Article

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

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Abstract

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 giraffe's 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 animal's 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.

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... The shoulder-hip length was calculated by scaling their reported limb lengths to fig. 1 in . Estimated MOI was also derived for a horse and giraffe from Henderson and Naish (2010). Shoulder and hip locations were estimated by comparing their fig. 1 with skeletal drawings or mounts. ...
... COM position was assumed to lie along the shoulder-hip line, and its bias towards the forelimbs (m′ F in Polet and Bertram, 2019) was determined from calculations using Buchner et al. (1997) for the horse (m′ F =0.50) and ground reaction forces from Basu et al. (2019a) for the giraffe (m′ F =0.65). The horse MOI was used to ground-truth the estimation method of Henderson and Naish (2010), and yieldedÎ=0.80, similar to the empirical value of 0.82 (Table 1). ...
Article
Many quadrupedal mammals transition from a four-beat walk to a two-beat run ( e.g. trot), but some transition to a four-beat run ( e.g. amble). Recent analysis shows that a two-beat run minimizes work only for animals with a small pitch moment of inertia (MOI), though empirical MOI were not reported. It also remains unclear whether MOI affects gait energetics at slow speeds. Here I show that a particular normalization of the pitch moment of inertia (the Murphy number) has opposite effects on walking and running energetics. During walking, simultaneous fore and hindlimb contacts dampen pitching energy, favouring a four-beat gait that can distribute expensive transfer of support. However, the required pitching of a four-beat walk becomes more expensive as Murphy number increases. Using trajectory optimization of a simple model, I show that both the walking and slow running strategies used by dogs, horses, giraffes and elephants can be explained by work optimization under their specific Murphy numbers. Rotational dynamics have been largely ignored in quadrupedal locomotion, but appear to be a central factor in gait selection.
... So far there has only been one attempt to quantify giraffe surface area (Henderson and Naish, 2010) and this was in the context of determining buoyancy and potential swimming ability not thermoregulation. Henderson & Naish used a computerized digital slicing method based on illustrations and calculated that in a theoretical giraffe weighing 1611 kg the surface area of the skin would be 17.7 m 2 . ...
... In assessing this possibility we set out to measure surface area and mass in G.c. giraffa extant in Zimbabwe. Contrary to the one previous estimate of the surface area of a~1600 kg giraffe (17.7 m 2 ; Henderson and Naish, 2010), our calculations show that the surface area of a giraffe of that body mass would be about 12.4 m 2 . Furthermore we have found that the total body surface area of giraffes is not significantly different to the surface area predicted from equations for standard mammals ( Fig. 3; Stahl, 1967). ...
Article
One of several hypotheses for the evolution of the shape of giraffes is that it evolved to maximize heat loss via a high surface area to mass ratio. We calculated the surface area (SA) of the head, neck, trunk and upper legs, and the lower legs in 60 giraffes of both sexes and a body mass range of 141–1358 kg. No sex differences were found for giraffes of equivalent body mass. Relative surface area (cm² kg⁻¹ body mass) declined from 145 in juvenile giraffes to 90 in adults. Average total body SA was 7.3 ± 2.5 m² (range 2.2–11.7), which is not significantly different to that of mammals of equivalent mass. The extra area of the neck and legs was offset by smaller trunk area. However, the narrow diameters of the neck and lower legs enhance the rate of convective and evaporative heat loss and reduce the incident solar radiant heat load when giraffe face the sun, a behaviour supplemented by seeking shade if it is available. We have concluded that giraffes do not have an unusually large SA for their mass, but their shape confers other thermoregulatory benefits that have advantages for survival in the arid habitat they prefer.
... The annual average ABIs of different animals in descending order are mammals, insects, reptiles, amphibians, and birds. Mammals are not good at swimming or flying (Henderson and Naish, 2010;Santori et al., 2014), so they are most seriously affected by floods. Although most insects can fly during the emergence period, their larvae crawl very slowly, so they are also seriously affected. ...
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Extreme floods seriously affect the biodiversity of terrestrial animals (birds, mammals, reptiles, amphibians, and insects). The degree of impact depends on many factors, e.g., animal characteristics, natural conditions, and flood characteristics. Previous evaluation methods are not suitable for assessing the impact of floods on the biodiversity of all species in the entire submerged area, nor do they accurately reflect variability in the degree of impact. First, the influencing factors were boiled down to four: ratio of flood duration to survival time of animals in floods (D), ratio of flood depth to plant height (S), migration ability of animals (M), and temperature (T), which are represented by a coefficient I. Then, we proposed a calculation method for I based on the four factors. Third, we proposed the total and average biodiversity impact indices, namely, the TBI and ABI, respectively, indicating the overall and average impacts of floods on biodiversity in the submerged area, with the calculation method considering both the number of species and I. An extreme flood was simulated to obtain the flood parameters. In addition, we analyzed monthly changes in partial influencing factors. Finally, the impact of extreme floods on the biodiversity of terrestrial animals in the submerged area was evaluated monthly, and it was found that (1) TBI and ABI changed with space; (2) the ABI of different animals in descending order were mammals, insects, reptiles, amphibians, and birds; (3) the ABI of different land use types in descending order were cropland, orchard and shrubland, grassland, and forest and for TBI were orchard and shrubland, cropland, forest, and grassland; and (4) the TBI and ABI of different animals and land use types changed over time. The proposed method and indices are suitable for assessing the impact of floods on the biodiversity of any organism in any area.
... high mountains (Happold 1978;Dagg 2014) and large rivers (MacClintock 1973;Henderson & Naish 2010). This might concern in particular females living in nursery herds with their calves (Bercovitch & Berry 2010), which tend to avoid the potential risk of overcoming biogeographic barriers (Petzold & Hassanin 2020). ...
Article
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Intensified exploration of sub-Saharan Africa during the 18th and 19th centuries led to many newly described giraffe subspecies. Several populations described at that time are now extinct, which is problematic for a full understanding of giraffe taxonomy. In this study, we provide mitochondrial sequences for 41 giraffes, including 19 museum specimens of high importance to resolve giraffe taxonomy, such as Zarafa from Sennar and two giraffes from Abyssinia (subspecies camelopardalis), three of the first southern individuals collected by Levaillant and Delalande (subspecies capensis), topotypes of the former subspecies congoensis and cottoni, and giraffes from an extinct population in Senegal. Our phylogeographic analysis shows that no representative of the nominate subspecies camelopardalis was included in previous molecular studies, as Zarafa and two other specimens assigned to this taxon are characterized by a divergent haplogroup, that the former subspecies congoensis and cottoni should be treated as synonyms of antiquorum, and that the subspecies angolensis and capensis should be synonymized with giraffa, whereas the subspecies wardi should be rehabilitated. In addition, we found evidence for the existence of a previously unknown subspecies from Senegal (newly described in this study), which is now extinct. Based on these results, we propose a new classification of giraffes recognizing three species and 10 subspecies. According to our molecular dating estimates, the divergence among these taxa has been promoted by Pleistocene climatic changes resulting in either savannah expansion or the development of hydrographical networks (Zambezi, Nile, Lake Chad, Lake Victoria). © 2020, Museum National d'Histoire Naturelle. All rights reserved.
... Although possessing a relatively small head, the elongate neck of the giraffe (Giraffa camelopardalis) could distribute a high mass on the forelegs. Henderson and Naish (1999) showed that the center of mass (COM) of the giraffe was located just behind the insertion of the forelegs of the short body indicating a substantial mass on the forelegs. The head and neck of the giraffe represent 10.8% of the body mass. ...
Article
Dogs have been bred for different sizes and functions, which can affect their locomotor biomechanics. As quadrupeds, dogs must distribute their mass between fore and hindlegs when standing. The mass distribution in dogs was studied to determine if the proportion of supported mass on each limb couplet is dependent on body size. A total of 552 dogs from 123 breeds ranging in size from Chihuahua to Mastiff were examined. Each dog was weighed on a digital scale while standing, alternating foreleg and hindleg support. The overall “grand” mean proportion of mass on the forelegs to the total mass was 60.4% (range: 47.6–74.4%). The dataset indicated no significant change in the ratio with total mass but there was a significant difference by sex. When separated into AKC categories, no group was notably different from the grand mean or from each other, but when sex was also considered, there was a significant difference that was not specifically discerned by post hoc analysis. The mean for female Hounds was notably below the grand mean. For clades based on genetics, the mean for European origin mastiffs was notably greater than the grand mean and significantly different from UK origin herders and coursers. The mass of the head, chest, and musculature for propulsion could explain the mass support differential. Mass distribution and terrestrial locomotion in dogs shows substantial variation among breeds. This article is protected by copyright. All rights reserved.
... Software was specially written to compute body masses, the centres of mass and buoyancy, and produce the sequence of small linear and angular displacements to bring a 3D, digital model to buoyant equilibrium, and display the final results in graphical form. The validity of the results of this modeling process and software have been successfully demonstrated with a variety of floating (and sometimes sinking) models of living forms-in particular American alligators (Henderson, 2003), elephants (Henderson, 2004), horses and giraffes (Henderson and Naish, 2010), sea turtles (Henderson, 2006), and penguins (Henderson, in press). We chose these particular ankylosaur species because their bauplans are representative of their respective families (Coombs Jr, 1978). ...
Article
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It is widely held that, within the Cretaceous fluvial and marine deposits of North America, ankylosaur remains are typically preserved upside-down; however, this anecdotal observation has yet to be substantiated. Likewise, none of the various hypotheses that purport to explain the frequent occurrence of overturned ankylosaurs has been tested either. This study is the first to apply quantitative and modeling approaches to address these shortcomings. We find strong statistical support for the dominance of upside-down occurrences, and favour a "bloat-and-float" model to account for them. According to this model, ankylosaur carcasses become reworked into fluvial or marine settings where they bloat and overturn prior to their final deposition. Differential floating behaviour between ankylosaurids and nodosaurids may have implications regarding the occurrence of the latter in marine depositional environments. This consideration of ankylosaur taphonomy might similarly help to explain the purported frequency of overturned glyptodonts, which share a similar bauplan with ankylosaurs.
... Most of terrestrial mammals can swim, generally for short stretches, as reported even for unexpected ones such as giraffes (Henderson & Naish 2010). Swimming, however, is neither natural nor easy for the majority of terrestrial mammals. ...
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Since the time of Darwin (1859) and Wallace (1869), islands have been regarded by scientists as a prime target for scrutinizing the forces that may influence evolution and diversification and important elements in biogeographic studies. This research aims to scrutinize whether and to what extent the composition and structure of past mammal insular faunas and their changes through time, may provide sound clues for inferring the paleogeographical evolution of a region. As a case study I have to critically analyzed the dynamics shown by the Plio-Pleistocene mammalian fauna of three Western Mediterranean insular districts, Balearic Islands, Sardinia, and Sicily, each characterized by its on peculiar paleobiogeographical evolutionary history. The revision of faunas and the critical analysis of the dispersal ability of the ancestors of island settlers allowed hypothesizing time and mode of island colonization. Results obtained confirm that the early isolation of Balearic Islands from the mainland led to the establishment of an endemic fauna since the pre-Messinian Miocene (?Astaracian European Land Mammal Age, MN7/8), Sardinia was definitely isolated since the Pliocene, although dispersal events led to some faunal turnovers during the Pleistocene, and suggest for Sicily a complex, still imperfectly disentangled history of alternate phases of complete separation and sporadic, more or less difficult connections with southern Italy. This article is protected by copyright. All rights reserved.
