When people think of crocodiles, they immediately think of ugly monsters with large mouths, dense fangs, and tough armor, staying in rivers, lakes and seas ready to attack their prey. In fact, the crocodile is a successful predator with a keen sense of sight and hearing, clumsy appearance and very flexible movements, and is born with a meat-eating appearance, and all animals, including humans, are included in the menu. In today's human occupation of the earth, crocodiles live in some large rivers and lakes and shallow seas, the space seems to be a little small, but they will never allow any animal to touch their own territory, even if humans step into it is still used as a snack, so even the fiercest animals see crocodiles may have to avoid three points. Some people will ask, why are crocodiles so domineering? There is still a long history that surpasses that of dinosaurs.
Crocodiles originated from a large family of crocodiles 220 million years ago, first represented by small bipedal carnivores. Ancient crocodiles were once brilliant, while the limited diversity of modern crocodiles masks the radiation and wide range of adaptability that preceded them. It can be said that the current situation of crocodiles is only a corner of the glorious history of its predecessors.
The world's first crocodile
Before we look for the first crocodile on Earth, let's talk about what a crocodile is. The meaning of the word crocodile can be divided into a broad and narrow sense. The broad sense of crocodile refers to the large class of crocodiles, while the narrow sense refers to what we usually call crocodiles. It is worth mentioning that in the history of life there are many names associated with "crocodiles", their shape is similar to crocodiles, and the equally huge and ferocious animals are not crocodiles. For example, the famous canine tooth crocodile, as well as alligators, bird crocodiles, Lawrence crocodiles, post-crocodiles, lizards, Ush crocodiles, etc., they are actually primitive animals like dinosaurs. Here, in every sense, scientists are looking for the first crocodile, but when it comes to the world's first crocodile, it refers to the earliest crocodile in a broad sense.
The origin of crocodiles can be traced back to a crocodile-like class in the late Triassic. This animal can be said to be the earliest crocodile and the ancestor of today's crocodile. Typical representatives of this animal are crocodiles from South Wales, England. The ancestors of this crocodile were not as long and thick as today's crocodiles, but light and strong, only 0.5 meters long, with a head as long as today's crocodiles, and thin and prominent teeth. Its hind legs are long, indicating that they may have been bipeds rather than tetrapods. Based on these traits, paleontologists deduce that they may feed on small reptiles, insects, and other invertebrates.
The crocodile ancestors mentioned above may have been bipeds. It's easy to ask this question: What do they have to do with crocodiles? Because they are entirely land animals, feeding on insects. The first is their body structure. Jumping crocodiles have many characteristics similar to crocodiles, such as the radial carpal bone and ulnar carpal bone elongated into a rod rather than a button, the beak bone has a ridge that protrudes backwards, and the pelvis has an open acetabular. In addition, there are many crocodile-like features on the skull: square bones and square yokes face the bottom of the brain, and scaly bones hang from the cheek area. This suggests that the crocodile's ancestors had many of the basic physiological characteristics of the crocodile family from a very young age.
There is also a representative group of crocodiles called the wedge crocodile family, which lived from the late Triassic to the early Jurassic and is very similar in appearance to crocodiles. Wedge crocodiles from the early Jurassic period in South Africa give us clues to the characteristics of this group: they are about 1.4 meters long, can run fast, and are likely to be four-legged walking. The skull is crocodile-shaped in many ways: the radial and ulnar carpal bones are tilted forward, as is the case with the jumping crocodile, with a square skull plate located posteriorly, with scaly and posterior orbital bones, suspended above the temporal foramen area. The location of the upper end of the square bone is typical of alligators: in wedge crocodiles, the square skull and anterior auricular bones come into contact with the scaly bones, while in later crocodiles they move forward and at the same time approach the lateral sphenoid bone, which is a midline structure, typical of the early dragon features, located before the basal wing bone and the foreopenia of the ear.
At the end of the Triassic period, the third mass extinction occurred in the history of life on Earth. This extinction not only made the dinosaurs the masters of the world, but also gave the crocodile a good chance to develop. After the Jurassic, crocodiles began to evolve in multiple directions, and quickly adapted to the new ecological space, evolving in the three directions of sea, land and amphibious.
Crocodiles of the age of the dinosaurs
The Jurassic and Cretaceous periods were the flourishing periods of the dinosaurs and the flourishing of the crocodile family. According to research, there are about 150 genera of crocodile fossils found during that period, while only 8 genera have been found today. According to classical classifications, crocodiles of the Jurassic and Cretaceous periods mostly belong to the middle crocodile. Most of them lived in water and had few of the physical characteristics of today's crocodiles. If today's crocodiles have the characteristics of adapting to the environment and the human era, then the crocodiles of the dinosaur era have the imprint characteristics of that era.
You probably know that the fiercest crocodile today is the bay crocodile, which lives in the ocean.
