Creationism in Crisis
A Large Trove of 'Transitional' Fossil Fish Shows How Jawed, Tetrapod Vertebrates Evolved
A Large Trove of 'Transitional' Fossil Fish Shows How Jawed, Tetrapod Vertebrates Evolved
According to a series of news items from the Chinese Academy of Sciences last September, which somehow passed beneath my radar, two huge collections of fossils in southwestern Chongqing municipality and Guizhou province, in China, in strata which have been dated to the Silurian Period that began around 440 million years ago, are providing new information about the evolution of fishes and the jawed vertebrates that eventually evolved into terrestrial tetrapods. These were direct ancestors of today’s amphibians, reptiles, mammals and birds.
These finds resulted in four articles in Nature which sadly lie behind paywalls, but according to one of the news releases:
…Chinese researchers reported finding fish fossils that provided the "missing link" about the origin of the jaw, a key trait that gave rise to 99.8 percent of all vertebrate species living on Earth today, from giant whales to humans.One fossil fish in particular, Tujiaaspis vividus, is especially interesting in that it shows primitive fins developing into what would become the terrestrial tetrapod limbs. What started as 'fin folds' were differentiating into front (pectoral) fins and rear (pelvic) fins that were to set the pattern of locomotion for its descendants and become the forerunners of the front and real limbs of the tetrapods.
It is the first time for China to publish this many studies by one research team in a single issue of the prestigious journal, which stands as a testament to the importance of the findings and for China's global recognition as a powerhouse in paleontology, experts said.
Deng Tao, the director of the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, said the recent breakthroughs represented China's original contribution to the basic sciences regarding evolution.
Deng said China's support for archaeology and paleoanthropology is one of the key reasons for the nation's recent discoveries. Having a wealth of unique and well-preserved fossil specimens and the advanced scientific instruments to study them, as well as extensive international collaborations are also beneficial, he added.An artist's impression of jawed fish dating back 440 million years.
Photo/China Daily
Zhu Min, a researcher from the institute who led the studies, said the findings drew a large amount of interest from the publisher and the international scientific community because the jaw is a game-changing innovation for vertebrates.
However, the rise of the jaw has been a mystery as the majority of early jawed vertebrate fossils found have been from the beginning of the Devonian period about 419 million years ago, but scientists have hypothesized that the origin of jawed vertebrates should have occurred about 450 million years ago or even earlier.[The jaw] allows the animal to bite and consume food, rather than rasping and funneling nutrients into their bodies like hagfish and lampreys, the only surviving lineages of jawless fish.
These fossils provide an unprecedented opportunity to peek into the 'dawn of fish' and help scientists trace many human body structures back to these ancient fish, thus filling some key gaps in the evolutionary history of how fish evolved into humans.
Therefore, there had been a massive 30-million-year gap in our paleontological record that wasn't filled for decades until now.
Zhu Min, Lead researcher Institute of Vertebrate Paleontology and Paleoanthropolgy
Chinese Academy of Sciences
The latest findings made by Zhu's team presented a set of five exceptionally well-preserved fish fossils from the early Silurian period, which contained three whole-bodied fish that helped scientists paint a more accurate evolutionary picture of the origin of the jaw.
In general, these fossils showed that jawed fish were already thriving in the ancient oceans at least 440 million years ago. By the late Silurian period, more diverse and larger jawed fish had evolved and began to spread around the world, paving the way for some fish to eventually go on land and evolve into other animals.
The fossil set included a 3-centimeter-long placoderm, an armored prehistoric fish that was the earliest known jawed vertebrate called Xiushanosteus mirabilis. This fossil shed light on the evolution of the skull for jawed vertebrates.
Another fossil was from a spiny shark-like fish that has a skeleton primarily composed of cartilage called Shenacanthus vermiformis. Unlike other cartilaginous fish species such as sharks and rays, this ancient fish had armor plates more commonly associated with placoderms, thus revealing a previously unknown diversification.
In another paper, scientists described the features of a type of galeaspids called Tujiaaspis vividus, a species of armored jawless fish known only from China and northern Vietnam.
