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Review of Lower and Middle Cretaceous ankylosaurs from North America

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... A posterior cervical vertebra (based on size) is well preserved (Fig. 5). The centrum is wider transversely than it is long anteroposteriorly, as in most ankylosaurs but in contrast to Struthiosaurus, Stegopelta and Hungarosaurus, in which the centra are elongate (Carpenter & Kirkland, 1998;} Osi, 2005;Pereda Suberbiola & Galton, 1997, 2001. The anterior and posterior articular facets are shallowly concave (Fig. 5E, F). ...
... The posterior-most dorsosacral vertebra in the rod is broken (Fig. 8F), so the total number of dorsosacrals cannot be determined. In Polacanthus , Zhejiangosaurus (L€ u et al., 2007), Europelta (Kirkland et al., 2013), Hungarosaurus ( } Osi, 2005) and Struthiosaurus languedocensis (UM2 OLV-D50 A-G CV), the presacral rod is composed of at least five dorsosacrals whose ribs extend laterally to fuse to the preacetabular process of the ilium, while Silvisaurus (Carpenter & Kirkland, 1998) had as many as six fused dorsosacrals; however, most ankylosaurs possess fewer vertebrae in the presacral rod. There are three in Pinacosaurus mephistocephalus and Talarurus (Godefroit et al., 1999;Marya nska, 1977), and four in Euoplocephalus, Gastonia lorriemcwhinneyae and Nodosaurus (Arbour & Currie, 2013a;Kinneer et al., 2016;Raven et al., 2020). ...
... It is deepest in the third sacral vertebra, and terminates gradually on the fourth, disappearing at the intercentral suture and is not present on the fifth. A similar groove is known in Edmontonia, Peloroplites, Cedarpelta, Niobrarasaurus, Polacanthus and Nodosaurus but is absent in Silvisaurus and Dongyangopelta (Burns et al., 2015;Carpenter & Kirkland, 1998;Chen et al., 2013;Raven et al., 2020). The cross section of the broken centrum of the first sacral vertebra is dorsoventrally compressed and heart-shaped, with a neural canal that excavates shallowly into the top of the centrum (Fig. 9E). ...
... In this context, the associated non-dermal bones could be the quadratojugal and the jugal. The overall shape resembles the symmetrical quadratojugal horn of Hungarosaurus, Sauropelta, Silvisaurus and Edmontonia (Carpenter & Kirkland 1998;Burns 2015;} Osi et al. 2021), contrasting with the asymmetrical boss of other nodosaurids (e.g. Europelta, Niobrarasaurus and Polacanthus; Carpenter & Everhart 2007;Kirkland et al. 2013;Blows 2015), the more asymmetrical and anteroposteriorly longer horn of ankylosaurids (Tumanova 2000;Arbour & Currie 2013a;Arbour et al. 2014), and the strongly reduced element in the parankylosaur Kunbarrasaurus (Leahey et al. 2015). ...
... This condition is common in nodosaurids (e.g. Europelta, Hungarosaurus, Niobrarasaurus, Nodosaurus, Polacanthus, Sauropelta, Struthiosaurus;Lull 1921;Ostrom 1970;Carpenter et al. 1995 (Ostrom 1970;Coombs 1971;Carpenter et al. 1995;Carpenter & Kirkland 1998;Pereda-Suberbiola & Galton 2001;Kirkland et al. 2013) strongly contrasts with the laterally placed trochanter in Edmontonia longiceps (Burns 2015). ...
... The lateral-most ridge (linea intermuscular sensu Arbour & Currie 2016) is associated with the anterior trochanter and extends laterodistally to one-third of the femoral length. The second and central ridge (linea muscularis caudalis sensu Arbour & Currie 2016) extends from the proximolateral corner anterior to the trochanters to the proximal region of the medial condyle (as stated by Coria & Salgado 2001 (Carpenter et al. 1995), Peloroplites , and Texasetes (Carpenter & Kirkland 1998) also bear subtle muscular ridges in the anterior surface of the femur. However, the femoral ridges in all these taxa are not as strong as those in Patagopelta. ...
