Schoch, R. R., and J. B. Desojo. 2016. Cranial anatomy of the aetosaur Paratypothorax andressorum Long & Ballew, 1985, from the Upper Triassic of Germany and its bearing on aetosaur phylogeny. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 279(1):73-95. DOI: http://dx.doi.org/10.1127/njgpa/2016/0542
http://www.ingentaconnect.com/content/schweiz/njbgeol/2016/00000279/00000001/art00008
Abstract - The large aetosaur Paratypothorax andressorum has so far been known only by its osteoderms. Here we describe for the first time the skull of a complete, articulated specimen of this taxon that was found in the type horizon at Murrhardt, southwestern Germany. Paratypothorax
andressorum has the following cranial autapomorphies: (1) upper jaw margin with deep notch between premaxilla and maxilla, (2) maxilla-lacrimal suture with finger-like projection, (3) upper
temporal fenestra triangular, and (4) first paramedian cervical osteoderms narrow and oval, much smaller than second row. Apart from these features, the skull of P. andressorum closely resembles that of the small aetosaur Aetosaurus ferratus known from the same horizons, despite major differences in the morphology of osteoderms. Both taxa share (1) the pointed, beak-shaped premaxilla which expands only gently anterior to the nasal, (2) maxilla and lacrimal excluding jugal
from margin of antorbital fenestra, (3) exclusion of squamosal from margin of infratemporal fenestra, and (4) posterior part of jugal not downturned. Phylogenetic analysis reveals poorly resolved relationships within Aetosauria, but exclusion of a problematic taxon Coahomasuchus results in a much better resolution, with Paratypothorax to nest with Rioarribasuchus, Tecovasuchus, Typothorax, and Redondasuchus within a monophyletic Typothoracinae. Interestingly, Aetosaurus and Stenomyti form successive sister taxa of this clade rather than fall within an aetosaurine grade of basal aetosaurs, as suggested by previous authors. The resemblance of Paratypothorax and Aetosaurus in many cranial features, their close relationship as suggested by the present analysis, and the immature state of all available Aetosaurus specimens suggest two new alternative hypotheses: (1) Aetosaurus is the juvenile of a close relative of Paratypothorax or (2) it is itself the juvenile of Paratypothorax.
Showing posts with label ontogeny. Show all posts
Showing posts with label ontogeny. Show all posts
Significance of Skeletal Variation in the Late Triassic Dinosauriform Silesaurus opolensis
Piechowski, P., Tałanda, M., and J. Dzik. 2014. Skeletal variation and ontogeny of the Late Triassic Dinosauriform Silesaurus opolensis. Journal of Vertebrate Paleontology 34:1383-1393 DOI:10.1080/02724634.2014.873045
Abstract - A principal component analysis (PCA) performed for a set of 24 measurements on 33 femora and 15 measurements on 20 ilia of Silesaurus opolensis from the early Late Triassic of Krasiejów, southern Poland, shows that this sample is highly variable but probably monospecific. Most of the morphological variation is concentrated in the muscle attachments and proportions of bones, which significantly change in both size and position during ontogeny. Despite the small sample size, femora of smaller individuals have less flattened shafts and a more sinusoidal appearance. In many large specimens, proximal parts of muscle tendons are ossified at their attachment site on femora and remain attached to the bone in the largest specimens. The specimens with attached ossifications are interpreted as mature females that were statistically larger than proposed males. It is suggested that ossifications developed in females under calcitonin control. The intrapopulation variability of ilia is high, but less dependant on ontogeny. The population represented by a few specimens from the lower level at Krasiejów may represent a different stage in the evolution of the species than that from the upper horizon.
Abstract - A principal component analysis (PCA) performed for a set of 24 measurements on 33 femora and 15 measurements on 20 ilia of Silesaurus opolensis from the early Late Triassic of Krasiejów, southern Poland, shows that this sample is highly variable but probably monospecific. Most of the morphological variation is concentrated in the muscle attachments and proportions of bones, which significantly change in both size and position during ontogeny. Despite the small sample size, femora of smaller individuals have less flattened shafts and a more sinusoidal appearance. In many large specimens, proximal parts of muscle tendons are ossified at their attachment site on femora and remain attached to the bone in the largest specimens. The specimens with attached ossifications are interpreted as mature females that were statistically larger than proposed males. It is suggested that ossifications developed in females under calcitonin control. The intrapopulation variability of ilia is high, but less dependant on ontogeny. The population represented by a few specimens from the lower level at Krasiejów may represent a different stage in the evolution of the species than that from the upper horizon.
