Slugs, sponges, fish, dinosaurs and mammals like us. True animals or metazoans are all multicellular eukaryotic organisms from planet Earth that fall into the biological kingdom of Animalia.
But what does all of that mean?
The best way to find out is to take a trip back in time to when the first true animals appeared on Prehistoric Earth…
About True Animals
Scientific Classification
Domain: Eukaryota
Clade: Amorphea; Holozoa
Kingdom: Animalia
Time Frame
Molecular Clock: Proterozoic, 1.5 bn years ago animals split from fungi
Biomarker Data: Cryogenian, 635–650 million years ago (Sponges) – contested!
First Trace Fossil: Ediacaran, 560–551 million years ago (Helminthoidichnites)
First Body Fossil: Ediacaran, 560–551 million years ago (Ikaria Wariootia, proposed maker of Helminthoidichnites trace fossil) – proposed!
What are True Animals (Animalia) Exactly?
All the animals you recognise and love – from your pets to wild animals, dinosaurs, birds, fish and even us humans – are what we call eukaryotic organisms. That’s because our bodies are built out of a complex type of cell called a eukaryote.
See, for billions of years, all life on Earth was not only microscopic and single-celled, the first types of cells were very small and loosely organised prokaryotes – cells without a nucleus and the many organelles we have in our cells today.
Bacteria and Archaea are still prokaryotic, which has a disadvantage – prokaryotes cannot form complex multicellular organisms like us animals.
Somewhere around 2 billion years ago, though, in the Proterozoic Eon (2.5bn to 538.8m years ago), prokaryotic bacterial cells developed a symbiotic relationship with some other prokaryotes and gave birth to specialised cell organelles like chloroplasts (what plants use to photosynthesize) and mitochondria (oxygen-powered energy sources inside your cells), and eukaryotes were born.
Eukaryotes would go on to become us animals, plants and fungi.
What Separates Us True Animals from Other Eukaryotes?
If plants and fungi are also eukaryotes, what makes us animals different? Well, plants and fungi are also technically multicellular, and we’re certainly very distantly related, but we animals evolved much more diversity of cell types.
While plants and fungi evolved only about 10–20 different types of cells in their bodies, we true animals evolved way more – over 100 to 150 different types.
In a way, you could say that what distinguishes true animals (Animalia) from plants and fungi is the fact that we are truly multicellular – we animals have orders of magnitude more cell types than other eukaryotes.
When and Where Were the First True Animal Fossils Found?
According to molecular clock data (a technique that uses DNA and genes to determine when an organism/clade/family diverged from ancestors), the first animals are thought to have split from fungi about 1.5 billion years ago (Hedges, S.B. et al. 2004).
And DA Gold et al. 2016 suggested that biomarker data shows sponges (who are totally true animals) might have been around 650 million+ years ago in the Cryogenian, but that’s contested by I Bobrovskiy et al. 2020 who say their work isn’t accurate and those markers could have been made by algae.
For years, we thought the first animal trace fossils were from the Ediacaran in Uruguay, but scientists now believe those rocks might have been dated wrongly (Verde et al. 2022). An Australian Ediacaran trace fossil from 560–551 million years ago called Helminthoidichnites is now proposed as the first trace fossil of a bilaterian animal.
What’s more, SD Evans et al. 2020 suggest that a proposed Ediacaran bilaterian called Ikaria Wariootia, from the same Australian rocks, is the first body fossil and the maker of those traces.
Other Ediacaran fossils, such as Kimberalla, Dickinsonia and even Charnia Masoni (which also falls into the kingdom of Animalia and potentially eumetazoa) have been proposed as proof of true animals in the Ediacaran.
But, of course, as soon as you go into the Cambrian (538–485 million years ago) you have undeniably true animal fossils of Porifera (sponges), ancestors of Cnidaria (corals and jellyfish) and bilaterians such as Mollusks, Arthropods, Annelida (worms), Brachiopods (bivalves that look like clams), Echinoderms (Starfish, urchins), Chordates and even the first Vertebrates.
