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To swim or not to swim, that is the question: a reply to van der Geer etal.
Abstract
No abstract is available for this article.
... The evolution of endemic hippopotamus species in fossil islands has been classically explained by their purported good swimming abilities (e.g., Sondaar, 1977). Although this has recently been challenged (Mazza, 2014(Mazza, , 2015 on the grounds that Hippopotamus amphibius Linnaeus, 1758 adults are too dense to float on freshwater (Coughlin and Fish, 2009), this does not apply to juvenile individuals and, hence, must not necessarily be the case for extinct hippopotamid species, particularly on saltwater due to increased buoyancy (van der Geer et al., 2015). ...
... There is no geological evidence for the land bridges hypothesized by Mazza (2014Mazza ( , 2015 to explain the dispersal of hippopotami to islands such as Cyprus, Madagascar, and Crete (van der Geer et al., 2015). In the case of the Iberian Peninsula during the latest Miocene, the earlier dispersal of hippopotami as compared with terrestrial mammals argues in favor of dispersal through seawater, once the Betic Seaway was already closed and the Riftian corridor very restricted . ...
The dispersal of Crocodylus from Africa to Europe during the Miocene is not well understood. A small collection of cranial fragments and postcranial elements from the latest Miocene (6.2 Ma) site of Venta del Moro (Valencia, Spain) have previously been referred to Crocodylus cf. C. checchiai Maccagno, 1947 without accompanying descriptions. Here we describe and figure for the first time the crocodylian remains from Venta del Moro, which represent at least two individuals. Our comparisons indicate that this material clearly does not belong to Diplocynodon or Tomis-toma-the only two other crocodylians described so far for the European late Miocene. The material is only tentatively referred to cf. Crocodylus sp. because the apomorphies of this genus are not preserved and a referral to C. checchiai cannot be supported on a morphological basis. However, it is likely that this late Miocene species, originally described from Libya (As Sahabi) and later identified also in Kenya, could have dispersed across the Mediterranean Basin multiple times and colonized the southern areas of Mediterranean Europe, as evidenced by several Crocodylus or Crocodylus-like remains described during the past years.
... Additional difficulties include the physiological facts that living hippopotamuses need 43-72 L of freshwater per day (Calder, 1984), and are highly sensitive to prolonged exposure to salt water and sunlight. The clincher, however, is that hippopotamuses are notoriously bad swimmers (Mazza, 2014(Mazza, , 2015, despite the claim that they are "known to swim significant ocean distances" (Ali & Huber, 2010, p. 653). They have poorly streamlined, barrel-like bodies (Coughlin & Fish, 2009;Fish, 2001) and their feet make bad paddles (Coughlin & Fish, 2009;Eltringham, 1999;Howell, 1930). ...
Aim: For 80 years, popular opinion has held that most of Madagascar's terrestrial vertebrates arrived from Africa by transoceanic dispersal (i.e. rafting or swimming). We reviewed this proposition, focussing on three ad hoc hypotheses proposed to render this unlikely scenario more feasible: (a) Could hibernation have helped mammals to reach Madagascar? (b) Could the aquatic abilities of hippopotamuses have enabled them to swim the Mozambique Channel? (c) How valid is the Ali-Huber model predicting that eastward Palaeogene surface currents allowed rafts to reach Madagascar in 3–4 weeks? Finally, we explored the alternative hypothesis of geodis-
persal via short-lived land bridges between Africa and Madagascar.
Location: East Africa, Madagascar, Mozambique Channel.
Taxa: Fish, amphibians, reptiles, birds, mammals.
Methods: We established colonization timeframes using molecular divergence dates estimated for Malagasy vertebrate lineages. We reviewed the likelihood of the “torpid waif” and “swimming hippopotamus” hypotheses, and re-investigated Ali and Huber's model of Eocene jet-like currents by tracking particle trajectories in currents simulated using the Institut Pierre-Simon Laplace Earth System Model. Finally, we summarized recent geological findings from the Mozambique Channel, and used them to compile palaeosedimentological maps using PLACA4D.
