Azendohsaurus postcrania – svp abstracts 2013
From the abstract:
Nesbitt et al. 2013 wrote, “During the Triassic, a number of highly disparate archosauromorphs populated both terrestrial (e.g., Trilophosaurus, rhynchosaurs) and marine ecosystems (e.g., tanystropheids) across Pangea. Unfortunately, the unique and sometimes utterly bizarre body plans of these reptiles (e.g., specialized feeding adaptations) create a major challenge in understanding early archosauromorph relationships and patterns of diversification, as teasing apart homology from homoplasy has been difficult with the current sample of taxa.
“Here we present the postcranial anatomy of Azendohsaurus madagaskarensis, an early archosauromorph from the Middle-Late Triassic of Madagascar. Azendohsaurus madagaskarensis comes from a monotypic bone bed containing an ontogenetically variable sample, with preservation ranging from whole, disarticulated bones, to articulated partial skeletons. From this bonebed, the entire anatomy of the taxon is represented. Azendohsaurus madagaskarensis possessed an elongated neck, short tail, and stocky limbs. The manus and pes have unexpectedly short digits, terminating in large, recurved ungual phalanges. Together with the skull, knowledge of the postcranial skeleton elevates A. madagaskarensis to another highly apomorphic and bizarre Triassic archosauromorph.
“Even so, recovery, description and analysis of the full anatomy of A. madagaskarensis provides clues to understanding the relationships of this species and other problematic and anatomically specialized taxa, including the North American Late Triassic archosauromorphs Trilophosaurus and Teraterpeton. For example, A. madagaskarensis, Trilophosaurus, and Teraterpeton share a dorsally hooked quadrate and enlarged, trenchant unguals, whereas Trilophosaurus and Teraterpeton alone share a number of other character states (e.g., restricted scapular blade, premaxillary beak). We tested these observations in a newly constructed phylogenetic analysis centered on Triassic archosauromorphs and archosauriforms. We find that A. madagaskarensis, Trilophosaurus, Spinosuchus, and Teraterpeton form a clade within Archosauromorpha, but the relationships of this clade to other groups of Triassic archosauromorphs (e.g., archosauriforms, rhynchosaurs, tanystropheids) remains poorly supported. The newly recognized clade containing A. madagaskarensis, Trilophosaurus, and Teraterpeton demonstrates high disparity of feeding adaptations even within a closely related group of basal archosauromorphs.”
Figure 1. Click to enlarge. On the left, the rhynchosaur Hyperodapedon, the protorhynchosaur, Mesosuchus and the two Trlophosaurs, Trilophosaurus and Azendohsaurus. On the right, basal archosauriforms and Azendohsaurs tucked in the bottom along with a tree segment.
First of all,
its great to hear the postcrania of Azendohsaurus is finally on the table, soon to be published, I presume. The skull nests it as a sister to Trilophosaurus, so the long neck is no surprise and Sapheosaurus. The short tail, short digits and stocky limbs of Azendohsaurus are found phylogenetically nearby in the rhynchosaur Hyperodapedon and the proto-rhynchosaur, Mesosuchus. So, again, no surprise there. This clade has surprising diversity.
Second of all,
Nesbitt et al. 2013 think these taxa are bizarre only because they are under the presumption that they are all archosauromorphs. They are not, as documented by the large reptile tree. It’s no surprise then that Nesbitt et al. report, “relationships remains poorly supported.” Evidently Nesbitt et al. 2013 don’t have a large enough gamut in their reptile tree to recovers their featured taxa as lepidosauromorphs, closer to lepidosaurs than to archosaurs.
When Nesbitt et al. finally do figure out how to nest those taxa, they’ll also find out that their new sister taxa provide a gradual accumulation of traits that lead to all their oddball traits. It’s the same problem Nesbitt 2011 made nesting pterosaurs with archosaurs. In reality, when you don’t exclude the better candidates, tritosaur lepidosaurs provide the gradual accumulation of pterosaurian traits.
