Robert Reisz
University of Toronto, Biology, Faculty Member
- Jilin University, College of Earth Sciences, Faculty Memberadd
- Professor in Biology and Paleontology. Main interest in the evolution of terrestrial vertebrates of the Paleozoic , w... moreProfessor in Biology and Paleontology. Main interest in the evolution of terrestrial vertebrates of the Paleozoic , with focus on the origin and early diversification of amniotes. Published mainly on Late Carboniferous and Permian tetrapods, but also delved into lungfish dental and cranial evolution, and dinosaur evolution and development. Current interest also includes dental development and evolutionedit
Abstract The stratigraphy and the fossil assemblage of a Lower Cretaceous ‘Lycoptera Bed’ of the Xinganling Group in Naketa, Arongqi area, Inner Mongolia, China are described, and the paleoenvironment is discussed as it relates to the... more
Abstract The stratigraphy and the fossil assemblage of a Lower Cretaceous ‘Lycoptera Bed’ of the Xinganling Group in Naketa, Arongqi area, Inner Mongolia, China are described, and the paleoenvironment is discussed as it relates to the Jehol Biota. The Naketa fossil bed belongs to the lower part of volcanic-sedimentary Jiufengshan Formation and preserves a typical EEL (Eosestheria-Ephemeropsis trisetalis-Lycoptera davidi) faunal assemblage, which indicates a strong affiliation to the Jehol Biota of western Liaoning, China. The fossil bed was deposited in a shallow to semi-deep lacustrine setting with occurrence of oil-shale facies, and this is different from the Lycoptera Bed of the Yixian Formation and more similar to the overlying Jiufotang Formation in western Liaoning. A layer of volcanic tuffite within the fossil bed is dated as 121.6 + 0.47 Ma using the Zircon U-Pb isotopic dating method. This age is contemporary with the age of the base of Jehol-Biota producing Jiufotang Formation in western Liaoning, thereby supporting the biostratigraphic correlation. However, the genus Lycoptera is almost entirely absent in western Liaoning, with only one species in the Jiufotang Formation, where the dominant fish genus is Jinanichthys. Therefore, Lycoptera in the Great Xing’an Mountain areas appears to have a longer record than in western Liaoning, which likely indicates that the fish fauna changed earlier in western Liaoning, and this observation supports the hypothesis that the Yanliao area was the diversification center of some Cretaceous new groups in NE Asia. Preliminary analysis of the taphonomy and the geology indicates that the mass mortality of fish at the Naketa site may not be related to volcanism. Additional taphonomic investigations would allow a better understanding of the Early Cretaceous aquatic paleoecology and paleoenvironment in the volcanic-rifting regions. The Great Xing’an Mountain area is a new opportunity for expanding the research on the Jehol Biota beyond the core localities in western Liaoning.
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Supplemental Figure 1. Results of phylogenetic analysis of Nanobamus macrorhinus in the matrix of Schoch (2019) (35 taxa, 108 characters); tree visually pruned to focus on Amphibamiforms. (1) majority rule consensus of the first... more
Supplemental Figure 1. Results of phylogenetic analysis of Nanobamus macrorhinus in the matrix of Schoch (2019) (35 taxa, 108 characters); tree visually pruned to focus on Amphibamiforms. (1) majority rule consensus of the first 107-character (removal of character 17) sampling permutation; (2) strict consensus tree of the same permutation with bootstrap support and Bremer decay index (the latter in parentheses); (3) majority rule consensus of the second 107-character sampling (removal of character 30) permutation; (4) strict consensus tree of the same permutation with bootstrap support and Bremer decay index
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Nanobamus macrorhinus is a small amphibamiform temnospondyl from the early Permian Arroyo Formation of Texas. It is most readily characterized by an elongate and partially subdivided naris. This condition is superficially reminiscent of... more
