....and the answer to the question we've all been wondering...what type of footprint would Poposaurus have left? It appears that Poposaurus probably could have left a Grallator-like track.
Farlow, J. O., Schachner, E. R., Sarrazin, J. C., Klein, H., and P. J. Currie. 2014. Pedal Proportions of Poposaurus gracilis: Convergence and Divergence in the Feet of Archosaurs. The Anatomical Record, Early View. DOI: 10.1002/ar.22863.
Abstract - The crocodile-line basal suchian Poposaurus gracilis had body proportions suggesting that it was an erect, bipedal form like many dinosaurs, prompting questions of whether its pedal proportions, and the shape of its footprint, would likewise “mimic” those of bipedal dinosaurs. We addressed these questions through a comparison of phalangeal, digital, and metatarsal proportions of Poposaurus with those of extinct and extant crocodile-line archosaurs, obligate or facultatively bipedal non-avian dinosaurs, and ground birds of several clades, as well as a comparison of the footprint reconstructed from the foot skeleton of Poposaurus with known early Mesozoic archosaurian ichnotaxa. Bivariate and multivariate analyses of phalangeal and digital dimensions showed numerous instances of convergence in pedal morphology among disparate archosaurian clades. Overall, the foot of Poposaurus is indeed more like that of bipedal dinosaurs than other archosaur groups, but is not exactly like the foot of any particular bipedal dinosaur clade. Poposaurus likely had a digitigrade stance, and its footprint shape could have resembled grallatorid ichnotaxa, unless digit I of the foot of Poposaurus commonly left an impression.
Showing posts with label Poposaurus. Show all posts
Showing posts with label Poposaurus. Show all posts
New Volume on Triassic Archosaurs/ New Cranial Material of Poposaurus gracilis
There is a new volume coming out that is sure to be of interest to all Triassic aficionados. It's titled "Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin" edited by Sterling Nesbitt, Julia Desojo, and Randall Irmis and published in the Special Publication series of the Geological Society of London. The volume stems from a symposium held in 2011 in San Juan, Argentina at the IV Congreso Latinoamericano de Paleontología de Vertebrados. It was a great meeting and you can read some more about it here [in Spanish].
The new volume includes overviews of many archosaurian clades including Euparkeriidae, Phytosauria, "Rauisuchia", Ornithosuchidae, and of course Aetosauria. There are also a plethora of other more specific papers. Currently the papers are being released "online first" and not all are up yet. I'm not even sure how many there are to be in the final volume, but you can consider this volume to be the " The Dinosauria" volume for non-ornithodiran archosauriforms and pseudosuchians. Keep checking back as more papers are released and at some point the printed volume should be available.
My own contribution is up. In 2003 a group from Yale University, assisted with staff from the Petrified Forest, excavated what turned out to be a nearly complete, articulated skeleton of the carnivorous pseudosuchian Poposaurus gracilis (more here and here). This specimen has been covered in several papers now (Gauthier et al., 2011; Schachner et al., 2011) and provides us with more information about poposauroids and their amazing convergence with theropod dinosaurs. Unfortunately, the skull of this specimen has eroded prior to dicovery. This was unfortunate because poposauroids show an amazing diversity of forms from presumably quadrupedal, sail-backed toothed forms (e.g., Arizonasaurus babbitti) , to bipedal edentulous forms (Effigia okeeffeae), and of course a quadrupedal sail-backed, edentulous form (Lotosaurus adentus) just to make things interesting. What is poorly understood is the congruence of the aquisition of these characters in poposauroid phylogeny. In this question, Poposaurus gracilis plays a key role as according to recent phylogenetic analyses of Archosauria (Nesbitt, 2011; Butler et al., 2011) it is a mid-grade poposauroid. It is clear from the Yale specimen that P. gracilis was bipedal and lacked a sail. A fragment of premaxilla found with the specimen suggested the presence of teeth but conformation was needed.