Nesbitt 2011 already made the big mistake of nesting Mesosuchus as a basal archosauromorph when it is way closer to sphenodontids. Youngina would have been a better choice as a basal archosauromorph. It’s way more plesiomorphic with regards to proterosuchids, erythrosuchids and choristorderes.
The exception
Figure 2. Teraterpeton, a former enigma that nests in the large reptile tree between Chanaresuchus and Tropidosuchus. While oddballs sometimes nest together, this taxon has little in common with Trilophosaurus.
Teraterpeton is the exception, a pararchosauriform archosaurormorph nesting between Chanaresuchus and Tropidosuchus in the large reptile tree. Earlier we looked at Teraterpeton here. Nesbitt et al. found that Teraterpeton, Trilophosaurus and Azendohsaurus shared a dorsally hooked quadrate and enlarged trenchant unguals. Unfortunately, more that 30 steps are added when Teraterpeton shifts to nest with the other two and the unguals are not really that big in Teraterpeton. They’re actually bigger in the sister taxon, Chanaresuchus. The quadrate often hooks in herbivores. That they have in common.
Gosh,
I hope the Nesbitt team goes to a larger gamut tree and tests their taxa against other candidates before they publish another problem-filled paper like Nesbitt (2011) with strange bedfellows (sisters that don’t share very many traits) all over the place. The nestings of these featured taxa in the large reptile tree are strongly supported.
References
Nesbitt, S, Flynn J, Ranivohrimanina L, Pritchard A and Wyss A 2013. Relationships among the bizarre: the anatomy of Azendohsaurus madagaskarensis and its implications for resolving early archosauromroph phylogeny. Journal of Vertebrate Paleontology abstracts 2013.
Source: http://pterosaurheresies.wordpress.com/2013/11/05/azendohsaurus-postcrania-svp-abstracts-2013/
Anyone can join.
Anyone can contribute.
Anyone can become informed about their world.
"United We Stand" Click Here To Create Your Personal Citizen Journalist Account Today, Be Sure To Invite Your Friends.
Before It’s News® is a community of individuals who report on what’s going on around them, from all around the world. Anyone can join. Anyone can contribute. Anyone can become informed about their world. "United We Stand" Click Here To Create Your Personal Citizen Journalist Account Today, Be Sure To Invite Your Friends.
LION'S MANE PRODUCT
Try Our Lion’s Mane WHOLE MIND Nootropic Blend 60 Capsules
Mushrooms are having a moment. One fabulous fungus in particular, lion’s mane, may help improve memory, depression and anxiety symptoms. They are also an excellent source of nutrients that show promise as a therapy for dementia, and other neurodegenerative diseases. If you’re living with anxiety or depression, you may be curious about all the therapy options out there — including the natural ones.Our Lion’s Mane WHOLE MIND Nootropic Blend has been formulated to utilize the potency of Lion’s mane but also include the benefits of four other Highly Beneficial Mushrooms. Synergistically, they work together to Build your health through improving cognitive function and immunity regardless of your age. Our Nootropic not only improves your Cognitive Function and Activates your Immune System, but it benefits growth of Essential Gut Flora, further enhancing your Vitality.
Our Formula includes: Lion’s Mane Mushrooms which Increase Brain Power through nerve growth, lessen anxiety, reduce depression, and improve concentration. Its an excellent adaptogen, promotes sleep and improves immunity. Shiitake Mushrooms which Fight cancer cells and infectious disease, boost the immune system, promotes brain function, and serves as a source of B vitamins. Maitake Mushrooms which regulate blood sugar levels of diabetics, reduce hypertension and boosts the immune system. Reishi Mushrooms which Fight inflammation, liver disease, fatigue, tumor growth and cancer. They Improve skin disorders and soothes digestive problems, stomach ulcers and leaky gut syndrome. Chaga Mushrooms which have anti-aging effects, boost immune function, improve stamina and athletic performance, even act as a natural aphrodisiac, fighting diabetes and improving liver function. Try Our Lion’s Mane WHOLE MIND Nootropic Blend 60 Capsules Today. Be 100% Satisfied or Receive a Full Money Back Guarantee. Order Yours Today by Following This Link.
