Just in time for Christmas...
Scheyer, T. M., Desojo, J. B., and I. A. Cerda. 2013. Bone histology of phytosaur, aetosaur, and other archosauriform osteoderms (Eureptilia, Archosauromorpha). Anatomical Record (early view) DOI: 10.1002/ar.22849
Abstract - As in other archosauriforms, phytosaurs and aetosaurs are characterized by the presence of well-developed osteoderms. Here we provide a comparative study on the microstructure of phytosaur (five taxa) and aetosaur (thirteen taxa) osteoderms. For outgroup comparison, we sampled osteoderms of the sister taxon to Aetosauria, Revueltosaurus callenderi, and the doswelliid Jaxtasuchus salomoni. Phytosaur, aetosaur, and Jaxtasuchus osteoderms are composed of a diploe structure, whereas the Revueltosaurus osteoderm microanatomy is more compact. The external cortex of phytosaurs, Revueltosaurus and Jaxtasuchus osteoderms is mainly composed of parallel-fibered bone. In aetosaurs, the external cortex mainly consists of lamellar bone, with lines of resorption within the primary bone indicating successive cycles of bone erosion and deposition. The basal cortex in all the specimens is composed of parallel-fibered bone, with the cancellous internal core being more strongly developed in aetosaurs than in phytosaurs. Woven or fibro-lamellar bone was recorded in both phytosaurian and aetosaurian taxa, as well as in Jaxtasuchus. Structural fibers, which at least partly suggest metaplastic origin, were only recorded in the internal core of two phytosaurs and in the
basal cortex of one aetosaur. Osteoderm thickness and cancellous to compact bone ratios appear to be subject to ontogenetic change. Minimum growth mark counts in osteoderms sampled indicate that some aetosaurs and phytosaurs lived for at least two decades. Bone microstructures are more uniform in phytosaur osteoderms and show a higher level of disparity among aetosaur osteoderms, and at least in the latter, histological features are potentially apomorphic for species/genus level.
Showing posts with label Revueltosaurus. Show all posts
Showing posts with label Revueltosaurus. Show all posts
Comparing the Tooth Enamel Microstructure of the Pseudosuchian Revueltosaurus and the Proposed Triassic Ornithischian Krzyzanowskisaurus
This is a new paper testing the relationships between the pseudosuchian Revueltosaurus callenderi and the hypothesized ornithischian Krzyzanowskisaurus hunti (originally Revueltosaurus hunti) utilizing tooth enamel microstructure. The study finds that the tooth enamel structure of these two taxa share many characters not found in other taxa and thus they are probably closely related. The authors advocate that generic distinction should be maintained until the skeletal remains of K. hunti are discovered. However, the teeth of K. hunti were recovered from a microvertebrate deposit in the Blue Mesa Member of the Chinle Formation near St. Johns Arizona. As mentioned by Parker et al (2005) and Irmis et al. (2007) the same deposit included an autapomorphic squamosal of Revueltosaurus as well as numerous osteoderms also referable to the taxon. Thus the assemblage possibly contains Revueltosaurus hunti or Revueltosaurus as well as a second taxon with Revueltosaurus-like teeth called Krzyzanowskisaurus. Heckert and Miller-Camp argue that this could be circumstantial given the purported lack of element association; however, no evidence exists either that they weren't originally found in association. There is simply just drawers of microvertebrate material from the same quarry. I and my colleagues have just maintained that the former is more parsimonious (Revueltosaurus hunti) and the shared characteristics of the teeth revealed by this study seem to support that hypothesis. In any case there still is no strong evidence for an ornithischian dinosaur affinity for K. hunti.