In 2008 Petrified Forest paleontology staff (Kate Hazlehurst and Jeff Martz) discovered a beautifully preserved ilium and pubis of Poposaurus gracilis from the base of the Sonsela Member in the park. Associated with this were a partial maxilla, dentary, and strangely a prearticular. These elements were not complete, but they were enough to show that the skull was very similar to other poposauroids like Arizonasaurus babbitti, but more importantly it confirmed that P. gracilis was toothed. The new paper by myself and colleague Sterling Nesbitt describes this new material and discusses its implications for specific character acquisition in the poposauroids. Essentially we find that character acquisition is very complex and evolving quickly within the group with a strong suggestion of convegent evolution not only with theropod dinosaurs but also within the clade Poposauroidea as well.
Parker, W. G., and S. J. Nesbitt. 2013. Cranial remains of Poposaurus gracilis (Pseudosuchia: Poposauroidea) from the Upper Triassic, the distribution of the taxon, and its implications for poposauroid evolution. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, http://dx.doi.org/10.1144/SP379.3
Abstract - The partial postcrania of Poposaurus gracilis, a bipedal poposauroid convergent with theropod dinosaurs, has been known for nearly a century, but the skull of P. gracilis has proven elusive. P. gracilis is part of a clade of morphologically divergent pseudosuchians (poposauroids) whose members are sometimes bipedal, lack dentition (i.e. beaks) and some have elongated neural spines (i.e. sails). However, the timing and acquisition of these character states is unknown given the uncertainty of the skull morphology of the ‘mid-grade’ poposauroid P. gracilis. Here, we present the first confirmed skull remains of P. gracilis directly associated with diagnostic pelvic elements that overlap with the holotype. The incomplete skeleton (PEFO 34865) from the Chinle Formation of Petrified Forest National Park (Arizona, USA) includes a left maxilla with a large, mediolaterally compressed tooth, left dentary, right prearticular and a partial postcranium. The character states of P. gracilis (bipedal, ‘sail-less’ and toothed) demonstrate that the evolution of bipedalism, the origin/loss of a dorsal ‘sail’ and the shift to an edentulous beak are complex in poposauroids. P. gracilis is widespread in the Upper Triassic formations in the western USA and is restricted temporally prior to the Adamanian–Revueltian faunal turnover during the Norian.
The new volume includes overviews of many archosaurian clades including Euparkeriidae, Phytosauria, "Rauisuchia", Ornithosuchidae, and of course Aetosauria. There are also a plethora of other more specific papers. Currently the papers are being released "online first" and not all are up yet. I'm not even sure how many there are to be in the final volume, but you can consider this volume to be the " The Dinosauria" volume for non-ornithodiran archosauriforms and pseudosuchians. Keep checking back as more papers are released and at some point the printed volume should be available.
My own contribution is up. In 2003 a group from Yale University, assisted with staff from the Petrified Forest, excavated what turned out to be a nearly complete, articulated skeleton of the carnivorous pseudosuchian Poposaurus gracilis (more here and here). This specimen has been covered in several papers now (Gauthier et al., 2011; Schachner et al., 2011) and provides us with more information about poposauroids and their amazing convergence with theropod dinosaurs. Unfortunately, the skull of this specimen has eroded prior to dicovery. This was unfortunate because poposauroids show an amazing diversity of forms from presumably quadrupedal, sail-backed toothed forms (e.g., Arizonasaurus babbitti) , to bipedal edentulous forms (Effigia okeeffeae), and of course a quadrupedal sail-backed, edentulous form (Lotosaurus adentus) just to make things interesting. What is poorly understood is the congruence of the aquisition of these characters in poposauroid phylogeny. In this question, Poposaurus gracilis plays a key role as according to recent phylogenetic analyses of Archosauria (Nesbitt, 2011; Butler et al., 2011) it is a mid-grade poposauroid. It is clear from the Yale specimen that P. gracilis was bipedal and lacked a sail. A fragment of premaxilla found with the specimen suggested the presence of teeth but conformation was needed.