Results: Madagascar's vertebrate fauna has complex origins. Hibernation is probably an adaptation to Madagascar's hypervariable climate, rather than a facilitator of mammal dispersal. Hippopotamus physiology precludes the ability to cross an oceanic channel deeper than 4 m and hundreds of km wide. The Ali-Huber model of Palaeogene currents considerably underestimated the time required to cross the Mozambique Channel under simulated palaeogeographic conditions. New geological data indicate the existence of three short-lived land bridges between Africa and
Madagascar at 66–60 Ma, 36–30 Ma and 12–05 Ma.
Main conclusion: The three Cenozoic land bridges afford a more grounded hypothesis for the dispersal of Madagascar's extant biota than transoceanic rafting or swimming, although vicariance, island hopping and limited rafting also played a role.
... Additional difficulties include the physiological facts that living hippopotamuses need 43-72 L of freshwater per day (Calder, 1984), and are highly sensitive to prolonged exposure to salt water and sunlight. The clincher, however, is that hippopotamuses are notoriously bad swimmers (Mazza, 2014(Mazza, , 2015, despite the claim that they are "known to swim significant ocean distances" (Ali & Huber, 2010, p. 653). They have poorly streamlined, barrel-like bodies (Coughlin & Fish, 2009;Fish, 2001) and their feet make bad paddles (Coughlin & Fish, 2009;Eltringham, 1999;Howell, 1930). ...
Aim
For 80 years, popular opinion has held that most of Madagascar's terrestrial vertebrates arrived from Africa by transoceanic dispersal (i.e. rafting or swimming). We reviewed this proposition, focussing on three ad hoc hypotheses proposed to render this unlikely scenario more feasible: (a) Could hibernation have helped mammals to reach Madagascar? (b) Could the aquatic abilities of hippopotamuses have enabled them to swim the Mozambique Channel? (c) How valid is the Ali‐Huber model predicting that eastward Palaeogene surface currents allowed rafts to reach Madagascar in 3–4 weeks? Finally, we explored the alternative hypothesis of geodispersal via short‐lived land bridges between Africa and Madagascar.
Location
East Africa, Madagascar, Mozambique Channel.
Taxa
Fish, amphibians, reptiles, birds, mammals.
Methods
We established colonization timeframes using molecular divergence dates estimated for Malagasy vertebrate lineages. We reviewed the likelihood of the “torpid waif” and “swimming hippopotamus” hypotheses, and re‐investigated Ali and Huber's model of Eocene jet‐like currents by tracking particle trajectories in currents simulated using the Institut Pierre‐Simon Laplace Earth System Model. Finally, we summarized recent geological findings from the Mozambique Channel, and used them to compile palaeosedimentological maps using PLACA4D.
Results
Madagascar's vertebrate fauna has complex origins. Hibernation is probably an adaptation to Madagascar's hypervariable climate, rather than a facilitator of mammal dispersal. Hippopotamus physiology precludes the ability to cross an oceanic channel deeper than 4 m and hundreds of km wide. The Ali‐Huber model of Palaeogene currents considerably underestimated the time required to cross the Mozambique Channel under simulated palaeogeographic conditions. New geological data indicate the existence of three short‐lived land bridges between Africa and Madagascar at 66–60 Ma, 36–30 Ma and 12–05 Ma.
Main conclusion
The three Cenozoic land bridges afford a more grounded hypothesis for the dispersal of Madagascar's extant biota than transoceanic rafting or swimming, although vicariance, island hopping and limited rafting also played a role.
