You Don't Need to Purchase Articles for Outrageous Fees Anymore. You Can Now RENT Them Instead!
In putting together my last post I noticed something interesting (disturbing?) from the Cambridge Journals site. If you would like to purchase a PDF of the Parringtonia gracilis redescription paper I just mentioned it will cost you $45.00 U.S. The atrociousness of this has been discussed in detail at several other blogs most notably by the SV-POW guys. Anyhow, for those of you who don't want to (or can't afford to) shell out this kind of cash for a single article there is now another option available. You can rent the article instead for the low(er) price of $5.99 U.S.!!! You get 24 hour access to the article, which is probably enough to cram in a couple of readings if you don't really want to fully comprehend the paper. Also just think of the hard drive space you'll save if all of your PDFs 'disappeared' after a 24 hour period. Currently I'm very hard pressed to think of a reason why this would be attractive. I suppose if you simply wanted to download the article and print it for future use.... Anyone else able to present this in a positive light?
Redescription of the Archosaur Parringtonia gracilis from the Middle Triassic Manda Beds of Tanzania
Here is another redescription of another of the enigmatic archosauriforms from the Middle Triassic Manda Formation. This study confirms the affinity of Parringtonia gracilis and Erpetosuchus granti, and reinforces the importance of redescribing these older taxa using an apomorphy-based approach and placing them in a modern phylogenetic analysis. Unfortunately the exact position of Erpetosuchidae with Archosauria was not able to be precisely determined.
Nesbitt, S. J., and R. J. Butler. 2012. Redescription of the archosaur Parringtonia gracilis from the Middle Triassic Manda beds of Tanzania, and the antiquity of Erpetosuchidae. Geological Magazine (FirstView article), 14p. doi:10.1017/S0016756812000362
Abstract - Parringtonia gracilis Huene, 1939 is represented by both cranial and postcranial material collected from the lower Middle Triassic (Anisian) Lifua Member of the Manda beds in southwestern Tanzania. This aberrant taxon was previously proposed to have affinities with pseudosuchian archosaurs, and specifically with the enigmatic Erpetosuchus granti from the Upper Triassic of Scotland. Here, we confirm the close affinities of Parringtonia gracilis and Erpetosuchus granti based on the following unambiguous synapomorphies: mediolaterally expanded posterior portion of the maxilla, alveoli present only in the anterior half of the maxilla, and absence of tooth serrations. Furthermore, the two taxa share osteoderms with deep sculpturing, a deep fossa on the dorsal margin of the neural spines and a heavily waisted shaft of the scapula. We added both Parringtonia gracilis and Erpetosuchus granti into a comprehensive phylogenetic analysis of early archosaurs and found that these taxa are clearly referable to Archosauria but that relationships are poorly resolved at the base of this clade. However, our analysis demonstrates that Erpetosuchus granti is not closely related to Crocodylomorpha, as has been hypothesized previously. The Erpetosuchidae are a clade of small-bodied archosaurs that have a poor fossil record but have members from both northern and southern Pangaea, ranging temporally from the Middle to Late Triassic. Thus, Erpetosuchidae is part of the early archosaurian radiation.
Diandongosuchus, A New Archosaur from Triassic of China
There are lots of incredible specimens coming out of the Middle Triassic in recent years (SVP attendees will see another in a talk this year by Sterling Nesbitt and colleagues), and this amazing fossil from the Ladinian of China does not disappoint. It consists of most of a partially articulated/associated skeleton found in marine sediments not far from where the early diverging poposauroid Qianosuchus mixtus was recovered some time ago.
The authors have provided color figures that allow the reader to see many of the details of the skeleton; however, the semi-articulated nature of the specimen seems to prelude dismantling of the specimen to see three dimensional views of the specimen. Furthermore, because it is in a marine shale, some crushing of the specimen has occurred. This is unfortunate because it does not allow clear study of the ilia or of the ends of the femora, which would provide key characters for the taxonomic placement of the specimen. Li et al. do code the specimen into Sterling Nesbitt's recent (2011) phylogenetic matrix of Archosauriformes and it is recovered, with much support, as the earliest diverging poposauroid. This is of interest of course because it suggests that the plesiomorphic conditions for poposauroids are quadrupedal, toothed, long-snouted forms that lack an expanded dorsal sail, possess osteoderms, and are possibly semi-aquatic. Compare this to other members of the clade such as Effigia okeeffae. The amount of morphological variation in this group is incredible.
