Dinosaurs: Dim-witted, cold-blooded and slow?

Dinosaurs were first thought to have appeared on earth over 260million years ago and subsequently remained for over 160million years. Having been the fascination of many a school child and adult too! You wouldn't be blamed in thinking Dinosaurs were just dim-witted, sluggish and cold blooded over-sized lizards, because during the first half of the 20th Century most of the scientific community believed this to be true also. With new research, the story of Dinosaur's is slowly unravelling and I would like to illustrate the diversity of this intriguing and varied group of species. Whilst tidying up there unfair rep and answering the question were they really stupid, cold-blooded and slow?

The word “cold-blooded” is rather scientifically vague, today we use terms such as poikilothermy or ectothermy in which body temperature is expected to fluctuate and is controlled by external means. Homeothermy and endothermy refer to “warm-blooded” animals, which regulate their temperature with the use of thermal homeostasis internally. Previously, it was widely believed that dinosaurs were ectotherms, similar to lizards of today but now it is believed that many could have been endotherms similar to modern day mammals.

Temperature records illustrate alternating warm and cool periods over millions of years. These suggest that during the Jurassic, Triassic and Cretaceous periods the climate was relatively warm through out. This could be evidence for the theory that all dinosaurs were ectotherms. Because of the steady temperatures that occurred throughout this period ectothermic animals would have flourished in this environment. Ectotherms could have maintained a relatively stable core body temperature because temperatures were not likely to fluctuate greatly; some biologists suggest that the smaller dinosaurs had body temperatures close to 25ºC – which is the expected average temperature of that time. With this constant environmental temperature there would be no need to regulate their temperatures internally, also if the conditions were often dry and arid then food and water may have been in short supply, this would have meant that mammalian like creatures could not have had obtained enough food for their high metabolic rates, whereas reptiles can tolerate ranges in temperature and are able to maintain water. But temperatures must have fluctuated seasonally so this would suggest a need for thermoregulation during the very cold or very hot months.

Evidence of dinosaur fossils at the poles could suggest endothermy in dinosaurs, although the climate would have been much warmer and forest was expected to reach towards the poles in the absence of ice caps, because of the Earths tilt this area would still experience long periods of cold and dark. Signifying that the dinosaurs must have had some sort of thermoregulatory system to survive the winter, but this could also be evidence for a migration because the pole areas would have flourished during the summer, so dinosaurs may have migrated during the 6 cold months of the year. Other theories such as the reason for the mass extinction of dinosaurs could have been that at the end of the cretaceous period temperatures dropped dramatically and there was increased variation across the Earth, this could have meant that ectothermic dinosaurs would have struggled to survive and regulate their temperature and therefore perish.

The evidence of growth rings on dinosaur teeth is valuable when suggesting whether the dinosaur was endothermic or ectothermic. Growth rings are attributed to the inability of ectotherms to maintain high levels of activity, feeding and growth during months in which food is sparse and temperatures are at extremes. Because endotherms can maintain a constant body temperature seasonal growth rings do not appear. The discovery of dinosaur teeth from Alberta Canada include that of Saurischia, Ornischia and Ceratopsidae from the late Cretaceous period. They show similarities to that of modern day crocodilians, affected by seasonal variations. The rings demonstrate periodicity of growth, when there is a narrow hypercalcified band this means a hard winter in which productivity was low and the dinosaur struggled to maintain a constant temperature and other bodily functions. Because of the similarities between crocodiles and dinosaurs of this area, this would suggest similar thermal physiologies, thus implying that these dinosaurs were ectotherms.

Using growth rate, mass of dinosaur, environmental temperature and productivity, temperature of dinosaur can be predicted. Results suggest that larger dinosaurs had higher constant body temperatures which could be evidence for endothermy. But other theories suggest that large dinosaurs maintained their temperature using thermal inertia. Dinosaur body temperatures change over the ontogeny of an individual, body temperatures increased by less than 3ºC over ontogeny for a species reaching 300kg but more than 20ºC for a species reaching 25000kg. This relative change in body temperature is similar to observed increase in temperature for extant crocodiles. The model suggests that larger dinosaurs were able to maintain a constant temperature because they were so big and not because they had thermoregulation. Soft tissue of Theropod dinosaurs suggests that they may have had unmodified septate lungs, ventilated with the assistance of an active hepatic piston-diaphragm mechanism. The presence of this mechanism could be the answer to why dinosaurs maintained a routine metabolic rate like ectotherms but still managed to sustain active oxygen consumption rates and activity levels beyond living reptiles.

