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Sereno, P. C. Lesothosaurus, “Fabrosaurids,” and the early evolution of Ornithischia. Journal of Vertebrate Paleontology
Journal of Verterbrate Paleontology
Abstract
New materials of Lesothosaurus diagnosticus permit a detailed understanding of one of the earliest and most primitive ornithischians. Skull proportions and suturai relations can be discerned from several articulated and disarticulated skulls. The snout is proportionately long with a vascularized, horn-covered tip. The premaxillary palate is broad and vomers are long and fused anteriorly. Unlike many later ornithischians, the postpalatine vacuities are broadly open. The basal tubera are short and gently depressed, and the epiotic contributes to the sidewall of the braincase. The mandibular symphysis is spout-shaped, and the dentition is marked by oblique wear facets, in contrast to earlier reports. The tooth-to-tooth wear facets and form of the predentary-dentary articulation suggest long-axis rotation of the mandibular rami during mastication.The forelimb is proportionately very short, with a partially opposable pollex. The ischium lacks an obturator process. The reduced hallux is held well above the substrate during locomotion.L. diagnosticus is diagnosed below on the basis of apomorphic features. Other “fabrosaurids” constitute a heterogeneous assemblage of poorly known ornithischians and hatchling prosauropods that do not share any apomorphic features with L. diagnosticus. Fabrosaurus australis is a nomen dubium, and, as a consequence, the family Fabrosauridae is invalid. Echinodon becklesii may represent a primitive heterodontosaur, and Tawasaurus, Fulengia, and portions of the holotype of Technosaurus represent hatchling prosauropods. Pisanosaurus mertii may be the most primitive ornithischian, as indicated by the form of the distal crus and astragalus, but a more precise phylogenetic assessment will require additional remains.
... The lack of denticles and high-crowned, slightly recurved morphology is reminiscent of known ornithischian premaxillary teeth, although we are unable to identify a clade with identical tooth morphology. Premaxillary teeth occur in early-diverging ornithischians such as Lesothosaurus (Porro et al., 2015;Sereno, 1991), some early ornithopods (Barrett & Han, 2009;Brown & Druckenmiller, 2011;Galton, 1974), Early Jurassic thyreophorans such as Scutellosaurus (Breeden et al., 2021;Colbert, 1981), Laquintasaura , Herrera-Castillo et al., 2021, heterodontosaurids (Butler et al., 2012;Sereno, 2012), ceratopsians, pachycephalosaurs (Sullivan, 2006), neornithischians such as Thescelosaurus and Jeholosaurus (Boyd, 2014), the ankylosaurs Silvisaurus (Eaton, 1960) and Cedarpelta (Carpenter, 2001), and the stegosaurs Huayangosaurus (Sereno & Dong, 1992) and Isaberrysaura (Salgado et al., 2017). Premaxillary crowns of Lesothosaurus are distally recurved with denticulate mesial and distal margins and lack a ridged surface ornamentation (Porro et al., 2015;Sereno, 1991). ...
... Premaxillary teeth occur in early-diverging ornithischians such as Lesothosaurus (Porro et al., 2015;Sereno, 1991), some early ornithopods (Barrett & Han, 2009;Brown & Druckenmiller, 2011;Galton, 1974), Early Jurassic thyreophorans such as Scutellosaurus (Breeden et al., 2021;Colbert, 1981), Laquintasaura , Herrera-Castillo et al., 2021, heterodontosaurids (Butler et al., 2012;Sereno, 2012), ceratopsians, pachycephalosaurs (Sullivan, 2006), neornithischians such as Thescelosaurus and Jeholosaurus (Boyd, 2014), the ankylosaurs Silvisaurus (Eaton, 1960) and Cedarpelta (Carpenter, 2001), and the stegosaurs Huayangosaurus (Sereno & Dong, 1992) and Isaberrysaura (Salgado et al., 2017). Premaxillary crowns of Lesothosaurus are distally recurved with denticulate mesial and distal margins and lack a ridged surface ornamentation (Porro et al., 2015;Sereno, 1991). Some premaxillary crowns of basally branching ornithopods and neornithischians, such as Hypsilophodon and Thescelosaurus (Fig. 5), also possess a superficially similar ridged ornamentation that extends from the crown apex to the base of the crown (Boyd, 2014;Brown & Druckenmiller, 2011;Galton, 1974); however, this ornamentation comprises much finer ridges than seen on the Kirtlington teeth. ...
... The small sub-triangular crowns of morphotype A (Fig. 8) closely resemble the cheek teeth of basally diverging thyreophorans, such as Scelidosaurus and Scutellosaurus (Fig. 10), and other early ornithischians, such as Lesothosaurus (Fig. 7), with unornamented labial and lingual surfaces, apart from a broad central eminence, and unequal mesial and distal margin lengths (Barrett, 2001;Breeden et al., 2021;Colbert, 1981;Sereno, 1991). Unlike more derived thyreophorans and Lesothosaurus, the basal swelling has not developed into a distinct cingulum, as also seen in ankylosaurs and stegosaurs (Coombs, 1990), but it is similar to that present in Scelidosaurus, Scutellosaurus, and Emausaurus (Barrett, 2001;Colbert, 1981;Haubold, 1990). ...
... The base of the medial process is as wide as the main body of the postorbital, as in Orodromeus (Scheetz, 1999) and Agilisaurus (Peng, 1992), while this process is narrower than the main body in Heterodontosaurus (Norman et al., 2011), Jeholosaurus (Barrett & Han, 2009), Hypsilophodon (Galton, 1974), Lesothosaurus (Sereno, 1991), and Gasparinisaura (Coria & Salgado, 1996;MUCPv-208, MGB pers. observ.). ...
... In dorsal view, the frontal-postorbital contact forms a laterally concave sinuous suture. In Manidens, the postorbital does not contact the parietals, whereas a postorbital-parietal contact is present in Heterodontosaurus (Norman et al., 2011), Lesothosaurus (Sereno, 1991;Porro et al., 2015), Agilisaurus (Peng, 1992), Orodromeus (Scheetz, 1999:fig. 7, c-par, c-f), and Jeholosaurus (Barrett & Han, 2009), among others. ...
... 82); however, the overall shape of this element is similar to the anatomy of the quadratojugal described here, but its brief description prevents discussion of its identity. Most descriptions and reconstructions represent the quadratojugal in Heterodontosauridae (Abrictosaurus and Heterodontosaurus) as a triradiate element, an uncommon condition compared with other ornithischians such as Lesothosaurus, Gasparinisaura, Parksosaurus, Hypsilophodon, and Jeholosaurus, where these elements are V-shaped in lateral view, or plate-like elements as in Iguanodontia and Psittacosauridae (Galton, 1973b(Galton, , 1974Sereno, 1991;Coria & Salgado, 1996;Norman, 2004;You & Dodson, 2004;Barrett & Han, 2009). ...
Heterodontosauridae is a clade that appears early in the ornithischian fossil record, and includes small-bodied, highly specialized species characterized by an unusual heterodont dentition. Although known from relatively few taxa, the early representation of the clade and unsolved phylogenetic relationships within heterodontosaurids and among early ornithischians implies that novel information has a marked effect on broader phylogenetic hypotheses and our understanding of early diversification patterns within Ornithischia. This paper describes the cranial osteology of the heterodontosaurid Manidens condorensis based on computed micro-tomographic scans of MPEF-PV 3211 and MPEF-PV 3809. This enabled more detailed descriptions of previously recognized bones, corrections to the literature, and the identification of undescribed elements. We present a new skull reconstruction and propose an emended diagnosis in light of novel anatomical information. Areas of jaw muscle attachment were identified and compared with Heterodontosaurus and Lesothosaurus, and mandibular function among heterodontosaurids is discussed. Our results indicate that diverse skull morphologies and functions existed among Early Jurassic ornithischians, with Manidens being intermediate between the plesiomorphic cranial shape and function associated with a generalist diet in ornithischians such as Tianyulong and Lesothosaurus, and the more derived cranial construction specialized for herbivory identified in heterodontosaurids from South Africa such as Heterodontosaurus.
... Posteriorly a short vertical process of the squamosal abuts the anterior surface of the paroccipital process ( Figure 4). Viewed posteriorly, the squamosal is exposed dorsally, but it is positioned only slightly higher than the paroccipital process, as also occurs in Lesothosaurus (Sereno, 1991). By contrast, the squamosal has a much greater exposure in posterior view in Scelidosaurus and ankylosaurians (Vickaryous and Russell, 2003;Norman, 2020c), although the degree of exposure varies among stegosaurs (Gilmore, 1914;Sereno and Dong, 1992). ...
... In posterior view, its quadrate ramus is a fan-shaped lamina that extends laterodorsally to meet the pterygoid wing of the quadrate ( Figure 5D). Its ventral margin curls dorsally to form a narrow trough that is visible in posterior view as in Lesothosaurus and Scelidosaurus (Sereno, 1991;Norman, 2020c). ...
... This notch appears to be unique to Yuxisaurus and is regarded as autapomorphic. By contrast, this margin is subtly concave in Scelidosaurus (NHMUK PV R1111; Norman, 2020c), convex in the early diverging ornithischian Lesothosaurus (Sereno, 1991) and is straight or slightly convex in stegosaurians and ankylosaurians (Gilmore, 1914;Sereno and Dong, 1992;Vickaryous and Russell, 2003;Norman, 2020c). On the left paroccipital process, at about the same level as the concavity, lies a tongue-like slit, resembling the condition in Scelidosaurus, where a spur-like process indicates the position of the posttemporal fenestra (NHMUK PV R1111: Norman, 2020c). ...
The early evolutionary history of the armoured dinosaurs (Thyreophora) is obscured by their patchily distributed fossil record and by conflicting views on the relationships of Early Jurassic taxa. Here, we describe an early-diverging thyreophoran from the Lower Jurassic Fengjiahe Formation of Yunnan Province, China, on the basis of an associated partial skeleton that includes skull, axial, limb and armour elements. It can be diagnosed as a new taxon based on numerous cranial and postcranial autapomorphies and is further distinguished from all other thyreophorans by a unique combination of character states. Although the robust postcranium is similar to that of more deeply nested ankylosaurs and stegosaurs, phylogenetic analysis recovers it as either the sister taxon of Emausaurus or of the clade Scelidosaurus+Eurypoda. This new taxon, Yuxisaurus kopchicki, represents the first valid thyreophoran dinosaur to be described from the Early Jurassic of Asia and confirms the rapid geographic spread and diversification of the clade after its first appearance in the Hettangian. Its heavy build and distinctive armour also hint at previously unrealised morphological diversity early in the clade's history.
... Posteriorly a short vertical process of the squamosal abuts the anterior surface of the paroccipital process ( Figure 4). Viewed posteriorly, the squamosal is exposed dorsally, but it is positioned only slightly higher than the paroccipital process, as also occurs in Lesothosaurus (Sereno, 1991). By contrast, the squamosal has a much greater exposure in posterior view in Scelidosaurus and ankylosaurians (Vickaryous and Russell, 2003;Norman, 2020c), although the degree of exposure varies among stegosaurs (Gilmore, 1914;Sereno and Dong, 1992). ...
... In posterior view, its quadrate ramus is a fan-shaped lamina that extends laterodorsally to meet the pterygoid wing of the quadrate ( Figure 5D). Its ventral margin curls dorsally to form a narrow trough that is visible in posterior view as in Lesothosaurus and Scelidosaurus (Sereno, 1991;Norman, 2020c). ...
... This notch appears to be unique to Yuxisaurus and is regarded as autapomorphic. By contrast, this margin is subtly concave in Scelidosaurus (NHMUK PV R1111; Norman, 2020c), convex in the early diverging ornithischian Lesothosaurus (Sereno, 1991) and is straight or slightly convex in stegosaurians and ankylosaurians (Gilmore, 1914;Sereno and Dong, 1992;Vickaryous and Russell, 2003;Norman, 2020c). On the left paroccipital process, at about the same level as the concavity, lies a tongue-like slit, resembling the condition in Scelidosaurus, where a spur-like process indicates the position of the posttemporal fenestra (NHMUK PV R1111: Norman, 2020c). ...
The early evolutionary history of the armoured dinosaurs (Thyreophora) is obscured by its patchily distributed fossil record and by conflicting views on the relationships of its Early Jurassic representatives. Here, we describe an early-diverging thyreophoran from the Lower Jurassic Fengjiahe Formation of Yunnan Province, China, on the basis of an associated partial skeleton that includes skull, axial, limb and armour elements. It can be diagnosed as a new taxon based on numerous cranial and postcranial autapomorphies and is further distinguished from all other thyreophorans by a unique combination of character states. Although the robust postcranium is similar to that of more deeply nested ankylosaurs and stegosaurs, phylogenetic analysis recovers it as either the sister taxon of Emausaurus or of the clade Scelidosaurus and Eurypoda. This new taxon, Yuxisaurus kopchicki, represents the first valid thyreophoran dinosaur to be described from the Early Jurassic of Asia and confirms the rapid geographic spread and diversification of the clade after its first appearance in the Hettangian. Its heavy build and distinctive armour also hint at previously unrealised morphological diversity early in the clade history.
