Jeffrey W. Martz

The Late Triassic (Norian) Adamanian–Revueltian tetrapod faunal transition in the Chinle Formation of Petrified Forest National Park, Arizona

Recent stratigraphic revisions of the Upper Triassic Chinle Formation of Petrified Forest National Park, in conjunction with precise and accurate documentation of fossil tetrapod occurrences, clarified the local biostratigraphy, with regional and global implications. A significant overlap between Adamanian and Revueltian faunas is rejected, as is the validity of the Lamyan sub-land vertebrate faunachron. The Adamanian–Revueltian boundary can be precisely placed within the lower Jim Camp Wash beds of the Sonsela Member and thus does not occur at the hypothesised Tr-4 unconformity. This mid-Norian faunal turnover, may coincide with a floral turnover, based on palynology studies and also on sedimentological evidence of increasing aridity. Available age constraints bracketing the turnover horizon are consistent with the age of the Manicouagan impact event. The rise of dinosaurs in western North America did not correspond to the Adamanian–Revueltian transition, and overall dinosauromorph diversity seems to have remained at a constant level across it. The paucity of detailed Late Triassic vertebrate biostratigraphic data and radioisotopic dates makes it currently impossible to either support or reject the existence of globally synchronous Late Triassic extinctions for tetrapods.

Revised Lithostratigraphy of the Sonsela Member (Chinle Formation, Upper Triassic) in the Southern Part of Petrified Forest National Park, Arizona

Background Recent revisions to the Sonsela Member of the Chinle Formation in Petrified Forest National Park have presented a three-part lithostratigraphic model based on unconventional correlations of sandstone beds. As a vertebrate faunal transition is recorded within this stratigraphic interval, these correlations, and the purported existence of a depositional hiatus (the Tr-4 unconformity) at about the same level, must be carefully re-examined. Methodology/Principal Findings Our investigations demonstrate the neglected necessity of walking out contacts and mapping when constructing lithostratigraphic models, and providing UTM coordinates and labeled photographs for all measured sections. We correct correlation errors within the Sonsela Member, demonstrate that there are multiple Flattops One sandstones, all of which are higher than the traditional Sonsela sandstone bed, that the Sonsela sandstone bed and Rainbow Forest Bed are equivalent, that the Rainbow Forest Bed is higher than the sandstones at the base of Blue Mesa and Agate Mesa, that strata formerly assigned to the Jim Camp Wash beds occur at two stratigraphic levels, and that there are multiple persistent silcrete horizons within the Sonsela Member. Conclusions/Significance We present a revised five-part model for the Sonsela Member. The units from lowest to highest are: the Camp Butte beds, Lots Wife beds, Jasper Forest bed (the Sonsela sandstone)/Rainbow Forest Bed, Jim Camp Wash beds, and Marthas Butte beds (including the Flattops One sandstones). Although there are numerous degradational/aggradational cycles within the Chinle Formation, a single unconformable horizon within or at the base of the Sonsela Member that can be traced across the entire western United States (the “Tr-4 unconformity”) probably does not exist. The shift from relatively humid and poorly-drained to arid and well-drained climatic conditions began during deposition of the Sonsela Member (low in the Jim Camp Wash beds), well after the Carnian-Norian transition.

Aetosauria: a clade of armoured pseudosuchians from the Upper Triassic continental beds

Abstract Aetosauria is a clade of obligately quadrupedal, heavily armoured pseudosuchians known from Upper Triassic (late Carnian–Rhaetian) strata on every modern continent except Australia and Antarctica. As many as 22 genera and 26 species ranging from 1 to 6 m in length, and with a body mass ranging from less than 10 to more than 500 kg, are known. Aetosauroides scagliai was recently recovered as the most basal aetosaur, placed outside of Stagonolepididae (the last common ancestor of Desmatosuchus and Aetosaurus). Interrelationships among the basal aetosaurs are not well understood but two clades with relatively apomorphic armour – the spinose Desmatosuchinae and the generally wide-bodied Typothoracisinae – are consistently recognized. Paramedian and lateral osteoderms are often distinctive at the generic level but variation within the carapace is not well understood in many taxa, warranting caution in assigning isolated osteoderms to specific taxa. The aetosaur skull and dentition varies across taxa, and there is increasing evidence that at least some aetosaurs relied on invertebrates and/or small vertebrates as a food source. Histological evidence indicates that, after an initial period of rapid growth, lines of arrested growth (LAGs) are common and later growth was relatively slow. The common and widespread Late Triassic ichnogenus Brachychirotherium probably represents the track of an aetosaur.

