Sphaerotholus

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Sphaerotholus
Temporal range: Late Cretaceous, 76–66  Ma
Sphaerotholus.png
S. buchholtzae specimen AMNH 0044
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Ornithischia
Clade: Neornithischia
Clade: Pachycephalosauria
Family: Pachycephalosauridae
Subfamily: Pachycephalosaurinae
Genus: Sphaerotholus
Williamson & Carr, 2002
Type species
Sphaerotholus goodwini
Williamson & Carr, 2002
Other species
  • S. buchholtzaeWilliamson & Carr, 2002
  • S. edmontonensis(Brown & Schlaikjer, 1943)
  • S. lyonsiWoodruff, Schott & Evans, 2023
  • S. triregnumWoodruff, Schott & Evans, 2023

Sphaerotholus is a genus of pachycephalosaurid dinosaur from the Upper Cretaceous of the western United States and Canada. To date, five species have been described: the type species, S. goodwini, from the Den-na-zin Member of the Kirtland Formation and possibly the Fossil Forest Member of the Fruitland Formation (Late Campanian) of San Juan County, New Mexico, USA; S. buchholtzae, from the Hell Creek Formation (Late Maastrichtian) of western Carter County, Montana, USA and the Frenchman Formation of Saskatchewan, Canada; S. edmontonensis, from the Horseshoe Canyon Formation of Alberta, Canada; S. lyonsi, from the Dinosaur Park Formation (Campanian) of Alberta, Canada; and S. triregnum from the Hell Creek Formation of Garfield County, Montana, USA.

Contents

History of discovery

The etymology of Sphaerotholus is a combination of the Greek sphaira, meaning "ball", and tholos, meaning "dome", and is a reference to the characteristically dome-shaped pachycephalosaurian skull. The survival of Sphaerotholus from the Campanian of New Mexico to the end of the Maastrichtian of Montana demonstrates that this taxon had both a relatively long duration (approximately 7-8 million years) and a widespread distribution. Williamson and Carr, who first described the genus in 2002, diagnose it as follows: "Differs from all other pachycephalosaurids where known in the possession of a parietosquamosal bar that decreases in depth laterally as seen in caudal view and is bordered by a single row of nodes and one lateroventral corner node." Sphaerotholus is considered a highly derived pachycephalosaur. [1]

Species

Sphaerotholus goodwini

The holotype of the type species (NMMNH P-27403, New Mexico Museum of Natural History) consists of an incomplete skull lacking the facial and palatal elements. The species is diagnosed as follows: "Sphaerotholus which in caudal view possesses a parietosquamosal bar that reduces in depth laterally to a lesser extent than in S. buchholtzae and the parietal is reduced to a thin slip between the squamosals." The species name honors paleontologist Mark Goodwin for his work with pachycephalosaurian dinosaurs. [1] It has been suggested that Stegoceras novomexicanum is a juvenile representative of this species, because the parietal shelf that morphologically distinguishes S. novomexicanum from Sphaerotholus goodwini disappears through growth in Stegoceras validum. [2] [3]

Sphaerotholus edmontonensis

Troodon edmontonensis was described by Brown and Schlaikjer in 1943 on the basis of three domes from the Horseshoe Canyon Formation of Alberta. [4] Williamson and Carr considered the species to be invalid, [1] but in 2010 Nicholas Longrich et al. created the novel combination Sphaerotholus edmontonensis that could be distinguished from S. goodwini by the paired hornlets on the back of the dome, and from S. buchholtzae by the elongate parietals. [5] It was once considered a species of Stegoceras and was about the same size, reaching 2 m (6.6 ft) in length and 40 kg (88 lb) in body mass. [6]

Sphaerotholus buchholtzae

Restoration of a pair of S. buchholtzae Sphaerotholus.jpg
Restoration of a pair of S. buchholtzae

The holotype of S. buchholtzae (TMP 87.113.3) consists of an incomplete skull, found in the Hell Creek Formation. The species was diagnosed as having a parietal that is widely exposed between the squamosals and wide enough to bear parietosquamosal nodes, a shallower caudal margin of the parietosquamosal shelf, the lateral corner node is reduced in size and located above the ventral margin of the parietosquamosal bar, and the nodes in the lateral margin of the parietosquamosal shelf reduced on the squamosal and coalescing into a ridge on the postorbital. [1] The specific name honors Emily A. Buchholtz for her extensive work with pachycephalosaurians.