In 2008 Petrified Forest paleontology staff (Kate Hazlehurst and Jeff Martz) discovered a beautifully preserved ilium and pubis of Poposaurus gracilis from the base of the Sonsela Member in the park. Associated with this were a partial maxilla, dentary, and strangely a prearticular. These elements were not complete, but they were enough to show that the skull was very similar to other poposauroids like Arizonasaurus babbitti, but more importantly it confirmed that P. gracilis was toothed. The new paper by myself and colleague Sterling Nesbitt describes this new material and discusses its implications for specific character acquisition in the poposauroids. Essentially we find that character acquisition is very complex and evolving quickly within the group with a strong suggestion of convegent evolution not only with theropod dinosaurs but also within the clade Poposauroidea as well.
Parker, W. G., and S. J. Nesbitt. 2013. Cranial remains of Poposaurus gracilis (Pseudosuchia: Poposauroidea) from the Upper Triassic, the distribution of the taxon, and its implications for poposauroid evolution. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, http://dx.doi.org/10.1144/SP379.3
Abstract - The partial postcrania of Poposaurus gracilis, a bipedal poposauroid convergent with theropod dinosaurs, has been known for nearly a century, but the skull of P. gracilis has proven elusive. P. gracilis is part of a clade of morphologically divergent pseudosuchians (poposauroids) whose members are sometimes bipedal, lack dentition (i.e. beaks) and some have elongated neural spines (i.e. sails). However, the timing and acquisition of these character states is unknown given the uncertainty of the skull morphology of the ‘mid-grade’ poposauroid P. gracilis. Here, we present the first confirmed skull remains of P. gracilis directly associated with diagnostic pelvic elements that overlap with the holotype. The incomplete skeleton (PEFO 34865) from the Chinle Formation of Petrified Forest National Park (Arizona, USA) includes a left maxilla with a large, mediolaterally compressed tooth, left dentary, right prearticular and a partial postcranium. The character states of P. gracilis (bipedal, ‘sail-less’ and toothed) demonstrate that the evolution of bipedalism, the origin/loss of a dorsal ‘sail’ and the shift to an edentulous beak are complex in poposauroids. P. gracilis is widespread in the Upper Triassic formations in the western USA and is restricted temporally prior to the Adamanian–Revueltian faunal turnover during the Norian.
Pelvic and Hindlimb Myology of the Basal Archosaur Poposaurus gracilis
Schachner, E. R., Manning, P. L., and P. Dodson. 2011. Pelvic and hindlimb myology of the basal archosaur Poposaurus gracilis (Archosauria: Poposauroidea). Journal of Morphology. doi: 10.1002/jmor.10997. [Epub ahead of print]
Abstract - The discovery of a largely complete and well preserved specimen of Poposaurus gracilis has provided the opportunity to generate the first phylogenetically based reconstruction of pelvic and hindlimb musculature of an extinct nondinosaurian archosaur. As in dinosaurs, multiple lineages of basal archosaurs convergently evolved parasagittally erect limbs. However, in contrast to the laterally projecting acetabulum, or "buttress erect" hip morphology of ornithodirans, basal archosaurs evolved a very different, ventrally projecting acetabulum, or "pillar erect" hip. Reconstruction of the pelvic and hindlimb musculotendinous system in a bipedal suchian archosaur clarifies how the anatomical transformations associated with the evolution of bipedalism in basal archosaurs differed from that of bipedal dinosaurs and birds. This reconstruction is based on the direct examination of the osteology and myology of phylogenetically relevant extant taxa in conjunction with osteological correlates from the skeleton of P. gracilis. This data set includes a series of inferences (presence/absence of a structure, number of components, and origin/insertion sites) regarding 26 individual muscles or muscle groups, three pelvic ligaments, and two connective tissue structures in the pelvis, hindlimb, and pes of P. gracilis. These data provide a foundation for subsequent examination of variation in myological orientation and function based on pelvic and hindlimb morphology, across the basal archosaur lineage leading to extant crocodilians.
