Donald M. Henderson

MY THEROPOD IS BIGGER THAN YOURS … OR NOT: ESTIMATING BODY SIZE FROM SKULL LENGTH IN THEROPODS

Abstract To develop a widely applicable method to estimate body size in theropods, the scaling relationship between skull length, body length, and body mass was investigated using 13 strictly carnivorous, non-avialan theropod taxa ranging in size from the 1-m Sinosauropteryx prima to the 12-m Tyrannosaurus rex. Body length was obtained from the literature for complete to nearly-complete specimens and body mass was obtained from three-dimensional mathematical slicing of those same specimens to ensure accurate body length-body mass associations. Least-square regressions reveal a tight correlation between skull length and body length (SK-BL) and skull length and body mass (SK-BM). The SK-BL regression is negatively allometric, which indicates that skulls become longer relative to body length with increasing body size. In contrast, the SK-BM regression is positively allometric, indicating that body mass increases faster than skull length with increasing body size. These conclusions confirm that the common practice of scaling isometrically smaller relatives of a given taxon to obtain body length and body mass estimates is not valid. Although predictive equations derived from the regressions fail to predict accurately body size in abelisaurids and juvenile theropods due to their different head/body proportions, they produce accurate body size estimates for theropods of known body size, thus validating their applicability. Body size estimates for Carcharodontosaurus and Giganotosaurus, approaching 13 m and 14 tons, suggest that they may have surpassed Tyrannosaurus in size. A revised body size estimate for a large Spinosaurus specimen suggests a much shorter and heavier animal than recently suggested.

Lower limits of ornithischian dinosaur body size inferred from a new Upper Jurassic heterodontosaurid from North America

The extremes of dinosaur body size have long fascinated scientists. The smallest (<1 m length) known dinosaurs are carnivorous saurischian theropods, and similarly diminutive herbivorous or omnivorous ornithischians (the other major group of dinosaurs) are unknown. We report a new ornithischian dinosaur, Fruitadens haagarorum, from the Late Jurassic of western North America that rivals the smallest theropods in size. The largest specimens of Fruitadens represent young adults in their fifth year of development and are estimated at just 65–75 cm in total body length and 0.5–0.75 kg body mass. They are thus the smallest known ornithischians. Fruitadens is a late-surviving member of the basal dinosaur clade Heterodontosauridae, and is the first member of this clade to be described from North America. The craniodental anatomy and diminutive body size of Fruitadens suggest that this taxon was an ecological generalist with an omnivorous diet, thus providing new insights into morphological and palaeoecological diversity within Dinosauria. Late-surviving (Late Jurassic and Early Cretaceous) heterodontosaurids are smaller and less ecologically specialized than Early (Late Triassic and Early Jurassic) heterodontosaurids, and this ecological generalization may account in part for the remarkable 100-million-year-long longevity of the clade.

Albertonectes vanderveldei, a new elasmosaur (Reptilia, Sauropterygia) from the Upper Cretaceous of Alberta

ABSTRACT A new elasmosaurid plesiosaur, Albertonectes vanderveldei, gen. et sp. nov., is described on the basis of an almost complete postcranial skeleton from the upper Campanian, Bearpaw Formation in Alberta, Canada. The new taxon is distinguished by a unique set of characters—76 cervicals, lateral longitudinal ridge on posterior-most cervicals, relatively wide clavicular arch, tapered ventral projection at the median symphysis of coracoids, pointed anterolateral projection of pubis, fused posterior-most caudal vertebrae, and a relatively slender humerus. Ninety-seven chert gastroliths were also recovered with the specimen, and their mean diameters range from <1 to 13.5 cm. Shape analysis indicates that most of the gastroliths were ingested in the vicinity of a beach environment. Evidence that the carcass was scavenged by sharks includes a tooth-marked coracoid, two shed Squalicorax sp. teeth, and small, localized disruptions to the skeleton. Preliminary phylogenetic analysis confirms the inclusion of Albertonectes in a clade comprised of ‘middle’ to Late Cretaceous, long-necked elasmosaurid plesiosaurs. The number of cervical vertebrae associated with different elasmosaur genera does not show any correlation with phylogeny. Both neck and total body length of Albertonectes are the longest among known elasmosaurs, and highlight the morphological extremes attained by this group of plesiosaurs.

