Redescription of Brachiosaurid Sauropod Dinosaur Material From the Upper Jurassic Morrison Formation, Colorado, USA

Abstract

Like many long‐standing dinosaur taxa, Brachiosaurus altithorax from the Upper Jurassic Morrison Formation of North America suffers from taxonomic issues stemming from a relatively incomplete holotype. Lack of anatomical overlap has precluded definitive referral of important specimens, including a mostly complete skull discovered in 1883. We redescribe this skull and some other significant brachiosaurid specimens based on new preparation and computed tomographic (CT) data. We argue that these elements are most parsimoniously referred to B. altithorax. Including these tentatively referred elements in a phylogenetic analysis does not alter the hypothesized relationships of B. altithorax, congruent with the presence of a single brachiosaurid taxon across western North America in the Late Jurassic. Based on CT data, we estimate that B. altithorax had a slower tooth replacement rate than Camarasaurus or the diplodocoids it shared Morrison Formation landscapes with, which suggests a difference in diet and/or feeding strategy. Anat Rec, 303:732–758, 2020. © 2019 Wiley Periodicals, Inc.

Sampling impacts the assessment of tooth growth and replacement rates in archosaurs: implications for paleontological studies

“… Note: Ranges of mean tooth formation times (TFTs) for tooth positions of the sauropods Diplodocus sp., Camarasaurus sp., Torneria africana , Giraffatitan brancai , Brachiosaurus sp., and Dicraeosaurus hansemanni and resultant tooth replacement rates (TRR) based on TFT from VEIW ± 1SD. D’Emic et al (2013) , D’Emic & Carrano (2019) only give TFT for some teeth, so the full range of TFTs found in the position is displayed, for other tooth positions the mean TFT found in this position in the jaw element is displayed. For explanation of TRR, TRR max-max, TRR min-min, TRR min-max, TRR max-min see methods.…”

“…We also explore the effect of applying the relative standard deviation of Alligator on calculations of tooth formation time and tooth replacement rate in sauropods using mean VEIW ± 1SD. We followed a similar approach using data from D’Emic et al (2013) , D’Emic & Carrano (2019) , Sattler (2014) , Kosch (2014) , Schwarz et al (2015) . For the sauropod data, we calculated the resulting minimum, maximum, and true formation times and replacement rates, and summarized these data for each tooth position (functional, replacement tooth one, replacement tooth two, etc.).…”

“…Tooth replacement rate provides key information on the function and evolution of the dentition ( Edmund, 1960 ; Osborn, 1970 , 1975 ; Richman, Whitlock & Abramyan, 2013 ; Whitlock & Richman, 2013 ; Schwarz et al, 2015 ; LeBlanc et al, 2016 ; Bramble et al, 2017 ). Such data can be used to infer aspects of the paleobiology of extinct taxa including metabolic activity/investment, dietary preferences, and behavior ( Johnston, 1979 ; Barrett, 2014 ; Salakka, 2014 ; D’Emic et al, 2013 , 2019 ; D’Emic & Carrano, 2019 ; Brink et al, 2015 ; Button et al, 2017 ; D’Emic et al, 2019 ). However, tooth growth and exfoliation cannot be directly observed in extinct species, therefore tooth replacement rate must be estimated via growth lines preserved within dentin (von Ebner Lines) and/or incremental growth lines of enamel that record different rhythms (see Smith (2004) for a review).…”

“…For example, because a researcher cannot always choose the location or orientation for consumptive sampling, they often have to calculate mean VEIW from one region of the tooth and apply these data to different transect locations within the same tooth ( Erickson, 1992 , 1996b ; Sereno et al, 2007 ; Gren, 2011 ; D’Emic et al, 2013 , 2019 ; Gren & Lindgren, 2013 ; Garcia & Zurriaguz, 2016 ; Kear et al, 2017 ; Ricart et al, 2019 ). Likewise, researchers may have to calculate mean VIEW from one tooth position within the jaw and then apply these values to other tooth positions ( Kosch, 2014 ; Schwarz et al, 2015 ; Garcia & Zurriaguz, 2016 ; D’Emic & Carrano, 2019 ; D’Emic et al, 2019 ). Moreover, because von Ebner lines are not always visible along the entire transect, mean VEIWs are typically derived from a transect subsample, as opposed to being calculated from the entire transect length ( Erickson, 1992 , 1996a , 1996b ; Gren, 2011 ; Gren & Lindgren, 2013 ; Button et al, 2017 ; Erickson et al, 2017 ; Kear et al, 2017 ; Ricart et al, 2019 ; D’Emic et al, 2019 ).…”

A possible brachiosaurid (Dinosauria, Sauropoda) from the mid-Cretaceous of northeastern China

“…Axial twisting of the maxillary dentition in YJDM 00008 (see below) was visualized and measured digitally, as in D’Emic & Carrano (2020) . To ensure accurate measurement of these angles for each tooth, the X, Y, and Z viewing planes were re-oriented in Dragonfly v.2021.1.0.977 so as to align with the mesiodistal, apicobasal, and labiolingual axes of the tooth, and the angle of twisting was measured across the entirety of the tooth crown.…”