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A primitive dome-headed dinosaur (Ornithischia: Pachycephalosauridae) from the Lower Cretaceous of England and the function of the dome of pachycephalosaurids
... A goodness of variance fit (GVF) of 0.7 or greater was considered acceptable to identify the presence of a natural break (Powers et al. 2020). Galton (1971) predicted that if the dome was used in intraspecific combat, there should be a high degree of intraspecific variation in dome thickness. As the purported dimorphism we observed was largely explained by frontonasal boss thickness, we hypothesised that this intraspecific variation was concurrent with intersexual variation, whereby the "thicker-bossed" sex engaged in intraspecific combat. ...
... Additionally, "Hanssuesia sternbergi" is indistinct from other Belly River Group pachycephalosaurians in PCA of both log 10 -transformed and frontal length proportional linear measurements, respectively. For these reasons, we agree with previous studies (Galton 1971;Chapman et al. 1981;Maryańska et al. 2004) that refer "Hanssuesia sternbergi" to Stegoceras validum (see Schott et al. 2009 andEvans 2017 for discussion on the distinction of "Hanssuesia sternbergi" from Colepiocephale lambei and Foraminacephale brevis respectively). "Hanssuesia sternbergi" is largely separated from Stegoceras validum by the temporal width of the parietal in PC 2 the Belly River Group PCA based on non-transformed linear measurements. ...
... This height is immediately adjacent to a lateral indentation in the side of the frontoparietal, which is diagnostic for Colepiocephale lambei. Sullivan (2003) (Galton 1971;Baird 1979;Sullivan 2003;Horner and Goodwin 2009 Sullivan 2011, 2016; "Stenotholus kohleri", Giffin et al. 1988; Sphaerotholus edmontonensis, Schlaikjer 1943, Woodruff et al. 2021, "Texacephale langstoni", Longrich et al. 2010), although this is largely because less-taphonomically robust skeletal elements are rarely preserved (non-skull roof; Evans et al. 2013, Brown et al. 2013b). This makes identification of diagnostic frontoparietal features exceedingly difficult without knowledge of the ontogenetic sequence. ...
The taxonomic validity of the holotype and sole specimen of the pachycephalosaurid Gravitholus albertae (TMP 1972.027.0001) from the Belly River Group (Alberta, Canada), remains unresolved forty years after its first description. The diagnosis for this species is tenuous at best and extensive cranial fusion has prevented a thorough description and taxonomic referral of TMP 1972.027.0001. We used synchrotron µCT imaging to identify fused sutures and segment the individual elements that comprise TMP 1972.027.0001. This allowed for a detailed description of the specimen in a more thorough comparative framework with other known pachycephalosaurid specimens. Using new observations of contacts between cranial elements, the morphological distinction of TMP 1972.027.0001 from other Belly River Group pachycephalosaurids was tested with bivariate and multivariate morphometric analyses. TMP 1972.027.0001 is morphologically consistent as an end-stage semaphorant of Stegoceras validum. Furthermore, we find no taxonomically significant morphometric distinctions between Gravitholus albertae, Hanssuesia sternbergi, and Stegoceras validum, and propose the former two are synonymous with the later. Large Stegoceras validum frontoparietals show statistically significant dimorphism in the thickness of the frontonasal boss, which is not apparent amongst juvenile and subadult specimens. Pathologies consistent with intraspecific combat (“headbutting”) appear restricted to frontoparietal domes with proportionally taller frontonasal bosses, and suggests that the two morphs represent sexual dimorphs, rather than separate species. Foraminacephale brevis and Stegoceras validum are the only named pachycephalosaurids recognised in the Dinosaur Park Formation. The stratigraphic and temporal range of Stegoceras validum is extended into the underlying Oldman Formation. Pachycephalosaurid diversity in the Campanian is reduced as a result of these revised taxonomic hypotheses. A revised phylogenetic character matrix, recognising taxonomic synonymies and ontogenetically dependent character states results in a largely unresolved Pachycephalosauria.
... Several hypotheses have arisen to describe the function of the dome: agonistic head-butting (Galton 1971), display and species recognition (Goodwin & Horner 2004), and thermoregulation (Rigby et al. 1987;Landry 1995). The head-butting hypothesis, analogous to modern bovids (Geist 1966;Galton 1971), has received the most attention and discussion. ...
