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Cephalaspis

Adventurer · ages 7–10Adapted from Wikipedia
An artist's reconstruction of Cephalaspis lyelli, an ancient armored jawless fish that lived in the Devonian period, over 350 million years ago.

The name Cephalaspis comes from two Greek words: Greek kephalḗ, meaning "head," and Greek aspís, meaning "shield." It is an extinct genus of jawless fish.

Cephalaspis is the most famous genus of the Osteostraci, a group of extinct Palaeozoic fish with armoured heads and no jaws. These fish are sometimes called "ostracoderms."

The type species of the genus, C. lyelli, was described in 1835. Its fossils were found in Old Red Sandstone rocks in Scotland. These rocks are from the early Devonian period (Lochkovian). However, this species is not well preserved. Many other species have since been placed in the genus. Scientists sometimes sort them into the group because they share features common to many osteostracans, which makes it a wastebasket taxon.

Description

Diagram of an osteostracan headshield. "orb" =orbit/eye socket, "med f." =median field, "lat f."=lateral fields, "cor" =cornual process/horn, "cor.ser"= cornual serrations

The holotype specimen of Cephalaspis lyelli would have been about 24.5 centimetres (9.6 in) long when alive. In 2026, El Fassi El Fehri and colleagues defined sensu stricto Cephalaspis more narrowly. Its head shield has few small bumps, called tubercles, on its upper surface. Its front part (rostral) tapers to a point, and the area behind its eyes is narrow. Its side grooves reach onto horns at the back edge of the head shield. The pineal plate is joined to the head shield. The body had a smooth outer layer, and it had a pair of pectoral fins.

Its mouth was under its head, so Cephalaspis is thought to have been a bottom-feeder. It was similar to a heavily armoured catfish or sturgeon. It moved its plow-like head from side to side. This stirred up sand and dust in the water and uncovered hidden food, such as worms, arthropods, and other small animals in the mud and algae. It also sifted through detritus. Scientists think this partly because it had no jaws and could not bite. Osteostracans were likely also able to sense electrical fields (electroreception).

Classification

Cephalaspis was the first "ostracoderm" to be given a scientific name. The genus has long been used as a wastebasket taxon, which is a name for a group that holds many different species. Agassiz created it in 1835 with four species. The type species, C. lyelli, was found in Old Red Sandstone rocks near Glamis, Angus, in the Midlands Valley of Scotland. These rocks are from the Early Devonian (Lochkovian) period. Some of the other species were later found to be parts of the heterostracan Pteraspis rostratus. C. lyelli was named after Sir Charles Lyell. It was kept as the type species of the genus.

Because it was the earliest described "ostracoderm," scientists argued for a long time about where it belonged among fish. Agassiz thought it was one of the most primitive fish known. William Patten thought it was somewhere between arthropods and fish. Today it is placed in the Osteostraci, a group of armoured jawless fish. These are among the closest known relatives of jawed vertebrates. Over time, many similar-looking species were added to the genus. A 2009 study found that only C. lyelli could be reliably placed in it. A 2026 study moved many former species into new genera. It kept three species as true members of the genus, including C. lyelli.

Cephalaspis lyellii reconstruction

Quiz time!

4 questions about Cephalaspis

Question 1 of 4

What do the two Greek words in the name Cephalaspis mean?

Pictures

An artist's reconstruction of Cephalaspis lyelli, an ancient armored fish that lived in the Devonian period, hundreds of millions of years ago.
An artist's reconstruction of Ateleaspis tesselata, a small, armored, jawless fish that lived hundreds of millions of years ago.
An artist's reconstruction of Hemicyclaspis murchisoni, an ancient armored fish that lived in the Devonian period, hundreds of millions of years ago.
A digital recreation of an ostracoderm, an armored, jawless fish that lived hundreds of millions of years ago during the Silurian and Devonian periods.
An artist's reconstruction of Zenaspis pagei, an ancient armoured fish that lived hundreds of millions of years ago.
A reconstruction of Thyestes verrucosus, an ancient armored jawless fish that lived in the seas of the Late Silurian period, about 420 million years ago. Its fossils have been found on Saaremaa Island in Estonia.
A computer-generated reconstruction of Boreaspis rostrata, a small armored jawless fish that lived in the Early Devonian period, around 400 million years ago. Fossils of this creature have been found in Spitsbergen, Norway.
A fossil of Cephalaspis, an ancient armored fish that lived about 400 million years ago, on display at a natural history museum in Bergamo, Italy.
A fossil of Cephalaspis, an ancient armoured fish that lived hundreds of millions of years ago, found in England and displayed at a museum.
A fossil of Pleuroceras solare, an ammonite (an extinct sea creature related to squid and octopuses) that lived about 180 million years ago during the Jurassic period.
An artist's reconstruction of Wladysagitta janvieri, an ancient armored fish that lived during the Early Devonian period, over 400 million years ago.

Keep exploring

Greek language
Old Red Sandstone
Devonian
Lochkovian
Sturgeon
Ostracoderm

This article is a child-friendly adaptation of the Wikipedia article on Cephalaspis, available under CC BY-SA 4.0.

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