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Sauropod gigantism
Abstract
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... Dinosaurs of the clade Sauropoda were the largest terrestrial animals that ever lived [1], [2], [3]. They also were the herbivorous vertebrates that were predominant in terrestrial ecosystems for the longest time of any major clade, around 120 million years, from the Middle Jurassic to the end of the Cretaceous [4], [5]. ...
... In the original version of the ECM, a feedback loop leads from the trait “Very high body mass” to the trait “No mastication” [1], [2]. This feedback loops, called “Large gut capacity” posited that very high body mass is favored by the positive scaling of the retention time of the ingested food in the gut, based on data from extant animals [107], [108]. ...
... However, all birds and non-avian dinosaurs that have a gastric mill are small (dinosaurs, >25 kg) or medium-sized (birds, >250 kg) [99], suggesting other limitations to their body size. Contrary to the suggestion by Sander & Clauss [1] and Sander et al. [2], the lack of a gastric mill thus may not have been a prerequisite for sauropod gigantism. ...
Sauropod dinosaurs are a group of herbivorous dinosaurs which exceeded all other terrestrial vertebrates in mean and maximal body size. Sauropod dinosaurs were also the most successful and long-lived herbivorous tetrapod clade, but no abiological factors such as global environmental parameters conducive to their gigantism can be identified. These facts justify major efforts by evolutionary biologists and paleontologists to understand sauropods as living animals and to explain their evolutionary success and uniquely gigantic body size. Contributions to this research program have come from many fields and can be synthesized into a biological evolutionary cascade model of sauropod dinosaur gigantism (sauropod gigantism ECM). This review focuses on the sauropod gigantism ECM, providing an updated version based on the contributions to the PLoS ONE sauropod gigantism collection and on other very recent published evidence. The model consist of five separate evolutionary cascades ("Reproduction", "Feeding", "Head and neck", "Avian-style lung", and "Metabolism"). Each cascade starts with observed or inferred basal traits that either may be plesiomorphic or derived at the level of Sauropoda. Each trait confers hypothetical selective advantages which permit the evolution of the next trait. Feedback loops in the ECM consist of selective advantages originating from traits higher in the cascades but affecting lower traits. All cascades end in the trait "Very high body mass". Each cascade is linked to at least one other cascade. Important plesiomorphic traits of sauropod dinosaurs that entered the model were ovipary as well as no mastication of food. Important evolutionary innovations (derived traits) were an avian-style respiratory system and an elevated basal metabolic rate. Comparison with other tetrapod lineages identifies factors limiting body size.
... They achieved a global distribution and spanned the Late Triassic (Buffetaut et al. 2000;Yates & Kitching 2003) to the very end of the Cretaceous (Fastovsky & Weishampel 2005;Schulte et al. 2010). These colossal animals, which could attain body lengths of more than 40 m (Sander & Clauss 2008;Sander et al. 2010) and weigh 100 tonnes Sander & Clauss 2008;Sander et al. 2010), are characterized by massive bodies with pillar-like limbs, extremely elongated necks and tails, and small skulls Fastovsky & Weishampel 2005, Chure et al. 2010. ...
... They achieved a global distribution and spanned the Late Triassic (Buffetaut et al. 2000;Yates & Kitching 2003) to the very end of the Cretaceous (Fastovsky & Weishampel 2005;Schulte et al. 2010). These colossal animals, which could attain body lengths of more than 40 m (Sander & Clauss 2008;Sander et al. 2010) and weigh 100 tonnes Sander & Clauss 2008;Sander et al. 2010), are characterized by massive bodies with pillar-like limbs, extremely elongated necks and tails, and small skulls Fastovsky & Weishampel 2005, Chure et al. 2010. ...
Nils Knötschke (2014): Cranial anatomy of the Late Jurassic dwarf sauropod Europasaurus holgeri (Dinosauria, Camarasauromorpha): ontogenetic changes and size dimorphism, Journal of Systematic Palaeontology, makes every effort to ensure the accuracy of all the information (the "Content") contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at
... This hypothesis awaits testing. Another hypothesis, namely ontogenetically reduced metabolic rates in adult sauropods [123], provides a convenient ad hoc explanation yet is more difficult to test. ...
... Allometries related to chewing and particle size reduction can potentially indicate that the absence of chewing in sauropods is a condition that does not necessarily drive but facilitate gigantism [1], [123]. An important part of mammalian foraging time is dedicated to the act of (ingestive) mastication [21]. ...
Digestive physiology has played a prominent role in explanations for terrestrial herbivore body size evolution and size-driven diversification and niche differentiation. This is based on the association of increasing body mass (BM) with diets of lower quality, and with putative mechanisms by which a higher BM could translate into a higher digestive efficiency. Such concepts, however, often do not match empirical data. Here, we review concepts and data on terrestrial herbivore BM, diet quality, digestive physiology and metabolism, and in doing so give examples for problems in using allometric analyses and extrapolations. A digestive advantage of larger BM is not corroborated by conceptual or empirical approaches. We suggest that explanatory models should shift from physiological to ecological scenarios based on the association of forage quality and biomass availability, and the association between BM and feeding selectivity. These associations mostly (but not exclusively) allow large herbivores to use low quality forage only, whereas they allow small herbivores the use of any forage they can physically manage. Examples of small herbivores able to subsist on lower quality diets are rare but exist. We speculate that this could be explained by evolutionary adaptations to the ecological opportunity of selective feeding in smaller animals, rather than by a physiologic or metabolic necessity linked to BM. For gigantic herbivores such as sauropod dinosaurs, other factors than digestive physiology appear more promising candidates to explain evolutionary drives towards extreme BM.
... Our results suggest that the egg masses of most dinosaurs match neither the egg masses of similar-sized or scaled-up birds nor those of reptiles, but were in fact in-between (Figure 1). This could reflect the reproductive strategy differences of most dinosaurs compared to the reproductive strategy seen in extant birds or reptiles [1] and suggests that their reproductive strategy was intermediary [24]. The great variability in egg mass to body mass relations found in dinosaurs (Figure 1) could indicate that different reproductive strategies existed in dinosaurs. ...
... The discovery of the gigantic sauropods and other large dinosaurs has stimulated scientists to understand the biology of dinosaurs. Several researchers [1–3] recently argued that the reproductive strategy of producing many small offspring contributed to the exceptional gigantism seen in the sauropods, a hypothesis introduced by Janis and Carrano [4] and recently corroborated by Werner and Griebeler [5]. ...
It has been hypothesized that a high reproductive output contributes to the unique gigantism in large dinosaur taxa. In order to infer more information on dinosaur reproduction, we established allometries between body mass and different reproductive traits (egg mass, clutch mass, annual clutch mass) for extant phylogenetic brackets (birds, crocodiles and tortoises) of extinct non-avian dinosaurs. Allometries were applied to nine non-avian dinosaur taxa (theropods, hadrosaurs, and sauropodomorphs) for which fossil estimates on relevant traits are currently available. We found that the reproductive traits of most dinosaurs conformed to similar-sized or scaled-up extant reptiles or birds. The reproductive traits of theropods, which are considered more bird-like, were indeed consistent with birds, while the traits of sauropodomorphs conformed better to reptiles. Reproductive traits of hadrosaurs corresponded to both reptiles and birds. Excluding Massospondyluscarinatus, all dinosaurs studied had an intermediary egg to body mass relationship to reptiles and birds. In contrast, dinosaur clutch masses fitted with either the masses predicted from allometries of birds (theropods) or to the masses of reptiles (all other taxa). Theropods studied had probably one clutch per year. For sauropodomorphs and hadrosaurs, more than one clutch per year was predicted. Contrary to current hypotheses, large dinosaurs did not have exceptionally high annual egg numbers (AEN). Independent of the extant model, the estimated dinosaur AEN did not exceed 850 eggs (75,000 kg sauropod) for any of the taxa studied. This estimated maximum is probably an overestimation due to unrealistic assumptions. According to most AEN estimations, the dinosaurs studied laid less than 200 eggs per year. Only some AEN estimates obtained for medium to large sized sauropods were higher (200-400 eggs). Our results provide new (testable) hypotheses, especially for reproductive traits that are insufficiently documented or lacking from the fossil record. This contributes to the understanding of their evolution.
... Furthermore, in some species, the long neck contributes to thermoregulation and dominance during male competition (Simmons and Scheepers 1996;Senter 2007;Ward et al. 2008). There have been many discussions about the evolutionary pressures underlying neck elongation in these species (Parrish 2006;Dzemski and Christian 2007;Sander and Clauss 2008;Mitchell et al. 2009;Stevens 2013), but mechanisms behind elongation of the cervical series are little understood. ...
Long necks have evolved independently in several different taxa, but the processes underlying the evolution of this trait are not yet fully understood. In this study, we examined the skeletal mechanism underlying the neck elongation in the tribe Antilopini (Bovidae, Artiodactyla). We calculated the growth patterns of the cervical vertebrae in the gerenuk (Litocranius walleri), which possesses the longest neck in this tribe, and compared it with those in two related species. The growth rates of the vertebrae were not significantly different between species, suggesting that the long neck of the gerenuk has resulted from the elongation of the cervical vertebrae during the fetal or juvenile stage. The morphology of the cervical vertebrae of gerenuks differed from that of the closely related, relatively long-necked dama gazelle (Nanger dama), with protrusions occurring on the dorsal surface of the ventral arch of the atlas. This implies that gerenuks possess a well-developed transverse ligament of the atlas that functions to hold the dens of the axis against the atlas. We also found that the atlas lies in close proximity to the neural spine of the axis in the gerenuk, suggesting that hyperextension of the atlantoaxial joint is osteologically limited in this species. While foraging on high foliage, gerenuks flex and extend their necks freely in a bipedal posture without moving their entire body. These morphological characteristics peculiar to the gerenuk enhance the rigidity of the atlantoaxial joint and decrease the risk of subluxation of the joint during this unique foraging behavior.
... Large-bodied herbivores, primarily represented by a diverse sauropod dinosaur assemblage, were the dominant faunal elements of the Morrison palaeoenvironment. The diversity of sauropods may have resulted because advantageous surfaceto-volume ratios allow large animals to survive preferentially in seasonally harsh climates, although a variety of physiological factors have been suggested for sauropod gigantism (Sander & Clauss 2008;Clauss 2011). In general, however, maximal body size in vertebrates is determined by the quantity and quality of available resources relative to the consumer's mobility and its rate of energy expenditure (McNab 2009). ...
A Late Jurassic sauropod bone-bed comprising thousands of individual skeletal elements in the Morrison Formation of Montana, USA, is re-analysed to further elucidate its taphonomic history. New data gained from detailed contextual sampling is assembled and presented to test the hypothesis of a drought-induced, mass-mortality assemblage, and its subsequent depositional emplacement by a debris flow. Large dinosaur bone-beds are well-known in the Morrison, yet the Mother's Day Quarry site is unique for the formation in depicting an apparent debris flow deposit. Use of a computer program tailored to the data allows three-dimensional reconstruction of the bone-bed and recreates the palaeoslope of the deposit, adding support to the debris flow hypothesis. Such digital manipulation of field data may allow a deeper understanding of other bone-bed origination events.
