The armored ‘shark’ that lived 439 million years ago is the oldest jawed ancestor of humans

An ancient armored ‘shark’ that roamed the oceans 436 million years ago is thought to be the oldest jawed ancestor of humans, predating the previous specimen by 15 million years.

Paleontologists reconstructed tiny bone fragments unearthed in China that belonged to a creature with external “armor” on its body and several pairs of fin spines that separate it from living jawed fish like cartilaginous sharks and rays.

The team also discovered about 20 teeth from this new species called Fanjingshania, allowing them to determine that they could only have come from a fish with an arched jaw margin similar to those found in sharks today.

The fossils “help trace many structures of the human body back to ancient fish, some 440 million years ago, and fill in some key gaps in the evolution of” from fish to human “, researchers from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP ) under said the Chinese Academy of Sciences.

This research also produced other fossils, specifically ones that revealed that galleaspids, members of an extinct clade of jawless fishes, possessed paired fins.

An ancient armored 'shark' that roamed the oceans 436 million years ago is thought to be the oldest jawed ancestor of humans.

An ancient armored ‘shark’ that roamed the oceans 436 million years ago is thought to be the oldest jawed ancestor of humans.

Corresponding author Professor Zhu Min of the Chinese Academy of Sciences in Beijing said in a statement: ‘This is the oldest jawed fish with known anatomy.

“The new data allowed us to place Fanjingshania on the family tree of early vertebrates and gain much-needed information about the evolutionary steps that lead to the origin of important vertebrate adaptations, such as jaws, sensory systems, and paired appendages.”

In 2013, scientists said they had found a 419-million-year-old fish fossil in China that disproved a long-standing theory that modern animals with bony skeletons (osteichthyans) evolved from a shark-like creature with a frame made of cartilage.

The ancient ancestor of humans was recovered from bone bed samples from the Rongxi Formation at a site in Shiqian county of southern China’s Guizhou province.

Fanjingshania had several features that differ from any known vertebrate, specifically dermal plates of the shoulder girdle that are fused as a unit with various pectoral, prepectoral, and prepelvic spines.

Paleontologists have reconstructed small fragments of skeletons unearthed in China.  A fragment of the pectoral dermal skeleton (part of a pectoral spine fused with the shoulder girdle of the new species) is shown in the image.

Paleontologists have reconstructed small fragments of skeletons unearthed in China.  A fragment of the pectoral dermal skeleton (part of a pectoral spine fused with the shoulder girdle of the new species) is shown in the image.

Paleontologists have reconstructed small fragments of skeletons unearthed in China. A fragment of the pectoral dermal skeleton (part of a pectoral spine fused with the shoulder girdle of the new species) is shown in the image.

The team also discovered around 20 teeth from this new species called Fanjingshania (pictured), allowing them to determine that they could only have come from a fish with an arched jaw margin similar to those found in sharks today. day.

The creature’s fin spines are among the biggest finds, as the feature helped scientists pinpoint the new species’ position on the evolutionary tree of early vertebrates.

The team also determined that fossilized bones from Fanjingshania reveal resorption (the absorption of cells or tissue into the circulatory system) and remodeling that are generally associated with skeletal development in bony fishes, including humans.

The resorption characteristics of Fanjingshania are most evident in isolated trunk scales that show evidence of tooth-like detachment of crown elements and removal of dermal bone from the base of the scale.

Lead author Dr. Plamen Andreev, a researcher at Qujing Normal University, said in a statement: “This level of hard tissue modification is unprecedented in chondrichthyans, a group that includes modern cartilaginous fishes and their ancestors. extinct”.

“It speaks to a greater developmental plasticity than is currently understood of the mineralized skeleton at the beginning of the diversification of jawed fishes.”

This research also produced other fossils, specifically ones that revealed that galleaspids, members of an extinct clade of jawless fishes, possessed paired fins.

This research also produced other fossils, specifically ones that revealed that galleaspids, members of an extinct clade of jawless fishes, possessed paired fins.

This research also produced other fossils, specifically ones that revealed that galleaspids, members of an extinct clade of jawless fishes, possessed paired fins.

Until now, only fossils of the creatures' heads have been found.  These fossilized remains reveal the first time paired fins evolved

Until now, only fossils of the creatures' heads have been found.  These fossilized remains reveal the first time paired fins evolved

Until now, only fossils of the creatures’ heads have been found. These fossilized remains reveal the first time paired fins evolved

The team also discovered the complete skeleton of a galleaspid, an extinct taxon of jawless marine and freshwater fish, in rocks in Hunan and Chongqing province and named Tujiaaspis after the indigenous Tujia people living in this region, contains their entire bodies.

And so far, only fossils of the creatures’ heads have been found.

These fossilized remains reveal the first time paired fins evolved.

First author Zhikun Gai, a University of Bristol alumnus, said: “The anatomy of galleaspids has been a mystery since they were first discovered more than half a century ago.”

“Tens of thousands of fossils are known from China and Vietnam, but almost all of them are just heads, nothing has been known about the rest of their bodies, until now.”

“The new fossils are spectacular, preserving the entire body for the first time and revealing that these animals possessed paired fins that extended continuously from the back of the head to the tip of the tail.”

Corresponding author Professor Donoghue said: “Tujiaaspis breathes new life into a century-old hypothesis about the evolution of paired fins, through the differentiation of pectoral (arm) and pelvic (leg) fins over evolutionary time. from a continuous precursor of the fin from head to tail”.

‘This ‘fin fold’ hypothesis has been very popular, but has so far lacked evidence to support it. The discovery of Tujiaaspis resurrects the finfold hypothesis and reconciles it with contemporary data on the genetic controls of embryonic fin development in living vertebrates.

.