Size has distinct advantages and disadvantages. Large animals, as you say, need lots of food and space, and there are design complications with supporting the animal. However, larger animals are also unlikely to become prey for smaller animals, and larger animals (if warm-blooded) also lose heat slower than smaller animals (when you take geometry, if you haven't already, you'll see why).
So, there are advantages to being big. Whales are much bigger than we are so that other creatures in the sea cannot prey upon them and so that they retain their heat inside their bodies. We, likewise, are bigger than ants, and for the same reasons: an anteater is harmless (to us), but it's a deadly terror if you're an ant!
Answer 2:Being a big animal has both advantages and disadvantages. Big animals lose far less body heat than small animals, and therefore don't need to rely as much on consuming high calorie food. Big animals conserve body heat very efficiently, and often don't even need hair (an elephant barely has any hair). They also can use their size for defense, and can live in places that have large fluctuations in heat and cold because they monitor their own temperature so well.
For many, many millions of years, dinosaurs dominated the planet, and small mammals existed in relatively small numbers. The benefit/cost of being a large animal depends entirely on the current environment. Some paleontologists think that the reason that mammals thrived after the meteor that hit Earth and caused the extinction of the dinosaurs is because they were small enough to be able to hide from the aftermath of the meteor strike. In that case, being big would have been a very bad disadvantage after many millions of years of large size being a great benefit.
Answer 3:That's a great question. You're right that big animals need a lot of food, so they need a lot of space for that food to grow. On the other hand, there are some benefits. For one, you may be so big that no predators can kill you. Elephants do not have any non-human predators. Even their babies are protected by the herd. Sometimes predators get together to attack large animals, but they can usually only kill the weakest.
As any object gets bigger, the ratio of its surface area (its outside) to its volume (its inside) gets smaller. In other words, its inside grows faster than its outside. You can see this by calculating the surface area and volume of a cube with 2-cm sides and one with 3-cm sides. What this means to the animal is that it loses heat much more slowly so they are much more efficient with their food. Mammals and birds have to spend huge amounts of energy to make heat. Small animals like shrews and hummingbirds have to make so much heat that they can starve in only a couple of hours. Their hearts have to beat almost as fast as a heart can beat. Huge animals have very slow heart rates. So they need LESS food PER KILOGRAM even though they need more total food.
So if you were a dinosaur, would you rather be the biggest in the herd or the smallest?
Does your food source matter?
Does the environment matter?
Do your predators matter?
By the way, there were once dwarf elephants on islands in what is now Greece. Why do you think island elephants might be so much smaller than their mainland relatives?
Answer 4:Organisms don't stick around too long if they're "useless." In some cases being large probably has advantages. Being big, for example, decreases the amount of surface are an animal has (per unit volume), which means they lose less heat (per unit volume) than do smaller animals, which in turn means that they can survive on poorer quality food than can smaller animals.
Being huge also protects some animals from being eaten.
Answer 5:Large animals are not useless - This is
attested to by the fact that big animals have
repeatedly evolved over time from smaller
ancestors in a really wide range of animal groups.
Some reasons include that
- when you are big, you have a
lower metabolic rate. Thus, while you need more
food overall, you need less food per pound of you
than if you were tiny
- when you are big, you
have a bigger stomach. Particularly among
herbivores, this means you can eat very low
quality food and then digest it over a long time
frame to gain nutrition. A small stomach cannot
do this.
- When you are big you do not
particularly have to worry about predators
-
When you are big you have a reduced surface area
relative to your volume
- so you lose less heat
from your surface. This is good in cool
places(polar environments; the ocean).
That's a good question, and I have both a short and a long answer for you.
The short answer is that animal species only ever evolve into forms that work best in their environment. That's the only reason any species ever evolves into any other species. "Working best in their environment" really means reproducing the most. Living longer, finding more food, being stronger or faster, or being better at hiding from predators all only matter because these things allow an animal more time to reproduce. Producing more offspring is, ultimately, the only evolutionary advantage that matters.
Sometimes a species will evolve into a new species not because the new species is better able to reproduce, but just because the new species is not WORSE at reproducing.