... Subsequently, it is reasonable to speculate their dolichomorphic shape as an evolutionary adaptation for heat loss with a large body. Compared to other large bodied mammals, giraffes do not possess traditional heat radiating organs like the ear of elephants nor are they known to make use of swimming to cool down (Henderson & Naish 2010). Giraffe skin may however have a thermoregulatory function, judging by the association of blood vessels with the patches and the presence of sweat glands , in which case a long dolichomorphic body shape would make sense. ...
Thesis
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Giraffes (Giraffa camelopardalis) have evolved into a unique and extreme shape. The principle determinant of its shape is the skeleton and the overarching theme of the study was to describe how this shape is achieved throughout ontogeny. Accordingly, the study had three main objectives: 1) To describe the growth of the giraffe postcranial skeleton allometrically, 2) To interpret the allometric patterns described in an evolutionary and functional sense and 3) To reconstruct the size and shape of the extinct Giraffa sivalensis using, if feasible, allometric equations obtained in this study. Secondary objectives were to a) establish if sexual dimorphism was evident in G. camelopardalis and b) determine if growth patterns in the foetus differed from those in postnatal G. camelopardalis. Data were collected from giraffes culled as part of conservancy management in Zimbabwe. The sample included 59 animals from which vertebral dimensions were taken in 48 animals and long bone dimensions in 47 animals. Body masses ranged from 21 kg to 77 kg in foetuses and 147 kg to 1412 kg postnatally, representing 29 males and 30 females. In addition to body mass, external body dimensions were recorded from each animal. Each vertebra and unilateral long bone was dissected from the carcasses and cleaned, after which dimensions were measured with a vernier calliper, measuring board or measuring tape. Vertebral dimensions measured included body (centrum) length, height and width as well as vertebral spinous process length. Long bone dimensions included length, two midshaft diameters and circumference. Allometric equations (y=bxk) were constructed from the data, with special interest in the scaling exponent (k) to illustrate regions of positively allometric, isometric or negatively allometric growth. In the first series of analyses the growth patterns of the components of the postcranial axial skeleton were analysed. The adaptations in vertebral growth to create and maintain extraordinary shape were identified as disproportionate elongation of the cervical vertebrae after birth, increasing cross sectional diameters of the cervical vertebrae from cranial to caudal and positively allometric spinal process growth. The theory of sexual selection as a driver for neck elongation in giraffes was brought into question by showing that male and female vertebral elongation rates are similar relative to increases in body mass. The second series of analyses described the growth pattern of the long bones of the appendicular skeleton. The allometric exponents seemed unremarkable compared to the few species described previously, and it was shown that the giraffe appendicular skeleton does not elongate in the dramatic way the neck does. Limbs at birth, after lengthening with positive allometry in utero, are already elongated and slender in shape and a further increase in the gracility of the bones is either not possible or not desirable. This result implies that it is neck elongation rather than leg elongation that is the dominant factor in the evolution of the giraffe shape. Nevertheless, the front limb bones and especially the humerus may show responsiveness to increasing high loads and/ or bending moments, which may be caused by the neck mass which increases with positive allometry, or with behaviours such as splaying the forelegs during drinking. In the third component of the study ontogenetic allometric equations in extant giraffes were applied to the remains of an extinct giraffid, G. sivalensis. The procedure was unusual as it employed ontogenetic regressions instead of the more commonly used interspecific regressions. The appropriateness of each equation to estimate body mass was evaluated by calculating the prediction error incurred in both extant giraffes and okapis (Okapia johnstoni). It was concluded that, due to body shape, ontogenetic equations were adequate and perhaps preferable to interspecific equations to estimate proportions in Giraffa species. This analysis showed that G sivalensis was smaller than extant giraffes and weighed around 400 kg (range 228 kg 575 kg), with a neck length of about 147 cm and a height of 390 cm. There may be evidence of sexual dimorphism in this species, with males being about twice the body weight of females. However, if sexual dimorphism was not present and all the bones were correctly attributed to this species, then G. sivalensis had a slender neck with a relatively stocky body. In conclusion, this study established ontogenetic regression equations for the skeleton of an animal of which the body shape seems to be at the extreme limits of mammalian possibility. The value of the current study lies especially in its sample size and quality, which included an unprecedented number of giraffe body masses, vertebral and long bone dimensions. This dataset had applications in the giraffe s evolutionary biology, palaeontology and even ecology. Future studies still need to compare the findings from giraffe growth with similar data from other taxa, especially those with long legs and necks. Specifically, it would interesting to determine if positively allometric neck growth combined with isometric leg growth is found in other mammalian species. In addition, the strength of giraffe long bones and vertebrae needs to be investigated with more accuracy using parameters like second moment of area. Lastly, further palaeontological studies on other giraffid sizes are necessary to validate the current and future interpretations of fossil giraffid findings.