... The suprageneric OTU of Ornithischia includes Lesothosaurus (Thulborn, 1972;Sereno, 1991;Norman et al. 2004;Butler, 2005), Heterodontosaurus (Santa Luca, 1980), Hypsilophodon (Galton, 1974), Abrictosaurus (Norman et al. 2004), Agilisaurus (Norman et al. 2004), Orodromeus (Norman et al. 2004), Parksosaurus (Norman et al. 2004) and ...
... The distribution of the character states seems to be a good predictor of obligate bipedality in dinosaurs. It is also present in the theropods Coelophysis (Rinehart et al., 2009), Liliensternus, Elaphrosaurus (Langer and Benton, 2006), and Allosaurus, in the latter the ridge does not extend onto the supraacetabular crest (Madsen, 1993); and the bipedal basal ornithischians Lesothosaurus (Sereno, 1991) and ...
... The term "dorsolateral trochanter" is used in several studies (e. g. Bonaparte et al., 1999;Langer, 2004;Butler, 2010;Kammerer et al., 2012;Griffin and Nesbitt, 2016;Müller et al., 2016), and matches consistently with the descriptions of the greater trochanter in other classic papers on dinosaur anatomy (e. g. Sereno, 1991;Novas, 1994). The term greater trochanter is used here instead of dorsolateral trochanter to avoid confusion when the torsion in the femur alters the orientation of the lateral and medial surfaces. ...
Non-sauropod sauropodomorphs, also known as 'basal sauropodomorphs' or 'prosauropods', have been thoroughly studied in recent years. Several hypotheses on the interrelationships within this group have been proposed, ranging from a complete paraphyly, where the group represents a grade from basal saurischians to Sauropoda, to a group on its own. The grade-like hypothesis is the most accepted; however, the relationships between the different taxa are not consistent amongst the proposed scenarios. These inconsistencies have been attributed to missing data and unstable (i.e., poorly preserved) taxa, nevertheless, an extensive comparative cladistic analysis has found that these inconsistencies instead come from the character coding and character selection, plus the strategies on merging data sets. Furthermore, a detailed character analysis using information theory and mathematical topology as an approach for character delineation is explored here to operationalise characters and reduce the potential impact of missing data. This analysis also produced the largest and most comprehensive matrix after the reassessment and operationalisation of every character applied to this group far. Additionally, partition analyses performed on this data set have found consistencies in the interrelationships within non-sauropod Sauropodomorpha and has found strong support for smaller clades such as Plateosauridae, Riojasauridae, Anchisauridae, Massospondylinae and Lufengosarinae. The results of these analyses also highlight a different scenario on how quadrupedality evolved, independently originating twice within the group, and provide a better framework to understand the palaeo-biogeography and diversification rate of the first herbivore radiation of dinosaurs.
... Colbert [18] assigned Scutellosaurus lawleri to the family Fabrosauridae but suggested that Scutellosaurus lawleri could possibly be a 'remote ancestor' of ankylosaurs and stegosaurs. Recent phylogenetic analyses and taxonomic reviews [1][2][3][4][5]20,[25][26][27][28][29][30][31][32][33] have recovered Scutellosaurus lawleri as one of the earliest branching members of Thyreophora, and Fabrosauridae is now considered polyphyletic [1,3,5,26,31,34]. Detailed knowledge of the anatomy of Scutellosaurus lawleri is important for several reasons: (i) character polarization during analyses of stegosaurian and ankylosaurian phylogeny and thyreophoran functional evolution. ...
... 'MNA V175', 'MNA V1752'). That change was not published at the time, and as a result, several subsequent publications cited the retired 'MNA P1.####' catalogue numbers used by Colbert [18] for the type specimens of Scutellosaurus lawleri [1,16,17,29,34,35,[75][76][77]. Additionally, the figure captions of Colbert [18] [81,82]; 'MNA PI.175' [83,84]; 'MNA Pl.175' and 'MNA Pl.1752' [2,79,80,[85][86][87][88]; and 'MNA.Pl.1752' [89]. ...
... As in other early ornithischians (e.g. Lesothosaurus diagnosticus: [34]), the first tooth of the premaxilla is inset a short distance from the anteriormost tip of [63]) or five (e.g. Agilisaurus louderbacki: [92]); the early thyreophorans Emausaurus ernsti [14] and Scelidosaurus harrisonii (BRSMG Ce12785) also have five, and the early diverging stegosaur Huayangosaurus taibaii (ZDM T7001; [93]) has seven. ...
The armoured dinosaurs, Thyreophora, were a diverse clade of ornithischians known from the Early Jurassic to the end of the Cretaceous. During the Middle and Late Jurassic, the thyreophorans radiated to evolve large body size, quadrupedality, and complex chewing mechanisms, and members of the group include some of the most iconic dinosaurs, including the plated Stegosaurus and the club-tailed Ankylosaurus ; however, the early stages of thyreophoran evolution are poorly understood due to a paucity of relatively complete remains from early diverging thyreophoran taxa. Scutellosaurus lawleri is generally reconstructed as the earliest-diverging thyreophoran and is known from over 70 specimens from the Lower Jurassic Kayenta Formation of Arizona, USA. Whereas Scutellosaurus lawleri is pivotal to our understanding of character-state changes at the base of Thyreophora that can shed light on the early evolution of the armoured dinosaurs, the taxon has received limited study. Herein, we provide a detailed account of the osteology of Scutellosaurus lawleri , figuring many elements for the first time. Scutellosaurus lawleri was the only definitive bipedal thyreophoran. Histological studies indicate that it grew slowly throughout its life, possessing lamellar-zonal tissue that was a consequence neither of its small size nor phylogenetic position, but may instead be autapomorphic, and supporting other studies that suggest thyreophorans had lower basal metabolic rates than other ornithischian dinosaurs. Faunal diversity of the Kayenta Formation in comparison with other well-known Early Jurassic-aged dinosaur-bearing formations indicates that there was considerable spatial and/or environmental variation in Early Jurassic dinosaur faunas.
... The anteriormost points of the nasals opposite the external nares from the ascending 5) is best considered a taphonomic artifact because confluent external nares (i.e., with loss of a complete internarial bar) are unknown among dinosaurs except for some diplodocoid and titanosaur sauropods (Upchurch, 1995;Wilson et al., 2016). In Haya, the surface of the premaxilla is smooth, in contrast to the rugose anterior premaxillary surfaces of Lesothosaurus, Jeholosaurus, Changchunsaurus, Oryctodromeus, Zephyrosaurus, Thescelosaurus, and Hypsilophodon (Galton, 1974a;Sues, 1980;Sereno, 1991;Varricchio et al., 2007; Barrett and Han, 2009;Jin et al., 2010;Boyd, 2014). Such rugose surfaces have been interpreted as evidence of a ramphotheca (Galton, 1974a), but the extent and attachment of a ramphotheca in Haya, if present, is unclear. ...
... Such rugose surfaces have been interpreted as evidence of a ramphotheca (Galton, 1974a), but the extent and attachment of a ramphotheca in Haya, if present, is unclear. The general morphology of the premaxilla anterior to the first premaxillary tooth is similar to Lesothosaurus (Sereno, 1991;Knoll, 2008), except Haya lacks even the limited pitting inferred to correspond to a short ramphotheca anterior to the first premaxillary tooth in Lesothosaurus (Sereno, 1991;Knoll, 2008). Future discoveries of morphologically mature skulls may reveal whether pitting and, by inference, a ramphotheca, developed on the premaxilla of Haya griva through ontogeny, as in Jeholosaurus (Barrett and Han, 2009 Boyd, 2014). ...
... Such rugose surfaces have been interpreted as evidence of a ramphotheca (Galton, 1974a), but the extent and attachment of a ramphotheca in Haya, if present, is unclear. The general morphology of the premaxilla anterior to the first premaxillary tooth is similar to Lesothosaurus (Sereno, 1991;Knoll, 2008), except Haya lacks even the limited pitting inferred to correspond to a short ramphotheca anterior to the first premaxillary tooth in Lesothosaurus (Sereno, 1991;Knoll, 2008). Future discoveries of morphologically mature skulls may reveal whether pitting and, by inference, a ramphotheca, developed on the premaxilla of Haya griva through ontogeny, as in Jeholosaurus (Barrett and Han, 2009 Boyd, 2014). ...
Haya griva is an early-diverging neornithischian (“hypsilophodontid”) dinosaur known from several well-preserved skulls and articulated postcranial skeletons, in addition to dozens of partial or isolated finds from the Upper Cretaceous Khugenetslavkant and Zos Canyon localities (Javkhlant Formation and equivalent beds) in the Gobi Desert of Mongolia. Collectively, nearly the entire skeletal anatomy of Haya is known, including partial growth series of skulls and femora. Detailed description and comparisons with other ornithischians, including novel anatomical information about the palate and braincase gleaned through high-resolution x-ray microcomputed tomography, reveals a wealth of osteological data for understanding the growth and relationships of this key taxon. Though the Haya specimens span a wide size range, bone histology reveals that all are likely perinatal to subadult individuals, with specimens of intermediate age the most common, and skel- etally mature specimens absent. Phylogenetic analyses place Haya as one of the few Asian members of Thescelosauridae, an important noncerapodan neornithischian group of the Late Cretaceous.
... Remarks Several characters of the maxillary/dentary teeth, such as low, sub-triangular shape in labial view, crowns mesiodistally expanded above the root such that the maximum mesiodistal length is greater than the maximum mesiodistal length of the root, labiolingual expansion of the crowns above the root forming a ''cingulum'', asymmetrical crowns in mesial and distal views, and crowns with enlarged denticles on the mesial and distal margins often associated with 'interdental pressure facet' were considered as synapomorphies of Ornithischia (Sereno 1986(Sereno , 1991Hunt and Lucas 1994;Heckert 2002Heckert , 2004Norman et al. 2004). However, recent reviews on Late Triassic dinosaurs have shown that some of these features are also present in non-dinosaurian Triassic archosaurs (Dzik 2003;Parkar et al. 2005;Butler et al. 2006;Irmis et al. 2007). ...
... The teeth of Phyllodon differ from DUGF/J1-4 and 12 in their lozenge shape, having apicobasal height greater than the mesiodistal length, and the labial side of the crown significantly higher than the lingual side. Similarly, A. kuehnei, referred variously to Fabrosauridae, Hypsilophodontidae, Ornithischia incertae sedis or Thyreophora (Thulborn 1973;Sereno 1991;Ruiz-Omeñaca 2001;Knoll 2002) or nomen dubium (Knoll 2002;Weishampel et al. 2004;Godefroit and Knoll 2003), differs from the Kota teeth in the presence of ridges on the lingual surface of the cheek teeth. ...
... Galton (1978) also felt that there are more differences than similarities between Echinodon and Trimucrodon. Though Weishampel and Witmer (1990) considered both T. cuneatus and A. kuehnei as nomina dubia, Sereno (1991) placed them in Ornithischia incertae sedis. In light of these taxonomic uncertainties, the teeth from the Kota Formation are referred here to Ornithischia indet. ...
The Middle Jurassic Kota Formation of the Pranhita-Godavari Valley in peninsular India is well known for its vertebrate fauna comprising fishes, sphenodontians, iguanian lizards, cryptodire turtle, crocodilians, pterosaurs, sauropod dinosaurs and early mammals. However, no theropod and undoubted ornithischian dinosaur remains have been reported from the Jurassic of India until now. Here we describe the first theropod dinosaur teeth representing five morphotypes of Dromaeosauridae, one Richardoestesia-like form, and one Theropoda indet. The ornithischian dinosaur teeth are described under five morphotypes of Ornithischia indet. The new dinosaur fauna improves the diversity of the Jurassic vertebrate fauna of India significantly. It also improves the impoversished Jurassic record of dromaeosaurid and primitive ornithischian dinosaurs of the Gondwana. At higher taxonomic levels, the Kota fauna demonstrates close compositional similarities with Laurasian Jurassic faunas, such as the Middle Jurassic fauna of England, and limited Gondwanan affinities, which may suggest closer connection with the Laurasian continents and existence of some biogeographic partitioning within the Gondwana in the Jurassic.
... Quadratojugal -The quadratojugal is trapezoidal in lateral view and mediolaterally compressed (Figs.2 and 6C); it participates in the caudoventral margin of the infratemporal fenestra. Its caudal portion extensively overlaps the rostroventral margin of the quadrate, but it does not reach the ventral process of the squamosal, unlike in Heterodontosaurus (Crompton & Charig, 1962), Lesothosaurus (Sereno, 1991), and the basal iguanodontians Dryosaurus and Dysalotosaurus (Norman, 2004). The rostral portion of the quadratojugal is overlapped by the caudal ramus of the jugal. ...
