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What does the fossil record show?

Fossils provide a unique view into the history of life by showing the forms and features of life in the past. Fossils tell us how species have changed across long periods of the Earth’s history. For instance, in 1998, scientists found a fossil showing an animal at the transition from sea creature to land creature. This tetrapod had a hand-like fin, confirming a prediction of evolutionary biology. Though the fossil record does not include every plant and animal that ever lived, it provides substantial evidence for the common descent of life via evolution. The fossil record is a remarkable gift for the study of nature.

Evidence of Gradual Change

Organisms have changed significantly over time. In rocks more than 1 billion years old, only fossils of single-celled organisms are found. Moving to rocks that are about 550 million years old, fossils of simple, multicellular animals can be found. At 500 million years ago, ancient fish without jawbones surface; and at 400 million years ago, fish with jaws are found. Gradually, new animals appear: amphibians at 350 million years ago, reptiles at 300 million years ago, mammals at 230 million years ago, and birds at 150 million years ago.1 As the rocks become more and more recent, the fossils look increasingly like the animals we observe today.

The Transition to Land: Sea Creatures to Land Animals

Fossils of land animals, or tetrapods, first appear in rocks that are about 370 million years old. In older rocks, only sea creatures are found. But in 1998, scientists found a fossilized fin, 370 million years old, with eight digits similar to the five fingers humans have on their hands, as shown in Figure 1. However, the fin was undoubtedly that of a fish, which means this fossil is strong evidence of a transitional form.

Figure 1: An Illustration of the fossilized fin found in 1998. Its resemblance to a Tetrapod is an indication of gradual evolutionary change from sea creatures to land animals. Source: Image is used by permission from Darrel R. Falk, <em>Coming to Peace with Science: Bridging the Worlds between Faith and Biology</em> (Downers Grove, IL: InterVarsity Press, 2004), 113.Figure 1:An Illustration of the fossilized fin found in 1998. Its resemblance to a tetrapod is an indication of gradual evolutionary change from sea creatures to land animals. Source: Image is used by permission from Falk, Coming to Peace, 113.

One of the great success stories in the examination of the fossil record was the finding of a near-perfect fossilized transition between a vertebrate adapted for water and one adapted for land. Evolutionary biologist Neal Shubin set out to find a more complete transitional specimen than the 1998 fin. He determined the exact age of rock that he expected would yield a transitional land/water animal, and then he and his team spent four summers in the Arctic scouring rocks of that age to find one. The results (see Figure 2 below) were spectacular.2

From Reptiles to Mammals

Mammals first appeared in the fossil record about 230 million years ago, nearly 70 million years after reptiles first appeared. One group of reptiles, the cynodonts, first appeared about 260 million years ago and became increasingly mammal-like in more recent fossils—circa 245 million years ago. This change can be seen most clearly in the bone structure of the ear, as illustrated in Figure 3.

Figure 3: As shown in the image above, transitional fossils of cynodonts had two jaw hinges. These fossils date from a time when the dentary and squamosal bones were beginning to take over the role of jaw hinge (hinge #2). This allowed the articular and quadrate bones to evolve into the second and third bones of the mammalian ear, as shown on the right. Source: Image used by permission from Falk, Coming to Peace, 119. Originally from F. H. Pough, J. B. Heiser, and W. N. McFarland, Vertebrate Life, 4th ed. (Upper Saddle River, NJ: Prentice Hall, 1996), 607.

Scientists found a species of cynodonts, dating to just before the emergence of mammals, that had a double jaw hinge like that of a mammal. A pair of bones found in even earlier cynodont fossils seems to have transitioned slowly into the ear. No other fossils have been found that share a similar structure to the transitional cynodonts and date back before the time of mammals. Likewise, soon after mammals appeared, these cynodonts became extinct. This timing implies that the cynodont fossils record the transition from reptiles to mammals.3

Transitional Forms: Few and Far Between

Transitional forms occur just when one might expect to see a change from one body type to another. However, a common objection is that few transitional fossils have been discovered; thus many lineages cannot be traced smoothly.

There are several reason for these gaps in the fossil record. First, fossilization is a very rare event. Plus, transitional species tend to appear in small populations, where rapid changes in the environment can provide a stronger evolutionary drive. Finally, because fossilization itself is a rare event, smaller populations are sure to produce fewer fossils. The fact that transitional species have been found at all is remarkable, and it offers further support of gradual, evolutionary change.

Learn More


Blog article: Where are the Transitional Fossils?

By Kelsey Luoma
A common argument leveled against the theory of evolution is that scientists have not been able to produce transitional fossils that show the change of one species into another. In this podcast, we address a common misconception about what transitional fossils actually are.

Blog article: The Fossil Record

By Keith Miller
There are two opposite errors which need to be countered about the fossil record: 1) that it is so incomplete as to be of no value in interpreting patterns and trends in the history of life, and 2) that it is so good that we should expect a relatively complete record of the details of evolutionary transitions within all or most lineages.

Blog series: Evolution Basics

By Dennis Venema
Written by BioLogos Fellow of Biology Dennis Venema, this series of posts is intended as a basic introduction to the science of evolution for non-specialists.

Blog series: The Human Fossil Record

By James Kidder
In this series, James Kidder provides an intriguing study on transitional fossils and the evolutionary history of modern humans. He begins by discussing the fossil record, explaining how new forms are classified. He then explains the physically distinguishing trait of humankind—bipedalism. From the discovery of Ardipithecus, the earliest known hominin, to the australopithecines, the most prolific hominin, Kidder focuses on the discovery, the anatomy, and the interpretation of these ancestral remains.

Blog series: The Cambrian "Explosion", Transitional Forms, and the Tree of Life

By Keith Miller
Many evolutionary critics have identified the Cambrian Explosion as a stumbling block to the theory of evolution, arguing that the “expected transitions between major invertebrate phyla are absent, and that the suddenness of their appearance in the fossil record demonstrates that evolutionary explanations are not viable.” Keith Miller argues that the Cambrian Explosion is not so problematic as these opponents claim after all.


  1. Darrel Falk, Coming to Peace with Science, 83-84.
  2. For a discussion of the science and the story of the discovery, see Darrel Falk, “In the Bones” (July 29, 2009), (accessed 10/21/2011) and Stephen Matheson, “New Limbs from Old Fins, Part 2” (Sept 16, 2011), (accessed 10/21/2011). Shubin’s 2008 book Your Inner Fish (Pantheon) is also very good.
  3. Falk, Coming to Peace, 115–120; F. H. Pough, J. B. Heiser, and W. N. McFarland, Vertebrate Life, 4th ed. (Upper Saddle River, NJ: Prentice Hall, 1996), 607; M. J. Benton, Vertebrate Palaeontology: Biology and Evolution (London: Unwin Hyman, 1990), 228–231; E. H. Colbert, M. Morales, and E. C. Minkoff, Colbert’s Evolution of the Vertebrates: A History of the Backboned Animals Through Time (New York: Wiley-Liss, 2001), 274–277; T. S. Kemp, The Origin and Evolution of Mammals (New York: Oxford University Press, 2005), 75–78.