Paleontologists are having a field day over a recently discovered trove of fish fossils that could reset our understanding of human evolution. The finds not only include the world's oldest teeth, but also strengthen the evidence for the emergence of jaws and limbs. Essentially, these discoveries could push back our understanding of humans' early animal ancestors by about 10 million years.
The international team responsible for these remarkable finds was led by Zhu Min of the Institute of Vertebrate Palaeontology and Palaeoanthropology (IVPP) in Beijing, China and was detailed in a quartet of papers published Wednesday in Nature.
The fossils date between 436 and 439 million years ago, during an epoch known as the Silurian Period, in which Earth experienced some dramatic events (such as developing an ozone layer) that had big impacts on the evolution of life. By the end of the Silurian, jawed fishes began to appear; the advantage of jaws is that it makes for better hunters, which allowed such fish to better pass down their genes. Indeed, having a jaw is quite an evolutionary advantage.
Many of the creatures in the oceans were quite squishy, meaning that they are less apt to survive in the fossil record. In general, scientists have relied on scraps and stray fossils of such animals to formulate theories on how life arose on Earth during this era, but these new discoveries reveal in greater detail what critters were like almost half a billion years ago.
Discovered near Lianghe village in Hunan Province, T. vividus resembled an ice cream cone with a massive bony shield around its head.
"The new fossils change everything. Now we know how big they are, what they look like, how they evolved over time," Zhu told Reuters. In terms of size, most of these fossils were quite small — but they have big implications.
One paper analyzed more than 1000 specimens of an extinct spiny shark-like fish called Fanjingshania renovata, so named because it was found near Mount Fanjingshan. It may be the oldest jawed ancestor of humans, pushing back the previous record by about 20 million years.
Another paper describes Tujiaaspis vividus, an extinct jawless fish whose name refers to the Tujia people, a minority ethnic group in China. Discovered near Lianghe village in Hunan Province, T. vividus resembled an ice cream cone with a massive bony shield around its head, making it what's called a galeaspid. What's amazing about this find is how intact the specimen is compared to previous finds.
"The anatomy of galeaspids has been something of a mystery since they were first discovered more than half a century ago," Gai Zhikun, the study's lead author and a professor at IVPP, said in a statement. "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."
These fossils lend weight to the "fin-fold theory," which describes how fish developed fins that separated and eventually evolved into legs. In other words, this is some of the earliest and strongest evidence for a leading theory on how humans eventually got our limbs.
Then there's a paper describing two new species. The first is Xiushanosteus mirabilis, a tiny placoderm, a type of jawed fish that was covered in armor. The other is Shenacanthus vermiformis, an early shark relative. However, unlike sharks (which have tiny scales) S. vermiformis is armored with plates that cover its body.
"Only 20 years ago it was still believed that sharks [were] primitive and other jawed fish evolved from a shark-like archetype. Now with the discovery of Shenacanthus, we can finally make certain that the opposite is true," the study's lead author Zhu You'an, associate research professor at IVPP, said in a statement. Both discoveries may change the timeline for when jawed vertebrates first emerged.
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The last paper describes the least complete fossil specimen out of the four, with just 23 teeth — still, enough information to identify the earliest direct evidence for jawed vertebrates like ourselves. The fish is called Qianodus duplicis, which was found in Guizhou province and had the oldest teeth of any animal previously known. Its mouth was filled with paired rows of tooth whorls, and like many first drafts, the teeth don't really resemble the pearly whites we typically think of. They're more of spiky blobs, like the back of a blue shell from "Mario Kart."
Nonetheless, this toothy discovery pushes back the date for the evolution of teeth by about 14 million years. It means a lot more activity was happening in the Silurian period (around 439 million years ago) than we thought.
It may seem weird to think about, but there really was a point in the evolutionary timeline when teeth didn't exist. Same for eyes, brains and even anuses. Each of these anatomical features arose through natural selection over millions of years. While there are many gaps in the fossil record, they are being filled in all the time and this recent dump of published results gives fascinating insight into where we acquired our teeth, our jaws, our limbs and essentially our human bodies.