... In lateral view, the neural spine is oriented posterodorsally at an angle of about 30 degrees to the horizontal. It is particularly elongate, extending well beyond the caudal border of the axial centrum to overlap cervical vertebra 3, as also observed in Lesothosaurus (Sereno, 1991), Heterodontosaurus (Santa Luca, 1980), Jeholosaurus (Han et al., 2012), Changchunsaurus (Butler et al., 2011) and Haya (Makovicky et al., 2011). Along its midline, the spine forms a particularly sharp crest extending along its entire length. ...
... Six sacral vertebrae occur in many basal ornithischians, ornithopods and ceratopsians, including Heterodontosaurus (Sereno, 2012), some specimens of Hypsilophodon (Galton, 1974), Jeholosaurus (Han et al., 2012), Haya (Makovicky et al., 2011), Orodromeus (Scheetz, 1999), Parksosaurus, Thescelosaurus , Psittacosaurus and Archaeoceratops (You & Dodson, 2003). Five sacral vertebrae are present in some basal ornithischians, including Lesothosaurus (Sereno, 1991), Agilisaurus (Peng, 1992), Hexinlusaurus (He & Cai, 1984;Barrett, Butler & Knoll, 2005), probably Eocursor (Butler, Smith & Norman, 2007) and some specimens of Hypsilophodon (Galton, 1974). Sacra with more than six sacral vertebrae occur in Oryctodromeus, likely Orodromeus (Varricchio, Martin & Katsura, 2007), derived iguanodontians (Norman, 2004) and ceratopsians (Dodson, Forster & Sampson, 2004). ...
A new basal ornithopod dinosaur, based on two nearly complete articulated skeletons, is reported from the Lujiatun Beds (Yixian Fm, Lower Cretaceous) of western Liaoning Province (China). Some of the diagnostic features of Changmiania liaoningensis nov. gen., nov. sp. are tentatively interpreted as adaptations to a fossorial behavior, including: fused premaxillae; nasal laterally expanded, overhanging the maxilla; shortened neck formed by only six cervical vertebrae; neural spines of the sacral vertebrae completely fused together, forming a craniocaudally-elongated continuous bar; fused scapulocoracoid with prominent scapular spine; and paired ilia symmetrically inclined dorsomedially, partially covering the sacrum in dorsal view. A phylogenetic analysis places Changmiania liaoningensis as the most basal ornithopod dinosaur described so far. It is tentatively hypothesized that both Changmiania liaoningensis specimens were suddenly entrapped in a collapsed underground burrow while they were resting, which would explain their perfect lifelike postures and the complete absence of weathering and scavenging traces. However, further behavioural inference remains problematic, because those specimens lack extensive sedimentological and taphonomic data, as it is also the case for most specimens collected in the Lujiatun Beds so far.
... Also, the apparent lack of replacement foramina in the Pi. mertii lower jaw may support its heterodontosaurid affinities within ornithischians 116 , as those are present in other early members of that group 123,124 , as well as in silesaurids 115,125 . ...
... Such a strong ridge and emargination is absent in silesaurids 115 and dinosaurs in general, including early sauropodomorphs 93,122 . On the contrary, this is seen in several 116,119,[126][127][128] , although not all, early ornithischians 123,124,129 . Accordingly, the presence of a buccal emargination in Pi. mertii better supports an ornithischian, rather than silesaurid affinity. ...
... mertii teeth. Yet, we concur with those authors that a blunt primary ridge, like that of ornithischians 116,123,124,127 is seen in some teeth. This produces a morphology that most closely resembles that of the constricted, cup-shaped bases of Heterodontosaurus tucki and Lycorhinus angustidens molariform Scientific RepoRtS | (2020) 10:12782 | https://doi.org/10.1038/s41598-020-67854-1 ...
Present knowledge of Late Triassic tetrapod evolution, including the rise of dinosaurs, relies heavily on the fossil-rich continental deposits of South America, their precise depositional histories and correlations. We report on an extended succession of the Ischigualasto Formation exposed in the Hoyada del Cerro Las Lajas (La Rioja, Argentina), where more than 100 tetrapod fossils were newly collected, augmented by historical finds such as the ornithosuchid Venaticosuchus rusconii and the putative ornithischian Pisanosaurus mertii. Detailed lithostratigraphy combined with high-precision U–Pb geochronology from three intercalated tuffs are used to construct a robust Bayesian age model for the formation, constraining its deposition between 230.2 ± 1.9 Ma and 221.4 ± 1.2 Ma, and its fossil-bearing interval to 229.20 + 0.11/− 0.15–226.85 + 1.45/− 2.01 Ma. The latter is divided into a lower Hyperodapedon and an upper Teyumbaita biozones, based on the ranges of the eponymous rhynchosaurs, allowing biostratigraphic correlations to elsewhere in the Ischigualasto-Villa Unión Basin, as well as to the Paraná Basin in Brazil. The temporally calibrated Ischigualasto biostratigraphy suggests the persistence of rhynchosaur-dominated faunas into the earliest Norian. Our ca. 229 Ma
age assignment to Pi. mertii partially fills the ghost lineage between younger ornithischian records and the oldest known saurischians at ca. 233 Ma.
... A large premaxillary foramen is located anteroventral to the narial opening. This foramen cut across the bone, as in most ornithischians (Sereno 1991) including Hypsilophodon and Dryosaurus (Galton 1974a(Galton , 1981Cambiaso 2007;Boyd 2016). A smaller foramen is located anteriorly on the premaxillary body. ...
... This process projects posterodorsally and is located in the section of the bone that shows its greatest curvature in anterior or posterior views. The slender proportions of the ectopterygoid in Talenkauen resemble those of basal ornithopods such as Hypsilophodon (Huxley 1869) and basal ornithischians, including Lesothosaurus (Sereno 1991;Knoll 2002;Porro et al. 2015), whereas in iguanodontians this bone is thicker and more massive (Norman 1980(Norman , 1986. ...
... The prequadratic process is transversely flat and dorsoventrally wide. This process is anteroposteriorly short, as in Hypsilophodon and Lesothosaurus (Galton 1974a;Sereno 1991;Knoll 2002;Porro et al. 2015). In lateral view, it is bifurcated with two digitiform expansions: a dorsal expansion that articulates with the medial surface of the quadrate and a ventral expansion that articulates with the quadrate wing. ...
Talenkauen santacrucensis represents one of the most complete South American ornithopods yet discovered. This dinosaur comes from the Mata Amarilla Formation (Turonian) of Santa Cruz Province, Argentina. The aim of this contribution is to present a detailed description of Talenkauen santacrucensis. Features of the cervical series of Talenkauen, which are shared with other elasmarians, indicate that these dinosaurs have a proportionally longer neck than other ornithopods. These traits were convergently acquired by several saurischian clades. Additionally, some features, including an ornamented labial surface of the mandibular teeth and a sigmoidal greater trochanter of femur, are traits shared by most elasmarians, and may prove to be synapomorphies of this clade. A phylogenetic analysis recovers most Cretaceous Gondwanan ornithopods in the clade Elasmaria. This analysis indicates that Elasmaria was distributed more widely geographically and temporally than previously thought.
... For example, the premaxilla in Thescelosaurus neglectus shows an anterodorsal shelf and the anteroventral tip bears rugosities and foramina (Boyd 2014). Similar structures, most likely supporting rhamphotheca during the animal's life (Sereno 1991) (Galton 1974, Sues 1980, Sereno 1991, Varricchio et al. 2007, Barrett and Han 2009, Jin et al. 2010, Boyd 2014, Andrzejewski et al. 2019, Yang et al. 2020. Similarly, in the majority of these taxa, a shallow fossa is present laterally, with the premaxillary foramen and anterior premaxillary foramen present just adjacent to the border of the rugose area. ...
... For example, the premaxilla in Thescelosaurus neglectus shows an anterodorsal shelf and the anteroventral tip bears rugosities and foramina (Boyd 2014). Similar structures, most likely supporting rhamphotheca during the animal's life (Sereno 1991) (Galton 1974, Sues 1980, Sereno 1991, Varricchio et al. 2007, Barrett and Han 2009, Jin et al. 2010, Boyd 2014, Andrzejewski et al. 2019, Yang et al. 2020. Similarly, in the majority of these taxa, a shallow fossa is present laterally, with the premaxillary foramen and anterior premaxillary foramen present just adjacent to the border of the rugose area. ...
At the climax of their evolutionary history in the latest Cretaceous, ceratopsian dinosaurs were among the most dominant components of North American and Asian land ecosystems. In other continental landmasses, however, ceratopsians were extraordinarily rare and the affinities of their proposed representatives often turned out to be inconclusive. Arguably the most significant evidence of Ceratopsia from outside North America and Asia is represented by Ajkaceratops kozmai from the Santonian (Upper Cretaceous) of Hungary. We provide a detailed osteological description of Ajkaceratops and highlight its bizarre anatomy. Ajkaceratops has been ‘traditionally’ interpreted to represent a Bagaceratops-like coronosaur, and its occurrence on the European islands was hypothesized to probably result from an early Late Cretaceous dispersal event from Asia. However, while the snout of Ajkaceratops may resemble that of some ceratopsians, closer inspection of the preserved elements indicates that these similarities are largely superficial. While it cannot be ruled out that Ajkaceratops represents a highly peculiar member of the clade, its placement is far from certain. Still, the discovery of Ajkaceratops exemplifies the importance and uniqueness of European dinosaur faunas.
... Similarly, five non-sauropodan sauropodomorph juveniles were reported from Lower Jurassic deposits: Arcusaurus (Yates et al., 2011), Ignavusaurus (Knoll, 2010), Lufengosaurus (Sekiya and Dong, 2010), Massospondylus (Sues et al., 2004), and Yunnanosaurus (Sekiya et al., 2014), as well as two indeterminate specimens (Young, 1982;Evans and Milner, 1989;Sereno, 1991). Juvenile remains attributed to Ammosaurus, Riojasaurus and Ruehleia have also been mentioned, but never properly described (Galton and Upchurch, 2004). ...
... Worldwide, seven specimens were reported from Lower Jurassic layers, two of which are presently Sauropodomorpha indet. (Young, 1982;Evans and Milner, 1989;Sereno, 1991). The others have been referred to three already existing species: Lufengosaurus huenei (Sekiya and Dong, 2010), Massospondylus carinatus (Gow et al., 1990;Sues et al., 2004) and Yunnanosaurus robustus (Sekiya et al., 2014), and to two other species: Arcusaurus pereirabdalorum (Yates et al., 2011) and Ignavusaurus rachelis (Knoll, 2010) (Table 4) which are the only instances of isolated immature specimens used to erect a new species. ...
An incomplete dinosaur skeleton, including a partial skull, recently discovered from the Lower Jurassic Lufeng Formation of Yunnan, China, is here described. Except for its small size, little anatomical evidence supports, a priori, the non‐adult status of this new sauropodomorph specimen. Thus, osteohistological analyses were conducted, which suggest that the new specimen is a fast‐growing juvenile. Despite the abundant early sauropodomorph fossils collected from the Lufeng Formation, it represents only the second occurrence of a juvenile non‐sauropodan sauropodomorph in the Lufeng Basin. The anatomy of the specimen does not match that of other Lower Jurassic immature specimens. Although cranial material is preserved, it does not display diagnostic characters of the early sauropodomorphs from the same horizon, namely Lufengosaurus, Yizhousaurus and Yunnanosaurus. Our phylogenetic analysis, which places the new specimen in a position relatively distant to other Chinese sauropodomorphs, corroborates the systematic hypothesis indicated by the anatomical evidence that it is not referable to a species already excavated in Yunnan. However, this result should be interpreted with caution considering that ontogeny affects phylogenetic reconstruction. A thorough comparison with adult forms, taking into account ontogeny‐related characters, suggests that this new juvenile specimen could represent an unknown species of early sauropodomorph.
... The shape of the ilium in Auroraceratops is also quite like that of Hypsilophodon (Galton, 1974). In contrast, the ilium of Auroraceratops differs greatly from the early Jurassic ornithischian Lesothosaurus (Sereno, 1991;Maidment and Barrett, 2011b) in that for the former, the preacetabular process is longer, wider, and more strongly laterally deflected, the brevis shelf is more strongly developed, the postacetabular process is longer, and the dorsal surface of the ilium is slightly everted. The slight eversion and dorsally convex border of the ilium is seen in basal neoceratopsians, including Ischioceratops (He et al., 2015) and Archaeoceratops (You and Dodson, 2003). ...
... The body of the pubis of Auroraceratops appears to be more strongly recurved at its base, like in Protoceratops (Brown and Schlaikjer, 1940), rather than the straighter bases seen in leptoceratopsids (Brown and Schlaikjer, 1942;Chinnery and Weishampel, 1998). The long, thin body of the pubis is seen throughout Ornithischia (Hatcher et al., 1907;Galton, 1974;Sereno, 1991). Sereno (2010) identifies the 'prepubic' process transversely wider than tall as an autapomorphy for Psittacosaurus sinensis. ...