... The theory of over-water dispersal is enjoying growing popularity among biogeographers, neontologists, and palaeontologists (de Queiroz, 2005(de Queiroz, , 2014Van den Hoek Ostende, Meijer & van der Geer, 2009;Ali & Huber, 2010;Van der Geer et al., 2010;Balme, 2013;Ceríaco et al., 2015;Hofman et al., 2015Hofman et al., , 2016Leppard, 2015;Taylor, Myers & Hoffman, 2015;Van der Geer, Anastasakis & Lyras, 2015;Anderson et al., 2016;Beard, 2016;Duggins et al., 2016;Holcomb, 2016;O'Dea et al., 2016;Carlton et al., 2017Carlton et al., , 2018Duffy & Vargas, 2018;Palombo, 2018). However, doubts are beginning to emerge (MacPhee & Iturralde-Vinent, 2005;Tattersall, 2006Tattersall, , 2008Alonso, Crawford & Bermingham, 2011;Heads, 2015), especially concerning homeotherms such as mammals (Masters, De Wit & Asher, 2006;Stankiewicz et al., 2006;Masters, Lovegrove & De Wit, 2007;Mazza et al., 2013;Mazza, 2014Mazza, , 2015. Over-sea dispersal is plausible only if intricate networks of variables are coordinated and various conditions satisfied. ...
Natural rafting is an easy, non‐evidence‐based solution often used to explain the presence of a variety of species on isolated islands. The question arises as to whether this solution is based on solid scientific grounds. It is a plausible colonisation route only if intricate networks of variables are considered and many different conditions satisfied. This review provides a descriptive account of some of the most critical issues underlying the theory of natural rafting that should be addressed by its supporters. These include: (i) biological variables; (ii) characteristics of the vessels; and (iii) physical variables. Natural rafting may explain the dispersal of poikilotherms with low metabolic rates and low resource requirements that could withstand trans‐oceanic crossings, but explaining the transport of homeothermic terrestrial mammals to oceanic islands is more problematic. Drifting at sea exposes organisms to high concentrations of salt, high temperature and humidity excursions, starvation, and above all to dehydration. A sufficiently large group of healthy reproductive individuals of the two sexes should either be transported together, or be able to reassemble after separate crossings, to prevent inbreeding, genetic drift and ultimately extinction. Any vessels of flotsam occupied must minimally provide the animals they transport with sufficient provisions to survive the journey, offer minimum friction and drag through water, and be transported by appropriately directed, sustained, high‐speed currents. Thus, a ‘sweepstakes colonisation’ event would be the result of a lucky combination of all, or at least the majority, of these factors. Some cases throw doubt on the use of a natural rafting model to explain known animal colonisations, with one of the most striking examples being Madagascar. This island is far from the nearest mainland coasts and the sea currents in the Mozambique Channel are directed towards Africa rather than Madagascar, yet, the island was colonised by terrestrial mammals (e.g. extinct hippopotamuses, lemurs, carnivores, rodents and tenrecs) unable to swim and to survive long journeys at sea. In order to assess the feasibility of the natural rafting model in a case such as Madagascar, tests were performed using three variables for which enough information could be obtained from the literature: length of survival without food, survival without water, and sea current speed. The distributions of these variables appear to be log‐normal and multiplicative, or follow a power‐law, rather than being Gaussian. The tests suggest that a distributional analysis is a more suitable approach than the use of geometric probability to calculate the probabilities associated with the examined data. Such non‐linear and self‐organising systems may reach a critical point governed by different competing factors. Mammals with high survival requirements, such as lemurs and hippopotamuses, thus may have a virtually zero probability of reaching distant islands by natural rafting. Our results raise doubts as to the validity of a natural rafting model, and we urge a rethinking of the modes in which numerous islands were colonised by land mammals and a careful revision of past geological and phylogeographic work.
The Bahamas are well known for their karst landscape, with vast cave systems and inundated caves called blue holes that formed during the Pleistocene. Despite this, the biota of these islands has not been well documented when compared to other West Indian islands. It is important that Bahamians have the knowledge and tools to preserve the flora and fauna of their islands in the face of increasing development. This review provides an accessible resource for Bahamians and researchers by consolidating the available knowledge on bat biology from literature and natural history collections. Bats represent the most diverse group of mammals in The Bahamas and no study has thoroughly characterized their biology on these islands. There are currently 10 species of bat in The Bahamas, one of which is endemic and considered “near threatened” by the IUCN. While 9 of the 10 are considered species of “least concern,” bats in The Bahamas may be at higher risk of local extinction than in other parts of their ranges. As previous local conservation efforts have shown, it is imperative to gain support for bat research and conservation through outreach and education. We hope this review enables outreach efforts and research projects key to the conservation of bat populations in The Bahamas.