Nanobamus macrorhinus is a small amphibamiform temnospondyl from the early Permian Arroyo Formation of Texas. It is most readily characterized by an elongate and partially subdivided naris. This condition is superficially reminiscent of that seen in the coeval trematopids, the group to which N. macrorhinus was originally referred to under an interpretation of the holotype as a larval form. This was discounted by later workers, but the amphibamiform affinities of the specimen were not formalized until recently. The specimen has never been described in the context of its amphibamiform affinities and remains poorly characterized, never having been sampled in a phylogenetic analysis. Here we present a complete, updated osteological description of N. macrorhinus, including an improved characterization of its unique mosaic of plesiomorphic and apomorphic features and clarification of the taxon’s autapomorphies. Our analysis of the taxon’s phylogenetic position within Amphibamiformes shows that N. macrorhinus is recovered as diverging after basal amphibamiforms such the micropholids and before derived amphibamiforms such as the amphibamids. This is supported by the unique mixture of retained plesiomorphies such as non-foreshortened postparietals and an oval choana and apomorphies such as a narrow interorbital region and slender palatal rami of the pterygoid. These results reflect the complexity of terrestrial amphibamiform diversity and provide further insight into the evolutionary history of the lissamphibian stem in terrestrial environments
Photographs of an indeterminate captorhinid right humerus (TMM 43628-11): (1) extensor profile; (2) flexor profile; (3) posterior profile; (4) anterior profile. Scale bar equal to 1 cm
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List of phylogenetic characters, data matri
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Images from CT reconstruction of the skull of a juvenile Thrinaxodon (BP/1/5372) used to score ontogenetic stages of teeth
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Images from CT reconstruction of the skull of an adult Thrinaxodon (BP/1/7199) used to score ontogenetic stages of teeth
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Labeled model of the hadrosaurid maxillary dental battery (illustration by Danielle Dufault). Abbreviations: ab, alveolar bone; ab/rc, alveolar bone (possible repair cementum); ac, acellular cementum; bv, blood vessels; cc, cellular... more
Labeled model of the hadrosaurid maxillary dental battery (illustration by Danielle Dufault). Abbreviations: ab, alveolar bone; ab/rc, alveolar bone (possible repair cementum); ac, acellular cementum; bv, blood vessels; cc, cellular cementum; de, dentine; do, denteon; en, enamel; jb, bone of the jaw; Li, lingual; lp, lingual plate; Me, mesial; spf, â special foramenâ ; pdl, periodontal ligament; pc, pulp cavity; ppc, plugged pulp cavity; rp, resorption pit. (TIF 6427 kb)
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Thin sections examined in this study. (DOCX 69 kb)
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Histological sections through the maxillae of two hadrosaurid dental batteries (ROM 00696, ROM 59042). (A) coronal section through a maxillary dental battery (ROM 00696) showing three generations of erupted teeth. (B) coronal section... more
Histological sections through the maxillae of two hadrosaurid dental batteries (ROM 00696, ROM 59042). (A) coronal section through a maxillary dental battery (ROM 00696) showing three generations of erupted teeth. (B) coronal section through the same maxillary dental battery showing three generations of unerupted teeth. These two sections were used to create the ontogenetic sequence of hadrosaur teeth presented in Fig. 3. (C) longitudinal section through the maxilla of ROM 59042 showing the lack of fusion of any of the teeth within the maxillary battery. (TIF 9243 kb)
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The Dolese Limestone Quarry near Richards Spur, Oklahoma includes an elaborate system of caves which have been infilled with early Permian fossil rich sediments. In operation for more than a century, the quarry yielded vast numbers of... more
The Dolese Limestone Quarry near Richards Spur, Oklahoma includes an elaborate system of caves which have been infilled with early Permian fossil rich sediments. In operation for more than a century, the quarry yielded vast numbers of disarticulated skeletal elements of the most diverse assemblage of fully terrestrial tetrapods from the Paleozoic. Excavations carried out in this century are distinct in producing large numbers of articulated and semiarticulated skeletons, including numerous new taxa. Dolese is therefore unique among early Permian localities in being home to a diverse assemblage of small parareptiles, including two species of Delorhynchus. Here we describe a new species of acleistorhinid, characterized by the presence of multiple tooth rows on the dentary, that can be identified with confidence as a third new species of Delorhynchus. The multiple tooth rowed condition is deemed not to be a pathological condition, and appears to have formed in the same manner as in the...