... RTMP staff and colleagues also have worked on a variety of other research projects. Notable examples include the following: computer modeling of tetrapod movement and buoyancy (e.g., Henderson 2006bHenderson , 2006cHenderson , 2010aHenderson and Naish 2010;Hone and Henderson 2014); biomechanical studies of bite forces and feeding (e.g., Hurum and Currie 2000;Therrien 2005aTherrien , 2005bTherrien et al. 2005;Henderson 2010b;Henderson and Nicholls 2015); estimating body sizes for dinosaurs and pterosaurs (Therrien and Henderson 2007;Butler et al. 2009;Henderson 2010a); palaeopathological studies (e.g., Tanke 1992, 2005;Tanke and Currie 1998;Tanke and Rothschild 2002, 2010; and articles about the history of vertebrate palaeontology in Alberta (e.g., Tanke 2004Tanke , 2010aTanke , 2010bTanke and Currie 2010). ...
... Full details on this method for estimating body mass and CM using 3D meshes are presented by Henderson (1999). This method of estimating body mass and CM has been validated with the studies of various extant taxa: alligators (Henderson, 2003), six species of birds ranging in mass from a few grams to tens of kilograms (Henderson, 2010a), elephants (Henderson, 2006a), giraffes and horses (Henderson and Naish, 2010b), and sea turtles (Henderson, 2006b). ...
Article
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. Rayosaurus 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 details of the low density regions associated with lungs, systems of air sacs, and pneumatised axial skeletal regions. These details, along with the surface meshes of the models, were used to estimate the body masses and centres 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 CM 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 R. tessonei with a maximum body mass of 850 kg and a body length of 8.3 m. This article is protected by copyright. All rights reserved. © 2015 Wiley Periodicals, Inc.
... During his professional career, Naish has not shied away from occasionally tackling rather offbeat subjects. He has, for example, recently co-authored at echnical paper that investigated the question whether the giraffe, as is often stated in the literature,r eally is incapableo f swimming (Henderson and Naish 2010). But his real pet subject is cryptozoology,i.e., the research on animalsthat are currently unknownt os cience.N aish makes no secret about this, and many of the articlest hat he has published on his blog, as well as agood few of thosethat have made it to the current compilation, have acryptozoologicalslant. ...
... This, we suggest, provides an anterior 'buoy' analogous to the air-filled sinuses in the crania of elephants (Todd 2010), which are also exceptional swimmers among land mammals (Nowak 1999). Although most species of deer swim proficiently at the water surface without particular narial adaptation, a narial buoy in the moose/elk might serve to counterbalance the relatively heavy forequarters of this species during foraging deep under water (see Henderson & Naish 2010). ...
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Tapirs (Perissodactyla: Tapiridae) are the only living vertebrates, beyond the order Proboscidea, found to possess a true proboscis, defined as a flexible tubular extension of the joint narial and upper labial musculature that serves, at least in part, to grasp food. Tapirs show only partial homology and analogy with elephants in the narial and upper labial structures, as well as in the skull bones and teeth. However, superficially similar extensions in other extant vertebrates differ greatly in anatomy and function. Therefore, they deserve new names: prorhiscis (e.g. Mammalia: Saiga tatarica), prorhinosis (e.g. Chondrichthyes: Callorhinchus spp.), prorhynchis (e.g. Osteichthyes: Campylomormyrus spp.) and progeneiontis (e.g. Osteichthyes: Gnathonemus spp.). Among non-mammalian vertebrates, no bird or reptile is known to possess a proboscis. Among fishes, there are various extensions of the rostrum, jaws, 'nose' and 'chin' that lack the required narial involvement. The skulls of extinct mammals within (e.g. deinotheres) and beyond (e.g. astrapotheres) the Proboscidea confirm that a proboscis evolved independently in several mammalian lineages before the Pliocene. This convergence with tapirs presumably reflects, in part, the advantages of concentrating the olfactory sensor on what is, effectively, the tip of a long mobile upper lip. However, the proboscis does not appear to have arisen de novo in any vertebrate post-Pliocene, and its continued evolution has apparently depended on the further development of its length, flexibility and innervations, as epitomized by elephants.
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The density, or specific gravity (SG), of organisms has numerous important implications for their form, function, ecology, and other facets of beings living and dead, and it is especially necessary to apply SG values that are as accurate as practical when estimating their masses which is itself a critical aspect of living things. Yet a comprehensive review and analysis of this notable subject of anatomy has never been conducted and published. This is such an effort, being as extensive as possible with the data on hand, bolstered by some additional observations, and new work focusing on extinct animals who densities are least unknown: pterosaurs and dinosaurs with extensive pneumatic complexes, including the most sophisticated effort to date for a sauropod. Often difficult to determine even via direct observation, techniques for obtaining the best possible SG data are explained and utilized, including observations of floating animals. Neutral SG (NSG) is proposed as the most important value for tetrapods with respiratory tracts of fluctuating volume. SGs of organisms range from 0.08 to 2.6, plant tissues from 0.08 to 1.39, and vertebrates from about 0.75 (some giant pterosaurs) to 1.2 (those with heavy armor and/or skeletons). Tetrapod NSGs tend to be somewhat higher than widely thought, especially those theropod and sauropod dinosaurs and pterosaurs with air-sacs because respiratory system volume is usually measured at maximum inhalation in birds. Also discussed is evidence that the ratio of the mass of skeletons relative to total body mass has not been properly assayed in the past.
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Most quadrupedal mammals transition from a four-beat walk to a two-beat run (e.g. trot), but some transition to a four-beat run (e.g. amble). Recent analysis shows that a two-beat run minimizes work only for animals with a small pitch moment of inertia (MOI), though empirical MOI were not reported. It also remains unclear whether MOI affects gait energetics at slow speeds. Here I show that a particular normalization of the pitch moment of inertia (the Murphy number) has opposite effects on walking and running energetics. During walking, simultaneous fore and hindlimb contacts dampen pitching energy, favouring a four-beat gait that can distribute expensive transfer of support. However, the required pitching of a four-beat walk becomes more expensive as Murphy number increases. Using trajectory optimization of a simple model, I show that both the walking and slow running strategies used by dogs, horses, giraffes and elephants can be explained by work optimization under their specific Murphy numbers. Rotational dynamics have been largely ignored as a determining factor in quadrupedal locomotion, but appear to be a central factor in gait selection.