Abstract - The discovery of a largely complete and well preserved specimen of Poposaurus gracilis has provided the opportunity to generate the first phylogenetically based reconstruction of pelvic and hindlimb musculature of an extinct nondinosaurian archosaur. As in dinosaurs, multiple lineages of basal archosaurs convergently evolved parasagittally erect limbs. However, in contrast to the laterally projecting acetabulum, or "buttress erect" hip morphology of ornithodirans, basal archosaurs evolved a very different, ventrally projecting acetabulum, or "pillar erect" hip. Reconstruction of the pelvic and hindlimb musculotendinous system in a bipedal suchian archosaur clarifies how the anatomical transformations associated with the evolution of bipedalism in basal archosaurs differed from that of bipedal dinosaurs and birds. This reconstruction is based on the direct examination of the osteology and myology of phylogenetically relevant extant taxa in conjunction with osteological correlates from the skeleton of P. gracilis. This data set includes a series of inferences (presence/absence of a structure, number of components, and origin/insertion sites) regarding 26 individual muscles or muscle groups, three pelvic ligaments, and two connective tissue structures in the pelvis, hindlimb, and pes of P. gracilis. These data provide a foundation for subsequent examination of variation in myological orientation and function based on pelvic and hindlimb morphology, across the basal archosaur lineage leading to extant crocodilians.
A New Nearly Complete Articulated Skeleton of the Bipedal Pseudosuchian Poposaurus gracilis from the Upper Triassic of Utah
Back in 2003 I was fortunate to be part of a research team that discovered a mostly complete articulated skeleton of Poposaurus gracilis from the Chinle Formation of Utah. Uncovering such an amazing specimen is definitely one of the highlights of my career, especially the moment when we realized how amazingly complete and articulated the specimen was. Below is a photo of the articulated hind limb and pelvis at that moment during the excavation.
I've seen the specimen a couple of times at Yale in the process of preparation and the specimen is definitely a beauty. Furthermore is is extremely important because prior to this find P. gracilis was only known from the pelvis, hind limbs, and some vertebrae. Unfortunately, the skull of this new specimen was unrecoverable, but the rest provides much information including an articulated forelimb and the pes (foot). I should also add that we met a lot of good friends on this trip.
The first paper out on this specimen is not a detailed osteological study but rather introduces the specimen and provides a detailed determination of the proposed locomotor abilities of this taxon, concluding from numerous lines of evidence (phylogenetic, extant phylogenetic bracketing, morphological) that Poposaurus was an obligatory biped. Morphological support for bipedality in P. gracilis includes a fully erect posture, relatively short forelimbs, elongate pes, five sacral vertebrae, partially open acetabulum, and an elongate tail. Gauthier et al. also provide an in-depth argument that the development of bipedality in Archosauria represents a major evolutionary innovation in vertebrate history.
Finally this paper gives a preview of Sterling Nesbitt's upcoming (in press, out very very shortly) extremely detailed phylogenetic analysis of the Archosauria (from his PhD dissertation). Sterling's analysis provides some pretty surprising (and well-supported) placements of various taxa that will turn some heads and cause a good bit of discussion, especially regarding the revised definitions of some beloved (by some) clade names.
Although I am told that the Poposaurus paper is officially out, it is not up yet on either the Yale Peabody Museum website or the BioOne site, but should be soon. I'll post the link as soon as it does. In the meantime you can read more about the initial find here. I'm also looking forward to the complete osteological description of this amazng specimen.
Gauthier, J. A., Nesbitt, S. J., Schachner, E. R., Bever, G. S., and W. G. Joyce. 2011. The bipedal stem crocodilian Poposaurus gracilis: inferring function in fossils and innovation in archosaur locomotion. Bulletin of the Peabody Museum of Natural History 52:107-126.