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The Lower Permian fossiliferous infills of the Dolese Brothers Limestone Quarry, near Richards Spur, Oklahoma, have preserved the most diverse assemblage of Paleozoic terrestrial vertebrates, including small-bodied reptiles and... more
The Lower Permian fossiliferous infills of the Dolese Brothers Limestone Quarry, near Richards Spur, Oklahoma, have preserved the most diverse assemblage of Paleozoic terrestrial vertebrates, including small-bodied reptiles and lepospondyl anamniotes. Many of these taxa were previously known only from fragmentary remains, predominantly dentigerous jaw elements and numerous isolated skeletal elements. The recent discovery of articulated skulls and skeletons of small reptiles permits the recognition that dentigerous elements, previously assigned at this locality to the anamniote lepospondyl Euryodus primus, belong to a new captorhinid eureptile, Opisthodontosaurus carrolli gen. et sp. nov. This mistaken identity points to a dramatic level of convergence in mandibular and dental anatomy in two distantly related and disparate clades of terrestrial tetrapods and sheds light on the earliest instance of durophagy in eureptiles.
Research Interests: Paleontology, Biology, Medicine, Multidisciplinary, Reptiles, and 9 moreFossils, Animals, Permian, Oklahoma, Mandible, Paleozoic, Naturwissenschaften, Tooth, and Taxon
The oldest known complex terrestrial vertebrate community included hypercarnivorous varanopids, a successful clade of amniotes with wide geographic and temporal distributions. Little is known about their dentition and feeding behaviour,... more
The oldest known complex terrestrial vertebrate community included hypercarnivorous varanopids, a successful clade of amniotes with wide geographic and temporal distributions. Little is known about their dentition and feeding behaviour, but with the unprecedented number of specimens of the varanopid Mesenosaurus from cave deposits in Oklahoma, we show that it exhibited serrations on the tooth crowns, and exceptionally rapid rates of development and reduced longevity relative to other terrestrial amniotes. In contrast, the coeval large apex predator Dimetrodon greatly increased dental longevity by increasing thickness and massiveness, whereas herbivores greatly reduced tooth replacement rates and increased dental longevity. Insectivores and omnivores represented the primitive condition and maintained modest replacement rates and longevity. The varied patterns of dental development among these early terrestrial amniotes reveal a hidden aspect of dental complexity in the emerging diver...
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The detailed description of the cranial anatomy of Cotylorhynchus romeri, a very large caseid synapsid from the lower Permian Hennessey Formation of Oklahoma, uncovered several potential autapomorphies, including parietal-postorbital... more
The detailed description of the cranial anatomy of Cotylorhynchus romeri, a very large caseid synapsid from the lower Permian Hennessey Formation of Oklahoma, uncovered several potential autapomorphies, including parietal-postorbital contact greatly reduced by broad anterior process of supratemporal; the postparietals are transversely broad and contact the supratemporals laterally; the quadratojugal has a pennant-like occipital process; the stapes has a short shaft and a ventral process that abuts against the palate; the bulbous marginal dentition narrows distally and carries three small denticles; the vomer has three large teeth along its medial edge; parasphenoidal dentition is present; and the surangular overlaps the posterodorsal tip of the dentary and excludes it from the coronoid eminence. Owing to lack of comparative cranial material in most large caseids, the evolutionary history of these autapomorphies remains ambiguous because they cannot be determined in the closest relat...
