Were Dinosaurs warm-blooded? Evidence supporting the claim that dinosaurs were warmblooded from strongest to weakest...

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1.Dinosaurs had vascularized bones very similar to bird bone structure and unlike ectothermic reptilian bone

Horner teamed up with Armand de Ricqles in an effort to investigate bone structure as a means to differentiate among endotherms and ectotherms (Morell 1987: pg11). The two scientists did studies that analyzed differences in bone structure during the growth series of a dinosaur, from embryo to adult. Through comparative anatomical studies of micro-thin sections of bone from dinosaurs, modern birds, and reptiles, the men found that both the dinosaur bones and the modern bird bones contained vascular canals within the bone, for blood vessels. This evidence suggested that there is a very significant similarity among bird and dinosaur bone, which indicated that dinosaurs had fast-growing bone. According to Horner, rapid growth and vascular bone development are characteristics of endothermic animals. Cold-blooded reptiles are marked with "arrest lines", which exhibit slow growing bone that lacks the many vascular canals (Morell 1987: pg11).

2. Dinosaurs grew quite rapidly and big from embryo to adult

Scientific research suggests that endothermic animals have higher growth rates and higher metabolisms because more energy is required, while ectotherms grow at a much slower rate because they are not capable of internal temperature control (Morell 1987: pg 7). Horner examined the embryonic, nestling, and juvenile stages of hadrosaurs, and he compared the hadrosaurs' growth rate to the growth series of an ostrich and a crocodile. According to his studies, he found that there were significant similarities between the growth rate of the ostrich and hadrosaur. He believed that because the growth series of the hadrosaur and the ostrich were growing at merely the same rate, the dinosaurs would have to have reasonably high metabolisms, and this evidence would support the notion that the dinosaurs were endothermic (Morell 1987: pg10).

3.Dinosaurs migrated from near and far

Bakker believed that dinosaurs were migrants. Fossil evidence showed that dinosaurs once inhabited modern areas that cannot sustain the survival of modern cold-blooded animals. If dinosaurs were cold-blooded and stayed in one place they probably would have evolutionarily selected for some modern descendents to inhabit these areas, but none such cold blooded mammals exist (Morell 1987: pg8). Therefore, the dinosaurs must have been quite active and able to cruise at various paces they must have steadily migrated from one location to another. Their high metabolism allowed the dinosaurs to move great distances. Dinosaurs could have migrated there in the summer when it was warmer, and emigrated during the cooler winters. Bakker argued, "You can't be cold-blooded and migrate," and exclaimed "You need a high metabolism for that" (Morell 1987: pg7). It is also believed that the dinosaurs migrated because the fossils can be found from the Artic into northern Europe and Asia, because it was believed that the earth's major land masses were still connected at this point in time, known as Pangea. It was discovered through fossil studies that dinosaurs traveled in herds probably for food and protection, which also suggests that migration did occur (Morell 1987: pg17).

4.Dinosaurs were upright cruisers

Bakker extensive scientific fossil research suggests that dinosaurs similarly to modern endotherms stood fully upright displaying an erect posture, which means their weight bearing limbs are oriented directly beneath the body like those of an elephant rather then sprawled out to the sides like those of a lizard. Bakker's contention is that dinosaurs must have been warm-blooded because "from the way their limbs are shaped, it's apparent they were adapted for moving continuously, they didn't lie about the way lizards do" (Morell 1987: pg7). By studying fossilized footprints, Bakker was able to estimate a dinosaur's cruising speeds. Dinosaurs were made to move around at a moderately fast pace and consistently expend energy in order to find food, protection, or migrate, so they must have high metabolic rate that would allow them to cruise from location to location, as most warm-blooded animals do. On the other hand, cold blooded tend to be more inactive and lie around. Ectothermic animals do not have the capacity to exercise and are rather lazy, which would imply that dinosaurs couldn't have been cold-blooded (Morell 1987: pg7).

5.Dinosaur fossils/bones have been discovered in variable ecological niches

Dinosaur bones and fossils have been excavated from a variety of archeological sites from around the world, such as mountain ranges and upland regions of ancient costal plains, which suggest hat the dinosaurs could sustain or adapt to life in various niches (Morell 1987: pg12). Dinosaur bones have been found in mountainous areas where the climate is cold, and ectotherms do not normally inhabit locations at high latitudes because they are not able to regulate their body temperature internally. Therefore, Dinosaurs must have been warm-blooded in order to cope with the cold environment, when the seasons would change. (Morell 1987: pg14). Endothermic animals have the ability to regulate their internal body temperature in under varying climatic conditions, while ectotherms solely depend on the environment to alter their inner temperature (Morell 1987: pg8).

