TABLE 1. Moulting behaviour terminology used throughout this work. Details of the specific moult configurations described for trilobites can be found in Drage et al. (2018a). For examples see Figure 1.
| Modes of moulting used in this study | Sutural Gape mode of moulting | Mode of moulting that involves only opening of the cephalic sutures, which may comprise the facial, rostral, and/or hypostomal sutures. |
| Salter’s mode of moulting | Mode of moulting that involves only opening of the cephalothoracic joint during moulting, causing disarticulation of the cephalon. | |
| Hybrid mode of moulting | Mode of moulting combining both the Sutural Gape and Salter’s modes, with both cephalic sutures and the cephalothoracic joint opening during moulting. | |
| Generalised moult configurations used in this study | Cephalic sutures configuration | Preserved moult configurations that have variously opened cephalic sutures, and so have related cephalic sclerites disarticulated from the body (librigenae, rostral plate, and/or hypostome). This includes moults in Harrington’s, Nutcracker, and Axial Shield configurations (of Drage et al., 2018a). |
| Cephalic sutures + inversion configuration | As above, but with some of the disarticulated cephalic sclerites, usually librigenae, either horizontally or vertically flipped, as in the Somersault and McNamara’s configurations respectively (Drage et al., 2018a). | |
| Salter’s configuration | Moult configuration with the entire cephalon disarticulated at the cephalothoracic joint, and horizontally inverted compared to the remaining thoracopygon (Drage et al., 2018a). | |
| Zombie configuration | Moult configuration with the entire cephalon disarticulated at the cephalothoracic joint, and displaced from the remaining thoracopygon (Drage, 2019b). | |
| Henningsmoen’s configuration | Moult configuration resulting from the hybrid mode of moulting, with the cephalon disarticulated at the cephalothoracic joint, but also the librigenae, rostral plate, and/or hypostome disarticulated (Drage et al., 2018a). |
TABLE 2. Number of specimens and unique species included in the dataset for each trilobite order, based on taxonomy of Adrain (2011). Count of specimens and unique species for each mode of moulting and generalised moult configuration (see Table 1 definitions) included in this study. ‘?’ indicates some species-level taxonomic uncertainty. All raw specimen data available in the Appendix data file.
| Order | # species |
# specimens |
Mode of moulting | # species |
# specimens |
Generalised moult configuration | # species |
# specimens |
| Asaphida | ?43 | 109 | Sutural Gape | 35 | 90 | Cephalic sutures | 34 | 88 |
| Salter’s | 10 | 11 | Cephalic sutures + inversion | 2 | 2 | |||
| Hybrid | 8 | 8 | Henningsmoen’s | 8 | 8 | |||
| Salter’s | 3 | 3 | ||||||
| Zombie | 7 | 8 | ||||||
| Aulacopleurida | 7 | 37 | Sutural Gape | 5 | 35 | Cephalic sutures | 5 | 35 |
| Salter’s | 1 | 1 | Cephalic sutures + inversion | 0 | 0 | |||
| Hybrid | 1 | 1 | Henningsmoen’s | 1 | 1 | |||
| Salter’s | 0 | 0 | ||||||
| Zombie | 1 | 1 | ||||||
| Corynexochida | 39 | 97 | Sutural Gape | 32 | 90 | Cephalic sutures | 31 | 89 |
| Salter’s | 3 | 3 | Cephalic sutures + inversion | 1 | 1 | |||
| Hybrid | 4 | 4 | Henningsmoen’s | 4 | 4 | |||
| Salter’s | 1 | 1 | ||||||
| Zombie | 2 | 2 | ||||||
| Lichida | 3 | 4 | Sutural Gape | 2 | 2 | Cephalic sutures | 2 | 2 |
| Salter’s | 1 | 1 | Cephalic sutures + inversion | 0 | 0 | |||
| Hybrid | 1 | 1 | Henningsmoen’s | 1 | 1 | |||
| Salter’s | 1 | 1 | ||||||
| Zombie | 0 | 0 | ||||||
| Odontopleurida | 11 | 23 | Sutural Gape | 8 | 20 | Cephalic sutures | 8 | 20 |
| Salter’s | 1 | 1 | Cephalic sutures + inversion | 0 | 0 | |||
| Hybrid | 2 | 2 | Henningsmoen’s | 2 | 2 | |||
| Salter’s | 1 | 1 | ||||||
| Zombie | 0 | 0 | ||||||
| Olenida | 15 | 28 | Sutural Gape | 10 | 21 | Cephalic sutures | 10 | 21 |
| Salter’s | 1 | 1 | Cephalic sutures + inversion | 0 | 0 | |||
| Hybrid | 4 | 6 | Henningsmoen’s | 4 | 6 | |||
| Salter’s | 1 | 1 | ||||||
| Zombie | 0 | 0 | ||||||
| Phacopida | 60 | 107 | Sutural Gape | 33 | 52 | Cephalic sutures | 28 | 46 |
| Salter’s | 31 | 46 | Cephalic sutures + inversion | 5 | 6 | |||
| Hybrid | 7 | 9 | Henningsmoen’s | 7 | 9 | |||
| Salter’s | 9 | 18 | ||||||
| Zombie | 24 | 28 | ||||||
| Proetida | 9 | 13 | Sutural Gape | 7 | 11 | Cephalic sutures | 6 | 10 |
| Salter’s | 1 | 1 | Cephalic sutures + inversion | 1 | 1 | |||
| Hybrid | 1 | 1 | Henningsmoen’s | 1 | 1 | |||
| Salter’s | 0 | 0 | ||||||
| Zombie | 1 | 1 | ||||||
| ?Ptychopariida | 11 | 30 | Sutural Gape | 9 | 28 | Cephalic sutures | 11 | 28 |
| Salter’s | 0 | 0 | Cephalic sutures + inversion | 0 | 0 | |||
| Hybrid | 2 | 2 | Henningsmoen’s | 2 | 2 | |||
| Salter’s | 0 | 0 | ||||||
| Zombie | 0 | 0 | ||||||
| Redlichiida | ?36 | 169 | Sutural Gape | 26 | 145 | Cephalic sutures | 32 | 130 |
| Salter’s | 4 | 6 | Cephalic sutures + inversion | 6 | 15 | |||
| Hybrid | 9 | 18 | Henningsmoen’s | 9 | 18 | |||
| Salter’s | 3 | 5 | ||||||
| Zombie | 1 | 1 |
TABLE 3. Descriptive statistics for the dataset, displaying the mean, standard deviation, and median values for each morphometry variable, grouped by mode of moulting. The hybrid mode of moulting represents moult specimens in Henningsmoen’s configuration, with both the cephalic moulting sutures and the cephalothoracic joint opened.
