News Article | April 17, 2017
Out in eastern Utah, where the rock is laid out in immense swaths of orange and red, there’s a very special impression. The fossil can be a little hard to find, hidden beneath an overhang, but, should you be lucky enough to spot it, there’s no mistaking what it is. Preserved in the ancient sandstone is the triangular outline of a phytosaur skull – a natural mold left by fossil bones from this superficially crocodilesque creature that lived over 200 million years ago. Paleontologists Michael Morales and Sidney Ash called this fossil The Last Phytosaur. In terms of geological layers, the fossil sits above most other finds of its ilk, pressed into the Wingate Sandstone which – somewhere in its depths – contains the transition between the Triassic and Jurassic world. Whether or not this fossil truly represents the last of these crocodile-like reptiles isn't known. We’d need a time machine to check that. But it stands in as a bookend for a lineage of diverse and widespread aquatic ambush predators that made their living among the Triassic waterways. The ultimate phytosaurs, like the Last Phytosaur itself, resembled modern crocodylians in many ways. They were pioneering a life lurking in the shallows while the ancestors of today’s crocodiles were still skittering around on land. But what were the first phytosaurs like? A recent find in China helps fill in the backstory of this oft-neglected group of reptiles. Back in 2012 paleontologist Chun Li and colleagues named Diandongosuchus fuyuanensis from the Middle Triassic rock of China. The initial analysis of the fossil concluded that this short-snouted, sharp-toothed animal was a poposaur, on a branch within the wider crocodile family. But a new study of the fossil by paleontologist Michelle Stocker, Li, and coauthors has come to a different conclusion. Diandongosuchus is now the earliest known phytosaur. Up until now, the oldest phytosaurs were about 228 million years old. Diandongosuchus now extends the family’s record back about 10 million years fruther, highlighting just how much these reptiles changed in that interval. The fact that Diandongosuchus was initially mistaken for a very different variety of reptile highlights the fact that the earliest phytosaurs didn’t look exactly like their more famous later relatives. The skull of Diandongosuchus is wedge shaped, with a short snout and nasal openings only slightly retracted from the tip of the nose. Still, Stocker and colleagues write, the skull and postcrania of this well-preserved reptile show anatomical hallmarks present among phytosaurs but lacking in early crocodiles. Other phytosaur fossils will hopefully fill in the millions of years between Diandongosuchus and the next phytosaurs. For now, though, this revised reptile shows that the postcranial skeletons of phytosaurs evolved some of their key characteristics before their skulls evolved into more elongate, gharial-like forms. Diandongosuchus also shows some specializations of the skull related to increased bite strength, the researchers point out, which may have helped open up the possibility for phytosaurs to become the widespread ambush predators they were. The sharp snout of Diandongosuchus not only points to the successful future of its kind, but how much more there is left to uncover about the dawn of the phytosaurs. Morales, M., Ash, S. 1993. The last phytosaurs? New Mexico Museum of Natural History and Science Bulletin. 3: 357-358 Stocker, M., Zhao, L., Nesbitt, S., Wu, X., Li, C. 2017. A short-snouted, Middle Triassic phytosaur and its implications for the morphological evolution and biogeography of Phytosauria. Scientific Reports. doi: 10.1038/srep46028
News Article | November 25, 2015
What if the dinosaur-killing asteroid never slammed into Earth and the paleo-beasts weren't vanquished from our planet 66 million years ago? That's the hypothetical that forms the basis of Pixar's "The Good Dinosaur," set to hit the big screens on Nov. 25. The movie maker's answer — that a young Apatosaurus would meet and befriend a cave boy — is cute, but totally off the mark, several paleontologists told Live Science. "It's completely impossible," said Thomas Williamson, curator of paleontology at the New Mexico Museum of Natural History and Science, referring to dinosaurs ever being alive alongside humans — something that could never happen if the dinosaurs were to survive. [Wipe Out: History's Most Mysterious Extinctions] Though there were mammals during the dinosaur's reign of the Mesozoic era, these animals were small, no larger than the size of a house cat. It's wasn't until the nonavian dinosaurs went extinct that mammals grew in size and specialty, eventually giving rise to the human lineage about 60 million years later. "Dinosaurs had been around for over 150 million years when the asteroid hit, and were doing quite well up until that fateful day," said Steve Brusatte, a paleontologist at the University of Edinburgh. If the asteroid hadn't hit