Arthropleura

I’ll start. This is a artistic rendition of a fern forest from the Devonian:

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What I’d really be interested in is a reconstruction of a colony of Prototaxites. There is currently one online, but it’s not very good.

“Fossil firsts” are fascinating because they clue us in to the age of both extant and extinct lineages, and provide a peek into an older time, when ecosystems were very different. Many of them signify a branching point on the tree of life. Some of these fossil firsts gave rise to thousands or even millions of distinct species in their ancestry, yet started off so simple and humble. Let’s take a look at some of the pioneer species in the evolution of life on Earth…

This post will cover the Precambrian through the Devonian.

Oldest evidence for multicellular life: “discoidal impressions and trace-like fossils”
Age: 2.0 - 1.2 billion years old, Stirling Range Formation
More information: BBC coverage
Quote: “the structures… suggest the presence of vermiform, mucus-producing, motile organisms”

Oldest likely arthropod: Spriggina floundensi
Age: 550 million years ago, Ediacaran
Distinguishing characteristics: genal spines, trilobite-like head, segmented body plan
Note: the affinity of Spriggina is under debate, but at least some researchers classify it as a ecdysozoan (arthropod or very closely related)

Oldest hard-shelled fossil: Namapoikia reitogensis
Age: 550 million years ago, Ediacaran
Distinguishing features: fully mineralized shell
Affinity: unknown, probably cnidarian or poriferan

Oldest fish: Myllokunmingia fengjiaoa
Age: 530 million years ago, Lower Cambrian, Chengjiang fauna
Distinguishing features: gills and a zigzag arrangement of muscles called myotomes
Note: also the first known chordate

Oldest jellyfish: “Exceptionally Preserved Jellyfishes”
Age: 505 million years ago, Middle Cambrian, Marjum Formation of Utah
Distinguishing characteristics: bell-shape, tentacles, muscle scars
More information: NY Times coverage

Oldest land animal: Pneumodesmus newmani
Affinity: millipede
Age: 428 million years old, Silurian
Distinguishing feature: spiracles used for breathing air
Note: trace fossils of myriapods are known from 450 million years ago

Oldest insect: Rhyniognatha hirsti
Age: 400 million years ago, Devonian, Rhynie Chert
Distinguishing features: mandibles with two points of articulation, possible wings

Oldest tree: Wattieza
Age: 380 million years ago, Devonian
Distinguishing features: taller trunks, more reproductive methods, leaf development
Unusual feature: reproduced with spores

One of the earliest known animals, and the first known bilateral animal, is Vernanimalcula guizhouena, from the Doushantuo phosphate formation in China. Dates for the oldest Doushantuo fossils, which include the first multicellular embryos, are variously cited from 580 Ma to 600 Ma, though the truth is that dating methods aren’t precise enough to determine the exact age. Here is a diagram of the animal:

Other animals found along with Vernanimalcula were various cnidarians and sponges. According to a recent genetic survey, it seems like basal metazoans were cnidarians rather than sponges, which is quite fascinating. Among other things, tells us that the earliest animals probably had a coelom (fluid-filled body cavity). The most numerous multicellular animal today, representative of all life, the nematode, has a pseudocoelom that probably evolved from a true coelom.

This fossil is from immediately after the Marinoan glaciations.The Marinoan glaciations are a controversial topic for many reasons, but two are: 1) scientists disagree on whether the Earth’s oceans froze solid during this period, 2) some believe that multicellular life emerged only after the ice thawed. To me, 2 seems unlikely. There is some evidence of trace fossils from a billion years ago, but even ignoring this, I think it’s only a matter of time before microscopic multicellular fossils from the Cryogenian (older than 600 million years ago), or more definitive trace fossils are found.

The evolution of trilobites is damn impressive. Below, check out a fossil trilobite from the mid Cambrian, about 500 million years ago:

This trilobite is under an inch long. Next, take a look at Terataspis grandis, a trilobite from the Devonian, which lived approximately 400 million years ago:

Terataspis grandis was a giant spiny trilobite whose name means “great monster shield”. It was one of the largest trilobites, at 2 feet in length. Trilobites obviously had to evolve some serious defenses to survive the predators of the Devonian. Like most other trilobites, Terataspis was wiped out in the end Devonian extinctions 364 million years ago. Here is a reconstruction: