What Was the First Animal on Earth? Tracing the Origins of Animal Life

The question of the first animal on Earth does not have a single settled answer. Scientists currently identify several candidate groups, including sponges, comb jellies, and the soft-bodied organisms of the Ediacaran biota, each supported by different lines of fossil and molecular evidence. This article synthesizes the leading hypotheses, explains how paleontologists and geneticists date the origin of animals, and presents the evidence in a timeline format for students, researchers, and life-science professionals.

The Scope of the Question

When researchers ask what the first animal was, they are asking about the most recent common ancestor of all living animals, often called the last common animal ancestor. This organism lived hundreds of millions of years ago and left no direct fossil record. Scientists therefore reconstruct its features by comparing living animal groups and by dating the branching points in the animal family tree using molecular clocks.

The search involves two distinct lines of evidence. Fossil evidence provides physical remains of ancient organisms, but early animals were mostly soft-bodied and rarely preserved. Molecular evidence uses differences in DNA sequences among living animals to estimate when lineages diverged. These two approaches sometimes agree and sometimes conflict, which is why the identity of the first animal remains an active research question.

The Animal Kingdom in Context

Animals are one of several major branches of eukaryotic life. The most unique feature of Earth is the existence of life, and the most extraordinary feature of life is its diversity, with approximately 9 million types of plants, animals, protists, and fungi inhabiting the planet [4]. Animals are distinguished from other eukaryotes by their multicellular organization, heterotrophic nutrition, and typically motile sperm cells.

The closest living relatives of animals are the choanoflagellates, single-celled organisms that resemble the collar cells found in sponges. This relationship places the origin of animals within a broader radiation of multicellular life that also produced fungi and several algal groups. Understanding the first animal therefore requires understanding the transition from single-celled ancestors to multicellular organisms with differentiated cell types.

The Ediacaran Biota: The First Large Complex Life Forms

The Ediacaran biota is a group of soft-bodied organisms that lived between roughly 575 and 541 million years ago, before the Cambrian explosion. These organisms are preserved in sandstone beds around the world, most famously in the Ediacara Hills of South Australia, Newfoundland, Namibia, Russia, and the United Kingdom.

What the Ediacaran Fossils Show

Ediacaran fossils include frond-like forms such as Charnia, quilted organisms such as Dickinsonia, and discoid forms such as Aspidella. Many of these organisms do not resemble any living animal group. Some paleontologists interpret them as early animals, while others argue they represent extinct experiments in multicellularity that left no living descendants.

The preservation of Ediacaran fossils is unusual. Many are preserved as impressions on the bases of sandstone beds, suggesting they were buried by event deposits of sediment. The absence of burrows and trails in most Ediacaran assemblages indicates that these organisms lived on or just above the seafloor and did not move through sediment.

The Challenge of Interpreting Ediacaran Biology

The biological affinities of Ediacaran organisms remain contested. Some researchers propose that frond-like forms were colonial bacteria or protists. Others argue that the quilted appearance of Dickinsonia and related forms indicates a unique body plan unrelated to any living phylum. A third interpretation places some Ediacaran organisms within the animal stem lineage, meaning they branched off before the common ancestor of living animal groups.

The discovery of fossilized fat molecules in Dickinsonia specimens has been cited as evidence that this organism was an animal. However, the interpretation of these molecular fossils depends on assumptions about how organic molecules degrade over hundreds of millions of years. The debate illustrates the difficulty of assigning ancient soft-bodied organisms to living groups.

Sponges: The Traditional Candidate for First Animal

Sponges, phylum Porifera, are often considered the most ancient living animal group. They lack true tissues, muscles, and nerves. Their bodies consist of a system of canals and chambers lined with collar cells that capture food particles from water. This simple body plan has led many researchers to place sponges at the base of the animal family tree.

Fossil Evidence for Ancient Sponges

The oldest claimed sponge fossils are tiny structures interpreted as spicules, the mineral elements that support sponge bodies. Some of these spicules have been reported from rocks dated to around 760 million years ago, although their identification is disputed. More secure sponge fossils appear in the Cambrian period, when sponge body fossils and abundant spicules become common.

The Ediacaran biota includes some forms that resemble sponges, such as the genus Palaeophragmodictya, which has a mesh-like body plan. However, the preservation of these fossils is too coarse to confirm the presence of sponge-specific features such as spicules or a distinct canal system.