Heckert, A. B., and J. A. Miller-Camp. 2013. Tooth enamel microstructure of Revueltosaurus and Krzyzanowskisaurus (Reptilia:Archosauria) from the Upper Triassic Chinle Group, USA: Implications for function, growth, and phylogeny. Palaeontologia Electronica Vol. 16, Issue 1; 1A,23p; palaeo-electronica.org/content/2013/344-revueltosaurus-tooth-enamel
Abstract - Tooth enamel microstructure can carry significant phylogenetic, ontogenetic, and functional information within amniotes. Here we provide the first descriptions of the tooth enamel microstructure of two Late Triassic taxa, the crurotarsan Revueltosaurus callenderi Hunt and the putative ornithischian Krzyzanowskisaurus hunti (Heckert), which some consider closely related. To test the hypotheses that enamel thickness corresponds to function and/or phylogeny we analyzed the enamel of each at various scales, measuring enamel thickness and examining microstructural features throughout both longitudinal and cross-sectional thickness using previously established techniques to facilitate comparisons. Both taxa possess thick (up to ~150 µm) enamel for their size (< 20 mm crown height). Enamel in R. callenderi ranged from ~5-152 µm across a premaxillary tooth in longitudinal section, and ~42-92 µm in a maxillary/dentary tooth transverse section. K. hunti enamel thickness was ~18-155 µm longitudinally and ~29-75 µm transversely. Both also had well-developed basal unit layers (BUL) and weakly developed columnar microstructure. Well-developed lines of incremental growth (LIG) are present in both taxa, through which the columnar enamel grades into parallel crystallite enamel. Their enamel microstructure is therefore grossly similar to that of several ornithischian taxa, especially ankylosaurs, with which they are strongly convergent, and also compares well to rauisuchids and tyrannosaurids. The relatively unique combination of microstructural characteristics in the schmelzmuster of R. callenderi and K. hunti supports the hypothesis that they are closely related, but does not conclusively preclude a different taxonomic placement for K. hunti so we retain its separate generic designation.
Heckert, A. B., and J. A. Miller-Camp. 2013. Tooth enamel microstructure of Revueltosaurus and Krzyzanowskisaurus (Reptilia:Archosauria) from the Upper Triassic Chinle Group, USA: Implications for function, growth, and phylogeny. Palaeontologia Electronica Vol. 16, Issue 1; 1A,23p; palaeo-electronica.org/content/2013/344-revueltosaurus-tooth-enamel
Abstract - Tooth enamel microstructure can carry significant phylogenetic, ontogenetic, and functional information within amniotes. Here we provide the first descriptions of the tooth enamel microstructure of two Late Triassic taxa, the crurotarsan Revueltosaurus callenderi Hunt and the putative ornithischian Krzyzanowskisaurus hunti (Heckert), which some consider closely related. To test the hypotheses that enamel thickness corresponds to function and/or phylogeny we analyzed the enamel of each at various scales, measuring enamel thickness and examining microstructural features throughout both longitudinal and cross-sectional thickness using previously established techniques to facilitate comparisons. Both taxa possess thick (up to ~150 µm) enamel for their size (< 20 mm crown height). Enamel in R. callenderi ranged from ~5-152 µm across a premaxillary tooth in longitudinal section, and ~42-92 µm in a maxillary/dentary tooth transverse section. K. hunti enamel thickness was ~18-155 µm longitudinally and ~29-75 µm transversely. Both also had well-developed basal unit layers (BUL) and weakly developed columnar microstructure. Well-developed lines of incremental growth (LIG) are present in both taxa, through which the columnar enamel grades into parallel crystallite enamel. Their enamel microstructure is therefore grossly similar to that of several ornithischian taxa, especially ankylosaurs, with which they are strongly convergent, and also compares well to rauisuchids and tyrannosaurids. The relatively unique combination of microstructural characteristics in the schmelzmuster of R. callenderi and K. hunti supports the hypothesis that they are closely related, but does not conclusively preclude a different taxonomic placement for K. hunti so we retain its separate generic designation.
David Peter's Take on Revueltosaurus
David Peters has a new post up on his blog that has been getting some attention including on Facebook. I'll address it shortly but first I'd like to apologize for the long delay in getting the full description of this taxon out in publication, especially since everyone has now seen Jeff Martz's amazing reconstruction. Originally I suggested he submit it for the Lanzandorf prize because I thought the paper would actually be submitted by that point. The main text has been near completion for some time now and very recently revised. The hang-up is in completing the figures and because I keep taking on other tasks and responsibilities keeping me from focusing on the project.
David Peters post with the suggestion that Revueltosaurus may be a paracrocodylomorph is actually fairly insightful given that he has not seen the material first hand and is relying solely on preliminary descriptions and Jeff's reconstruction. Revueltosaurus is an amazing critter because it possesses character states found in a variety of suchian taxa, including paracrocodylomorphs; however, it has many characters only shared with aetosaurs which results in the position found by Nesbitt (2011). Sterling's coding was based on a thorough examination of all presently known material and although I don't agree with 100% of his codings I don't think the phylogenetic position of Revueltosaurus will change with the publication of the full description and revised phylogenetic analysis.
I'd ask everyone to please be a bit more patient and we'll get the paper out. I realize that it is an important taxon and as a result a lot of people want/need to see the material.
