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. 2014 Feb 13:2:e252.
doi: 10.7717/peerj.252. eCollection 2014.

Craniofacial ontogeny in Centrosaurus apertus

Joseph A Frederickson  1 , Allison R Tumarkin-Deratzian  1
Affiliations

Craniofacial ontogeny in Centrosaurus apertus

Joseph A Frederickson et al. PeerJ. .

Abstract

Centrosaurus apertus, a large bodied ceratopsid from the Late Cretaceous of North America, is one of the most common fossils recovered from the Belly River Group. This fossil record shows a wide diversity in morphology and size, with specimens ranging from putative juveniles to fully-grown individuals. The goal of this study was to reconstruct the ontogenetic changes that occur in the craniofacial skeleton of C. apertus through a quantitative cladistic analysis. Forty-seven cranial specimens were independently coded in separate data matrices for 80 hypothetical multistate growth characters and 130 hypothetical binary growth characters. Both analyses yielded the max-limit of 100,000 most parsimonious saved trees and the strict consensus collapsed into large polytomies. In order to reduce conflict resulting from missing data, fragmentary individuals were removed and the analyses were rerun. Among both the complete and the reduced data sets the multistate analyses recovered a shorter tree with a higher consistency index (CI) than the additive binary data sets. The arrangement within the trees shows a progression of specimens with a recurved nasal horn in the least mature individuals, followed by specimens with straight nasal horns in relatively more mature individuals, and finally specimens with procurved nasal horns in the most mature individuals. The most mature individuals are further characterized by the reduction of the cranial horn ornamentations in late growth stages, a trait that similarly occurs in the growth of other dinosaurs. Bone textural changes were found to be sufficient proxies for relative maturity in individuals that have not reached adult size. Additionally, frill length is congruent with relative maturity status and makes an acceptable proxy for ontogenetic status, especially in smaller individuals. In adult-sized individuals, the fusion of the epiparietals and episquamosals and the orientation of the nasal horn are the best indicators of relative maturity. This study recovers no clear evidence for sexually specific display structures or size dimorphism in C. apertus.

Keywords: Centrosaurus; Ceratopsia; Cladistics; Dinosauria; Fossil; Growth; Ontogeny.

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Conflict of interest statement

Neither author has declared any competing interests regarding financial, non-financial, professional, or personal relationships that could in any way bias this research.

Figures

Figure 1
Figure 1. Bone fusion character states for the middle premaxillary suture (white arrow) in rostral view.
(A) CMN 348, open; (B) UALVP 11735, partially obliterated.; (C) YPM 2015, fully obliterated. Images not to scale. Division of Vertebrate Paleontology, YPM 2015. Courtesy of the Peabody Museum of Natural History, Yale University, New Haven, Connecticut, USA.
Figure 2
Figure 2. 50% majority rule consensus tree for 100,000 MPTs, based on multistate character coding.
This tree is 234 steps long, and has a CI of 0.5297. The numbers above each node represent the percent frequency of each grouping out of the 100,000 total trees. Underlined specimens are also found in the reduced analysis.
Figure 3
Figure 3. 50% majority rule consensus tree for 100,000 MPTs, based on additive binary character coding.
This tree is 265 steps long, has a CI of 0.4868. The numbers above each node represent the percent frequency of each grouping out of the 100,000 total trees. Underlined specimens are also found in the reduced analysis.
Figure 4
Figure 4. The single tree recovered for the reduced multistate data set.
The tree is 206 steps long, with a CI of 0.5874. The tree on the left represents ACCTRAN optimization and the tree on the right represents DELTRAN optimization. The numbers above the nodes represent the Bremer Decay Index (upper) and the Bootstrap value (lower; <50% not shown). Synontomorphies for lettered nodes are listed in Table 1.
Figure 5
Figure 5. Strict consensus tree based the 13 MPTs recovered for the reduced binary data set.
The tree is 236 steps long, with a CI of 0.5443. The tree on the left represents ACCTRAN optimization and the tree on the right represents DELTRAN optimization. The numbers above the nodes represent the Bremer Decay Index. Synontomorphies for lettered nodes are listed in Table 2.
Figure 6
Figure 6. Complete skulls in lateral view arranged in ontogenetic order from the relatively least mature to the relatively most mature specimens, based on the reduced multistate tree.
Skulls are not to scale. (A) TMP 1992.082.0001; (B) ROM 767; (C) TMP 1994.182.0001, (D) AMNH FARB 5351, (E) CMN 348; (F) UALVP 11735; (G) USNM 8897; (H) TMP 1997.085.0001; (I) CMN 8795; (J) YPM 2015. Images of TMP 1994.182.0001, AMNH FARB 5351, and CMN 8795 are reversed (mirrored). AMNH FARB 5351 and TMP 1997.085.0001 are represented here by casts. Division of Vertebrate Paleontology, YPM 2015. Courtesy of the Peabody Museum of Natural History, Yale University, New Haven, Connecticut, USA.
Figure 7
Figure 7
Three nasal horn character states. (A) recurved, TMP 1992.082.0001; (B) straight, TMP 1994.182.0001 (composite, mirror imaged); (C) procurved, UALVP 11735. Scale is equal to 10 cm.
Figure 8
Figure 8. Parietals in dorsal view arranged in an ontogenetic progression from top to bottom based on the reduced multistate analysis.
(A) TMP 1982.016.0011; (B) TMP 1980.054.0001; (C) CMN 971; (D) TMP 1978.06.0001. Scale is equal to 10 cm.
Figure 9
Figure 9. Dorsal view of parietals demonstrating the withered (A; TMP 1982.018.0277) and non-withered (B; TMP1982.018.0790) character states.
Scale is equal to 10 cm.
See this image and copyright information in PMC

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Grants and funding

Funding was provided in the form of scholarships through the Dinosaur Research Institute and the Delaware Valley Paleontological Society. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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