Article
The most representative ankylosaurian remains from Argentina have been found in sediments of the Allen Formation (Campanian–Maastrichtian) in Salitral Moreno, Río Negro Province. Several authors have discussed the identity and history of these remains. In this study, we review all published material along with some new remains in order to summarize all the knowledge about these ankylosaurs. Previously published material includes a tooth, dorsal and anterior caudal vertebrae, a femur and several osteoderms. The new remains include synsacral and caudal elements, a partial femur and osteoderms. The anatomy of the tooth, the synsacrum, the mid-caudal vertebra, the femur and the osteoderms, and the histology of the post-cervical osteoderms, support a nodosaurid identification, as proposed in previous descriptions of the Salitral Moreno material. Patagopelta cristata gen. et sp. nov. is a new nodosaurid ankylosaur characterized by the presence of unique cervical half-ring and femoral anatomies, including high-crested lateral osteoderms in the half rings and a strongly developed muscular crest in the anterior surface of the femur. The ∼2 m body length estimated for Patagopelta is very small for an ankylosaur, comparable with the dwarf nodosaurid Struthiosaurus. We recovered Patagopelta within Nodosaurinae, related to nodosaurids from the ‘mid’-Cretaceous of North America, contrasting the previous topologies that related this material with Panoplosaurini (Late Cretaceous North American nodosaurids). These results support a palaeobiogeographical context in which the nodosaurids from Salitral Moreno, Argentina, are part of the allochthonous fauna that migrated into South America during the late Campanian as part of the First American Biotic Interchange. https://zoobank.org/urn:lsid:zoobank.org:pub:FBA24443-F365-49FD-A959-10D2848C2400
... In posterior view, the fourth trochanter is prominent and extends to approximately midlength of the femoral shaft, and although it is less prominent than that of Lesothosaurus and Scutellosaurus (Colbert, 1981;Baron et al., 2017) it is more strongly developed than in most other eurypodans (Vickaryous et al., 2004;Maidment et al., 2008). Carpenter and Kirkland (1998) have argued that this prominence is due to taphonomic crushing and suggested that Polacanthus exhibits a condition similar to other ankylosaurs (Arbour and Currie, 2013a), although we consider the feature to be the true morphology. On the fourth trochanter of the left femur a fragment of unidentifiable bone is attached. ...
... The type and only specimen consists of both femora, portions of the right scapula and coracoid, two fragments of humerus, two vertebral centra, rib fragments, and dermal armor. Given the potential stratigraphic overlap and anatomical similarities of the humerus, femur, and dermal armor, Hoplitosaurus was regarded as a junior subjective synonym of Polacanthus by Blows (1987) and Pereda-Suberbiola (1994), although this synonymy was rejected by Carpenter and Kirkland (1998) and has not been accepted by subsequent workers (e.g., Vickaryous et al., 2004;Parish, 2005;Thompson et al., 2012;Arbour and Currie, 2016). None of the autapomorphies of Polacanthus are found in the material of Hoplitosaurus, there are morphological differences in the femora of Hoplitosaurus and Polacanthus (see description above), and several of the unique characters that were thought to link Hoplitosaurus and Polacanthus, such as the groove separating the anterior and greater trochanters of the femora, have a wider distribution within Ankylosauria (e.g. in Gastonia burgei; Carpenter and Kirkland, 1998), meaning that the two taxa are distinct. ...
... Given the potential stratigraphic overlap and anatomical similarities of the humerus, femur, and dermal armor, Hoplitosaurus was regarded as a junior subjective synonym of Polacanthus by Blows (1987) and Pereda-Suberbiola (1994), although this synonymy was rejected by Carpenter and Kirkland (1998) and has not been accepted by subsequent workers (e.g., Vickaryous et al., 2004;Parish, 2005;Thompson et al., 2012;Arbour and Currie, 2016). None of the autapomorphies of Polacanthus are found in the material of Hoplitosaurus, there are morphological differences in the femora of Hoplitosaurus and Polacanthus (see description above), and several of the unique characters that were thought to link Hoplitosaurus and Polacanthus, such as the groove separating the anterior and greater trochanters of the femora, have a wider distribution within Ankylosauria (e.g. in Gastonia burgei; Carpenter and Kirkland, 1998), meaning that the two taxa are distinct. ...