... Several hypotheses have arisen to describe the function of the dome: agonistic head-butting (Galton 1971), display and species recognition (Goodwin & Horner 2004), and thermoregulation (Rigby et al. 1987;Landry 1995). The head-butting hypothesis, analogous to modern bovids (Geist 1966;Galton 1971), has received the most attention and discussion. Galton (1971) argued that because the dome is comprised of dense compact bone (revised as porous compact bone (Goodwin et al. 1998) rather than porous trabecular bone, and the density of the dome increased through ontogeny (Goodwin & Horner 2004;Schott et al. 2011;Schott & Evans 2016)), the dome would not have been strictly used as a display feature, but was adapted to resisting the forces of intraspecific combat. ...
... The head-butting hypothesis, analogous to modern bovids (Geist 1966;Galton 1971), has received the most attention and discussion. Galton (1971) argued that because the dome is comprised of dense compact bone (revised as porous compact bone (Goodwin et al. 1998) rather than porous trabecular bone, and the density of the dome increased through ontogeny (Goodwin & Horner 2004;Schott et al. 2011;Schott & Evans 2016)), the dome would not have been strictly used as a display feature, but was adapted to resisting the forces of intraspecific combat. Longrich et al. (2010) converged on a similar argument, elaborating on the unlikelihood of natural selection favouring such a physiologically expensive structure for the sole purpose of species recognition. ...
Recent studies have identified numerous pathologies in the cranial domes of pachycephalosaurid dinosaurs. These studies utilized CT images of domes to identify secondary woven bone and sclerosis associated with the pathologies. These features were critical for diagnosing post-traumatic osteomyelitis, which supported the head-butting behaviour hypothesis. However, conventional CT image resolution may not be sufficient to identify secondary woven bone or sclerotic bone in fossil specimens. UALVP 8504 (cf. Foraminacephale brevis), a dome possessing putative bone lesions, was thin-sectioned and micro-CT scanned. Thin sections revealed the lesions are lytic, without any secondary woven bone or sclerosis, falsifying the diagnosis of osteomyelitis. The morphology and histology of the lesions of UALVP 8504 are not diagnostic and resemble both post-traumatic and non-traumatic lesions. However, UALVP 8504 possesses shifted vascular canals (repositioning via remodeling, which maintains anatomical position throughout ontogeny) that are decoupled from growth (), and drifting osteons (secondary osteons where resorption occurs longitudinally and transversely). These demonstrate that the dome has sustained external mechanical loading, likely resulting from an impact or multiple impacts, consistent with the head-butting hypothesis. These impacts may have damaged overlying soft tissues and formed the lesions along the surface. Therefore, we suspect that the pathologies in UALVP 8504 are post-traumatic.
... The ensuing decades post- Galton (1970Galton ( , 1971) saw a flury of pchycephalosaurid research. Interestingly, these works were not in uniform agreement over the specifics of hypothesized pachycephalosaurid behaviors, and some, like Rigby Jr. et al. (1987), Landry (1995), and Reid (1996) advocated for the dome being a heat-exchange organ. ...
... Previously, Galton (1970) had noted the microstructure of the dome and had commented on the radiating trabeculae and fibers which ran perpendicular to the external surface. Galton (1971) went further to claim that this structural arrangement was "ideal" for resisting apical forces. Conducting a photoelastic analysis involving a piece of plexiglass stressed into the shape of a pachycephalosaurid dome, Sues (1978) produced a radial pattern similar to the internal tissue of the dome, concluding it was favorable to resist compressional loads. ...
Headbutting is a combative behavior most popularly portrayed and exemplified in the extant bighorn sheep (Ovis canadensis). When behaviorally proposed in extinct taxa, these organisms are oft depicted Ovis‐like as having used modified cranial structures to combatively slam into one another. The combative behavioral hypothesis of headbutting has a long and rich history in the vertebrate fossil literature (not just within Dinosauria), but the core of this behavioral hypothesis in fossil terrestrial vertebrates is associated with an enlarged osseous cranial dome—an osteological structure with essentially no current counterpart. One confounding issue found in the literature is that while the term “headbutting” sounds simplistic enough, little terminology has been used to describe this hypothesized behavior. And pertinent to this special issue, potential brain trauma and the merits of such proposed pugilism have been assessed largely from the potential deformation of the overlying osseous structure; despite the fact that extant taxa readily show that brain damage can and does occur without osteological compromise. Additionally, the extant taxa serving as the behavioral counterpart for comparison are critical, not only because of the combative behaviors and morphologies they display, but also the way they engage in such behavior. Sheep (Ovis), warthogs (Phacochoerus), and bison (Bison) all engage in various forms of “headbutting”, but the cranial morphologies and the way each engages in combat is markedly different. To hypothesize that an extinct organism engaged in headbutting like an extant counterpart in theory implies specific striking:contacting surfaces, speed, velocity, and overall how that action was executed. This review examines the history and usage of the headbutting behavioral hypothesis in these dome‐headed fossil taxa, their respective extant behavioral counterparts, and proposes a protocol for specific behavioral terms relating to headbutting to stem future confusion. We also discuss the disparate morphology of combative cranial structures in the fossil record, and the implications of headbutting‐induced brain injury in extinct taxa. Finally, we conclude with some potential implications for artistic reconstructions of fossil taxa regarding this behavioral repertoire.