David Peters post with the suggestion that Revueltosaurus may be a paracrocodylomorph is actually fairly insightful given that he has not seen the material first hand and is relying solely on preliminary descriptions and Jeff's reconstruction. Revueltosaurus is an amazing critter because it possesses character states found in a variety of suchian taxa, including paracrocodylomorphs; however, it has many characters only shared with aetosaurs which results in the position found by Nesbitt (2011). Sterling's coding was based on a thorough examination of all presently known material and although I don't agree with 100% of his codings I don't think the phylogenetic position of Revueltosaurus will change with the publication of the full description and revised phylogenetic analysis.
I'd ask everyone to please be a bit more patient and we'll get the paper out. I realize that it is an important taxon and as a result a lot of people want/need to see the material.
Triassic Ornithischian? Krzyzanowskisaurus hunti revisited.
http://www.azstarnet.com/news/local/article_d4138dc4-60a2-544c-8ba8-45ed550df2c2.html
The Arizona Daily Star (Tucson, AZ), published this story earlier on local fossil collector Stan Krzyzanowski. Those of you familiar with dinosaur taxonomy may recognize the name in regards to the Triassic tooth taxon Krzyzanowskisaurus hunti, to which the story alludes.
This taxon, known from only a handful of isolated teeth, was originally described as a new species of the putative ornithichian dinosaur Reveultosaurus by Heckert (2002). When it was subsequently discovered that the type species of Revueltosaurus, R. callenderi, actually represented a non-dinosaurian pseudosuchian archosaur (Parker et al. 2005), Heckert (2005) referred R. hunti to this new genus, Krzyzanowskisaurus. Heckert's (2005:77) support for this new referral is that the teeth of K. hunti "appear more derived than R. callenderi, and are in fact more 'typically' ornithischian than those of R. callenderi". By more 'typically' ornithischian Heckert (2005:78) is referring to the presence of a "pronounced bulge on the lingual surface", which he hypothesizes as being homologous with the 'cingulum' found in basal ornithischian teeth. However, there is no strong evidence for this homology and thus there are no apomorphies whatsoever to support the referral of K. hunti to Ornithischia (Irmis et al. 2007). Likewise, no phylogentic analysis exists to support the claim that this tooth morphology would be more derived. In fact co-occurring fossils from the St. Johns area actually support the original referral of these teeth to Revueltosaurus, thus I maintain that no material from North America currently exists that can be unambiguously referred to Ornithischia (Parker et al. 2005; Nesbitt et al. 2007; Irmis et al. 2007), and the reconstruction below is most likely erroneous (and apparently plagiarized from Greg Paul, see the copyright and read the comments below).
The Krzyzanowski bonebed is a potentially interesting vertebrate microsite from the Chinle Formation near St. Johns (similar to sites in the same area collected by Charles Camp in the late 1920s), but to date has only received limited coverage in publications (e.g., Heckert et al. 2004; Heckert et al. 2005), including a claim by these authors as to the presence of what would be the only sauropodomorph material from the Upper Triassic of North America (besides Greenland, which is physiogeographically considered part of that continent).
REFERENCES
Heckert, A.B. 2002. A revision of the upper Triassic ornithischian dinosaur Revueltosaurus, with a description of a new species. New Mexico Musuem of Natural History and Science Bulletin 21:253–267.
Heckert, A.B. 2005. Krzyzanowskisaurus, a new name for a probable ornithischian dinosaur from the upper Triassic Chinle Group, Arizona and New Mexico, USA. New Mexico Museum of Natural History and Science Bulletin 29: 77–83.
Heckert, A.B., Lucas, S.G., and A.P. Hunt. 2005. Triassic vertebrate fossils in Arizona. New Mexico Museum of Natural History and Science Bulletin 29:16-44.
Heckert, A. B., Rinehart, L. F., Krzyzanowski, S. E., Lucas, S. G., and S.K. Harris. 2004. The Krzyzanowski bonebed: an Upper Triassic (Adamanian: latest Carnian) vertebrate fauna and its implications for microvertebrate studies. New Mexico Geology 26:64.
Irmis, R.B., Parker, W.G., Nesbitt, S.J., and J. Liu. 2006. Early ornithischian dinosaurs: the Triassic record. Historical Biology 19:3-22.
Nesbitt, S.J., Irmis, R.B., and W.G. Parker. 2007. A critical re-evaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology 5:209-243.