... To simulate structure and abundances of dinosaurian and mammalian communities, we specified species (populations) over a variety of size (body mass, M, in kg log2-transformed) classes, representing the full body mass range described for both groups. For dinosaurs, this range (i) extended in log2M increments from −9 to 17, and for mammals from −9 to 14, i.e. species ranged in M from ∼2 g to 131 and 16 tons, respectively (see Sander et al. [32] for size limits of dinosaur and mammal species). Life tables for each population were constructed, sub-divided by mass classes (x) ranging from offspring to adult M, again in log2M increments. ...
Because egg-laying meant that even the largest dinosaurs gave birth to very small offspring, they had to pass through multiple ontogenetic life stages to adulthood. Dinosaurs' successors as the dominant terrestrial vertebrate life form, the mammals, give birth to live young, and have much larger offspring and less complex ontogenetic histories. The larger number of juveniles in dinosaur as compared to mammal ecosystems represents both a greater diversity of food available to predators, and competitors for similar-sized individuals of sympatric species. Models of population abundances across different-sized species of dinosaurs and mammals, based on simulated ecological life tables, are employed to investigate how differences in predation and competition pressure influenced dinosaur communities. Higher small- to medium-sized prey availability leads to a normal body mass-species richness (M-S) distribution of carnivorous dinosaurs (as found in the theropod fossil record), in contrast to the right-skewed M-S distribution of carnivorous mammals (as found living members of the order Carnivora). Higher levels of interspecific competition leads to a left-skewed M-S distribution in herbivorous dinosaurs (as found in sauropods and ornithopods), in contrast to the normal M-S distribution of large herbivorous mammals. Thus, our models suggest that differences in reproductive strategy, and consequently ontogeny, explain observed differences in community structure between dinosaur and mammal faunas. Models also show that the largest dinosaurian predators could have subsisted on similar-sized prey by including younger life stages of the largest herbivore species, but that large predators likely avoided prey much smaller than themselves because, despite predicted higher abundances of smaller than larger-bodied prey, contributions of small prey to biomass intake would be insufficient to satisfy meat requirements. A lack of large carnivores feeding on small prey exists in mammals larger than 21.5 kg, and it seems a similar minimum prey-size threshold could have affected dinosaurs as well.
... Since the first massive bones of sauropods were discovered, many scientists have investigated how these animals evolved to their gigantic size [1][2][3]. Analyses and interpretation of sauropod gigantism are essential for the understanding of evolutionary constraints and how these constraints impact Earth's geological and biological history. Bones of sauropods, of course, are not their only remains in the fossil record, but the second most common evidence for their former existence are footprints and entire trackways. ...
To better understand the biology of extinct animals, experimentation with extant animals and innovative numerical approaches have grown in recent years. This research project uses principles of soil mechanics and a neoichnological field experiment with an African elephant to derive a novel concept for calculating the mass (i.e., the weight) of an animal from its footprints. We used the elephant's footprint geometry (i.e., vertical displacements, diameter) in combination with soil mechanical analyses (i.e., soil classification, soil parameter determination in the laboratory, Finite Element Analysis (FEA) and gait analysis) for the back analysis of the elephant's weight from a single footprint. In doing so we validated the first component of a methodology for calculating the weight of extinct dinosaurs. The field experiment was conducted under known boundary conditions at the Zoological Gardens Wuppertal with a female African elephant. The weight of the elephant was measured and the walking area was prepared with sediment in advance. Then the elephant was walked across the test area, leaving a trackway behind. Footprint geometry was obtained by laser scanning. To estimate the dynamic component involved in footprint formation, the velocity the foot reaches when touching the subsoil was determined by the Digital Image Correlation (DIC) technique. Soil parameters were identified by performing experiments on the soil in the laboratory. FEA was then used for the backcalculation of the elephant's weight. With this study, we demonstrate the adaptability of using footprint geometry in combination with theoretical considerations of loading of the subsoil during a walk and soil mechanical methods for prediction of trackmakers weight.
