinctions on the family level are observed (the same has been shown to be the case for the Ladinian-Carnian extinction). [Krystyn, 2003)
A strong turnover at the Lower to Middle Norian substage boundary, in which a tropitacean-rich association of tropical, low palaeolatitude affinity is suddenly replaced by a Trachycerataceae dominated fauna of less palaeoclimatic restriction [Krystyn, 2003], seems to indicate a sudden climatic cooling. This was also a period of extinction and turn-over for reef organisms, as the Late Carnian-early Norian reefs made up of corals and sponges died out, to be replaced by the mid-Norian to Rhaetian associations involving sphinctozoid sponges and dominating corals. [Stanley 2001]
A more gradual faunal shift, with overlapping generic ranges, occurred at the Middle (=Alaunian) to Upper Norian (=Sevatian) substage boundary; which seems to be the period during which prosauropod dinosaurs came to dominate terrestrial ecosystems
A much larger extinction event occurs at the traditional Norian-Rhaetian stage boundary (i.e., top of the Reticulatus Zone) and is characterized by the demise of all trachyostracean ammonoids of the superfamilies Trachycerataceae, Clydonitaceae and, Tropitaceae. [Krystyn, 2003] As a result of this, the Rhaetian ammonoid fauna was much more impoverished.
At the base of the Rhaetian, defined by the FAD of M. posthernsteini and C. suessi / C. amoenum, a distinct faunal change can be observed not only for ammonoids, but also , , and . [Kozur 2003]
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As for fish, the Late Triassic saw the first real radiation of the Neopterygii, a radical ecological shift equivalent to the ascendancy of the during the . Significantly, more primitive forms - and "sub-holosteans" - remain important, especially at the top of the food chain. In localities like the richly fossilferous Zorzino Limestone (Calcari di Zorzino), where at 50 genera have been described, all the large predators (Birgeria, Saurichthys) are chondrostean [ref Prof. Andrea Tintori, ].
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The warm Triassic seas are home to a rich marine fauna. Reefs of brilliantly coloured corals and sponges provide shelter for fish, , and other animals. Rising upon the water column of the open seas we find the trophic food chain that has supported higher life on Earth for hundreds of millions of years. Warm sunlight nurtures phytoplankton, which supporting millions of tiny zooplanktonic organisms, which provide food for small fish.
These fish are in turn preyed upon by larger fish and the coiled-shell ceratite ammonoids and squid-like cephalopods. These in turn fall victim to the snapping jaws of small to medium-sized , marine reptiles not unlike modern dolphins, and averaging some 3 meters in length. But even these ichthyosaurs are not the top of the food chain. For ruling the Triassic waves in the earliest Norian, as it did in the late Carnian and will continue to do so throughout the Norian, is the mighty Shonisaurus, a whale-sized predator on anything smaller than itself. For a span of at least fifteen million years - from early Late Carnian to Late Norian and maybe beyond, these ichthyosaurs - far larger than any Cretaceous T. rex - will continue with only minor (species-level) change.
The great diversity of ichthyosaurs is indicated by fossil remains from the Sulphur Mountain and Pardonet formations of British Columbia. Late Triassic ichthyosaurs seem to have belonged to two distinct clades, the medium-sized to gigantic , which were the more common group, and the (as yet still mostly) medium-sized , including Californosaurus and Parvipelvia; the latter being the ancestors of some later Rhaetian types that ushered in the age of "classic" Jurassic marine monsters.
There is some disagreement regarding the phylogenetic position of the shastosaurs; Nicholls and Manabe 2001 argue that the Shastasauridae form a monophyletic taxon, while Maisch & Matzke, 2000 present them as a grade - transitional between Middle Triassic and typical Early Jurassic forms - rather than a clade. Regardless of their exact status, these were often spectacular animals.
Norian Shonisaurs of the Himalayas
It is hard to believe that the mighty snow-capped Himalayas were once shallow sea beds where tropical invertebrates flourished, and above which fish swam and giant ichthyosaurs frolicked, but such is the case, and fossils found here indicate the continuity in time and wide (probably global) dispersion in space of the shastosaurian ichthyosaurs (specifically shonisaurs).
