Prehistoric Arachnids

Spiders, scorpions, and their ancient relatives have stalked the land for over 430 million years — some reaching terrifying sizes in the oxygen-rich Carboniferous.

Time Range

430 Ma–Present

First scorpions

~430 Ma

First spiders

~380 Ma

Status

Extant class

Overview

Arachnids — spiders, scorpions and their relatives — were among the first terrestrial predators, leaving the water by the Silurian. Their fossil record includes giant Carboniferous scorpions, the earliest known spider webs, and exquisite amber-preserved faunas.

Quick Facts

Geological Range

Silurian (~430 Ma) – Present

Major Habitat

Primarily terrestrial; earliest scorpions were aquatic or amphibious

Known Genera

Species Documented

Data currently being expanded.

Registry Specimens

0 — grows with the Global Registry

Countries Represented

Data currently being expanded.

Key Characteristics

•Eight walking legs and body of prosoma and opisthosoma
•Chelicerae mouthparts (fangs in spiders)
•Book lungs and/or tracheae for air breathing
•Spinning silk from abdominal spinnerets — spider webs preserved in amber
•Some Carboniferous scorpions reached over 70 cm leg-span

Fossil Record

Terrestrial arachnids appear in the Rhynie Chert (Scotland) and Coal Measures; Mazon Creek preserves trigonotarbids; Cretaceous ambers (Myanmar, Lebanon) contain complete spiders with silk and webs.

Global Distribution

Global where terrestrial sediments preserve fine detail — Europe, North America and Cretaceous amber deposits.

Evolutionary & Scientific Importance

Arachnids record the conquest of land by chelicerates, the evolution of silk and flightless aerial predation, and the persistence of body plans for over 400 million years.

Classification

Kingdom

Animalia

Phylum

Arthropoda

Subphylum

Chelicerata

Class

Arachnida

Major orders

Araneae (spiders) · Scorpiones · Trigonotarbida (extinct) · Ricinulei · pseudoscorpions and mites (acarids)