I'll admit that I'm not entirely convinced of the phylogenetic placement of this specimen, but unfortunately I cannot get into the details of why at this time. Let's just say that this is an extremely interesting taxon that should be the subject of debate for a while to come. I do really wish the ilia were better preserved or more visible, but it is really hard to complain about such a beautiful fossil.
Li, C., Wu, X.-C., Zhao, L.-J., Sato, T. and L.-T. Wang. 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China. Journal of Vertebrate Paleontology 32(5): 1064-1081. DOI:10.1080/02724634.2012.694383http://www.tandfonline.com/doi/abs/10.1080/02724634.2012.694383
Abstract - A new Middle Triassic archosaur, Diandongosuchus fuyuanensis, gen. et
sp. nov., is described on the basis of a skeleton from the Zhuganpo Member (Ladinian) of the Falang Formation, eastern Yunnan Province, China. It is primarily characterized by the nasal process of the premaxilla extending posteriorly well beyond the external naris, the super-sized coracoid foramen laterally bordered by the scapula, the ischium with a strongly expanded medial portion anteroposteriorly longer than the proximodistal height of the bone, and anteriorly notched cervical osteoderms. D. fuyuanensis is a pseudosuchian on the basis of the crocodile-normal tarsal joint and other features, such as the distal end of the ulna in posterolateral view squared off, osteoderms with a distinct anterior process, the presacral vertebrae dorsally covered by more than one osteoderm, dorsal osteoderm alignment dorsal to presacrals 10–24 staggered, the pubis-ischium contact reduced to a thin proximal contact, and the medial contact of the ischia extensive but the dorsal margins separate. It is from a marine deposit but shows few morphological adaptations of the postcranial skeleton for a semiaquatic way of life when compared with Qianosuchus from the Anisian limestone of the same area. A phylogenetic analysis derived from an existing data matrix suggests that the new archosaur occupies the basal-most position in Poposauroidea and further confirms the poposauroid status of Qianosuchus. On the basis of current information, the discovery of Diandongosuchus does not firmly underscore the affinity of the semiterrestrial vertebrate faunas between the eastern and western regions along the northern coastline of the Tethys.
The authors have provided color figures that allow the reader to see many of the details of the skeleton; however, the semi-articulated nature of the specimen seems to prelude dismantling of the specimen to see three dimensional views of the specimen. Furthermore, because it is in a marine shale, some crushing of the specimen has occurred. This is unfortunate because it does not allow clear study of the ilia or of the ends of the femora, which would provide key characters for the taxonomic placement of the specimen. Li et al. do code the specimen into Sterling Nesbitt's recent (2011) phylogenetic matrix of Archosauriformes and it is recovered, with much support, as the earliest diverging poposauroid. This is of interest of course because it suggests that the plesiomorphic conditions for poposauroids are quadrupedal, toothed, long-snouted forms that lack an expanded dorsal sail, possess osteoderms, and are possibly semi-aquatic. Compare this to other members of the clade such as Effigia okeeffae. The amount of morphological variation in this group is incredible.
I'll admit that I'm not entirely convinced of the phylogenetic placement of this specimen, but unfortunately I cannot get into the details of why at this time. Let's just say that this is an extremely interesting taxon that should be the subject of debate for a while to come. I do really wish the ilia were better preserved or more visible, but it is really hard to complain about such a beautiful fossil.