Patterns of delta progradation in rapidly subsiding basins have been used previously as a proxy for Quaternary sea-level change. Major transgression surfaces and maximum lowstand positions are readily recognizable in seismic reflection profiles. Quaternary sea-level change can be approximated by stacked and tuned oxygen isotope records, but significant departures from this proxy result from variation in isotopic composition of ice sheets, temperature variations in the deep sea, and the effect of bioturbation in degrading the isotopic record. We analyze the influence of rapid Quaternary sea-level change on delta progradation in the eastern Mediterranean using DELTA, a multi-process sediment transport model. Subsidence rates and sediment inputs may vary through time, but compared to Quaternary sea-level change, such variations were minor and had little effect on model results. For a variety of geologically reasonable sediment inputs and subsidence rates, the delta architecture observed in seismic profiles could not be reproduced when the sea-level estimates were taken directly from a scaled global oxygen isotopic curve. However, when this sealevel curve was corrected to include independent estimates of sea level from geological data elsewhere in the world, previously used sediment inputs and subsidence rates invariably predict the general form of the observed architecture. The difference between isotopic and geological estimates of sea level for the last 200 ha follows a linear trend that was applied to previous glacial-interglacial cycles, producing a corrected sea-level history for the last 540 ka, Using DELTA over this time span, the sea-level history based directly on the oxygen isotope curve was again less able to reproduce the observed delta architecture compared with a corrected sea-level history. This study shows the importance of modeling delta progradation as an avenue for testing and exploring Quaternary sea-level history.
The kinematics of surface swimming of the Virginia opossum (Didelphis virginiunu) and water opossum (Chironectes minimus) were studied to determine locomotor changes asso- ciated with the evolutionary transition from terrestrial to semiaquatic existence. Films of individual animals swimming across an aquarium were made and analyzed. Didelphis swam with a modified quadrupedal gait similar to a diagonal sequence run. Besides providing propulsive forces, this gait generated an upward force allowing the nasal apertures to remain above the water for breathing. In contrast, Chironectes paddled exclusively with the hind limbs in a manner similar to other semiaquatic mammals. The non-wettable fur of Chiro- nectes seemed to provide sufficient buoyancy so that no additional forces were required to maintain the nares above the water surface. Transition to exclusive hind limb paddling in semiaquatic mammals appears to be associated with development of non-wettable fur for increased buoyancy and with increased swimming effectiveness resulting from lack of in- terference between forelimbs and hind limbs during the stroke cycle. Eliminating use of the forelimbs in paddling also permitted unrestricted movement of the hind limbs.
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.
Upper Cretaceous strata of the Mahajanga Basin, northwestern Madagascar, yield some of the most significant and exquisitely preserved vertebrate fossils known from Gondwana. The sedimentology of these strata and their stratigraphic relations have been the focus of renewed geological investigations during the course of five expeditions since 1993. We here designate stratotypes and formalize the terrestrial Maevarano Formation, with three new members (Masorobe, Anembalemba, Miadana), and the overlying marine Berivotra Formation. The Maevarano Formation accumulated on a broad, semiarid alluvial plain bounded to the southeast by crystalline highlands and to the northwest by the Mozambique Channel. The Berivotra Formation was deposited in an open marine setting that evolved from a clastic- to a carbonate-dominated shelf, resulting in deposition of the overlying Betsiboka limestone of Danian age. New stratigraphic data clearly indicate that the Maevarano Formation correlates, at least in part, with the Maastrichtian Berivotra Formation, and this in turn indicates that the most fossiliferous portions of the Maevarano Formation are Maastrichtian in age, rather than Campanian as previously reported. This revised age for the Maevarano vertebrate assemblage indicates that it is approximately contemporaneous with the vertebrate fauna recovered from the Deccan basalt volcano-sedimentary sequence of India. The comparable age of these two faunas is significant because the faunas appear to be more similar to one another than either is to those from any other major Gondwanan landmass. The revised age of the Maevarano Formation, when considered in the light of our recent fossil discoveries, further indicates that the ancestral stocks of Madagascar's overwhelmingly endemic modern vertebrate fauna arrived on the island in post-Mesozoic times. The basal stocks of the modern vertebrate fauna are conspicuously absent in the Maevarano Formation. Finally, the revised age of the Maevarano Formation serves to expand our global perspective on the K/T event by clarifying the age of a diverse, and arguably the best preserved, sample of Gondwanan vertebrates from the terminal Cretaceous.
