Seriously, is this guy a fish or a dragon?

The "guest" we are interviewing today is a plesiosaur fossil specimen, which is located in the Dragon Age Exhibition Hall of our museum. This exhibit is from the Late Cretaceous of Goulmima in eastern Morocco. Its scientific name is Libonectes morgani, and its Chinese translation is Morgan Liberosaurus. It belongs to the Elasmosauridae family of the Plesiosauria suborder.

This collection is a well-preserved fossil skeleton, with a total length of about 5.3 meters, 54 cervical vertebrae, a neck length of about 3 meters, and a neck length of more than half of the body length, strong flippers, and very rare, this specimen has 100% preserved head. This fossil skeleton is the best preserved individual of this species, and it is worth visiting.

The Jurassic and Cretaceous oceans were filled with a variety of fish and their predators. Pterosaurs and crocodiles preyed on fish near the surface of the water. Ichthyosaurs and plesiosaurs were the main reptile predators. Mosasaurs were important carnivores in the Late Cretaceous. Ichthyosaur and plesiosaur fossils were first discovered in the 1820s and 1830s, especially after Mary Anning discovered the first complete type specimen of ichthyosaur and plesiosaur fossils in southern England, these two types of marine reptiles began to be known to people.

Plesiosaurs are usually divided into two lineages, the plesiosauroidea and the pliosauroidea.

The long-necked plesiosaurs consisted of five families:

Plesiosauridae,

Elasmosauridae,

Cryptodclididae,

Leptocleididae,

Polycotylidae;

The short-necked pliosaurs consisted of two families:

Rhomaleosauridae and Pliosauroidae.

Were plesiosaurs marine dinosaurs?

Plesiosaurs are reptiles that lived at the same time as dinosaurs, but they are not dinosaurs.

The "dragon" in the name of plesiosaur is because the species are named in Latin. In the naming system, the names of certain reptiles often end with "saurus", which means lizard. The Latin name of dinosaur is Dinosaurs, which originally means "big, scary lizard". Although dinosaurs are not lizards, Chinese paleontologists translated saurus into "dragon" when translating this word in the early years. Since then, people have translated the Latin names of various reptiles with "saurus" into "such and such dragon". Although the names of plesiosaurs, mosasaurs, ichthyosaurs, etc. all contain "dragon", they are actually reptiles living in water and have no direct relationship with dinosaurs, let alone dinosaurs living in the ocean . Dinosaurs specifically refer to the two branches of Saurischia and Ornithischia, while plesiosaurs belong to the order of fins, which is a completely different group from dinosaurs. Since they are all reptiles, plesiosaurs and dinosaurs are at most distant relatives. So next time you see various creatures with "dragon" in their names, don't mistake them for dinosaurs.

Did all plesiosaurs have long necks?

People often think of plesiosaurs as having long necks that resemble long snakes, which is even more obvious in their name. Do all plesiosaurs have long necks? The answer is no.

As we know from the previous introduction, plesiosaurs are a large group. Most of the plesiosaurs have long necks. For example, the Middle Jurassic Ankylosaur has 30 cervical vertebrae, and the Late Cretaceous Elasmosaurus has 76 cervical vertebrae. Their necks are longer than the body and tail combined. The members of the pliosaur family have relatively short necks and fewer cervical vertebrae. The famous top killer in the Jurassic ocean, Liopleurodon, belongs to the pliosaur family. They can be more than 15 meters long and are the natural enemies of ichthyosaurs and other small plesiosaurs.

How did plesiosaurs reproduce?

Scientists had been unsure of how plesiosaurs reproduced until the discovery of a specimen of the Late Cretaceous Dimopodius in 2011.

Scientists found an embryo in the specimen's abdomen, which led to the discovery that plesiosaurs were viviparous, and that their size and strong flippers made it difficult for them to land, so they had to give birth directly in the ocean. These authors believe that plesiosaurs apparently gave birth to large, possibly single, litters. They believe that plesiosaurs reproduced using the K strategy, similar to modern mammals but different from ichthyosaurs (ichthyosaurs gave birth to larger litters, usually 1-2, but sometimes 10-11). It is unknown whether plesiosaurs raised their young after giving birth.

(LACM 129639 specimen photo (A) and interpretation diagram (B). Adult parts are represented in light brown, embryonic material is represented in black, and reconstructed skeletons are represented in white. Image source: O'Keefe and Chiappe, 2011.)

(Restored female Dimorphopoda and newborn. Image source: O'Keefe and Chiappe, 2011.)

References

O'Keefe and Chiappe, 2011. Viviparity and K-selected life history in a plesiosaur (Reptilia, Sauroperyfia). Science, 333, 870-73.

Benton, J., Dong, W. (2019). Vertebrate Paleontology: 4th edition. Beijing: Science Press, 278-279.

Zhou Zhonghe [Editor-in-Chief], Wang Xiangdong, Wang Yuan [Deputy Editors-in-Chief], 2013. 100,000 Whys: 6th Edition, Paleontology. Shanghai: Children's Publishing House, 98-100.