Evolution is a slow but sure process that in most instances takes millions of years before any serious notable changes can be noticed. One question that has puzzled many people (scientists and non-scientists alike) is, why were animals so big in the past?
Some of the animals that we have around today were once so gigantic that they would have been a nuisance hadn’t evolution taken its toll on them. Some like the sloth used to be bigger than elephants.
There are many theories out there that offer explanations as to why prehistoric animals were so gigantic.
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List of Reasons Why Were Animals So Big in the Past
The animals included mammoths, dinosaurs, and mastodons, and here are some of the reasons for their increased growth:
- Self Defense
Even without a lot of defensive capabilities, a huge opponent is already threatening enough. Paleontologists believe that most of the herbivorous animals grew so large to better increase their chances of survival in a harsh world.
Giant animals such as those belonging to the genus Shantungosaurus were almost immune to predators. It would have taken a lot of Tyrannosaurus Rex working together to be able to bring down such humongous animals.
- Hollow Bones (pneumatized)
Another reason why animals were so big in the past is the hollow bones found in animals such as the Sauropods. The hollow bones were lighter which made them capable of supporting the dinosaurs without adding to their weight.
These hollow bones were also used for breathing to help sustain the dinosaurs’ active lifestyles. Dinosaurs developed these pneumatized bones around 240 million years.
Theropods are one of the main dinosaur groups represented by pneumatized bones.
- Environmental Conditions
The levels of CO²were quite high which led to an increase in vegetation which meant the availability of food for most dinosaurs. It also meant the availability of a lot of oxygen for these prehistoric animals to sustain themselves.
Abundant oxygen can be a major factor when it comes to the accelerated growth of some animals in prehistoric times.
A good example is the cockroaches of the Paleozoic era which were able to grow as big as modern-day domesticated cats. These cockroaches benefited from the excess oxygen that was available in the atmosphere.
- Eating Habits
Due to the abundance of food, these animals didn’t have to worry too much about their next meal. They were also able to swallow their food in huge chunks eliminating the process of chewing thus accelerating their rate of consumption.
This led to the already huge animals’ continuous growth, which in turn kept them safe from a lot of predators –in prehistoric times there were numerous hazards for herbivorous animals.
No chewing also meant that they had lighter heads –this contributed to the elongation of the neck to help them reach food from the treetops.
- Cope’s Rule
Cope’s rule dictates that competition –in this case for survival, will always encourage the evolution of the disadvantaged.
In the wilderness, if the weak animal doesn’t evolve to better deal with threats, it’s bound to go extinct in no time. This explains where most of the herbivorous prehistoric humongous animals are the huge ones; being massive ensured that no predator bothered them.
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Large Prehistoric Animals
To better understand why some of these giant mammals existed, you first need to familiarize yourself with several of them. The following are some of the large prehistoric animals;
Dinosaurs are some of the most popular prehistoric animals known today. They are widely known and elicit curiosity, amazement, and/or fear in different people.
They were able to dominate the planet for a long time and lived through the Triassic, Jurassic, and Cretaceous periods. This was when they met their sad fate around 65 million years ago.
These beautiful humongous animals can be classified into two broad groups which are;
Ornithischians (mostly herbivores) were distinguished by their bird-like hips. They were herbivores and had jaws and beaks for feeding.
Ceratopsia (horned faces) were herbivores and were found in Europe, Asia, and North America during the cretaceous period. Their sizes varied from 1 to 9 meters and weighed up to 9 tons. Their mouths were beak-like and they were quadrupeds.
This family included the Psittacosaurus, Centrosaurus, and the famous Triceratops (large, bony frill at the back of the head, and 3 distinguishing spikes on its face.
Thyreophora (shield bearers) – these dinosaurs were heavily armored with rows of plates on their bodies and thick skin to boot. Many of them also had powerful tails that were covered in spikes or clubs.
Their best-known groups included the Ankylosauria and the Stegosauria.
The stegosauria group included dinosaurs such as the Kentrosaurus, Hesperosaurus, Stegosaurus, and the Wuerhosaurus. Their bodies were covered in protective plates located along their backs.
Ankylosaurus lived through the Mesozoic period and had protective thick skin and a strong tail with huge clubs used for defensive purposes.
Saurischians (mainly carnivores) could be distinguished by their lizard-hipped hips. They are divided into two main groups which are sauropods and theropods.
Theropods were vicious meat-eaters who were bipeds. They were around from the late Triassic era up to their extinction during the Cretaceous period.
They were a large family that was mainly made up of:
Coelurosaurs (hollow-tailed lizards) were a lot more like birds and they included the tyrannosaurus Rex.
Maniraptora is the dinosaurs that evolved into modern-day birds. They also include the raptor family (Dromaeosauridae). This family was of medium-sized dinosaurs that had feathers such as the Velociraptor and Microraptor.
Abelisauridae – this species of theropods lived during the cretaceous period in Asia, African South America. Some of its examples are the Carnotaurus and Abelisaurus.
Tyrannosauridae (tyrant lizard) – these theropods had huge skulls, short arms, and powerful jaws. The family consists of the T Rex, Albertosaurus, Tarbosaurus, and Gorgosaurus.
Spinosauride- this family consisted of large bipeds that had long, thin skulls that looked like that of a crocodile. They included Spinosaurus, Irritator, Baryonyx, and the Suchomimus.