In fact, as early as the Jurassic, there were crocodiles living in the ocean, and the sea crocodiles of the true crocodile in the jurassic primitive were a taxon that was completely adapted to marine life. During the early and middle Jurassic periods, a class of crocodiles known as steneosaurids lived in the shallow and man-made seas around Europe, with long, narrow beaks that preyed on fish. By the late Jurassic period, crocodiles of the ground lizard crocodile type appeared on the European continent, representing the ground dragon. At this time, the crocodile's body became stronger and fully adapted to aquatic life, and they could swim through the powerful fluctuations of the body. The caudal vertebrae are bent downwards to support the caudal fin, the wing limbs are paddle-shaped, and the disappearance of body armor improves the efficiency of the body's fluid mechanics. Paleontologists have deduced that ground lizard crocodiles may have difficulty walking on land, preying on cephalopods and fish by sudden acceleration in the water.
The Bernice crocodile and the Sea Crocodile were produced in Europe in the early Cretaceous Period and resembled the real crocodiles of later times in many ways. What they commonly feature is that the inserted posterior orbital plate is a pair of convex first tail vertebrae, i.e. both joint surfaces are spherical, and the bony scales are distributed along the body in multiple columns instead of two longitudinal columns.
In South America, during the Jurassic Period, many crocodiles lived on land, with habits almost like mammals. For example, argentine crocodiles are less than 1 meter long and have differentiated teeth, protruding teeth in the front may be used to catch prey, and flatter cheek teeth are used to cut flesh. However, many of the lineages of these crocodiles have shrunk over time. At that time, the crocodile was considered a "big brother", with a body length of more than 4 meters, strong teeth and mandibles, and long and strong limbs. In the late Cretaceous period, terrestrial crocodiles such as the Noto crocodile and the Koma-painted crocodile appeared, but our habits are not yet clear.
During the Jurassic Period, large and fierce crocodiles appeared on the African continent, not only preying on fish, but also coveting ferocious animals that came to the shore to drink water. In fact, the environment at that time made them extremely adaptable, and fossils have been found in many parts of Europe and Africa. Especially in the later period, the body length of this type of crocodile can reach eight or nine meters. In the Cretaceous Period, the Libigo crocodile appeared in southwest Africa, which is much smaller than the large-headed crocodile, generally no more than 2.5 meters long, and is a small and medium-sized carnivore.
They have sharp shark-like teeth and armor, and are most notably characterized by a protruding snout that protrudes like a pig's beak. Spending most of his life in tall grass and shrubs, he preyed on insects, lizards, or small mammals in his infancy; in adulthood, they would gang up to attack small and medium-sized dinosaurs. Most notably, Africa in the early Cretaceous period produced the giant of all crocodiles, the "emperor crocodile". Scientists found the fossil of this prehistoric crocodile in the Sahara Desert, and its skull reached 2 meters long! According to calculations, its body length is 13 meters, its weight is about 10 tons, and its bite force is more than 8,000 kilograms, which means that the imperial crocodile can effortlessly bite the dinosaurs that drink water by the river. Therefore, although the dinosaurs were dominant at that time, they did not dare to cause trouble in the territory of the imperial crocodile.
The Sichuan Basin is really a veritable Jurassic Park, when the basin formed a large lake and became a paradise for crocodiles, with animals such as the Western Shu crocodile appearing. The bones indicate that they are all carnivores that live in the water. You may not imagine that crocodiles are not all meat-eating, and there was a class of ridged crocodiles in early Cretaceous China, and the Camilla crocodile was most likely vegetarian.
At the end of the Cretaceous period, when T. rex appeared on the North American continent, a giant crocodile called a crocodile called a crocodile also appeared, which may have reached a length of 8 meters to more than 10 meters. Scientists have deduced that these crocodiles mainly live in some parts of the United States and Mexico, and they like to haunt places such as delta shoals, most likely clashing with T. rex, and even included the latter in their menus. But their fate, like that of Tyrannosaurus rex, disappeared from the earth at the end of the Cretaceous period due to environmental changes.
In addition to the above, crocodile fossils were abundant in freshwater and marine sediments from the middle Jurassic to the end of the Cretaceous. There are also crocodiles known as dyrosaurids that appeared in the early Cretaceous and survived until the late Eocene, and they survived tenaciously even though dinosaurs disappeared from the earth. It is also worth mentioning that in the late Cretaceous period, real crocodiles appeared, which is what we call crocodiles today.
Real crocodiles
What we call crocodiles today belong to the Eusuchia class in scientific research, officially known as "true crocodiles", first appeared in the late Cretaceous period, and most of the original members were very similar to modern crocodiles. They differ significantly from the primitive crocodiles: a complete secondary upper jaw is formed from the maxilla, palate, and wingbones, in addition to a number of other skull features. After the earth's history entered the Cenozoic Miocene, the climate began to gradually become dry, the tropical rainforests that used to spread around the world gradually became grasslands, and the crocodile family shrank greatly. The impact of all this on land animals is very large, and many new mammals adapted to dry climates, such as cats, bears and other new carnivores, have risen rapidly and occupied the upper end of the food chain. And all this is bad news for large land crocodiles. The incompatibility with climate change and the strength of competitors led to the fact that by the end of the Miocene, almost all large terrestrial crocodiles and a considerable number of amphibian crocodiles around the world were no longer available.