How hippopotamuses managed to cross tens or even hundreds
of kilometres of open sea to islands and why they did so are, as
Mazza (2014) formulates it, challenging problems. The formidable
body mass, barrel-shaped build and the relatively stocky,
short limbs do not look as those of an apt swimmer. Furthermore,
hippopotamuses have been described as bottom-walkers
rather than surface swimmers (for details see below). Yet, the fossil
record proves their existence on six islands during the Pleistocene.
Mazza (2014, p. 2) suggests they were on ‘probably most
other Mediterranean islands’, but there is no evidence to support
this claim, despite the abundant fossil record from Sardinia, Corsica,
the Balearics, Tilos, Rhodes and Karpathos. Arguing that
hippopotamuses cannot swim in open sea, Mazza postulates that
in all of these cases the only remaining option for colonization is
by land bridge, either fully exposed or only one or two metres
deep. If Mazza is right, and hippopotamuses cannot survive overseas
dispersal, the available geological evidence should be reconsidered
or an alternative explanation has to be looked for. There
are some inconsistencies in Mazza’s reasoning, which we address
below in light of effective collaboration among biologists, palaeontologists,
geologist and biogeographers as recommended by
Mazza (2014).
There is not one explanation for hippos on islands. A number
of insular populations arrived overland or via a very shallow
strait that otherwise hampered dispersal of most other faunal elements.
This is the case during cold phases of the Pleistocene for
Sicily (Hippopotamus pentlandi), Malta (H. melitensis), Java
(Hexaprotodon sivajavanicus) and probably during the Holocene
for continental shelf islands as Zanzibar and Maf�ıa (Tanzania)
(H. amphibius). Mazza cites Bridgland & Schreve (2004) for the
temporary connections that enabled hippopotamuses to spread
into these islands, but this is misplaced. Bridgland & Schreve
(2004) describe the quaternary deposits of the Lower Thames
and do not mention insular conditions of the British Isles and
say nothing about Sicily, Malta, Zanzibar and Maf�ıa. The British
Isles were part of the mainland during the entire Pleistocene and
the hippos here (H. amphibius) are not considered insular
hippopotamuses (in contrast to Mazza). The problem concerns
the remaining islands for which there is no geological evidence
for a land bridge during the time of colonization. These are
Cyprus (H. minor), Madagascar (H. madagascariensis, H. lemerlei,
H. laloumena) and Crete (H. creutzburgi).
Owing to their aquatic lifestyle, hippopotamuses are normally believed to have reached islands by swimming. Yet, some studies suggest they cannot swim due to their relatively high density. If so, this raises the question of how hippopotamuses would have reached some islands. Their immigration into the British Isles, Sicily, Malta, Zanzibar and Mafia can be accounted for, because these islands sit on continental shelves and were often linked to the mainland during the Pleistocene glacio-eustatic sea-level falls. In contrast, their occurrence in Crete, Cyprus and Madagascar would be more difficult to explain. Available geological evidence does not seem to rule out that the latter islands might have been connected with the nearest mainland areas in very recent times. This study intends to consider possibilities about how hippopotamuses reached islands and to show that more effective collaboration is required among specialists involved with the study of insular evolution, colonization and speciation.