The species Auroraceratops rugosus was originally described based upon a single skull. With the recovery of over 80 individuals, a complete description of the postcranial skeleton is presented. Auroraceratops is currently the most complete exemplar we have of ceratopsian postcranial anatomy between Psittacosaurus and Leptoceratops. Adult Auroraceratops had a length of approximately 125 cm and an approximate hip height of 44 cm. Osteological correlates of stance in the fore- and hind limb unequivocally indicate a bipedal gait. The phylogenetically corrected quadrupedal mass-estimation equation modified for mass estimation of bipedal terrestrial vertebrates estimates an average mass of Auroraceratops at 15.5 kg. It has the phylogenetically and temporally earliest documentation of the syncervical in Ceratopsia. The mid-caudal neural spines are elongate and erect, a feature previously only known in Leptoceratopsidae and Protoceratopsidae. Despite being longer than in most ceratopsians, the mid-caudal neural spines are not as tall as in some leptoceratopsids. Most of the phylogenetically relevant characters of the postcranial skeleton in Auroraceratops are a mosaic of features plesiomorphic to Neoceratopsia and features previously considered to be unique to later diverging clades, such as Leptoceratopsidae and Protoceratopsidae.
Citation for this article: Morschhauser, E. M., H. You, D. Li, and P. Dodson. 2019. Postcranial morphology of the basal neoceratopsian (Ornithischia: Ceratopsia) Auroraceratops rugosus from the Early Cretaceous (Aptian–Albian) of northwestern Gansu Province, China; pp. 75–116 in Hailu You, Peter Dodson, and Eric Morschhauser (eds.), Auroraceratops rugosus (Ornithischia, Ceratopsia) from the Early Cretaceous of northwestern Gansu Province, China. Society of Vertebrate Paleontology Memoir 18. Journal of Vertebrate Paleontology 38(Supplement). DOI: 10.1080/02724634.2017.1524383.
... Therefore, most dietary inferences have been based on observations of craniodental morphology in early dinosaurs, with a particular focus on teeth (2,10,11). The curved, finely serrated teeth typically seen in early saurischians and theropods (12,13) are considered indicators of carnivory, while the denticulated, lanceolate teeth of sauropodomorphs (14) and the triangular teeth of ornithischians (15) were traditionally associated with herbivorous habits. These observations formed the basis for the idea that the ancestral diet of dinosaurs was carnivory, and herbivory evolved independently at the origin of sauropodomorphs and ornithischians (16). ...
Dinosaurs evolved a remarkable diversity of dietary adaptations throughout the Mesozoic, but the origins of different feeding modes are uncertain, especially the multiple origins of herbivory. Feeding habits of early dinosaurs have mostly been inferred from qualitative comparisons of dental morphology with extant analogs. Here, we use biomechanical and morphometric methods to investigate the dental morphofunctional diversity of early dinosaurs in comparison with extant squamates and crocodylians and predict their diets using machine learning classification models. Early saurischians/theropods are consistently classified as carnivores. Sauropodomorphs underwent a dietary shift from faunivory to herbivory, experimenting with diverse diets during the Triassic and Early Jurassic, and early ornithischians were likely omnivores. Obligate herbivory was a late evolutionary innovation in both clades. Carnivory is the most plausible ancestral diet of dinosaurs, but omnivory is equally likely under certain phylogenetic scenarios. This early dietary diversity was fundamental in the rise of dinosaurs to ecological dominance.
... The parasphenoid lies anterior to the basipterygoid processes, forming a circular fenestra, and it is fused to the ventral surface of the orbitosphenoid. There are three small foramina that represent the exits of the hypoglossal nerve (XII), as in the basally branching ornithischian Lesothosaurus (Sereno, 1991). Anterior to cranial nerve XII, there is a large, heartshaped foramen, which is the combined fissura metotica and fenestra ovalis. ...
Stegosaurs are a major clade of ornithischian dinosaurs, yet because of their fragmentary fossil record, their interrelationships and early evolution are poorly understood. Here, we describe a new stegosaur, Bashanosaurus primitivus, gen. et sp. nov., and some other indeterminate stegosaur materials. We provide new U-Pb detrital zircon ages for horizons bounding the holotypic quarry in the Lower Member of the Shaximiao Formation, Yunyang, Chongqing Municipality, China, which indicate a Middle Jurassic (Bajocian) age. Bashanosaurus represents the earliest record of stegosaurs in Asia and one of the earliest records of this clade in the world. The dorsal vertebrae, scapula, coracoid, femur, and plates of Bashanosaurus primitivus possess several unique characters among Stegosauria, including the elevation of the parapophyses of dorsal vertebrae on stalks at the base of the transverse processes, a flared distal end of the scapula, and a small acromial process. Among armored dinosaurs (thyreophorans), these features are reminiscent of the basally branching taxon Scelidosaurus, indicating that Bashanosaurus possesses a unique mosaic of plesiomorphic thyreophoran and derived stegosaur features. Phylogenetic analysis shows that Bashanosaurus primitivus is the earliest-diverging stegosaur, along with Chungkingosaurus, from the Upper Member of the Shaximiao Formation, consistent with the early age of the taxon.
... An elongate coronoid, like that of Mambawakale ruhuhu, is probably plesiomorphic for Archosauriformes (though coronoid length and/or shape has generally not been included as a character in recent phylogenetic analyses, e.g. [6,37]), being found in, for example, erythrosuchids [2,57], Euparkeria capensis [58], proterochampsids [59], at least some avemetatarsalians [60], the loricatans Etjosuchus recurvidens [61] and possibly Saurosuchus galilei [55]. Shorter coronoids are present in some archosaurs, such as Prestosuchus chiniquensis [62]. ...
The Manda Beds of southwest Tanzania have yielded key insights into the early evolutionary radiation of archosaurian reptiles. Many key archosaur specimens were collected from the Manda Beds in the 1930s and 1960s, but until recently, few of these had been formally published. Here, we describe an archosaur specimen collected in 1963 which has previously been referred to informally as Pallisteria angustimentum . We recognize this specimen as the type of a new taxon, Mambawakale ruhuhu gen. et sp. nov. The holotype and only known specimen of M. ruhuhu comprises a partial skull of large size (greater than 75 cm inferred length), lower jaws and fragments of the postcranium, including three anterior cervical vertebrae and a nearly complete left manus. Mambawakale ruhuhu is characterized by several cranial autapomorphies that allow it to be distinguished with confidence from all other Manda Beds archosaurs, with the possible exception of Stagonosuchus nyassicus for which comparisons are highly constrained due to very limited overlapping material. Phylogenetic analysis suggests that M. ruhuhu is an early diverging pseudosuchian, but more precise resolution is hampered by missing data. Mambawakale ruhuhu is one of the largest known pseudosuchians recovered to date from the Middle Triassic.
... The anterior margin of the lacrimal is transversely thin and articulates with the prefrontal (Fig. 10A), which is not preserved in TMM 43664-1. Along the anterior margin between the raised rugose surface and the antorbital fossa is a distinct subtriangular notch for articulation with a slender process of the maxilla (Fig. 10A), as in Lesothosaurus diagnosticus (Sereno, 1991;Porro et al., 2015). The lateral surface of the curved posteroventral process of the lacrimal is overlain by the anterior process of the jugal along a scarf-joint articulation (Fig. 10A), as in both Emausaurus ernsti and Scelidosaurus harrisonii (Norman, 2020a). ...
We describe new specimens of the ornithischian dinosaur Scutellosaurus lawleri Colbert, 1981 Colbert, E. H. 1981. A primitive ornithischian dinosaur from the Kayenta Formation of Arizona. Museum of Northern Arizona Bulletin Series 53:1–60. [Google Scholar], from the Lower Jurassic Kayenta Formation of Arizona and discuss their systematic importance. The new specimens represent at least 46 individuals and include two associated skeletons that preserve regions that were poorly known until now, including the skull and pelvis. Computed tomography (CT) assisted our interpretation of these specimens. Using an ornithischian data matrix, we first tested whether the two associated skeletons were justifiably assigned to Scutellosaurus lawleri and found that they group unequivocally with the holotype and paratype specimens. This enabled scoring of 35 character states that were previously unknown, raising the scoring completeness of Scutellosaurus lawleri from 52% to 67%. The results recovered Lesothosaurus diagnosticus as the basal-most member of Neornithischia, while corroborating the monophyly of Thyreophora and Scutellosaurus lawleri as its most basally branching member. In terms of numbers of specimens, Scutellosaurus lawleri is now the most abundant dinosaur known in any Early Jurassic vertebrate fauna. The presence of a second thyreophoran in the Kayenta Formation, along with the presence of Early Jurassic thyreophorans in Europe and Asia, suggests that Thyreophora may have originated in the northern hemisphere. The ornithischians from the Kayenta Formation support a pattern of dinosaurian diversification after the end-Triassic extinction in North America, if not a broader area, that was fueled by independent northward dispersals from the southern hemisphere, supporting dispersal as an early driver of dinosaurian evolution.
... The basioccipital and supraoccipital are also embedded in a matrix, preventing determination as to whether the supraoccipital contributes to the dorsal margin of the foramen magnum. Although the fusion of exoccipitals and opisthotics are widely observed in ornithischian dinosaurs 26,27 , the opisthotic contribution cannot be clearly observed as there is no definitive exposure from the occipital view. There is a horizontal ridge on the posterior surface of exoccipital separating it into equally sized upper and lower parts. ...
Ceratopsia is a diverse dinosaur clade from the Middle Jurassic to Late Cretaceous with early diversification in East Asia. However, the phylogeny of basal ceratopsians remains unclear. Here we report a new basal neoceratopsian dinosaur Beg tse based on a partial skull from Baruunbayan, Ömnögovi aimag, Mongolia. Beg is diagnosed by a unique combination of primitive and derived characters including a primitively deep premaxilla with four premaxillary teeth, a trapezoidal antorbital fossa with a poorly delineated anterior margin, very short dentary with an expanded and shallow groove on lateral surface, the derived presence of a robust jugal having a foramen on its anteromedial surface, and five equally spaced tubercles on the lateral ridge of the surangular. This is to our knowledge the earliest known occurrence of basal neoceratopsian in Mongolia, where this group was previously only known from Late Cretaceous strata. Phylogenetic analysis indicates that it is sister to all other neoceratopsian dinosaurs.
... The anterior margin of the supratemporal fossa is depressed into the rear dorsal surface of the frontal (Fig. 43.7). The anterior end of the frontal tapers anteriorly like that of Cryolophosaurus ellioti , some early ornithischians (Sereno, 1991(Sereno, , 2012, and most pseudosuchian archosaurs (Nesbitt, 2011). ...
Dilophosaurus wetherilli was the largest animal known to have lived on land in North America during the Early Jurassic. Despite its charismatic presence in pop culture and dinosaurian phylogenetic analyses, major aspects of the skeletal anatomy, taxonomy, ontogeny, and evolutionary relationships of this dinosaur remain unknown. Skeletons of this species were collected from the middle and lower part of the Kayenta Formation in the Navajo Nation in northern Arizona. Redescription of the holotype, referred, and previously undescribed specimens of Dilophosaurus wetherilli supports the existence of a single species of crested, large-bodied theropod in the Kayenta Formation. The parasagittal nasolacrimal crests are uniquely constructed by a small ridge on the nasal process of the premaxilla, dorsoventrally expanded nasal, and tall lacrimal that includes a posterior process behind the eye. The cervical vertebrae exhibit serial variation within the posterior centrodiapophyseal lamina, which bifurcates and reunites down the neck. Iterative specimen-based phylogenetic analyses result in each of the additional specimens recovered as the sister taxon to the holotype. When all five specimens are included in an analysis, they form a monophyletic clade that supports the monotypy of the genus. Dilophosaurus wetherilli is not recovered as a ceratosaur or coelophysoid, but is instead a non-averostran neotheropod in a grade with other stem-averostrans such as Cryolophosaurus ellioti and Zupaysaurus rougieri. We did not recover a monophyletic ‘Dilophosauridae.’ Instead of being apomorphic for a small clade of early theropods, it is more likely that elaboration of the nasals and lacrimals of stem-averostrans is plesiomorphically present in early ceratosaurs and tetanurans that share those features. Many characters of the axial skeleton of Dilophosaurus wetherilli are derived compared to Late Triassic theropods and may be associated with macropredation and an increase in body size in Theropoda across the Triassic-Jurassic boundary.
... Most notable and contentious is Pisanosaurus (Casamiquela, 1967), which has consistently been claimed to be the earliest (Norian) ornithischian, following the early descriptive work of Casamiquela (e.g. Sereno, 1991Sereno, , 2012). However, this taxon has been doubted to be an ornithischian (Norman et al., 2004a;Padian, 2013;Baron et al., 2017c) and recently Agnolin & Rozadilla (2018) have established a strong case for this taxon being a silesaurid dinosauromorph (as reasoned independently by Baron et al., 2017c). ...
Scelidosaurus harrisonii is an early (Late Sinemurian) armoured ornithischian dinosaur whose remains have, to date, only been recovered from a restricted location on the south coast of Dorset (Charmouth), England. This dinosaur has been known since 1859, but only on the basis of a partial description found in two articles published in the early 1860s by Richard Owen. The original material, discovered in 1858, comprised the majority of the skull and its associated postcranial skeleton, and represents the first ever, more or less complete dinosaur discovered. In addition to the original material, a number of further discoveries have been made at Charmouth; these latter supplement the information that can be gleaned from the original specimen. This article describes the skull of Scelidosaurus.
