The Jehol Dinosaur Caudipteryx: Nuclear Cell Preservation in The Cartilage

"Scientists have now discovered that this dinosaur was preserved with its original nucleus intact, which was quite rare. Read more about it here."

The Caudipteryx is the first fossil example of organic matrix preservation in a long-dead, long-extinct animal. Caudipteryx lived about 120 million years ago and was about the size of a turkey. It had feathers like a modern bird but no beak. 

It also had teeth and a fan-shaped tail. Scientists classify the Caudipteryx as an early bird. It has many features only found in birds, such as feathers and a strong wishbone. It also has features that only dinosaurs have, such as teeth and three toes on each foot. 

Finding nuclear material in fossils this old suggests that some biomolecules might persist for more than 100 million years. If the cells did form part of the cartilage, then this will mean we may be able to find preserved DNA from dinosaur specimens. 

While it might be pretty degraded, it may be possible to reconstruct some bits of DNA sequence for this group. The DNA would also allow researchers to look at how dinosaurs were part of each other and how fast they evolved. 

jehol dinosaur caudipteryx
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The Discovery of the Caudipteryx Fossil

The Jehol Biota is an extinct group of organisms preserved in lake sediments of the Jehol Group. It is in western Liaoning Province, northeastern China. The remains of Caudipteryx were first discovered during the summer of 1996. 

Scientists announced that Caudipteryx was an actual bird based on the anatomy and structure of its forelimb, hindlimb, and pectoral girdle. Bird-like dinosaurs were becoming known for their relationship to birds. 

Scientists suggest that this creature could have had quill knobs used to anchor feathers to the bone. These findings imply that Caudipteryx was a close relative of birds rather than an actual bird. We have a lot to learn about birds and dinosaurs from these discoveries.

jehol dinosaur caudipteryx

The Caudipteryx

Caudipteryx is a genus of paravian dinosaurs. Caudipteryx (“tail feather”) had long, solid legs and slender feet. The limbs of Caudipteryx are short but with extended hands, which are not adapted for grasping. 

In this regard, it more resembles Microraptor than the maniraptoran dromaeosaurs to which it is closely related. Like other primitive birds (including Archaeopteryx and Confuciusornis), its tail was vertebrae, with elongated dorsal processes that supported long feathers. 

Some scientists consider that the elongated caudal vertebrae belong to the rectrices. The skull is small and delicate, with a long pointy beak-like modern bird-eating hawks, such as Accipiter or hunting dogs such as a greyhound or whippet. There is little space between the eyes and the nose. Unlike many other dinosaurs, the nostrils are high on the snout.

jehol dinosaur caudipteryx
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Cell Structure, Function, and Metabolism

Caudipteryx stands out in the fossil record as an oddity. The taxonomic position of Caudipteryx is also quite controversial. The shape of the skull and beak suggests that it was an herbivore. The cells of theropod dinosaurs were very like those of modern birds. It means dinosaurs must have had many of the same biological capabilities as birds.

Cells in modern birds are almost always about half the size of those found in comparable reptiles. It indicates that their metabolisms may have been more efficient. The dinosaurs’ genetic material contains more AT molecules than GC molecules, but the opposite pattern is true for birds.

New evidence indicates that dinosaurs might not have been cold-blooded like reptiles but warm-blooded like birds. It means they may have had much higher metabolisms than previously suspected.

The Cartilage

Cartilage is a type of connective tissue, a part of the body that holds other tissues and organs together. Cartilage has several essential functions for the proper functioning of many animals, including humans. Cartilage lacks blood vessels, which means it needs nutrients from the surrounding tissues. 

Cells in cartilage called chondrocytes produce collagen and other protein fibers, which gives cartilage its stiffness. Have you ever taken a blow to the knee? If so, you probably know firsthand how vital cartilage is. The knee’s cartilage works with other soft tissues and bones to absorb blows and help keep the knee stable.

The cartilage in your nose helps protect your brain from shocks when you take a hit to the head. Your ears are partly made of cartilage, too — it makes them flexible and resistant to wear and tear. Cartilage is an essential structure that we may not think about very often.

The tail of the caudipteryx contained a flexible rod made up of cartilage instead of bone, known as a chevron, which is what the fossil study focused on. This research aimed to answer whether fossils would preserve cellular details in the cartilage. 

The researchers used high-resolution transit electron microscopy to study thin cartilage slices from the caudipteryx’s tail. The researchers found chondrocytes in the cartilaginous matrix with preserved cell membrane details and dense spherical inclusions with well-defined membranes and clear boundaries.

Another fossil examined contained what seems like a large blood vessel in the center of the chevron. It has circular cells filled with erythrocytes aligned around it. This research demonstrates that nature can preserve nuclear and cellular details in fossilized cartilage tissue millions of years later.

jehol dinosaur caudipteryx

Nuclear Preservation in Caudipteryx Cartilage

Approximately 11 million dinosaurs died during the Cretaceous-Tertiary extinction event. The most famous dinosaur discoveries are usually not complete skeletons. Nuclei exist within the chondrocyte cells of cartilage. 

This discovery is the first definitive study that provided evidence for preserving ancient DNA. Paleontologists recovered only seven specimens of this dinosaur in China during the Mesozoic era. It makes it a rare dinosaur according to its physical appearance.

Limestone can preserve soft tissue, such as cartilage and muscle because it acts as a preservative by inhibiting decomposition. Scientists found a complete specimen of this dinosaur in 1998 within rocks of the Yixian Formation in Liaoning, China. 

The discovery of ancient nuclei indicates that DNA can remain preserved within a fossil for millions of years. Scientists would not have found nuclei if bone existed in the fossils because bone can interfere with DNA preservation. The fossilization process itself does not preserve structures well.

Potential Mechanisms for Nuclear Preservation in Fossil Birds

Unlike other dinosaurs, fossil birds provide evidence of a high-resolution, secondary nuclear framework. The close relationship of Caudipteryx to other known birds and its early phylogenetic position makes it an ideal model for potential testing mechanisms of nuclear preservation in a dinosaurian lineage.

The discovery of a contemporary dinosaur with Archaeopteryx suggests that the preservation of nuclei may be neither random nor unique to birds but may be characteristic of nonavian dinosaurs from this period (and even earlier). The preserved ovary of Caudipteryx illustrates that at least some nonavian oviparous dinosaurs possessed characteristics like those found in modern birds.

Although we currently lack sufficient information about the biology and taphonomy of Caudipteryx and its contemporaries, preliminary results state that further investigations focusing on the mechanisms leading to the preservation of such fossils will be highly rewarding. Preservation mechanisms in fossil birds might not have been as rare as once thought.

jehol dinosaur caudipteryx

Final Thoughts

We have concluded that the caudipteryx fossil represents a peculiar case of nuclear preservation. The sample was rich in carbonaceous material with enough structural stability to undergo mineralization. Several factors influenced the preservation. It includes biological (cell type), environmental (habitat/sedimentary deposit), and taphonomic factors (preservation of bones within the skeleton). 

This unique composition may have allowed this organism to be partially converted into carbonaceous material with minimal destruction to its original cellular morphology, responsible for its current near-perfect state. The small size of the organism may have also contributed to its preservation.

Picture of Charmaine Smit

Charmaine Smit


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