Cretaceous period- The last of dinosaurs ⋆ TheScientificRevelation (2023)

Namaste everyone. Welcome to another post on the “history of earth” series. Previously we had focused on the physical sides of the Cretaceous period like environment, geology, geography, and tectonic movements. In the recent post, Cretaceous period- The last of dinosaurs, we will go for the most advanced dinosaurs, marine reptiles, and flying reptile species. Cretaceous ended with another major mass extinction that wiped all the major mega reptiles in air, land, and water.

Cretaceous life

When we think about cretaceous life we imagine all kinds of mega reptiles dominating the earth. When the Cretaceous ended these amazing life forms ended too. Cretaceous is an important transition period from the Mesozoic life of reptiles to the Cenozoic life of mammals. In cretaceous periods all the dinosaurs, marine reptiles, and pterosaurs were in their apex and most advanced forms. Flowering plants had made their debut in the Early Cretaceous and became the dominant land flora till the end of the period. Both major mammal groups placental and marsupial originated in the Cretaceous period. Other animal groups like marine invertebrates and fishes developed forms with the end of the Cretaceous period.

Marine animals

The cretaceous marine realm is divided into two paleobiogeographic regions, the Tethyan and the boreal. You can think of Tethyan as tropical water and boreal as temperate waters. This division is based on rudist-dominated organic reef-like structures. Rudist were large and unusual bivalves that had dominated over corals and formed the Cretaceous waters. The few exceptions found outside the Tethyan had never made the reefs. These rudist reefs of the Cretaceous had formed the petroleum deposits of Mexico, Venezuela, and the middle east.

The other dominant Tethyan invertebrates were nerineid snails, calcareous algae, and large benthic foraminifera along with some ammonites and echinoids. on the other hand, belemnites were confined to colder boreal waters. Along with them bivalves exogyra and gryphaea and inoceramids were widespread invertebrates of the boreal region.

Marine diversity

As the cretaceous ended most plankton developed modern forms. Coccolithophores (extremely important for the modern marine food web) became so abundant that their carcasses had made the famous chalk deposits of the Cretaceous period. Along with coccolithophores, foraminiferans had also contributed to the Cretaceous chalk deposits. Some other notable animals were diatoms, radiolarians, and dinoflagellates. The most famous cretaceous and Mesozoic invertebrate was Ammonites. Countless species had swum the Mesozoic waters. Coiled forms were most abundant followed by other varied shapes. Ammonites were the food of many marine predators notably sharks and famous mosasaurs.

Mosasaurs were equivalent to modern killer whales, swift and lethal. Along with them long-necked Plesiosaurs and ichthyosaurs had ruled over the marine world. I have already detailed about Plesiosaurs and Ichthyosaurs in my previous post-Jurassicanimals. You can go and read it. Sharks and rays were widespread. Teleost (ray-finned) fishes were widespread back then too.

Terrestrial life

Although it wasn’t that significant, some minor extinctions happened at the end of the Jurassic period. This fossil record is incomplete and irregular at the early cretaceous. The late cretaceous fossil record is the best for Asia and North America. Although tyrannosaurs, triceratops, and Iguanodons were the most famed land animals, we have found fossils of other medium and small-sized herbivorous and carnivorous dinosaurs. Most stem mammals and mammal-like reptiles had long gone leaving the true mammals to live on. Both placental and marsupials have originated till the late cretaceous period.

Life in the air

Pterosaurs had dominated the air for all the Mesozoic era. Meanwhile, one specific pterosaur, Quetzalcoatlus, was the biggest thing to fly in the air. Birds developed from archaeopteryx and related forms.

Land plants

The lands plants were similar to the preceding Jurassic period except for the presence of angiosperms. Most gymnosperms had developed in Triassic and subsequent Jurassic. These cycads, ginkgoes, conifers, and ferns had retained their classic forms till now. On the other hand, the angiosperms that appeared in the early Cretaceous became the dominant flora. Figs, magnolias, poplars, willow, sycamores, and other herbaceous species first appeared in the fossil record. Insects had followed the suit and diversified to the modern levels.

The famous reptiles of the cretaceous period

Albertosaurus

Albertosaurus, close kin of Tyrannosaurus, had lived in North America and eastern Asia during the late Cretaceous period. It had reduced forelimbs, a large skull, and jaws but it was smaller than Tyrannosaurus. Albertosaurus was 9 meters long and its head was 3.5 meters high off the ground. Hands were similar to Tyrannosaurus with only 2 fingers. Its jaws had sharp and recurved teeth with a rounded shape. They were nearly perfect for puncturing the flesh. It was most possibly a scavenger too, like feeding on dead carcasses and protecting its kill from other small dinosaurs.