The external surface of individual skull bones in ontogenetically relatively mature individuals displays exostoses, a patina of fibrous or granular-textured bone that anchored an external shielding of keratinous scales. There is a small, edentulous rostral beak, behind which is found a row of five heterodont premaxillary teeth. There is a minimum of 22 maxillary teeth and 27 dentary teeth in jaws of the largest well-preserved individuals known to date. Both dentitions (upper and lower) are bowed medially and are sinuous longitudinally. Maxillary and dentary crowns are tilted lingually on their roots, trapezoidal in outline and have crenellate (coarsely denticulate) margins. Adjacent crowns of teeth have mesiodistally (anteroposteriorly) expanded bases that overlap slightly and are consequently arranged en echelon. The dentitions are flanked by deep cheek pouches. Tooth abrasion is usually discontinuous along the dentition. In one individual nearly all teeth seem to be fully emerged and there is little evidence of abrasion. There is no physical evidence of a predentary, but the presence of this (typically ornithischian) element may be inferred from the structure of the symphyseal region of the dentary. The external narial and antorbital fenestrae are comparatively small, whereas the orbit and temporal fenestrae are large and open. A sclerotic ring was undoubtedly present and supported the eyeball, but it is too poorly preserved to allow it to be reconstructed with accuracy. A prominent supraorbital brow ridge overhangs the orbit. There are three osteoderms: palpebral, middle supraorbital and posterior supraorbital, sutured to the dorsal margin of the orbit. The occiput provides an area for attachment of a pair of curved, keratin-sheathed, osteodermal horns.
Epistyloid bones project from the ventrolateral region of the braincase; their distal ends flank the anterolateral region of the neck. Rugose facets on either side of the basioccipital are suggested to have provided attachment sites for the epistyloid bones. Internally, the skull has a deeply vaulted snout and the nasal chambers are roofed by what are here named epivomer bones that appear to have been sutured to the dorsolateral edges of the vomers. Unusually, among dinosaurs generally, an epipterygoid is preserved attached to the dorsolateral surface of the pterygoid; there is no obvious point of articulation for the epipterygoid against the lateral wall of the braincase. A deep pit on the posterior surface of the quadrate of an immature specimen is suggestive of the existence of a remnant of cranial pneumatism. This pit becomes occluded in larger, more mature specimens.
... Egawa et al (2018) further investigated the developmental mechanism of acetabular perforation in the avian hip joint, and proposed that the evolution of a membranous inner acetabular wall in dinosaurs resulted from the loss of cartilaginous anlagen at the inner acetabular wall during embryogenesis. Presence of a perforate acetabulum has thus been used by numerous authors (Sereno, 1991a;Kubo & Benton, 2007;Brusatte et al. 2010) as an indicator of adducted hind limb postures in archosaurs. These postural inferences based on acetabular perforation do not necessarily contradict our inference of acetabular perforation as an osteological correlate for intracapsular ligaments. ...
Extant archosaurs exhibit highly divergent articular soft tissue anatomies between avian and crocodilian lineages. However, the general lack of understanding of the dynamic interactions among archosaur joint soft tissues has hampered further inferences about the function and evolution of these joints. Here we use contrast-enhanced computed tomography to generate 3D surface models of the pelvis, femora, and hip joint soft tissues in an extant archosaur, the American alligator. The hip joints were then animated using marker-based X-Ray Reconstruction of Moving Morphology (XROMM) to visualize soft tissue articulation during forward terrestrial locomotion. We found that the anatomical femoral head of the alligator travels beyond the cranial extent of the bony acetabulum and does not act as a central pivot, as has been suggested for some extinct archosaurs. Additionally, the fibrocartilaginous surfaces of the alligator's antitrochanter and femoral neck remain engaged during hip flexion and extension, similar to the articulation between homologous structures in birds. Moreover, the femoral insertion of the ligamentum capitis moves dorsoventrally against the membrane-bound portion of the medial acetabular wall, suggesting that the inner acetabular foramen constrains the excursion of this ligament as it undergoes cyclical stretching during the step cycle. Finally, the articular surface of the femoral cartilage model interpenetrates with those of the acetabular labrum and antitrochanter menisci; we interpret such interpenetration as evidence of compressive deformation of the labrum and of sliding movement of the menisci. Our data illustrate the utility of XROMM for studying in vivo articular soft tissue interactions. These results also allow us to propose functional hypotheses for crocodilian hip joint soft tissues, expanding our knowledge of vertebrate connective tissue biology and the role of joint soft tissues in locomotor behavior.
... The systematic relationship of basal neornithischians is one of the most problematic areas in ornithischian phylogeny (Sereno 1999;Butler and Knoll 2005;Butler et al. 2008). At present, there are only a few records of basal neornithischians, including Lesothosaurus diagnosticus from the Early Jurassic upper Elliot Formation of South Africa and Lesotho (Thulborn 1970(Thulborn , 1971(Thulborn , 1972Galton 1978;Sereno 1991;Knoll 2002), Kulindadromeus zabaikalicus from the Middle Jurassic Ukureyskaya Formation of Chita Region, Russia (Godefroit et al. 2014), Hexinlusaurus multidens and Agilisaurus louderbacki from the Middle Jurassic Lower Shaximiao Formation of Zigong, Sichuan, China (He and Cai 1983;Peng 1990Peng , 1992Barrett et al. 2005), and Nanosaurus agilis from the Late Jurasssic Morrison Formation of USA (Marsh 1877;Galton 1983Galton , 2007Carpenter and Galton 2018). In 2016, a field team from the No. 208 Hydrogeological and Engineering Geological Team, Chongqing Bureau of Geological and Mineral Resource Exploration and Development discovered a new fossilbearing bed from the Middle Jurassic Xintiangou Formation of Laojun Village, Puan Township, Yunyang County, Chongqing Municipality, People's Republic of China. ...
A new neornithischian dinosaur, Sanxiasaurus modaoxiensis gen. et sp. nov., is described based on a partial postcranial skeleton from the Middle Jurassic Xintiangou Formation of Yunyang, Chongqing Municipality, China. It is the first neornithischian dinosaur from the Middle Jurassic Xintiangou Formation of Sichuan Basin, and also the earliest record of a neornithischian dinosaur in Asia. It differs from other neornithischians in possessing the following unique combination of characters: at least four sacrals; humerus strongly bowed laterally along its length; obturator process located at mid-length of ischial shaft; lesser trochanter of femur broadened, wing shaped and subequal in anteroposterior width to greater trochanter; distal tibia with elongate posterolateral process. Phylogenetic analysis shows that Sanxiasaurus modaoxiensis is positioned near the base of neornithischia. This find extends the Asia neornithischian stratigraphic horizon to the lower Middle Jurassic.
... Canals that housed palatine vessel branches have also been reported in Maiasaura (Horner 1983). This same condition was described in Lesothosaurus by Sereno (1991), providing further evidence that a wide array of ornithischians housed the palatine anastomotic branches within the premaxilla. ...
Body size has thermal repercussions that impact physiology. Large‐bodied dinosaurs potentially retained heat to the point of reaching dangerous levels, whereas small dinosaurs shed heat relatively easily. Elevated body temperatures are known to have an adverse influence on neurosensory tissues and require physiological mechanisms for selective brain and eye temperature regulation. Vascular osteological correlates in fossil dinosaur skulls from multiple clades representing different body‐size classes were identified and compared. Neurovascular canals were identified that differentiate thermoregulatory strategies involving three sites of evaporative cooling that are known in extant diapsids to function in selective brain temperature regulation. Small dinosaurs showed similarly sized canals, reflecting a plesiomorphic balanced pattern of blood supply and a distributed thermoregulatory strategy with little evidence of enhancement of any sites of thermal exchange. Large dinosaurs, however, showed a more unbalanced vascular pattern whereby certain sites of thermal exchange were emphasized for enhanced blood flow, reflecting a more focused thermal strategy. A quantitative, statistical analysis of canal cross‐sectional area was conducted to test these anatomical results, confirming that large‐bodied, and often large‐headed, species showed focused thermal strategies with enhanced collateral blood flow to certain sites of heat exchange. Large theropods showed evidence for a plesiomorphic balanced blood flow pattern, yet evidence for vascularization of the large antorbital paranasal air sinus indicates theropods may have had a fourth site of heat exchange as part of a novel focused thermoregulatory strategy. Evidence presented here for differing thermoregulatory strategies based on size and phylogeny helps refine our knowledge of dinosaur physiology. Anat Rec, 303:1075–1103, 2020. © 2019 American Association for Anatomy
... This sedimentary unit was deposited during the latest Ladinian−early Carnian (Marsicano et al., 2016;Ezcurra et al., 2017) and the lower member preserves at least two distinct vertebrate assemblages , the upper of which yielded three or four species of early dinosauromorphs: the lagerpetid Lagerpeton chanarensis (Romer, 1971;Sereno and Arcucci, 1994a), the earliest branching dinosauriform Marasuchus lilloensis (Romer, 1971;Bonaparte, 1975;Sereno and Arcucci, 1994b), and Lewisuchus admixtus and Pseudolagosuchus major (Romer, 1972;Arcucci, 1987Arcucci, , 1997Bittencourt et al., 2014), two possible silesaurids . The anatomical knowledge provided by these early species of the avian lineage has been pivotal to shed light on the higher-level relationships of dinosaurs among Triassic archosauriforms (e.g., Bonaparte, 1975;Gauthier, 1986;Sereno, 1991;Novas, 1996) and the relatively generalized skeletons of Marasuchus lilloensis, Lewisuchus admixtus, and Pseudolagosuchus major, in comparison to other dinosauriforms (e.g., Asilisaurus kongwe, Silesaurus opolensis, Sacisaurus agudoensis), provide key information about the body plan of the closest members to Dinosauria, character transformations, and evolutionary scenarios (e.g., Bonaparte, 1975;Arcucci, 1994a, 1994b;Bittencourt et al., 2014). Nevertheless, the anatomical and, hence, phylogenetic information provided by the Chañares dinosauromorphs have been limited by missing information of some anatomical regions, such as the skull and forelimb of Lagerpeton chanarensis, the axial skeleton of Pseudolagosuchus major, and the limbs of Lewisuchus admixtus . ...
The lower Carnian levels of the Chañares Formation (Ischigualasto‐Villa Unión Basin, La Rioja Province) have yielded some of the most informative dinosaur precursor species known so far. However, these species are based on partial skeletons that in several cases hamper the comparison between them because of the absence of overlapping bones. This has generated a contentious debate during the last 20 years about the synonymy between two of these species, Lewisuchus admixtus and Pseudolagosuchus major. Here, we describe a new dinosauriform partial skeleton (CRILAR‐Pv 552) recently collected in the Chañares Formation that preserves previously unknown anatomical regions for the dinosaur precursors of this unit (e.g., premaxilla, inner ear, anterior zeugopodium) and allows comparisons with other dinosauriform specimens. CRILAR‐Pv 552 is referred to Lewisuchus admixtus because it possesses a proportionally large skull, a laterally projected, shelf‐like ridge on the jugal, and recurved, finely serrated middle–posterior maxillary and dentary teeth ankylosed to the bone, and the absence of a coracoid foramen. The new specimen preserves a dorsally bowed dentary with a lateroventral shelf that is identical to a dentary associated with the holotype of Lewisuchus admixtus. Additionally, the morphology of the new specimen is completely congruent with that of specimens of Pseudolagosuchus major, bolstering the hypothesis that the latter species is a subjective junior synonym of Lewisuchus admixtus. A preliminary phylogenetic analysis with updated scorings for Lewisuchus admixtus found this species at the base of Silesauridae. Anat Rec, 303:1393–1438, 2020. © 2019 American Association for Anatomy
... The crista prootica is not as well preserved on the right side. On both sides, posterior to the fenestra ovalis, are two small foramina that likely represent the exits of the hypoglossal nerve (XII), as in the basal ornithischian Lesothosaurus (Sereno 1991). Anterior to the fenestra ovalis, a groove is present extending anteroventrally. ...
Two partial skeletons from Montana represent the northernmost occurrences of Stegosauria within North America. One of these specimens represents the northernmost dinosaur fossil ever recovered from the Morrison Formation. Consisting of fragmentary cranial and postcranial remains, these specimens are contributing to our knowledge of the record and distribution of dinosaurs within the Morrison Formation from Montana. While the stegosaurs of the Morrison Formation consist of Alcovasaurus, Hesperosaurus, and Stegosaurus, the only positively identified stegosaur from Montana thus far is Hesperosaurus. Unfortunately, neither of these new specimens exhibit diagnostic autapomorphies. Nonetheless, these specimens are important data points due to their geographic significance, and some aspects of their morphologies are striking. In one specimen, the teeth express a high degree of wear usually unobserved within this clade—potentially illuminating the progression of the chewing motion in derived stegosaurs. Other morphologies, though not histologically examined in this analysis, have the potential to be important indicators for maturational inferences. In suite with other specimens from the northern extent of the formation, these specimens contribute to the ongoing discussion that body size may be latitudinally significant for stegosaurs—an intriguing geographical hypothesis which further emphasizes that size is not an undeviating proxy for maturity in dinosaurs.