... The highly vascularized and nearly continuously deposited FLB of the Pistosaurus humerus suggests high growth rates. FLB also suggests endothermy (e.g., [36,52,77,90,91]) because fast growth requires a high basal metabolic rate. This implies that the high basal metabolic rate of plesiosaurs [85] arose in the last common ancestor of Plesiosauria and Pistosauridae, although an earlier origin among basal Pistosauroidea is possible [59]. ...
Background
Eosauropterygians consist of two major clades, the Nothosauroidea of the Tethysian Middle Triassic (e.g., Nothosaurus) and the Pistosauroidea. The Pistosauroidea include rare Triassic forms (Pistosauridae) and the Plesiosauria of the Jurassic and Cretaceous. Long bones of Nothosaurus and Pistosaurus from the Muschelkalk (Middle Triassic) of Germany and France and a femur of the Lower Jurassic Plesiosaurus dolichodeirus were studied histologically and microanatomically to understand the evolution of locomotory adaptations, patterns of growth and life history in these two lineages.
Results
We found that the cortex of adult Nothosaurus long bones consists of lamellar zonal bone. Large Upper Muschelkalk humeri of large-bodied Nothosaurus mirabilis and N. giganteus differ from the small Lower Muschelkalk (Nothosaurus marchicus/N. winterswijkensis) humeri by a striking microanatomical specialization for aquatic tetrapods: the medullary cavity is much enlarged and the cortex is reduced to a few millimeters in thickness. Unexpectedly, the humeri of Pistosaurus consist of continuously deposited, radially vascularized fibrolamellar bone tissue like in the Plesiosaurus sample. Plesiosaurus shows intense Haversian remodeling, which has never been described in Triassic sauropterygians.
Conclusions
The generally lamellar zonal bone tissue of nothosaur long bones indicates a low growth rate and suggests a low basal metabolic rate. The large triangular cross section of large-bodied Nothosaurus from the Upper Muschelkalk with their large medullary region evolved to withstand high bending loads. Nothosaurus humerus morphology and microanatomy indicates the evolution of paraxial front limb propulsion in the Middle Triassic, well before its convergent evolution in the Plesiosauria in the latest Triassic. Fibrolamellar bone tissue, as found in Pistosaurus and Plesiosaurus, suggests a high growth rate and basal metabolic rate. The presence of fibrolamellar bone tissue in Pistosaurus suggests that these features had already evolved in the Pistosauroidea by the Middle Triassic, well before the plesiosaurs radiated. Together with a relatively large body size, a high basal metabolic rate probably was the key to the invasion of the Pistosauroidea of the pelagic habitat in the Middle Triassic and the success of the Plesiosauria in the Jurassic and Cretaceous.
... Sauropod dinosaurs represent one of the most diverse and evolutionary successful groups of terrestrial vertebrates that lived during the Mesozoic [1]. The clade comprises the largest vertebrates that ever walked on land, with adult individuals of some species estimated to have reached up to 30 metres in length [2], [3]. ...
The study of a small sauropod trackway from the Late Cretaceous Fumanya tracksite (southern Pyrenees, Catalonia) and further comparisons with larger trackways from the same locality suggest a causative relationship between gait, gauge, and body proportions of the respective titanosaur trackmakers. This analysis, conducted in the context of scaling predictions and using geometric similarity and dynamic similarity hypotheses, reveals similar Froude numbers and relative stride lengths for both small and large trackmakers from Fumanya. Evidence for geometric similarity in these trackways suggests that titanosaurs of different sizes moved in a dynamically similar way, probably using an amble gait. The wide gauge condition reported in trackways of small and large titanosaurs implies that they possessed similar body (trunk and limbs) proportions despite large differences in body size. These results strengthen the hypothesis that titanosaurs possessed a distinctive suite of anatomical characteristics that are well reflected in their tracks and trackways.