Earth, "I have no doubt that they would have kept evolving and thriving." If dinosaurs hadn't perished, "mammals would have never gotten their chance to evolve in that brave new world, free of their dinosaur overlords," Brusatte told Live Science. "Without mammals getting their chance, then there would have been no primates, and then no humans." Mammals originated about 220 million years ago, about the same time as the dinosaurs during the Late Triassic. But dinosaurs got the upper hand — they diversified into thousands of species, spread around the world and grew to gargantuan sizes. "Mammals stayed in the shadows," and none of them seemed to dominate their environment, Brusatte said. Instead, early mammals mostly ate insects, maybe seeds and the occasional tiny dinosaur, according to fossil evidence. When the 6-mile-wide (10 kilometers) asteroid collided with Earth, mammals and dinosaurs alike suffered great losses. All of the dinosaurs — except birds — bit the dust, and about 75 percent of all mammals died, said Gregory Wilson, an adjunct curator of vertebrate paleontology at the Burke Museum of Natural History and Culture in Seattle. But there were some survivors. "A few plucky mammals made it through the devastation of the extinction," Brusatte said. "These mammals seemed to be ones that were particularly small and had generalist diets, so they could survive by hiding and eating lots of different foods — traits that helped them endure the chaos after the asteroid hit." Once the nonavian dinosaurs were kaput, the mammals took over their ecological niches. Within a few hundred thousand years, mammals rapidly evolved (geologically speaking) into new species, diversified their diets and achieved new sizes. About 500,000 years after the dinosaur's demise, some mammals had reached the size of German shepherds, Williamson said. These spirited survivors are the reasons why there are more than 5,000 species of mammals today, Brusatte said. [In Photos: Mammals Through Time] "It's pretty obvious to me that none of this could have happened if the dinosaurs didn't die out," he said. "The mammals that lived with the dinosaurs had about 150 million years to make it happen, but they could never do it. But then, boom, right when the dinosaurs died, the mammals began to explosively diversify." Still, once "The Good Dinosaur" opens in theaters, Brusatte plans to see the film. "I'm not expecting the film to be an accurate portrayal of dinosaurs," he said. "It's obviously not trying to be a dinosaur documentary, and that's OK. The dinosaurs may not look or behave like real dinosaurs would have, but I hope it's a good story and an entertaining film." Copyright 2015 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
News Article | February 15, 2017
Katherine Jetter announces the opening of an exhibition of opals from around the globe at the New Mexico Museum of Natural History and Science on Friday, Feb. 10, 2017, of which she is the guest curator. The Wonderful World of Opals features cut and uncut stones from Australia, Mexico, Ethiopia and Peru, as well as some set opal jewels from Jetter’s own collection. A one-of-a-kind rough opal specimen from Australia that weighs over 160 pounds is also part of the show. Grand opening events for the public include short talks, displays, and demonstrations at the museum on Feb. 10, and Feb. 11, 2017. Jetter was approached by the New Mexico Department of Cultural Affairs in 2016 and worked to produce a collection of over 50 specimens, some of the finest in the world, one of which is encased in a fossilized dinosaur bone. Jetter collaborated with some of the world’s foremost opal miners, two of who will be present at a private reception on February 9: Bill Kasso of Eagle Creek Opals and Charlie Alsen of Opal Country. Other contributing miners include Andrew and Damien Cody of Cody Opal, Juergen Schuetz of Emil Weis and Susan Cooper of Broken River Mining. Jetter was recently selected by jewelry historian Olivier Dupon as one of his top picks of 35 contemporary jewelers in the world, featured in his newly launched book Fine Jewelry Couture: Contemporary Heirlooms. "This is an exceptional collection of opals curated by a leader in the opal industry,” said Margie Marino, director of the New Mexico Museum of Natural History & Science. “The Museum is very proud to be able to work with world-wide partners to bring this exhibition to the people of New Mexico. This is a rare opportunity for visitors to the Museum to see a whole opal in its raw state and examine how it is formed,” she said. A number of collaborative and educational events have been scheduled for the opening weekend to enhance the visitor experience. Events Scheduled for Saturday, Feb. 11, 2017 Free with Museum Admission 10am to 3pm: Rock, mineral and gem demonstrations and displays by the Albuquerque Gem and Mineral Club/Museum Lapidary Studio FOR MEDIA INQUIRIES (including images and information about the private reception on February 9): Jennifer