Norman, D. B., Crompton, A. W., Butler, R. J., Porro, L. B., and A. J. Charig. 2011. The Lower Jurassic ornithischian dinosaur Heterodontosaurus tucki Crompton & Charig, 1962: cranial anatomy, functional morphology, taxonomy, and relationships. Zoological Journal of the Linnaean Society published first online 20 May 2011. DOI: 10.1111/j.1096-3642.2011.00697.x
Abstract - The cranial anatomy of the Lower Jurassic ornithischian dinosaur Heterodontosaurus tucki Crompton & Charig, 1962 is described in detail for the first time on the basis of two principal specimens: the holotype (SAM-PK-K337) and referred skull (SAM-PK-K1332). In addition several other specimens that have a bearing on the interpretation of the anatomy and biology of Heterodontosaurus are described. The skull and lower jaw of Heterodontosaurus are compact and robust but perhaps most notable for the heterodont dentition that merited the generic name. Details of the cranial anatomy are revealed and show that the skull is unexpectedly specialized in such an early representative of the Ornithischia, including: the closely packed, hypsodont crowns and ‘warping’ of the occlusal surfaces (created by progressive variation in the angulation of wear on successive crowns) seen in the cheek dentition; the unusual sutural relationships between the bones along the dorsal edge of the lower jaw; the very narrow, deeply vaulted palate and associated structures on the side wall of the braincase; and the indications of cranial pneumatism (more commonly seen in basal archosaurs and saurischian dinosaurs). Evidence for tooth replacement (which has long been recognized, despite frequent statements to the contrary) is suggestive of an episodic, rather than continuous, style of tooth replacement that is, yet again, unusual in diapsids generally and particularly so amongst ornithischian dinosaurs. Cranial musculature has been reconstructed and seems to conform to that typically seen in diapsids, with the exception of the encroachment of M. adductor mandibulae externus superficialis across the lateral surface of the temporal region and external surface of the lower jaw. Indications, taken from the unusual shape of the occlusal surfaces of the cheek dentition and jaw musculature, are suggestive of a novel form of jaw action in this dinosaur. The taxonomy of currently known late Karoo-aged heterodontosaurids from southern Africa is reviewed. Although complicated by the inadequate nature of much of the known material, it is concluded that two taxa may be readily recognized: H. tucki and Abrictosaurus consors. At least one additional taxon is recognized within the taxa presently named Lanasaurus and Lycorhinus; however, both remain taxonomically problematic and their status needs to be further tested and may only be resolved by future discoveries. The only other named taxon, Geranosaurus atavus, represents an invalid name. The recognition of at least four distinct taxa indicates that the heterodontosaurids were speciose within the late Karoo ecosystem. The systematics of Heterodontosaurus and its congeners has been analysed, using a restricted sample of taxa. A basal (nongenasaurian) position within Ornithischia is re-affirmed. There are at least four competing hypotheses concerning the phylogenetic placement of the Heterodontosauridae, so the evidence in support of the various hypotheses is reviewed in some detail. At present the best-supported hypothesis is the one which places Heterodontosauridae in a basal (non-genasaurian) position; however, the evidence is not fully conclusive and further information is still needed in respect of the anatomy of proximate outgroups, as well as more complete anatomical details for other heterodontosaurids. Heterodontosaurids were not such rare components of the late Karoo ecosystem as previously thought; evidence also suggests that from a phylogenetic perspective they occupied a potentially crucial position during the earliest phases of ornithischian dinosaur evolution.
Showing posts with label heterodontosaur. Show all posts
Showing posts with label heterodontosaur. Show all posts
First Well-Preserved Heterodontosaurid Material from South America: Manidens condorensis from the Middle Jurassic of Argentina
Pol, D., Rauhut, O. W. M., and M. Becerra. 2011. A Middle Jurassic heterodontosaurid dinosaur from Patagonia and the evolution of heterodontosaurids. Naturwissenschaften (online first) DOI 10.1007/s00114-011-0780-5
Abstract - Heterodontosauridae is a morphologically divergent group of dinosaurs that has recently been interpreted as one of the most basal clades of Ornithischia. Heterodontosaurid remains were previously known from the Early Jurassic of southern Africa, but recent discoveries and studies have significantly increased the geographical and temporal range for this clade. Here, we report a new ornithischian dinosaur from the Middle Jurassic Cañadón Asfalto Formation in central Patagonia, Argentina. This new taxon, Manidens condorensis gen. et sp. nov., includes well-preserved craniomandibular and postcranial remains and represents the only diagnostic ornithischian specimen yet discovered in the Jurassic of South America so far. Derived features of its anatomy indicate that Manidens belongs to Heterodontosauridae, as the sister taxon of Heterodontosaurus and other South African heterodontosaurids. The presence of posterior dentary teeth with high crowns but lacking extensive wear facets in Manidens suggests that this form represents an intermediate stage in the development of the remarkable adaptations to herbivory described for Heterodontosaurus. The dentition of Manidens condorensis also has autapomorphies, such as asymmetrically arranged denticles in posterior teeth and a mesially projected denticle in the posteriormost teeth. At an estimated total length of 60–75 cm, Manidens furthermore confirms the small size of basal heterodontosaurids.