Molecular Support for Sponge Ancestry

Molecular phylogenies, which reconstruct evolutionary relationships from DNA sequences, often place sponges as the sister group to all other animals. This position means that sponges branched off first, and all other animals, including comb jellies, cnidarians, and bilaterians, share a more recent common ancestor.

The sponge-first hypothesis is consistent with the idea that animal evolution proceeded from simple to complex body plans. Under this view, the first animal resembled a simple sponge, and features such as nerves, muscles, and digestive systems evolved later in lineages leading to other animal groups.

Comb Jellies: A Challenging Alternative

Comb jellies, phylum Ctenophora, are marine predators that use sticky cells called colloblasts to capture prey. They move using rows of cilia, and some species have a simple nerve net. Despite their apparently simple body plan, several molecular phylogenies place comb jellies as the sister group to all other animals, even below sponges.

The Molecular Evidence for Comb Jelly Ancestry

The comb jelly-first hypothesis emerged from phylogenomic studies that compared large numbers of genes across animal groups. These studies found that comb jellies branched off before sponges, making them the most ancient living animal lineage. If this result is correct, the first animal had nerves and muscles, and sponges lost these features secondarily.

This hypothesis is controversial because it contradicts the traditional view that animal complexity increased over time. It also requires that sponges, which lack nerves and muscles, descended from an ancestor that had these structures. Some researchers argue that the comb jelly-first result is an artifact of the methods used to analyze the data, caused by the rapid evolution of comb jelly genes.

The Debate Over Comb Jelly Placement

The placement of comb jellies at the base of the animal tree remains unresolved. Different analytical methods and different gene datasets produce conflicting results. Some studies support the sponge-first hypothesis, while others support the comb jelly-first hypothesis. A third possibility places sponges and comb jellies together in a group that branched off before the cnidarians and bilaterians.

The resolution of this debate matters for understanding the first animal. If comb jellies are the most ancient living animals, then the last common animal ancestor had a nervous system and muscle-like cells. If sponges are the most ancient, then the first animal was a simple filter feeder without these features.

Molecular Clocks and the Timing of Animal Origins

Molecular clocks estimate the time of evolutionary divergence by measuring the number of genetic differences between living species and calibrating the rate of change using fossil dates. These estimates place the origin of animals between roughly 800 and 650 million years ago, during the Cryogenian period.

How Molecular Clocks Work

Molecular clocks rely on the assumption that genetic changes accumulate at a roughly constant rate over time. Researchers calibrate the clock using fossil dates for known divergence events, such as the split between vertebrates and invertebrates or between insects and crustaceans. They then apply the calibrated rate to estimate the timing of deeper divergences, including the origin of animals.

The results of molecular clock analyses depend heavily on the choice of calibration points and the statistical model used. Different studies have produced estimates ranging from over 800 million years ago to less than 600 million years ago. This uncertainty makes it difficult to correlate the origin of animals with specific environmental events.

The Cryogenian and the Origin of Animals

The Cryogenian period, from roughly 720 to 635 million years ago, included episodes of global glaciation known as Snowball Earth events. Some researchers propose that these glaciations created selective pressures that drove the evolution of multicellular animals. Others argue that animals originated after the glaciations, during a period of increasing oxygen levels and nutrient availability.

The fossil record does not resolve this timing question. The oldest widely accepted animal fossils appear in the Ediacaran period, after the Cryogenian glaciations. However, molecular clocks suggest that animal lineages diverged earlier, during or before the glaciations. The gap between molecular estimates and fossil evidence remains a major unresolved issue.

The Cambrian Explosion and the Diversification of Animals

The Cambrian period, beginning around 541 million years ago, saw the rapid appearance of most major animal body plans in the fossil record. This event, often called the Cambrian explosion, marks the transition from the soft-bodied Ediacaran biota to the shelly and skeletal fossils that dominate later Paleozoic rocks.

What the Cambrian Fossil Record Shows

Cambrian deposits such as the Burgess Shale in Canada and the Chengjiang biota in China preserve soft-bodied animals in exceptional detail. These deposits contain early representatives of arthropods, annelids, mollusks, and chordates, along with many extinct groups that do not fit into living phyla.