... It has been allied with caenagnathids (Naish and Martill, 2002) but may more closely resemble ornithomimosaurs (Allain et al., 2014); in either case it is distinct from Vectiraptor. Yaverlandia bitholos, represented by a pair of fused and thickened frontals, was traditionally classified as a pachycephalosaurid ornithischian (Galton, 1971). More recently, it has been interpreted as a theropod, perhaps a troodontid (Naish and Martill, 2008). ...
... Neovenator salerii (Hutt et al., 1996) Tyrannosauroidea Eotyrannus lengi (Hutt et al., 2001) Calamosaurus foxii (Lydekker, 1889) ?Ornithomimosauria Thecocoelurus daviesi (Seeley, 1888) Aristosuchus pusillus (Owen, 1876) ?Troodontidae Yaverlandia bitholos (Galton, 1971) ...
A B S T R A C T
The Lower Cretaceous of England has produced a diverse assemblage of dinosaurs, including ornithischians, sauropods, and theropods. The origins of this assemblage are poorly understood. Here, we describe a new dromaeosaurid, Vectiraptor greeni gen. et sp. nov., from the Barremian Wessex Formation of the Isle of Wight. The animal is represented by associated dorsal vertebrae and a partial sacrum. Dorsal vertebrae are short, with pleurocoels, camellate pneumatization, stalked parapophyses and enlarged neural canals. Neural spines are tall, with large ligament scars. Sacral centra lack pleurocoels but have large neural canals and foramina suggesting pneumatization. These characters suggest affinities with Dromaeosauridae and specifically the derived, large-bodied Eudromaeosauria. Vectiraptor resembles Early Cretaceous eudromaeosaurs from North America, suggesting a faunal exchange between Europe and North America. The diverse Early Cretaceous dinosaur assemblage found in England and Europe resulted from dispersal from North America, Asia, and West Gondwana, likely involving both land bridges and oceanic dispersal. Europe served as a biotic crossroads in the Early Cretaceous, allowing faunal interchange between landmasses.
... Goodwin & Horner (2004) demonstrated that the 'bony fibers' in Galton (1970:31) and the 'fibrous columns' in the frontoparietal noted by Galton (1971:45) are (1) visible along broken surfaces of various pachycephalosaurid domes in a hypothesized growth series; (2) the result of the frontoparietal dome growing rapidly in juveniles and subadults; and (3) absent in adults. Goodwin & Horner (2004) rejected the hypothesis of headbutting behavior at that time solely on the fact that cranial characters, in particular the radiating trabeculae, invoked to support head-butting by Galton (1970Galton ( , 1971 and later by Sues (1978) and Alexander (1997), were a product of fast-growing primary bone, ephemeral, and transitory ontogenetically. As a result, these features are absent in more mature individuals who would likely engage in Ovis-like head-butting. ...
A partial skull of a pachycephalosaurid from the Upper Cretaceous Hell Creek Formation, Montana, is interpreted as a new taxon, Platytholus clemensi gen. et sp. nov. MOR 2915 does not fit into an ontogenetic continuum of known pachycephalosaurids from the Hell Creek Formation, Montana, and contemporaneous sediments from the Western Interior. Comparisons to known ontogimorphs of Sphaerotholus and Pachycephalosaurus preclude including this specimen into an ontogenetic series of either taxon. We hypothesize that MOR 2915 is a new species based on a relatively low, broad dome at this advanced ontogenetic age that is neither round nor oval in dorsal view, distinct but fused lateral cranial elements fully incorporated into the dome without any dorsal lobe differentiation, and individual tab-like tubercle ornamentation dorsolaterally. Phylogenetic analysis posits that Platytholus clemensi is a Prenocephale-grade taxon deeply nested within Pachycephalosaurinae, but it is not a member of Pachycephalosaurini. Platytholus clemensi is intermediate in size between the other contemporaneous pachycephalosaurids in the Hell Creek Formation and suggests a diverse set of taxa-partitioned ecological niches by body size. We confirm a well organized, major internal vascular network using high resolution computed tomography. Foramina present on the orbital roofs indicate these canals penetrated the entire ceiling of the orbits within the frontal and supraorbital bones. Abundant neurovascular canals passing through the dome to the ectocranial surface indicate a keratinous structure of some kind, possibly with a vertical structural framework, was present on the dome. We review the history of the head-butting hypothesis and associated behavioral implications.