What Creatures (Phylums) Fall Under Animalia?
True animals, aka Metazoa, aka Animalia, are represented by these phyla:
- Porifera (sponges)
- Cnidarians (corals, sea anemones, jellyfish)
- Echinoderms (starfish, sea urchins, sea cucumbers and other deuterostomes)
- Chordates (lancelets, tunicates and all vertebrates – all fish, amphibians, reptiles, birds, mammals and other deuterostomes)
- Brachiopods (shelled marine creatures resembling bivalve molluscs and other protostomes)
- Annelids (segmented worms like ragworms, earthworms, leeches and other protostomes)
- Molluscs (snails, gastropods and cephalopods like octopus, cuttlefish and other protostomes)
- Arthropods (crustaceans, insects, spiders, scorpions and other protostomes)
- Nematodes (largely parasitic roundworms or eelworms and other protostomes)
- Platyhelminthes (flatworms like the tapeworm and other protostomes)
Also discover the exciting next chapter on animals called eumetazoa and which animals would go on to become bilateria.
Fossil locations: Where can you go to see First Animal fossils?
If you live nearby or can make the trip, there are a few great places to go and see some of the first animals for yourself…
1. Mistaken Point, Newfoundland Canada
Although it’s on the other side of the world, the Mistaken Point Ecological Reserve in Newfoundland’s Avalon Peninsula in Canada is of the same Avalon Assemblage as the original Charnia specimen. And it has loads more examples of Charnia and other Ediacaran biota.
It’s a UNESCO World Heritage site. And there’s an area of 5.7km of rocks with various Ediacran fossils all over the place. Not to mention it’s a beautiful place just on its own.
Email MistakenPointTour@gov.nl.ca to book a tour
Or visit their website for more info
2. Ediacaran Hills, Australia
Although not part of the same assemblage, the Ediacaran Hills in the Flinders Ranges of mountains in Southern Australia (about 650km from Adelaide) are extremely important. This is where the first Ediacaran trace fossils were discovered. It’s where the Ediacaran gets its name.
The White Sea Assemblage here is both younger and from shallower water than where the original Charnia was first found in the UK. But some forms of Charnia were also found here, as were the first trace and body fossils of bilateria.
Email hello@ediacarafoundation.org to book a tour
Or visit their website for more info
3. Royal Ontario Museum’s Burgess Shale (Cambrian) Experiences
The Royal Ontario Museum in Toronto, Canada is famous for its connection to the world-famous Cambrian site, the Burgess Shale. They have both an amazing fossil collection if you visit in-person or even here online and a cool virtual sea odyssey you can experience online right now.
Phone: 416 586 8000 (Canada)
Or visit their website
Documentaries featuring the First Animals
They’re not always 100% accurate because we make new scientific discoveries all the time. But documentaries at least deliver the gist of the information in a fun and engaging way. Just click play, hit full screen and enjoy hours’ worth of awesome documentaries on first animals, right here…
1. First Life
David Attenborough, BBC, 2010
Episode 1 of David Attenborough’s First Life features the discovery of Charnia and the evolution of the first complex life. It was produced by the BBC in 2010. You can also buy it on DVD or Blu-ray via Amazon. And it is available to watch in some regions via Prime Video.
2. David Attenborough’s Rise of Animals: Triumph of the Vertebrates
BBC, 2013
Although more focused on the evolution of vertebrates, it’s still an awesome documentary to watch. It’s available to purchase from Amazon.
3. Australia: The Time Traveller’s Guide
ABC, 2012
Despite focusing more on the geology of early Earth, later episodes in the series unpack some wonderfully bizarre first animals and plants from down under. You can also buy it via Amazon.
4. Walking with Monsters
BBC, 2005
A bit older now and flashing past early animals a bit too quickly, this one in the “Walking With” series is still pretty cool for its Cambrian bits. It’s also available via Amazon.
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Enjoy the journey of discovery through Earth’s ancient past, geology, big ideas and, of course, awesome prehistoric life.