The sudden appearance of diverse animal body plans in the Cambrian has been interpreted as a rapid evolutionary radiation. However, molecular clocks suggest that many animal lineages diverged before the Cambrian, meaning their origins are hidden in the Ediacaran fossil record or in unfossilized lineages.

The Relationship Between Ediacaran and Cambrian Animals

The relationship between Ediacaran organisms and Cambrian animals is unclear. Some Ediacaran forms, such as the segmented organism Kimberella, have been interpreted as early mollusks. Others, such as the burrow-forming organisms that produced trace fossils, may have been early bilaterians. However, most Ediacaran body fossils do not show clear features that link them to Cambrian animal groups.

The transition from the Ediacaran to the Cambrian also involved ecological changes. Ediacaran ecosystems were dominated by mat-ground communities with little burrowing activity. Cambrian ecosystems saw the appearance of predators, burrowing animals, and animals that disturbed the seafloor. These ecological changes may have driven the diversification of animal body plans.

The Last Common Animal Ancestor

The last common animal ancestor is the hypothetical population from which all living animals descended. Reconstructing this ancestor requires combining evidence from living animal groups, fossils, and molecular clocks.

Features of the Last Common Animal Ancestor

Based on comparisons of living animals, the last common animal ancestor likely had the following features: multicellularity with differentiated cell types, a method of cell-cell communication, a body plan with at least two germ layers, and a mechanism for producing collagen and other extracellular matrix proteins. Whether it had a nervous system depends on the placement of comb jellies in the animal tree.

The ancestor probably lived in the ocean and was small, possibly microscopic. It may have resembled a simple planktonic or benthic organism that fed on bacteria and organic particles. The transition from a single-celled ancestor to this multicellular organism involved the evolution of cell adhesion molecules, signaling pathways, and developmental gene regulatory networks.

The Role of Developmental Biology

Understanding the first animal also requires understanding how novel complex traits arise. Work on the origins of insect wings has shown that novel structures can emerge through the modification, fusion, and elaboration of ancestral component parts [8]. This principle likely applies to the origin of animals as well. The first animal probably arose through the co-option of genes and cell behaviors that existed in its single-celled ancestors.

The evolution of animal multicellularity involved the appearance of genes for cell adhesion, cell signaling, and transcriptional regulation. Many of these genes are present in choanoflagellates, the closest living relatives of animals. The transition to animal multicellularity therefore involved the reorganization of existing genetic toolkits instead of the invention of entirely new genes.

The Search for the Earliest Animal Fossils

The oldest claimed animal fossils are controversial. Researchers have reported sponge spicules from rocks dated to around 760 million years ago, but these identifications are disputed. Other claims include fossil embryos from the Doushantuo Formation in China, dated to around 600 million years ago, and possible animal trace fossils from even older rocks.

The Doushantuo Embryos

The Doushantuo Formation in South China preserves microscopic fossils that resemble animal embryos in early stages of development. These fossils consist of clusters of cells enclosed in a membrane, and some show evidence of cell division. If these are animal embryos, they would push the origin of animals back to around 600 million years ago.

However, the interpretation of Doushantuo fossils is contested. Some researchers argue that they are not embryos but rather the resting cysts of single-celled eukaryotes. Others suggest they could be the remains of bacteria or algae. The absence of adult fossils associated with the embryos makes it difficult to confirm their animal affinities.

The Limits of Fossil Preservation

The fossil record of early animals is limited by preservation. Soft-bodied organisms are rarely fossilized, and the earliest animals were likely small and delicate. The appearance of abundant animal fossils in the Ediacaran and Cambrian periods may reflect changes in preservation conditions as much as changes in animal diversity.

The development of biomineralization, the ability to produce mineral skeletons, greatly improved the preservation potential of animals. The first biomineralizing animals appeared near the end of the Ediacaran period, and their skeletons became common in the Cambrian. The evolution of biomineralization was likely driven by predation pressure and the advantages of skeletal support.

At a Glance: Candidate First Animals

Practical Assessment Steps for Evaluating Evidence

Researchers and students evaluating claims about the first animal should follow a structured approach to assess the quality of evidence.

Step 1: Identify the Type of Evidence

Determine whether the claim is based on fossils, molecular data, or developmental biology. Each type of evidence has different strengths and limitations. Fossil evidence provides direct physical remains but is incomplete. Molecular evidence provides quantitative estimates of divergence times but depends on assumptions about evolutionary rates. Developmental evidence provides insights into how traits evolve but cannot directly date the origin of animals.