Li, C., Wu, X.-C., Zhao, L.-J., Sato, T. and L.-T. Wang. 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China. Journal of Vertebrate Paleontology 32(5): 1064-1081. DOI:10.1080/02724634.2012.694383http://www.tandfonline.com/doi/abs/10.1080/02724634.2012.694383
Abstract - A new Middle Triassic archosaur, Diandongosuchus fuyuanensis, gen. et
sp. nov., is described on the basis of a skeleton from the Zhuganpo Member (Ladinian) of the Falang Formation, eastern Yunnan Province, China. It is primarily characterized by the nasal process of the premaxilla extending posteriorly well beyond the external naris, the super-sized coracoid foramen laterally bordered by the scapula, the ischium with a strongly expanded medial portion anteroposteriorly longer than the proximodistal height of the bone, and anteriorly notched cervical osteoderms. D. fuyuanensis is a pseudosuchian on the basis of the crocodile-normal tarsal joint and other features, such as the distal end of the ulna in posterolateral view squared off, osteoderms with a distinct anterior process, the presacral vertebrae dorsally covered by more than one osteoderm, dorsal osteoderm alignment dorsal to presacrals 10–24 staggered, the pubis-ischium contact reduced to a thin proximal contact, and the medial contact of the ischia extensive but the dorsal margins separate. It is from a marine deposit but shows few morphological adaptations of the postcranial skeleton for a semiaquatic way of life when compared with Qianosuchus from the Anisian limestone of the same area. A phylogenetic analysis derived from an existing data matrix suggests that the new archosaur occupies the basal-most position in Poposauroidea and further confirms the poposauroid status of Qianosuchus. On the basis of current information, the discovery of Diandongosuchus does not firmly underscore the affinity of the semiterrestrial vertebrate faunas between the eastern and western regions along the northern coastline of the Tethys.
More Photos from the Petrified Forest
I'm currently creating a database of all of our photos from the last decade of paleontological work at Petrified Forest National Park and am working through 2002. These photos were taken by Daniel Woody who was investigating the Sonsela Member of the Chinle Formmation and assisting with the paleontology work. I'm amazed how far the quality of digital photos have over the decade!
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| Phytosaur lower jaw in the Crystal Forest |
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| Phytosaur quadrate bone in the Blue Mesa Member |
Triassic Fieldwork in Utah
Randall Irmis of the Utah Museum of Natural History is posting about current fieldwork in the Triassic of Utah. You can check out the first post here and check back for more to follow.
Reevaluating the 'Prosauropods' of the Upper Triassic Caturrita Formation of Brazil
Bittencourt, J. S., Stock da Rosa, A. A., and M. C. Langer. in press. Dinosaur remains from the ‘Botucaraí Hill’ (Caturrita Formation), Late
Triassic of south Brazil, and their stratigraphic context. Historical Biology. DOI:10.1080/08912963.2012.694881
Abstract - Vertebrate fossils recovered from sites nearby the
Botucaraí Hill and Candelária (Caturrita Formation) depict a diverse Late
Triassic tetrapod fauna from south Brazil. These records are of key importance
to the biostratigraphy of the upper sections of the Rosario do Sul Group. A
lithological and biostratigraphic survey on the main fossil localities of the
Botucaraí Hill area confirms the occurrence of the lower Hyperodapedon
and the upper Riograndia Assemblage Zones in the region, the latter
yielding early saurischians. In this paper, three incomplete dinosaur specimens,
an isolated sacral vertebra, an articulated left pubis–ischium and an isolated
right ischium, from the ‘Botucaraí Hill’ site are described. A comparative
survey suggests that these specimens have sauropodomorph affinities, but
probably more primitive than typical ‘prosauropods’ from the Norian-Early
Jurassic. Regardless of the phylogenetic position of Guaibasaurus as
theropod or sauropodomorph, their occurrence in the Caturrita Formation, which
also yielded ‘core prosauropods’ from the Santa Maria region, suggests either
the survival of early members of the clade with more derived ‘prosauropods’ or
that heterochronous faunas are sampled from that stratigraphic unit.
Examining the Effects of Dataset Quality on Paleodiversity Studies
I would love to do a similar study for the Chinle Formation...
Irmis, R. B., Whiteside, J. H., and C. F. Kammerer. In press. Non-biotic controls of observed diversity in the paleontologic record: An example from the Permo-Triassic Karoo Basin of South Africa. Palaeogeography, Palaeoclimatology, Palaeoecology. doi: 10.1016/j.palaeo.2012.07.014.