Evolution on islands differs essentially from evolution on mainlands. Especially islands of the past are uniquely intriguing. Due to millions of years of isolation, exceptional and sometimes bizarre mammals evolved, such as pig-sized elephants and hippos, giant rats and gorilla-sized lemurs, formidable to their mainland ancestors. This timely and innovative book is the first of its kind to offer a much-needed synthesis of recent advances in the exciting field of the evolution and extinction of fossil insular placental mammals. It provides a comprehensive overview of current knowledge on fossil island mammals worldwide, ranging from the Oligocene to the onset of the Holocene. This book addresses evolutionary processes and key aspects of insular mammal biology, exemplified by a variety of fossil species. The authors discuss the human factor in past extinction events and loss of insular biodiversity. This accessible and richly illustrated textbook is written for graduate level students and professional researchers in evolutionary biology, palaeontology, biogeography, zoology, and ecology.
We investigated the use of the pelvic fins for locomotion along the bottom in the little skate, Leucoraja erinacea by video recording locomotor behavior of skates both in the field and in captivity and by examining various anatomical preparations of their pelvic fins. An external notch or concavity in the lateral margin of the pelvic fins partially separates each fin into anterior and posterior lobes. The skeletal elements and musculature of the anterior lobe are highly modified and comprise a functionally distinct appendage (the crus) that possesses three flexible joints. Locomotion of skates along the bottom is almost always due to the exclusive activity of the crura of the pelvic fins pushing off the substrate synchronously to generate thrust. The skate then glides through the water a short distance as the crura are repositioned for the next thrust phase. This type of thrust and glide locomotion is called punting. We conclude that punting is a significant form of locomotion suited to the benthic lifestyle of skates.
Osteological characteristics of extant, quadrupedal, aquatic or amphibious mammals are compared and used to determine the presence and state of development, or absence, of aquatic adaptations in the order Desmostylia. The specimens compared include seventeen bones from in each species four higher taxa: Rodentia, Carnivora, Mustelidae and Artiodactyla. The aquatic form is compared with its terrestrial counterpart within each group. Quantitative evidence of convergence is used to sort out characters that are adaptive in relation to aquatic habits. Aquatic conformations or tendencies are identified as those characters, displayed by aquatic forms in different taxonomic groups, that have more in common with each other than with corresponding characters of land animals in the same taxa. About 80% of the 49 aquatic adaptive characters identified are also found in desmostylians. This analysis documents the gradual evolutionary transition of desmostylians to an aquatic mode of life. Furthermore, the results show that the desmostylian swam better using its hind‐limbs at least than the hippopotamus.
The basking behaviour of the Nile Crocodile on Central Island is discussed in relation to various environmental conditions and compared with the findings of other authorities. This is followed by accounts of the effect of territorial, courting and mating activity on basking patterns, and of interspecific behaviour on basking grounds.
The Phanerozoic structural and stratigraphic history of Mozambique can be separated into a “Karoo” and a post-Karoo phase. Outcrops of Karoo rocks, limited to the Zambezi valley and small outliers in the Mozambique belt to the north show an eastward facies change marked by an increased argillaceous content and the appearance of carbonates. The wide coastal plain and immediate offshore of southern Mozambique is marked by extensional horsts and grabens with a Mesozoic fill covered by Cenozoic sediments. Little is known of lower stratigraphic horizons. In this coastal province there is a facies transition from continental clastics in the northwest and west to more lacustrine and marine deposits to the southeast and east. Upwards the succession passes into the Cenozoic without a noticeable break.
An eight-year-old, neutered male Airedale terrier was presented for the evaluation of a 45-minute episode of continuous seizure activity after ingesting a salt-flour mixture used as clay for the sculpting of small figurines. Levels of serum sodium (211 mEq/L; reference range, 145 to 158 mEq/L) and chloride (180 mEq/L; reference range, 105 to 122 mEq/L) were elevated. The dog died despite aggressive therapy directed at the hypernatremia. Tissue levels of sodium and chloride were elevated. Brain sodium level (108 mEq/L; reference range, has less than 80 mEq/L) was diagnostic for salt toxicosis. All necropsy findings, except severe hepatocellular necrosis, were consistent with reports of salt poisoning in humans and other species. Hypernatremia from ingestion of salt has not been described previously in the dog.