Step 2: Evaluate the Phylogenetic Method

For molecular studies, assess the choice of genes, the number of taxa included, and the analytical methods used. Studies that include more genes and more taxa generally produce more reliable results. Check whether the authors tested alternative hypotheses and whether their results are robust to changes in the analysis.

Step 3: Assess the Fossil Interpretation

For fossil claims, examine whether the specimens preserve features that are diagnostic of the proposed group. Sponge spicules must show the characteristic shapes and internal structures of sponge spicules. Embryo-like fossils must show patterns of cell division consistent with animal development. Consider whether alternative interpretations, such as algal or protistan affinities, have been excluded.

Step 4: Compare Independent Lines of Evidence

The strongest conclusions come from studies that integrate multiple lines of evidence. A phylogenetic hypothesis that is supported by both molecular and morphological data is more reliable than one supported by only a single data type. Similarly, a divergence time estimate that is consistent with the fossil record is more credible than one that requires a long gap between molecular and fossil dates.

Records and Measurements in Paleontological Research

Paleontological research on early animals relies on careful documentation of fossil specimens and their geological context.

Geological Context

The age of a fossil is determined by the age of the rock in which it is found. Researchers use radiometric dating of volcanic ash layers, which can be precisely dated using the decay of radioactive isotopes. They also use biostratigraphy, the correlation of rock layers based on their fossil content, and chemostratigraphy, the correlation of layers based on chemical signatures such as carbon isotope ratios.

Specimen Documentation

Fossil specimens must be documented with detailed photographs, drawings, and descriptions. Type specimens, the specimens that define a species, are deposited in museum collections where other researchers can examine them. The discovery location, stratigraphic position, and associated fossils are recorded for each specimen.

Molecular Data Deposition

Molecular phylogenies are based on DNA sequence data that must be deposited in public databases such as GenBank, which is maintained by the National Center for Biotechnology Information [1]. Researchers can search for published sequences and phylogenetic analyses through PubMed, the database of biomedical literature maintained by the National Library of Medicine [2]. Access to these databases allows other researchers to reproduce and verify molecular analyses.

Common Failure Patterns in Early Animal Research

Several recurring problems affect research on the origin of animals.

Overinterpretation of Fragmentary Fossils

Small, fragmentary fossils are often assigned to animal groups based on limited features. Spicule-like structures could be produced by non-sponge organisms, and embryo-like clusters could be produced by algae or protists. The most reliable identifications require multiple diagnostic features and careful comparison with living organisms.

Reliance on Single Molecular Markers

Early molecular phylogenies of animals were based on single genes, such as ribosomal RNA. These studies produced conflicting results because single genes do not contain enough information to resolve deep evolutionary relationships. Modern phylogenomic studies use hundreds or thousands of genes, but even these can produce misleading results if the analytical methods are inappropriate.

Circular Reasoning in Molecular Clock Calibration

Molecular clock analyses require calibration points from the fossil record. If the fossil record is incomplete, the calibration points may be too young, causing the clock to underestimate divergence times. Conversely, if fossils are misidentified, the calibration points may be too old, causing overestimates. Researchers must carefully justify their choice of calibration points.

Confirmation Bias in Interpretation

Researchers may interpret ambiguous evidence in ways that support their preferred hypothesis. A fossil that resembles a sponge may be described as a sponge if the researcher favors the sponge-first hypothesis, while a researcher who favors the comb jelly-first hypothesis may interpret the same fossil differently. Independent evaluation by multiple research groups helps reduce this bias.

Limitations of Current Knowledge

The identity of the first animal remains unresolved because of fundamental limitations in the available evidence.

The Incompleteness of the Fossil Record

The earliest animals were likely small, soft-bodied organisms with low preservation potential. The fossil record of the Cryogenian and early Ediacaran periods is sparse, and many lineages probably left no fossils at all. The absence of fossils cannot be used as evidence that animals did not exist at a particular time.

The Uncertainty of Molecular Clocks

Molecular clocks provide estimates, not exact dates. The confidence intervals around molecular divergence estimates are often wide, spanning tens of millions of years. Different analytical methods can produce substantially different estimates, and the choice of calibration points has a major influence on the results.