Pterosaur body mass estimates from three-dimensional mathematical slicing

ABSTRACT Body masses for 14 species of pterosaur spanning four orders of magnitude were estimated using three-dimensional, digital models. The modeled taxa comprised seven paraphyletic ‘rhamphorhynchoids’: Anurognathus ammoni, Dimorphodon macronyx, Eudimorphodon ranzii, Jeholopterus ningchengensis, Preondactylus buffarinii, Rhamphorhynchus muensteri, and Sordes pilosus; and seven pterodactyloids: Anhanguera santanae, Dsungaripterus weii, Pteranodon longiceps, Pterodaustro guinazui, Pterodactylus sp., Quetzalcoatlus northropi, Tupuxuara longicristatus. The reliability of the mass estimation methods were tested with equivalent models of six extant species of bird with masses that spanned three orders of magnitude. The close agreement between model bird mass estimates and those of the living forms provides a level of confidence in the results obtained for the extinct pterosaurs. The masses of the axial body regions (tail, trunk, neck, head), limbs, and patagia of the pterosaurs were individually estimated and distinct differences in relative body proportions were found between species. Allometric relationships between body length and wingspan and body mass were derived for ‘rhamphorhynchoids’ and pterodactyloids to facilitate the estimation of body masses for other pterosaurs known from incomplete material, and these relationships also highlight differences in phyletic shape change between the two groups. The estimated mass for the largest pterosaur known, Quetzalcoatlus northropi, exceeds the previous highest estimates by more than 100%, and it is argued that this extremely large pterosaur is better interpreted as a secondarily flightless form.

Predicting the buoyancy, equilibrium and potential swimming ability of giraffes by computational analysis

Giraffes (Giraffa camelopardalis) are often stated to be unable to swim, and while few observations supporting this have ever been offered, we sought to test the hypothesis that giraffes exhibited a body shape or density unsuited for locomotion in water. We assessed the floating capability of giraffes by simulating their buoyancy with a three-dimensional mathematical/computational model. A similar model of a horse (Equus caballus) was used as a control, and its floating behaviour replicates the observed orientations of immersed horses. The floating giraffe model has its neck sub-horizontal, and the animal would struggle to keep its head clear of the water surface. Using an isometrically scaled-down giraffe model with a total mass equal to that of the horse, the giraffes proportionally larger limbs have much higher rotational inertias than do those of horses, and their wetted surface areas are 13.5% greater relative to that of the horse, thus making rapid swimming motions more strenuous. The mean density of the giraffe model (960 gm/l) is also higher than that of the horse (930 gm/l), and closer to that causing negative buoyancy (1000 gm/l). A swimming giraffe - forced into a posture where the neck is sub-horizontal and with a thorax that is pulled downwards by the large fore limbs - would not be able to move the neck and limbs synchronously as giraffes do when moving on land, possibly further hampering the animals ability to move its limbs effectively underwater. We found that a full-sized, adult giraffe will become buoyant in water deeper than 2.8m. While it is not impossible for giraffes to swim, we speculate that they would perform poorly compared to other mammals and are hence likely to avoid swimming if possible.

A specimen of Rhamphorhynchus with soft tissue preservation, stomach contents and a putative coprolite

Despite being known for nearly two centuries, new specimens of the derived non-pterodactyloid pterosaur Rhamphorhynchus continue to be discovered and reveal new information about their anatomy and palaeobiology. Here we describe a specimen held in the collections of the Royal Tyrrell Museum of Palaeontology, Alberta, Canada that shows both preservation and impressions of soft tissues, and also preserves material interpreted as stomach contents of vertebrate remains and, uniquely, a putative coprolite. The specimen also preserves additional evidence for fibers in the uropatagium.

What drove reversions to quadrupedality in ornithischian dinosaurs? Testing hypotheses using centre of mass modelling.

The exceptionally rare transition to quadrupedalism from bipedal ancestors occurred on three independent occasions in ornithischian dinosaurs. The possible driving forces behind these transitions remain elusive, but several hypotheses—including the development of dermal armour and the expansion of head size and cranial ornamentation—have been proposed to account for this major shift in stance. We modelled the position of the centre of mass (CoM) in several exemplar ornithischian taxa and demonstrate that the anterior shifts in CoM position associated with the development of an enlarged skull ornamented with horns and frills for display/defence may have been one of the drivers promoting ceratopsian quadrupedality. A posterior shift in CoM position coincident with the development of extensive dermal armour in thyreophorans demonstrates this cannot have been a primary causative mechanism for quadrupedality in this clade. Quadrupedalism developed in response to different selective pressures in each ornithischian lineage, indicating different evolutionary pathways to convergent quadrupedal morphology.

