History of paleontology

The history of paleontology traces the history of the effort to understand the history of life on Earth by studying the fossil record left behind by living organisms. Since it is concerned with understanding living organisms of the past, paleontology can be considered to be a field of biology, but its historical development has been closely tied to geology and the effort to understand the history of Earth itself.

In ancient times, Xenophanes (570–480 BC), Herodotus (484–425 BC), Eratosthenes (276–194 BC), and Strabo (64 BC–24 AD) wrote about fossils of marine organisms, indicating that land was once under water. The ancient Chinese considered them to be dragon bones and documented them as such. During the Middle Ages, fossils were discussed by Persian naturalist Ibn Sina (known as ''Avicenna'' in Europe) in ''The Book of Healing'' (1027), which proposed a theory of petrifying fluids that Albert of Saxony would elaborate on in the 14th century. The Chinese naturalist Shen Kuo (1031–1095) would propose a theory of climate change based on evidence from petrified bamboo.

In early modern Europe, the systematic study of fossils emerged as an integral part of the changes in natural philosophy that occurred during the Age of Reason. The nature of fossils and their relationship to life in the past became better understood during the 17th and 18th centuries, and at the end of the 18th century, the work of Georges Cuvier had ended a long running debate about the reality of extinction, leading to the emergence of paleontology – in association with comparative anatomy – as a scientific discipline. The expanding knowledge of the fossil record also played an increasing role in the development of geology, and stratigraphy in particular.

In 1822, the word "paleontology" was used by the editor of a French scientific journal to refer to the study of ancient living organisms through fossils, and the first half of the 19th century saw geological and paleontological activity become increasingly well organized with the growth of geologic societies and museums and an increasing number of professional geologists and fossil specialists. This contributed to a rapid increase in knowledge about the history of life on Earth, and progress towards definition of the geologic time scale largely based on fossil evidence. As knowledge of life's history continued to improve, it became increasingly obvious that there had been some kind of successive order to the development of life. This would encourage early evolutionary theories on the transmutation of species. After Charles Darwin published ''On the Origin of Species'' in 1859, much of the focus of paleontology shifted to understanding evolutionary paths, including human evolution, and evolutionary theory.

The last half of the 19th century saw a tremendous expansion in paleontological activity, especially in North America. The trend continued in the 20th century with additional regions of the Earth being opened to systematic fossil collection, as demonstrated by a series of important discoveries in China near the end of the 20th century. Many transitional fossils have been discovered, and there is now considered to be abundant evidence of how all classes of vertebrates are related, much of it in the form of transitional fossils. The last few decades of the 20th century saw a renewed interest in mass extinctions and their role in the evolution of life on Earth. There was also a renewed interest in the Cambrian explosion that saw the development of the body plans of most animal phyla. The discovery of fossils of the Ediacaran biota and developments in paleobiology extended knowledge about the history of life back far before the Cambrian.

Prior to the 17th century

As early as the 6th century BC, the Greek philosopher Xenophanes of Colophon (570–480 BC) recognized that some fossil shells were remains of shellfish, which he used to argue that what was at the time dry land was once under the sea.Desmond pp. 692–697. Leonardo da Vinci (1452–1519), in an unpublished notebook, also concluded that some fossil sea shells were the remains of shellfish. However, in both cases, the fossils were complete remains of shellfish species that closely resembled living species, and were therefore easy to classify.

In 1027, the Persian naturalist, Ibn Sina (known as ''Avicenna'' in Europe), proposed an explanation of how the stoniness of fossils was caused in ''The Book of Healing''. He modified an idea of Aristotle's, which explained it in terms of vaporous exhalations. Ibn Sina modified this into the theory of petrifying fluids (''succus lapidificatus''), which was elaborated on by Albert of Saxony in the 14th century and was accepted in some form by most naturalists by the 16th century.Rudwick ''The Meaning of Fossils'' p. 24

Shen Kuo () (1031–1095) of the Song Dynasty used marine fossils found in the Taihang Mountains to infer the existence of geological processes such as geomorphology and the shifting of seashores over time. In 1088 AD, he discovered preserved petrified bamboos found underground in Yan'an, Shanbei region, Shaanxi province. Using his observation, he argued for a theory of gradual climate change, since Shaanxi was part of a dry climate zone that did not support a habitat for the growth of bamboos.Needham, Volume 3, p. 614.

As a result of a new emphasis on observing, classifying, and cataloging nature, 16th-century natural philosophers in Europe began to establish extensive collections of fossil objects (as well as collections of plant and animal specimens), which were often stored in specially built cabinets to help organize them. Conrad Gesner published a 1565 work on fossils that contained one of the first detailed descriptions of such a cabinet and collection. The collection belonged to a member of the extensive network of correspondents that Gesner drew on for his works. Such informal correspondence networks among natural philosophers and collectors became increasingly important during the course of the 16th century and were direct forerunners of the scientific societies that would begin to form in the 17th century. These cabinet collections and correspondence networks played an important role in the development of natural philosophy.