As an animal moves from air to water, its effective weight is substantially reduced by buoyancy while the fluid-dynamic forces (e. g. lift and drag) are increased 800-fold. The changes in the magnitude of these forces are likely to have substantial consequences for locomotion as well as for resistance to being overturned. We began our investigation of aquatic pedestrian locomotion by quantifying the kinematics of crabs at slow speeds where buoyant forces are more important relative to fluid-dynamic forces. At these slow speeds, we used reduced-gravity models of terrestrial locomotion to predict trends in the kinematics of aquatic pedestrian locomotion. Using these models, we expected animals in water to use running gaits even at slow speeds. We hypothesized that aquatic pedestrians would (1) use lower duty factors and longer periods with no ground contact, (2) demonstrate more variable kinematics and (3) adopt wider stances for increased horizontal stability against fluid-dynamic forces than animals moving at the same speed on land. We tested these predictions by measuring the three-dimensional kinematics of intertidal rock crabs (Grapsus tenuicrustatus) locomoting through water and air at the same velocity (9 cm s-1) over a flat substratum. As predicted from reduced-gravity models of running, crabs moving under water showed decreased leg contact times and duty factors relative to locomotion on land. In water, the legs cycled intermittently, fewer legs were in contact with the substratum and leg kinematics were much more variable than on land. The width of the crab's stance was 19 % greater in water than in air, thereby increasing stability against overturning by hydrodynamic forces. Rather than an alternating tetrapod or metachronal wave gait, crabs in water used a novel gait we termed 'underwater punting', characterized by alternating phases of generating thrust against the substratum and gliding through the water.
Food and water restriction protocols are common in animal research, yet they often elicit discussion and controversy among institutional animal care and use committee members who review them. Determining a single standard by which all restriction protocols can be evaluated or performed may not be realistic. However, information about the physiologic and behavioral impact of food and water restriction can provide a basis for making rational judgments about these issues in general. This review will discuss the physiologic and behavioral consequences of food or water deprivation periods of 24 h or less and of chronic restriction schedules, with special reference to protocols that use food or water restriction as a motivational tool for behavioral training.
Based on morphological analyses, hippos have traditionally been classified as Suiformes, along with pigs and peccaries. However, molecular data indicate hippos and cetaceans are sister taxa (see review in Uhen, 2007, this issue). This study analyzes soft tissue characters of the pygmy hippo forelimb to elucidate the functional anatomy and evolutionary relationships of hippos within Artiodactyla. Two specimens from the National Zoological Park in Washington, D.C. were dissected, revealing several adaptations to an aquatic lifestyle. However, these adaptations differ functionally from most aquatic mammals as hippos walk along river or lake bottoms, rather than swim. Several findings highlight a robust mechanism for propelling the trunk forward through the water. For example, mm. pectoralis superficialis and profundus demonstrate broad sites of origin, while the long flexor tendons serve each of the digits, reflecting the fact that all toes are weight-bearing. Pygmy hippos also have eight mm. interossei and a well-developed m. lumbricalis IV. Retention of intrinsic adductors functions to prevent splaying of the toes, an advantageous arrangement in an animal walking on muddy substrates. Published descriptions indicate common hippos share all of these features. Hippo and ruminant forelimbs share several traits; however, hippos are unique among artiodactyls in retaining several primitive muscles (e.g., mm. palmaris longus and flexor digitorum brevis). These findings are consistent with the hypothesis that hippos diverged from other Artiodactyla early in the history of this group. Additional analyses of hindlimb and axial muscles may help determine whether this trajectory was closely allied to that of Cetacea.
Upper Quaternary climatic cycles as evidenced by lithofacies associations and planctonic foraminifera of sapropel sequences in the outer periphery of the Hellenic Arc
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Owen & Mzee: The True Story of a Remarkable Friendship
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Aquatic Mammals 338 pp
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