Hobson-Hinsley Jennifer(@)jlhmedia(.)com 505 603 8643 ### ABOUT KATHERINE JETTER LTD: Katherine Jetter was born in Melbourne, Australia and spent her youth in England, Germany, Italy, and Switzerland. After attending SevenOaks School in Kent, UK, Katherine received a Bachelors Degree in Clinical Psychology from University College of London followed by an analyst position at JP Morgan. After attending the globally renowned Gemological Institute of America (GIA) and receiving certification as a Graduate Gemologist and Jewelry Designer, Katherine put her expertise to use by working for various international, high-end designer jewelers, including De Beers. Launching Katherine Jetter Ltd. in 2008, her collection was immediately picked up by Saks Fifth Avenue and Neiman Marcus after showcasing at the prestigious Couture Jewelry Show in 2009. Katherine’s beautiful collections are featured in numerous retailers worldwide from Moscow to China including a selection of Neiman Marcus stores and high profile independent retailers across the U.S. Katherine and her husband, Daniel Burrell, moved to Santa Fe in 2010. They are active philanthropists in the community, with a key focus on furthering education for young people in New Mexico and have formed a foundation to support these efforts, the New Mexico Leadership Institute (NMLI), of which Katherine is President. NMLI partners with The University of New Mexico (UNM), New Mexico State University (NMSU) and top business leaders to provide New Mexico high school students with training and mentoring designed to develop effective leadership skills. Katherine is also on the Executive Board for NDI (New Mexico Dance Institute), and ran the Garfield Street Foundation on behalf of Rosemont Realty for 3 years. Katherine and Daniel have a daughter, Dylan, who is two years old. ABOUT THE NEW MEXICO MUSEUM OF NATURAL HISTORY & SCIENCE: The New Mexico Museum of Natural History and Science is a Division of the New Mexico Department of Cultural Affairs. The Department of Cultural Affairs is New Mexico’s cultural steward and is charged with preserving and showcasing the state’s cultural riches. With its eight museums, eight historic monuments, arts, archaeology, historic preservation and library programs, the New Mexico Department of Cultural Affairs is the largest state cultural agency in the nation.
News Article | October 30, 2015
Dinosaur remains that were discovered in the New Mexico wilderness were recently airlifted out of the area by a helicopter of the state's National Guard and transferred to a museum in Albuquerque. Experts from the New Mexico Museum of Natural History and Science watched as the full skeletal fossils of a young Pentaceratops were encased in a plaster and airlifted away from the wilderness. The young Pentaceratops was once an herbivorous dinosaur with large horns that lived roughly 10 million years ago in the area which is now known as North America. Scientists from the museum took a special interest in the dinosaur when they found the remains during a trek to the Bisti wilderness in 2011. They knew that they had to find a way to unearth the fossils and get them into their museum. Aside from the young Pentaceratops, the National Guard also airlifted the skull of an adult Pentaceratops which was discovered about 10 miles away from the site. Museum curator Spencer Lucas explained that since the fossils were found in federal area that is off-limits to vehicles, the National Guard had to deploy their Blackhawk helicopters to get the remains. Lucas said that the team had to pack in countless water jugs, hundreds of pounds of plaster, and a battery of heavy tools for the operation. The museum's Facebook page posted several photos that showed the transfer, and the experts announced that one plaster of the fossils will be on display on Nov. 5. Captain Kevin Doo, the National Guard aviator who performed the transfer, said that the event was one of the highlights of his career. He also said that the skull of the adult Pentaceratops weighed 4,500 pounds, and that even with the upgraded engines of the Blackhawk, lifting the fossils was a real challenge. Meanwhile, Lucas said that the event marks the first skeleton and skull of a baby Pentaceratops ever to be recovered. She also said that a total of less than 10 adult Pentaceratops have been excavated over the past century. "We know what the adult skull of a Pentaceratops looks like, but we've never seen a juvenile skull. So it will be interesting to see what the differences are in shape, the size of the horns and other kinds of features," he said. Scientists have yet to uncover how the baby Pentaceratops met its demise, but they said that the remains seem to have been washed down. Lucas added that they still have to clean up and arrange the dinosaur's bones, and that they will be examining it for tooth marks. It will take a while before they find answers, he said, but the museum is very interested and dedicated in the study of these fossils.
