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Fanjingshania renovata, an Ancient ‘Shark’ from China Is Humans’ Oldest Jawed Ancestor

Palaeontologists discover a 439-million-year-old ‘shark’ that forces us to rethink the timeline of vertebrate evolution

Living sharks are often portrayed as the apex predators of the marine realm. Paleontologists have been able to identify fossils of their extinct ancestors that date back hundreds of millions of years to a time known as the Palaeozoic period. These early “sharks,” known as acanthodians, bristled with spines. In contrast to modern sharks, they developed bony “armor” around their paired fins.

A recent discovery of a new species of acanthodian from China surprised scientists with its antiquity. The find predates by about 15 million years the earliest acanthodian body fossils and is the oldest undisputed jawed fish.

These findings were published in Nature on Sept. 28.

Fanjingshania renovata, an ancient 'Shark' from China is Humans' oldest jawed ancestor; the study has been published on Nature — Fig. 1 Life reconstruction of Fanjingshania renovata. (Image by ZHANG Heming)

Reconstructed from thousands of tiny skeletal fragments, Fanjingshania, named after the famous UNESCO World Heritage Site Fanjingshan, is a bizarre fish with an external bony “armor” and multiple pairs of fin spines that set it apart from living jawed fish, cartilaginous sharks and rays, and bony ray- and lobe-finned fish.

Examination of Fanjingshania by a team of researchers from the Chinese Academy of Sciences, Qujing Normal University, and the University of Birmingham revealed that the species is anatomically close to groups of extinct spiny “sharks” collectively known as acanthodians. Unlike modern sharks, acanthodians have skin ossifications of the shoulder region that occur primitively in jawed fish.

Fig. 3 Life reconstruction of Fanjingshania renovata. (Image by FU Boyuan and FU Baozhong)

The fossil remains of Fanjingshania were recovered from bone bed samples of the Rongxi Formation at a site in Shiqian County of Guizhou Province, South China.

These findings present tangible evidence of a diversification of major vertebrate groups tens of millions of years before the beginning of the so called “Age of Fishes” some 420 million years ago.

Fig. 4 Fragment of the pectoral dermal skeleton (part of a pectoral spine fused to shoulder girdle plate) of Fanjingshania renovata shown in ventral view. (Image by Andreev, et al.)

The researchers identified features that set apart Fanjingshania from any known vertebrate. It has dermal shoulder girdle plates that fuse as a unit to a number of spines—pectoral, prepectoral and prepelvic. Additionally, it was discovered that the ventral and lateral portions of the shoulder plates extend to the posterior edge of the pectoral fin spines. The species has distinct trunk scales with crowns composed of a row of tooth-like elements (odontodes) adorned by discontinuous nodose ridges. Peculiarly, dentine development is recorded in the scales but is missing in other components of the dermal skeleton such as the fin spines.

“This is the oldest jawed fish with known anatomy,” said Prof. ZHU Min from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences. “The new data allowed us to place Fanjingshania in the phylogenetic tree of early vertebrates and gain much needed information about the evolutionary steps leading to the origin of important vertebrate adaptations such as jaws, sensory systems, and paired appendages.”

From the outset, it was clear to the scientists that Fanjingshania’s shoulder girdle, with its array of fin spines, is key to pinpointing the new species’ position in the evolutionary tree of early vertebrates. They found that a group of acanthodians, known as climatiids, possess the full complement of shoulder spines recognized in Fanjingshania. What is more, in contrast to normal dermal plate development, the pectoral ossifications of Fanjingshania and the climatiids are fused to modified trunk scales. This is seen as a specialization from the primitive condition of jawed vertebrates where the bony plates grow from a single ossification center.

Unexpectedly, the fossil bones of Fanjingshania show evidence of extensive resorption and remodelling that are typically associated with skeletal development in bony fish, including humans.

“This level of hard tissue modification is unprecedented in chondrichthyans, a group that includes modern cartilaginous fish and their extinct ancestors,” said lead author Dr. Plamen Andreev, a researcher at Qujing Normal University. “It speaks about greater than currently understood developmental plasticity of the mineralized skeleton at the onset of jawed fish diversification.”

The resorption features of Fanjingshania are most apparent in isolated trunk scales that show evidence of tooth-like shedding of crown elements and removal of dermal bone from the scale base. Thin-sectioned specimens and tomography slices show that this resorptive stage was followed by deposition of replacement crown elements. Surprisingly, the closest examples of this skeletal remodelling are found in the dentition and skin teeth (denticles) of extinct and living bony fish. In Fanjingshania, however, the resorption did not target individual teeth or denticles, as occurred in bony fish, but instead removed an area that included multiple scale denticles. This peculiar replacement mechanism more closely resembles skeletal repair than the typical tooth/denticle substitution of jawed vertebrates.

A phylogenetic hypothesis for Fanjingshania that uses a numeric matrix derived from observable characters confirmed the researchers’ initial hypothesis that the species represents an early evolutionary branch of primitive chondrichthyans. These results have profound implications for our understanding of when jawed fish originated since they align with morphological clock estimates for the age of the common ancestor of cartilaginous and bony fish, dating it to around 455 million years ago, during a period known as the Ordovician.