Dilong

Dilong is known from fossils found in Liaoning province, China that dates back to 127 million years ago. It belongs to the Tyrannosaurus group and was one of its primitive members. This proves the theory that tyrannosaurids first originated in Asia and then migrated to North America. This also tells us that during early cretaceous times Asia and North America were joined together on various points. Dilong is also the first tyrannosaurs found with feathers. It was a small dinosaur with a body length of 1.6 meters and 5 kg of weight. It had longer forelimbs and three-fingered hands. Dilong had a skull very similar to later more advanced tyrannosaurus.

Shockingly enough, the anatomy of an adult Dilong resembles the juvenile of later tyrannosaurs. It had protofeathers that were 2 cm long, more like a coat of feathers. Dilong along with other feathered dinosaurs could not fly which explains that feathers might have developed for insulation.

Dominant herbaceous dinosaurs (hadrosaurus/ duck-billed)

Anatosaurus

This lineage of hadrosaurus lived in North America from 70 million to 66 million years. It was closely related to Edmontosaurus and Shantungosaurus, other dominant herbivores that lived in the northern hemisphere. Anatosaurus had an average length of 9-12 meters and was heavily built. It had a long skull and broad, flat beak much like a duck, hence the name. Similar to other groups of Hadrosaurs Anatosaurus didn’t have any teeth in beak which was rather covered with a sheath. It had many blunt teeth alongside the cheek. Anatosaurus also had extra teethes for the replacement of worn-out teeth. Fossil finds have suggested that it had leathery and rough skin. It might have fed on twigs, seeds, fruits, pine needles. They had flat, blunt, and hoof-like claws very similar to modern browsing animals. They lived in groups and didn’t have elaborate head crests on skulls.

Lambeosaurus

Lambeosaurus had a hallow bone crest on the top of its skull, which was a noticeable feature. It lived in North America during the cretaceous period. Lambeosaurus belongs to the Lambeosaurinae family full of crest dinosaurs. The use of skull crest is not confirmed as there are different suggestions. It might have been used for sound formation or for better smell or perhaps it was just a display for species recognition. Along with the head crest, it also had a different pelvic bone configuration from other hadrosaurus.

Maiasaura

Maiasura is another group of hadrosaur dinosaurs. Like its other two sister groups, Maiasaura dinosaurs were also browsing animals that lived in North America during the late Cretaceous period. Their fossils have been found in hundreds with both adults and juveniles in close proximity. This had led scientists to believe that perhaps Maiasura cared for their kids. Fossil finds also suggest that Maiasaura were migratory animals and returned to the same nesting site year after year. Research revealed that it would have taken 7-8 years for hatchlings to develop into adults.

Small carnivorous dinosaurs

Dromaeosaur

dromaeosaur (family- Dromaeosauridae) lived in Asia and North America during the Cretaceous period. They were small to medium-sized carnivorous dinosaurs. They were agile, swift, lightly built, and possessed sharp claws. Dromaeosaurs were bipedal and the second toe of each foot had a sharp talon-like structure. This toe was always off ground and much larger in size. Their head was small and elongated, with sharp razor-like teeth. Their wrist had the same type of motion and flexibility as modern birds. It would have helped them seize the prey. Along with that, they had a very long and strong tail.

Scientists believe that Dromaesaur would have leaped on the prey and stuck both of the talon lags on the prey. At that time the tail would have acted as a counterbalance giving stability to the animal. Dromaeosaur brains were bigger in comparison to other dinosaurs that had allowed them to carry out such complex hunts. It had an average length of 1.8 meters and its prey were small and medium-sized herbivorous dinosaurs.

Deinonychus

Deinonychus was a kind of Dromaeosaur dinosaur. It lived during the early Cretaceous period in western America. Deinonychus was bipedal and killed with sharp, 13 cm long talons. Its talons were on the second toe of both feet much like Dromaeosaurs. Similar to Dromaeosaurus it had a long and flexible tail used for balance. Deinonychus had inspired the Jurassic movie’s velociraptor. Deinonychus was 2.5 meters in length with 50 kg of weight. It had a bigger brain for carrying out complex tasks smoothly. Dromaeosaurs are closely related to Archaeopteryx and existing birds. They share a lot of similarities like flexible wrist and sharp talons.

Velociraptor

Velociraptors like Deinonychus had sharp-clawed toes. It lived in central and eastern Asia during the late cretaceous period. It had similar adaptations to sister species. Sharp claw and strong tail that helped them maintain balance during a hunt. Velociraptor was the smallest among them with an estimated length of 1.8 meters and 45 kg weight. It had hunted small and medium-sized herbivores with its agile motion.