Silcox M.T.,University of Toronto |
Williamson T.E.,New Mexico Museum of Natural History and Science
Journal of Human Evolution | Year: 2012
Primates underwent a period of diversification following the extinction of non-avian dinosaurs. Although the Order first appeared near the Cretaceous-Paleogene boundary, it is not until the Torrejonian (the second North American Land Mammal Age of the Paleocene) that a diversity of families began to emerge. One of the lithological units critical to understanding this first primate adaptive radiation is the early Paleocene Nacimiento Formation of the San Juan Basin (SJB; New Mexico). Primates previously described from this formation comprise six species of palaechthonid and paromomyid plesiadapiforms, all known from very limited material. Collecting has increased the sample of primate specimens more than fivefold. Included in the new sample is the first specimen of a picrodontid plesiadapiform from the Torrejonian of the SJB, referable to Picrodus calgariensis, and the first paromomyid specimen complete enough to allow for a species level taxonomic assignment, representing a new species of Paromomys. With respect to the 'Palaechthonidae', the current report describes large collections of Torrejonia wilsoni and Palaechthon woodi, and the first new specimens attributed to Plesiolestes nacimienti and Anasazia williamsoni since 1972 and 1994, respectively. These collections demonstrate previously unknown morphological variants, including the presence of a metaconid on the p4 of some specimens of T. wilsoni, a discovery that supports previous inferences about a close relationship between Torrejonia and Plesiolestes problematicus. This new sample considerably improves our knowledge of the poorly understood 'Palaechthonidae', and about the biostratigraphy, biogeography, and early evolution of North American primates. In particular, the rarity of paromomyids, the continuing absence of plesiadapid and carpolestid plesiadapiforms, and the presence of a number of endemic palaechthonid species in the SJB contrast with plesiadapiform samples from contemporaneous deposits to the north. Together, these data suggest that by the latter part of the early Paleocene primates had already developed not only an impressive diversity, but patterns of regional endemism. © 2012 Elsevier Ltd.
News Article | October 30, 2015
The various skeletal pieces that researchers uncovered of the ancient bird that lived just after the age of the dinosaurs. More A teeny-tiny fossilized bird skeleton is helping researchers understand the explosive rate at which birds diversified after the dinosaur age, new research shows. The newfound skeleton dates back to about 62.5 million to 62 million years ago, making it the oldest known modern bird specimen in North America to live after the dinosaur-killing mass extinction, the researchers said. Its mere existence suggests that birds rapidly evolved in the 3 million to 4 million years after the dinosaurs died — much faster than previously thought, they said. "Birds were explosively diversifying right after the end of the Cretaceous, right after the big mass extinction," said study co-author Tom Williamson, curator of paleontology at the New Mexico Museum of Natural History and Science. [Avian Ancestors: Dinosaurs That Learned to Fly (Gallery)] Birds have a lengthy past. They began their evolutionary split from dinosaurs during the Jurassic period, about 150 million years ago. But like their scaly relatives, many bird lineages went extinct when a roughly 6-mile-long (10 kilometers) asteroid smashed into Earth about 66 million years ago. "Maybe a dozen or less lineages of birds survived," said study co-author Daniel Ksepka, curator of science at the Bruce Museum in Greenwich, Connecticut. (Today, there are about 40 lineages of birds that include more than 10,000 living species, he said.) Without dinosaurs and the other extinct animals in the way, bird diversity suddenly skyrocketed, and the newfound skeleton shows just how quickly it did so, Ksepka told Live Science. Williamson's 12-year-old twin sons found the delicate skeleton during a fossil dig in northwestern New Mexico in 2007. Williamson later excavated the fragmented bones, which are so small that the bird was likely no larger than