Article
Ankylosaurs, dinosaurs possessing extensive body armor, were significant components of terrestrial ecosystems from the Middle Jurassic–latest Cretaceous. They diversified during the Early Cretaceous, becoming globally widespread. The Lower Cretaceous Wealden Supergroup (Berriasian–Aptian) of Britain has produced abundant ankylosaur material, with three currently recognized taxa: Hylaeosaurus armatus (Grinstead Clay Formation, West Sussex); Polacanthus foxii (Wessex Formation, Isle of Wight); and Horshamosaurus rudgwickensis (Weald Clay Group, West Sussex). However, these taxa are poorly understood; the initial descriptions of Hylaeosaurus and Polacanthus date from the 1800s and subsequent referrals of specimens have been based largely on provenance rather than morphological comparisons. This has led to uncertainty over the definitions of these taxa and the compositions of their hypodigms. Here, we redescribe the holotypes of Hylaeosaurus and Polacanthus, provide comparisons between these taxa, and use this information to assess the taxonomy of all ankylosaur specimens from the British Wealden Supergroup. We conclude that Hylaeosaurus and Polacanthus are valid, distinct taxa, which can be diagnosed by a combination of autapomorphies and a unique combination of characters. However, in both cases, we restrict their hypodigms to the holotypes. ‘Horshamosaurus rudgwickensis’ is a nomen dubium (an indeterminate nodosaurid dinosaur) and the majority of ankylosaur specimens from the Wealden Supergroup are taxonomically indeterminate. Hylaeosaurus and Polacanthus are separated stratigraphically, with Hylaeosaurus from the Valanginian of the Weald Sub-basin and Polacanthus from the Barremian of the Wessex Sub-basin. This separation supports the hypothesis of distinct lower and upper dinosaur faunas in the Wealden Supergroup of Britain.
... Examination of this flora has the potential to provide suitable evidence of vegetation available to Borealopelta and other herbivorous dinosaurs in this region (Brown et al., 2020). Numerous nodosaurid discoveries, both ichnofossils and body fossils, have been found in Albian-aged sediments ranging geographically from Texas to northern Alberta, Canada (Fig. 1A) (Carpenter and Kirkland, 1998;McCrea, 2000;Paulina-Carabajal et al., 2016;Brown et al., 2020). Ichnofossils found near Grande Cache, AB (Fig. 1B) in the Gates Fm include a high abundance of trackways made by nodosaurids, suggesting that animals similar to Borealopelta markmitchelli were native to the region ( Fig. 1) (Carpenter, 1984;McCrea and Currie, 1998;McCrea, 2000). ...
... These data were census-collected to provide insight into (Brown et al., 2017); 2) Cloverly Fm-Sauropelta edwardsorum; 3) Frontier Fm-Stegopelta landerensis; 4) Arundel Fm-Priconodon crassus; 5) Dakota Fm-Silvisaurus condrayi; 6) Paw Paw Fm-Pawpawsaurus campbelli; 7) Paw Paw Fm-Taxasetes pleurhalio. Nodosaurid occurrences from Carpenter and Kirkland (1998) and Brown et al. (2017). B. Fossil plant sites utilized in this study. ...