Parker, W.G., Irmis, R.B., Nesbitt, S.J., Martz, J.W., and L.S. Browne. 2005. The
Late Triassic pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. Proceedings of the Royal Society of London, B 272:963–969.
The image above is from the linked article.
The Arizona Daily Star (Tucson, AZ), published this story earlier on local fossil collector Stan Krzyzanowski. Those of you familiar with dinosaur taxonomy may recognize the name in regards to the Triassic tooth taxon Krzyzanowskisaurus hunti, to which the story alludes.
This taxon, known from only a handful of isolated teeth, was originally described as a new species of the putative ornithichian dinosaur Reveultosaurus by Heckert (2002). When it was subsequently discovered that the type species of Revueltosaurus, R. callenderi, actually represented a non-dinosaurian pseudosuchian archosaur (Parker et al. 2005), Heckert (2005) referred R. hunti to this new genus, Krzyzanowskisaurus. Heckert's (2005:77) support for this new referral is that the teeth of K. hunti "appear more derived than R. callenderi, and are in fact more 'typically' ornithischian than those of R. callenderi". By more 'typically' ornithischian Heckert (2005:78) is referring to the presence of a "pronounced bulge on the lingual surface", which he hypothesizes as being homologous with the 'cingulum' found in basal ornithischian teeth. However, there is no strong evidence for this homology and thus there are no apomorphies whatsoever to support the referral of K. hunti to Ornithischia (Irmis et al. 2007). Likewise, no phylogentic analysis exists to support the claim that this tooth morphology would be more derived. In fact co-occurring fossils from the St. Johns area actually support the original referral of these teeth to Revueltosaurus, thus I maintain that no material from North America currently exists that can be unambiguously referred to Ornithischia (Parker et al. 2005; Nesbitt et al. 2007; Irmis et al. 2007), and the reconstruction below is most likely erroneous (and apparently plagiarized from Greg Paul, see the copyright and read the comments below).
The Krzyzanowski bonebed is a potentially interesting vertebrate microsite from the Chinle Formation near St. Johns (similar to sites in the same area collected by Charles Camp in the late 1920s), but to date has only received limited coverage in publications (e.g., Heckert et al. 2004; Heckert et al. 2005), including a claim by these authors as to the presence of what would be the only sauropodomorph material from the Upper Triassic of North America (besides Greenland, which is physiogeographically considered part of that continent).
REFERENCES
Heckert, A.B. 2002. A revision of the upper Triassic ornithischian dinosaur Revueltosaurus, with a description of a new species. New Mexico Musuem of Natural History and Science Bulletin 21:253–267.
Heckert, A.B. 2005. Krzyzanowskisaurus, a new name for a probable ornithischian dinosaur from the upper Triassic Chinle Group, Arizona and New Mexico, USA. New Mexico Museum of Natural History and Science Bulletin 29: 77–83.
Heckert, A.B., Lucas, S.G., and A.P. Hunt. 2005. Triassic vertebrate fossils in Arizona. New Mexico Museum of Natural History and Science Bulletin 29:16-44.
Heckert, A. B., Rinehart, L. F., Krzyzanowski, S. E., Lucas, S. G., and S.K. Harris. 2004. The Krzyzanowski bonebed: an Upper Triassic (Adamanian: latest Carnian) vertebrate fauna and its implications for microvertebrate studies. New Mexico Geology 26:64.
Irmis, R.B., Parker, W.G., Nesbitt, S.J., and J. Liu. 2006. Early ornithischian dinosaurs: the Triassic record. Historical Biology 19:3-22.
Nesbitt, S.J., Irmis, R.B., and W.G. Parker. 2007. A critical re-evaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology 5:209-243.
Parker, W.G., Irmis, R.B., Nesbitt, S.J., Martz, J.W., and L.S. Browne. 2005. The
Late Triassic pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. Proceedings of the Royal Society of London, B 272:963–969.
The image above is from the linked article.
The Ex-Ornithischian Revueltosaurus callenderi
Lukas Panzarin guessed correctly. The reconstruction below is of the Late Triassic pseudosuchian Revueltosaurus callenderi courtesy of Jeff Martz. The new reconstruction is based on new material of this taxon from the Chinle Formation of Petrified Forest National Park.
For those readers not familiar with Revueltosaurus, it was named in 1989 by Adrian Hunt based on isolated teeth from near Revuelto Creek in east-central New Mexico (Bull Canyon Formation of the Dockum Group). The teeth are highly distinctive, leaf-shaped with denticles, and very similar to the teeth of basal ornithischians. Based on these similarities Hunt (1989) tentatively referred Revueltosaurus to the Ornithischia. Below are teeth of Revueltosaurus from Petrified Forest National Park.