The Difficulty of Interpreting Ancient Soft-Bodied Organisms

Ediacaran organisms do not closely resemble living animals, making their interpretation difficult. The features used to classify living animals, such as the presence of a gut, nerves, or muscles, are rarely preserved in Ediacaran fossils. Researchers must infer these features from indirect evidence, such as body shape and surface texture.

The Problem of Extinct Lineages

The animal family tree includes many extinct lineages that branched off before the origin of living animal groups. These lineages may have had combinations of features that do not exist in living animals. Reconstructing the first animal from living groups alone may therefore miss important aspects of early animal evolution.

Welfare and Safety Context

Research on early animals does not involve live animals, so animal welfare concerns are limited. However, researchers who study living animals for comparative purposes must follow institutional animal care guidelines. Fieldwork to collect fossils may involve safety considerations, including work in remote locations, handling of heavy equipment, and compliance with local fossil collection regulations.

Researchers should also consider the ethical dimensions of their work. The study of biodiversity loss and its impact on humanity highlights the importance of understanding the history of life on Earth [4]. The extinction of ancient animal groups, such as the placoderms, which were the most abundant and diverse vertebrates for over 70 million years before their extinction at the end of the Devonian [6], provides context for understanding modern biodiversity crises.

Professional Escalation Criteria

Students and early-career researchers who encounter disagreements about the identity of the first animal should seek guidance from more experienced researchers. The following situations warrant professional consultation:

• When a molecular phylogeny produces a result that conflicts with well-established morphological evidence
• When a fossil identification would require revising the age of a major animal group
• When a molecular clock estimate differs from fossil evidence by more than 100 million years
• When a researcher proposes to name a new species or revise the classification of a major group

Researchers should also consult the primary literature through databases such as PubMed [2] and the National Center for Biotechnology Information [1] to verify that their understanding of the evidence is current.

The Role of Comparative Biology

Comparative biology provides essential evidence for reconstructing the first animal. By comparing the genomes, development, and anatomy of living animals, researchers can infer the features of their common ancestor.

Genomic Comparisons

The genomes of living animals contain genes that were present in the last common animal ancestor. Comparisons of gene content across animal groups reveal which genes are ancestral and which are derived. For example, the presence of genes for cell adhesion and signaling in both sponges and comb jellies indicates that these genes were present in the common ancestor.

Developmental Comparisons

Comparisons of embryonic development across animal groups reveal conserved developmental processes. The genes that pattern the body axes of bilaterian animals, such as Hox genes, are also present in cnidarians and some other non-bilaterian groups. The evolution of these developmental toolkits was a key step in the origin of animal body plans.

Morphological Comparisons

Comparisons of adult anatomy across animal groups reveal the features that are shared by all animals. These shared features, such as the presence of collagen and the use of gap junctions for cell communication, were likely present in the last common animal ancestor. The absence of these features in non-animal groups helps define the boundary of the animal kingdom.

The Future of Early Animal Research

The search for the first animal continues to advance with new methods and new discoveries.

New Fossil Discoveries

Ongoing fieldwork in Ediacaran and Cryogenian rocks around the world continues to produce new fossils. Discoveries in Namibia, China, Siberia, and other regions have expanded the known diversity of early animals and their relatives. Each new discovery provides an opportunity to test existing hypotheses about the origin of animals.

Advances in Molecular Methods

Improvements in DNA sequencing and analytical methods are providing more reliable estimates of animal relationships and divergence times. The inclusion of more taxa and more genes in phylogenomic analyses is resolving some long-standing controversies, although new debates continue to emerge.

Integration of Evidence

The most promising approach to understanding the first animal is the integration of fossil, molecular, and developmental evidence. Researchers who combine these lines of evidence can test hypotheses more rigorously than those who rely on a single data type. The development of methods for combining morphological and molecular data in a single analysis is a major advance.

Frequently Asked Questions

Why is there no single answer to what the first animal was?

The first animal lived hundreds of millions of years ago and left no direct fossil record. Scientists reconstruct its identity from molecular comparisons of living animals and from fossils of early animal relatives, but these lines of evidence sometimes conflict. The placement of comb jellies and sponges at the base of the animal tree remains unresolved, which means the features of the first animal are still uncertain.

What is the difference between the first animal and the last common animal ancestor?