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During the Cretaceous, large herbivorous dinosaurs (megaherbivores) acted as keystone species—just as large mammals do today (e.g., elephants)—yet despite their significance in Cretaceous ecosystems, what plant taxa these dinosaurs ate is unclear. The Albian armoured dinosaur Borealopelta markmitchelli (Ornithischia; Nodosauridae) was discovered in northern Alberta, Canada and has well-preserved stomach contents dominated by fern leaf tissues, with low amounts of gymnosperm material, implying selective feeding. The lower Albian Gates Formation (Grande Cache Member) macroflora of central Alberta is contemporaneous and spatially proximal with B. markmitchelli and therefore provides information on local vegetation available to this nodosaurid and other megaherbivores in this area. In this study we provide census-sampled abundance data for the Gates Formation macroflora. These data also provide the means to further investigate the feeding ecology of Borealopelta by summarizing the vegetation and local food options available. Census collections at five sites within the Grande Cache Member exposed in the Grande Cache Coal Mine reveal that the local vegetation there was dominated by conifers (44–70%) across all sites. Athrotaxites, Elatides, and Pityocladus were the most common conifers. Other gymnosperms present were ginkgophytes (e.g., Ginkgoites; 11%) and Taeniopteris (9%). Caytoniales (Sagenopteris) were found at one study site but uncommon (2%). Ferns (e.g., Cladophlebis, Coniopteris, Gleichenites) accounted for 14% of the total site counts while cycadophytes (Bennettitales; 4%) and Equisetites (1%) were less common. When comparing the Gates Formation macroflora to the stomach contents of Borealopelta, these data suggest that B. markmitchelli was selectively feeding on ferns, or in a recently disturbed fern-dense area within the local landscape.
... Numerous nodosaur discoveries, both ichnofossils and body fossils, have been found in Albianaged sediments ranging geographically from Texas to northern Alberta, Canada (Brown et al., 2020;Carpenter & Kirkland, 1998;McCrea, 2000;Paulina-Carabajal et al., 2016) (Fig. 1A). These ankylosaurs would have fed on the local vegetation; however, what plant taxa-ferns, various gymnosperm groups or angiosperms-these dinosaur megaherbivores ate is not well understood (Brown et al., 2020;Coe et al., 1987;Tiffney, 2012;Weishampel & Norman, 1989), nor is the relative importance of these plant groups within the landscapes in which these animals lived. ...
... (Brown, 2017), 2) Cloverly Fm-Sauropelta edwards, 3) Frontier Fm-Stegopelta landerensis, 4) Arundel Fm-Priconodon crassus, 5) Dakota Fm-Silvisaurus condrayi , 6) Paw Paw Fm-Pawpawsaurus campbelli, 7) Paw Paw Fm-Taxasetes pleurhalio. Nodosaur occurrences from Carpenter and Kirkland (1998) and Brown (2017). B. Fossil plant sites utilized in this study. ...
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During the Cretaceous, large herbivorous dinosaurs (megaherbivores) acted as keystone species—just as large mammals do today (e.g., elephants)—yet despite their significance in Cretaceous ecosystems, what plant taxa these dinosaurs ate is unclear. The Albian armoured dinosaur Borealopelta markmitchelli (Ornithischia; Nodosauridae) was discovered in northern Alberta, Canada and has well-preserved stomach contents dominated by fern leaf tissues, with only trace amounts of gymnosperm material, implying selective feeding. The Lower Albian Gates Formation (Grand Cache Member) macroflora of central Alberta is contemporaneous and spatially proximal with B. markmitchelli and therefore provides information on local vegetation available to this nodosaur and other megaherbivores in this area. In this study we provide unbiased abundance data for the Gates Fm macroflora. These data also provide the means to further investigate the feeding ecology of Borealopelta by summarizing the vegetation and local food options available. Census collections at five sites within the Grande Cache Mbr exposed in the Grande Cache Coal Mine reveal that the local vegetation there was dominated by conifers (44–70%) across all sites. Athrotaxites, Elatides, and Pityocladus were the most common conifers. Other gymnosperms present were ginkgophytes (e.g., Ginkgo, Ginkgoites; 11%) and Taeniopteris (9%). Caytoniales (Sagenopteris) were found at one study site but uncommon (2%). Ferns (e.g., Cladophlebis, Coniopteris, Gleichenites) accounted for 14% of the total site counts while cycadophytes (Bennettitales; 4%) and Equisetites (1%) were less common. When comparing the Gates Fm macroflora to the stomach contents of Borealopelta, these data suggest that B. markmitchelli was selectively feeding on ferns or in a recently disturbed fern-dense area within the local landscape.