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Photographs of a diadectid humerus (TMM 43628-4) from the D-1 site. (1) extensor profile; (2) posterior profile; (3) flexor profile; (4) anterior profile. Scale bar equal to 5 cm
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Photographs of diadectid vertebral material: (1) isolated centrum in anterior and dorsal profile (TMM 43628-4) from the D-1 site; (2) articulated vertebrae in dorsal profile (TMM 43628-6) from the D-3 site. Scale bars equal to 1 cm
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Alligator tooth development viewed in serial sections of a 40-day old Alligator (ROM R6252). (A), section through a functional tooth and a newly developing replacement tooth. (B) section through a functional tooth with a larger... more
Alligator tooth development viewed in serial sections of a 40-day old Alligator (ROM R6252). (A), section through a functional tooth and a newly developing replacement tooth. (B) section through a functional tooth with a larger replacement tooth that has invaded the pulp cavity. (C) section through a tooth position in which the functional tooth has been shed and the new tooth has not yet erupted into the oral cavity. (D) section in which a newly erupted functional tooth has formed a ligamentous connection to the alveolus, with a new tooth beginning to form lingually. These sections were used to reconstruct dental ontogeny in Alligator in Fig. 3. Abbreviations: ac, acellular cementum; cc, cellular cementum; de, dentine; en, enamel; pdl, periodontal ligament. (TIF 4685 kb)
Teeth are often thought of as structures that line the margins of the mouth; however, tooth-like structures called odontodes are commonly found on the dermal bones of many Palaeozoic vertebrates including early jawless fishes.... more
Teeth are often thought of as structures that line the margins of the mouth; however, tooth-like structures called odontodes are commonly found on the dermal bones of many Palaeozoic vertebrates including early jawless fishes. 'Odontode' is a generalized term for all tooth-like dentine structures that have homologous tissues and development. This definition includes true teeth, and the odontodes of early 'fishes', which have been recently examined to gain new insights into the still unresolved origin of teeth. Two leading hypotheses are frequently referenced in this debate: the 'outside-in' hypothesis, which posits that dermal odontodes evolutionarily migrate into the oral cavity, and the 'inside-out' hypothesis, which posits that teeth originated in the oropharyngeal cavity and then moved outwards into the oral cavity. Here, we show that unlike the well-known one-to-one replacement patterns of marginal dentition, the palatal dentition of the early Pe...
Electronic supplementary material is available The oldest parareptile and the early Carboniferous Period, and that the diversity of end-Carboniferous reptiles is 80 % greater than suggested by previous work. Latest Carboniferous reptiles... more
Electronic supplementary material is available The oldest parareptile and the early Carboniferous Period, and that the diversity of end-Carboniferous reptiles is 80 % greater than suggested by previous work. Latest Carboniferous reptiles on January 17,
A comprehensive description of the holotype skeleton is presented here for the first time of the lower Permian (Artinskian) reptile Eudibamus cursoris from the Bromacker locality of Germany since the brief description of the holotype in... more
A comprehensive description of the holotype skeleton is presented here for the first time of the lower Permian (Artinskian) reptile Eudibamus cursoris from the Bromacker locality of Germany since the brief description of the holotype in 2000. The holotype is essentially complete and is the only known bolosaurid represented by a well-preserved articulated skeleton. Included in the description here is a superbly preserved, partial, articulated second specimen of E. cursoris discovered at the same locality that includes a short portion of the vertebral column associated with the pelvis and right hindlimb. Descriptions of the holotype and new specimen add substantially to features of the skull and postcranium that not only confirm a bolosaurid assignment, but also add significantly to an already long list of structural features supporting an ability unique among Paleozoic vertebrates to reach relatively high bipedal and quadrupedal running speeds employing a parasagittal stride and digi...
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Background Weigeltisauridae is a clade of small-bodied diapsids characterized by a horned cranial frill, slender trunk and limbs, and a patagium supported by elongated bony rods. Partial skeletons and fragments are definitively known only... more
Background Weigeltisauridae is a clade of small-bodied diapsids characterized by a horned cranial frill, slender trunk and limbs, and a patagium supported by elongated bony rods. Partial skeletons and fragments are definitively known only from upper Permian (Lopingian) rocks in England, Germany, Madagascar and Russia. Despite these discoveries, there have been few detailed descriptions of weigeltisaurid skeletons, and the homologies of many skeletal elements—especially the rods supporting the patagium—remain the subject of controversy. Materials & Methods Here, we provide a detailed description of a nearly complete skeleton of Weigeltisaurus jaekeli from the upper Permian (Lopingian: Wuchiapingian) Kupferschiefer of Lower Saxony, Germany. Briefly addressed by past authors, the skeleton preserves a nearly complete skull, postcranial axial skeleton, appendicular skeleton, and patagial supports. Through comparisons with extant and fossil diapsids, we examine the hypotheses for the homo...