a sparrow — smaller than the size of a human fist, he said. The tiny bones piqued Williamson's interest, so he teamed up with Ksepka and Thomas Stidham, an avian paleontologist at the Institute for Vertebrate Paleontology and Paleoanthropology in Beijing. The researchers analyzed the fossils, looking at 120 different size and shape characteristics. They found that the newfound species (which they have yet to name) is part of an extinct family of birds that is closely related to owls and mouse birds — a group of small, long-tailed birds that live only in sub-Saharan Africa. If this tiny, newfound bird was already living about 62 million years ago, it suggests that other modern birds, especially its close relatives, developed earlier than previously thought. For instance, the new evidence indicates that the mouse bird evolved some 6 million years earlier than researchers had thought, Ksepka said. "This bird has some wide implications for the timing of the radiation [diversification] of modern birds," Ksepka said. But "to pinpoint exactly when these birds are popping up, we really need the fossil record," he added. In 1980, other researchers, in New Zealand, discovered the fossilized skeleton of a penguin (Waimanu manneringi) that dates to between 60.5 million and 61.6 million years ago. "Together, the new bird and Waimanu show that the diversifications of aquatic and terrestrial birds were both well underway just a few million years after the mass extinction that hit 66 million years ago," Ksepka said. In fact, the compressed but explosive 4-million-year diversification that modern birds likely underwent after the dinosaur extinction is similar to the diversification of placental mammals, which also rapidly diversified after the nonavian dinosaurs died, he said. The researchers presented the unpublished findings earlier this month at the 75th annual Society of Vertebrate Paleontology conference in Dallas. Copyright 2015 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Williamson T.E.,New Mexico Museum of Natural History and Science |
Brusatte S.L.,University of Edinburgh
PLoS ONE | Year: 2014
Studying the evolution and biogeographic distribution of dinosaurs during the latest Cretaceous is critical for better understanding the end-Cretaceous extinction event that killed off all non-avian dinosaurs. Western North America contains among the best records of Late Cretaceous terrestrial vertebrates in the world, but is biased against small-bodied dinosaurs. Isolated teeth are the primary evidence for understanding the diversity and evolution of small-bodied theropod dinosaurs during the Late Cretaceous, but few such specimens have been well documented from outside of the northern Rockies, making it difficult to assess Late Cretaceous dinosaur diversity and biogeographic patterns. We describe small theropod teeth from the San Juan Basin of northwestern New Mexico. These specimens were collected from strata spanning Santonian - Maastrichtian. We grouped isolated theropod teeth into several morphotypes, which we assigned to higher-level theropod clades based on possession of phylogenetic synapomorphies. We then used principal components analysis and discriminant function analyses to gauge whether the San Juan Basin teeth overlap with, or are quantitatively distinct from, similar tooth morphotypes from other geographic areas. The San Juan Basin contains a diverse record of small theropods. Late Campanian assemblages differ from approximately co-eval assemblages of the northern Rockies in being less diverse with only rare representatives of troodontids and a Dromaeosaurus-like taxon. We also provide evidence that erect and recurved morphs of a Richardoestesia-like taxon represent a single heterodont species. A late Maastrichtian assemblage is dominated by a distinct troodontid. The differences between northern and southern faunas based on isolated theropod teeth provide evidence for provinciality in the late Campanian and the late Maastrichtian of North America. However, there is no indication that major components of small-bodied theropod diversity were lost during the Maastrichtian in New Mexico. The same pattern seen in northern faunas, which may provide evidence for an abrupt dinosaur extinction. © 2014 Williamson, Brusatte.