... The histology of fossil tetrapod bones has proven to be a rich source of paleobiological and evolutionary information [1]–[4], particularly for groups that have no living relatives or in which the living relatives occupy a fundamentally different ecological niche. This is particularly true for sauropod dinosaurs, the largest land-living animals ever [4], [5], for which a large amount of histological data have become available in recent years [4], [6], [7]. Sauropod long bone histology so far has been viewed as rather uniform [4], [6], allowing broad comparisons between taxa [6]. ...
Long bone histology of the most derived Sauropoda, the Titanosauria suggests that titanosaurian long bone histology differs from the uniform bone histology of basal Sauropoda. Here we describe the long bone histology of the titanosaur Ampelosaurus atacis and compare it to that of basal neosauropods and other titanosaurs to clarify if a special titanosaur bone histology exists.
Ampelosaurus retains the laminar vascular organization of basal Sauropoda, but throughout most of cortical growth, the scaffolding of the fibrolamellar bone, which usually is laid down as matrix of woven bone, is laid down as parallel-fibered or lamellar bone matrix instead. The remodeling process by secondary osteons is very extensive and overruns the periosteal bone deposition before skeletal maturity is reached. Thus, no EFS is identifiable. Compared to the atypical bone histology of Ampelosaurus, the large titanosaur Alamosaurus shows typical laminar fibrolamellar bone. The titanosaurs Phuwiangosaurus, Lirainosaurus, and Magyarosaurus, although differing in certain features, all show this same low amount or absence of woven bone from the scaffolding of the fibrolamellar bone, indicating a clear reduction in growth rate resulting in a higher bone tissue organization. To describe the peculiar primary cortical bone tissue of Phuwiangosaurus, Ampelosaurus, Lirainosaurus, and Magyarosaurus, we here introduce a new term, "modified laminar bone" (MLB).
Importantly, MLB is as yet not known from extant animals. At least in Lirainosaurus and Magyarosaurus the reduction of growth rate indicated by MLB is coupled with a drastic body size reduction and maybe also a reduction in metabolic rate, interpreted as a result of dwarfing on the European islands during the Late Cretaceous. Phuwiangosaurus and Ampelosaurus both show a similar reduction in growth rate but not in body size, possibly indicating also a reduced metabolic rate. The large titanosaur Alamosaurus, on the other hand, retained the plesiomorphic bone histology of basal neosauropods.
... The largest sauropods might have almost reached biomechanical and physiological limits. Recent findings indicate fast growth and high metabolic rates in sauropods (Sander & Clauss 2008). Consequently, the rate of food intake must have been very high. ...
A very long neck that is apparently suitable for feeding at great heights is a characteristic feature of most sauropod dinosaurs. Yet, it remains controversial whether any sauropods actually raised their necks high. Recently, strong physiological arguments have been put forward against the idea of high-browsing sauropods, because of the very high blood pressure that appears to be inevitable when the head is located several metres above the heart. For the sauropod Euhelopus zdanskyi, however, biomechanical evidence clearly indicates high browsing. Energy expenditure owing to high browsing is compared with energy costs for walking a distance. It is demonstrated for Euhelopus as well as for the much larger Brachiosaurus that despite an increase in the metabolic rate, high browsing was worthwhile for a sauropod if resources were far apart.
The ongoing controversy centered on neck posture and function in sauropod dinosaurs is misplaced for a number of reasons. Because of an absence of pertinent data it is not possible to accurately restore the posture and range of motion in long necked fossil animals, only gross approximations are possible. The existence of a single "neutral posture" in animals with long, slender necks may not exist, and its relationship to feeding habits is weak. Restorations of neutral osteological neck posture based on seemingly detailed diagrams of cervical articulations are not reliable because the pictures are not sufficiently accurate due to a combination of illustration errors, and distortion of the fossil cervicals. This is all the more true because fossil cervical series lack the critical inter-centra cartilage. Maximum vertical reach is more readily restorable and biologically informative for long necked herbivores. Modest extension of 10 degree between each caudal cervical allowed high shouldered sauropods to raise the cranial portion of their necks to vertical postures that allowed them to reach floral resources far higher than seen in the tallest mammals. This hypothesis is supported by the dorsally extended articulation of the only known co-fused sauropod cervicals. Many sauropods appear to have been well adapted for rearing in order to boost vertical reach, some possessed retroverted pelves that may have allowed them to walk slowly while bipedal. A combination of improved high browsing abilities and sexual selection probably explains the unusually long necks of tall ungulates and super tall sauropods. This article is protected by copyright. All rights reserved.