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Lateralized behaviors have been reported in a variety of extant vertebrates, including birds and reptiles [1-3] and non-human mammals [4-6]. However, evidence of lateralized behaviors in extinct vertebrates is rare, primarily because of... more
Lateralized behaviors have been reported in a variety of extant vertebrates, including birds and reptiles [1-3] and non-human mammals [4-6]. However, evidence of lateralized behaviors in extinct vertebrates is rare, primarily because of the difficulty of identifying such behaviors with confidence in fossils. In rare instances, paleontologists can infer asymmetry in predatory or foraging behavior, including predation scars on trilobites [7], directionality of invertebrate traces [8], and even behavioral asymmetry in fossil non-human primates [9, 10]. Because lateralized behaviors have been linked to hemispheric (brain) lateralization in some vertebrates [11-15], evidence of lateralized behaviors in ancient vertebrates might yield clues about the evolutionary origins of vertebrate brain lateralization. Here, we show the earliest evidence of lateralized behavior in a fossil reptile based on repeatable observations of tooth wear in a large sample of intact jaws. The patterns of dental wear along the tooth rows of nearly one hundred jaws of the small, early Permian (289 million years ago) reptile Captorhinus aguti indicate that it exhibited lateralized behavior, preferring to feed using the right side of the jaw. Discovery of such a feeding behavior in this ancient, terrestrial, and omnivorous animal provides direct evidence of the deep history of directional behavior among amniotes and may indicate an early origin of brain lateralization.
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Teeth are often thought of as structures that line the margins of the mouth; however, tooth-like structures called odontodes are commonly found on the dermal bones of many Palaeozoic vertebrates including early jawless fishes. ‘Odontode’... more
Teeth are often thought of as structures that line the margins of the mouth; however, tooth-like structures called odontodes are commonly found on the dermal bones of many Palaeozoic vertebrates including early jawless fishes. ‘Odontode’ is a generalized term for all tooth-like dentine structures that have homologous tissues and development. This definition includes true teeth and the odontodes of early ‘fishes’, which have been recently examined to gain new insights into the still unresolved origin of teeth. Two leading hypotheses are frequently referenced in this debate: the ‘outside-in’ hypothesis, which posits that dermal odontodes evolutionarily migrate into the oral cavity, and the ‘inside-out’ hypothesis, which posits that teeth originated in the oropharyngeal cavity and then moved outwards into the oral cavity. Here, we show that, unlike the well-known one-to-one replacement patterns of marginal dentition, the palatal dentition of the early Permian tetrapods, including the d...
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The oldest known captorhinid reptile, and the only Carboniferous representative of this important clade of early eureptiles was named Concordia cunninghami. This was done on the basis of the cranial material from two specimens, but the... more
The oldest known captorhinid reptile, and the only Carboniferous representative of this important clade of early eureptiles was named Concordia cunninghami. This was done on the basis of the cranial material from two specimens, but the name is preoccupied by an extant hippolytid crustacean. We therefore coined the new combination, Euconcordia, as a replacement name for this taxon. In addition, the recent significant increases in our understanding of dental anatomy in early amniotes in general, and captorhinid reptiles in particular, has allowed us to reinterpret the anatomy of the marginal and palatal teeth of this taxon.