However, although no non-dental material of Revueltosaurus was yet known Hunt and Lucas (1994) did consider it to be a bona-fide Ornithischian. Furthermore, these authors erected several other "Ornithischian" taxa from North America based solely on teeth. Heckert (2002) fully redescribed the holotype material and also erected a second species, Revueltosaurus hunti, also based on isolated teeth. As a result, the entire Late Triassic ornithischian record from Narth America and Europe was based solely on isolated teeth. Below is a reconstruction of a hypothesized basal ornithischian.
In 2004 I discovered skeletal material of R. callenderi from the Petrified Forest Member (Chinle Formation) of Petrified Forest National Park. This amazing site (named the Revueltosaurus Quarry) has provided hundreds of bones of numerous individuals of R. callenderi. This was the first recognized non-dental material of this taxon. Below are Randy Irmis, Lori Browne, and Jeff Martz initially excavating the site in 2004.
In 2005 we published a preliminary description of this material. Interestingly the recovered skeletons were not of an ornithischian, or even a dinosaur, but rather from a crocodile-line archosaur (Pseudosuchia). Amazingly, the ornithischian-like dentition was simply a convergence. We argued that none of the North American and European teeth could be unambiguously considered to represent ornithischians. Thus, the entire Late Triassic record of ornithischians from these continents was essentially erased. Below is a cladogram showing the revised position of Revueltosaurus.
A few authors (e.g., Heckert, 2005) have argued against this interpretation, insisting that some of these teeth do represent ornithischians; however, there are no clear characters of these teeth that support this interpretation (Irmis et al, 2007).
In 2006 the Revueltosaurus Quarry yielded a superbly preserved almost complete skeleton of R. callenderi, which I featured at a recent Society of Vertebrate Paleontology meeting. A full description of this specimen (and thus the taxon) is almost complete. One really neat character (I think) apparent in Jeff's reconstruction is the large size of the skull in relation to the postcranial skeleton. The skull is quite a bit longer than the femur, and this is a bit odd considering the skull "accomplishes" this without elongating the forward portion of the skull as in champsosaurids, phytosaurs, and crocodiles.
I have jokingly refered to Revueltosaurus as the "duck-billed platypus" of the Triassic because of its ornithichian-like dentition, aetosaur-like armor carapace, and other characteristics found only in rauisuchians and crocodylomorphs.
Indeed Revueltosaurus belongs to a previously unrecognized clade of archosaur, which hopefully will elucidate phylogentic relationships within Pseudosuchia.
By the way...the PDF of Parker et al (2005) is freely available from the link in the reference below.
REFERENCES
Heckert, A. B. 2002 A revision of the Upper Triassic ornithischian dinosaur Revueltosaurus, with a description of a new species. New Mexico Museum of Natural History and Science Bulletin 21:253–267.
Heckert, A.B. 2005. Krzyzanowskisaurus, a new name for a probable ornithischian dinosaur from the Upper Triassic Chinle Group, Arizona and New Mexico, USA. New Mexico Museum of Natural History and Science Bulletin 29: 77-83.
Hunt, A. P. 1989. A new ?ornithischian dinosaur from the Bull Canyon Formation (Upper Triassic) of east-central New Mexico. pp. 355–358 in Dawn of the age of dinosaurs in the American Southwest (ed. S. G. Lucas & A. P. Hunt). New Mexico Museum of Natural History, Albuquerque, NM.
Hunt, A. P., and S.G. Lucas. 1994. Ornithischian dinosaurs from the Upper Triassic of the United States. pp. 227–241 in In the Shadows of the Dinosaurs: Early Mesozoic Tetrapods (ed. N. C. Fraser & H.-D. Sues). Cambridge University Press.
Irmis, R.B., Parker, W.G., Nesbitt, S.J., and Liu, J. 2006. Early ornithischian dinosaurs: the Triassic record. Historical Biology 19:3-22.
Parker, W.G., Irmis, R.B., Nesbitt, S.J., Martz, J.W., and L.S. Browne. 2005. The Late Triassic pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. Proceedings of the Royal Society B 272:963-969. doi:10.1098/rspb.2004.3047
For those readers not familiar with Revueltosaurus, it was named in 1989 by Adrian Hunt based on isolated teeth from near Revuelto Creek in east-central New Mexico (Bull Canyon Formation of the Dockum Group). The teeth are highly distinctive, leaf-shaped with denticles, and very similar to the teeth of basal ornithischians. Based on these similarities Hunt (1989) tentatively referred Revueltosaurus to the Ornithischia. Below are teeth of Revueltosaurus from Petrified Forest National Park.