The longer answer I have is a list of possible reasons why being big like a dinosaur or a blue whale might allow some animals to reproduce more. In the ocean, there are fewer disadvantages to being huge, since you can float in the water and let it support your weight instead of having to have your legs support your whole weight. The food that blue whales eat is extremely abundant--there are literally tons of it everywhere. Being unable to find enough food is often a thing that stops animals from getting bigger, but large whales don't have that problem. Also, the huge size of a Blue Whale protects it from most of the ocean's predators, since few of them are big enough to kill and eat them. There might be other advantages to being that big, or it might be simply that there aren't many disadvantages.
Dinosaurs probably had similar reasons for evolving into such big species,but scientists don't really know. The ones that lived on land didn't have the ocean to help support their weight, but the warmer climate probably made it easier for them to maintain their body temperatures (whether they were cold-blooded or warm-blooded). The body temperatures of small animals change much more quickly than those of large animals. Generally, though, I think the fact that there are such huge marine animals but so few huge land animals means that being huge on land doesn't work as well as being huge in the ocean.
So, remember the short answer: all species only ever evolve into new species if doing so makes them better at reproducing (or, at the very least, if it doesn't make them worse at reproducing). Also remember that individual animals don't evolve, animal SPECIES evolve--and that evolution happens over many generations. Keep those things in mind, and you'll be on the right track in thinking about evolution! And keep asking great questions!
Answer 7:"Useless" is a little harsh, don't you think? Things evolve to be big because that's one of the only sure-fire ways to avoid getting eaten. The blue whales are larger than the largest predatory animals in the sea:
killer whales and white sharks. Sure, if enough killer whales and white sharks ganged up on a humpback whale it might not be able to escape predation, and humans have certainly evolved ways of killing blue whale with guns and harpoons, but even then, it still involves a huge struggle.
Size definitely has its advantages. In fact, you could have asked why aren't most animals as big as blue whales? Most animals are limited in their size by something. Insects, for example, are pretty much limited in their size by the fact that they don't have lungs. Most insects rely on oxygen diffusing into their bodies through tiny holes in their sides,near the legs. They can't just take deeper breaths to get more oxygen. In prehistoric times when there were lots more plants, there was actually more oxygen in the atmosphere than there is now, and insects were bigger (imagine fending off four inch cockroaches and giant predatory centipedes five feet long and a foot wide!). Blue whales have an advantage in the ocean because water bears most of their weight, and they don't need to worry about having massive skeletons to support all the blubber, but the dinosaurs showed us that it was definitely possible to have skeletons strong enough to support lots of weight.
It does seem like many organisms in the past were larger: there are fossil penguins from Antarctica that stood almost 6 feet tall. On the other hand, humans have been getting taller since we first evolved, probably as our diet improved because of agriculture and tools for hunting. We may be 20 feet tall someday.
The latest research on how sauropod dinosaurs reached their massive sizes, authored by Michael D’Emic, PhD, associate professor of biology, has overturned decades of thinking on the topic. His groundbreaking research has been covered globally and will appear in Scientific American in September.
Michael D’Emic, PhD, associate professor of biology at Adelphi, has upended decades of conventional wisdom about how dinosaurs evolved to be giants.
For years, scientists believed dinosaurs reached their large body sizes via speedy growth spurts. Dr. D’Emic discovered that dinosaurs grew at a variety of rates, and that getting massive quickly wasn’t the only strategy for evolution. Some gigantic dinosaurs grew slowly, taking decades to reach full size. In fact, some smaller dinos grew in size quickly.
Dr. D’Emic’s findings, which were published in the journal Science in February 2023 and will be the subject of an article in Scientific American this fall, are only his latest to have a major impact on his field. He has produced evidence suggesting that dinosaurs were warm-blooded and that carnivorous dinosaurs could replace their teeth as fast as sharks. He also rewrote the evolutionary record by showing that flowering trees appeared in North America 15 million years earlier than previously thought.