... This is notable just north of the type area above the Cleveland-Lloyd Quarry and on Cedar Mountain on the north end of the San Rafael Swell. The recent discovery of a possible ankylosaur (armored dinosaur) skeleton within the Buckhorn Conglomerate in this area (figure 7D) suggests a Cretaceous age, as these dinosaurs are rare in the Jurassic and are abundant in the Lower Cretaceous (Carpenter and Kirkland, 1998;Kirkland, 2005a;Kirkland and Madsen, 2007). Elsewhere, the sole body fossils identified in the Buckhorn Conglomerate consist of isolated sauropod bones, which unfortunately do not provide any biostratigraphic information. ...
... Tenontosaurus until further research is carried out. One site, south of Green River, Utah (DMNH 2840), yielded an incomplete large nodosaurid (Warren and Carpenter, 2004) that was within 10 m of the underlying Poison Strip Member and appears to be similar to Sauropelta (Ostrom, 1970;Carpenter and Kirkland, 1998) The fauna from the Albian strata at the top of the Ruby Ranch is best documented at the Price River Quarries (figures 27 and 30) which have been excavated since the 1990s others, 1997, 1999;others, 2001, 2008). The only dinosaurs described to date are ankylosaurs, including a gigantic nodosaurine nodosaurid Peloroplites cedrimontanus (figure 30F) that is perhaps related to Sauropelta (Carpenter and others, 2008). ...
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Although only recognized as a discrete stratigraphic unit since 1944, the Cedar Mountain Formation represents tens of millions of years of geological and biological history on the central Colorado Plateau. This field guide represents an attempt to pull together the results of recent research on the lithostratigraphy, chronostratigraphy, sequence stratigraphy, chemostratigraphy, and biostratigraphy of these medial Mesozoic strata that document the dynamic and complex geological history of this region. Additionally, these data provide a framework by which to examine the history of terrestrial faunas during the final breakup of Pangaea. In fact, the medial Mesozoic faunal record of eastern Utah should be considered a keystone in understanding the history of life across the northern hemisphere. Following a period of erosion and sediment bypass spanning the Jurassic–Cretaceous boundary, sedimentation across the quiescent Colorado Plateau began during the Early Cretaceous. Thickening of these basal Cretaceous strata across the northern Paradox Basin indicate that salt tectonics may have been the predominant control on deposition in this region leading to the local preservation of fossiliferous strata, while sediment bypass continued elsewhere. Thickening of overlying Aptian strata west across the San Rafael Swell provides direct evidence of the earliest development of a foreland basin with Sevier thrusting that postdates geochemical evidence for the initial development of a rain shadow.
... In nodosaurids, such as Sauropelta, the femoral head is slightly offset medially, and a saddle-shaped region separates the head from the greater trochanter. Polacanthus shows the remnant of the anterior trochanter separated by a narrow cleft from the greater trochanter (Carpenter & Kirkland, 1998: fig. 29), and the fourth trochanter is a thickened ridge positioned on the proximal half of the shaft. ...
Article
Scelidosaurus fossils were first discovered during the commercial quarrying of the Liassic sea-cliffs between Charmouth and Lyme Regis in Dorset during the late 1850s. The original specimens included a well-preserved skull embedded in a block of argillaceous limestone (marlstone). Shortly after this skull was retrieved, a series of more-or-less contiguous marlstone slabs were recovered, containing most of the skeleton of the same animal (NHMUK R1111). After rudimentary (hammer and chisel) mechanical preparation, Owen published descriptions of this material (Owen, 1861, 1863). These two monographs have been the sole references pertaining to the anatomy of Scelidosaurus for >150 years. The skeleton of the lectotype of Scelidosaurus harrisonii (NHMUK R1111) has since been extracted from the surrounding matrix using an acid-immersion technique. Some additional specimens held in the collections of the Natural History Museum London, the Bristol City Museum and the Sedgwick Museum in Cambridge provide anatomical material that allows detailed description of this taxon, for which we have had, until now, a surprisingly poor understanding. Axial skeleton: The axial skeleton of Scelidosaurus comprises eight cervical, 16 dorsal, four sacral and > 40 caudal vertebrae. During ontogeny, the posterior centrum articular surface of the 16th dorsal vertebra develops a firm, ligament-bonded junction with the succeeding sacral centrum. Apart from the atlas rib, which is single headed, double-headed ribs are present throughout the presacral vertebral series, and none shows any indication of fusion to its associated vertebra. However, those ribs attached to cervical vertebrae 2–4 were evidently bound firmly by connective tissue to rugose diapophyses. The last two (presacral) dorsal ribs show merger of the capitulum and tuberculum, meaning that they are separated by only a step. The angulation and arching of the dorsal ribs suggest that these animals had a broad (barrel-like) torso. Intercostal uncinate plates were present, attached to the posterior margins of some of the largest dorsal ribs. Their attachment sites are clearly marked, and these plates might have been composed of calcified cartilage in larger individuals. The sacral vertebrae fuse progressively during ontogeny, in an anterior-to-posterior sequence. The sacral ribs are long and robust, and tilt the iliac blade outward dorsally. A sacricostal ‘yoke’ (created by the fusion of the distal ends of adjacent sacral ribs) never forms. The base of the tail has a unique ball-and-socket-style joint between the centra of caudal vertebrae 1 and 2 in only one skeleton. This might have permitted powerful, but controlled, movements of the tail as a defensive weapon (or increased flexibility at the base of the tail, which might have been necessary for reproduction). Caudal ribs are initially long, blade-shaped projections that gradually decrease in size and become stub-like remnants that persist as far back as the midtail (approximately caudal vertebra 25). Haemal arches (chevrons) disappear nearer to the distal end of the tail (approximately caudal vertebra 35). Ossified tendons are preserved as epaxial bundles that are clustered in the ‘axillary’ trough (between the neural spine and transverse processes on either side of the midline). Ossified tendons are restricted to the dorsal and sacral region. Flattened ossified tendons are fused to the sides of sacral neural spines. In life, the ossified tendons might have formed a low-angled trellis-like arrangement. Appendicular skeleton: The pectoral girdle comprises a long scapula, with a distally expanded blade. The proximal portion is expanded and supports an oblique promontory, forming an acromial process anteriorly and a thick, collar-like structure posteriorly above the glenoid. Between these two features is a shallow basin, bordered ventrally by a sutural edge for the coracoid. The scapula–coracoid suture remains unfused in large (5-m-long) individuals. The coracoid bears a discrete foramen and forms a subcircular dished plate, with the shallowest of embayments along its posterior edge. Clavicles are present as small fusiform bones attached to the acromial process of the scapulae and leading edge of each coracoid. A sternum was reported as ‘some partially ossified element of the endoskeleton’ Owen (1863: 13), but subsequent preparation of the skeleton has removed all trace of this material. The humerus is relatively long and has a prominent rectangular and proximally positioned deltopectoral crest. The ulna is robust and tapers distally, but there is no evidence of an olecranon process. The radius is more rod-like and terminates distally in an enlarged, subcircular and convex articular surface for the carpus. The carpus is represented by an array of five discoid carpals. The manus is pentadactyl and asymmetrical, with short, divergent