Showing posts with label convergence. Show all posts
Showing posts with label convergence. Show all posts
Platypus-like Hupehsuchian from Early Triassic of China
Cheng, L., Motani, R., Jiang, D., Yan, C., Tintori, A. and O. Rieppel. 2019. Early Triassic marine reptile representing the oldest record of unusually small eyes in reptiles indicating non-visual prey detection. Scientific Reports 9, number 152. DOI: 10.1038/s41598-018-37754-6
Abstract - The end-Permian mass extinction (EPME) led to reorganization of marine predatory communities, through introduction of air-breathing top predators, such as marine reptiles. We report two new specimens of one such marine reptile, Eretmorhipis carrolldongi, from the Lower Triassic of Hubei, China, revealing superficial convergence with the modern duckbilled platypus (Ornithorhynchus anatinus), a monotreme mammal. Apparent similarities include exceptionally small eyes relative to the body, snout ending with crura with a large internasal space, housing a bone reminiscent of os paradoxum, a mysterious bone of platypus, and external grooves along the crura. The specimens also have a rigid body with triangular bony blades protruding from the back. The small eyes likely played reduced roles during foraging in this animal, as with extant amniotes (group containing mammals and reptiles) with similarly small eyes. Mechanoreceptors on the bill of the animal were probably used for prey detection instead. The specimens represent the oldest record of amniotes with extremely reduced visual capacity, utilizing non-visual cues for prey detection. The discovery reveals that the ecological diversity of marine predators was already high in the late Early Triassic, and challenges the traditional view that the ecological diversification of marine reptiles was delayed following the EPME.
Examining Functional Convergence Between Triassic Phytosaurs and Slender-Snouted Crocodylians
A new preprint in PeerJ.
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.
If Azendohsaurus is not a Sauropodomorph Then What is it?
Would you believe an basal archosauromorph?
Flynn, J. J., Nesbitt, S. J., Parrish, J. M., Ranivoharimanana, L., and A. R. Wyss. 2010. A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible. Palaeontology 53:669-688.
As if the Triassic couldn't get any weirder. If this discovery does not finally demonstrate the peril of assigning isolated jaw fragments and teeth to various dinosaurian subgroups, I do not know what will. The placement of Azendohsaurus as a basal archosauromorph demonstrates that herbivory has evolved independently numerous times within Archosauromorpha and was actually much more common in this clade than previously believed. Some of the primitive cranial features found in Azendohsaurus include a pineal opening, an incomplete lower temporal bar, and palatal teeth. One unique feature of Azendohsaurus is that the palatal teeth are actually leaf-shaped with denticles, very similar to the marginal teeth.
Abstract - Here, we describe a new species of Azendohsaurus from the Middle–Late Triassic of Madagascar, extending the geographical range of a taxon known otherwise only by a single species from Morocco. Although Azendohsaurus has consistently been regarded as an early dinosaur (based on various advanced dental and gnathic features resembling those characterizing certain dinosaur subgroups), the relatively complete skeletal material, now available from Madagascar, argues strongly against its dinosaurian affinities. Rather, the retention of numerous primitive cranial and postcranial features indicates a surprisingly early divergence of Azendohsaurus within Archosauromorpha and an unusual mosaic of characters in this taxon. Features considered diagnostic of Sauropodomorpha thus are inferred to occur homoplastically in at least one clade of nondinosaurian archosauromorphs, indicating a complex evolution and distribution of features traditionally thought to be derived within archosaurs. Azendohsaurus has teeth resembling those of both early sauropodomorph and ornithischian dinosaurs, yet also possesses numerous inarguable basal archosauromorph cranial and postcranial attributes. This highlights the risk of uncritically referring isolated, Middle–Late Triassic (or even later), ‘leafshaped’ teeth with denticles to the Dinosauria. Similarly, the occurrence of such teeth in an early diverging archosauromorph indicates that specializations for herbivory originated more frequently within this clade than conventionally assumed. For example, Azendohsaurus and numerous basal sauropodomorph dinosaur taxa share an array of convergently acquired features associated with herbivory, including tooth denticles, expanded tooth crowns, a downturned dentary and the articular located at the ventral margin of the mandible. Some of these features (denticles, expanded crowns and the ventrally deflected articular) are even more widespread among archosauromorphs, including aetosaurs, silesaurs and ornithischian dinosaurs. A downturned dentary also occurs in Trilophosaurus, a taxon further marked by unique specializations for herbivory, including transversely lophate, tricuspid teeth. An array of features associated with herbivory also occur in rhynchosaurs and certain crocodilians (e.g. Simosuchus). This distribution suggests that craniodental features associated with herbivory were much more pervasive across the archosauromorph clade than previously recognized, possibly evolving at least six to eight times independently.