Sullivan (2003) considered S. buchholtzae a junior synonym of Prenocephale edmontonensis (or Sphaerotholus edmontonensis). [7] However, Mallon et al. (2015), in their description of a new S. buchholtzae specimen from the Frenchman Formation of Saskatchewan, Canada, noted that S. edmontonensis was distinct from S. buchholtzae based on comparative morphology and morphometrics. [8] Additionally, a redescription of S. buchholtzae used geometric morphometrics to distinguish the two species. [9]

Sphaerotholus lyonsi

Described by Woodruff, Schott, and Evans in 2023 based on an immature specimen. Lived in the Dinosaur Park Formation in Canada, c. 76 million years ago. It is characterized by a double row of small bony nodes along the back of its skull, as opposed to the single row of large nodes in S. goodwini, S. edmontonensis, and S. buchholtzae. [10]

Sphaerotholus triregnum

Described by Woodruff, Schott, and Evans in 2023 based on a subadult specimen. Lived in the middle section of the Hell Creek Formation in Montana, USA. [10] It is characterized by a triple row of small bony nodes along the back of its skull, as opposed to the single row of large nodes in S. buchholtzae and S. edmontonensis. [10] It is named for the resemblance of its domed skull with a triple "crown"-like appearance of nodes to the Papal tiara or "Triregnum". [10]

Classification

Sphaerotholus buchholtzae (small) fighting below larger pachycephalosaurs Hell Creek pachycephalosaurs.jpg
Sphaerotholus buchholtzae (small) fighting below larger pachycephalosaurs

In their 2023 description of S. lyonsi and S. triregnum, Woodruff, Schott & Evans analyzed the placement of the genus Sphaerotholus within the Pachycephalosauria. They recovered all proposed species of Sphaerotholus as a monophyletic group of derived pachycephalosaurines, as the sister taxon to the Pachycephalosaurini. The results of their phylogenetic analyses are shown in the cladogram below: [10]

Pachycephalosauria

See also

Related Research Articles

<span class="mw-page-title-main">Pachycephalosauria</span> Extinct clade of dinosaurs

Pachycephalosauria is a clade of ornithischian dinosaurs. Along with Ceratopsia, it makes up the clade Marginocephalia. With the exception of two species, most pachycephalosaurs lived during the Late Cretaceous Period, dating between about 85.8 and 66 million years ago. They are exclusive to the Northern Hemisphere, all of them being found in North America and Asia. They were all bipedal, herbivorous/omnivorous animals with thick skulls. Skulls can be domed, flat, or wedge-shaped depending on the species, and are all heavily ossified. The domes were often surrounded by nodes and/or spikes. Partial skeletons have been found of several pachycephalosaur species, but to date no complete skeletons have been discovered. Often isolated skull fragments are the only bones that are found.

<i>Pachycephalosaurus</i> Genus of pachycephalosaurid dinosaurs

Pachycephalosaurus is a genus of pachycephalosaurid ornithischian dinosaur. The type species, P. wyomingensis, is the only known species, but some researchers argue that Stygimoloch might be a second species, P. spinifer, or a juvenile specimen of P. wyomingensis. It lived during the Maastrichtian age of the Late Cretaceous period in what is now western North America. Remains have been excavated in Montana, South Dakota, Wyoming, and Alberta. The species is known mainly from a single skull, plus a few extremely thick skull roofs. More complete fossils would come to be found in the following years.