Dr. D’Emic is one of a number of Adelphi researchers making significant contributions to scholarship in the study of ancient life. Bryan Wygal, PhD, professor and chair of anthropology, and Kathryn Krasinski, PhD, assistant professor of anthropology, have unearthed specimens in Alaska that shed light on the environment and its effect on patterns of human migration and subsistence in the late Pleistocene era. Anagnostis Agelarakis, PhD, professor of history, has produced fascinating finds on the island of Thasos that have illuminated the history of the ancient Greeks.
To determine dinosaur growth rates, Dr. D’Emic studied the bones of about three dozen species of dinosaurs in the theropod group, which includes two-legged carnivores like Tyrannosaurus rex and Velociraptor. Specifically, he looked at the growth rings in the dino bones. Yes, dinosaur bones have growth rings similar to trees that show how fast the creatures grew each year of their lives.
Dr. D’Emic affixed slices of dinosaur leg bones to glass slides, sanded them down to the thickness of a human hair so light could shine through them, then counted and measured the rings.
The results were surprising.
“Our study showed there’s no one way to grow a dinosaur,” he said. “The largest dinosaurs sometimes reached their adult size in just 10 years and some others took decades. There were vastly different growth rates in dinosaurs.
“Getting bigger faster wasn’t always a better evolutionary survival strategy,” Dr. D’Emic found. “Our study shows it’s just as likely they slowed their growth and grew for longer,” he said.
Dr. D’Emic found there were advantages and disadvantages to being a dinosaur that evolved to grow big, quickly. “Evolving to grow faster than your ancestors meant you could possibly outcompete other species in your environment for resources,” Dr. D’Emic said. “You could outpace the growth of your predators. You’re not small for as long, so maybe you’re not potential dinner for as long.”
But animals that grew fast didn’t always come out on top of the evolution game. “The disadvantage to evolving to grow fast is it takes a lot of energy,” Dr. D’Emic said. “If lean times come, like a drought, and there’s not much food around, you might be more prone to extinction. Sometimes slow and steady growth gives an advantage.”
Dr. D’Emic’s dinosaur bone study has been an epic project, which he conducted with an international group of colleagues from across the United States and in Argentina. He started looking at dinosaur bone growth rings in 2012. It took his team nine years to crunch all the data and reach his conclusions. They wrote up the results and submitted them for peer review, which took seven months.
The paper he and his team wrote on his research is titled “Developmental Strategies Underlying Gigantism and Miniaturization in Non-Avialan Theropod Dinosaurs.” Three of his Adelphi graduate students—Riley Sombathy, MS ’21, Anjali Dave ’17, DDS, and Thomas Pascucci, MS ’19—co-wrote the research paper, which makes Dr. D’Emic a proud professor. “They used that research as their capstone projects. For two, it was their master’s thesis that got folded into our paper.”
At Adelphi, Dr. D’Emic teaches biology classes, including anatomy and physiology. He also teaches a class on evolution for graduate students and senior undergraduates. In the summers, he puts on his fieldwork hat and takes students out on digs in Wyoming or Utah. “We find crocodile, turtle and mammal fossils as well as dinosaur ones,” he said. “We found baby dinosaurs one summer and that was really interesting. One was only four or five years old. It was like a teenager, gangly with long legs.”
His research into the variety of dinosaur growth rates connects them to animals still alive today, who also grow at different rates. “We show that (dinosaurs) are just like animals today, in that they lived in an ecosystem that impacted how they grew and evolved. It’s really interesting to see the parallels between past and present.”
For his next project, he’d like to determine the environmental factors affecting the dinosaur growth rates he sees in those bone growth rings. Did climate affect growth rates? Competitors? He’ll need to match the bones against ancient climate patterns and he’ll need to collect a lot more dinosaur bone samples.
Since it took him a decade to locate and examine the dinosaur bone samples he used in the growth research, he plans to look at mammal and bird bones to figure out what factors influence evolutionary growth rates. “Mammals and birds have a much, much better fossil record,” he said. “You can do the study in about a 10th of the time because there’s more data and there’s more fossils.” He’s already been collecting mammal and bird fossils with an eye to this future research. Dr. D’Emic said he can find them near his dig site in Wyoming, in a different rock layer than the one where he usually digs for dinosaurs.
“It’s only a half hour drive from where I usually dig, so I started a new project a couple of years ago,” he said. “We’re already investigating.”