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A recent interpretation of the fossil remains of the enigmatic, large predatory dinosaur Spinosaurus aegyptiacus Stromer 1915 proposed that it was specially adapted for a semi-aquatic mode of life—a first for any predatory dinosaur. To test some aspects of this suggestion, a three-dimensional, digital model of the animal that incorporates regional density variations, lungs and air sacs was generated, and the flotation potential of the model was investigated using specially written software. It was found that Spinosaurus would have been able to float with its head clear of the water surface, although it was laterally unstable and would tend to roll onto its side. Similarly detailed models of another spinosaurid Baryonyx ( Suchomimus ) tenerensis Sereno et al. 1998, along with models of the more distantly related Tyrannosaurus rex Osborn 1905, Allosaurus fragilis Marsh 1877, Struthiomimus altus Lambe 1902, and Coelophysis bauri Cope 1887 were also able to float in positions that enabled the animals to breathe freely, showing that there is nothing exceptional about a floating Spinosaurus . Validation of the modelling methods was done with floated models of an alligator and an emperor penguin. The software also showed that the center of mass of Spinosaurus was much closer to the hips than previously estimated, similar to that observed in other theropods, implying that this dinosaur would still have been a competent walker on land. With its pneumatised skeleton and a system of air sacs (modelled after birds), the Spinosaurus model was found to be unsinkable, even with its lungs deflated by 75%, and this would greatly hinder a semi-aquatic, pursuit predator. The conclusion is that Spinosaurus may have been specialized for a shoreline or shallow water mode of life, but would still have been a competent terrestrial animal.
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The submerged sill in the Strait of Messina, which is located today at a minimum depth of 81 m below sea level (bsl), represents the only land connection between Sicily and mainland Italy (and thus Europe) during the last lowstand when the sea level locally stood at about 126 m bsl. Today, the sea crossing to Sicily, although it is less than 4 km at the narrowest point, faces hazardous sea conditions, made famous by the myth of Scylla and Charybdis. Through a multidisciplinary research project, we document the timing and mode of emergence of this land connection during the last 40 kyr. The integrated analysis takes into consideration morphobathymetric and lithological data, and relative sea-level change (both isostatic and tectonic), resulting in the hypothesis that a continental land bridge lasted for at least 500 years between 21.5 and 20 cal ka BP. The emergence may have occurred over an even longer time span if one allows for seafloor erosion by marine currents that have lowered the seabed since the Last Glacial Maximum (LGM). Modelling of palaeotidal velocities shows that sea crossings when sea level was lower than present would have faced even stronger and more hazardous sea currents than today, supporting the hypothesis that earliest human entry into Sicily most probably took place on foot during the period when the sill emerged as dry land. This hypothesis is compared with an analysis of Pleistocene vertebrate faunas in Sicily and mainland Italy, including a new radiocarbon date on bone collagen of an Equus hydruntinus specimen from Grotta di San Teodoro (23-21 cal ka BP), the dispersal abilities of the various animal species involved, particularly their swimming abilities, and the Palaeolithic archaeological record, all of which support the hypothesis of a relatively late land-based colonization of Sicily by Homo sapiens.
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Giraffe (Giraffa camelopardalis) are thought to be introduced aliens in KwaZulu-Natal, an area in which they flourish today. This perception was based on the lack of reference to sightings of giraffe in early colonial literature and the lack of giraffe remains in archaeological sites within KwaZulu-Natal. We have reviewed the literature and found no reliable reference to giraffe in early colonial writings and no reports of rock art featuring giraffe in the area. However, there are recent reports of the recovery of giraffe bones from the Middle Stone Age deposits at Sibudu Shelter, the Holocene hunter-gatherer deposits at Maqonqo Shelter and from the Early Iron Age agriculturist site of KwaGandaganda, all within KwaZulu-Natal. We argue that giraffe were present 1000 BP (date of most recent excavation evidencing giraffe remains), but had died out or been extirpated by c. 220 BP (date of written accounts). The demise of giraffe between 1000 and 220 BP may be linked to disease, climate change or anthropogenic causes. The finding of giraffe remains within KwaZulu-Natal raises the possibility that they should be considered as native to the area.
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A classic example of extreme morphological adaptation to the environment is the neck of the giraffe (Giraffa camelopardalis), a trait that most biologists since Darwin have attributed to competition with other mammalian browsers. However, in searching for present-day evidence for the maintenance of the long neck, we find that during the dry season (when feeding competition should be most intense) giraffe generally feed from low shrubs, not tall trees; females spend over 50% of their time feeding with their necks horizontal; both sexes feed faster and most often with their necks bent; and other sympatric browsers show little foraging height partitioning. Each result suggests that long necks did not evolve specifically for feeding at higher levers. Isometric scaling of neck-to-leg ratios from the okapi Okapia johnstoni indicates that giraffe neck length has increased proportionately more than leg length-an unexpected and physiologically costly method of gaining height. We thus find little critical support for the Darwinian feeding competition idea. Ne suggest a novel alternative: increased neck length has a sexually selected origin. Males fight for dominance and access to females in a unique way: by clubbing opponents with well-armored heads on long necks. Injury and death during intrasexual combat is not uncommon, and larger-necked males are dominant and gain the greatest access to estrous females. Males' necks and skulls are not only larger and more armored than those of females' (which do not fight), but they also continue growing with age. Larger males also exhibit positive allometry, a prediction of sexually selected characters, investing relatively more in massive necks than smaller males. Despite being larger, males also incur higher predation costs than females. We conclude that sexual selection has been overlooked as a possible explanation for the giraffe's long neck, and on present evidence it provides abetter explanation than one of natural selection via feeding competition.