The partial skull and skeleton of Himalayasaurus tibetensis Dong, 1972 was collected from Norian marine strata near Mt Everest, at an altitude of some 4800 meters above sea-level [Lucas 2001 p.117]. Himalayasaurus is a clear descendent or close relative of the late Carnian Shonisaurus popularis, which it resembles closely in size and build. This species is distinguished by the cutting-edges on its flattened tooth crowns, which are otherwise unknown among ichthyosaurs. The large size (around 15 meters) and extensive cutting edges of the teeth indicate a diet of other , and hence a lifestyle perhaps not unlike that of a modern killer whale [Motani et al 1999]. The 10 meter long Tibetosaurus tingjiensis Young, Lui & Zhang, based on a partial skeleton from the Tingi district of Tibet, is indistinguishable in the published diagnosis, and being from the same stratigraphic unit (Langjiexue Group) in nearby localities, are considered by Lucas 2001 p.118 to be synonyms. According to Motani et al 1999, the similarities between H. tibetensis and S. popularis are so small as to indicate the two forms belong to the same genus, the only clear difference between the two being the shape of the tooth crown. If the two species are congeneric, the name Himalayasaurus Dong, 1972 has priority over Shonisaurus Camp, 1976 (being earlier), and the shonisaur species would have to be renamed Himalayasaurus, although it is hoped this won't happen because the name Shonisaurus is already so well known! Maisch and Matzke, 2000 in contrast consider both Himalayasarus and Tibetosaurus as , while in their paper Nicholls and Manabe 2001 use the term Shonisaurus.
Whatever the exact identity of the Himalayan giants, it would be a pretty safe bet to consider them shastosaurs, and almost certainly shonisaurs. The existence of very similar animals on opposite ends of (Shonisaurus is known from the Carnian of California and the Norian of Canada) need not surprise us. The great whales of today have no problem swimming across oceans, and 10 to 25 meter shonisaurs would likewise have swum the Triassic Panthalassan ocean with ease.
Wherever you were in the late Triassic, if you had to go out into the open sea, at the right time, chances are you would glimpse one of these marvelous reptiles surfacing to breath, with a huge spray of water and foam.
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Like the Carnian before it, the Norian age was both a time a change and a time of continuity.
Norian freshwater faunas were little changed from those of the Carnian, including various invertebrates, a diverse selection of fishes, sharks, both chondrostean and primitive neopterygian , and , and amphibians and reptiles. These latter, being at the top of the freshwater food chain, were more susceptible to environmental stress than fish and invertebrates. So we find that among the temnospondyls and phytosaurs a number of Carnian forms have disappeared, such as the and most of the phytosaurs (all belonging to the paraphyletic subfamily (or grade) Rutiodontinae, which experienced a dramatic turn-over, similar to the middle of the late Carnian phytosaur extinction. All Norian phytosaurs are of the subfamily Pseudopalatinae, which evolved from rutiodontines, and like them filled a diverse selection of ecological roles.
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Originally it was believed that there was a mass extinction at the end of the Carnian, even a meteor impact. However, it seems that some of the apparent extinctions were due to sampling bias, as continental drift means the moist environments that favour the typically Carnian biota are under-represented because the rich fossil localities now correlate with higher and more arid latitudes [Olsen et al]. In Eastern North America (centra Pangea) at least, Norian terrestrial assemblages differed little from those of the Latest Carnian (late Tuvalian / Adamanian)). (footprint taxa) found widely across the Newark Supergroup basins in this period include Brachychirotherium (), Apatopus (phytosaur), Rhynchosauroides ( or basal ), Atreipus ( dinosaur) and Grallator (coelophysid dinosaur) [Olsen and Huber 1998]. These taxa generally represent family or related generic groupings, rather than individual species.
This is not to say there was no turn-over at all. During the Norian age the fortunes of the many types of Carnian terrestrial herbivores seem to have declined. The common and cosmopolitan stagonolepine and hyperodopedontine , and the big lizard-like (which in contrast were limited to western equatorial Lausasia), seem to have disappeared completely. The large kannemeyeriid are still present in moist equatorial West Pangea, as are the dog-like . The large aetosaurs are replaced by small ones. The and dinosaurs and the small stocky lizard-like are unaffected, and it seems that the extinctions were insignificant in comparison to the diversity of those that were unaffected. [Hunt, et al]
Unlike the semi-aquatic phytosaurs, terrestrial carnivores have done well. The late Carnian rauisuchian Postosuchus kirkpatricki continues into the early or middle Norian [Lucas 1998, Hunt et al], while the medium-sized predator guild was similarly little affected - dinosaurs are known in the Norian, and "thecodonts", while unknown at this time, are represented in the Late Norian/Rhaetian Los Colorados of Argentina. continue to flourish.
