Distributions of cranial pathologies provide evidence for head-butting in dome-headed dinosaurs (Pachycephalosauridae).
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ABSTRACT:
SUBMITTER: Peterson JE
PROVIDER: S-EPMC3712952 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:BackgroundDuring much of the Late Cretaceous, a shallow, epeiric sea divided North America into eastern and western landmasses. The western landmass, known as Laramidia, although diminutive in size, witnessed a major evolutionary radiation of dinosaurs. Other than hadrosaurs (duck-billed dinosaurs), the most common dinosaurs were ceratopsids (large-bodied horned dinosaurs), currently known only from Laramidia and Asia. Remarkably, previous studies have postulated the occurrence of latitudinally arrayed dinosaur "provinces," or "biomes," on Laramidia. Yet this hypothesis has been challenged on multiple fronts and has remained poorly tested.Methodology/principal findingsHere we describe two new, co-occurring ceratopsids from the Upper Cretaceous Kaiparowits Formation of Utah that provide the strongest support to date for the dinosaur provincialism hypothesis. Both pertain to the clade of ceratopsids known as Chasmosaurinae, dramatically increasing representation of this group from the southern portion of the Western Interior Basin of North America. Utahceratops gettyi gen. et sp. nov.-characterized by short, rounded, laterally projecting supraorbital horncores and an elongate frill with a deep median embayment-is recovered as the sister taxon to Pentaceratops sternbergii from the late Campanian of New Mexico. Kosmoceratops richardsoni gen. et sp. nov.-characterized by elongate, laterally projecting supraorbital horncores and a short, broad frill adorned with ten well developed hooks-has the most ornate skull of any known dinosaur and is closely allied to Chasmosaurus irvinensis from the late Campanian of Alberta.Conclusions/significanceConsidered in unison, the phylogenetic, stratigraphic, and biogeographic evidence documents distinct, co-occurring chasmosaurine taxa north and south on the diminutive landmass of Laramidia. The famous Triceratops and all other, more nested chasmosaurines are postulated as descendants of forms previously restricted to the southern portion of Laramidia. Results further suggest the presence of latitudinally arrayed evolutionary centers of endemism within chasmosaurine ceratopsids during the late Campanian, the first documented occurrence of intracontinental endemism within dinosaurs.
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Project description:The island effect is a well-known evolutionary phenomenon, in which island-dwelling species isolated in a resource-limited environment often modify their size, anatomy, and behaviors compared with mainland relatives. This has been well documented in modern and Cenozoic mammals, but it remains unclear whether older, more primitive Mesozoic mammals responded in similar ways to island habitats. We describe a reasonably complete and well-preserved skeleton of a kogaionid, an enigmatic radiation of Cretaceous island-dwelling multituberculate mammals previously represented by fragmentary fossils. This skeleton, from the latest Cretaceous of Romania, belongs to a previously unreported genus and species that possesses several aberrant features, including an autapomorphically domed skull and one of the smallest brains relative to body size of any advanced mammaliaform, which nonetheless retains enlarged olfactory bulbs and paraflocculi for sensory processing. Drawing on parallels with more recent island mammals, we interpret these unusual neurosensory features as related to the island effect. This indicates that the ability to adapt to insular environments developed early in mammalian history, before the advent of therian mammals, and mammals with insular-related modifications were key components of well-known dwarfed dinosaur faunas. Furthermore, the specimen suggests that brain size reduction, in association with heightened sensory acuity but without marked body size change, is a novel expression of the island effect in mammals.
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Project description:BackgroundA frontoparietal dome of a large pachycephalosaurid collected from the Upper Cretaceous Hell Creek Formation in 2001 is identified as Pachycephalosaurus wyomingensis. The specimen features two large oval depressions on the dorsal surface, accompanied by numerous circular pits on the margin and inner surface of the larger depressions.Methodology/principal findingsIn order to identify the origin of these structures, computed tomography (CT) data and morphological characteristics of the specimen are analyzed and compared with similar osteological structures in fossil and extant archosaurs caused by taphonomic processes, non-pathologic bone resorption, and traumatic infection/inflammatory origins. The results of these analyses suggest that the structures are pathologic lesions likely resulting from a traumatic injury and followed by secondary infection at the site.Conclusions/significanceThe presence of lesions on a frontoparietal dome, and the exclusivity of their distribution along the dorsal dome surface, offers further insight into frontoparietal dome function and supports previously hypothesized agonistic behavior in pachycephalosaurids.
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