Using positional homology in aetosaur (Archosauria: Pseudosuchia) osteoderms to evaluate the taxonomic status of Lucasuchus hunti

ABSTRACT The Otis Chalk quarries in the Upper Triassic Dockum Group of West Texas have produced aetosaur material that most workers have suggested represents two distinct morphotypes. We use characters from aetosaur specimens with articulated or semi-articulated carapaces in which the anteroposterior placement of osteoderms can be established with certainty to compare homologous osteoderms in the Otis Chalk material. This study confirms that the genera Longosuchus and Lucasuchus are distinct morphotypes, which differ in that the former taxon has paramedian osteoderms with random pitted ornamentation and low pyramidal bosses that contact the posterior margin, and spines on the lateral osteoderms that are posteriorly emarginated, whereas the latter taxon has paramedians with a strongly radial ornamentation and large conical eminences, and spines on the lateral osteoderms that are not posteriorly emarginated. Both taxa also have paramedians that are overlapped anteriorly by the laterals, a character that may be a synapomorphy of desmatosuchine aetosaurs. The arguments that these morphotypes represent ontogenetic stages or sexual dimorphs of a single biological species cannot be corroborated using either comparisons with modern pseudosuchians, other aetosaur taxa, or stratigraphic ranges. Longosuchus is known only from the type area and has no utility as an index taxon of the Otischalkian land-vertebrate faunachron, although Lucasuchus suggests a tentative correlation between part of the Dockum Group of Texas and the Pekin Formation of North Carolina.

A taxonomic and biostratigraphic re-evaluation of the Post Quarry vertebrate assemblage from the Cooper Canyon Formation (Dockum Group, Upper Triassic) of southern Garza County, western Texas

The Post Quarry, within the lower part of the type section of the Upper Triassic Cooper Canyon Formation in southern Garza County, western Texas, contains a remarkably diverse vertebrate assemblage. The Post Quarry has produced: the small temnospondyl Rileymillerus cosgriffi; the metoposaurid Apachesaurus gregorii; possible dicynodonts and eucynodonts; a clevosaurid sphenodontian; non-archosauriform archosauromorphs (Trilophosaurus dornorum, simiosaurians, and possibly Malerisaurus); the phytosaur Leptosuchus; several aetosaurs (Calyptosuchus wellesi, Typothorax coccinarum, Paratypothorax, and Desmatosuchus smalli); the poposauroid Shuvosaurus inexpectatus (“Chatterjeea elegans”); the rauisuchid Postosuchus kirkpatricki; an early crocodylomorph; several dinosauromorphs (the lagerpetid Dromomeron gregorii, the silesaurid Technosaurus smalli, a herrerasaurid, and an early neotheropod); and several enigmatic small diapsids. Revised lithostratigraphic correlations of the lower Cooper Canyon Formation with the Tecovas Formation, the occurrence of Leptosuchus, and the overall composition of the assemblage indicate that the Post Quarry falls within the Adamanian biozone, and not the Revueltian biozone. Stratigraphic subdivision of the Adamanian biozone may be possible, and the Post Quarry may be correlative with the upper part of the Adamanian biozone in Arizona. The age of the Post Quarry assemblage is possibly late Lacian or earliest Alaunian (late early Norian or earliest middle Norian), between 220 and 215 Ma.