The were the big winners of the Norian, increasing in diversity and size. The theropods increase almost four-fold in linear dimensions from the early Tuvalian (mid Carnian) to the Mid Norian, while at least double the number of dinosaurian species are known from any one time span.
The Norian therefore was an age dominated by . As we have seen, the larger herbivores - the lumbering dicynodonts, and the traversodontid - were now reduced in both diversity and range, confined as Carnian relics to a narrow wet tropical band, although still locally common. The medium-sized carnivorous chiniquodontids were replaced by much smaller, and more mammal-like, forms called Dromatheriidae, the ecological equivalent of a shrew. These advanced tiny cynodonts were probably very successful, but remain poorly known, because such tiny remains are only rarely fossilized.
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As with the Carnian, the Norian is a long period of time (in fact it is the longest age in the Triassic, in terms of duration) that embraces several distinct tetrapod faunas. We find that a number of different ecological and biogeographic communities existed, developed, and were replaced by new communities, the most dramatic being the takeover. A review of these is given here. As large predators are relatively rare, we have - following the "empires" of Anderson & Cruikshank 1978, Bakker 1977, etc - defined these by the most common herbivores or (in the case of the lepidosaurs or common terrestrial metoposaur Apachesaurus) insectivores. They can be represented as follows:
Tetrapods of the Earliest Norian (Early Lacian Age)
Description of this first stage is very speculative, due to incomplete strata.
Following the Carnian-Norian turnover, there is an impoverished fauna. Of the large herbivores the , , and stagonolepine are completely extinct, whilst and have completely disappeared from the north-west and form eastern (but still found in in south-west Pangea). Of the carnivores the (represented by the single genus Saurosuchus) are also gone. Among the semi-aquatics , the rutiodontine and the large are extinct, replaced by and (and in the south). The are the big winners, with several new types appearing.
The West Pangean Aetosaur-Apachesaur Community: As explained, no Earliest Norian terrestrial faunas are known for sure from south-western North America. But it does seem that at some point, perhaps the end of the Carnian, some groups - like the rhynchosaurs and trilophosaurs on land, and the rutiodontine phytosaurs and large metaposaurs in freshwater, disappeared from this region entirely. In fact, the rhynchosaurs and large metaposaurs seem to have died out worldwide, and no post-Carnian trilophosaurs are known with certainty. However, a number of latest Carnian (Adamanian) species seem to have continued unchanged right through to the Late Early Norian, so we can assume that they were present at this time, even if fossils are absent. These species would include the large Postosuchus kirkpatricki, the large aetosaurs Desmatosuchus haplocerus and Paratypothorax andressum, the small metoposaurid Apachesaurus gregorii, and small podokesaur dinosaurs ( or similar)
The Middle Pangean Metoposaur Community: To the north and east, in Central Laurasia, Metoposaurus stuttgartensis is known from the Lehrbergstuff of Stuttgart-Sonnenberg, Germany. This is the only known Norian metaposaur from Europe. Like Apachesaurus the fragmentary remains belonged to a relatively small animal [Milner 1994, p.11]. It seems then that metoposaurs had been drastically diminished at the end of the Carnian, with only a few specialized forms surviving. Interestingly, in , chigutosaurs take their place (as is evident from late Triassic deposits in India), in Europe it is the (Cyclotosaurus) that takes over.
The South-West Pangean Kannemeyeriid-Traversodont Community: In southern Brazil meanwhile, the Catturita Formation of Latest Carnian to Early Norian age, the highest level, informally called the Jachaleria Level [Scherer 1994] includes the Jachaleria candelariensis and the very primitive dinosaur Guaibasaurus candelariensis (which has features indicating affinities with both the Sauropodomorpha and the , implying that it may belong to the ancestral group for both of them; it has been given its own family: the Guaibasauridae. Also found in the Catturita Formation is the earliest known proper, Unaysaurus tolentinoi; preliminary phylogenetic analysis indicates it to be closely related to the European Plateosaurus (Plateosauridae). [Leal et al 2004]
Tetrapods of the Late Early Norian (Late Lacian Age) - Age of the Aetosaurs and Small Dinosaurs - Early Revueltian
In the arid equatorial west, new advanced phytosaurs (Pseudopalatus) and aetosaurs (Typothorax) appear (although these may have evolved in the preceding stage and not been recorded because of absence of equivalent strata). And for the first time, both herbivorous and carnivorous dinosaurs grow as large as the bigger "thecodonts".