These results tell us that the absence of undisputed remains of jawed fish of Ordovician age might be explained by under sampling of sediment sequences of comparable antiquity. They also point towards a strong preservation bias against teeth, jaws, and articulated vertebrate fossils in strata coeval with Fanjingshania.

“The new discovery puts into question existing models of vertebrate evolution by significantly condensing the timeframe for the emergence of jawed fish from their closest jawless ancestors. This will have profound impact on how we assess evolutionary rates in early vertebrates and the relationship between morphological and molecular change in these groups,” said Dr. Ivan J. Sansom from the University of Birmingham.

Press release from the Chinese Academy of Sciences

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Rare Fossil Teeth from China Overturn Long-held Views about Evolution of Vertebrates

An international team of researchers has discovered 439-million-year-old remains of a toothed fish that suggest the ancestors of modern osteichthyans (ray- and lobe-finned fish) and chondrichthyans (sharks and rays) originated much earlier than previously thought.

Related findings were published in Nature on Sept. 28.

Rare Fossil Teeth from China Overturn Long-held Views about Evolution of Vertebrates. Fig. 1 Life reconstruction of Qianodus duplicis. (Image by ZHANG Heming)

A remote site in Guizhou Province of south China, containing sequences of sedimentary layers from the distant Silurian period (around 445 to 420 million years ago), has produced spectacular fossil finds, including isolated teeth identified as belonging to a new species (Qianodus duplicis) of primitive jawed vertebrate. Named after the ancient name for modern-day Guizhou, Qianodus possessed peculiar spiral-like dental elements carrying multiple generations of teeth that were added throughout the life of the animal.

The tooth spirals (or whorls) of Qianodus turned out to be one of the least common fossils recovered from the site. They are small elements that rarely reach 2.5 mm and as such had to be studied under magnification with visible light and X-ray radiation.

A conspicuous feature of the whorls is that they contained a pair of teeth rows set into a raised medial area of the whorl base. These so-called primary teeth show an incremental increase in size towards the inner (lingual) portion of the whorl. What makes the whorls of Qianodus unusual in comparison with those of other vertebrates is the clear offset between the two primary teeth rows. A similar arrangement of neighboring teeth rows is also seen in the dentitions of some modern sharks but has not been previously identified in the tooth whorls of fossil species.

The discovery indicates that the well-known jawed vertebrate groups from the so-called “Age of Fishes” (420 to 460 million years ago) were already established some 20 million years earlier.

“Qianodus provides us with the first tangible evidence for teeth, and by extension jaws, from this critical early period of vertebrate evolution,” said LI Qiang from Qujing Normal University.

Unlike the continuously shedding teeth of modern sharks, the researchers believe that the tooth whorls of Qianodus were kept in the mouth and increased in size as the animal grew. This interpretation explains the gradual enlargement of replacement teeth and the widening of the whorl base as a response to the continuous increase in jaw size during development.

For the researchers, the key to reconstructing the growth of the whorls was two specimens at an early stage of formation, easily identified by their noticeably smaller sizes and fewer teeth. A comparison with the more numerous mature whorls provided the palaeontologists with a rare insight into the developmental mechanics of early vertebrate dentitions. These observations suggest that primary teeth were the first to form whereas the addition of the lateral (accessory) whorl teeth occurred later in development.

Fig. 2 Volumetric reconstruction of a tooth whorl viewed from its lingual side (holotype of Qianodus duplicis). The specimen is just over 2 mm in length. (Image by Zhu, et al.)

“Despite their peculiarities, tooth whorls have, in fact, been reported in many extinct chondrichthyan and osteichthyan lineages,”said Plamen Andreev, the lead author of the study. “Some of the early chondrichthyans even built their dentition entirely from closely spaced whorls.”

The researchers claim that this was also the case for Qianodus. They made this conclusion after examining the small (1–2 mm long) whorls of the new species with synchrotron radiation—a CT scanning process that uses high energy X-rays from a particle accelerator.

“We were astonished to discover that the tooth rows of the whorls have a clear left or right offset, which indicates positions on opposing jaw rami,” said Prof. ZHU Min from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences.

Fig. 3 Virtual section along the length of a tooth whorl in side view (holotype of Qianodus duplicis). The specimen is just over 2 mm in length (Image by Zhu, et al.)

These observations are supported by a phylogenetic tree that identifies Qianodus as a close relative to extinct chondrichthyan groups with whorl-based dentitions.

“Our revised timeline for the origin of the major groups of jawed vertebrates agrees with the view that their initial diversification occurred in the early Silurian,” said Prof. ZHU.

The discovery of Qianodus provides tangible proof for the existence of toothed vertebrates and shark-like dentition patterning tens of millions of years earlier than previously thought. The phylogenetic analysis presented in the study identifies Qianodus as a primitive chondrichthyan, implying that jawed fish were already quite diverse in the Lower Silurian and appeared shortly after the evolution of skeletal mineralization in ancestral lineages of jawless vertebrates.

“This puts into question the current evolutionary models for the emergence of key vertebrate innovations such as teeth, jaws, and paired appendages,” said Ivan Sansom, a co-author of the study from the University of Birmingham.

Press release from the Chinese Academy of Sciences about the fossil teeth overturning long-held views on the evolution of vertebrates

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