A new aetosaur from the Upper Triassic Chinle Formation of the Eagle Basin, Colorado, USA

Abstract A small aetosaur skull and skeleton and referred material from the Chinle Formation, Eagle Basin of Colorado, USA, is described as a new taxon, Stenomyti huangae gen. et sp. nov, distinguished from other aetosaurs by the following autapomorphies: three premaxillary teeth; four palpebrals; pronounced midline ridge on frontals and parietals; paired ridges flanking midline ridge on parietal and frontal; exclusion of quadratojugal from ventral margin of skull by contact between jugal and quadrate; exclusion of postorbital from infratemporal fenestra; infratemporal fenestra a horizontally oriented oval that embays the posterior edge of the jugal; retroarticular process longer than distance between articular glenoid and posterior edge of external mandibular fenestra; oval to irregularly shaped ventral osteoderms that do not contact each other. Paramedian and lateral osteoderms of S. huangae are nearly identical to those of Aetosaurus ferratus, and other shared cranial characters suggest that these taxa are closely related and lie outside the clade Typothoracisinae + Desmatosuchinae. This discovery indicates that other reports of Aetosaurus across Laurasia based on osteoderms should be reassessed. Similar confusion with the osteoderms of other non-typothoracisine/desmatosuchine aetosaurs such as Aetosauroides, Stagonolepis and Calyptosuchus suggests that osteoderms are not always reliable taxonomic indicators.

The taxonomic status of the phytosaurs (Archosauriformes) Machaeroprosopus and Pseudopalatus from the Late Triassic of the western United States

The genus Machaeroprosopus has long been considered invalid because the type specimen of the Late Triassic phytosaur species, M. validus, has been lost. Re-examination of the primary literature regarding the establishment of the Late Triassic phytosaur genus Machaeroprosopus demonstrates that M. buceros is the correct type species, not M. validus. Thus, the genus level name Machaeroprosopus has priority over the genera Pseudopalatus and Arribasuchus and all nominal species should be reassigned. Reassignment of these species to Machaeroprosopus satisfies the requirements of the International Code of Zoological Nomenclature (ICZN) and preserves historical context. The name Pseudopalatinae is retained as the valid clade name for these phytosaurs because its usage falls outside of the ICZN.

A Review of “Jurassic West”, by John Foster. 2007. Indiana University Press, 389 pp. US