The West Pangean Aetosaur-Apachesaur Community: later Early Norian terrestrial faunas are so far only well known from the middle Chinle Group of south-western North America, where it seems that while some groups - like the rhynchosaurs and trilophosaurs on land, and the phytosaurs and metaposaurs in freshwater, disappeared entirely, many of latest Carnian species seem to have continued unchanged, alongside a few newcomers. In the Cooper Canyon Formation of Texas we find a transitional Adamanian-Revueltian fauna characterized by the rauisuchians Postosuchus kirkpatricki and Chatterjeea elegans, the large aetosaur Desmatosuchus haplocerus, all late Carnian, as well as a small metoposaurid (perhaps this is Apachesaurus or a relative) and other temnospondyl amphibians, the advanced phytosaur Pseudopalatus buceros, the small dinosaur Technosaurus smalli, and the procolophonid Libognathus [Small 2002]
In New Mexico the type Revueltian fossil assemblage of the Bull Canyon Formation in New Mexico is dated Early to Middle Norian, and probably extends over some time, as Hunt 1989 distinguishes two biochrons. The "Anaschisma (here = Apachesaurus?) -Belodon- (=Pseudopalatus) Typothorax-Desmatosuchus-Paratypothorax biochron" includes the rauisuchians Postosuchus kirkpatricki and Chatterjeea elegans, Revueltosaurus (formerly thought to be an ornithithischian dinosaur), a diverse aetosaur fauna consisting of Typothorax coccinarum, Desmatosuchus sp. and Paratypothorax sp., the sphenosuchian Hesperosuchus, and the possible ornithischian dinosaur Lucianosaurus wildi [Hunt 1989, Lucas 1998].
The wide diversity of large aetosaurs suggests that they have taken over the role of big herbivore vacated by the trilophosaurs, rhynchosaurs, and dicynodonts with their disappearance from the region at the end of the Carnian.
A small prosauropod is known from fragmentary postcrania from the Cooper Member of the Dockum Formation of Texas, this was previously thought to be an ornithischian because of the presence of ornithischian teeth (Technosaurus) in this locality. However it seems the two animals were distinct [Hunt and Lucas 1994 p.236]. Neither ornithischians nor prosauropods seem to have been as common or important ecologically as aetosaurs, no more than a single species of ornithischian is known from any one locality, and these dinosaurs are rare throughout the Late Triassic [ibid p.236].
A significant new addition to these faunas is the large (5.5 meter) coelophysid theropod Gojirasaurus quayi, from the late early or middle Norian Cooper Canyon Formation of New Mexico. This was the first of the larger carnivorous dinosaurs, although it is unlikely it ever competed directly with the heavily built rauisuchians of the time. It correlates with the appearance of larger theropod footprints in the Newark Supergroup during the middle Norian
See also Therrien and Fastovsky 2000 for a description of this and nearby paleoenvironments (Table 2 in that document includes a list of species)
In this seasonally arid environments, the terrestrial metoposaur Apachesaurus gregorii makes up a common element, while the Carnian aquatic metaposaurs are either very rare or completely absent.
The Middle and East Pangean Aetosaur-Prosauropod-Proterochersid Community: The Lower Stubensandstein fauna of South-west Germany is very similar to that of the Upper Chinle or Upper Dockum of Western North America, and the associated Neshanician stage of the Newark Supergroup of eastern North America (New England, etc). Included here are basic pseudopalatine phytosaurs (Nicrosaurus kampfi), and the large aetosaur Paratypothorax andressum [Rauhut and Hungerbuhler 1998]. These are typical of Revueltian tetrapod assemblages of Lucas 1998. Dinosaurs are represented by the medium- to large-sized (4 to 6 meters long) prosauropod Plateosaurus gracilis, a species which would seem to be directly seem to have been directly ancestral to the later plateosaurs. Temnospondyl amphibians (Cyclotosaurus and Gerrothorax), phytosaurs, and the earliest known turtles (Proterochersis) are all found. No doubt smaller animals were also present. (Aetosaurus ferratus dates from either the Lower or Middle Stubensandstein, the original location is not certain)
No ornithischians have as yet been found, indicating a different community or environment to that of the contemporary West Pangean (SW USA). The only indication of cosmopolitanism is the large aetosaur Paratypothorax andressum which occurs in both regions. Other elements are similar but not identical. There are cyclotosaur capitosaurs instead of apachesaur metoposaurids, the phytosaur Nicrosaurus rather than Pseudopalatus, and prosauropods instead of ornithischians. These differences may be the result of geographic isolation between the two faunas.
