The Russian title of this page mistakenly says “the earliest vertebrate dinosaurs”. Its subject is not dinosaurs. The fossils discussed are small, fish-like animals from the Early Cambrian of China, more than 250 million years older than the first dinosaurs. Myllokunmingia and Haikouichthys are among the earliest known animals interpreted as vertebrates or close early craniates.
Fossils from the Chengjiang biota
The fossils come from fine-grained Cambrian deposits near Chengjiang in Yunnan Province. Exceptional burial preserved soft body outlines that are rarely recorded in ordinary rocks. These animals were only a few centimetres long. Their anatomy is known from flattened fossils, so researchers must distinguish visible structures from folds, decay patterns and preparation artefacts.
Two landmark descriptions appeared in 1999. Myllokunmingia fengjiaoa was described from a specimen with a distinct head region, a series of muscle blocks and structures interpreted as gill supports. Haikouichthys ercaicunensis was described from a slender body with repeated muscle segments and a dorsal fin fold. The fossils preserve combinations of features associated with chordates and early vertebrates, but not a mineralised backbone like the familiar bones of later fishes.
What makes an animal a vertebrate?
Vertebrate ancestry is identified from anatomical systems, not from the presence of a large bony skeleton. Early members could have cartilaginous supports, a notochord and specialised structures around the head and gills. In flattened Cambrian fossils, many of these tissues appear only as impressions. Researchers compare the pattern and arrangement of features with living vertebrates, hagfish, lampreys and other chordates.
Whether these fossils are best called vertebrates, craniates or stem relatives can depend on the definition and the characters included in an analysis. Their exact positions on the evolutionary tree remain under discussion. Some later work proposed that certain specimens assigned to Myllokunmingia and Haikouichthys could represent the same species, while other studies recognise anatomical differences. This is a taxonomic question about sparse, flattened material, not a reason to doubt the broader Cambrian record of early vertebrate-like animals.
What can be reconstructed?
The fossils support small aquatic animals with elongated bodies, repeated muscle segments and structures for swimming. Body segmentation helps explain how the trunk could flex from side to side. A dorsal fin fold would have stabilised the body, although its exact shape in life is reconstructed from the preserved outline. The gill region is interpreted from repeated structures near the head; delicate soft tissues are less secure than the overall body axis.
These animals were jawless. They predate the jawed vertebrates that later diversified into major fish groups and eventually all other jawed vertebrates, including humans. They were not necessarily direct ancestors of any living species. Most fossil species are better understood as branches near the base of a larger tree rather than links in a simple chain leading to modern animals.
Why the oldest record is hard to define
The first appearance of a group in the fossil record is a minimum age for its existence, not necessarily the moment it evolved. Soft-bodied early vertebrates were unlikely to fossilise except under unusual conditions. The Chengjiang deposits preserve them because burial and sediment chemistry favoured exceptional preservation. Earlier relatives may have existed without leaving recognisable fossils.
Age estimates come from the stratigraphic position and geological dating of the enclosing sequence, not from directly dating the animal itself. The Cambrian period spans a long interval, and fossil localities may differ in age. Phrases such as “the first vertebrate” therefore need qualification: a fossil can be one of the oldest known examples, while new discoveries may extend the record.
A first glimpse of the vertebrate body plan
Myllokunmingia and Haikouichthys matter because their fossils preserve several systems in one small body. Muscle blocks, fin folds and head structures provide evidence for an early chordate swimming animal. Later discoveries from Cambrian and Silurian rocks have expanded the range of early vertebrate anatomy and shifted estimates for the origins of jawed fishes.
The evidence is impressive but incomplete. It shows that vertebrate-like animals were present in Cambrian seas; it does not reveal every tissue, exact behaviour or direct ancestry. Correcting the Russian page’s title is essential to the story: these fossils illuminate early vertebrate evolution, not the age of dinosaurs.
Frequently asked questions
Were Myllokunmingia and Haikouichthys dinosaurs?
No. They lived in the Cambrian, hundreds of millions of years before dinosaurs evolved.
Where were the fossils found?
They come from exceptional Early Cambrian deposits in the Chengjiang region of Yunnan, China.
Were these animals definitely vertebrates?
They are widely treated as among the earliest vertebrate or craniate fossils, but their exact positions and some species assignments remain debated.
Were they direct ancestors of humans?
The fossils document early branches near the base of vertebrate history; they are not known to be direct ancestors of humans or any living species.