Other evidence for endothermy is need for high arterial pressures particularly in large dinosaurs. In dinosaurs such as the brachiosaurus reaching heights of 25 meters high arterial pressures must have been essential, because of its large vertical distance from heart to head it would have required a 6.5meter blood column producing pressures of 500mmHg to provide adequate exchange of metabolites. No reptiles of today show such large heart to head ratios and are often low lying animals, these dinosaurs may have bowed their heads but skeletal structure suggests it remained in fairly up right position. If these large animals were aquatic then this would have suggested that the pressure needed for the blood column would have been equalized by hydrostatic pressure. Pterosaurs, like birds possessed an insulating cover of hair like structures similar to feathers this would suggest a need of insulation and therefore an endothermic animal. A lot of other dinosaurs did not posses this so could be considered as ectotherms. Histologically dinosaur bone is neither like that of endotherms or ectotherms but in some dinosaurs primary bone shows fibro-lamella bone deposited in zones separated by lines of arrested growth. This fairly slow growth punctuated by slow or even ceased growth is evidence of seasonal alterations between fast and slow rates of bone deposition. There is little evidence for this kind of growth in endotherms today however some dinosaurs such as the small ornithopod have azonal fibro-lamella suggesting continuous growth.

For many years dinosaurs have been considered as being slow moving animals, especially large dinosaurs as rapid gaits would have been impossible because of their sheer size this is similar to modern day elephants who are relatively slow movers so absolute speed does not increase with body size. Other evidence suggests that their physiology simply would not allow it. The position of the dinosaur scapula in relation to the vertical humerus is also maximally protracted position for the scapilohumeral complex, further protraction of glenoid would have resulted in impossible positions. Also further reach of the vertebrate could have only been accomplished by flexing fore limb and elbow and for a heavy animal this would create sheer forces which would ultimately increase with speed. This shows that in some dinosaurs such as the triceratops reaching high speeds would have been impossible. Other ideas on dinosaur locomotion suggest that certain dinosaurs would not have enough knee extensor muscles to run slowly and hip extensor muscles would not have been able to sustain high speeds.

Although dinosaur morphology has suggested that many of them were slow moving new evidence from track sites states that some species could be fast moving. Previous trackway sites in British Columbia and Queensland state that many of the trails show slow moving animals. In Texas a new trackway site has been used to estimate the speed of the dinosaurian trail maker from the size of its foot prints and stride. Here some species of dinosaur appear to be reaching speeds of 22msֿ¹ much faster than previous evidence. Although this evidence doesn’t categorically prove the speeds of these dinosaurs it states that either these were the speeds they were traveling or they had unusually long legs. It’s also worth noting that in these investigations it was largely found to be a smaller species that was fast moving and that in fact speed decreased as the animals size increased.

When looking at creatures that lived millions of years ago it is difficult to determine intelligence with only skeletal structures and a few soft tissues as evidence. But one method used in determining the complexity of neural development is comparing brain size of a particular animal to that expected of an animal of that size. By using endocasts developed from dinosaur skulls brain size and size of brain sections can be determined or at least estimated. Brain size and therfore intellect is important in predicting behavior of dinosaurs, for example sense of smell and foraging ability or predation skills.

When exploring the neurology of a dinosaur it is difficult to make a measure of intelligence, for example just using brain size isn’t enough as a larger brain size could imply better eyesight but not necessarily increased intelligence. Dinosaurs are thought to have had some of the smallest brains for their body size of any vertebrates with the view that they could only produce simple behaviors but if you compare the brain size of the animal to that of an expected brain size for an animal of that size dinosaurs fall well within the expected range for their body size. Soft tissue structure or imprints can be retained inside the skulls of dinosaurs, taking endocasts of these skulls enables us to interpret brain size and function. The large Sauropod dinosaurs had comparatively small brains for their size but this could have been influenced by adaptive requirements of head size and weight so far from ground so is not used in the relationship between brain and body size. An equation was used to estimate intelligence which was the size of dinosaur divided by the size of brain of an animal of that size, known as EQ the lower the EQ the less complex its brain. Dinosaurs such as the stegosaurus had low a low EQ and this can be confirmed by its limb structure which suggests a lack of agility and speed which was not essential it also had defensive weapons on its tail suggesting a passive defence. Theropods were found to have larger brains and therefore higher EQs which is understandable as they were mostly carnivores and would have required a more complex neurology to hunt with an agile, lightly built physique and grasping fore limbs.

