TABLE 1. Definitions relating to trilobite moulting used within this work.

Moulting configuration The general term for any assemblage of disarticulated exoskeletal units (sclerites) produced through the behaviours of a moulting individual. This is left behind and becomes preserved in the fossil record (see Drage et al., 2018a).
Style of moulting The generalised type of exoskeleton moulting, involving a number of moulting characteristics, which produces a moulting configuration. There are two main styles, involving use of the cephalic sutures (facial, rostral, hypostomal, and median), or use of the cephalothoracic joint (joining the cephalon or cranidium to the thoracopygon), although a single moult specimen can show both of these together. A third unusual style involves the use of a marginal suture running laterally along the anterior margin of the entire cephalon.
Moulting characteristic Any of the characteristic exoskeletal disarticulations produced during moulting, and found in a moulting configuration. Specifically, opening of the facial sutures and/or ventral sutures, and disarticulation of the cranidium, cephalon, thorax, and/or pygidium.

The ‘normal’ moulting characteristic is the one of these that is most commonly produced during moulting for a particular species.

Exuviation The stage of moulting during which the organism actually sheds the old exoskeleton.
Exuvial gape The opening produced in the old exoskeleton through which the organism exuviates.

 

 

TABLE 2. Summary of moulting behaviour for the seven trilobite orders.

Order1 Usual style
of moulting
Moulting
characteristics2
#
species
#
specimens
Geological range
Asaphida Cephalic sutures 1. Facial sutures
=2. Thorax
=2. Pygidium
3. Cephalon
4. Cranidium
5. Ventral sutures
61 150 Miaolingian - late Silurian
Corynexochida Cephalic sutures 1. Facial sutures
2. Cranidium
3. Thorax
=4. Cephalon
=4. Pygidium
5. Ventral sutures
44 112 Cambian Series 2 - Early Devonian
Lichida Cephalic sutures 1. Facial sutures
=2. Cephalon
=2. Ventral sutures
=2. Thorax
=2. Pygidium
3. Cranidium
18 33 Middle Ordovician - Middle Devonian
Phacopida Cephalothoracic joint 1. Cephalon
2. Facial sutures
3. Thorax
4. Pygidium
5. Cranidium
6. Ventral sutures
93 140 Middle Ordovician - Late Devonian
Proetida Cephalic sutures 1. Facial sutures
2. Cephalon
3. Thorax
4. Cranidium
=5. Pygidium
=5. Ventral sutures
22 21 Late Ordovician - early Permian
Ptychopariida Cephalic sutures 1. Facial sutures
2. Thorax
3. Cranidium
4. Pygidium
5. Ventral sutures
6. Cephalon
71 169 Cambrian Series 2 - Late Ordovician
Redlichiida Cephalic sutures 1. Facial sutures
2. Ventral sutures
3. Cranidium
4. Thorax
5. Pygidium
6. Cephalon
46 207 Cambrian Series 2 - Miaolingian

1For each order the number of species and specimens representing them in the dataset is given, and their geological age range.
2The six moulting characteristics are in sequence from most to least common amongst species of that order.