Cranial Morphology of the Plagiosaurid Gerrothorax pulcherrimus as an Extreme Example of Evolutionary Stasis
Schoch, R. R. and F. Witzmann. 2011. Cranial morphology of the plagiosaurid Gerrothorax pulcherrimus as an extreme example of evolutionary stasis. Lethaia, DOI: 10.1111/j.1502-3931.2011.00290.x
Abstract - The plagiosaurid Gerrothorax pulcherrimus from the Triassic of Greenland and Germany is represented by skulls ranging from 4 to 12 cm in length and sheds light on ontogeny, individual variation, and variation in time and space. Ontogeny was remarkably stable in G. pulcherrimus, with the smallest known specimens resembling the adults closely in most features. A true ontogenetic change is evident in the ornament of dermal bones, in that the smallest specimens have ridges whereas in the successively larger ones, pustules spread over increasingly larger areas. The skull becomes proportionally longer, and the adductor chambers relatively narrower. The positive allometry of both the orbits and the interpterygoid vacuities suggests that the eye supporting musculature – rather than the jaw adductors – increased proportionally during growth. Individual, not age-related variation in the dermal skull roof affects partial fusion of parietals, presence and extent of the interfrontoparietal, and the morphological pattern of the posterior skull table. The ventral surface of the basal plate of the parasphenoid ranges from smooth over poorly to heavily ornamented or dentigerous. Considering the impressive longevity of more than 35 Myr, the morphological changes of G. pulcherrimus are minor. Our ecological interpretation for G. pulcherrimus is that it relied on the permanent presence of water, but was flexible with respect to the size and nature of the water body as well as to changes in salinity. The unparalleled extent of evolutionary stasis may therefore be based on the ecological flexibility of this morphologically so tightly constrained temnospondyl.
Abstract - The plagiosaurid Gerrothorax pulcherrimus from the Triassic of Greenland and Germany is represented by skulls ranging from 4 to 12 cm in length and sheds light on ontogeny, individual variation, and variation in time and space. Ontogeny was remarkably stable in G. pulcherrimus, with the smallest known specimens resembling the adults closely in most features. A true ontogenetic change is evident in the ornament of dermal bones, in that the smallest specimens have ridges whereas in the successively larger ones, pustules spread over increasingly larger areas. The skull becomes proportionally longer, and the adductor chambers relatively narrower. The positive allometry of both the orbits and the interpterygoid vacuities suggests that the eye supporting musculature – rather than the jaw adductors – increased proportionally during growth. Individual, not age-related variation in the dermal skull roof affects partial fusion of parietals, presence and extent of the interfrontoparietal, and the morphological pattern of the posterior skull table. The ventral surface of the basal plate of the parasphenoid ranges from smooth over poorly to heavily ornamented or dentigerous. Considering the impressive longevity of more than 35 Myr, the morphological changes of G. pulcherrimus are minor. Our ecological interpretation for G. pulcherrimus is that it relied on the permanent presence of water, but was flexible with respect to the size and nature of the water body as well as to changes in salinity. The unparalleled extent of evolutionary stasis may therefore be based on the ecological flexibility of this morphologically so tightly constrained temnospondyl.
Introducing Dromomeron gregorii a New Lagerpetid Dinosauromorph from the Lower Chinle Formation of Arizona and Dockum Group of Texas
The new issue (June 2009) of the Journal of Vertebrate Paleontology features an article by Sterling Nesbitt, Randy Irmis, and colleagues featuring new data on the Late Triassic North American lagerpetid dinosauromorphs first mentioned by Irmis et al. (2007). This new data includes:
1) A complete decription of the hindlimb material of Dromomeron romeri Irmis et al. 2007.
2) A description of a second species of Dromomeron, D. gregorii.
3) A phylogenetic analysis of basal dinosauromorphs.
4) A detailed discussion of ontogenetic changes in the femur of Dromomeron, which has implications for the phylogeny of early dinosaurs. Specifically that a well-developed anterior trochanter and trochanteric shelf is developed from a low rugosity as femoral size increases. Thus the lack of a trochanteric shelf in some dinosauromorph specimens (e.g., D. romeri and Lagerpeton) may simply indicate immaturity of the specimen rather than a taxonomic or phylogenetic distinction.
Note that Lagerpetidae is formally diagnosed in this paper as a converted clade name to include both species of Dromomeron and Lagerpeton chanarensis.
Also note that lagerpetids now are know from the basal Chinle Formation of Arizona, the upper Chinle of west-central New Mexico, and the lower and middle Dockum Group of Texas. These animals were much more diverse and widespread than previously believed. However, I'm still waiting to recover one in the Petrified Forest. They should be present along with our "silesaurid", Chindesaurus bryansmalli, and coelophysoid theropods.