However, although no non-dental material of Revueltosaurus was yet known Hunt and Lucas (1994) did consider it to be a bona-fide Ornithischian. Furthermore, these authors erected several other "Ornithischian" taxa from North America based solely on teeth. Heckert (2002) fully redescribed the holotype material and also erected a second species, Revueltosaurus hunti, also based on isolated teeth. As a result, the entire Late Triassic ornithischian record from Narth America and Europe was based solely on isolated teeth. Below is a reconstruction of a hypothesized basal ornithischian.
In 2004 I discovered skeletal material of R. callenderi from the Petrified Forest Member (Chinle Formation) of Petrified Forest National Park. This amazing site (named the Revueltosaurus Quarry) has provided hundreds of bones of numerous individuals of R. callenderi. This was the first recognized non-dental material of this taxon. Below are Randy Irmis, Lori Browne, and Jeff Martz initially excavating the site in 2004.
In 2005 we published a preliminary description of this material. Interestingly the recovered skeletons were not of an ornithischian, or even a dinosaur, but rather from a crocodile-line archosaur (Pseudosuchia). Amazingly, the ornithischian-like dentition was simply a convergence. We argued that none of the North American and European teeth could be unambiguously considered to represent ornithischians. Thus, the entire Late Triassic record of ornithischians from these continents was essentially erased. Below is a cladogram showing the revised position of Revueltosaurus.A few authors (e.g., Heckert, 2005) have argued against this interpretation, insisting that some of these teeth do represent ornithischians; however, there are no clear characters of these teeth that support this interpretation (Irmis et al, 2007).In 2006 the Revueltosaurus Quarry yielded a superbly preserved almost complete skeleton of R. callenderi, which I featured at a recent Society of Vertebrate Paleontology meeting. A full description of this specimen (and thus the taxon) is almost complete. One really neat character (I think) apparent in Jeff's reconstruction is the large size of the skull in relation to the postcranial skeleton. The skull is quite a bit longer than the femur, and this is a bit odd considering the skull "accomplishes" this without elongating the forward portion of the skull as in champsosaurids, phytosaurs, and crocodiles.
I have jokingly refered to Revueltosaurus as the "duck-billed platypus" of the Triassic because of its ornithichian-like dentition, aetosaur-like armor carapace, and other characteristics found only in rauisuchians and crocodylomorphs.
Indeed Revueltosaurus belongs to a previously unrecognized clade of archosaur, which hopefully will elucidate phylogentic relationships within Pseudosuchia.
By the way...the PDF of Parker et al (2005) is freely available from the link in the reference below.
REFERENCES
Heckert, A. B. 2002 A revision of the Upper Triassic ornithischian dinosaur Revueltosaurus, with a description of a new species. New Mexico Museum of Natural History and Science Bulletin 21:253–267.
Heckert, A.B. 2005. Krzyzanowskisaurus, a new name for a probable ornithischian dinosaur from the Upper Triassic Chinle Group, Arizona and New Mexico, USA. New Mexico Museum of Natural History and Science Bulletin 29: 77-83.
Hunt, A. P. 1989. A new ?ornithischian dinosaur from the Bull Canyon Formation (Upper Triassic) of east-central New Mexico. pp. 355–358 in Dawn of the age of dinosaurs in the American Southwest (ed. S. G. Lucas & A. P. Hunt). New Mexico Museum of Natural History, Albuquerque, NM.
Hunt, A. P., and S.G. Lucas. 1994. Ornithischian dinosaurs from the Upper Triassic of the United States. pp. 227–241 in In the Shadows of the Dinosaurs: Early Mesozoic Tetrapods (ed. N. C. Fraser & H.-D. Sues). Cambridge University Press.
Irmis, R.B., Parker, W.G., Nesbitt, S.J., and Liu, J. 2006. Early ornithischian dinosaurs: the Triassic record. Historical Biology 19:3-22.
Parker, W.G., Irmis, R.B., Nesbitt, S.J., Martz, J.W., and L.S. Browne. 2005. The Late Triassic pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. Proceedings of the Royal Society B 272:963-969. doi:10.1098/rspb.2004.3047
Subscribe to:
Posts (Atom)