A similar fauna occurs in southern Gondwana, since the lower part of Dharmaran Formation, India, which might tentatively be dated at around this time, includes Nicrosaurus, a Paratypothorax-like aetosaur, and prosauropods. [Lucas 1998]
Tetrapods of the Early Middle Norian (Early Alaunian Age) - Age of the Aetosaurs and Small Dinosaurs - Middle Revueltian
The West Pangean Aetosaur-Apachesaur Community: (continued). The upper Bull Canyon Formation in New Mexico represents the Apachesaurus-Pseudopalatus-Typothorax biochron. Filling the medium predator niche is Chatterjeea elegans, which continues from the earlier stage, and a new, small, advanced , Pseudotriconodon chaterjeei, appears. The ornithischian Lucianosaurus replaces Technosaurus. The upper Petrified Forest Member near San Ysidro might be the same age [Hunt 1989]. The aetosaur Aetosaurus arcuatus (I don't know if this occurs in the upper or lower parts of the formation) is known from both New Mexico and the Newark Supergroup of Eastern North America, indicating that, like its larger cousin Paratypothorax andressorum known from both western North America and Europe (although its long stratigraphic range (late Carnian to middle Norian) means it isn't of much help in determining age of the faunas) Hunt and Lucas 1992, these animals traveled widely cross northern .
Understanding the nature of vertebrate faunas of south-western North America depends on the interpretation of the stratigraphy. There is disagreement regarding whether the Whitaker (Ghost Ranch) quarry dates from the early Norian or the . If the latter, then the dinosaurs is Eucoelophysis baldwini, whose fossil remains are known from the Upper Triassic Petrified Forest Formation of the Chinle Group in north-central New Mexico [Sullivan and Lucas 1999]. This was a small animal closely related to (either a near cousin or perhaps an ancestor) to Coelophysis bauri and the Syntarus rhodesiensis. If the former then Eucoelophysis would be Latest Carnian in age. The type horizon of E. baldwini is the upper part of the Petrified Forest Formation, about 45 meters stratigraphically below the locality of the neotype of Coelophysis bauri.
The Central West Pangean Equatorial Aetosaur-Traversodont Community: During the Middle Norian a narrow swath around the Pangean Equator remains home to a persistent Carnian-type biotic province characterized by the presence of small herbivorous traversodont cynodonts, (Plinthogomphodon), rare kannemeyerid dicynodonts, the ubiquitous aetosaur Aetosaurus (Stegomus), a poposaurid rauisuchian similar to Postosuchus, the sphenosuchian Dromicosuchus, and phytosaurs and temnospondyl amphibians. [Olsen et al]
Elsewhere, fossil footprints indicate the presence of , , phytosaurs, a possible herrerasaurid and both small and small- to medium-sized podokesaurid theropod dinosaurs [ref Olsen et al 2002].
Tetrapods of the Late Middle Norian (Alaunian) - Time of Transition - Late Revueltian
In places fairly large sauropodomorphs come to dominate the environment (certainly in the Keuper, and it can be expected elsewhere too). The Middle Stubensandstein of Germany, some of the fissure fillings of Bristol, England, the Ørsted Dal Member of the Fleming Fjord Formation, Greenland; the Zorzino Limestone and Forni Dolomite, northern Italy, share very similar faunas (including the same species, or closely related ones) and can probably be considered more or less contemporary.
This stage then sees the appearance of both advanced forms (e.g. Mystriosuchus) and, curiously, a resurgence of several primitive types (Aetosaurus, Proganochelys, and Thecodontosauridae - Efraasia).