... The anatomy of the cervical vertebrae is important in the assessment of the phylogenetic position of basal dinosaurs, because this region can contain several potential saurischian synapomorphies. The presence of epipophyses on the postzygapophyses of cranial cervical vertebrae, for instance, was regarded as a synapomorphy of Saurischia by Gauthier (1986), although this structure is also present in basal ornithischians (Santa Luca 1980;Sereno 1991a;Langer & Benton 2006), and in some non-dinosaur archosaurs (Langer & Benton 2006;Nesbitt et al. 2007). and Langer & Benton (2006) considered the presence of epipophyses on mid-caudal cervical vertebrae as a saurischian synapomorphy. ...
We redescribe the holotype of the saurischian dinosaur Staurikosaurus pricei Colbert, 1970 from Late Triassic Santa Maria Formation (southern Brazil), following additional preparation that revealed new anatomical features. A revised diagnosis is proposed and the published synapomorphies for Dinosauria and less inclusive clades (e.g. Saurischia) are evaluated for this species. Some characters previously identified as present in the holotype, including the intramandibular joint, hyposphene-hypantrum articulations in dorsal vertebrae, and a cranial trochanter and trochanteric shelf on the femur, cannot be confirmed due to poor preservation or are absent in the available material. In addition, postcranial characters support a close relationship between S. pricei and Herrerasaurus ischigualastensis Reig, 1963 (Late Triassic, Argentina), forming the clade Herrerasauridae. Several pelvic and vertebral characters support the placement of S. pricei as a saurischian dinosaur. Within Saurischia, characters observed in the holotype, including the anatomy of the dentition and caudal vertebrae, support theropod affinities. However, the absence of some characters observed in the clades Theropoda and Sauropodomorpha suggests that S. pricei is not a member of Eusaurischia. Most morphological characters discussed in previous phylogenetic studies cannot be assessed for S. pricei because of the incompleteness of the holotype and only known specimen. The phylogenetic position of S. pricei is constrained by that of its sister taxon H. ischigualastensis, which is known from much more complete material.
... Although eurypodans are currently unknown from Early Jurassic deposits, non-eurypodan ("basal") thyreophorans were diverse and widespread at this time. These include: Scutellosaurus (Colbert 1981) and another indeterminate taxon (Padian 1989) from the Sinemurian-Pliensbachian Kayenta Formation of Arizona, USA; Scelidosaurus (Owen 1861) from the Sinemurian-lower Pliensbachian Charmouth Mudstone Formation of England; Emausaurus (Haubold 1990) from the Toarcian of Germany; an indeterminate thyreophoran ("Lusitanosaurus") from the Sinemurian of Portugal (Norman et al. 2004); and Lesothosaurus from the upper Elliot and Clarens Formations of South Africa and Lesotho (Sereno 1991;Porro et al. 2015;Baron et al. 2017b), which is thought to be of Hettangian-Sinemurian age (Olsen and Galton 1984). In addition, the recently described Laquintasaura (Barrett et al. 2014), from the earliest Hettangian La Quinta Formation of Venezuela, has been identified as an early-diverging thyreophoran dinosaur in recent cladistic analyses (Baron et al. 2017b;Raven and Maidment 2017). ...
The earliest definitive ornithischian dinosaurs are from the Early Jurassic and are rare components of early dinosaur faunas. The Lower Lufeng Formation (Hettangian–Sinemurian) of Yunnan Province, China, has yielded a diverse Early Jurassic terrestrial vertebrate fauna. This includes several incomplete specimens have been referred to Ornithischia, including the type specimen of the thyreophoran “Tatisaurus” and other generically indeterminate material. The highly fragmentary Lufeng ornithischian Bienosaurus lufengensis was described briefly in 2001 and identified as an ankylosaurian dinosaur. Recent studies have cast doubt on this hypothesis, however, and given that the referral of Bienosaurus to Ankylosauria would result in an extensive ghost-lineage extending between it and the first definitive eurypodans (ankylosaurs + stegosaurs) in the Middle Jurassic, the holotype specimen is re-examined and re-described. We identify Bienosaurus as a probable thyreophoran dinosaur, although the fragmentary nature of the material and the absence of autapomorphies means that the specimen should be regarded as a nomen dubium.
... Another challenging issue concerns the detailed analysis of fossil records to test the aforementioned hypothetical scenario. At a glance, in most basal dinosaurs, the acetabula are perforated but the femoral head shape is mismatched [1,[51][52][53], which cannot be explained only by the mechanism we elucidate here (interaction of the pelvic anlagen with secretory molecules from the interzone) and would require auxiliary hypotheses, e.g. partial ossification failure similar to Charig's hypothesis [1], and a sophisticated methodology for scientific inference of the morphogenesis in extinct organisms. ...
Understanding morphological evolution in dinosaurs from a mechanistic viewpoint requires the elucidation of the morphogenesis that gave rise to derived dinosaurian traits, such as the perforated acetabulum. In the current study, we used embryos of extant animals with ancestral- and dinosaur-type acetabula, namely, geckos and turtles (with unperforated acetabulum), and birds (with perforated acetabulum). We performed comparative and experimental analyses, focusing on inter-tissue interaction during embryogenesis, and found that the avian perforated acetabulum develops via a secondary loss of cartilaginous tissue in the acetabular region. This cartilage loss might be mediated by inter-tissue interaction with the hip interzone, a mesenchymal tissue that exists in the embryonic joint structure. Furthermore, the data indicate that avian pelvic anlagen is more susceptible to paracrine molecules, e.g. Wnt ligand, secreted by the hip interzone than ‘reptilian’ anlagen. We hypothesize that during the emergence of dinosaurs, the pelvic anlagen became susceptible to the Wnt ligand, which led to the loss of the cartilaginous tissue and to the perforation in the acetabular region. Thus, the current evolutionary-developmental biology study deepens our understanding of morphological evolution in dinosaurs and provides it with a novel perspective.
... For instance, skeletal consistency of the silesaurid T. smalli was resolved after a long examination process and appears to be the closest example to the TTU-P11254 assemblage. Departing from the original diagnosis of Chatterjee (1984), the holotype of T. smalli is now restricted to two anterior jaw fragments; whereas the associated posterior jaw fragment now referred to S. inexpectatus and the affinity of the other bones remain unresolved (Sereno, 1991b;Hunt and Lucas, 1994;Irmis et al., 2007;Nesbitt et al., 2007;Martz et al., 2013). The entangled condition of the T. smalli and TTU-P11254 assemblages may be a result of the burial process. ...
A bone assemblage composed of intermixed small cranial and postcranial fragments from the Post Quarry of Texas, USA, is described. The skeletal elements represent multiple individuals of different taxa, including a partial dorsal column assigned to Vancleavea campi and an incomplete dentary referred to a new genus and species of a small-sized basal dinosauriform. Ankylothecodont dental implantation of the dinosauriform dentary bears strong resemblance to silesaurids. A fragmentary archosauromorph braincase is another intriguing element of the assemblage; it displays a striking contrast of a derived otoccipital on a plesiomorphic basioccipital. Poor preservation prevents more conclusive taxonomic assignments for the rest of the skeletal elements. The observed attrition and entangling in this bone assemblage reflect the complexities of the Dockum land tetrapod taphonomy.
... A total of 11 nonankylosaurid taxa were also included to make sure character-states were optimized correctly at the base of Ankylosauridae. The Jurassic ornithischian Lesothosaurus diagnosticus was constrained as the outgroup taxon because it is just basal to the Thyreophora-Neornithischia split and known from nearly complete remains (Crompton, 1968;Thulborn, 1971;Galton, 1978;Sereno, 1991). The 10 nonankylosaurid thyreophoran taxa include the early thyreophorans Scutellosaurus (Colbert, 1981), Emausaurus (Haubold, 1990), and Scelidosaurus (Owen, 1859), the stegosaurs Huayangosaurus (Dong, Tang & Zhou, 1982) and Tuojiangosaurus (Dong et al., 1977), the basal ankylosaurian Minmi (Molnar, 1980), the nodosaurids Europelta and Cedarpelta , and the polacanthids Mymoorapelta (Kirkland & Carpenter, 1994) and Gargoyleosaurus (Carpenter, Miles & Cloward, 1998 The analysis contains 24 putative ankylosaurid taxa and include recently described taxa such as Ziapelta sanjuanensis and Zaraapelta nomadis (Arbour, Currie & Badamgarav, 2014), Akainacephalus johnsoni (described herein), as well as the recently re-evaluated Dyoplosaurus acutosquameus (Arbour, Burns & Sissons, 2009), Scolosaurus cutleri (Penkalski & Blows, 2013), and Oohkotokia horneri (Penkalski, 2014). ...
A partial ankylosaurid skeleton from the upper Campanian Kaiparowits Formation of southern Utah is recognized as a new taxon, Akainacephalus johnsoni , gen. et sp. nov. The new taxon documents the first record of an associated ankylosaurid skull and postcranial skeleton from the Kaiparowits Formation. Preserved material includes a complete skull, much of the vertebral column, including a complete tail club, a nearly complete synsacrum, several fore- and hind limb elements, and a suite of postcranial osteoderms, making Akainacephalus johnsoni the most complete ankylosaurid from the Late Cretaceous of southern Laramidia. Arrangement and morphology of cranial ornamentation in Akainacephalus johnsoni is strikingly similar to Nodocephalosaurus kirtlandensis and some Asian ankylosaurids (e.g., Saichania chulsanensis , Pinacosaurus grangeri , and Minotaurasaurus ramachandrani ); the cranium is densely ornamented with symmetrically arranged and distinctly raised ossified caputegulae which are predominantly distributed across the dorsal and dorsolateral regions of the nasals, frontals, and orbitals. Cranial caputegulae display smooth surface textures with minor pitting and possess a distinct conical to pyramidal morphology which terminates in a sharp apex. Character analysis suggests a close phylogenetic relationship with N. kirtlandensis , M. ramachandrani , Tarchia teresae , and S. chulsanensis , rather than with Late Cretaceous northern Laramidian ankylosaurids (e.g., Euoplocephalus tutus , Anodontosaurus lambei , and Ankylosaurus magniventris ). These new data are consistent with evidence for distinct northern and southern biogeographic provinces in Laramidia during the late Campanian. The addition of this new ankylosaurid taxon from southern Utah enhances our understanding of ankylosaurid diversity and evolutionary relationships. Potential implications for the geographical distribution of Late Cretaceous ankylosaurid dinosaurs throughout the Western Interior suggest multiple time-transgressive biogeographic dispersal events from Asia into Laramidia.
Thescelosaurines are a group of early diverging, ornithischian dinosaurs notable for their conservative bauplans and mosaic of primitive features. Although abundant within the latest Cretaceous ecosystems of North America, their record is poor to absent in earlier assemblages, leaving a large gap in our understanding of their evolution, origins, and ecological roles. Here we report a new small bodied thescelosaurine—Fona herzogae gen. et sp. nov.—from the Mussentuchit Member of the Cedar Mountain Formation, Utah, USA. Fona herzogae is represented by multiple individuals, representing one of the most comprehensive skeletal assemblages of a small bodied, early diverging ornithischian described from North America to date. Phylogenetic analysis recovers Fona as the earliest member of Thescelosaurinae, minimally containing Oryctodromeus, and all three species of Thescelosaurus, revealing the clade was well‐established in North America by as early as the Cenomanian, and distinct from, yet continental cohabitants with, their sister clade, Orodrominae. To date, orodromines and thescelosaurines have not been found together within a single North American ecosystem, suggesting different habitat preferences or competitive exclusion. Osteological observations reveal extensive intraspecific variation across cranial and postcranial elements, and a number of anatomical similarities with Oryctodromeus, suggesting a shared semi‐fossorial lifestyle.
A reversion to secondary quadrupedality is exceptionally rare in nature, yet the convergent re-evolution of this locomotor style occurred at least four separate times within Dinosauria. Facultative quadrupedality, an intermediate state between obligate bipedality and obligate quadrupedality, may have been an important transitional step in this locomotor shift, and is proposed for a range of basal ornithischians and sauropodomorphs. Advances in virtual biomechanical modeling and simulation have allowed for the investigation of limb anatomy and function in a range of extinct dinosaurian species, yet this technique has not been widely applied to explore facultatively quadrupedal gait generation. This study places its focus on Scutellosaurus, a basal thyreophoran that has previously been described as both an obligate biped and a facultative quadruped. The functional anatomy of the musculoskeletal system (myology, mass properties, and joint ranges of motion) has been reconstructed using extant phylogenetic bracketing and comparative anatomical datasets. This information was used to create a multi-body dynamic locomotor simulation that demonstrates that whil quadrupedal gaits were physically possible, they did not outperform bipedal gaits is any tested metric. Scutellosaurus cannot therefore be described as an obligate biped, but we would predict its use of quadrupedality would be very rare, and perhaps restricted to specific activities such as foraging. This finding suggests that basal thyreophorans are still overwhelmingly bipedal but is perhaps indicative of an adaptive pathway for later evolution of quadrupedality.