The great dinosaur graveyards of the Upper Jurassic Morrison Formation need little introduction. The Morrison’s long and often intensive history of collection has given us a window into a vitally important chapter in the history of vertebrate evolution and paleoecology on the North American continent. Dinosauromorph diversity preserved in Upper Triassic strata (most notably the Chinle Formation and Dockum Group) is composed almost entirely of modest-sized carnivorous forms surviving in a world dominated by crocodilian-line archosaurs, whereas the small vertebrate fauna contains few elements in common with modern ecosystems (e.g., Fraser, 2006). The Lower and Middle Jurassic vertebrate record preserved in the Glen Canyon Group gives tantalizing glimpses of an increase in dinosaurian size and diversity, but is disappointingly spotty. However, in the spectacular vertebrate record of the Morrison Formation, we see a Late Jurassic ecosystem dominated by a diverse dinosaur fauna, including some of the most gigantic land animals ever to walk the Earth, and a well-preserved and fairly modern small vertebrate fauna. The Morrison gives us our earliest look at the true Age of Dinosaurs in western North America. John Foster’s Jurassic West is neither a strictly technical nor strictly popular book. As with Nick Fraser’s (2006) overview of the global Triassic biota (reviewed by Parker, 2008), it is best suited for a popular audience with some background in geology and paleontology, and vertebrate paleontologists with other specializations who are interested in learning about the Morrison ecosystem. However, the book also contains abundant footnotes for literature citations, which also makes it a valuable reference for Morrison specialists. It is a comprehensive, logically structured, well-illustrated, and extremely well-written book. What gripes I have are fairly minor (although they may be taking up a disproportionate amount of this review compared to what I liked). Foster also mercifully avoids the tendency of some semitechnical books to waste text waxing autobiographical, which is rarely as interesting as some writers seem to think. We are picking up Jurassic West to find out about the Morrison Formation and its dinosaurs, not what Foster ate for lunch or thought about on the way to the field one day, and we get what we wanted. Not all subjects get equal treatment, although particular attention is given to Morrison Formation geology, collection history, vertebrate systematics, and vertebrate paleoecology. I liked that when covering the Morrison sedimentary record, Foster discusses not only the individual members, but also particular sedimentary facies and what they tell us about the environmental conditions under which they were deposited. Unfortunately, we are not provided with paleogeographic maps, which would have aided greatly in grasping the temporal and geographic relationships between the Morrison’s varied depositional environments. When reading the first chapter, I recommend keeping a copy of Blakey and Ranney’s (2008) Ancient Landscapes of the Colorado Plateau on hand. Jurassic West’s coverage of the history of collection in the Morrison Formation (Chapters 3 and 4) is truly exhaustive, discussing 150 years of expeditions and excavations throughout the Western Interior, peppered with comments on the fauna and depositional environments of the quarries. Foster’s discussion of the vertebrate fauna (Chapters 5 and 6) is just as extensive, and gives fair coverage to non-dinosaurian vertebrates as well as to dinosaurs. He does not restrict himself to taxonomic overview (which would have been boring as hell), but combines systematics, functional morphology, and paleoecology to give a comprehensive overview of the animals and their place in the Morrison habitat. The paleoecological analyses of Chapter 7 are interesting, and give us some possible insights as to how the Morrison ecosystems may have been structured. These studies are largely dependent on counts of numbers of individuals housed in museum collections being an accurate reflection of the original ecosystem. This is obviously problematic when preservational biases come into play, but Foster, to his credit, recognizes (and even tries to correct for) these biases. It will be interesting to see if the paleoecological patterns he lays out will hold up in future decades as sample sizes for Morrison vertebrates continue to increase. Other subjects get somewhat short shrift. In particular, the Morrison flora and non-vertebrate fauna gets relatively little discussion (only three pages!). This is a little surprising given that the subtitle of Foster’s book is “the dinosaurs of the Morrison Formation and their world,” and that the cover illustration features a lonely Ceratosaurus head poking out of a sea of vegetation. I was also somewhat disappointed by the discussion of vertebrate biostratigraphy in Chapter 7. Although the biostratigraphic distribution of different taxa were touched on in the fifth and sixth chapters, and laid out in a table in the appendix, Foster does not synthesize or discuss much of this information aside from noting that there appears to be a decrease in theropod diversity and a rarity of really large dinosaurs in the uppermost Morrison Formation, and touching on the possible impact of sampling biases. It would have been interesting to analyze how the taxonomic composition of the Morrison fauna changed over time, and how the abundance and diversity of various alpha taxa and clades varied in relation to each other, and in relation to changing environmental conditions in the western United States. The imaginary 2-month safari across the Morrison landscape in Chapter 8 (another chapter where a paleogeographic map showing the expedition route would have been a nice addition) is arguably the most clever and fun section of the book. Foster does a nice job of synthesizing the information covered in previous chapters into a convincing and detailed picture of what it really might have been like to wander through the Late Jurassic landscape of the Western Interior. My favorite touch is when it is revealed that the party members are carrying shotguns for protection against large theropods. That is awesome. Were any expedition paleontologists devoured, or at least hideously mauled? I’m not telling. Jurassic West is an excellent example of what a semitechnical/semi-popular synthesis should be, and I would even go so far as to say it should serve as an example of how this sort of book should be structured and written. Foster’s ability to incorporate such a large body of information, and yet make