Author: Liao Junqi
Edit: kamin
Full of fangs, full of tendon meat, coupled with cute little short hands, this is the most classic image of tyrannosaurus in people's hearts. The more well-known tyrannosaur is the species that dominated North America at the end of the Cretaceous period, also known as "Tyrannosaurus rex". They can reach a length of up to 13 meters, and the bite force can reach a staggering 6 tons, and they can bite through the steel plate of the car in one bite.
The size differences of the "descendants" of the Tyrannosaurus family are from left: Tyrannosaurus (red), Tyrannosaurus (purple), Ebertaurus (green), Dinosaur (orange), and Snake-haired Female Monster Dragon (blue). Image credit: Dinoguy2 | Wikimedia Commons
However, tyrannosaur dinosaurs were a large family, with different heights and heights. Most of the "juniors" in the Tyrannosaurus rex family are large tyrannosaurus, such as the Gorgosaurus in North America, the Zhuchengtyrannus in Asia, and so on. In contrast, the original Tyrannosaurus was much smaller, just like the Grandmother Tyrannosaurus rex was not as big as your dog.
Most of these fossils of primitive tyrannosaurs are found in Asia, but are rare in North America. So scientists have been wondering if the Cretaceous North American land was also inhabited by primitive tyrannosaurs. Recently, Communications Biology reported that paleontologists at institutions such as the Natural Science Museum in North Carolina have discovered a small primitive tyrannosaur. It lived in the late Cretaceous period and was small in size, but had a frightening name: the Fearless Moros Dragon, which means "fearless, impending incarnation of destruction".
The primitive tyrannosaur taxa was smaller. 1.Tyrannosaurus rex 2.Cockstrend 3.Hakassosaurus 4.Tyrannosaurus 5.Crowned Dragon 6.Tyrannosaurus Rex 7.Grandmother Tyrannosaurus. Image credit: Conty | Wikimedia Commons
01 How did a dinosaur leg become the embodiment of destruction?
The small tyrannosaur fossils reported here are from Utah, USA, buried about 97 million years ago (early Late Cretaceous)[4], and excavated fossil specimens contain a right leg (femur, tibia, metatarsal, etc.) and a small number of teeth. Its appearance eliminated the gap in North America from the Late Jurassic to the Late Cretaceous period without tyrannosaur fossils for nearly 70 million years.
The paleontologists who presided over the excavations decided to name the tyrannosaurus "Moros intrepidus." "Moros" is Greek for the embodiment of imminent destruction, while "fearless" is Latin for the state of fearlessness. This name must be very confusing to you: isn't it a dinosaur thigh, and it's not a terrifying T-Rex? How did it become the embodiment of fearless and earth-shattering destruction?
The main fossil material for the dauntless Moros dragon. Image source: References [3]
In fact, paleontologists named it because the dragon's evolutionary significance is extraordinary. In morphological comparisons, researchers found that the skeletal morphology of Morososaurus was between the Asian primitive ancestors of Tyrannosaurus rex and late tyrannosaurs such as Tyrannosaurus rex, and was more similar to that of The Asian Tyrannosaurus rex (Tyrannosaurus rex, etc.) of the same period. According to the "generational division", the tyrannosaurs that appeared in the late stages such as the Tyrannosaurus rex had to call it "Grandpa". [3] As such, Moros dragons represented the transition from primitive to late forms of Tyrannosaurus rex and would eventually evolve into a massive "avatar of destruction". The "fearless" in the name praises its fearlessness, spreading from Asia to the Americas, taking a new piece of land for the Tyrannosaurus family.
02 Small physique is bullied, and Tyrannosaurus also has a history of heartache and blood and tears
According to fossil speculation, Morososaurus had a leg length of 1.2 meters, although it was definitely a large-legged Oba for humans, but it was only a small short foot in the family of tyrannosaurs, and even the smallest of the Cretaceous tyrannosaurs. Because the legs carry a body weight load, the length and thickness of the legs often reflect the weight, while the Moros dragon estimates to weigh only 78 kilograms. If it is compared to the Tyrannosaurus rex with a hip height of 4 meters and a weight of more than 5 tons, it is a small witch.