However, most 16th-century Europeans did not recognize that fossils were the remains of living organisms. The etymology of the word ''fossil'' comes from the Latin for things having been dug up. As this indicates, the term was applied to a wide variety of stone and stone-like objects without regard to whether they might have an organic origin. 16th-century writers such as Gesner and Georg Agricola were more interested in classifying such objects by their physical and mystical properties than they were in determining the objects' origins. In addition, the natural philosophy of the period encouraged alternative explanations for the origin of fossils. Both the Aristotelian and Neoplatonic schools of philosophy provided support for the idea that stony objects might grow within the earth to resemble living things. Neoplatonic philosophy maintained that there could be affinities between living and non-living objects that could cause one to resemble the other. The Aristotelian school maintained that the seeds of living organisms could enter the ground and generate objects resembling those organisms.

Leonardo da Vinci and the development of paleontology

Leonardo da Vinci established a line of continuity between the two main branches of paleontology: body fossil palaeontology and ichnology. In fact, Leonardo dealt with both major classes of fossils: (1) body fossils, e.g. fossilized shells; (2) ichnofossils (also known as trace fossils), i.e. the fossilized products of life-substrate interactions (e.g. burrows and borings). In folios 8 to 10 of the Leicester code, Leonardo examined the subject of body fossils, tackling one of the vexing issues of his contemporaries: why do we find petrified seashells on mountains? Leonardo answered this question by correctly interpreting the biogenic nature of fossil mollusks and their sedimentary matrix. The interpretation of Leonardo da Vinci appears extraordinarily innovative as he surpassed three centuries of scientific debate on the nature of body fossils. Da Vinci took into consideration invertebrate ichnofossils to prove his ideas on the nature of fossil objects. To da Vinci, ichnofossils played a central role in demonstrating: (1) the organic nature of petrified shells and (2) the sedimentary origin of the rock layers bearing fossil objects. Da Vinci described what are bioerosion ichnofossils:Baucon, A. 2010. Da Vinci’s ''Paleodictyon'': the fractal beauty of traces. Acta Geologica Polonica, 60(1). Available from th
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‘‘The hills around Parma and Piacenza show abundant mollusks and bored corals still attached to the rocks. When I was working on the great horse in Milan, certain peasants brought me a huge bagful of them’’

— Leicester Code, folio 9r

Such fossil borings allowed Leonardo to confute the Inorganic theory, i.e. the idea that so-called petrified shells (mollusk body fossils) are inorganic curiosities. With the words of Leonardo da Vinci:

‘‘ he Inorganic theory is not truebecause there remains the trace of the nimal’smovements on the shell which tconsumed in the same manner of a woodworm in wood …’’

— Leicester Code, folio 9v

Da Vinci discussed not only fossil borings, but also burrows. Leonardo used fossil burrows as paleoenvironmental tools to demonstrate the marine nature of sedimentary strata:

‘‘Between one layer and the other there remain traces of the worms that crept between them when they had not yet dried. All the sea mud still contains shells, and the shells are petrified together with the mud’’

— Leicester Code, folio 10v

Other Renaissance naturalists studied invertebrate ichnofossils during the Renaissance, but none of them reached such accurate conclusions. Leonardo's considerations of invertebrate ichnofossils are extraordinarily modern not only when compared to those of his contemporaries, but also to interpretations in later times. In fact, during the 1800s invertebrate ichnofossils were explained as fucoids, or seaweed, and their true nature was widely understood only by the early 1900s. For these reasons, Leonardo da Vinci is deservedly considered the founding father of both the major branches of palaeontology, i.e. the study of body fossils and ichnology.

17th century

During the Age of Reason, fundamental changes in natural philosophy were reflected in the analysis of fossils. In 1665 Athanasius Kircher attributed giant bones to extinct races of giant humans in his ''Mundus subterraneus''. In the same year Robert Hooke published ''Micrographia'', an illustrated collection of his observations with a microscope. One of these observations was entitled "Of Petrify'd wood, and other Petrify'd bodies", which included a comparison between petrified and ordinary wood. He concluded that petrified wood was ordinary wood that had been soaked with "water impregnated with stony and earthy particles". He then suggested that several kinds of fossil sea shells were formed from ordinary shells by a similar process. He argued against the prevalent view that such objects were "Stones form'd by some extraordinary Plastick virtue latent in the Earth itself". Hooke believed that fossils provided evidence about the history of life on Earth writing in 1668:

...if the finding of Coines, Medals, Urnes, and other Monuments of famous persons, or Towns, or Utensils, be admitted for unquestionable Proofs, that such Persons or things have, in former times had a being, certainly those Petrifactions may be allowed to be of equal Validity and Evidence, that there have formerly been such Vegetables or Animals... and are true universal Characters legible to all rational Men.Bowler ''The Earth Encompassed'' (1992) pp. 118–119

Hooke was prepared to accept the possibility that some such fossils represented species that had become extinct, possibly in past geological catastrophes.

In 1667 Nicholas Steno

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