Other evidence is obtained from the similarities of neurological features in dinosaurs and animals from today. The caiman endocasts and alligator brain exhibit notable similarity with A.fragilis endocasts. In the A.fragilis endocasts there are well defined structures of vestibular sense organs with distinct similarities to the alligators vestibular apparatus not shared with turtles, iguanas or birds. Behavior can be proposed based on modern day reptiles, substantial elaboration of cerebrum imparts greater neuronal complexity enabling organisms to extend foraging ability.

In conclusion, Dinosaurs were pretty awesome. Ok, so they won't loose their name...- from the greek 'potent lizard' but I hope you're now inspired to find out more about these varied creatures as I have only touched on there facinating physiology and behaviour. So what were Dinosaurs? Not just over-sised lizards thats for sure....

Rapid evolution: Swept under the proverbial oceanic carpet...

It is clear that human activities are effecting the environment at an unprecedented rate.
Fishing is a major source of food and other resources for humankind. Today most marine fish stocks are heavily exploited, and many are overexploited. Such intensive utilization has raised concerns about the sustainability of the modern fishing industry. But the problem lies deeper than this, as fish stocks crash, it is likely that other environmental variables are experiencing the secondary effects of such large scale disturbances. In recent times it has become clear that such actions by humans may be responsible for the rapid evolution of a species.

An understandably tentative theory involving the genetic changes of exploited fish stocks in a diverse and variable environment. Over the last few decades scientists have been observing phenotypic changes in fish populations, producing theories as to why such changes may be occurring.

Due to the high levels of mortality, size and selective nature of commercial fisheries, it is likely that particular life history traits will be selected for in exploited fish populations. Differentials have been found to be high for characteristics such as body size and age of maturation. Historically, larger fish are more valuable and more sort after, a late maturation means species spend more time in areas that are at risk from fishing practices, being caught before they even spawn. With such risk, there has been a reversal of fitness. With those that a smaller less easily caught and spawn early becoming more fit within the population. For example, heavy harvesting of Pacific salmon of a population returning to spawning streams; severely alters selection on life history traits. By differentially removing larger fish from harvested populations, fishing exerts intense selection on age and size at sexual maturity, this response to harvesting practices has been reported for many fish stocks.

Using the BFF (Big Female Fish) rule, when maturation takes place earlier and average size of fish is decreases, sustainable yield of large fish, producing many more offspring decreases and so does the market value of catches. If the observed changes in maturation have a genetic component, unless harvesting methods are radically changed it is unlikely that stocks will recover and more importantly it is unlikely that species will never recover to their former large sizes and late maturations. Genetic recovery occurs much more slowly than ecological recovery. It is therefore in the interest of fisheries managers to prevent unwanted genetic changes as early as possible.

It is important to acknowledge that there is till much conflict surrounding the role of fisheries induced evolution, however, most scientists agree that it does occur in some form yet to what extent in debateable. For example present day cod mature at a much younger and smaller size than their ancestors at the begining of the 20th century would have done when faced with similar growing conditions. Suggesting genetic changes rather than a plastic response to environmental variation.

Not only is the suggestion that the over exploitation of the oceans is causing a rapid evolution of many species alarming, but these effects may cascade to other species causing impacts on biodiversity and ecosystem functioning. Or quite simply, the monsters our Great Great Great Grandfathers caught off Britains coast line will be a thing of the past and remain there indefinately.

The Plight of the Coral Reefs

The forests of the sea.

Although only making up 0.1% of the worlds oceans, they are home to over 25% of all marine species. Coral reefs are some of the most diverse places on earth, yet relatively little is know about the complex interactions between the thousands of species that call them home.