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Use of the aquatic environment by hippopotami (Hippopotamus amphibius) allows locomotive styles impossible to achieve on land by such heavy animals. Videos of the underwater locomotion of 2 hippopotami were analyzed frame by frame. Average horizontal velocity underwater was 0.47 m/s. Hippopotami used a gait underwater that was similar to a gallop with extended unsupported intervals. Ground contact time decreased with increasing horizontal velocity, vertical displacement during the unsupported intervals increased with an increase in ground contact time, and time between consecutive footfalls decreased with an increase in horizontal velocity. Hippopotami use an unstable gait underwater, which is facilitated by the increased buoyancy of water. Despite restrictions to movement on land due to its massive weight, locomotion of the hippopotamus underwater is analogous to movement in a microgravity environment.
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The purpose of this study was to assess whether our method of inducing forced expiration detects small airway obstruction in horses. Parameters derived from forced expiratory flow-volume (FEFV) curves were compared with lung mechanics data obtained during spontaneous breathing in nine healthy horses, in three after histamine challenge, and in two with chronic obstructive pulmonary disease (COPD) pre- and posttherapy with prednisone. Parameters measured in the healthy horses included forced vital capacity (FVC = 41.6 +/- 5.8 liters; means +/- SD) and forced expiratory flow (FEF) at various percentages of FVC (range of 20.4-29.7 l/s). Histamine challenge induced a dose-dependent decrease in FVC and FEF at low lung volume. After therapy, lung function of the two COPD horses improved to a point where one horse had normal lung mechanics during tidal breathing; however, FEF at 95% of FVC (4.9 l/s) was still decreased. We concluded that FEFV curve analysis allowed the detection of induced or naturally occurring airway obstruction.
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With their vertically elongated body form, giraffes generally feed above the level of other browsers within the savanna browsing guild, despite having access to foliage at lower levels. They ingest more leaf mass per bite when foraging high in the tree, perhaps because smaller, more selective browsers deplete shoots at lower levels or because trees differentially allocate resources to promote shoot growth in the upper canopy. We erected exclosures around individual Acacia nigrescens trees in the greater Kruger ecosystem, South Africa. After a complete growing season, we found no differences in leaf biomass per shoot across height zones in excluded trees but significant differences in control trees. We conclude that giraffes preferentially browse at high levels in the canopy to avoid competition with smaller browsers. Our findings are analogous with those from studies of grazing guilds and demonstrate that resource partitioning can be driven by competition when smaller foragers displace larger foragers from shared resources. This provides the first experimental support for the classic evolutionary hypothesis that vertical elongation of the giraffe body is an outcome of competition within the browsing ungulate guild.
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The giraffe (Giraffa camelopardalis) still survives in four countries of West and central Africa. The populations of Niger and Cameroon are generally assigned to the subspecies peralta, but those of Chad and the Central African Republic are taxonomically problematic, as they are referred to as either peralta, or antiquorum, or congoensis. In this study, a mitochondrial fragment of 1765 nucleotide sites, covering the complete cytochrome b gene, three transfer RNAs and a large part of the control region, was sequenced to assess the relationships between several populations of giraffe. The phylogenetic analyses performed on the 12 identified haplotypes indicate that northern giraffes constitute a natural group, distinct from that of southern giraffes. Surprisingly, the giraffes of Niger are found to be more closely related to the giraffes of East Africa (subspecies rothschildi and reticulata) than to those of central Africa. We conclude therefore that the subspecies peralta contains only the Niger giraffes, whereas the subspecies antiquorum includes all populations living in Cameroon, Chad, the Central African Republic, and southwestern Sudan. We suggest that the ancestor of the Nigerian giraffe dispersed from East to North Africa during the Quaternary period and thereafter migrated to its current Sahelian distribution in West Africa, in response to the development of the Sahara desert. This hypothesis implies that Lake Mega-Chad acted as a strong geographical barrier during the Holocene, preventing any contact between the subspecies peralta and antiquorum. Our study has direct implications for conservation management, as we show that no subspecies peralta is represented in any European zoos, only in Niger, with a small population of less than 200 individuals.
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A central question in the evolutionary diversification of large, widespread, mobile mammals is how substantial differentiation can arise, particularly in the absence of topographic or habitat barriers to dispersal. All extant giraffes (Giraffa camelopardalis) are currently considered to represent a single species classified into multiple subspecies. However, geographic variation in traits such as pelage pattern is clearly evident across the range in sub-Saharan Africa and abrupt transition zones between different pelage types are typically not associated with extrinsic barriers to gene flow, suggesting reproductive isolation. By analyzing mitochondrial DNA sequences and nuclear microsatellite loci, we show that there are at least six genealogically distinct lineages of giraffe in Africa, with little evidence of interbreeding between them. Some of these lineages appear to be maintained in the absence of contemporary barriers to gene flow, possibly by differences in reproductive timing or pelage-based assortative mating, suggesting that populations usually recognized as subspecies have a long history of reproductive isolation. Further, five of the six putative lineages also contain genetically discrete populations, yielding at least 11 genetically distinct populations. Such extreme genetic subdivision within a large vertebrate with high dispersal capabilities is unprecedented and exceeds that of any other large African mammal. Our results have significant implications for giraffe conservation, and imply separate in situ and ex situ management, not only of pelage morphs, but also of local populations.