<i>Stegoceras</i> Genus of pachycephalosaurid dinosaurs

Stegoceras is a genus of pachycephalosaurid (dome-headed) dinosaur that lived in what is now North America during the Late Cretaceous period, about 77.5 to 74 million years ago (mya). The first specimens from Alberta, Canada, were described in 1902, and the type species Stegoceras validum was based on these remains. The generic name means "horn roof", and the specific name means "strong". Several other species have been placed in the genus over the years, but these have since been moved to other genera or deemed junior synonyms. Currently only S. validum and S. novomexicanum, named in 2011 from fossils found in New Mexico, remain. The validity of the latter species has also been debated, and it may not even belong to the genus Stegoceras.

<i>Homalocephale</i> Extinct genus of dinosaurs

Homalocephale is a genus of pachycephalosaurid dinosaur that lived during the Late Cretaceous period of what is now the Nemegt Formation, Mongolia, about 70 million years ago. The genus was described in 1974 by Halszka Osmólska and Teresa Maryańska, and consists of a single species, H. calathocercos. Though Homalocephale has been regarded as a synonym of Prenocephale, juvenile specimens of the latter indicate that they were distinct. Homalocephale was 1.8 m (5.9 ft) long and possibly a omnivore.

<i>Prenocephale</i> Extinct genus of dinosaurs

Prenocephale is a genus of small pachycephalosaurid dinosaur from the Late Cretaceous Nemegt Formation of Mongolia. It was similar in many ways to its close relative, Homalocephale.

<i>Tylocephale</i> Extinct genus of dinosaurs

Tylocephale is a genus of pachycephalosaurid dinosaur, a group of dome-headed, herbivorous ornithischians, that lived during the Late Campanian stage of the Late Cretaceous in what is now Mongolia. It is known from a partial skull and associated mandible that were unearthed in 1971 by a Polish-Mongolian Expedition to the Barun Goyot Formation of the Gobi Desert. The specimen was described in 1974 by Polish paleontologists Teresa Maryańska and Halszka Osmólska as a new genus and species.

<i>Colepiocephale</i> Extinct genus of dinosaurs

Colepiocephale is a genus of pachycephalosaurid dinosaur from Late Cretaceous deposits of Alberta, Canada. It was collected from the Foremost Formation. The type species, C. lambei, was originally described by Sternberg, and later renamed by Sullivan in 2003. C. lambei is a domed pachycephalosaur characterized principally by the lack of a lateral and posteriosquamosal shelf, a steeply down-turned parietal, and the presence of two incipient nodes tucked under the posterior margin of the parietosquamosal border.

<i>Nodocephalosaurus</i> Extinct genus of dinosaurs

Nodocephalosaurus is a monospecific genus of ankylosaurid dinosaur from New Mexico that lived during the Late Cretaceous in what is now the De-na-zin member of the Kirtland Formation. The type and only species, Nodocephalosaurus kirtlandensis, is known only from a partial skull. It was named in 1999 by Robert M. Sullivan. Nodocephalosaurus has an estimated length of 4.5 metres and weight of 1.5 tonnes. It is closely related and shares similar cranial anatomy to Akainacephalus.

<i>Goyocephale</i> Extinct genus of dinosaurs

Goyocephale is an extinct genus of pachycephalosaurian ornithischian that lived in Mongolia during the Late Cretaceous about 76 million years ago. It was first described in 1982 by Altangerel Perle, Teresa Maryańska and Halszka Osmólska for a disarticulated skeleton with most of a skull, part of the forelimb and hindlimb, some of the pelvic girdle, and some vertebrae. Perle et al. named the remains Goyocephale lattimorei, from the Mongolian гоё (goyo), meaning "decorated", and the Ancient Greek κεφαλή (kephale), for head. The species name honours Owen Lattimore.