The Middle and East Pangean Prosauropod-Proganochelyid-Aetosaur Community: To the east, in Central Laurasia, in the Middle Stubensandstein, which could be considered contemporary with the above, or nearly so, we find a sudden radiation of sauropodomorphs, which increase in both quantitative numbers and diversity. Sellosaurus is now joined by the small, rare Thecodontosaurus and the large (6 meters long) common Efraasia. Curiously both these species are of a more primitive, basal, type, and would appear to be immigrants, as they have no ancestors in the Lower Stubensandstein. Similarly, Proterochersis has disappeared, and is replaced, by a likewise more primitive form, Proganochelys.
As for other reptiles, the advanced phytosaur Mystriosuchus now joins the more generalized Nicrosaurus. As with the dinosaurs, this is almost certainly an immigrant (perhaps from the , where it is also known), as no obvious ancestors are known. These genera were all provincial (however it has been suggested that Nicrosaurus also occurs in North America, although the interpretation of buceros as Nicrosaurus [Zeigler et al 2001] is controversial [see different interpretation in Hungerb�hler 2002 where it is considered Pseudopalatus], the aetosaur Aetosaurus ferratus is different in species but generically similar and again closely related to its west Laurasian counterpart. Here we also find the rauisuchian Teratosaurus that can be compared to Postosuchus and Chatterjeea.
Two small theropod dinosaurs are also known from this level, the small Procompsognathus triassicus and the medium-sized Halticosaurus longotarsus, the latter too fragmentary identify properly (nomen dubium).
These early dinosaurs lived alongside amphibians (Cyclotosaurus posthumus continues from the Lower Stubensandstein), aetosaurs, and new species of phytosaurs (Mystriosuchus) and sphenosuchids (Saltoposuchus).
This European (Central Laurasian) fauna extended as far as East Laurasia (Thailand), where one finds in the Huai Hin Lat Formation (dated as Norian on the basis of plants and , , , the temnospondyl Cyclotosaurus robustus, indeterminate , a distinct species of Proganochelys (P. ruchae) , and phytosaurs Mystriosuchus and "a Beledon [=Nicrosaurus) -like form" [Buffetaut et al 2000].
The Tethyan Pterosaur-Drepanosaur Community: When we move south to the Tethyan coast, and west to western Laurasia, we find another unique ecosystem. A distinct endemic fauna has been found at the Zorzino Limestone and Forni Dolomite in northern Italy, and represents a tropical coastal environment. Being marine sediments, these can be very accurately dated by and . The Zorzino Limestone turns out to be very close in age to the Alaunian-Sevatian boundary, being placed in the younger part of the Mesohimavatites columbianus zone. The Forni Dolomite, also Mesohimavatites columbianus zone, is dated at Middle-Late Alaunian; it contains different species of and so may be slightly older. The common presence of the aetosaur Aetosaurus ferratus and the phytosaur Mystriosuchus planirostris indicates that the Middle Stubensandstein and the Zorzino Limestone are probably the same age - Latest Middle Norian - or at least fairly contemporary.
The Thecodontosaur-Sphenodont Community: During the late Triassic and early Jurassic in middle north Pangea, limestone caves and crevices in presumably upland regions, served as traps into which animals would stumble into, fall, and be unable to get out. Eventually their bodies were mummified, preserved, and fossilized as the caves filled with sediments. These became the Anglo-Welsh (and French and German) limestone fissure fillings, which have provided fossil remains of a diverse range of small reptiles and early . Although traditionally dated as "Rhaetic" or "Rhaeto-Liassic", it is now considered that many of these faunas are actually Middle or Late Norian, and some may be as early as the late Carnian onwards. In these regions away from the broad floodplains and braided streams that favoured the large sauropodomorphs, a provincial thecodontosaur community developed, perhaps as a subset of a larger prosauropod community. Its endemic nature makes this fauna difficult to correlate with that of larger middle and east Laurasia. Representative forms include thecodontosaur sauropodomorphs, sphenosuchid (Terrestrisuchus) crocodylomorphs, gliding lepidosaurs (Kuehnosaurus), sphenodonts, advanced cynodonts, early mammals, and other small animals. Comparisons are sometimes made between Terrestrisuchus and Thecodontosaurus and the Middle Stubensandstein Saltoposuchus and Thecodontosaurus, in order to suggest a similar date for the Bristol fissure fillings, but similarity does not guarantee they are contemporary; Terrestrisuchus is now considered distinct from Saltoposuchus [Fraser et al 2002], and the Stubensandstein "Thecodontosaurus" is too fragmentary to identify with that genus with certainty.