Flynn, J. J., Nesbitt, S. J., Parrish, J. M., Ranivoharimanana, L., and A. R. Wyss. 2010. A new species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of southwestern Madagascar: cranium and mandible. Palaeontology 53:669-688.
As if the Triassic couldn't get any weirder. If this discovery does not finally demonstrate the peril of assigning isolated jaw fragments and teeth to various dinosaurian subgroups, I do not know what will. The placement of Azendohsaurus as a basal archosauromorph demonstrates that herbivory has evolved independently numerous times within Archosauromorpha and was actually much more common in this clade than previously believed. Some of the primitive cranial features found in Azendohsaurus include a pineal opening, an incomplete lower temporal bar, and palatal teeth. One unique feature of Azendohsaurus is that the palatal teeth are actually leaf-shaped with denticles, very similar to the marginal teeth.
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| Skull reconstruction of Azendohsaurus. From Flynn et al. 2010. |
Abstract - Here, we describe a new species of Azendohsaurus from the Middle–Late Triassic of Madagascar, extending the geographical range of a taxon known otherwise only by a single species from Morocco. Although Azendohsaurus has consistently been regarded as an early dinosaur (based on various advanced dental and gnathic features resembling those characterizing certain dinosaur subgroups), the relatively complete skeletal material, now available from Madagascar, argues strongly against its dinosaurian affinities. Rather, the retention of numerous primitive cranial and postcranial features indicates a surprisingly early divergence of Azendohsaurus within Archosauromorpha and an unusual mosaic of characters in this taxon. Features considered diagnostic of Sauropodomorpha thus are inferred to occur homoplastically in at least one clade of nondinosaurian archosauromorphs, indicating a complex evolution and distribution of features traditionally thought to be derived within archosaurs. Azendohsaurus has teeth resembling those of both early sauropodomorph and ornithischian dinosaurs, yet also possesses numerous inarguable basal archosauromorph cranial and postcranial attributes. This highlights the risk of uncritically referring isolated, Middle–Late Triassic (or even later), ‘leafshaped’ teeth with denticles to the Dinosauria. Similarly, the occurrence of such teeth in an early diverging archosauromorph indicates that specializations for herbivory originated more frequently within this clade than conventionally assumed. For example, Azendohsaurus and numerous basal sauropodomorph dinosaur taxa share an array of convergently acquired features associated with herbivory, including tooth denticles, expanded tooth crowns, a downturned dentary and the articular located at the ventral margin of the mandible. Some of these features (denticles, expanded crowns and the ventrally deflected articular) are even more widespread among archosauromorphs, including aetosaurs, silesaurs and ornithischian dinosaurs. A downturned dentary also occurs in Trilophosaurus, a taxon further marked by unique specializations for herbivory, including transversely lophate, tricuspid teeth. An array of features associated with herbivory also occur in rhynchosaurs and certain crocodilians (e.g. Simosuchus). This distribution suggests that craniodental features associated with herbivory were much more pervasive across the archosauromorph clade than previously recognized, possibly evolving at least six to eight times independently.
Amazing Convergence: Crustacean vs. Aetosaur
Wow! Check out this blog post at Amphidrome on an amazing (I think) extant gammaroid crustacean from Siberia. I will be damned if the anterior portion of the carapace on Acanthogammarus is not a dead ringer for the cervical armor of the Triassic aetosaur Desmatosuchus spurensis (see Parker, 2008)! Especially check out the last photo on the post (and reproduced below) and compare to the postcard photo of the Petrified Forest mount. Note that the proposed purpose for these structures in the crustacean is defensive, whereas I have argued recently that such spines in aetosaurs may also be used for species recognition and display (Parker, 2007).
Parker, W.G. 2008. Description of new material of the aetosaur Desmatosuchus spurensis (Archosauria: Suchia) from the Chinle Formation of Arizona and a revision of the genus Desmatosuchus. PaleoBios 28:1–40.
Very cool crustacean. Where can I get one? ;)
top photo is from here.
REFERENCES
Parker, W.G. 2008. Description of new material of the aetosaur Desmatosuchus spurensis (Archosauria: Suchia) from the Chinle Formation of Arizona and a revision of the genus Desmatosuchus. PaleoBios 28:1–40.
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