Body Size as a Driver of Scavenging in Theropod Dinosaurs

AbstractLarge body sizes among nonavian theropod dinosaurs is a major feature in the evolution of this clade, with theropods reaching greater sizes than any other terrestrial carnivores. However, the early evolution of large body sizes among theropods is obscured by an incomplete fossil record, with the largest Triassic theropods represented by only a few individuals of uncertain ontogenetic stage. Here I describe two neotheropod specimens from the Upper Triassic Bull Canyon Formation of New Mexico and place them in a broader comparative context of early theropod anatomy. These specimens possess morphologies indicative of ontogenetic immaturity (e.g., absence of femoral bone scars, lack of co-ossification between the astragalus and calcaneum), and phylogenetic analyses recover these specimens as early-diverging neotheropods in a polytomy with other early neotheropods at the base of the clade. Ancestral state reconstruction for body size suggests that the ancestral theropod condition was small (~240 mm femur length), but the ancestral neotheropod was larger (~300–340 mm femur length), with coelophysoids experiencing secondary body size reduction, although this is highly dependent on the phylogenetic position of a few key taxa. Theropods evolved large body sizes before the Triassic–Jurassic extinction, as hypothesized in most other ancestral state reconstructions of theropod body sizes, but remained rare relative to smaller theropods until the Jurassic.

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Using striated tooth marks on bone to predict body size in theropod dinosaurs: a model based on feeding observations of Varanus komodoensis, the Komodo monitor

Paleobiology ◽

10.1666/09079.1 ◽

2012 ◽

Vol 38 (1) ◽

pp. 79-100 ◽

Cited By ~ 7

Author(s):

Domenic C. D'Amore ◽

Robert J. Blumenschine

Keyword(s):

Body Size ◽

Model Based ◽

Theropod Dinosaurs ◽

Feeding Observations ◽

Tooth Marks

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Using striated tooth marks on bone to predict body size in theropod dinosaurs: a model based on feeding observations of Varanus komodoensis, the Komodo monitor

Paleobiology ◽

10.1017/s0094837300000415 ◽

2012 ◽

Vol 38 (1) ◽

pp. 79-100 ◽

Cited By ~ 8

Author(s):

Domenic C. D'Amore ◽

Robert J. Blumenschine

Keyword(s):

Body Size ◽

Capra Hircus ◽

Tooth Size ◽

Variable Degree ◽

Degree Of Branching ◽

Theropod Dinosaurs ◽

Feeding Trials ◽

Degree Of Convergence ◽

Feeding Observations ◽

Tooth Marks

Mesozoic tooth marks on bone surfaces directly link consumers to fossil assemblage formation. Striated tooth marks are believed to form by theropod denticle contact, and attempts have been made to identify theropod consumers by comparing these striations with denticle widths of contemporaneous taxa. The purpose of this study is to test whether ziphodont theropod consumer characteristics can be accurately identified from striated tooth marks on fossil surfaces. We had three major objectives (1) to experimentally produce striated tooth marks and explain how they form; (2) to determine whether body size characteristics are reflected in denticle widths; and (3) to determine whether denticle characters are accurately transcribed onto bone surfaces in the form of striated tooth marks. We conducted controlled feeding trials with the dental analogue Varanus komodoensis (the Komodo monitor). Goat (Capra hircus) carcasses were introduced to captive, isolated individuals. Striated tooth marks were then identified, and striation width, number, and degree of convergence were recorded for each. Denticle widths and tooth/body size characters were taken from photographs and published accounts of both theropod and V. komodoensis skeletal material, and regressions were compared among and between the two groups. Striated marks tend to be regularly striated with a variable degree of branching, and may co-occur with scores. Striation morphology directly reflects contact between the mesial carina and bone surfaces during the rostral reorientation when defleshing. Denticle width is influenced primarily by tooth size, and correlates well with body size, displaying negative allometry in both groups regardless of taxon or position. When compared, striation widths fall within or below the range of denticle widths extrapolated for similar-sized V. komodoensis individuals. Striation width is directly influenced by the orientation of the carina during feeding, and may underestimate but cannot overestimate denticle width. Although body size can theoretically be estimated solely by a striated tooth mark under ideal circumstances, many caveats should be considered. These include the influence of negative allometry across taxa and throughout ontogeny, the existence of theropods with extreme denticle widths, and the potential for striations to underestimate denticle widths. This method may be useful under specific circumstances, especially for establishing a lower limit body size for potential consumers.

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Vertebral Adaptations to Large Body Size in Theropod Dinosaurs

PLoS ONE ◽

10.1371/journal.pone.0158962 ◽

2016 ◽

Vol 11 (7) ◽

pp. e0158962 ◽

Cited By ~ 8

Author(s):

John P. Wilson ◽

D. Cary Woodruff ◽

Jacob D. Gardner ◽

Holley M. Flora ◽

John R. Horner ◽

...

Keyword(s):

Body Size ◽

Large Body ◽

Large Body Size ◽

Theropod Dinosaurs

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Why sauropods had long necks; and why giraffes have short necks

PeerJ ◽

10.7717/peerj.36 ◽

2013 ◽

Vol 1 ◽

pp. e36 ◽

Cited By ~ 40

Author(s):

Michael P. Taylor ◽

Mathew J. Wedel

Keyword(s):

Body Size ◽

Respiratory System ◽

Cervical Vertebrae ◽

Large Body ◽

World Record ◽

Large Body Size ◽

Anatomical Features ◽

Theropod Dinosaurs ◽

The World ◽

Cervical Ribs

The necks of the sauropod dinosaurs reached 15 m in length: six times longer than that of the world record giraffe and five times longer than those of all other terrestrial animals. Several anatomical features enabled this extreme elongation, including: absolutely large body size and quadrupedal stance providing a stable platform for a long neck; a small, light head that did not orally process food; cervical vertebrae that were both numerous and individually elongate; an efficient air-sac-based respiratory system; and distinctive cervical architecture. Relevant features of sauropod cervical vertebrae include: pneumatic chambers that enabled the bone to be positioned in a mechanically efficient way within the envelope; and muscular attachments of varying importance to the neural spines, epipophyses and cervical ribs. Other long-necked tetrapods lacked important features of sauropods, preventing the evolution of longer necks: for example, giraffes have relatively small torsos and large, heavy heads, share the usual mammalian constraint of only seven cervical vertebrae, and lack an air-sac system and pneumatic bones. Among non-sauropods, their saurischian relatives the theropod dinosaurs seem to have been best placed to evolve long necks, and indeed their necks probably surpassed those of giraffes. But 150 million years of evolution did not suffice for them to exceed a relatively modest 2.5 m.

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