The extent to which evolution is deterministic is a key question in biology,¹,²,³,⁴,⁵,⁶,⁷,⁸,⁹ with intensive debate on how adaptation⁶,¹⁰,¹¹,¹²,¹³ and constraints¹⁴,¹⁵,¹⁶ might canalize solutions to ecological challenges.⁴,⁵,⁶ Alternatively, unique adaptations¹,⁹,¹⁷ and phylogenetic contingency¹,³,¹⁸ may render evolution fundamentally unpredictable.³ Information from the fossil record is critical to this debate,¹,²,¹¹ but performance data for extinct taxa are limited.⁷ This knowledge gap is significant, as general morphology may be a poor predictor of biomechanical performance.¹⁷,¹⁹,²⁰ High-fiber herbivory originated multiple times within ornithischian dinosaurs,²¹ making them an ideal clade for investigating evolutionary responses to similar ecological pressures.²² However, previous biomechanical modeling studies on ornithischian crania¹⁷,²³,²⁴,²⁵ have not compared early-diverging taxa spanning independent acquisitions of herbivory. Here, we perform finite-element analysis on the skull of five early-diverging members of the major ornithischian clades to characterize morphofunctional pathways to herbivory. Results reveal limited functional convergence among ornithischian clades, with each instead achieving comparable performance, in terms of reconstructed patterns and magnitudes of functionally induced stress, through different adaptations of the feeding apparatus. Thyreophorans compensated for plesiomorphic low performance through increased absolute size, heterodontosaurids expanded jaw adductor muscle volume, ornithopods increased jaw system efficiency, and ceratopsians combined these approaches. These distinct solutions to the challenges of herbivory within Ornithischia underpinned the success of this diverse clade. Furthermore, the resolution of multiple solutions to equivalent problems within a single clade through macroevolutionary time demonstrates that phenotypic evolution is not necessarily predictable, instead arising from the interplay of adaptation, innovation, contingency, and constraints.
Lesothosaurus diagnosticus is a small ornithischian dinosaur from the Lower Jurassic Massospondylus Assemblage Zone of the upper Elliot Formation of the Karoo Basin of South Africa and Lesotho. The Early Jurassic age, comparatively large sample size, and multiple growth stages of Lesothosaurus make it an excellent taxon for investigating the plesiomorphic condition of ornithischian growth. Here, we examine the osteohistology of an ontogenetic series of Lesothosaurus diagnosticus using multiple limb elements to assess the maximum body size, life history, growth dynamics and potential for sociality in one of the earliest‐branching ornithischian dinosaurs. We found that Lesothosaurus grew rapidly during early and mid‐ontogeny (as shown by its highly vascularized woven‐parallel complex) with its growth rate decreasing between 2–4 years of age, possibly indicating the onset of reproductive maturity. However, an external fundamental system, indicating a cessation in growth, could not be confirmed in any of the individuals studied, suggesting that at 6 years of age, this taxon was still not fully grown. The presence of multiple individuals of varying ontogenetic stages in a monodominant bone bed strongly suggests that it lived in multigenerational herds, indicating that, along with the Venezuelan Laquintasaura venezuelae, social behaviour developed very early in ornithischian evolutionary history.
Dinosaur evolution is marked by numerous independent shifts from bipedality to quadrupedality. Sauropodomorpha is one of the lineages that transitioned from small bipedal forms to graviportal quadrupeds, with an array of intermediate postural strategies evolving in non-sauropodan sauropodomorphs. This locomotor shift is reflected by multiple modifications of the appendicular skeleton, coupled with a drastic rearrangement of the limb musculature. Here, we describe the osteological correlates of appendicular muscle attachment of the Late Triassic sauropodomorph Thecodontosaurus antiquus from multiple well-preserved specimens and provide the first complete forelimb and hindlimb musculature reconstruction of an early-branching sauropodomorph. Comparisons with other sauropodomorphs and early dinosaurs reveal a unique combination of both plesiomorphic and derived musculoskeletal features. The diversity of appendicular osteological correlates among early dinosaurs and their relevance in muscle reconstruction are discussed. In line with previous evidence, aspects of the limb muscle arrangement, such as conspicuous correlates of lower limb extensors and flexors and low moment arms of hip extensors and flexors, suggest Thecodontosaurus was an agile biped. This reconstruction helps to elucidate the timing of important modifications of the appendicular musculature in the evolution of sauropodomorphs which facilitated the transition to quadrupedalism and contributed to their evolutionary success.
Knowledge regarding the early evolution within the dinosaurian clade Ankylopollexia drastically increased over the past two decades, in part because of an increase in described taxa from the Early Cretaceous of North America. These advances motivated the recent completion of extensive preparation and conservation work on the holotype and only known specimen of Dakotadon lakotaensis , a basal ankylopollexian from the Lakota Formation of South Dakota. That specimen (SDSM 8656) preserves a partial skull, lower jaws, a single dorsal vertebra, and two caudal vertebrae. That new preparation work exposed several bones not included in the original description and revealed that other bones were previously misidentified. The presence of extensive deformation in areas of the skull is also noted that influenced inaccuracies in prior descriptions and reconstructions of this taxon. In addition to providing an extensive re-description of D. lakotaensis, this study reviews previously proposed diagnoses for this taxon, identifies three autapomorphies, and provides an extensive differential diagnosis. Dakotadon lakotaensis is distinct from the only other ankylopollexian taxon known from the Lakota Formation, Osmakasaurus depressus , in the presence of two prominent, anteroposteriorly oriented ridges on the ventral surfaces of the caudal vertebrae, the only overlapping material preserved between these taxa. The systematic relationships of Dakotadon lakotaensis are evaluated using both the parsimony and posterior probability optimality criteria, with both sets of analyses recovering D. lakotaensis as a non-hadrosauriform ankylopollexian that is more closely related to taxa from the early Cretaceous (e.g., Iguanacolossus , Hippodraco , and Theiophytalia ) than to more basally situated taxa from the Jurassic (e.g., Camptosaurus, Uteodon ). This taxonomic work is supplemented by field work that relocated the type locality, confirming its provenance from unit L2 (lower Fuson Member equivalent) of the Lakota Formation. Those data, combined with recently revised ages for the members of the Lakota Formation based on charophyte and ostracod biostratigraphy, constrain the age of this taxon to the late Valanginian to early Hauterivian. The only other equivalent-aged ankylopollexian taxon from North America, the poorly known Planicoxa venenica from the Poison Strip Sandstone of Utah, preserves caudal vertebrae that bear the same ventral ridges seen in D. lakotaensis , raising the possibility of a close affinity between these taxa.
Knowledge regarding the early evolution within the dinosaurian clade Ankylopollexia drastically increased over the past two decades, in part because of an increase in described taxa from the Early Cretaceous of North America. These advances motivated the recent completion of extensive preparation and conservation work on the holotype and only known specimen of Dakotadon lakotaensis , a basal ankylopollexian from the Lakota Formation of South Dakota. That specimen (SDSM 8656) preserves a partial skull, lower jaws, a single dorsal vertebra, and two caudal vertebrae. That new preparation work exposed several bones not included in the original description and revealed that other bones were previously misidentified. The presence of extensive deformation in areas of the skull is also noted that influenced inaccuracies in prior descriptions and reconstructions of this taxon. In addition to providing an extensive re-description of D. lakotaensis, this study reviews previously proposed diagnoses for this taxon, identifies two autapomorphies, and provides an extensive differential diagnosis. Dakotadon lakotaensis is distinct from the only other ankylopollexian taxon known from the Lakota Formation, Osmakasaurus depressus , in the presence of two prominent, anteroposteriorly oriented ridges on the ventral surfaces of the caudal vertebrae, the only overlapping material preserved between these taxa. The systematic relationships of D. lakotaensis are evaluated using both the parsimony and posterior probability optimality criteria, with both sets of analyses recovering D. lakotaensis as a non-hadrosauriform ankylopollexian that is more closely related to taxa from the Early Cretaceous (e.g., Iguanacolossus , Hippodraco , and Theiophytalia ) than to more basally situated taxa from the Jurassic (e.g., Camptosaurus, Uteodon ). This taxonomic work is supplemented by field work that relocated the type locality, confirming its provenance from unit L2 (lower Fuson Member equivalent) of the Lakota Formation. Those data, combined with recently revised ages for the members of the Lakota Formation based on charophyte and ostracod biostratigraphy, constrain the age of this taxon to the late Valanginian to early Barremian.
Knowledge regarding the early evolution within the dinosaurian clade Ankylopollexia drastically increased over the past two decades, in part because of an increase in described taxa from the Early Cretaceous of North America. These advances motivated the recent completion of extensive preparation and conservation work on the holotype and only known specimen of Dakotadon lakotaensis , a basal ankylopollexian from the Lakota Formation of South Dakota. That specimen (SDSM 8656) preserves a partial skull, lower jaws, a single dorsal vertebra, and two caudal vertebrae. That new preparation work exposed several bones not included in the original description and revealed that other bones were previously misidentified. The presence of extensive deformation in areas of the skull is also noted that influenced inaccuracies in prior descriptions and reconstructions of this taxon. In addition to providing an extensive re-description of D. lakotaensis, this study reviews previously proposed diagnoses for this taxon, identifies two autapomorphies, and provides an extensive differential diagnosis. Dakotadon lakotaensis is distinct from the only other ankylopollexian taxon known from the Lakota Formation, Osmakasaurus depressus , in the presence of two prominent, anteroposteriorly oriented ridges on the ventral surfaces of the caudal vertebrae, the only overlapping material preserved between these taxa. The systematic relationships of D. lakotaensis are evaluated using both the parsimony and posterior probability optimality criteria, with both sets of analyses recovering D. lakotaensis as a non-hadrosauriform ankylopollexian that is more closely related to taxa from the Early Cretaceous (e.g., Iguanacolossus , Hippodraco , and Theiophytalia ) than to more basally situated taxa from the Jurassic (e.g., Camptosaurus, Uteodon ). This taxonomic work is supplemented by field work that relocated the type locality, confirming its provenance from unit L2 (lower Fuson Member equivalent) of the Lakota Formation. Those data, combined with recently revised ages for the members of the Lakota Formation based on charophyte and ostracod biostratigraphy, constrain the age of this taxon to the late Valanginian to early Barremian.
Taxonomic identification of fossils based on morphometric data traditionally relies on the use of standard linear models to classify such data. Machine learning and decision trees offer powerful alternative approaches to this problem but are not widely used in palaeontology. Here, we apply these techniques to published morphometric data of isolated theropod teeth in order to explore their utility in tackling taxonomic problems. We chose two published datasets consisting of 886 teeth from 14 taxa and 3020 teeth from 17 taxa, respectively, each with five morphometric variables per tooth. We also explored the effects that missing data have on the final classification accuracy. Our results suggest that machine learning and decision trees yield superior classification results over a wide range of data permutations, with decision trees achieving accuracies of 96% in classifying test data in some cases. Missing data or attempts to generate synthetic data to overcome missing data seriously degrade all classifiers predictive accuracy. The results of our analyses also indicate that using ensemble classifiers combining different classification techniques and the examination of posterior probabilities is a useful aid in checking final class assignments. The application of such techniques to isolated theropod teeth demonstrate that simple morphometric data can be used to yield statistically robust taxonomic classifications and that lower classification accuracy is more likely to reflect preservational limitations of the data or poor application of the methods.
Dental replacement in Heterodontosauridae has been debated over the last five decades primarily on indirect evidence, such as the development of wear facets and the position of erupted teeth. Direct observation of unerupted teeth provides unambiguous data for understanding tooth replacement but this has been done only for Heterodontosaurus and Fruitadens. This study addresses dental replacement in Manidens condorensis based on the positioning of functional and replacement teeth using microcomputed tomography data, differential wear along the dentition and the differences in labiolingual/apicobasal level of functional teeth. Dental replacement in Manidens condorensis was continuous in an anterior-to-posterior wave pattern, with asynchronous tooth eruption and the addition of new teeth posteriorly to the toothrow during ontogeny. Manidens shows the first evidence of dental replacement for the large dentary caniniform in Heterodontosauridae, which possibly had replacement timing distinct from the cheek dentition. Newly erupted teeth imbricate in a mesial cavity-distal crown base relationship during eruption, so that imbrication of the mid-posterior dentition remains unaltered during tooth replacement. The presence/absence of a small caniniform tooth in the D3 position of several specimens suggests possible intraspecific dimorphism in Manidens. On longitudinal sections of isolated crowns, the histological features such as Howship's lacunae and odontoclast spaces are similar in size to extant reptiles. The differential wear decreasing posteriorly and hypothetical Z-spacing below 2.3 in Manidens are similar to basal ornithischians. Tooth replacement in Heterodontosauridae (and other early ornithischians) provides key information for understanding the dynamics of jaw function and craniomandibular specialization to herbivory.