... The methods proposed here can be useful to study some paleobiological scenarios involving collisions between predators and prey or during intraspecific fighting. For example, it was proposed that pachycephalosaurs' domed skulls were adaptations for head butting behavior (Galton, 1971). However, the hypothesis of agonistic head-to-head butting was considered questionable because the small contact area of opposing heads would produce serious injuries (Alexander, 1989). ...
Leopards have been observed to ambush prey by jumping down on it from trees. There are both anecdotal reports and video recordings of this hunting behavior. Here we conducted a biomechanical analysis of this technique to assess the degree of risk for the predator in such cases. We concluded that the risk of suffering severe injuries seems to be too high for this technique to be a usual way of predation on horned mammals such as male impalas. Our results can be useful in discussing proposed paleobiological hunting scenarios and living predators’ strategies of managing risks.
... El comportamiento de los bóvidos y otros artiodáctilos y la anatomía comparada sirvieron para interpretar este engrosamiento (Snively & Theodor, 2011). Se entendió como una respuesta ante las embestidas frontales que los machos mantenían con otros machos de su misma especie en luchas por rango, territorio o apareamiento con las hembras (Colbert, 1955;Galton, 1971;Sues, 1978). También se ha propuesto que las embestidas podrían haber sido en los flancos (Sues, 1978;Carpenter, 1997) y otras posibles funciones, como la termorregulación (Rigby et al., 1987) o la exhibición (Knell & Sampson, 2011), que actuaría al mismo tiempo de identifi cación sexual y reconocimiento de la especie (Goodwin & Horner, 2004). ...
Desde mediados del siglo XX, los movimientos feministas han centrado buena parte de sus críticas en la presencia de sesgos androcéntricos en la mayoría de las disciplinas científicas, lo que en algunas de ellas ha generado una auténtica revolución a nivel teórico y práctico que ha conseguido transformarlas de una forma sustancial y significativa. Durante este tiempo, la paleontología ha quedado relativamente al margen de este proceso, quizás porque su aparente objetividad y las particulares características de su principal objeto de estudio parecen aislarla de las influencias procedentes de las modernas corrientes de pensamiento social. No obstante, al igual que cualquier otra ciencia, la paleontología es un reflejo de la sociedad en la que se desarrolla. En consecuencia, también se encuentra influenciada, directa o indirectamente, por una ideología patriarcal que continúa presente y discrimina lo femenino en todos los ámbitos. En este artículo se describen algunos ejemplos de cómo esta ideología y sus sesgos asociados se han manifestado en la práctica profesional y en la investigación paleontológica; en las expresiones y el lenguaje utilizados en sus interpretaciones; en la reproducción de estereotipos, y en la exposición y comunicación del conocimiento resultado de sus investigaciones, especialmente en los museos. El objetivo es proponer una reflexión a partir de una crítica constructiva, la cual permita incorporar una nueva mirada que acerque la paleontología a la realidad del siglo XXI, donde el papel de la mujer es cada día más reconocido y los estudios científicos intentan ser inclusivos y libres de prejuicios
Pachycephalosauridae (pachcycephalosaurids) were small to medium sized bipedal ornithischians, known solely from the Late Cretaceous of North America and Asia. These dinosaurs are characterised by thick, often domed frontals and parietals (frontoparietal dome), which are thought to have been used in intraspecific head-butting combat rituals. The dome, along with their thickened skull bones have a high preservation potential, particularly compared to the rest of the skeleton. Thus, the vast majority of pachycephalosaurid fossils consist of their unique skull bones, and so much research on the group has focused on these elements. The morphology of the thickened skull roof is included in the diagnosis of every species, yet the skull roof changes dramatically through ontogeny, and numerous putative species have been reidentified as juvenile or subadult representatives of other species.
