←

Stratum Quarterly · Core Log No. 249

Five hundred million years, read downward.

A single continuous column of the Phanerozoic, drawn strictly to scale: every period band is as tall as it is long. Scroll and the sight-line reads your depth in millions of years. Fossils are pinned at the horizon where they were actually found.

Ma

Era

Strata

Horizon notes

508 Ma

Marrella splendens

Lace crab · Burgess Shale

The most abundant animal in the quarry and still the strangest: a lattice of backswept spines over a body no longer than a thumbnail.

  • Bed Phyllopod
  • Count 15,000+

470 Ma

Isotelus rex

Giant trilobite · Churchill float

Seventy centimetres of armoured plate, ploughing a warm epicontinental sea floor for worms.

  • Bed Boas River
  • Length 720 mm

425 Ma

Cooksonia pertoni

Early vascular plant · Welsh borders

A green stem two centimetres tall with a sporangium on top. Land begins here, at this line in the mudstone.

  • Bed Ludlow
  • Height 22 mm

385 Ma

Tiktaalik roseae

Fishapod · Ellesmere Island

Flat skull, mobile neck, wrist bones inside a fin. Found by walking a frost-shattered slope for four summers.

  • Bed Fram Fm.
  • Field season 4

360 Ma

Dunkleosteus terrelli

Armoured placoderm · Cleveland Shale

No teeth — self-sharpening bone shears that closed in a fiftieth of a second. Only the head ever fossilises.

  • Bed Cleveland
  • Bite ~6,000 N

315 Ma

Arthropleura armata

Coal-forest millipede · Northumberland

Two and a half metres of segmented arthropod, recorded mostly as trackways across a fossil sand bar.

  • Bed Stainmore
  • Trace Diplichnites

290 Ma

Dimetrodon grandis

Sail-backed synapsid · Red Beds

Closer to us than to any dinosaur. The sail's spines carry healed fractures — these animals fought.

  • Bed Arroyo
  • Spines 26

250 Ma

Lystrosaurus murrayi

Disaster taxon · Karoo Basin

Immediately above the great extinction boundary, one barrel-chested burrower makes up most of every bone bed for a thousand kilometres.

  • Bed Katberg
  • Share of fauna ~90%

230 Ma

Eoraptor lunensis

Early dinosaur · Valle de la Luna

A metre long, lightly built, unremarkable in its own ecosystem. Everything after it inherits the posture.

  • Bed Ischigualasto
  • Mass ~10 kg

152 Ma

Archaeopteryx lithographica

Feathered theropod · Solnhofen

Lithographic limestone so fine it holds the barbs of each primary feather. Twelve specimens in a century and a half.

  • Bed Altmühltal
  • Specimens 12

100 Ma

Spinosaurus aegyptiacus

River predator · Kem Kem beds

Dense limb bone, paddle tail, retracted nostrils. The first large dinosaur read convincingly as a swimmer.

  • Bed Gara Sbaa
  • Tail fin-like

68 Ma

Tyrannosaurus rex

Apex theropod · Hell Creek

Two million years below the iridium layer. Growth rings say it put on two kilograms a day through its teens.

  • Bed Hell Creek
  • To boundary 2 Ma

52 Ma

Icaronycteris index

Earliest bat · Green River

Flight fully formed, echolocation not yet. Preserved in varved lake shale with its last meal of moths still in place.

  • Bed Fossil Butte
  • Wingspan 370 mm

23 Ma

Proconsul africanus

Stem ape · Rusinga Island

No tail, flexible wrists, a forest canopy quadruped. The branch we are on starts thickening here.

  • Bed Hiwegi
  • Mass ~17 kg

3.2 Ma

Australopithecus afarensis

Upright hominin · Hadar

Forty per cent of one skeleton, and a pelvis that settles the argument: walking came long before the large brain.

  • Bed Denen Dora
  • Complete 40%