Abstract - Paleodiversity trends through geologic time can be affected by a number of geologic, taphonomic, and anthropogenic biases that obscure or prejudice paleoecological patterns in the fossil record. Although much work has concentrated on the relationship between geologic exposure, sample size, and taxonomic richness (i.e., number of taxa), few studies have investigated the potential effects of dataset quality and changing taxonomy. We use four different specimen-level datasets of Permo-Triassic tetrapods from the Karoo Basin of South Africa to investigate how sample size, geologic outcrop, dataset quality, and taxonomic revision all affect observed estimates of generic richness, evenness, and relative abundance. Our results indicate that large-scale patterns of richness, evenness, and abundance, such as the effects of the end-Permian mass extinction, are generally robust to these potential biases across the four different datasets. In contrast, absolute values vary significantly as do finer-scale patterns. In agreement with past studies, taxonomic errors, revised taxonomy, and new taxa have little effect on patterns of richness and evenness; instead, the addition of large numbers of new specimens to the dataset has the largest effect on these paleodiversity metrics, despite application of samplestandardization. We conclude that although large specimen datasets (hundreds to thousands of specimens) are robust to various potential biases, and can recover large-scale paleobiologic trends, they are still affected by many non-biotic controls, and workers should strive to improve dataset quality and understand the underlying reasons for observed paleodiversity patterns.
Irmis, R. B., Whiteside, J. H., and C. F. Kammerer. In press. Non-biotic controls of observed diversity in the paleontologic record: An example from the Permo-Triassic Karoo Basin of South Africa. Palaeogeography, Palaeoclimatology, Palaeoecology. doi: 10.1016/j.palaeo.2012.07.014.
Abstract - Paleodiversity trends through geologic time can be affected by a number of geologic, taphonomic, and anthropogenic biases that obscure or prejudice paleoecological patterns in the fossil record. Although much work has concentrated on the relationship between geologic exposure, sample size, and taxonomic richness (i.e., number of taxa), few studies have investigated the potential effects of dataset quality and changing taxonomy. We use four different specimen-level datasets of Permo-Triassic tetrapods from the Karoo Basin of South Africa to investigate how sample size, geologic outcrop, dataset quality, and taxonomic revision all affect observed estimates of generic richness, evenness, and relative abundance. Our results indicate that large-scale patterns of richness, evenness, and abundance, such as the effects of the end-Permian mass extinction, are generally robust to these potential biases across the four different datasets. In contrast, absolute values vary significantly as do finer-scale patterns. In agreement with past studies, taxonomic errors, revised taxonomy, and new taxa have little effect on patterns of richness and evenness; instead, the addition of large numbers of new specimens to the dataset has the largest effect on these paleodiversity metrics, despite application of samplestandardization. We conclude that although large specimen datasets (hundreds to thousands of specimens) are robust to various potential biases, and can recover large-scale paleobiologic trends, they are still affected by many non-biotic controls, and workers should strive to improve dataset quality and understand the underlying reasons for observed paleodiversity patterns.
New Ladinian Biostratigraphic Correlation Between South America and South Africa
Nice biostratigraphic correlation between the Santa Maria Formation of Brazil and the Karoo of South Africa. Partially fills the 'Ladinian Gap' in the Karoo.
