VERTEBRATES IN TIME

when each group appeared · five hundred million years on one axis

Built as a memo rather than a table: the thing worth hanging it up for reads across the room, with the full reference in smaller type below it.

Three sizes in one archive — from a sheet on the fridge to a poster on the wall.

Formats: A4 · A3 · A2
What you get: Print-ready PDFs, one per size, with every letterform converted to outlines — nothing to install, nothing to shift.
Subject: science · school · reference · classroom

A bar begins at the age of the oldest known find, hence the "≈": it is a lower bound, not a measurement. A cross marks extinction. The dashed verticals are the five mass extinctions. Period boundaries follow the ICS scale.

THE FOOTPRINTS ON LAND ARE OLDER THAN THE BONES THAT MADE THEM

A quarry at Zachełmie near Kielce holds footprints 395 million years old — Eifelian, Middle Devonian, securely dated by the marine rock around them. The oldest known skeleton of a four-legged animal is thirty million years younger.

For thirty million years, then, vertebrates walked the shallows and left us tracks but no bones. On this sheet that interval is drawn as a dashed outline: where the bar is not yet solid, the animal was there and the fossil is not.

The moral is wider than the one case. A date of first appearance on any such chart is the age of the oldest find, not the age of the group. It can only get older: a new discovery moves it back, never forward.

On the sheet

A bar begins at the age of the oldest known find, hence the "≈": it is a lower bound, not a measurement. A cross marks extinction. The dashed verticals are the five mass extinctions. Period boundaries follow the ICS scale.
Colour carries meaning, but meaning never rests on colour alone — the sheet reads in black and white.
Nothing about how it was made: the sheet carries only what the reader needs.

Printing

Three sizes in the archive: A4 — 210×297 mm, A3 — 297×420 mm, A2 — 420×594 mm.
All text is converted to outlines. No fonts to install, and nothing shifts on another machine.
White background and sparing fills — it prints on a home printer without draining the cartridge.
Margins of at least 10 mm: a home printer cannot print to the edge.
No stroke thinner than 0.3 mm, so nothing disappears in print.

Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 7 independent checks before it is allowed to build — how many items there are, the order they come in, and the claim in the highlighted box itself. If one fails, there is no file.

VERTEBRATES IN TIME

THE FOOTPRINTS ON LAND ARE OLDER THAN THE BONES THAT MADE THEM

On the sheet

Printing

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THE VERTICAL PLANET

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BASIC PHYSICS FORMULAS

ANIMALS