metacarpals and digits that terminate in small, arched and pointed unguals on digits 1–3 (only). The phalangeal formula of the manus is 2-3-4-3-2. The pelvis is dominated by a long ilium; the preacetabular process is arched, transversely broad, and curves laterally. In juveniles, this process is short and horizontal, but during ontogeny it increases considerably in length and becomes arched. The iliac blade is tilted laterally, meaning that its dorsal blade partly overhangs the femur. The acetabulum forms a partial cupola, and there is a curtain-like medial wall that reduces the acetabular fenestra to a comparatively low, triangular opening between the pubis and ischium. The postacetabular portion of the ilium is long and supports a brevis shelf. The ischium has a long, laterally compressed shaft that hangs almost vertically beneath the ilium, and there is no obturator process. The pubis has a long, narrow shaft and a relatively short, deep, laterally compressed prepubic process that twists laterally (its distal end lies almost perpendicular to the long axis of the ilium). The articular pad on the pubis for the femoral head faces posteriorly. The obturator foramen is not fully enclosed within the pubis, but its foramen is closed off posteriorly by the pubic peduncle of the ischium. The femur is stout and has a slightly medially offset femoral head, and the greater trochanter forms a sloping shoulder continuous with, and lateral to, the femoral head. The anterior (lesser) trochanter is prominent and forms a thick, thumb-shaped projection on the anterolateral corner of the femoral shaft. The fourth trochanter is pendent and positioned at midshaft. In larger individuals, it appears to become thickened and reinforced by becoming coated with metaplastic bone derived from the tendons attached to its surface. The distal end of the femoral shaft is slightly curved and expands to form condyles. There is a deep and broad posterior intercondylar groove, but the anterior intercondylar groove is barely discernible in juveniles and not much better developed in subadults. The tibia and fibula are shorter than the femur. The tibia is structurally dominant, and the shorter fibula is comparatively slender and bowed. The proximal tarsals are firmly bound by connective tissue to the distal ends of the tibia and fibula. The distal end of the tibia is stepped, which aids the firm interlock between the crus and proximal tarsals. There appear to be two roughly discoid tarsals (distal tarsals 3 and 4), and a rudiment of distal tarsal 5 appears to be sutured to the lateral margin of distal tarsal 4. Five metatarsals are preserved, but the fifth is a splint of bone attached to the proximal end of metatarsal 4. Metatarsals 2–4 are dominant, long and are syndesmotically interlocked proximally, but their shafts splay apart distally. Metatarsal 1 is much shorter than the other three, but it retains two functional phalanges (including a short, pointed ungual). The foot is anatomically tetradactyl but functionally tridactyl. The pedal digit formula is 2-3-4-5-0. The digits diverge, but each appears to curve medially along its length, creating the impression of asymmetry. This asymmetry is emphasized, because the three principal unguals are also twisted medially. The ungual of digit 2 is the largest and most robust of the three, whereas that of digit 4 is the smallest and least robust. The general girth of the torso and the displacement of the abdomen posteriorly (a consequence of the opisthopubic pelvic construction in this dinosaur) constrained the excursion of the hindlimb during the protraction phase of the locomotor cycle. The anterolateral displacement of the hindlimb during protraction is in accord with the freedom of motion that is evident at the acetabulum, the susceptibility of the hindlimb to torsion between and within its component parts, and the asymmetry of the foot. It is probable that thyreophorans (notably, ankylosaurs) used a similar oblique-parasagittal hindlimb excursion to accommodate their equally large and wide abdomens. This surmise accords with the structure of the pelves and hindlimbs of ankylosaurs. Derived stegosaurs might have obviated this ‘problem’, in part, because their hindlimbs were longer and their torsos and abdomens narrower and capable of being ‘stretched’ vertically to a greater extent. Nevertheless, the structure of their acetabula and hindlimbs indicates that the oblique-parasagittal style of hindlimb excursion remained a possibility and might be an evolutionary remnant of the locomotor style of basal, shorter-limbed stegosaurs. A reconstruction of the endoskeleton of Scelidosaurus is presented on the basis of this updated description. Although quadrupedal, this animal was only facultatively so, judged by its forelimb-to-hindlimb proportions and structure; it therefore betrays bipedality in its ancestry.