Abdala, F., Marsicano, C. A., Smith, R. M. H., and R. Swart. 2012. Strengthening western Gondwanan correlations: a Brazilian dicynodont (Synapsida, Anomodontia) in the Middle Triassic of Namibia. Gondwana Research (advance online publication)
http://dx.doi.org/10.1016/j.gr.2012.07.011
Abstract - Terrestrial Middle Triassic strata occur throughout continental Africa, and are particularly well exposed in South Africa, Tanzania, Zambia, and Namibia. The youngest age for all these African deposits is widely accepted as early Middle Triassic (Anisian). Fossils collected recently from the uppermost strata of the upper Omingonde Formation in Namibia highlighted the presence of Chiniquodon, a carnivorous cynodont previously only found in Ladinian-Carnian aged rocks of South America. In addition, work in progress indicates that a large archosaur, originally reported as Erythrosuchus, also discovered from levels close to the top of this unit, is in fact a rauisuchian, a group of archosaurs well known from Ladinian-Carnian beds of southern South America. Here we present the first record of the tuskless dicynodont Stahleckeria potens, from the top of the upper Omingonde Formation in central Namibia. This taxon was up until now only known from the Ladinian Dinodontosaurus Assemblage Zone of the Santa Maria Formation in southern Brazil. Thus, compelling evidence for a Ladinian age for the upper levels of the upper Omingonde Formation is provided by two therapsid and one archosaur taxa. The tetrapod fauna of the upper Omingonde Formation partially fills the gap of the well-documented hiatus (Ladinian gap), prevalent throughout the Karoo basins of south and central Africa. The presence of the same therapsid taxa in the Namibian Waterberg Basin and the Paraná Basin of Brazil during Middle Triassic suggests that these basins were biogeographically linked through a series of interconnecting lowlands, with no major ecological, climatic and/or physical barriers.
Abdala, F., Marsicano, C. A., Smith, R. M. H., and R. Swart. 2012. Strengthening western Gondwanan correlations: a Brazilian dicynodont (Synapsida, Anomodontia) in the Middle Triassic of Namibia. Gondwana Research (advance online publication)
http://dx.doi.org/10.1016/j.gr.2012.07.011
Abstract - Terrestrial Middle Triassic strata occur throughout continental Africa, and are particularly well exposed in South Africa, Tanzania, Zambia, and Namibia. The youngest age for all these African deposits is widely accepted as early Middle Triassic (Anisian). Fossils collected recently from the uppermost strata of the upper Omingonde Formation in Namibia highlighted the presence of Chiniquodon, a carnivorous cynodont previously only found in Ladinian-Carnian aged rocks of South America. In addition, work in progress indicates that a large archosaur, originally reported as Erythrosuchus, also discovered from levels close to the top of this unit, is in fact a rauisuchian, a group of archosaurs well known from Ladinian-Carnian beds of southern South America. Here we present the first record of the tuskless dicynodont Stahleckeria potens, from the top of the upper Omingonde Formation in central Namibia. This taxon was up until now only known from the Ladinian Dinodontosaurus Assemblage Zone of the Santa Maria Formation in southern Brazil. Thus, compelling evidence for a Ladinian age for the upper levels of the upper Omingonde Formation is provided by two therapsid and one archosaur taxa. The tetrapod fauna of the upper Omingonde Formation partially fills the gap of the well-documented hiatus (Ladinian gap), prevalent throughout the Karoo basins of south and central Africa. The presence of the same therapsid taxa in the Namibian Waterberg Basin and the Paraná Basin of Brazil during Middle Triassic suggests that these basins were biogeographically linked through a series of interconnecting lowlands, with no major ecological, climatic and/or physical barriers.
New ICS International Chronostratigraphy Chart Uses the Long Norian
The base of the Norian stage is set at ~228 Ma on the new chronstratigraphy chart of the International Commission on Stratigraphy. Still needs further support and eventially a golden spike, but this is the first time the ICS has used the long Norian hypothesis on its published chart.
You can download the latest timescale from here:
http://www.stratigraphy.org/ics%20chart/ChronostratChart2012.pdf
You can download the latest timescale from here:
http://www.stratigraphy.org/ics%20chart/ChronostratChart2012.pdf
First Record of Late Triassic Vertebrate Fossils from Lithuania and the Paleobiogeography of Phytosaurs
Brusatte, S. L., Butler, R. J., Niedźwiedzki, G., Sulej, T., Bronowicz, R., and J. Satkūnas. 2012. First record of Mesozoic terrestrial vertebrates from Lithuania: phytosaurs (Diapsida: Archosauriformes) of probable Late Triassic age, with a review of phytosaur biogeography. Geological Magazine (early online) 13 pp. doi:10.1017/S0016756812000428
Abstract – Fossils of Mesozoic terrestrial vertebrates from Lithuania and the wider East Baltic region
of Europe have previously been unknown.We here report the first Mesozoic terrestrial vertebrate fossils
from Lithuania: two premaxillary specimens and three teeth that belong to Phytosauria, a common
clade of semiaquatic Triassic archosauriforms. These specimens represent an uncrested phytosaur,
similar to several species within the genera Paleorhinus, Parasuchus, Rutiodon and Nicrosaurus.