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A mathematical-computational method for determining the volume, mass, and center of mass of any bilaterally symmetric organism is presented. Cavities within the body of an organism such as lungs are easily accommodated by this method. Sagittal and frontal profiles, obtained from tracings of 'fleshed-out' skeletal reconstructions, are used to provide limits for defining transverse slices of the body. Any internal cavities are defined by their own sagittal and frontal profiles. The computations consist of mathematically slicing the body and any cavities into independent sets of transverse laminae and computing their masses, centroids, and moments with respect to the three coordinate axes. Further calculations produce the masses and the (x,y,z) coordinates for the centers of mass of the body, any cavities, and the body + cavities. Predicted body masses of large, extant mammals (elephant, giraffe, hippopotamus, and rhinoceros) are in close agreement with actual body masses. New, lower estimates for body masses of selected large dinosaurs, based on modern skeletal reconstructions, are also presented, along with numerical estimates of their centers of mass. This method is an improvement over earlier ones that relied on measuring displaced volumes of water or sand by scale models to estimate the masses, and suspending models by threads to estimate their centers of mass.
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Comparative analysis of gastrolith distribution suggests a role in buoyancy control rather than food processing. Gastroliths occur in most tetrapods which "fly' underwater with hydrofoil limbs, including plesiosaurs, penguins, and otariid pinnipeds, but not the marine chelonians. They do not usually occur in cetaceans, ichthyosaurs, mosasaurs, and odobenid and phocid pinnipeds, which swim with caudal fin or the equivalent. Occurence in amphibous forms is variable: crocodilians often have gastroliths, but nothosaurs and placodonts do not. -from Author
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No other book on the market today can match the 30-year success of Halliday, Resnick and Walker's Fundamentals of Physics! In a breezy, easy-to-understand style the book offers a solid understanding of fundamental physics concepts, and helps readers apply this conceptual understanding to quantitative problem solving. This book offers a unique combination of authoritative content and stimulating applications.
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A three-dimensional mathematical/computational model of the crocodilian Alligator mississippiensis has been developed to investigate the influence of gastroliths on crocodilian buoyancy. The model is self-correcting, recovers from large perturbations, and can replicate the body orientations and degrees of immersion seen in living crocodilians that have attained equilibrium with respect to the competing forces of buoyancy and weight. For a range of lung deflations where the model was still positively buoyant, adding gastroliths of mass equal to 1% of the body mass has the effect of lowering the body, on average, by 2.6% of the maximum trunk depth while simultaneously increasing the inclination of the body with its sagittal plane. With the lungs fully inflated, the model would become negatively buoyant only when loaded with stones weighing more than 6% of the total body mass. Without gastroliths the body would sink when the lungs were deflated by 40%–50%. In all situations the model was resistant to capsizing. The relatively small amounts of gastroliths (<2% body mass) found in aquatic tetrapods are considered to be inconsequential for buoyancy and stability, and the lungs are the principle agent for hydrostatic buoyancy control.
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The largest known swimming, walking and flying animals are all vertebrates. They include the blue whale (up to 190 tonnes), the largest sauropod dinosaurs (probably about 80 tonnes) and two flying animals estimated to have had masses of at least 75 kg, the pterosaur Quetzalcoatlus and the bird Argentavis. Even larger sizes might be physically possible, but may not have been attained because problems associated with size may make excessively large animals competitively inferior. These problems are discussed with frequent reference to basic consequences of geometric similarity (areas are proportional to the squares of lengths and volumes to the cubes) and to the empirical rule that metabolic rates of similar animals tend to be proportional to (body mass)0·75. Excessively large animals would be liable to overheat, both in water and on land. Larger animals tend to have fewer individuals in each species, suggesting the possibility that the largest whales and dinosaurs approach the limits of size above which numbers would be unlikely to be large enough for long term viability. Even the largest dinosaurs seem to have been well able to support their weight on land. Flying animal size may have been limited more by the problem of taking off than by the power requirement for flight. The largest swimming animals are filter feeders and the largest land animals were herbivores, so neither are at the top of a long food chain.
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The evolutionary origin of the long neck of giraffes is enigmatic. One theory (the ‘sexual selection’ theory) is that their shape evolved because males use their necks and heads to achieve sexual dominance. Support for this theory would be that males invest more in neck and head growth than do females. We have investigated this hypothesis in 17 male and 21 female giraffes with body masses ranging from juvenile to mature animals, by measuring head mass, neck mass, neck and leg length and the neck length to leg length ratio. We found no significant differences in any of these dimensions between males and females of the same mass, although mature males, whose body mass is significantly (50%) greater than that of mature females, do have significantly heavier (but not longer) necks and heavier heads than mature females. We conclude that morphological differences between males and females are minimal, that differences that do exist can be accounted for by the larger final mass of males and that sexual selection is not the origin of a long neck in giraffes.
Article
Unique features of giraffe Giraffa camelopardalis anatomy are its long neck and slender long limbs. Its neck vertebrae should be light and have low density to make it manoeuvrable while the limb bones should have high density to provide the strength to support the giraffe's mass. Giraffes also have a very high vertical growth rate, a diet with a high Ca:P ratio, and a skeleton that constitutes a high proportion of its body mass. To investigate whether the giraffe skeleton is affected by its anatomy and biology, giraffe bone density and morphology were compared with those of African buffalo Syncerus caffer, an artiodactyl of similar mass, more conventional anatomy, a lower vertical growth rate, and different diet. Our results show that except for minor differences the density of giraffe bones is the same as that of buffaloes. Giraffe limb bones have a slightly greater diameter and much thicker walls than equivalent bones in buffaloes. Giraffe cervical vertebrae, unlike those in buffaloes, decrease in mass with cranial distance. We conclude that giraffe biology and anatomy do not affect bone deposition or density. However, other characteristics of their skeletons seem to be adaptations to their unique anatomy.