... In Gastonia (Kinneer et al., 2016) and Gargoyleosaurus (Kilbourne and Carpenter, 2005), an otoccipital contribution has been documented. In the nodosaurids Sauropelta (Ostrom, 1970;Carpenter and Kirkland, 1998;Parsons and Parsons, 2009: Figs. 11B, 14B;Paulina-Carabajal et al., 2018), Pawpawsaurus (Lee, 1996), Silvisaurus (Eaton, 1960), Europelta (Kirkland et al., 2013), Struthiosaurus (Pereda-Suberbiola and Galton, 1994), andHungarosaurus (Ösi et al., 2014), it was explicitly stated that the condyle is composed only of the basioccipital. ...
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We describe in detail three braincases of the ankylosaur Bissektipelta archibaldi from the Late Cretaceous (Turonian) of Uzbekistan with the aid of computed tomography, segmentation, and 3D modeling. Bissektipelta archibaldi is confirmed as a valid taxon and attributed to Ankylosaurinae based on the results of a phylogenetic analysis. The topographic relationships between the elements forming the braincase are determined using a newly referred specimen with preserved sutures, which is an exceedingly rare condition for ankylosaurs. The mesethmoid appears to be a separate ossification in the newly referred specimen ZIN PH 281/16. We revise and discuss features of the neurocranial osteology in Ankylosauria and propose new diagnostic characters for a number of its subclades. We present a 3D model of the braincase vasculature of Bissektipelta and comment on vascular patterns of armored dinosaurs. A complex vascular network piercing the skull roof and the wall of the braincase is reported for ankylosaurs for the first time. We imply the presence of a lepidosaur-like dorsal head vein and the venous parietal sinus in the adductor cavity of Bissektipelta. We suggest that the presence of the dorsal head vein in dinosaurs is a plesiomorphic diapsid trait, and extant archosaur groups independently lost the vessel. A study of two complete endocranial casts of Bissektipelta allowed us to compare endocranial anatomy within Ankylosauria and infer an extremely developed sense of smell, a keen sense of hearing at lower frequencies (100–3000 Hz), and the presence of physiological mechanisms for precise temperature control of neurosensory tissues at least in derived ankylosaurids.
... Other Cenomanian terrestrial vertebrate remains from North America are so far limited to those from the Belle Fourche Member of the Frontier Formation of Wyoming, the Willow Tank Formation of Nevada, and the Woodbine Formation of Texas. The Belle Fourche Member of the Frontier Formation of southeast and central Wyoming has produced remains from the nodosaurs Nodosaurus and Stegopelta (Marsh 1889;Williston 1905;Carpenter and Kirkland 1998). The Willow Tank Formation has produced a modest assemblage including ...
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The Mussentuchit Member of the Cedar Mountain Formation of eastern Utah represents the best source of data on Cenomanian vertebrate assemblages from North America. However, increasing data has recently been forthcoming from the late Albian to Cenomanian Wayan Formation of Idaho and Vaughn Member of the Blackleaf Formation of Montana, which are both at least partially coeval with the Mussentuchit Member. While the paleontological assemblages of the Wayan Formation and Vaughn Member are fragmentary, numerous vertebrate forms are represented, with the small burrowing neornithischian Oryctodromeus cubicularis dominating these assemblages. The differences between the Wayan Formation and Vaughn Member assemblages, the Mussentuchit and few other mid-Cretaceous assemblages are likely a result of some combination of preservational biases, paleogeography, and paleoenvironmental differences. The chronostratigraphy, fossil content, bracketing facies, and ages of the Wayan Formation and Vaughn Member suggest these sediments represent the same depositional system prior to disruption by subsequent tectonic and volcanic events. This assemblage from the Wayan Formation and Vaughn Member is here termed the Wayan-Vaughn Assemblage (WVA). Continued work in the WVA, particularly with microvertebrate materials, may reveal additional shared taxa between the WVA and other coeval units.
... based on their similarity to the holotype specimen (USNM 2135) described by Marsh (1888: figures 7-9). Though morphologically similar to most ankylosaurian teeth, Carpenter and Kirkland (1998) diagnosed P. crassus as a tentatively valid genus and species based on large tooth size and a suite of characters, relating to the cingulum and denticles that cannot be seen together in other taxa. ...
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