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The holotype and only known specimen of Bathygnathus borealis is a partial snout with maxillary dentition of a presumed sphenacodontid from the Lower Permian (Artinskian 283–290 Ma) redbeds of Prince Edward Island, Canada. Due to its... more
The holotype and only known specimen of Bathygnathus borealis is a partial snout with maxillary dentition of a presumed sphenacodontid from the Lower Permian (Artinskian 283–290 Ma) redbeds of Prince Edward Island, Canada. Due to its incomplete nature, assessment of the taxon’s systematic position within a cladistic analysis had never been performed. However, recent recognition of the phylogenetic utility of tooth characters in sphenacodontids now allows for a modern phylogenetic evaluation of B. borealis. Results show that B. borealis is the sister taxon of Dimetrodon grandis, which is supported by dental characters: crowns with mesial and distal denticles and roots elongate, lacking plicidentine. An autapomorphy of B. borealis is the large facial exposure of the septomaxilla. As Bathygnathus has priority over Dimetrodon in the scientific literature, we suggest a reversal of precedence is required to preserve the familiar name Dimetrodon and to maintain universality, thus recognizi...
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Amniotes, tetrapods that evolved the cleidoic egg and thus independence from aquatic larval stages, appeared ca 314 Ma during the Coal Age. The rapid diversification of amniotes and other tetrapods over the course of the Late... more
Amniotes, tetrapods that evolved the cleidoic egg and thus independence from aquatic larval stages, appeared ca 314 Ma during the Coal Age. The rapid diversification of amniotes and other tetrapods over the course of the Late Carboniferous period was recently attributed to the fragmentation of coal-swamp rainforests ca 307 Ma. However, the amniote fossil record during the Carboniferous is relatively sparse, with ca 33% of the diversity represented by single specimens for each species. We describe here a new species of reptilian amniote that was collected from uppermost Carboniferous rocks of Prince Edward Island, Canada. Erpetonyx arsenaultorum gen. et sp. nov. is a new parareptile distinguished by 29 presacral vertebrae and autapomorphies of the carpus. Phylogenetic analyses of parareptiles reveal E. arsenaultorum as the closest relative of bolosaurids. Stratigraphic calibration of our results indicates that parareptiles began their evolutionary radiation before the close of the Ca...
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The extensive Early Jurassic continental strata of southern Africa have yielded an exceptional record of dinosaurs that includes scores of partial to complete skeletons of the sauropodomorph Massospondylus , ranging from embryos to large... more
The extensive Early Jurassic continental strata of southern Africa have yielded an exceptional record of dinosaurs that includes scores of partial to complete skeletons of the sauropodomorph Massospondylus , ranging from embryos to large adults. In 1976 an incomplete egg clutch including in ovo embryos of this dinosaur, the oldest known example in the fossil record, was collected from a road-cut talus, but its exact provenance was uncertain. An excavation program at the site started in 2006 has yielded multiple in situ egg clutches, documenting the oldest known dinosaurian nesting site, predating other similar sites by more than 100 million years. The presence of numerous clutches of eggs, some of which contain embryonic remains, in at least four distinct horizons within a small area, provides the earliest known evidence of complex reproductive behavior including site fidelity and colonial nesting in a terrestrial vertebrate. Thus, fossil and sedimentological evidence from this nest...
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Two articulated, partial vertebral columns of the Early Permian captorhinid Eocaptorkinus laticeps (Williston) exhibit the following serial changes in the axial skeleton: robust and unswollen neural arches on the First five presacrals... more
Two articulated, partial vertebral columns of the Early Permian captorhinid Eocaptorkinus laticeps (Williston) exhibit the following serial changes in the axial skeleton: robust and unswollen neural arches on the First five presacrals gradually swell dorsally and laterally on presacrals 6–25; alternation of neural spine height of the presacrals with an interruption at presacral 9 is superimposed upon a gradual posterior decrease of spine height; slope of zygapophyseal articular surfaces changes from ventromedial on the first six presacrals to horizontal on the remaining presacrals; and spines for epaxial muscle attachment present on the neural arches of presacrals 6–14 decrease in size posteriorly. Midventral lips are present on the centra and intercentra of all presacrals. Fine cracks on the centra of caudal vertebrae 8–11 are evidence of caudal autotomy.The pattern of vertebral morphology suggests specializations in the cervical region for support of the massive head and in the do...