Armored dinosaurs

Nodosaurus

Nodosaurus belongs to the Ankylosauria group, the armored dinosaurs along with Ankylosaurus. Its fossils have been found in North America dating to 95 to 90 million years ago. Although Nodosaurus was the smallest, it was heavy with a height of 5.5. It had supported a small head and long tail. It had thick and knobby plates on its back for protection against predators. Its front legs were much smaller than hind legs consequently its back was arched. Nodosauridae were more primitive and they lived before the Ankylisaurids. Nodosaurus didn’t have a tail club like ankylosaurus and their head was not covered with bony plates/scutes.

Horned dinosaurs

Protoceratops

The darlings of the Cretaceous were horned dinosaurs/ceratopsians that lived in Asia and North America. One of the earliest protoceratops originated in east Asia, specifically Mongolia and China. Although Protoceratops had evolved from the small bipedal dinosaur Psittacosaurus, they walked on four limbs. Hind limbs were more strongly developed than forelimbs . Due to this, it had arched back. Protoceratops was 1.8 meters long and weighed about 180 kg. Its skull like other ceratopsians was very large, almost ⅕ of the full body. The skull bones grew backward like a frill and the jaws were pointed into a beak. The fossils are abundant with all the growth stages.

Psittacosaurus

The oldest member of the ceratopsian family is Psittacosaurus lived around 122 million to 100 million years ago in the early cretaceous. It was 2 meters long and mostly bipedal. Its skull was small and narrow and supported a primitive beak. Its upper jaw had developed into a beak that covered the lower jaw, hence the name. It’s still unclear but Psittacosaur might have evolved from ornithopods in the early Jurassic.

Triceratops

The showstopper of ceratopsians was Triceratops that lived in North America during the late cretaceous. It was 9 meters long and weighed up to 4-5 tons. Its skull was some of the largest, almost 2 meters long. Triceratops had two 1 meter longhorns above their eyes. Its back frills were completely made out of bones and its beaklike mouth was well suited for ripping the vegetation apart. Teeth were present alongside the cheeks for grinding and chewing the harsh vegetation. Hindlimbs were longer than forelimbs and feet ended in hooves. It was a browsing animal and have traveled in groups.

Spinosaurus

You might think the largest carnivorous dinosaur are Tyrannosaurs however this title belongs to Spinosaurus. This African dinosaur had a distinctive sail back created by a tall vertebral spine. Its skull was 1.75 meters long much like a crocodile with a body length of 14-18 meters. It had a whopping weight of 13-22 tons. It had straight and conical teeth much like our beloved crocs. That is to say, Its features suggest piscivory means consumption of fish. Spinosaur’s major diet was fish but It might have hunted juvenile plesiosaurs too. Its teeth marks have been found on plesiosaur fossils. Although spinosaurus lived mostly in estuaries and freshwater bodies, it was adapted to live in the ocean.

I Have written in my previous blog post-Cretaceous period- the conclusion about paleo continents. Cretaceous was a turbulent time when all tectonic plates were moving in random motion. Consequently, ocean water had continuously flooded the land. In this scenario, spinosaurus had to deal with marine reptiles. We are not sure about the use of sail however some estimate that it is either for lipid and salt storage or recognition of the species.

Mosasaurus

Wonderful marine reptile mosasaurs were the T-rex of oceans. It had competed with Plesiosaur and Ichthyosaurus for food and dominance. All these marine reptiles are secondary aquatic means descended from land ancestors. Its major diet was ammonites, cuttlefish, squid, and occasionally other predators. It had a monitor lizard-like head and numerous sharp teeth. Mosasaurus had paddle-like limbs suited for swimming. Its backbone had more than 100 vertebrae for smooth motion. Its lower jaw could slide open for eating the larger prey, a very advanced feature indeed.

Plesiosaurus

These long-necked marine reptiles had shared the oceans with other marine reptiles. They had pan ocean distribution and they dominated during the late cretaceous period. It had a dominating neck, flat body, and relatively short tail. Plesiosaur would flip its limb to swim much like sea lions. It had swum near the school of fish, moving head side by side to feed upon them.

I have written about these 2 species in my previous blog post on Jurassic animals, Ichthyosaurus, and pterosaurs

Resources:

1. The biggest resource is obviously the book “Mesozoic era- the age of dinosaurs“. Give it a try, you will like it.
2. I have been biased in this post and only written about reptiles. However, no worries, read this post to know more about some cool cretaceous animals that weren’t dinosaurs.

I can’t say much here as this is the end. In the next blog post, we will see the last major mass extinction. Until then Stay tuned and DO REVELATION.

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