itThe great dinosaur graveyards of the Upper Jurassic Morrison Formation need little introduction. The Morrison’s long and often intensive history of collection has given us a window into a vitally important chapter in the history of vertebrate evolution and paleoecology on the North American continent. Dinosauromorph diversity preserved in Upper Triassic strata (most notably the Chinle Formation and Dockum Group) is composed almost entirely of modest-sized carnivorous forms surviving in a world dominated by crocodilian-line archosaurs, whereas the small vertebrate fauna contains few elements in common with modern ecosystems (e.g., Fraser, 2006). The Lower and Middle Jurassic vertebrate record preserved in the Glen Canyon Group gives tantalizing glimpses of an increase in dinosaurian size and diversity, but is disappointingly spotty. However, in the spectacular vertebrate record of the Morrison Formation, we see a Late Jurassic ecosystem dominated by a diverse dinosaur fauna, including some of the most gigantic land animals ever to walk the Earth, and a well-preserved and fairly modern small vertebrate fauna. The Morrison gives us our earliest look at the true Age of Dinosaurs in western North America. John Foster’s Jurassic West is neither a strictly technical nor strictly popular book. As with Nick Fraser’s (2006) overview of the global Triassic biota (reviewed by Parker, 2008), it is best suited for a popular audience with some background in geology and paleontology, and vertebrate paleontologists with other specializations who are interested in learning about the Morrison ecosystem. However, the book also contains abundant footnotes for literature citations, which also makes it a valuable reference for Morrison specialists. It is a comprehensive, logically structured, well-illustrated, and extremely well-written book. What gripes I have are fairly minor (although they may be taking up a disproportionate amount of this review compared to what I liked). Foster also mercifully avoids the tendency of some semitechnical books to waste text waxing autobiographical, which is rarely as interesting as some writers seem to think. We are picking up Jurassic West to find out about the Morrison Formation and its dinosaurs, not what Foster ate for lunch or thought about on the way to the field one day, and we get what we wanted. Not all subjects get equal treatment, although particular attention is given to Morrison Formation geology, collection history, vertebrate systematics, and vertebrate paleoecology. I liked that when covering the Morrison sedimentary record, Foster discusses not only the individual members, but also particular sedimentary facies and what they tell us about the environmental conditions under which they were deposited. Unfortunately, we are not provided with paleogeographic maps, which would have aided greatly in grasping the temporal and geographic relationships between the Morrison’s varied depositional environments. When reading the first chapter, I recommend keeping a copy of Blakey and Ranney’s (2008) Ancient Landscapes of the Colorado Plateau on hand. Jurassic West’s coverage of the history of collection in the Morrison Formation (Chapters 3 and 4) is truly exhaustive, discussing 150 years of expeditions and excavations throughout the Western Interior, peppered with comments on the fauna and depositional environments of the quarries. Foster’s discussion of the vertebrate fauna (Chapters 5 and 6) is just as extensive, and gives fair coverage to non-dinosaurian vertebrates as well as to dinosaurs. He does not restrict himself to taxonomic overview (which would have been boring as hell), but combines systematics, functional morphology, and paleoecology to give a comprehensive overview of the animals and their place in the Morrison habitat. The paleoecological analyses of Chapter 7 are interesting, and give us some possible insights as to how the Morrison ecosystems may have been structured. These studies are largely dependent on counts of numbers of individuals housed in museum collections being an accurate reflection of the original ecosystem. This is obviously problematic when preservational biases come into play, but Foster, to his credit, recognizes (and even tries to correct for) these biases. It will be interesting to see if the paleoecological patterns he lays out will hold up in future decades as sample sizes for Morrison vertebrates continue to increase. Other subjects get somewhat short shrift. In particular, the Morrison flora and non-vertebrate fauna gets relatively little discussion (only three pages!). This is a little surprising given that the subtitle of Foster’s book is “the dinosaurs of the Morrison Formation and their world,” and that the cover illustration features a lonely Ceratosaurus head poking out of a sea of vegetation. I was also somewhat disappointed by the discussion of vertebrate biostratigraphy in Chapter 7. Although the biostratigraphic distribution of different taxa were touched on in the fifth and sixth chapters, and laid out in a table in the appendix, Foster does not synthesize or discuss much of this information aside from noting that there appears to be a decrease in theropod diversity and a rarity of really large dinosaurs in the uppermost Morrison Formation, and touching on the possible impact of sampling biases. It would have been interesting to analyze how the taxonomic composition of the Morrison fauna changed over time, and how the abundance and diversity of various alpha taxa and clades varied in relation to each other, and in relation to changing environmental conditions in the western United States. The imaginary 2-month safari across the Morrison landscape in Chapter 8 (another chapter where a paleogeographic map showing the expedition route would have been a nice addition) is arguably the most clever and fun section of the book. Foster does a nice job of synthesizing the information covered in previous chapters into a convincing and detailed picture of what it really might have been like to wander through the Late Jurassic landscape of the Western Interior. My favorite touch is when it is revealed that the party members are carrying shotguns for protection against large theropods. That is awesome. Were any expedition paleontologists devoured, or at least hideously mauled? I’m not telling. Jurassic West is an excellent example of what a semitechnical/semi-popular synthesis should be, and I would even go so far as to say it should serve as an example of how this sort of book should be structured and written. Foster’s ability to incorporate such a large body of information, and yet make it