Because phytosaurs are currently only known from the Upper Triassic, their discovery in northwestern
Lithuania (the Šaltiškiai clay-pit) suggests that at least part of the Triassic succession in this region
is Late Triassic in age, and is not solely Early Triassic as has been previously considered. The new
specimens are among the most northerly occurrences of phytosaurs in the Late Triassic, as Lithuania
was approximately 7–10◦ further north than classic phytosaur-bearing localities in nearby Germany and
Poland, and as much as 40◦ further north than the best-sampled phytosaur localities in North America.
The far northerly occurrence of the Lithuanian fossils prompts a review of phytosaur biogeography
and distribution, which suggests that these predators were widely distributed in the Triassic monsoonal
belt but rarer in more arid regions.
Reanalysis of the Archosauriform Proterochampsa from the Late Triassic of Argentina
Dilkes,
D., and A. Arcucci. 2012. Proterochampsa
barrionuevoi (Archosauriformes: Proterochampsia) from The Late Triassic
(Carnian) of Argentina and a phylogenetic analysis of Proterochampsia.
Palaeontology early online. doi: 10.1111/j.1475-4983.2012.01170.x http://onlinelibrary.wiley.com/doi/10.1111/j.1475-4983.2012.01170.x/abstract
Abstract - Restudy of skulls and available postcrania of the proterochampsian archosauriform Proterochampsa barrionuevoi from the Ischigualasto Formation (Upper Triassic, Carnian) in the San Juan Province, Argentina, confirms that the genus is diagnosed by autapomorphies that include dermal sculpturing consisting of prominent ridges and nodular protuberances, a large hook-like lateral projection on the quadratojugal, an antorbital fossa restricted to a depression along the maxilla, lateral expansion of the premaxilla anterior to the premaxilla–maxilla contact, absence of a supratemporal fossa, exclusion of jugal from suborbital fenestra, basal tubera of parabasisphenoid facing ventrally and reaching laterally beyond the basipterygoid process, and a ventral lamina on the angular. Proterochampsa nodosa is a valid species distinguished from P. barrionuevoi by fewer cranial ridges with larger protuberances, relatively smaller supratemporal fenestrae and width of frontals between orbits less than that of the nasals. A phylogenetic analysis supports the monophyly of Proterochampsia consisting of Proterochampsa, Chanaresuchus bonapartei, Gualosuchus reigi, Tropidosuchus romeri and Cerritosaurus binsfeldi. A temporal separation between the two basal proterochampsians with earliest records in the Late Triassic (Proterochampsa and Cerritosaurus) and Chanaresuchus, Gualosuchus and Tropidosuchus in the Middle Triassic indicates hidden proterochampsian diversity in the Middle Triassic.
Abstract - Restudy of skulls and available postcrania of the proterochampsian archosauriform Proterochampsa barrionuevoi from the Ischigualasto Formation (Upper Triassic, Carnian) in the San Juan Province, Argentina, confirms that the genus is diagnosed by autapomorphies that include dermal sculpturing consisting of prominent ridges and nodular protuberances, a large hook-like lateral projection on the quadratojugal, an antorbital fossa restricted to a depression along the maxilla, lateral expansion of the premaxilla anterior to the premaxilla–maxilla contact, absence of a supratemporal fossa, exclusion of jugal from suborbital fenestra, basal tubera of parabasisphenoid facing ventrally and reaching laterally beyond the basipterygoid process, and a ventral lamina on the angular. Proterochampsa nodosa is a valid species distinguished from P. barrionuevoi by fewer cranial ridges with larger protuberances, relatively smaller supratemporal fenestrae and width of frontals between orbits less than that of the nasals. A phylogenetic analysis supports the monophyly of Proterochampsia consisting of Proterochampsa, Chanaresuchus bonapartei, Gualosuchus reigi, Tropidosuchus romeri and Cerritosaurus binsfeldi. A temporal separation between the two basal proterochampsians with earliest records in the Late Triassic (Proterochampsa and Cerritosaurus) and Chanaresuchus, Gualosuchus and Tropidosuchus in the Middle Triassic indicates hidden proterochampsian diversity in the Middle Triassic.