This work attempts at providing a revised framework for ornithischian phylogeny, based on an exhaustive data compilation of already published analyses, a critical re-evaluation of osteological characters and an in-depth checking of characters scoring to fix mistakes that have accumulated in previous analyses; we have also included recently described basal ornithischians, marginocephalians and ornithopods. ‘Heterodontosaurids’ are recovered as a paraphyletic group of basal Marginocephalia that progressively lead to the dome-headed ‘true’ pachycephalosaurs. ‘Heterodontosaurids’ consequently fall within Pachycephalosauria sensu Sereno, 1998. The reconfiguration of basal cerapodan relationships pulls the origins of ornithopods to the earliest stages of the Jurassic. Based on the present analysis, we also discuss ornithopod relationships, with a particular focus on basal Iguanodontia. Tenontosaurus is found as the basalmost iguanodontian. The monophyly of Rhabdodontomorpha in a position more derived than Tenontosaurus is supported by the present analysis.
Choristoderes are extinct neodiapsid reptiles that are well known for their unusual cranial anatomy, possessing an elongated snout and expanded temporal arches. Although choristodere skulls are well described externally, their internal anatomy remains unknown. An internal description was needed to shed light on peculiarities of the choristodere skull, such as paired gaps on the ventral surface of the skull that may pertain to the fenestra ovalis, and a putative neomorphic ossification in the lateral wall of the braincase. Our goals were: (i) to describe the cranial elements of Champsosaurus lindoei in three dimensions; (ii) to describe paired gaps on the ventral surface of the skull to determine if these are indeed the fenestrae ovales; (iii) to illustrate the morphology of the putative neomorphic bone; and (iv) to consider the possible developmental and functional origins of the neomorph. We examined the cranial anatomy of the choristodere Champsosaurus lindoei (CMN 8920) using high‐resolution micro‐computed tomography scanning. We found that the paired gaps on the ventral surface of the skull do pertain to the fenestrae ovales, an unusual arrangement that may be convergent with some plesiosaurs, some aistopods, and some urodeles. The implications of this morphology in Champsosaurus are unknown and will be the subject of future work. We found that the neomorphic bone is a distinct ossification, but is not part of the wall of the brain cavity or the auditory capsule. Variation in the developmental pathways of cranial bones in living amniotes was surveyed to determine how the neomorphic bone may have developed. We found that the chondrocranium and splanchnocranium show little to no variation across amniotes, and the neomorphic bone is therefore most likely to have developed from the dermatocranium; however, the stapes is a pre‐existing cranial element that is undescribed in choristoderes and may be homologous with the neomorphic bone. If the neomorphic bone is not homologous with the stapes, the neomorph likely developed from the dermatocranium through incomplete fusion of ossification centres from a pre‐existing bone, most likely the parietal. Based on the apparent morphology of the neomorph in Coeruleodraco, the neomorph was probably too small to play a significant structural role in the skull of early choristoderes and it may have arisen through non‐adaptive means. In neochoristoderes, such as Champsosaurus, the neomorph was likely recruited to support the expanded temporal arches. The skull of a well preserved specimen of Champsosaurus lindoei was computed tomography (CT) scanned to describe the cranial elements and comment on the putative choristoderan neomorphic bone. These data provide the first exhaustive description of a choristodere skull using CT scanning, and confirm the presence of the neomorphic bone lateral to the braincase. Developmentally, the neomorphic bone is most likely to be homologous with the pre-existing stapes, but if not, may be a development of the dermatocranium.
Basal neoceratopsians are a relatively diverse group of small- to medium-sized herbivorous dinosaurs from the Early to Late Cretaceous of Asia and North America. Although known for over a century, this group has only relatively recently received intense independent study, tied to the rapid increase in known diversity since 1997. Auroraceratops rugosus is one of these recently discovered species and is one of the best-known basal neoceratopsians, being represented by over 80 specimens, and is also the most completely represented neoceratopsian from the Early Cretaceous. A phylogenetic analysis focusing on non-ceratopsid ceratopsians examines the phylogenetic context of Auroraceratops. The analysis is based on a new matrix of 41 taxa and 257 characters. The results recover an Auroraceratops-Aquilops-ZPAL MgD-I/156 clade within basal Neoceratopsia that is sister to a clade composed of Asiaceratops, Yamaceratops, Mosaiceratops, and the larger clades Leptoceratopsidae and Coronosauria. This phylogeny recovers a monophyletic Coronosauria, Leptoceratopsidae, and Protoceratopsidae. Helioceratops is recovered as sister to the rest of Leptoceratopsidae, Ischioceratops is recovered nested within Leptoceratopsidae, and the enigmatic genus Mosaiceratops is recovered as a basal neoceratopsian, sister to Yamaceratops. Yinlong, and Hualianceratops are recovered in an expanded Chaoyangsauridae, and the genus Psittacosaurus is recovered as the earliest diverging lineage in Ceratopsia. Ajkaceratops, the only European ceratopsian, is robustly recovered as sister to the rest of Ceratopsoidea.
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Citation for this article: Morschhauser, E. M., H. You, D. Li, and P. Dodson. 2019. Phylogenetic history of Auroraceratops rugosus (Ceratopsia: Ornithischia) from the Lower Cretaceous of Gansu Province, China; pp. 117–147 in Hailu You, Peter Dodson, and Eric Morschhauser (eds.), Auroraceratops rugosus (Ornithischia, Ceratopsia) from the Early Cretaceous of northwestern Gansu Province, China. Society of Vertebrate Paleontology Memoir 18. Journal of Vertebrate Paleontology 38(Supplement). DOI: 10.1080/02724634.2017.1509866.
A detailed description of the skull and mandible of the Chinese cerapodan ornithischian dinosaur Jeholosaurus shangyuanensis (Lower Cretaceous, Yixian Formation) is presented for the first time and this information is used to reassess its phylogenetic position. Jeholosaurus can be distinguished from all other cerapodans on the basis of one autapomorphy (a row of small foramina on the nasal) and a character combination that is unique among ornithischians. Previously undescribed specimens add considerably to our knowledge of Jeholosaurus, providing new insights into its anatomy and ontogeny. Revised character scores increase the resolution of phylogenetic hypotheses and provide additional support for placement of Jeholosaurus within Ornithopoda.
A nearly complete right dentary originally noted by Mantell in 1848 is redescribed. The specimen, NHMUK 28660, was discovered in a quarry near Cuckfield, West Sussex, from the same formation as the original teeth of Iguanodon anglicus. Fresh examination reveals that NHMUK 28660 exhibits a single autapomorphy (a row of foramina extending from the ventral surface of the symphysis onto the lateral surface of the dentary) and a unique combination of characters that distinguish it from all other iguanodontian dentaries. In light of this and because I. anglicus is regarded as a nomen dubium to which additional material cannot be unambiguously referred, NHMUK 28660 is made the holotype of the new genus and species Kukufeldia tilgatensis.
The joint of the occipital skull region and two first cervical vertebrae of Psittacosaurus sibiricus from the Shestakovo locality (Barremian–Aptian), Kemerovo Region, Russia is described. The morphological differences in the atlas–axis complex between the infraorders Psittacosauria and Neoceratopsia connected with their functional features are revealed. The atlas–axis complex of P. sibiricus consists of two unfused vertebrae. The atlas includes the centrum, neural arch, and intercentrum. The axis consists of fused centrum, neural arch, and intercentrum, which is fused with its centrum. The cranial processes of the neural arch of the atlas are well developed, could have indicated the presence of a proatlas. The shape of the occipital condyle and anterior articular surface of the atlas are evidence that the occiput–atlas joint was only slightly flexible in the vertical plane. The atlas–axis complex and occipital condyle of P. sibiricus are similar in morphology to that of ornithopods.
The tarsus and distal end of the tibia are described in Herrerasauridae, a family that includes the oldest known dinosaurs. This tarsal configuration is compared to those of more advanced dinosaurs and to other archosaurs. Through phylogenetic analysis of the morphological characters, a picture emerges of the evolutionary changes in the ankles of early dinosaurs.
The tibia of the herrerasaurids has a quadrangular distal articular surface, with a shallow ventrolateral notch. This morphology is strikingly similar to that of the lagosuchid thecodonts Pseudolagosuchus and Lagosuchus and represents the most primitive tibial condition known for Dinosauria.
Aside from the derived states possessed by Theropoda, Sauropodomorpha, and Ornithischia, respectively, it was impossible to recognize synapomorphies in tibiotarsal anatomy shared by these groups exclusive of Herrerasauridae. The transverse broadening of the distal end of the tibia seems to have been attained independently by ornithischians, theropods, and sauropodomorphs.
The tarsus of herrerasaurids is characterized by an astragalus with a small but conspicuous lateroventral depression, by a pyramidal calcaneum with a ventromedial projection that articulates into the cavity of the astragalus just mentioned, and by a posterolaterally directed calcaneal tuber. These characters are also seen in Lagosuchus (a close relative of dinosaurs), in the prosauropod Riojasaurus and, insofar as the astragalus is concerned, in the primitive dinosaur Walkeria , which suggests that dinosaurs of different lineages shared the same tarsal condition.
By definition, this type of articulation between the astragalus and calcaneum follows the “crocodile-reversed” tarsal condition, suggesting that the tarsus in lagosuchids and dinosaurs could be derived from the “crocodile-reversed” pattern present in Ornithosuchidae and Euparkeria . In contrast, the mesotarsal ankle of lagosuchids and dinosaurs lacks the synapomorphies of the “crocodile-normal” ankle present in Crocodylia, Rauisuchidae, Aetosauria, and other archosaurs.
It is concluded that Herrerasauridae retained the primitive tibiotarsal condition for Dinosauria, from which those of the Ornithischia, Sauropodomorpha, and Theropoda were derived. Furthermore, tibiotarsal anatomy supports monophyly of Dinosauria.
Approximately half of existing dinosaur species belonging to the Order Ornithischia, or the 'bird-hipped' dinosaurs, which include such familiar forms as the stegosaurs, ankylosaurs, hadrosaurs, and ceratopsids. Although ornithischians are generally conceded to have descended from a common ancestor, little is known about the pattern of descent. Comparison of more recently discovered ornithischian fossils from China and Mongolia to better-known North American forms has shed light on the pattern of evolutionary diversification among ornithischians, a pattern that began approximately 200 My ago and ended abruptly nearly 140 My later at the end of the Cretaceous.-from Author
Colbert notes that the forelimb of Scutellosaurus is half the length of the hindlimb and that the manus is fairly large that suggests that Scutello was at least a facultative quadruped
In fabrosaurids the upper jaw is flat and the lower jaw is slender so the ’cheek’ teeth are marginal and not inset as is the
case in all other ornithischian dinosaurs. The ’cheek’ teeth of fabrosaurids have anteroposteriorly expanded crowns but lack
wear surfaces formed by tooth to tooth contact. Two genera are recognized from the Triassic-Jurassic boundary of Lesotho with
good material previously referred toFabrosaurus as a new genus that represents the most conservative ornithopod described to date. The anatomy ofNanosaurus (Upper Jurassic, U.S.A.) andEchinodon (Jurassic-Cretaceous boundary, England) is redescribed; in both genera the tooth bearing bone of the lower jaw is deepened
posteriorly and inEchinodon there is a true canine tooth in the upper jaw.
Bei den Fabrosauridae ist der Oberkiefer flach und der Unterkiefer schlank gebaut, so daß die »Backenzähne« randlich stehen
und nicht wie bei allen anderen Ornithischiern eingelassen sind. Die »Backenzähne« haben in der Längsrichtung gestreckte Kronen,
aber keine durch Zahnkontakt gebildete Abkauflächen. Das von der Trias-Jura-Grenze in Lesotho (= Basutoland) bisher alsFabrosaurus beschriebene Material umfaßt eine weitere Gattung(Lesothosaurus n. gen.), welche den altertümlichsten bisher bekannten Ornithopoden darstellt. Die Anatomie vonNanosaurus (Oberjura U.S.A.) undEchinodon (Jura-Kreide-Grenze, England) wird neu beschrieben. Der zahntragende Unterkieferknochen beider Gattungen ist rückwärts eingetieft,
während sich im Oberkiefer vonEchinodon außerdem ein richtiger Eckzahn findet.
LIZARDS are the most numerous, varied and widespread of living reptiles. An essentially modern lizard fauna has existed throughout the Tertiary and members of many modern lizard families are known from the late Cretaceous. Earlier in the Mesozoic, very few fossils of lizards are known. Lizards from the Upper Jurassic may be related to the ancestors of modern groups, but are placed in distinct families. Lizards previously described from the Upper Triassic of Europe1 and North America2 are considerably more primitive, retaining many cranial features in common with their ancestors from the Upper Permian and Lower Triassic3. We give here the first description of an Upper Triassic lizard with an essentially modern cranial morphology. This specimen is interesting with respect to the origin, differentiation and zoogeography of the modern lizard groups.
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