Abstract - Heterodontosauridae is a morphologically divergent group of dinosaurs that has recently been interpreted as one of the most basal clades of Ornithischia. Heterodontosaurid remains were previously known from the Early Jurassic of southern Africa, but recent discoveries and studies have significantly increased the geographical and temporal range for this clade. Here, we report a new ornithischian dinosaur from the Middle Jurassic Cañadón Asfalto Formation in central Patagonia, Argentina. This new taxon, Manidens condorensis gen. et sp. nov., includes well-preserved craniomandibular and postcranial remains and represents the only diagnostic ornithischian specimen yet discovered in the Jurassic of South America so far. Derived features of its anatomy indicate that Manidens belongs to Heterodontosauridae, as the sister taxon of Heterodontosaurus and other South African heterodontosaurids. The presence of posterior dentary teeth with high crowns but lacking extensive wear facets in Manidens suggests that this form represents an intermediate stage in the development of the remarkable adaptations to herbivory described for Heterodontosaurus. The dentition of Manidens condorensis also has autapomorphies, such as asymmetrically arranged denticles in posterior teeth and a mesially projected denticle in the posteriormost teeth. At an estimated total length of 60–75 cm, Manidens furthermore confirms the small size of basal heterodontosaurids.
New Diminutive Heterodontosaur from North America
Good to see this out. Available online today is a new paper describing a new heterodontosaurid, Fruitadens haagarorum, from the Late Jurassic on Colorado, U.S.A.
There are lots of cool things about this critter:
1) Small size. Specimens of Fruitadens have a maximum body length of about 75 cm, making it the smallest known ornithischian. Histological work was done to determine the relative age of the specimens. It is estimated that the largest individual was about 4-5 years old at death, but had already slowed down its growth as is seen in sub-adult and adult non-avian dinosaurs.
2) Age. The specimen is Late Jurassic, making it one of the youngest known heterodontosaurids. Only Echinodon from the Early Cretaceous of England is younger. Interestingly both Echinodon and Fruitadens have small adult sizes, but it is possible to differentiate the two.
3) Plesiomorphic dentition. Fruitadens differs from older heterodontosaurs in possessing less sophisticated craniodental adaptations, thus was probably more of a generalist feeder. The authors believe that this adaptation, as well as small size, allowed the group to survive into the Late Triassic and Early Cretaceous. Also cool is that it seems to have regularly undergone tooth replacement, which is unknown in most other heterodontosaurs.
4) Theropod-like femur. One feature of Fruitadens that I find interesting is that the femur closely resembles that of theropods like Dilophosaurus and is very unlike that of ornithischians. Richard Butler assures me that the material represents a single taxon so this is an interesting characteristic. I often like to play devil's advocate and claim that there are no Triassic ornithischians (not even Pisanosaurus) despite a wealth of saurischians, and although I've been assured over and over by dinosaur workers that the saurischian line could not have given rise to the ornithischians, I always find synapomorphies like this (basal ornithischian with saurischian-like characters) of great interest. Hey, someones got to keep stirring the pot or we'll get too complacent.
4) Biogeography. Fruitadens is from the Upper Jurassic Morrison Formation of Colorado. This is the first described heterodontosaurid from North America. As it is from the Brushy Basin Member it was a contemporary of the classic dinosaurs such as Allosaurus, Camarasaurus, Stegosaurus, and Diplodocus.
Overall another great find. They just keep coming. Read more here and here.
Butler, R. J., Galton, P. M., Porro, L. B., Chiappe, L. M., Henderson, D. M., and G. M. Erickson. 2009. Lower limits of ornithischian dinosaur body size inferred from a new Upper Jurassic heterodontosaurid from North America. Proceedings of the Royal Society B. doi:10.1098/rspb.2009.1494.
Abstract-The extremes of dinosaur body size have long fascinated scientists. The smallest (<1>Fruitadens haagarorum, from the Late Jurassic of western North America that rivals the smallest theropods in size. The largest specimens of Fruitadens represent young adults in their fifth year of development and are estimated at just 65–75 cm in total body length and 0.5–0.75 kg body mass. They are thus the smallest known ornithischians. Fruitadens is a late-surviving member of the basal dinosaur clade Heterodontosauridae, and is the first member of this clade to be described from North America. The craniodental anatomy and diminutive body size of Fruitadens suggest that this taxon was an ecological generalist with an omnivorous diet, thus providing new insights into morphological and palaeoecological diversity within Dinosauria. Late-surviving (Late Jurassic and Early Cretaceous) heterodontosaurids are smaller and less ecologically specialized than Early (Late Triassic and Early Jurassic) heterodontosaurids, and this ecological generalization may account in part for the remarkable 100-million-year-long longevity of the clade.