This fossil specimen was about 436 million years old and showed the primitive feature of paired fins before they separated into pectoral and pelvic fins, the precursors that later became our arms and legs."It's really an awesome, game-changing set of fossil discoveries. It rewrites almost everything we know about the early history of jawed animal evolution.
John Long
Former president of the Society of Vertebrate Paleontology (Quoted in China Daily)
The other studies described the fossil of a cartilaginous fish called Fanjingshania renovate, and fossil teeth from a previously unknown shark relative named Qianodus duplicis. Both specimens dated back to around 439 million years ago.
The Fanjingshania renovate fossil provided evidence supporting the theory that jawed vertebrates had witnessed increased taxonomic diversity during the early Silurian period. The teeth specimen was the oldest of its kind from jawed vertebrates to date.
This fossil fish is the subject of a paper in Nature by a Bristol University team.
Life reconstructions of Tujiaaspis vividus
Image: ZHENG Qiuyang
Life reconstructions of Tujiaaspis vividus
Image: ZHENG Qiuyang
The holotype specimen and its interpretative drawing of Tujiaaspis vividus from 436 million years old rocks of Chongqing, China
Image: Gai, et al.
Tujiaaspis vividus
Video: IVPP
Fanjingshania renovata
Video: IVPP
The new fossils are spectacular, preserving the whole body for the first time and revealing that these animals possessed paired fins that extended all the way from the back of the head to the very tip of the tail. This is a great surprise since scientists had thought galeaspids lack paired fins altogether.
This "fin-fold" hypothesis has been very popular, but it has lacked any supporting evidence until now. The discovery of Tujiaaspis resurrects the fin-fold hypothesis and reconciles it with contemporary data on genetic control of the embryonic development of fins in living vertebrates.Tujiaaspis breathes new life into a century old hypothesis for the evolution of paired fins, through differentiation of pectoral (arms) and pelvic (legs) fins over evolutionary time from a continuous head-to-tail fin precursor.
Professor Philip C. J. Donoghue, corresponding author
Bristol Palaeobiology Group
School of Earth Sciences
University of Bristol, Bristol, UK
Tujiaaspis shows the "primitive condition" for the evolution of paired fins, according to Prof. ZHU, who said that later jawless fish showed the first evidence for the separation of this fin-fold into pectoral and pelvic fins. Prof. ZHU also noted that the vestiges of elongate fin-folds could be seen in the embryos of living jawed fishes, which could be manipulated to produce them.
Bristol’s Dr. Humberto Ferron, a co-author, used computational engineering approaches to simulate the behaviour of models of Tujiaaspis with and without the paired fins.The paired fins of Tujiaaspis act as hydrofoils, passively generating lift for the fish without any muscular input from the fins themselves. The lateral fin-folds of Tujiaaspis allowed it to swim more efficiently.
Humberto G. Ferrón, co-author
Bristol Palaeobiology Group
School of Earth Sciences
University of Bristol, Bristol, UK
And Instituto Cavanilles de Biodiversidad i Biología Evolutiva
Universitat de València, Valencia, Spain
[Dr Keating] noted that the primitive fins evolved musculature and skeletal support that allowed our fish ancestor to better steer their swimming and add propulsion.Our new analyses suggest that the ancestor of jawed vertebrates likely possessed paired fin-folds, which became separated into pectoral and pelvic regions.
It is amazing to think that the evolutionary innovations seen in Tujiaaspis underpin locomotion in animals as diverse as birds, whales, bats, and humans.
Dr. Joseph N. Keating, co-author
Bristol Palaeobiology Group
School of Earth Sciences
University of Bristol, Bristol, UK.
With evidence such as this hoard of fossils with its examples of 'transition' from jawless to jawed vertebrates and then from primitive skin folds to fins and from fins running the length of the body to bilateral, pectoral and pelvic fins, setting the pattern for tetrapodal locomotion in terrestrial vertebrates and gaps in the fossil record being filled with scientific evidence not neededing magic, no wonder creationist cult leaders need to work so hard to recruit new fools into their money-making and right-wing political cults.
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