Information on aging, maturation, and growth is important for understanding life histories of organisms. In extinct dinosaurs, such information can be derived from the histological growth record preserved in the mid-shaft cortex of long bones. Here, we construct growth models to estimate ages at death, ages at sexual maturity, ages at which individuals were fully-grown, and maximum growth rates from the growth record preserved in long bones of six sauropod dinosaur individuals (one indeterminate mamenchisaurid, two Apatosaurus sp., two indeterminate diplodocids, and one Camarasaurus sp.) and one basal sauropodomorph dinosaur individual (Plateosaurus engelhardti). Using these estimates, we establish allometries between body mass and each of these traits and compare these to extant taxa. Growth models considered for each dinosaur individual were the von Bertalanffy model, the Gompertz model, and the logistic model (LGM), all of which have inherently fixed inflection points, and the Chapman-Richards model in which the point is not fixed. We use the arithmetic mean of the age at the inflection point and of the age at which 90% of asymptotic mass is reached to assess respectively the age at sexual maturity or the age at onset of reproduction, because unambiguous indicators of maturity in Sauropodomorpha are lacking. According to an AIC-based model selection process, the LGM was the best model for our sauropodomorph sample. Allometries established are consistent with literature data on other Sauropodomorpha. All Sauropodomorpha reached full size within a time span similar to scaled-up modern mammalian megaherbivores and had similar maximum growth rates to scaled-up modern megaherbivores and ratites, but growth rates of Sauropodomorpha were lower than of an average mammal. Sauropodomorph ages at death probably were lower than that of average scaled-up ratites and megaherbivores. Sauropodomorpha were older at maturation than scaled-up ratites and average mammals, but younger than scaled-up megaherbivores.
Sauropods were the largest terrestrial tetrapods (>10(5) kg) in Earth's history and grew at rates that rival those of extant mammals. Magyarosaurus dacus, a titanosaurian sauropod from the Upper Cretaceous (Maastrichtian) of Romania, is known exclusively from small individuals (<10(3) kg) and conflicts with the idea that all sauropods were massive. The diminutive M. dacus was a classical example of island dwarfism (phyletic nanism) in dinosaurs, but a recent study suggested that the small Romanian titanosaurs actually represent juveniles of a larger-bodied taxon. Here we present strong histological evidence that M. dacus was indeed a dwarf (phyletic nanoid). Bone histological analysis of an ontogenetic series of Magyarosaurus limb bones indicates that even the smallest Magyarosaurus specimens exhibit a bone microstructure identical to fully mature or old individuals of other sauropod taxa. Comparison of histologies with large-bodied sauropods suggests that Magyarosaurus had an extremely reduced growth rate, but had retained high basal metabolic rates typical for sauropods. The uniquely decreased growth rate and diminutive body size in Magyarosaurus were adaptations to life on a Cretaceous island and show that sauropod dinosaurs were not exempt from general ecological principles limiting body size.
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was supported by the German Research Foundation (grant FOR 533) This is contribution number 46 of the DFG Research Unit 533 " Biology of the Sauropod Dinosaurs: The Evolution of Gigantism
- P M S The Research Of
The research of P.M.S. and M.C. was supported by the
German Research Foundation (grant FOR 533). This is
contribution number 46 of the DFG Research Unit 533
" Biology of the Sauropod Dinosaurs: The Evolution of
Gigantism. "
10.1126/science.1160904