Tetrapods of the early Late Norian (Sevatian) - Age of Sauropodomorphs
During this time (Late Norian to ) large sauropodomorphs dominate most terrestrial environments (except the north-west). Often a single taxon will be very common: Plateosaurus in Europe / Central and North Laurasia, Euskelosaurus in Southern Africa / South Gondwana, and Riojasaurus in Argentina / South-West Gondwana. This is not to say that a number of other taxa are not often present as well, but these are always much fewer in number. Earlier types of aetosaurs and phytosaurs die out, while new phytosaurs, aetosaurs, and dinosaurs (Syntarsus) appear.
The West Pangean Aetosaur-Apachesaur Community: (continued). Animals of west equatorial Pangea seem to be best represented by the diverse remains discovered at the Whitaker (Ghost Ranch) quarry (Rock Point Member of the Chinle Formation, New Mexico), although a little to the north the Chinle Church Rock Member (Utah) might be considered a similar age [Benton 1994].
This can be considered then the earliest date of the Apachean Land Vertebrate Age, as indicated by the presence of the phytosaur Redondasaurus [Lucas 1998]. Curiously, the predominance of large sauropodomorphs that characterizes the rest of the world is absent here, this indicates either locally distinct conditions or an incorrect date for these strata.
The Low Latitude Central-West Pangea Hypsognathus Community: Further east, and north of the high rainfall band, in what is now eastern USA (Newark Supergroup), the Laurasian desert continues, but here instead of the typical plateosaur community is a more restricted assemblage characterized by the procolophonid Hypsognathus [Lucas 1998], although fossil footprints indicate the presence of lepidosauromorphs, tanystropheids, phytosaurs, rauisuchians, crocodylomorph-like , advanced crocodylomorphs, ornithischian dinosaurs, and both small and small- to medium-sized podokesaurid theropod dinosaurs [ref Olsen et al 2002]. Curiously, ornithischians rather than sauropodomorphs seem to be the main herbivore here.
In Europe the Late (Upper) Stubensandstein witnessed a further increase in dinosaurs. Plateosaurus is ubiquitous, having descended from and replaced the earlier forms. It is represented by a single species, Plateosaurus longiceps (P. trossingensis is a junior synonym [Galton 2001, Galton 2002]) and accompanied by phytosaurs and the long-lived turtle Proganochelys quendstedti, which continues from the Early and Middle Stubensandstein. We can assume many other animals were also present, although they have not been preserved as fossils.
According to Dr Bob Bakker, the pattern of emergence of the anchisaur-plateosaur empire follows very closely that of the earlier lystrosaurid-kannemeyeriid empire. As Bakker explains, in the faunal zone following the Carnian extinctions prosauropod dinosaurs of several closely related families make up nearly all big herbivore specimens.
- "In any one local basin, the diversity appears to be very low, reminiscent of that of the Lystrosaurus Zone; usually one genus of big prosauropod dominates the collections, although various growth stages sometimes have been recognized as distinct genera (Rozdestvenski). Surprisingly, the top predators of these early prosauropod zones are holdovers from the mid-Triassic - ornithosuchid and rauisuchid thecodonts. Advanced theropod dinosaurs take over this trophic role at the Triassic-Jurassic boundary"
This ecological community probably extended for some distance, since prosauropods and turtles are common in the Fleming Fjord Formation (Malmros Klint and Ørsted Dal Members) of East Greenland, where a diverse assemblage of fossil vertebrates very similar to that of the middle Norian Stubensandstein of Germany has been found [ Jenkins et al 1995, Lucas 1998 ] including fish, temnospondyl amphibians (Gerrothorax, Cyclotosaurus), turtles (c.f. Proganochelys sp.), sphendontids, aetosaurs (Aetosaurus ferratus, Paratypothorax andressi), a pterosaur, prosauropod (Plateosaurus), a theropod dinosaur and footprints, and several species of mammals (Kuehneotherium, c.f. Brachyzostrodon, and Haramayavia) . During the Late Triassic, Greenland and continental Europe were adjacent during time, and dinosaurs and other animals clearly migrated widely. The environment was controlled by Milankovitch cycles, with climatic conditions varying from humid to seasonal to arid. Because a number of animals of different time periods are represented, it is likely that several stratigraphic levels are represented here.