Associated Evolution Of Bipedality And Cursoriality Among Triassic Archosaurs
Kubo,
T., and M. O. Kubo. 2012. Associated evolution of bipedality and cursoriality
among Triassic
archosaurs: a phylogenetically controlled evaluation. Paleobiology 38: 474–485.
http://www.bioone.org/doi/full/10.1666/11015.1
Abstract - Bipedalism evolved more than twice among archosaurs, and it is a characteristic of basal dinosaurs and a prerequisite for avian flight. Nevertheless, the reasons for the evolution of bipedalism among archosaurs have barely been investigated. Comparative analysis using phylogenetically independent contrasts showed a significant correlation between bipedality (relative length of forelimb) and cursoriality (relative length of metatarsal III) among Triassic archosaurs. This result indicates that, among Triassic archosaurs, bipeds could run faster than quadrupeds. Bipedalism is probably an adaptation for cursoriality among archosaurs, which may explain why bipedalism evolved convergently in the crocodilian and bird lineages. This result also indicates that the means of acquiring cursoriality may differ between archosaurs and mammals.
Abstract - Bipedalism evolved more than twice among archosaurs, and it is a characteristic of basal dinosaurs and a prerequisite for avian flight. Nevertheless, the reasons for the evolution of bipedalism among archosaurs have barely been investigated. Comparative analysis using phylogenetically independent contrasts showed a significant correlation between bipedality (relative length of forelimb) and cursoriality (relative length of metatarsal III) among Triassic archosaurs. This result indicates that, among Triassic archosaurs, bipeds could run faster than quadrupeds. Bipedalism is probably an adaptation for cursoriality among archosaurs, which may explain why bipedalism evolved convergently in the crocodilian and bird lineages. This result also indicates that the means of acquiring cursoriality may differ between archosaurs and mammals.
As "Leisurely" Divers, Triassic Ichthyosaurs Did Not Suffer From "The Bends"
Rothschild, B. M.,
Xiaoting, Z., and L. D. Martin. 2012. Adaptations for marine
habitat and the effect of Triassic and Jurassic predator pressure on
development of decompression syndrome in ichthyosaurs. Naturwissenschaften 99:443–448 DOI 10.1007/s00114-012-0918-0
Abstract - Decompression
syndrome (caisson disease or the “the bends”) resulting in avascular necrosis has been documented in
mosasaurs, sauropterygians, ichthyosaurs, and turtles from the Middle Jurassic
to Late Cretaceous, but it was unclear that this disease occurred as far back
as the Triassic. We have examined a large Triassic sample of ichthyosaurs and
compared it with an equally large post- Triassic sample. Avascular necrosis was
observed in over 15%of LateMiddle Jurassic to Cretaceous ichthyosaurs with the
highest occurrence (18 %) in the Early Cretaceous, but was rare or absent in
geologically older specimens. Triassic reptiles that dive were either
physiologically protected, or rapid changes of their position in the water column
rare and insignificant enough to prevent being recorded in the skeleton. Emergency
surfacing due to a threat from an underwater predator may be the most important
cause of avascular necrosis for air-breathing divers, with relative frequency
of such events documented in the skeleton. Diving in the Triassic appears to
have been a “leisurely” behavior until the evolution of
large predators in the Late Jurassic that forced sudden depth alterations
contributed to a higher occurrence of bends.