Article
Mammalian cervical vertebrae 6 and 7 and thoracic vertebra 1 possess many distinguishing characteristics. In the giraffe, bone morphology, muscle origins and insertions, as well as the location of the brachial plexus (described as many osteological and some soft tissue characters) are identical to those in other mammals but are all displaced posteriorly by one vertebra. There are two exceptions to these observations: the pre-sacral vertebral count is unchanged when compared with that in the okapi and C7 supports the first rib. Thus, one vertebra has been added in the neck of the giraffe between cervical 2 and 6, and some type of structural blending has occurred in the region of the first rib. The junction of the giraffe neck with the thorax is unusual and results in a protruding forelimb. It is possible that the unusual position of the neck relates to balancing of a cantilevered neck and head upon a relatively slight body. Characteristic drinking postures may have also influenced the observed anatomical modifications.
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Three-dimensional mathematical/computational models of three types of plesiosaur ( Liopleurodon – short neck, Cryptoclidus – medium neck, and Thalassomedon – long neck) were used to investigate aspects of their flotation and stability. Equivalent models of an extant alligator ( Alligator mississippiensis ) and leatherback sea turtle ( Dermochelys coriacea ) were used as tests. With full lungs, and uniform tissue densities of 1,050 g/l, all five models would float at the surface, with the alligator and sea turtle models replicating the depths of immersion and inclinations observed in living forms. Impractically large amounts of gastroliths were needed to initiate sinking – even with the lungs 50% inflated,10 kg of stones were still required in a 218 kg Cryptoclidus to produce negative buoyancy, and the hypothesis that gastroliths were for control of buoyancy is rejected. However, gastroliths equal to 1% of body weight in the Thalassomedon model were effective at damping out buoyant oscillations of the neck when at the surface and minimizing instability when fully immersed at 10 meters depth. The oblate bodies of Cryptoclidus and Liopleurodon provided effective passive mechanisms for righting the body if perturbed by waves at the surface, but the almost circular cross-section of the Thalassomedon body was ineffective in self-righting. The relatively longer flippers of Thalassomedon may have provided higher drag to resist rolling. The idea that plesiosaurs could maintain their necks above the water surface in an erect manner is rejected due to unbalanced buoyancy torques acting on the body.
Article
Acclaimed and coveted by both naturalists and lovers of wildlife illustration, Jonathan Kingdon's seven-volume East African Mammals has become a classic of modern natural history. This paperback edition makes Kingdon's remarkable artistic and scientific achievement—his hundreds of drawings and perceptive study of all the mammals in East Africa's species-rich fauna—available to the wide audience it deserves. Volume IIIB celebrates the large mammals for which the African plains are so famous—elephants, rhinos, zebras, bushpigs, and warthogs, hippopotamuses, camels, chevrotains, giraffes. Kingdon brings his artist's eye to such puzzles as the zebra's stripes and the giraffe's spots, making original observations throughout the seven volumes about the evolutionary and functional significance of coat color, facial expressions, and curious forms and markings. The beauty of the animals, so vivid in these incomparable drawings, is made more poignant by the acknowledgment of their increasingly endangered status. Kingdon discusses the inevitable problems posed by large mammal communities in a developing continent and includes numerous maps indicating their declining ranges and populations.
Article
Despite possession of a well developed larynx and a gregarious nature, the Giraffe is able to utter only low moans or bleats. Morphological and histological examination, together with measurements of trachea and subglottic area, on three fresh larynges (Giraffa camelopardalis) has made it possible to explain the lack of vocal power. Factors such as thoracic expiratory flow rate, length of trachea and recurrent laryngeal nerves, together with morphological details of vocal folds, and intrinsic laryngeal muscles have all been considered, providing a unique example of the relationship between morphology and function in the mammalial larynx.
Article
Sauropod dinosaurs were the largest terrestrial animals to have ever existed, and are difficult to interpret as living animals owing to their lack of living descendants. With computer models that employ the basic physics of buoyancy and equilibrium, it is possible to investigate how the bodies of these animals would have reacted when immersed in water. Multi-tonne sauropods are found to be extremely buoyant and unstable in water when aspects of their probable respiratory anatomy are considered, which obviates the old problem of them being unable to breathe when fully immersed. Interpretations of 'manus-only' trackways made by floating sauropods will depend on the details of buoyancy as not all sauropods float in the same manner.
Human Biology: Health, Homeostasis, and the Environment
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The past distribution of giraffe in Zululand and its implications for reserve management
  • Goodman
Goodman, P.S., Tomkinson, A.J., 1987. The past distribution of giraffe in Zululand and its implications for reserve management. South African Journal of Wildlife Research 17, 28-32.
Circulation and respiration in the giraffe
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A Natural History of Giraffes. Charles Scribner's Sons
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A Practical Guide to Vertebrate Mechanics
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McGowan, C., 1999. A Practical Guide to Vertebrate Mechanics. Cambridge University Press, Cambridge, UK.
A Practical Field Guide to Horse Behavior: The Equine Ethogram. The Blood-Horse Inc
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Early ranching in Alberta
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Biomechanics of the giraffe larynx and trachea
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A Natural History of Giraffes
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The Mammals of South West Africa. Wm. Heinemann, Ltd., London 2 vols
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The Book of the Giraffe
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