6. Dinosaurs were warm-blooded because there was far more prey then predators

Modern ecological studies show that warm-blooded animals need a steady supply of food, unlike cold-blooded animals, where one meal can last them many days, or even weeks. Therefore, there should be far greater prey than predators in an endothermic population. Modern endothermic predators account for one to six percent of the total population (Morell 1987: pg8). Obtained fossil evidence suggests that dinosaur predator/prey ratios were relatively low. Bakker calculated that predators were only composed of one to three percent of the total populations studied; therefore, he argued that dinosaurs must have been endotherms (Morell 1987: pg8).

The best evidence for suggesting that dinosaurs were warm-blooded is that their bone structure is significantly more similar to the modern day fast growing, vascularized bone of the modern bird in a cross section than it is to slow growing, "arrested lines" of bone of the cold-blooded reptiles such as crocodiles (Morell 1987: pg11). Therefore, Dinosaur bone histology has indicated that the majority of dinosaurs had fast growth rates, much like those of present day endothermic animals. The hypothesis is that the striking correlation between the homologous bone structures of the two organisms indicates that dinosaurs were indeed endothermic. This is the best solid evidence for endothermy because a bone sample that is similar in structure to that of an endotherm most likely indicates that the bone is from an endotherm. It is very unlikely that dinosaurs are ectotherms because their bone structure is highly variable and does not exhibit any of the same slow bone growth characteristics (Morell 1987: pg11).

The weakest evidence comes from the ecological studies, which indicate that dinosaur predator/prey levels were low, so they must have been endotherms. It is believed that warm-blooded predator/prey ratios are lower than ectothermic predator/prey levels because warm-blooded predators need a consistent food supply, while cold-blooded predators eating habits may greatly fluctuate (Morell 1987: pg8). This argument is the weakest because dinosaur fossils are not the most reliable source to obtain and calculate predator/prey ratios. The data we obtain through the fossil records is incomplete, because many animals may not have been fossilized; therefore, this data is not at all conclusive. At this point in time there is a lot of bias and no solid evidence from fossils that have been obtained that would accurately indicate what the dinosaur predator/prey ratios may have been, so this argument does not necessarily help to prove that dinosaurs were endotherms (Morell 1987: pg 9).

Scientific investigations are ways to help people to know and to try to understand things that they may be curious about, in this instance, the internal and external structure, behavior, habitat, biota, and overall ecology of the dinosaur were examined. These studies provide techniques that allow scientists to explain life forms that have been extinct for more than 65 million years. One usually begins by making an empirical observation utilizing their senses. In this case, after studying dinosaur bones, Dr. Bakker believed that dinosaurs appeared to be designed to walk upright like an endotherm (Morell 1987: pg7). Based upon what he observed, he developed a hypothesis, which is an educated guess or a possible explanation to some question. He claimed that because dinosaurs had an erect posture, it indicates endothermy. The hypothesis was then tested in order to analyze its validity. Based upon the evidence gained from experimentation, the hypothesis can either be rejected or accepted for the time being, and further testing can take place to evaluate its reliability. The evidence he found from fossil/geological data seemed to support his claim, and these findings lead to his development of other hypotheses, such as homologous bone development and fast growth rate among dinosaurs and modern endotherms, which attempt to prove that dinosaurs were indeed warm-blooded creatures (Morell 1987: pg11).

There are numerous specific examples of the scientific methods notion of hypothetical deductive thinking answering questions about dinosaurs; one such example refers to the brontosaurus habitat and biota. Many assumed that the brontosaurs spent most of the time in an aquatic environment swimming aimlessly around in bodies of water. This assumption was so firm that these dinosaurs would appear in the background of exhibits frolicking in the water, while horned animals fought meat-eaters in the foreground on land. However, this belief changed when scientists discovered that a brontosaur fossil bed existed in an area that was once a wet-land. Bakker argued that "their feet were totally wrong for walking on muck. It was a hard, firm cushioned foot, like an elephant's. It was a foot for walking on dry land" (Morell 1987: pg 13). After studying the geology of the environment where the fossils were discovered, Bakker stumbled upon caliches, which are evidence of a monsoon-like climate, were heavy rain is followed by a long drought. He believed that the region the brontosaur bones were found in was a seasonal flood plain, which consisted of an "open-canopy forest," which was an amazing discovery because it contradicted the previous notion that the brontosaur dwelled in a rain forest type area with bountiful vegetation and lakes (Morelly 1897:pg14). Fossils track ways found elsewhere also supported Bakker's hypothesis, and lead him to believe that brontosaurs migrated in herds along the flat flood plains in search of the blooming conifers through the seasonal climate. Earlier scientists believed that the brontosaur ate soft, swampy vegetation, while Bakker contradictorily suggested that brontosaurs had diets similar to those of giraffes and ostriches based upon new found evidence (Morelly 1897:pg14). From his utilization of the scientific method, his observations about their bones (paws), the fossil record, and geology, Bakker was able to construct and test hypothesis' that have changed our knowledge and understanding of the pre-historic brontosaur.

Works Cited

Morell, V. 1987. "Announcing the Birth of a Heresy." Discover 6: 26- 50.