<i>Hanssuesia</i> Extinct genus of dinosaurs

Hanssuesia is a genus of pachycephalosaurid dinosaurs from the late Cretaceous period. It lived in what is now Alberta and Montana, and contains the single species Hanssuesia sternbergi.

<i>Gravitholus</i> Extinct genus of dinosaurs

Gravitholus was a genus of pachycephalosaurid dinosaur from the late Cretaceous period. It was a pachycephalosaur, and like other pachycephalosaurids the skull roof formed a thick dome made of dense bone, which may have been used in head-butting contests over mates or territory. It lived in what is now Alberta, Canada, and was described in 1979 by W. P. Wall and Peter Galton. The type species is Gravitholus albertae.

<span class="mw-page-title-main">Kirtland Formation</span> Geological formation in New Mexico and Colorado, United States

The Kirtland Formation is a sedimentary geological formation.

<i>Alaskacephale</i> Extinct genus of dinosaurs

Alaskacephale is an extinct genus of pachycephalosaurid, a group of dome-headed, herbivorous ornithischian dinosaurs, that lived during the Campanian stage of the Late Cretaceous period in what is now northern Alaska. The genus is one of the few known Arctic dinosaurs and was found in the Prince Creek Formation, which preserves a menagerie of fossils. The only known specimen, a squamosal bone, was found in 1999 and later described in 2005. However, Alaskacephale was not formally named until the next year.

<i>Texacephale</i> Extinct genus of dinosaurs

Texacephale is a pachycephalosaurid dinosaur from the Campanian stage of the Late Cretaceous. Its fossils come from the Aguja Formation of Big Bend National Park, in Texas, and were described in 2010 by Longrich, Sankey and Tanke. The generic name means Texas + "head" in reference to its place of discovery, and the specific name langstoni honors Wann Langston.

<i>Foraminacephale</i> Extinct genus of dinosaurs

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<i>Acrotholus</i> Extinct genus of dinosaurs

Acrotholus is an extinct genus of pachycephalosaur dinosaur that lived during the Santonian of the late Cretaceous, in the Milk River Formation of Canada. The type species, A. audeti, was named after Roy Audet allowing access to his ranch leading to the discovery of the species. The discovery of this specimen lead to several new revelations in the fossil records questioning the preservation of small-bodied organisms along with the evolution of early pachycephalosaurs. The iconic cranial dome found on Acrotholus makes it one of the earliest indisputable known members of the pachycephalosaur family.

<span class="mw-page-title-main">Timeline of pachycephalosaur research</span> The progression of pachycephalosaur research over time

This timeline of pachycephalosaur research is a chronological listing of events in the history of paleontology focused on the pachycephalosaurs, a group of dome-skulled herbivorous marginocephalian dinosaurs. One of the first major events related to the history of pachycephalosaur research actually regards the discovery of an unrelated dinosaur called Troodon, reported from the western United States by Joseph Leidy in 1856. The type specimen of Troodon was simply an unusual tooth, but the close resemblance between Troodon teeth and pachycephalosaur teeth would cause taxonomic confusion for over a century. This was resolved by Phil Currie in 1987, who realized that Troodon belonged to a group of bird-like carnivores then known as saurornithoidids, but since renamed Troodontidae after Troodon itself. The first scientifically documented true pachycephalosaur remains were discovered in Early Cretaceous rocks from England and named Stenopelix not long after Troodon was named in America. Other notable early finds include the well-known pachycephalosaur Stegoceras validum.

Sinocephale is a genus of pachycephalosaurid dinosaur that lived in Inner Mongolia, China during the Cretaceous period. The only species, Sinocephale bexelli, was originally named as a species of the genus Troodon in 1953, and later transferred to the genus Stegoceras. After decades of being considered dubious, it was re-evaluated in 2021 and recognized as a valid taxon, being given a unique generic name. The original holotype was lost, with modern research conducted using rediscovered plaster casts. Scant material makes for limited knowledge of its life appearance, but it is distinguished by an embayment on the back of the domed skull, which would give it a heart shape as seen from above. It is potentially the oldest known pachycephalosaurid and falls within the subset of the family called Pachycephalosaurinae, related to animals such as Pachycephalosaurus and Prenocephale. The geologic context of the species has been historically unclear but it is currently thought to originate in rocks belonging to the Ulansuhai Formation.