Tetrapods of the late Late Norian (Sevatian) - Age of Sauropodomorphs
The Middle Pangean Prosauropod-Proganochelyid (Plateosaur) Community: In middle Laurasia (middle latitude north-central Pangea) the formerly mixed and diverse fauna becomes increasingly dominated by sauropodomorph dinosaurs at the end of the Norian. This appears to be a global trend. The plateosaur community extended widely throughout all of central Laurasia, as the most common plateosaur species (Plateosaurus longiceps, not P. engelhardti as usually identified) is known from Germany, France, Switzerland and Greenland. At this time, the climate in Greenland was very lush, and a rich assortment of plant species thrived (some 200 species are known from the Scoresby Sound area of eastern Greenland, although this represents a stratigraphic sequence extended in time, so not all were contemporary) in the warm and wet (even though high latitude (45 - 50 degrees north) climate. Yet the genus Plateosaurus is found in this part of the world, from the Fleming Fjord Formation, just as in the deserts, and as we have seen is associated with typical Keuper species.
In Germany, the Knollenmergel is almost entirely dominated by plateosaurs. Three species are known - the common Plateosaurus longiceps, the rare Plateosaurus engelhardti (known from Bavaria, probably a geographically distinct form), and a new genus and species Ruehleia bedheimensis [Galton 2001, Galton 2001b, Galton 2002] which however appears to be very similar to Plateosaurus [Headden 2003]. A fourth species of plateosaur, P. erlenbergiensis from this time is known from incomplete remains and hence indeterminate, it is probably a synonym of one of the others. But regardless of how many species one counts, there is little variation, and only one dominate species.
These large dinosaurs are accompanied by phytosaurs - Angistorhinopsis ruetimeyeri replaces the earlier Mystriosuchus and Nicrosaurus - and the ubiquitous early turtle Proganochelys. Cyclotosaurus robustus has been replaced by Cyclotosaurus carinides, and the plagiosaur Gerrothorax pulcherrimus by a related species, Plagiosaurus depressus.
In the trees and the underbrush living alongside these large dinosaurs were many smaller animals. The locality of Saint-Nicolas-de-Port (Late Norian to Early Rhaetian in age) is famous for having yielded numerous mammal teeth.
The South Pangean Melanorosaur-Sauropod (Euskelosaurus) Community: (High Latitude South Pangea) Going south to Gondwana, the Lower Elliott Formation of Southern Africa provides a glimpse of a rich assemblage of advanced early dinosaurs. The Lower Elliot is traditionally dated as Late Carnian on the basis of Dicrodium plants and the presence of typically Carnian elements like traversodonts. However the advanced sauropodomorph elements indicate a later date [Lucas and Hancox 2000], and there is no reason why the Dicrodium biota could not have continued in Gondwana well into the Norian.
In the Lower Elliott of Southern Africa (south Gondwana) then, we find a high latitude location with at least four different proto-sauropod and basal genera (Melanorosaurus, Euskelosaurus, Blikanosaurus, and Antetonitrus). There are no mastodontosaurid (Cyclotosaurus) or plagiosaur amphibians; instead, brachyopoids fill the role of medium to large semi-aquatic predator. Intriguingly, and adding to the distinct Gondwanan flavour of this community, large synapsid herbivores (a kannemeyeriid dicynodont (represented by footprints) and the large cynodont Scalenodontoides) are also present, although rarer than the dinosaurs. The dominance of giant dinosaur herbivores (in this case Euskelosaurus is especially common) shows an ecological equivalence with the plateosaur community to the north, and we can assume that these large animals were found worldwide. Again, the climate is seasonal monsoonal (savannah-like) to semi-arid. One also finds in Gondwana large rauisuchians - represented by Fasolosuchus in the west (Argentina) and "Basutodon" further south and east. Podokesaurid (= Coelophysid) theropods are indicated by the presence of numerous small to medium-large sized tridactyl footprints (Grallator and larger forms, the nomenclature of the latter (by Ellenberger 1970) is very oversplit.)
Also in Gondwana, the slightly younger (probably Rhaetian) Los Colorados of Argentina reveals a similar preponderance of large sauropodomorphs. It would seem likely in any case that the Sauropodomorph fauna continues through to the Rhaetian with little change; although the extreme provinciality of this time makes comparative dating difficult (so some formations attributed to Late Norian may be Rhaetian, and vice versa).
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