There are lots of cool things about this critter:
1) Small size. Specimens of Fruitadens have a maximum body length of about 75 cm, making it the smallest known ornithischian. Histological work was done to determine the relative age of the specimens. It is estimated that the largest individual was about 4-5 years old at death, but had already slowed down its growth as is seen in sub-adult and adult non-avian dinosaurs.
2) Age. The specimen is Late Jurassic, making it one of the youngest known heterodontosaurids. Only Echinodon from the Early Cretaceous of England is younger. Interestingly both Echinodon and Fruitadens have small adult sizes, but it is possible to differentiate the two.
3) Plesiomorphic dentition. Fruitadens differs from older heterodontosaurs in possessing less sophisticated craniodental adaptations, thus was probably more of a generalist feeder. The authors believe that this adaptation, as well as small size, allowed the group to survive into the Late Triassic and Early Cretaceous. Also cool is that it seems to have regularly undergone tooth replacement, which is unknown in most other heterodontosaurs.
4) Theropod-like femur. One feature of Fruitadens that I find interesting is that the femur closely resembles that of theropods like Dilophosaurus and is very unlike that of ornithischians. Richard Butler assures me that the material represents a single taxon so this is an interesting characteristic. I often like to play devil's advocate and claim that there are no Triassic ornithischians (not even Pisanosaurus) despite a wealth of saurischians, and although I've been assured over and over by dinosaur workers that the saurischian line could not have given rise to the ornithischians, I always find synapomorphies like this (basal ornithischian with saurischian-like characters) of great interest. Hey, someones got to keep stirring the pot or we'll get too complacent.
4) Biogeography. Fruitadens is from the Upper Jurassic Morrison Formation of Colorado. This is the first described heterodontosaurid from North America. As it is from the Brushy Basin Member it was a contemporary of the classic dinosaurs such as Allosaurus, Camarasaurus, Stegosaurus, and Diplodocus.
Overall another great find. They just keep coming. Read more here and here.
Butler, R. J., Galton, P. M., Porro, L. B., Chiappe, L. M., Henderson, D. M., and G. M. Erickson. 2009. Lower limits of ornithischian dinosaur body size inferred from a new Upper Jurassic heterodontosaurid from North America. Proceedings of the Royal Society B. doi:10.1098/rspb.2009.1494.
Abstract-The extremes of dinosaur body size have long fascinated scientists. The smallest (<1>Fruitadens haagarorum, from the Late Jurassic of western North America that rivals the smallest theropods in size. The largest specimens of Fruitadens represent young adults in their fifth year of development and are estimated at just 65–75 cm in total body length and 0.5–0.75 kg body mass. They are thus the smallest known ornithischians. Fruitadens is a late-surviving member of the basal dinosaur clade Heterodontosauridae, and is the first member of this clade to be described from North America. The craniodental anatomy and diminutive body size of Fruitadens suggest that this taxon was an ecological generalist with an omnivorous diet, thus providing new insights into morphological and palaeoecological diversity within Dinosauria. Late-surviving (Late Jurassic and Early Cretaceous) heterodontosaurids are smaller and less ecologically specialized than Early (Late Triassic and Early Jurassic) heterodontosaurids, and this ecological generalization may account in part for the remarkable 100-million-year-long longevity of the clade.
New Feathered Cretaceous Heterodontosaur From China
Wow...I cannot believe I just typed all of the those words in the title together. Today's issue of Nature magazine includes an article on a new heterodontosaurid ornithischian (Tianyulong confuciusi) from the Cretaceous of China. Not only are heterodontosaurs pretty much unknown from the Cretaceous (previously restricted to the Latest Triassic (?) and early-middle Jurassic only), this one is covered with patches of filaments similar to the protofeathers found in many saurischian taxa.
These filaments are already known from the basal ceratopsian Psittacosaurus; however, a heterodontosaurid with feathers pushes this occurence to the base of Ornithischia (Butler et al. 2008).
It is not entirely clear whether the ornithischian filaments and saurischian protofeathers are the same, but if they are this would strongly suggest that protofeathers may be plesiomorphic for Dinosauria, and it is even hypothetical now that the successive ornithodiran outgroups to the dinosaurs may have also possessed this character. Now we just need a silesaurid from these Chinese deposits now or some better preservation in the Triassic! You can read more about this here, here, and here.
REFERENCES
Butler, R., Upchurch, P., & Norman, D. (2007). The phylogeny of the ornithischian dinosaurs Journal of Systematic Palaeontology, 6 (01) DOI: 10.1017/S1477201907002271
Zheng, X., You, H., Xu, X., & Dong, Z. (2009). An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures Nature, 458 (7236), 333-336 DOI: 10.1038/nature07856
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