Lucas S.G.,New Mexico Museum of Natural History and Science
Geological Society Special Publication | Year: 2010
The Triassic timescale based on nonmarine tetrapod biostratigraphy and biochronology divides Triassic time into eight land-vertebrate faunachrons (LVFs) with boundaries defined by the first appearance datums (FADs) of tetrapod genera or, in two cases, the FADs of a tetrapod species. Definition and characterization of these LVFs is updated here as follows: the beginning of the Lootsbergian LVF = FAD of Lystrosaurus; the beginning of the Nonesian = FAD Cynognathus; the beginning of the Perovkan LVF = FAD Eocyclotosaurus; the beginning of the Berdyankian LVF = FAD Mastodonsaurus giganteus; the beginning of the Otischalkian LVF = FAD Parasuchus; the beginning of the Adamanian LVF = FAD Rutiodon; the beginning of the Revueltian LVF = FAD Typothorax coccinarum; and the beginning of the Apachean LVF = FAD Redondasaurus. The end of the Apachean (= beginning of the Wasonian LVF, near the beginning of the Jurassic) is the FAD of the crocodylomorph Protosuchus. The Early Triassic tetrapod LVFs, Lootsbergian and Nonesian, have characteristic tetrapod assemblages in the Karoo basin of South Africa, the Lystrosaurus assemblage zone and the lower two-thirds of the Cynognathus assemblage zone, respectively. The Middle Triassic LVFs, Perovkan and Berdyankian, have characteristic assemblages from the Russian Ural foreland basin, the tetrapod assemblages of the Donguz and the Bukobay svitas, respectively. The Late Triassic LVFs, Otischalkian, Adamanian, Revueltian and Apachean, have characteristic assemblages in the Chinle basin of the western USA, the tetrapod assemblages of the Colorado City Formation of Texas, Blue Mesa Member of the Petrified Forest Formation in Arizona, and Bull Canyon and Redonda formations in New Mexico. Since the Triassic LVFs were introduced, several subdivisions have been proposed: Lootsbergian can be divided into three sub-LVFs, Nonesian into two, Adamanian into two and Revueltian into three. However, successful inter-regional correlation of most of these sub-LVFs remains to be demonstrated. Occasional records of nonmarine Triassic tetrapods in marine strata, palynostratigraphy, conchostracan biostratigraphy, magnetostratigraphy and radioisotopic ages provide some basis for correlation of the LVFs to the standard global chronostratigraphic scale. These data indicate that Lootsbergian = uppermost Changshingian, Induan and possibly earliest Olenekian; Nonesian = much of the Olenekian; Perovkan = most of the Anisian; Berdyankian = latest Anisian? and Ladinian; Otischalkian = early to late Carnian; Adamanian = most of the late Carnian; Revueltian = early-middle Norian; and Apachean = late Norian-Rhaetian. The Triassic timescale based on tetrapod biostratigraphy and biochronology remains a robust tool for the correlation of nonmarine Triassic tetrapod assemblages independent of the marine timescale. © The Geological Society of London 2010.
Lucas S.G.,New Mexico Museum of Natural History and Science
Geological Society Special Publication | Year: 2010
The Triassic chronostratigraphic scale is a hierarchy of three series, seven stages and 15 substages developed during nearly two centuries of research. The first geological studies of Triassic rocks began in Germany in the late 1700s and culminated in 1834 when Friedrich August von Alberti coined the term 'Trias' for the Bunten Sandsteins, Muschelkalk and Keuper, a thick succession of strata between the Zechstein and the Lias. Recognition of the Trias outside of Germany soon followed, and by the 1860s Austrian geologist Edmund von Mojsisovics began constructing a detailed Triassic chronostratigraphy based on ammonoid biostratigraphy. In 1895, Mojsisovics and his principal collaborators, Wilhelm Waagen and Carl Diener, published a Triassic timescale that contains most of the stage and substage names still used today. In 1934, Leonard Spath proposed a Triassic ammonoid-based biochronological timescale that differed little from that of Mojsisovics and his collaborators. In the 1960s, E. Timothy Tozer proposed a Triassic ammonoid-based timescale based on North American standards, and his timescale included proposal of four Lower Triassic stages (Griesbachian, Dienerian, Smithian and Spathian). The work of the Subcommission on Triassic Stratigraphy began in the 1970s and resulted in current recognition of seven Triassic stages in three series: Lower Triassic-Induan, Olenekian; Middle Triassic-Anisian, Ladinian; Upper Triassic-Carnian, Norian and Rhaetian. The 1990s saw the rise of Triassic conodont biostratigraphy so that four intervals that have agreed on Triassic GSSPs use conodont occurrences as defining features: bases of Induan, Olenekian, Anisian and Rhaetian. The bases of the Ladinian and Carnian are defined by ammonoid events. The base of the Norian remains undefined, but will most likely be defined by conodonts. Except for the Rhaetian, the Middle and Upper Triassic stages and substages have been fairly stable for decades, but there has been much less agreement on Lower Triassic chronostratigraphic subdivisions. Issues in the development of a Triassic chronostratigraphic scale include those of: stability and priority of nomenclature and concepts; disagreement over and changing taxonomy; the use of ammonoid v. conodont biostratigraphy; differences in the perceived significance of biotic events for chronostratigraphic classification; disagreements about the utility of relatively short stages; correlation problems between the Tethyan and Boreal realms (provinces); and competing standards from the Old and New worlds. Most of these issues have been resolved in the recognition of three Triassic series and seven stages. Further development of the Triassic chronostratigraphic scale needs to focus on definition and characterization of the 15 Triassic substages as these will provide a much more detailed basis for subdivision of Triassic time than do the seven stages. © The Geological Society of London 2010.