Abstract - We introduce a spectacular new specimen of a Late Triassic stem crocodilian identified as Poposaurus gracilis. It is part of a poorly known group, Poposauroidea, that, because of its striking similarities with contemporaneous stem avians (“dinosaurs”), has long puzzled archosaur paleontologists. Observed vertebrate locomotor behaviors, together with exceptional preservation of distinctive anatomical clues in this fossil, enable us to examine locomotor evolution in light of new advances in phylogenetic relationships among Triassic archosaurs. Because this stem crocodilian is unambiguously an archosaur, a diapsid, a tetrapod and a choanate sarcopterygian, we can safely infer major components of its locomotor behavior. These inferences, together with form-function constraints, suggest that P. gracilis was a fleet-footed, obligately erect-postured, striding biped. That behavior seems to have been superimposed on the ancestral archosaur’s innovative locomotor repertoire, which includes the capacity to “high walk.” These novelties persist in a recognizable form in archosaurs for at least 245 million years and are widely distributed across Earth’s surface in diverse ecological settings. They thus qualify as evolutionary innovations regardless of significant differences in diversification rates among extant diapsid reptiles.
I've seen the specimen a couple of times at Yale in the process of preparation and the specimen is definitely a beauty. Furthermore is is extremely important because prior to this find P. gracilis was only known from the pelvis, hind limbs, and some vertebrae. Unfortunately, the skull of this new specimen was unrecoverable, but the rest provides much information including an articulated forelimb and the pes (foot). I should also add that we met a lot of good friends on this trip.
The first paper out on this specimen is not a detailed osteological study but rather introduces the specimen and provides a detailed determination of the proposed locomotor abilities of this taxon, concluding from numerous lines of evidence (phylogenetic, extant phylogenetic bracketing, morphological) that Poposaurus was an obligatory biped. Morphological support for bipedality in P. gracilis includes a fully erect posture, relatively short forelimbs, elongate pes, five sacral vertebrae, partially open acetabulum, and an elongate tail. Gauthier et al. also provide an in-depth argument that the development of bipedality in Archosauria represents a major evolutionary innovation in vertebrate history.
Finally this paper gives a preview of Sterling Nesbitt's upcoming (in press, out very very shortly) extremely detailed phylogenetic analysis of the Archosauria (from his PhD dissertation). Sterling's analysis provides some pretty surprising (and well-supported) placements of various taxa that will turn some heads and cause a good bit of discussion, especially regarding the revised definitions of some beloved (by some) clade names.
Although I am told that the Poposaurus paper is officially out, it is not up yet on either the Yale Peabody Museum website or the BioOne site, but should be soon. I'll post the link as soon as it does. In the meantime you can read more about the initial find here. I'm also looking forward to the complete osteological description of this amazng specimen.
Gauthier, J. A., Nesbitt, S. J., Schachner, E. R., Bever, G. S., and W. G. Joyce. 2011. The bipedal stem crocodilian Poposaurus gracilis: inferring function in fossils and innovation in archosaur locomotion. Bulletin of the Peabody Museum of Natural History 52:107-126.
Abstract - We introduce a spectacular new specimen of a Late Triassic stem crocodilian identified as Poposaurus gracilis. It is part of a poorly known group, Poposauroidea, that, because of its striking similarities with contemporaneous stem avians (“dinosaurs”), has long puzzled archosaur paleontologists. Observed vertebrate locomotor behaviors, together with exceptional preservation of distinctive anatomical clues in this fossil, enable us to examine locomotor evolution in light of new advances in phylogenetic relationships among Triassic archosaurs. Because this stem crocodilian is unambiguously an archosaur, a diapsid, a tetrapod and a choanate sarcopterygian, we can safely infer major components of its locomotor behavior. These inferences, together with form-function constraints, suggest that P. gracilis was a fleet-footed, obligately erect-postured, striding biped. That behavior seems to have been superimposed on the ancestral archosaur’s innovative locomotor repertoire, which includes the capacity to “high walk.” These novelties persist in a recognizable form in archosaurs for at least 245 million years and are widely distributed across Earth’s surface in diverse ecological settings. They thus qualify as evolutionary innovations regardless of significant differences in diversification rates among extant diapsid reptiles.
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