<i>Torosaurus</i>Marsh, 1891, is<i>Triceratops</i>Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny

Scannella, John B.; Horner, John R.

doi:10.1080/02724634.2010.483632

Cited by 118 publications

(204 citation statements)

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“…Four disparity metrics were calculated for each set of species in each time bin: the sum and product of the ranges and the variances on the set of PCO axes that together described 90% of total variance. The number of axes used for each clade is as follows: coelurosaurs (20), tyrannosauroids (6), pachycephalosaurs (11), ceratopsids (15), hadrosauroids (37), sauropods (11), and ankylosaurs (9). The disparity metrics were calculated using the software program RARE 46 , and the two multiplicative metrics were normalized by taking the root corresponding to the number of PCO axes used (for example, in the case of coelurosaurs, they were normalized by taking the twentieth root).…”

Section: Methodsmentioning

confidence: 99%

“…Diversity counts, however, are problematic because of the emerging realizations that observed taxonomic richness is heavily biased by uneven sampling of the fossil record 16,17 and that many supposed Late Cretaceous dinosaur species are likely juveniles or sexual morphs of other known taxa [18][19][20] . Attempts to 'correct' terminal Cretaceous diversity counts for such biases have produced conflicting results [10][11][12][13][14][15] .…”

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confidence: 99%

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Dinosaur morphological diversity and the end-Cretaceous extinction

et al. 2012

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confidence: 99%

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Dinosaur morphological diversity and the end-Cretaceous extinction

et al. 2012

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“…Triceratops (Ceratopsidae: Chasmosaurinae) is the most abundant dinosaur in the HCF; >50 skulls, including previously unknown or rare growth stages, have been collected throughout the entire formation (spanning ∼1-2 million y) (2) over the course of the Hell Creek Project (1,(3)(4)(5). The combination of a stratigraphically controlled robust sample from the entire ∼90-m-thick HCF and identification of ontogenetic stages makes Triceratops a model organism for testing hypotheses proposed for the modes of dinosaur evolution (e.g., refs.…”

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Evolutionary trends inTriceratopsfrom the Hell Creek Formation, Montana

Scannella

Fowler

Goodwin

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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The placement of over 50 skulls of the well-known horned dinosaur Triceratops within a stratigraphic framework for the Upper Cretaceous Hell Creek Formation (HCF) of Montana reveals the evolutionary transformation of this genus. Specimens referable to the two recognized morphospecies of Triceratops, T. horridus and T. prorsus, are stratigraphically separated within the HCF with the T. prorsus morphology recovered in the upper third of the formation and T. horridus found lower in the formation. Hypotheses that these morphospecies represent sexual or ontogenetic variation within a single species are thus untenable. Stratigraphic placement of specimens appears to reveal ancestor-descendant relationships. Transitional morphologies are found in the middle unit of the formation, a finding that is consistent with the evolution of Triceratops being characterized by anagenesis, the transformation of a lineage over time. Variation among specimens from this critical stratigraphic zone may indicate a branching event in the Triceratops lineage. Purely cladogenetic interpretations of the HCF dataset imply greater diversity within the formation. These findings underscore the critical role of stratigraphic data in deciphering evolutionary patterns in the Dinosauria.T he Hell Creek Project (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010), a multiinstitutional survey of the fauna, flora, and geology of the Upper Cretaceous Hell Creek Formation (HCF), provides insights into the paleobiology and evolution of the last nonavian dinosaurs (1). Triceratops (Ceratopsidae: Chasmosaurinae) is the most abundant dinosaur in the HCF; >50 skulls, including previously unknown or rare growth stages, have been collected throughout the entire formation (spanning ∼1-2 million y) (2) over the course of the Hell Creek Project (1, 3-5). The combination of a stratigraphically controlled robust sample from the entire ∼90-m-thick HCF and identification of ontogenetic stages makes Triceratops a model organism for testing hypotheses proposed for the modes of dinosaur evolution (e.g., refs. 6-8).Since its initial discovery (9), as many as 16 species of Triceratops were named based on variations in cranial morphology (10, 11). Forster (12) recognized only two species, Triceratops horridus and Triceratops prorsus, based on cranial features including differences in relative length of the postorbital horn cores (long in T. horridus and shorter in T. prorsus), morphology of the rostrum (elongate in T. horridus and shorter in T. prorsus), and closure of the frontoparietal fontanelle (sensu Farke) (13) (open in T. horridus and closed in T. prorsus). Marsh initially distinguished these two species by the morphology of the nasal horn (14); the type specimen of T. horridus possesses a short, blunt nasal horn whereas the nasal horn in T. prorsus is elongate. Whether or not these taxa were largely biogeographically separated or represented ontogenetic variants or sexual dimorphs within a single species has remained unresolved (8,10,12,(15)(16)(...

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“…A very small Triceratops with a skull 30 cm long (Goodwin et al, 2006) (adult skulls reach 3 m) imitates elders of his species in aspects of horn and frill ornamentation, yet he is years away from reproducing. Mid-sized Triceratops have horn and frill configurations that are still different from full-grown forms (Scannella & Horner, 2010). And the related pachycephalosaurs went through some staggering ontogenetic changes in skull form well before sexual maturity (Horner & Goodwin, 2009).…”

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confidence: 99%

“…There is increasing evidence of anagenetic change between species that previously were considered sister taxa (e.g. Evans, 2010;Scannella & Horner, 2010), and these changes may have taken thousands to tens of thousands of years or less, judging by biostratigraphic distributions. However, we are making a rather different point that we would not expect directional trends within clades in which species are simply evolving to be recognizably different from each other.…”

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confidence: 99%