References

  1. 1 2 3 4 Williamson Thomas E.; Carr Thomas D. (2002). "A new genus of highly derived pachycephalosaurian from western North America". Journal of Vertebrate Paleontology. 22 (4): 779–801. doi:10.1671/0272-4634(2002)022[0779:angodp]2.0.co;2.
  2. Williamson, T. E.; Brusatte, S. L. (2016). "Pachycephalosaurs (Dinosauria: Ornithischia) from the Upper Cretaceous (upper Campanian) of New Mexico: A reassessment of Stegoceras novomexicanum". Cretaceous Research. 62: 29–43. Bibcode:2016CrRes..62...29W. doi: 10.1016/j.cretres.2016.01.012 .
  3. Dyer, Aaron D.; Powers, Mark J.; Currie, Philip J. (2023). "Problematic putative pachycephalosaurids: Synchrotron µCT imaging shines new light on the anatomy and taxonomic validity of Gravitholus albertae from the Belly River Group (Campanian) of Alberta, Canada". Vertebrate Anatomy Morphology Palaeontology. 10 (1): 65–110. doi: 10.18435/vamp29388 . ISSN   2292-1389.
  4. Brown B.; Schlaikjer E. M. (1943). "A study of the troödont dinosaurs with a description of a new genus and four new species". Bulletin of the American Museum of Natural History. 82 (5): 115–149.
  5. Longrich N. R.; Sankey J. T.; et al. (2010). "Texacephale langstoni, a new genus of pachycephalosaurid (Dinosauria: Ornithischia) from the upper Campanian Aguja Formation, southern Texas, USA". Cretaceous Research. 31 (2): 274–284. Bibcode:2010CrRes..31..274L. doi:10.1016/j.cretres.2009.12.002.
  6. Paul, Gregory S. (2016). The Princeton Field Guide to Dinosaurs. Princeton University Press. p. 269. ISBN   978-1-78684-190-2. OCLC   985402380.
  7. Robert M. Sullivan (2003). "Revision of the dinosaur Stegoceras Lambe (Ornithischia, Pachycephalosauridae)". Journal of Vertebrate Paleontology. 23 (1): 181–207. doi:10.1671/0272-4634(2003)23[181:rotdsl]2.0.co;2.
  8. Mallon Jordan C.; Evans David C.; Tokaryk Tim T.; Currie Margaret L. (2015). "First pachycephalosaurid (Dinosauria: Ornithischia) from the Frenchman Formation (upper Maastrichtian) of Saskatchewan, Canada". Cretaceous Research. 56: 426–431. Bibcode:2015CrRes..56..426M. doi:10.1016/j.cretres.2015.06.005.
  9. Woodruff, D Cary; Goodwin, Mark B; Lyson, Tyler R; Evans, David C (2021-02-01). "Ontogeny and variation of the pachycephalosaurine dinosaur Sphaerotholus buchholtzae, and its systematics within the genus". Zoological Journal of the Linnean Society. 193 (2): 563–601. doi:10.1093/zoolinnean/zlaa179. ISSN   0024-4082.
  10. 1 2 3 4 5 Woodruff, D. Cary; Schott, Ryan K.; Evans, David C. (2023-11-15). "Two new species of small-bodied pachycephalosaurine (Dinosauria, Marginocephalia) from the uppermost Cretaceous of North America suggest hidden diversity in well-sampled formations". Papers in Palaeontology. 9 (6). e1535. Bibcode:2023PPal....9E1535W. doi:10.1002/spp2.1535. ISSN   2056-2799.

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