In this thesis, I focus on exploring morphological variation amongst pachycephalosaurid skulls, particularly the frontoparietal dome, and address its utility in pachycephalosaurid taxonomy and phylogenetics. I begin with describing the anatomy of the only known specimen of the controversial Gravitholus albertae, from the Late Cretaceous of Alberta, Canada. The specimen represents a heavily fused partial skull roof, and the degree of fusion has prevented a detailed description of the specimen, thus the validity of the species has been repeatedly justified and challenged. Alternative taxonomic hypotheses suggest Gravitholus albertae may be synonymous with Hanssuesia sternbergi or Stegoceras validum). I utilise synchrotron μCT imaging to identify the locations of the holotype’s fused contacts, which facilitates a detailed description of the specimen. Gravitholus albertae was then included with Hanssuesia sternbergi and Stegoceras validum in morphometric analyses, to evaluate the distinctness of these three species. There are no ontogenetic-independent features of “Gravitholus albertae” that would justify a unique species. Instead, Gravitholus albertae and Hanssuesia sternbergi are morphologically consistent with mature Stegoceras validum. Thus, Gravitholus albertae and Hanssuesia sternbergi are synonymous with Stegoceras validum. Interestingly, Stegoceras validum appears to possess adult dimorphism in the thickness of the frontonasal boss, which is not explained by previous taxonomic hypotheses. Instances of post-traumatic injuries, consistent with head-butting, appear restricted to individuals with thicker frontonasal bosses. The dimorphism in Stegoceras validum is interpreted as sexual dimorphism, with the thicker bossed sex engaging in ritualistic intraspecific combat.
I then move onto assessing morphological variation in pachycephalosaurid frontoparietals by statistically testing previously proposed discrete character states used in phylogenetic analyses, attempt to identify new characters and states, and comment on the validity of Stegoceras novomexicanum. The use of several features previously used as structures for phylogenetic characters are supported, and the distinction of their character stares are statistically demonstrated. These states are broadly consistent with previous taxonomic assessments, although a few species in each revised character are reassessed. There is no morphological support for “Stegoceras novomexicanum” and is regarded as Pachycephalosauridae indeteterminate. “Stegoceras novomexicanum “, along with other invalidated pachycephalosaurids, were removed from a phylogenetic analysis based on a revised morphological character matrix. This phylogenetic tree of Pachycephalosauria (pachycephalosaurians) is broadly similar to pervious analyses. The main differences include recovering Colepiocephale lambei as a basal Pachycephalosaurinae (pachycephalosaurines), and a polyphyletic Sphaerotholus. Derived pachycephalosaurines appear to be united by a cranial dome that initially develops on the parietals (as opposed to initially developing on the frontals). This distinction deserves further investigation with histological and CT methodologies to determine the developmental pathways that different pachycephalosaurid species took to grow their domes.
Despite reports of sexual dimorphism in extinct taxa, such claims in non-avian dinosaurs have been rare over the last decade and have often been criticized. Since dimorphism is widespread in sexually reproducing organisms today, under-reporting in the literature might suggest either methodological shortcomings or that this diverse group exhibited highly unusual reproductive biology. Univariate significance testing, especially for bimodality, is ineffective and prone to false negatives. Species recognition and mutual sexual selection hypotheses, therefore, may not be required to explain supposed absence of sexual dimorphism across the grade (a type II error). Instead, multiple lines of evidence support sexual selection and variation of structures consistent with secondary sexual characteristics, strongly suggesting sexual dimorphism in non-avian dinosaurs. We propose a framework for studying sexual dimorphism in fossils, focusing on likely secondary sexual traits and testing against all alternate hypotheses for variation in them using multiple lines of evidence. We use effect size statistics appropriate for low sample sizes, rather than significance testing, to analyse potential divergence of growth curves in traits and constrain estimates for dimorphism magnitude. In many cases, estimates of sexual variation can be reasonably accurate, and further developments in methods to improve sex assignments and account for intrasexual variation (e.g. mixture modelling) will improve accuracy. It is better to compare estimates for the magnitude of and support for dimorphism between datasets than to dichotomously reject or fail to reject monomorphism in a single species, enabling the study of sexual selection across phylogenies and time. We defend our approach with simulated and empirical data, including dinosaur data, showing that even simple approaches can yield fairly accurate estimates of sexual variation in many cases, allowing for comparison of species with high and low support for sexual variation.
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