Here is the abstract from the new paper:
Nesbitt, S.J., Irmis, R.B., Parker, W.G., Smith, N.D., Turner, A.H., and T. Rowe. 2009. Hindlimb osteology and description of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29:498-516.
ABSTRACT—The recent discovery of early dinosauromorphs from North America demonstrates that they were contemporaries with dinosaurs and other basal archosaurs during a substantial portion of the Late Triassic Period. Hindlimb material (femora, tibiae, a fibula, astragalocalcanea, and phalanges) of Dromomeron romeri, a non-dinosauriform dinosauromorph from the Petrified Forest Member of the Chinle Formation from north-central New Mexico, is described. A new species of Dromomeron from the lower portion of the Chinle Formation (eastern Arizona) and Dockum Group (northern Texas) is also described, based on several disarticulated femora and tibiae. D. romeri, Lagerpeton, and the new taxon form the sister group to all other dinosauromorphs and demonstrate that this clade, Lagerpetidae, persisted well into the Norian. Lagerpetidae is supported by several synapomorphies: femoral head hook-shaped in medial and lateral views; ventral emargination on the anterolateral side of the femoral head; an enlarged posteromedial tuber of the proximal end of the femur; femoral crista tibiofibularis larger than the medial condyle; anteromedial corner of the distal end of the femur forms 90 degree or acute (>90 degree) angle; and a posterior ascending process of the astragalus. An ontogenetic series of the femur of Dromomeron indicates that some character states previously used in phylogenetic analyses of early dinosaurs may be ontogenetically variable.
REFERENCES
Irmis, R. B., Nesbitt, S.J., Padian, K., Smith, N.D., Turner, A.H., Woody, D., and A. Downs. 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science
317:358–361.
1) A complete decription of the hindlimb material of Dromomeron romeri Irmis et al. 2007.
2) A description of a second species of Dromomeron, D. gregorii.
3) A phylogenetic analysis of basal dinosauromorphs.
4) A detailed discussion of ontogenetic changes in the femur of Dromomeron, which has implications for the phylogeny of early dinosaurs. Specifically that a well-developed anterior trochanter and trochanteric shelf is developed from a low rugosity as femoral size increases. Thus the lack of a trochanteric shelf in some dinosauromorph specimens (e.g., D. romeri and Lagerpeton) may simply indicate immaturity of the specimen rather than a taxonomic or phylogenetic distinction.
Note that Lagerpetidae is formally diagnosed in this paper as a converted clade name to include both species of Dromomeron and Lagerpeton chanarensis.
Also note that lagerpetids now are know from the basal Chinle Formation of Arizona, the upper Chinle of west-central New Mexico, and the lower and middle Dockum Group of Texas. These animals were much more diverse and widespread than previously believed. However, I'm still waiting to recover one in the Petrified Forest. They should be present along with our "silesaurid", Chindesaurus bryansmalli, and coelophysoid theropods.
Here is the abstract from the new paper:
Nesbitt, S.J., Irmis, R.B., Parker, W.G., Smith, N.D., Turner, A.H., and T. Rowe. 2009. Hindlimb osteology and description of basal dinosauromorphs from the Late Triassic of North America. Journal of Vertebrate Paleontology 29:498-516.
ABSTRACT—The recent discovery of early dinosauromorphs from North America demonstrates that they were contemporaries with dinosaurs and other basal archosaurs during a substantial portion of the Late Triassic Period. Hindlimb material (femora, tibiae, a fibula, astragalocalcanea, and phalanges) of Dromomeron romeri, a non-dinosauriform dinosauromorph from the Petrified Forest Member of the Chinle Formation from north-central New Mexico, is described. A new species of Dromomeron from the lower portion of the Chinle Formation (eastern Arizona) and Dockum Group (northern Texas) is also described, based on several disarticulated femora and tibiae. D. romeri, Lagerpeton, and the new taxon form the sister group to all other dinosauromorphs and demonstrate that this clade, Lagerpetidae, persisted well into the Norian. Lagerpetidae is supported by several synapomorphies: femoral head hook-shaped in medial and lateral views; ventral emargination on the anterolateral side of the femoral head; an enlarged posteromedial tuber of the proximal end of the femur; femoral crista tibiofibularis larger than the medial condyle; anteromedial corner of the distal end of the femur forms 90 degree or acute (>90 degree) angle; and a posterior ascending process of the astragalus. An ontogenetic series of the femur of Dromomeron indicates that some character states previously used in phylogenetic analyses of early dinosaurs may be ontogenetically variable.
REFERENCES
Irmis, R. B., Nesbitt, S.J., Padian, K., Smith, N.D., Turner, A.H., Woody, D., and A. Downs. 2007. A Late Triassic dinosauromorph assemblage from New Mexico and the rise of dinosaurs. Science
317:358–361.
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