Lucas S.G.,New Mexico Museum of Natural History and Science
Geological Society Special Publication | Year: 2010
German geologists began to study rocks now recognized as Triassic during the late 1700s. In 1823, one of those German geologists, a very astute mining engineer named Friedrich August von Alberti (1795-1878), coined the term 'Trias formation' for an c. 1 km thick, tripartite succession of strata in southwestern Germany - the Bunten Sandsteins, Muschelkalk and Keuper of the German miners. Alberti also recognized Triassic rocks outside of Germany, throughout much of Europe and as far away as India and the United States. By the end of the nineteenth century, Triassic rocks had been identified across Europe and Asia, and in North America, South America and Africa. Indeed, in 1895, the Austrian geologist Edmund von Mojsisovics (1839-1907) and his collaborators published a complete subdivision of Triassic time based on ammonoid biostratigraphy and, in so doing, introduced many of the Triassic chronostratigraphic terms still used today. The twentieth century saw the elaboration of an ammonoid-based Triassic timescale, especially due to the work of Canadian palaeontologist E. Timothy Tozer (1928-). During the last few decades, work also began on developing a global magnetic polarity timescale for the Triassic, a variety of precise numerical ages tied to reliable Triassic biostratigraphy have been determined, and conodont biostratigraphy has become an important tool in Triassic chronostratigraphic definition and correlations. The current Triassic chronostratigraphic scale is a hierarchy of three series (Lower, Middle, Upper) divided into seven stages (Lower = Induan, Olenekian; Middle = Anisian, Ladinian; and Upper = Carnian, Norian, Rhaetian) further divided into 15 substages (Induan = upper Gries-bachian, Dienerian; Olenekian = Smithian, Spathian; Anisian = Aegean, Bithynian, Pelsonian, Illyrian; Ladinian = Fassanian, Longobardian; Carnian = Julian, Tuvalian; Norian = Lacian, Alaunian, Sevatian). Ammonoid and conodont biostratigraphies provide the primary basis for the chronostratigraphy. A sparse but growing database of precise radioisotopic ages support these calibrations: base of Triassic c. 252 Ma, base Olenekian c. 251 Ma, base Anisian c. 247 Ma, base Ladinian c. 242 Ma, base Jurassic c. 201 Ma. A U/Pb age of c. 231 Ma from the Italian Pignola 2 section is lower Tuvalian, and U/Pb ages on detrital zircons from the non-marine Chinle Group of the western USA of c. 219 Ma are in strata of late Carnian (Tuvalian) age based on the biostratigraphy of palynomorphs, conchostracans and tetrapods. These data support placement of the Norian base at c. 217 Ma, and indicate that the Tuvalian is more than 10 million years long and that the Carnian and Norian are the longest Triassic stages. Magnetostratigraphic data establish normal polarity for all of the Triassic stage bases except Anisian and Ladinian. An integrated biostratigraphic correlation web for the marine Triassic consists of ammonoids, bivalves, radiolarians and conodonts, whereas a similar web exists for the nonmarine Triassic using palynomorphs, conchostracans and tetrapods. Critical to cross correlation of the two webs is the Triassic section in the Germanic basin, where a confident correlation of nonmarine biostratigraphy to Triassic stage boundaries has been achieved. The major paths forward in development of the Triassic timescale are: finish formal definition of all Triassic stage boundaries, formally define the 15 Triassic substages, improve the integration of the Triassic biostratigraphic webs and develop new radioisotopic and magnetostratigraphic data, particularly for the Late Triassic. © The Geological Society of London 2010.