Carnosauria – this group is made up of two families (Allosauridae and the Carcharodontosauridae). The Allosauridae existed in the late Jurassic and early cretaceous periods. They were predatory and at the top of the food chain at the time.
Some examples of allosaurids include the Allosaurus and the Saurophaganax.
The Carcharodontosauridae (shark-toothed lizards) are some of the largest land carnivores to have ever walked the earth. Examples of these dinosaurs include the Tyrannotitan, Giganotosaurus, and the Carcharodontosaurus.
Sauropods- this group contained dinosaurs that were quadrupeds, with large round bodies, small heads, long necks, and a lengthy powerful tail.
Some of the largest prehistoric animals to ever grace the earth such as the Diplodocus (Supersaurus, Diplodocus, Brontosaurus, and Apatosaurus), and Titanosaurus (Argentinosaurus and Saltasaurus) belonged in this group.
Though they had lizard-like features, these animals eventually evolved to become birds millions of years later.
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2. Indricotherium (Paraceratherium)
The Indricotherium was a mammal that lived in the Oligocene epoch about 23 million to 33 million years ago. They are some of the largest mammals to ever walk the earth.
They are the ancestors of the modern-day rhinos and they could grow to weigh 20 tons. However, unlike the rhinos, they had no horns. They were herbivorous and therefore had plenty of food to support their enormous appetites.
These great appetites are what contributed to their extinction due to dwindling sources of food. When the Asian forests that they used as their source of food became replaced by grasslands, they had no chance of long-term survival.
Both their necks and feet were long, and they had three toes on their feet.
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3. Blue Whale (Balaenoptera musculus)
The blue whale is another humongous mammal from the prehistoric era that has managed to survive to date. They experienced a near-extinction event, but they are still around and slowly growing their numbers.
Though they have no natural enemies courtesy of their huge size, they nearly went extinct as a result of hunting and ship accidents. The hard and flexible part of their jaws known as baleen was used for making corsets, hats, and other clothing items back in the day.
These carnivorous animals can live for as many as 80 – 90 years of age. In this time, they could grow as long as 105 feet and weigh up to 200 tons.
They feed on animals called krill that look more tiny shrimps. They feed by swallowing a lot of water with krill and then sieving out the water and swallowing the krill.
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4. Andrewsarchus (mongoliensis)
In the middle of the Eocene epoch, Andrewsarchus roamed the earth in search of something to sink its teeth in. This was somewhere between 45 and 35 million years ago.
The available evidence of this magnificent beast is a single skull that was discovered in 1923 in the Gobi desert, Mongolia. However, the shape and appearance of the rest of its body remain a mystery to date.
It weighed over 2000 pounds and could grow up to a length of 13 feet – its discovered skull is 3 feet long.
The large jaws of this mammal made it capable of feeding on prey and even protecting itself from other hostile animals.
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5. Pterosaurs (Quetzalcoatlus)
Before there were birds in the skies, the Pterosaurs (winged lizards) were the first to do so millions of years ago. These vertebrates flew the skies of the earth during the cretaceous period, and by the time they went extinct they had spread all across the planet.
The largest type of the pterosaur species is the Quetzalcoatlus northropi which is the size of a small airplane at 36 feet across. They are reptilian and first appeared in the scene about 250 million years ago.
There have been around 130 species of Pterosaurs that have been identified by paleontologists. Some of these types of large prehistoric animals include Nyctosaurus, Tapejara imperator (late cretaceous), pterodaustro (early cretaceous), and the Pteranodon (had a wingspan of 22 feet.)
Their most distinctive feature was their head crests that were made of soft tissue fussed with hornlike materials and supported by bones.
They could have served any purpose from attracting mates, regulating heat, and maybe even for defense; paleontologists haven’t been able to figure out the specific of these beautiful head crests.
6. Gigantopithecus blacki
Even about a hundred thousand years ago, some animals were still massive compared to their modern-day cousins. Animals such as the Gigantopithecus, a not so distant relative of the Gorillas that lived during the Early to Middle Pleistocene
These ancient primates measured up to 10 feet and weighed over 1 ton. They lived in the part of Asia that’s now China. Due to their massive sizes, they required a huge amount of food to keep them going, and that might have been their undoing.
However, some believe that Gigantopithecus blacki is still alive and kicking –just hiding from people. Although this isn’t proven, stories of people running into big-foot or a Yeti are associated with Gigantopithecus by some.
Just imagine if this huge primate had been around in prehistoric times when food was in abundance, he would have given some dinosaurs a run for their money.
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7. Josephoartigasi monesi
This was a rodent from the Dinomyidae family, a species of the caviomorph rodent that became extinct about 2 million years ago -its main habitat was in South America
It’s the largest rodent ever known and is believed to have weighed up to 1000 pounds. It was present between the Pliocene to the beginning of the Pleistocene era.
Its closest living relative is the pacarana –Dinomys branickii, and it only has one other species in its genus -the J magna.
It had an estimated body length of 10 feet, a height of 5 feet, and weighed anywhere from 770 pounds to 3370 pounds. This rodent was bigger than some –if not most, of the modern-day bulls.
Josephoartigasi monesi was first introduced in a study that was conducted by Andres Rinkerknecht, a paleontologist at the National Museum of Natural History and Anthropology in Montevideo, Uruguay.
Though some of the reasons offered to explain why prehistoric animals grew so big are data-backed, the rest are just estimations and extrapolations.
Recently, natural selection seems to be going for smaller animals and plants, unlike the prehistoric giants.