Balance and Strength—Estimating the Maximum Prey‐Lifting Potential of the Large Predatory Dinosaur Carcharodontosaurus saharicus

Motivated by the work of palaeo‐art “Double Death (2011),” a biomechanical analysis using three‐dimensional digital models was conducted to assess the potential of a pair of the large, Late Cretaceous theropod dinosaur Carcharodontosaurus saharicus to successfully lift a medium‐sized sauropod and not lose balance. Limaysaurus tessonei from the Late Cretaceous of South America was chosen as the sauropod as it is more completely known, but closely related to the rebbachisaurid sauropods found in the same deposits with C. saharicus. The body models incorporate the details of the low‐density regions associated with lungs, systems of air sacs, and pneumatized axial skeletal regions. These details, along with the surface meshes of the models, were used to estimate the body masses and centers of mass of the two animals. It was found that a 6 t C. saharicus could successfully lift a mass of 2.5 t and not lose balance as the combined center of mass of the body and the load in the jaws would still be over the feet. However, the neck muscles were found to only be capable of producing enough force to hold up the head with an added mass of 424 kg held at the midpoint of the maxillary tooth row. The jaw adductor muscles were more powerful, and could have held a load of 512 kg. The more limiting neck constraint leads to the conclusion that two, adult C. saharicus could successfully lift a L. tessonei with a maximum body mass of 850 kg and a body length of 8.3 m. Anat Rec, 298:1367–1375, 2015.

Sauropod necks: are they really for heat loss?

Three-dimensional digital models of 16 different sauropods were used to examine the scaling relationship between metabolism and surface areas of the whole body, the neck, and the tail in an attempt to see if the necks could have functioned as radiators for the elimination of excess body heat. The sauropod taxa sample ranged in body mass from a 639 kg juvenile Camarasaurus to a 25 t adult Brachiosaurus. Metabolism was assumed to be directly proportional to body mass raised to the ¾ power, and estimates of body mass accounted for the presence of lungs and systems of air sacs in the trunk and neck. Surface areas were determined by decomposing the model surfaces into triangles and their areas being computed by vector methods. It was found that total body surface area was almost isometric with body mass, and that it showed negative allometry when plotted against metabolic rate. In contrast, neck area showed positive allometry when plotted against metabolic rate. Tail area show negative allometry with respect to metabolic rate. The many uncertainties about the biology of sauropods, and the variety of environmental conditions that different species experienced during the groups 150 million years of existence, make it difficult to be absolutely certain about the function of the neck as a radiator. However, the functional combination of the allometric increase of neck area, the systems of air sacs in the neck and trunk, the active control of blood flow between the core and surface of the body, changing skin color, and strategic orientation of the neck with respect to wind, make it plausible that the neck could have functioned as a radiator to avoid over-heating.

Using three-dimensional, digital models of pterosaur skulls for the investigation of their relative bite forces and feeding styles

Abstract Simple, three-dimensional, digital models of the crania and mandibles of 22 pterosaurs – 13 pterodactyloids and nine non-pterodactyloids (‘rhamphorhynchoids’) – were generated to investigate gross-level mechanical aspects of the skulls as they would related to feeding behaviour such as bite force and speed of jaw motions. The key parameter was the determination of second moments of area of the mid-muzzle region and the computation of the bending moment relative to the occiput. The shorter, stockier skulls of basal ‘rhamphorhynchoids’ were the strongest for their size in terms of potential resistance to dorso-ventral bending, and this finding correlates with their robust dentitions. More derived ‘rhamphorhynchoids’ showed the start of a trend towards weaker skulls, but faster jaw adduction was interpreted to be an adaptation for the snatching of small prey. Pterodactyloids continued the trend to lengthen the skull and to reduce its cross-sectional area, resulting in less stiff skulls, but more rapid opening and closing of the jaws. Changes in the rear of the skulls and the development of coronoid eminences on the mandibles of all the pterodactyloids are correlated with the reduction in bite force and a concomitant increase in jaw closing speed.