The first animal is the earliest organism that can be classified as an animal. The last common animal ancestor is the population from which all living animals descended. These may be the same population, but the first animal could also be an earlier lineage that branched off before the common ancestor of living animals. The distinction matters because extinct early animal lineages may not be represented in the living animal tree.

How do molecular clocks estimate the age of the first animal?

Molecular clocks measure the number of genetic differences between living species and use a calibrated rate of genetic change to estimate when lineages diverged. The rate is calibrated using fossils with known ages. Molecular clock estimates for the origin of animals range from roughly 800 to 650 million years ago, but the results depend heavily on the choice of calibration points and analytical methods.

What is the Ediacaran biota and why is it important?

The Ediacaran biota is a group of soft-bodied organisms that lived between roughly 575 and 541 million years ago. These organisms are the oldest large complex life forms in the fossil record. Some Ediacaran organisms may be early animals, but their biological affinities are contested. The Ediacaran biota is important because it represents the transition from microscopic life to the large multicellular organisms that dominate modern ecosystems.

Why are sponges considered a candidate for the first animal?

Sponges have the simplest body plan of any living animal group. They lack true tissues, nerves, and muscles, and they feed by filtering particles from water. Molecular phylogenies often place sponges as the sister group to all other animals, meaning they branched off first. If this is correct, the first animal resembled a simple sponge.

Why are comb jellies considered a candidate for the first animal?

Some phylogenomic studies place comb jellies as the sister group to all other animals, even below sponges. Comb jellies have nerves and muscle-like cells, which would mean the first animal had these features. This hypothesis is controversial because it requires that sponges lost nerves and muscles secondarily, and some researchers argue the result is an artifact of analytical methods.

What is the Cambrian explosion and how does it relate to the first animal?

The Cambrian explosion was a period of rapid diversification of animal body plans beginning around 541 million years ago. Most major animal groups appear in the fossil record during this period. The Cambrian explosion does not mark the origin of animals, which occurred earlier, but it marks the appearance of abundant animal fossils with hard skeletons and complex ecologies.

How can I evaluate claims about the first animal?

Evaluate the type of evidence presented, the methods used, and whether the conclusions are supported by multiple independent lines of evidence. Check whether fossil identifications are based on diagnostic features and whether molecular analyses include sufficient data and appropriate methods. Compare the claims with the primary literature available through databases such as PubMed [2] and the National Center for Biotechnology Information [1].

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References and Further Reading

• NCBI Literature Resources. National Center for Biotechnology Information.
• PubMed. National Library of Medicine.
• What is the placenta?. American journal of obstetrics and gynecology, 2015.
• Biodiversity loss and its impact on humanity.. Nature, 2012.
• Plesiosaurs.. Current biology : CB, 2023.
• Placoderms.. Current biology : CB, 2024.
• Manganese.. Journal of toxicology. Clinical toxicology, 1999.
• Taking flight!. Developmental biology, 2025.
• Magnetoreception in fish.. Journal of fish biology, 2019.
• Unravelling UVA-induced mutagenesis.. Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology, 2012.
• Space Research Ethics.. 2026.
• Life science research in extreme environments: a conversation with astronaut Jessica Meir.. 2026.
• Weaving and Binding: Immigrant Gods and Female Immortals in Ancient Japan. 2011.
• From the Blogosphere. Nature, 2009.
• Making the paper: Marcel Kuypers. Nature, 2009.
• What is the Unit of Intelligence? Artificial Intelligence, Relational Ethics and the Earth System. Topoi, 2025.
• A history of grounding and earthing practices in the United States: Part 1: A discussion of how the earth has been used for electrical conduction through the 1920s. IEEE Industry Applications Magazine, 2019.
• Motivated science: What humans gain from denying animal sentience. Animal Sentience, 2021.
• Evolving animals: The story of our Kingdom. Evolving Animals the Story of Our Kingdom, 2014.
• Duties to Not Harm Ecological Systems, Plants, and Animals. Routledge Handbook of Applied Climate Change Ethics, 2023.
• EXTINCT ANIMALS: An Encyclopedia of Species That Have Disappeared during Human History. Extinct Animals an Encyclopedia of Species that have Disappeared During Human History, 2009.

This article is educational and does not replace institutional policy, professional advice, or applicable safety and regulatory requirements.