New in PNAS. I assume by terrestrial apex predators in the Carnian they are thinking about phytosaurs and/or large rauisuchids as they (p. 3) state that "Although large predators such as the rauisuchians Erythrosuchus and Ticinosuchus appear in the terrestrial rock record in the Anisian (Nesbitt, 2011), it has been suggested that full recovery on land was not reached until the Late Triassic, 30 My after the P/T extinction (Sahney & Benton, 2008)" [full references and edit added]. Unfortunately this ignores a good bit of new evidence published since 2008 that has changed our understanding of the timing of recovery on land (Xilousuchus, Nyassasaurus). However, I still think the existance of giant (almost 9 meter long) ichthyosaurs is incredible. More than a decade ago I got to see the 21 meter long holotype specimen of Shastasaurus sikanniensis (Late Triassic, British Columbia) when it was being prepared at the Royal Tyrell Museum. To get a photograph of just the rear portion of the skull I had to stand at the top of a fully extended ladder. I used a meter stick for the scale bar! This new specimen is not quite 9 meters in length, but is still huge as the average is 2-4 meters, and it has 12 cm long teeth.
Fröbisch, N. B., Fröbisch, J., Sander, P. M., Schmitz, L., and O. Rieppel. 2013. Macropredatory ichthyosaur from the Middle Triassic and the origin of modern trophic networks. PNAS Early Edition, January 7, 2013. doi:10.1073/pnas.1216750110
Abstract - The biotic recovery from Earth’s most severe extinction event at the Permian-Triassic boundary largely reestablished the preextinction structure of marine trophic networks, with marine reptiles assuming the predator roles. However, the highest trophic level of today's marine ecosystems, i.e., macropredatory tetrapods that forage on prey of similar size to their own, was thus far lacking in the Paleozoic and early Mesozoic. Here we report a top-tier tetrapod predator, a very large (>8.6 m) ichthyosaur from the early Middle Triassic (244 Ma), of Nevada. This ichthyosaur had a massive skull and large labiolingually flattened teeth with two cutting edges indicative of a macropredatory feeding style. Its presence documents the rapid evolution of modern marine ecosystems in the Triassic where the same level of complexity as observed in today’s marine ecosystems is reached within 8 My after the Permian-Triassic mass extinction and within 4 My of the time reptiles first invaded the sea. This find also indicates that the biotic recovery in the marine realm may have occurred faster compared with terrestrial ecosystems, where the first apex predators may not have evolved before the Carnian.
Showing posts with label amazing specimens. Show all posts
Showing posts with label amazing specimens. Show all posts
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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