The latest research has found that the ancestor of today's crocodile is an extinct shield armor crocodile, named after its thick shield-like skin on its head.
The fossils were found in Morocco, Africa, dating back to the late Cretaceous period, about 95 million years ago. Studies of blood vessel marks left behind in fossil bones have shown that the shield-armored crocodile has a special crusty tissue growing on the top of its head, somewhat similar to a shield. These features have never been reported in the past, and scientists speculate that the shield armor may be used to attract the opposite sex, intimidate enemies, or play a role in regulating the body temperature of the crocodile's head. By comparing it with other crocodile skull fossils, scientists have found that the skull of this shield-armored crocodile is flatter than other crocodiles. They look less likely to wrestle with dinosaurs on land, and their long, flattened faces are more conducive to ambushes, using their flat jaws to prey on fish. In addition, based on the analysis of skull fossils, scientists deduced that the length of the shield-armored crocodile's head could reach 1.5 meters, while the total length of the body could reach 9 meters, which is much larger than the size of modern and most crocodile fossils.
In the early Cenozoic, many crocodile taxa lived entirely on land, and in South America they even lived with birds and carnivorous mammals.
To this day, the crocodile family has experienced an extraordinary history, and the history of the family can be concisely identified by a diagram. Today's crocodiles have become a small group of only 23 species, living in tropical freshwater and brackish water, which can be divided into three families: the true crocodile family, the alligator family, and the long 'alligator family]. The first two families originated in the Late Cretaceous period, both survived the Paleogene and Neogene periods, and have a much wider distribution range than they are today, with dozens of fossils reported from Europe and North America, north to Sweden and Canada, and all tropical regions and southern continents. The giraffe crocodile is a more complete aquatic molecule with a long, narrow mouth for eating fish, dating back to the Eocene. Only fossils have been found in several other taxa, some with thick, broad, flat-billed heads, and others with jagged dinosaur-like teeth.
Crocodiles have this long evolutionary history because of the fact that their body structure rarely changes. The kinship between modern crocodiles is not yet fully understood, but Chinese scientists have made important progress in this regard. They used DNA rematch kinetics methods and DNA molecular clock techniques to study the origin of the Yangtze crocodile and the molecular evolution of the crocodile, confirming that the Yangtze crocodile (belonging to the alligator) and the Missy crocodile (belonging to the alligator) were once related. They compared the genome structure of the two types of crocodiles and found that although the DNA sequence species were quite different, the overall complexity was similar. Using their own DNA molecular clock technique, they demonstrated that the Yangtze crocodile had a common ancestor with the Thai crocodile (belonging to the true crocodile) 35 million years ago, a common ancestor with the bay crocodile (belonging to the true crocodile) 45 million years ago, and a common ancestor with the Missy crocodile 65 million years ago. The genetic distance between the Missy crocodile and the Yangtze crocodile is the farthest, indicating that Eurasia was separated from North America at the end of the Cretaceous Period, resulting in them remaining in genetic isolation. In addition, it is also proved that the Yangtze crocodile originated in Asia. They first found that crocodiles evolved at a slower rate than birds and mammals at the DNA molecular level, and proposed a theory that explained the slow evolution of reptiles.
Today crocodiles are characterized by a long mouth with nostrils at the tip of the mouth, so they only need to expose the nostrils out of the air above the surface of the water to breathe.
The maxillary, palate, and pterygium grow inward to form a secondary palate that separates airflow from the mouth, allowing crocodiles to open their mouths to breathe while eating underwater. The typical way crocodiles catch antelopes and other mammals is to grab one of their legs and drag them underwater until they drown, then insert their sharp teeth into the side of the prey's body and tear off large pieces of flesh by twisting their bodies. In this way, they gain more power when tearing slices of meat.
Billions of years of evolution have given today's crocodiles four ways of moving on land: crawling on their abdomen, using only their hind limbs to push their bodies forward like a sleigh in order to climb up from the riverbank; slow crawling, a slow movement with knees and elbows sticking outward; walking at high speeds, bending the limbs under the body for quick movement; and galloping, which is the least common way, with the forelimbs and hind limbs moving at the same time.
The last way to gallop seems a bit incredible for crocodiles. The crocodile's spine is fixed like a box beam, with two rows of scales clinging to the spine in the skin, and the spine is fixed by a longitudinal muscular system, which attaches to the dorsal carapace above the back and tail. In this way, it is possible for the crocodile to run fast.