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Anningia megalops Broom, 1927 is based upon a poorly preserved, incomplete skull and was interpreted originally as an intermediate form between therapsids and primitive nontherapsid synapsids (pelycosaurs). Restudy of the type specimen... more
Anningia megalops Broom, 1927 is based upon a poorly preserved, incomplete skull and was interpreted originally as an intermediate form between therapsids and primitive nontherapsid synapsids (pelycosaurs). Restudy of the type specimen indicates that A. megalops is a nondiagnosable primitive synapsid and is, therefore, declared to be a nomen vanum.
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Captorhinids were Paleozoic eureptiles that originated in the Late Pennsylvanian in Laurasia and dispersed across the major landmasses of Pangaea by the Late Permian. Their evolutionary success as omnivorous and herbivorous members of... more
Captorhinids were Paleozoic eureptiles that originated in the Late Pennsylvanian in Laurasia and dispersed across the major landmasses of Pangaea by the Late Permian. Their evolutionary success as omnivorous and herbivorous members of Permian terrestrial communities has been attributed to the evolution of multiple marginal tooth rows. Multiple tooth rows evolved at least twice within Captorhinidae: once in the omnivorous Captorhinus aguti and again in the diverse subfamily of herbivorous moradisaurines. The earliest known moradisaurines co-occured with C. aguti in Lower Permian strata of Texas; however C. aguti is also known from much older fissure fills in the famous Dolese Brothers quarry near Richards Spur, Oklahoma, suggesting that C. aguti preceded any other multiple-rowed captorhinid. Here we report on new material of multiple-rowed captorhinids from the Lower Permian fissure fills of the Bally Mountain locality in Oklahoma, only 35 miles from Richards Spur. Some of this mater...
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Rare occurrences of dinosaurian embryos are punctuated by even rarer preservation of their development. Here we report on dental development in multiple embryos of the Early Jurassic Lufengosaurus from China, and compare these to patterns... more
Rare occurrences of dinosaurian embryos are punctuated by even rarer preservation of their development. Here we report on dental development in multiple embryos of the Early Jurassic Lufengosaurus from China, and compare these to patterns in a hatchling and adults. Histology and CT data show that dental formation and development occurred early in ontogeny, with several cycles of tooth development without root resorption occurring within a common crypt prior to hatching. This differs from the condition in hatchling and adult teeth of Lufengosaurus, and is reminiscent of the complex dentitions of some adult sauropods, suggesting that their derived dental systems likely evolved through paedomorphosis. Ontogenetic changes in successive generations of embryonic teeth of Lufengosaurus suggest that the pencil-like teeth in many sauropods also evolved via paedomorphosis, providing a mechanism for the convergent evolution of small, structurally simple teeth in giant diplodocoids and titanosa...
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Permian bolosaurid parareptiles are well-known for having complex tooth crowns and complete tooth rows in the jaws, in contrast to the comparatively simple teeth and frequent replacement gaps in all other Paleozoic amniotes. Analysis of... more
Permian bolosaurid parareptiles are well-known for having complex tooth crowns and complete tooth rows in the jaws, in contrast to the comparatively simple teeth and frequent replacement gaps in all other Paleozoic amniotes. Analysis of the specialized dentition of the bolosaurid parareptiles Bolosaurus from North America and Belebey from Russia, utilizing a combination of histological and tomographic data, reveals unusual patterns of tooth development and replacement. The data confirm that bolosaurid teeth have thecodont implantation with deep roots, the oldest known such example among amniotes, and independently evolved among much younger archosauromorphs (including dinosaurs and crocodilians) and among synapsids (including mammals). High-resolution CT scans were able to detect the density boundary between the alveolar bone and the jawbone, as confirmed by histology, and revealed the location and size of developing replacement teeth in the pulp cavity of functional teeth. Evidence...