New U-Pb Dates for the Middle Triassic of Monte San Giorgio
Stockar, R., Baumgartner, P. O., and D. Condon. 2012. Integrated Ladinian
bio-chronostratigraphy and geochrononology of Monte San Giorgio (Southern Alps,
Switzerland). Swiss Journal of Geosciences 105:85-108.
Abstract - New biostratigraphic data significantly improve the age assignment of the Ladinian succession of Monte San Giorgio (UNESCO World Heritage List site, Southern Alps, Switzerland), whose world-famous fossil marine vertebrate faunas are now dated to the substage and zone levels. High-resolution single-zircon U–Pb dating was performed using ID-TIMS and chemical abrasion (CA) pre-treatment technique on volcanic ash layers intercalated in the biostratigraphically-defined intervals of the Meride Limestone. It yielded ages of 241.07 ± 0.13 Ma (Cava superiore beds, P. gredleri Zone), 240.63 ± 0.13 Ma (Cassina beds, P gredleri/P. archelaus transition Zone) and 239.51 ± 0.15 Ma (Lower Kalkschieferzone, P. archelaus Zone). Our results suggest that the time interval including the vertebrate-bearing Middle Triassic section spans around 4 Myr and is thus significantly shorter than so far assumed. The San Giorgio Dolomite and the Meride Limestone correlate with intervals of the Buchenstein Formation and the Wengen Formation in the reference section at Bagolino, where the Global boundary Stratotype Section and Point (GSSP) for the base of the Ladinian was defined. The new radio-isotopic ages of the Meride Limestone are up to 2 Myr older than those published for the biostratigraphically-equivalent intervals at Bagolino but they are consistent with the recent re-dating of the underlying Besano Formation, also performed using the CA technique. Average sedimentation rates at Monte San Giorgio are by more than an order of magnitude higher compared to those assumed for the Buchenstein Formation, which formed under sediment starved pelagic conditions, and reflect prevailing high subsidence and high carbonate mud supply from the adjoining Salvatore/Esino platforms. Finally, the high-resolution U–Pb ages allow a correlation of the vertebrate faunas of the Cava superiore/Cava inferior beds with the marine vertebrate record of the Prosanto Formation (Upper Austroalpine), so far precluded by the poor biostratigraphic control of the latter.
Abstract - New biostratigraphic data significantly improve the age assignment of the Ladinian succession of Monte San Giorgio (UNESCO World Heritage List site, Southern Alps, Switzerland), whose world-famous fossil marine vertebrate faunas are now dated to the substage and zone levels. High-resolution single-zircon U–Pb dating was performed using ID-TIMS and chemical abrasion (CA) pre-treatment technique on volcanic ash layers intercalated in the biostratigraphically-defined intervals of the Meride Limestone. It yielded ages of 241.07 ± 0.13 Ma (Cava superiore beds, P. gredleri Zone), 240.63 ± 0.13 Ma (Cassina beds, P gredleri/P. archelaus transition Zone) and 239.51 ± 0.15 Ma (Lower Kalkschieferzone, P. archelaus Zone). Our results suggest that the time interval including the vertebrate-bearing Middle Triassic section spans around 4 Myr and is thus significantly shorter than so far assumed. The San Giorgio Dolomite and the Meride Limestone correlate with intervals of the Buchenstein Formation and the Wengen Formation in the reference section at Bagolino, where the Global boundary Stratotype Section and Point (GSSP) for the base of the Ladinian was defined. The new radio-isotopic ages of the Meride Limestone are up to 2 Myr older than those published for the biostratigraphically-equivalent intervals at Bagolino but they are consistent with the recent re-dating of the underlying Besano Formation, also performed using the CA technique. Average sedimentation rates at Monte San Giorgio are by more than an order of magnitude higher compared to those assumed for the Buchenstein Formation, which formed under sediment starved pelagic conditions, and reflect prevailing high subsidence and high carbonate mud supply from the adjoining Salvatore/Esino platforms. Finally, the high-resolution U–Pb ages allow a correlation of the vertebrate faunas of the Cava superiore/Cava inferior beds with the marine vertebrate record of the Prosanto Formation (Upper Austroalpine), so far precluded by the poor biostratigraphic control of the latter.
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