The restoration of the Fearless Moros Dragon, compared with the fallen trunk in the picture, shows that this Tyrannosaurus rex is petite. Image source: References[3]
However, if moros dragons are still just a child, it is certainly unfair to compare this data with other strong adult tyrannosaurs. Just like comparing the size of newly hatched eagles and adult pigeons, it is obviously unreasonable to say that the pigeons are larger. To do this, the scientists chose to cut open the thigh bone of the Moros dragon to understand its age at the time of its death.
The principle of "cutting legs to see age" is that the reptile body will continue to grow throughout its life, and with the migration of the seasons, the growth cycle of the bones will also be fast and slow, so it will form a structure similar to the annual rings of trees. Just like counting the rings of trees, we can tell the age of death of dinosaurs by counting the number of these bone dividing lines. In addition, the growth rate can also be judged by the width and narrowness between the rings, and the spacing width grows faster, and vice versa.
The results of the experiment showed that the Moros dragon was between the ages of 6 and 7 years old, and although it was still a teenager, it was close to an adult. In other words, the small size of the Moros dragon is not due to age, and even if it is an adult, there is little hope of growing up again.
A slice of the femur of a Moros dragon can be seen in a structure similar to an annual ring. Image source: References[3]
Researchers believe that in addition to its petite size, moros dragon is also a "scud". You know, whether an animal is running fast or not can be seen from the anatomical characteristics. Animals with slender legs and relatively long calves and feet are generally good at running, and Moros dragons belong to this type. In contrast, the giant tyrannosaurus in Jurassic World has bulky legs, so the running speed is not fast, and even people in high heels in the movie can't catch up.
But why did the Moros Dragon commit to a small size, scud, and live a sneaky fringe life? In this regard, paleontologists have also proposed a hypothesis: the reason why Moros dragons adopted this small size and scud survival strategy was because there were large-sized top predators of Allosaurus in North America at that time. Just as the so-called one mountain does not tolerate two tigers, tyrannosaurs have to live a small and low-key life because they are oppressed by this group of bullies.
It was not until the allosaurs, the group of bullies, became extinct, and the liberated tyrannosaurs rose up at an alarming rate. The Tyrannosaurus family has been breeding on Earth for more than 100 million years, and finally survived in the last 16 million years and grew into a prehistoric behemoth that dominated the world. Unfortunately, the feng shui took turns, and the tyrannosaurus did not escape the mass extinction of 65 million years ago, and finally ceded the chair of the earth's overlord to today's mammals.
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Typography: Xiao Shuang
Title Image Source: References[3]
bibliography:
1.Brochu, Christopher A.; Richard A. Ketcham, 2003. Osteology of Tyrannosaurus Rex: Insights from a Nearly Complete Skeleton and High-resolution Computed Tomographic Analysis of the Skull. Northbrook, Illinois: Society of Vertebrate Paleontology.
2.Erickson, Gregory M.; Makovicky, Peter J.; Currie, Philip J.; Norell, Mark A.; Yerby, Scott A.; &Brochu, Christopher A., 2004. Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. Nature: 430 (7001): 772–775.
3.Lindsay E. Zanno et al., 2019. Diminutive fleet-footed tyrannosauroid narrows the 70-million-year gap in the North American fossil record. Communications biology.https://doi.org/10.1038/s42003-019-0308-7
4.Garrison, J. R. et al., 2007. A multidisciplinary study of the Lower Cretaceous Cedar Mountain Formation, Mussentuchit Wash, Utah: a determination of the paleoenvironment and paleoecology of the Eolambiacaroljonesa dinosaur quarry. Cretac. Res. 28, 461–494.