Only a few get the opportunity to experience the wonder and the beauty of this Xanadu, but of places on earth that deserve conserving the reefs come top of the list.

Climate change and its influence of marine and estuarine species is still relatively unknown yet it is apparent that large scale changes are likely to occur.

This is likely to impact upon not only commercial valuable or ecologically important fish species but also the structural and non-structural invertebrates and plants that play an important role in ecosystem functioning. Research and evidence of how species have changed in their distribution, abundance and composition as a result of increasing sea temperature is growing.

Scientists however, face a predicament. The effect of non-climatic variables and how these can be disentangle from direct human exploitation and the expected impacts of climate change.

For the moment coral reefs have an uncertain future. Scientists believe that without intervention, after 50 years these diverse marine habitats pulsing with life and colour will give way to banks of eroding limestone covered in suffocating algae.

To date only 0.5% of the earths oceans are protected, a shocking statistic that requires desperate action. Marine protected areas are, in some cases, the only option. Parts of the ocean are still yet to be explored, however such unique habitats and species could be lost even before the are discoverd. An ocean without reefs would set the scene for the dire changes the world is experiencing, a world that is worth nothing if these 'forests of life' are lost forever.

Somewhere,

something incredible

is waiting to be known.

- Carl Sagan

Underwater Love

Today was the day I explored the underwater world. It had been pouring with monsoon rains as I woke the morning before my dive. I had been reassured by my instructer that it didn’t matter as you would already be wet! My thoughts went to how different and undetectable rain must be under water.

After learning the basics I felt confident about diving, however, things are very different when your dumped in the middle of the ocean. The sun was bright when we took the boat to the dive site, the water was rough, the boat was at the whim of the waves bobbing from side to side, with a nauseating feeling encroaching on my excitement I was desperate to get into the water. Once my diving gear was secured I took a ‘giants step’ into the water following my instructor. I was slightly apprehensive to be having this experience for the first time alone. But the best experiences are personal and when you are in a world made of water you are alone with your thoughts any way.

As we were about to descend my nerves got the better of me, I was surrounded by an expanse of blue, deep and endless, with no idea of what lay below. Finally I controlled my breathing, all that I could hear was the rhythmic bubble making and of my regulator and a slight crackling noise surrounding me. In front of me was murky blue, I didn’t know how deep we were then as I turned to look below, a whole new world was opened. Life was swarming; rock shelf gave way to an expanse of corals in every colour. The first fish we came across were small and electric blue, feeding on the rock. As we swam forward so much more colour appeared, fish of purples, greens and blues surrounded us. I recognised many fish I had seen before in aquariums and it made me feel at awe that I was seeing these creatures in their wild and natural habitat.

As we ventured deeper, schools of fish weaved their way in and out of rock crevices. As I looked ahead a black and white zebra fish came right up to my mask. It looked so inquisitive and un alarmed by my presence. It made me think, we don’t know just how intelligent fish are and just referring to them as seafood is not giving them enough credit!

There was so much diversity in the world I was observing, I tried to capture every moment in my head so I could refer to it later, an imprint, an ingrained memory. But there was just so much to see, and as soon as I saw it I felt the image already beginning to fade. The colours were unimaginable, such intense blues and yellows, it was hard to think that such colours were a product of nature and not an artist. I struggled to think of places on land which would be home to such diversity of life, such different organisms inhabiting one small slice of the earth.

Then the dive was over, I knew we must have been down there a while but it seemed like we had only just begun. As we ascended, shafts of light began to break through the surface, painting all the microscopic creatures which began to shimmer, the water was full of golden filaments. It was good to breathe the air once more but strangely foreign after breathing under water.

The boat was still swaying, a monotonous and nauseating movement but we were soon on our way back with fresh ocean spray in our faces. As we returned I began to think about what I had just witnessed a great richness of life that comparatively few people are fortunate to see. To my surprise I felt saddened after the experience, my thoughts were on just how much harm we are doing to the oceans and how much we have already harmed the land. In my life time I had witnessed such great diversity but wondered how long this would last with the rate of human destruction. For too few the oceans don’t seem to be an important part of their lives but our oceans and seas affect us all, they should be our priority. As I looked out at the un interrupted waters I had a renewed understanding as I now knew just what lay beneath, I had fallen in love with the ocean all over again.