| Mode of moulting |
Morphometry variable | Mean (mm) |
Standard deviation |
Median (mm) |
| Sutural Gape | thoracic tergite # | 12 | 4.2 | 11 |
| thoracic width | 22.4 | 14.8 | 17.4 | |
| thoracic length | 18.1 | 12.1 | 15.7 | |
| cephalothoracic joint width | 21.3 | 13.8 | 16.9 | |
| anterior cranidial width | 13.4 | 9.8 | 10.8 | |
| cranidial length | 13.7 | 8.6 | 11.2 | |
| pygidial width | 16.8 | 16.1 | 10.8 | |
| pygidial length | 10.1 | 10.1 | 5.9 | |
| total body length | 39.2 | 25.5 | 31.1 | |
| Salter’s | thoracic tergite # | 11 | 2.6 | 11 |
| thoracic width | 22.8 | 11.3 | 21.2 | |
| thoracic length | 20.2 | 10.8 | 18.1 | |
| cephalothoracic joint width | 20.9 | 11.7 | 18.8 | |
| anterior cranidial width | 11.7 | 4.9 | 10.6 | |
| cranidial length | 13.0 | 6.8 | 11.6 | |
| pygidial width | 17.4 | 10.5 | 15.8 | |
| pygidial length | 10.1 | 7.7 | 7.5 | |
| total body length | 40.2 | 22.6 | 35.0 | |
| Hybrid | thoracic tergite # | 12 | 3.9 | 13 |
| thoracic width | 20.4 | 13.0 | 15.7 | |
| thoracic length | 19.9 | 17.7 | 14.0 | |
| cephalothoracic joint width | 22.8 | 31.1 | 14.9 | |
| anterior cranidial width | 11.2 | 7.1 | 8.7 | |
| cranidial length | 11.7 | 7.7 | 9.8 | |
| pygidial width | 13.3 | 11.8 | 9.0 | |
| pygidial length | 7.59 | 7.2 | 5.6 | |
| total body length | 32.3 | 22.8 | 24.6 |
TABLE 4. Descriptive statistics for the dataset, displaying the mean, standard deviation, and median values for each morphometry variable, grouped by generalised moult configuration.
| Generalised moult configuration | Morphometry variable | Mean (mm) | Standard deviation | Median (mm) |
| Cephalic sutures | thoracic tergite # | 12 | 4.1 | 11 |
| thoracic width | 22.4 | 14.9 | 17.2 | |
| thoracic length | 18.0 | 12.3 | 15.5 | |
| cephalothoracic joint width | 21.3 | 13.9 | 16.8 | |
| anterior cranidial width | 13.4 | 9.9 | 10.7 | |
| cranidial length | 13.8 | 8.7 | 11.2 | |
| pygidial width | 17.1 | 16.1 | 11 | |
| pygidial length | 10.2 | 10.2 | 6.0 | |
| total body length | 39.5 | 25.9 | 30.8 | |
| Cephalic sutures + inversion | thoracic tergite # | 15 | 4.0 | 17 |
| thoracic width | 21.5 | 12.6 | 18.3 | |
| thoracic length | 23.7 | 13.0 | 22.3 | |
| cephalothoracic joint width | 21.5 | 13.2 | 17.8 | |
| anterior cranidial width | 13.7 | 7.1 | 13.8 | |
| cranidial length | 14.0 | 9.5 | 11.0 | |
| pygidial width | 11.0 | 13.0 | 5.4 | |
| pygidial length | 7.0 | 7.5 | 4.5 | |
| total body length | 33.1 | 12.9 | 33.2 | |
| Henningsmoen’s | thoracic tergite # | 12 | 3.8 | 13 |
| thoracic width | 20.4 | 13.3 | 15.4 | |
| thoracic length | 17.7 | 16.0 | 12.8 | |
| cephalothoracic joint width | 23.0 | 32.1 | 14.6 | |
| anterior cranidial width | 10.8 | 6.7 | 8.7 | |
| cranidial length | 10.8 | 5.4 | 9.7 | |
| pygidial width | 13.8 | 12.2 | 9.2 | |
| pygidial length | 7.8 | 7.5 | 5.7 | |
| total body length | 31.7 | 23.0 | 24.2 | |
| Salter’s | thoracic tergite # | 12 | 2.1 | 11 |
| thoracic width | 23.3 | 9.0 | 24.3 | |
| thoracic length | 20.3 | 7.9 | 21.3 | |
| cephalothoracic joint width | 21.0 | 8.7 | 24.5 | |
| anterior cranidial width | 12.9 | 5.1 | 12.7 | |
| cranidial length | 12.7 | 5.6 | 12.2 | |
| pygidial width | 16.7 | 9.0 | 15.5 | |
| pygidial length | 8.7 | 6.5 | 6.5 | |
| total body length | 39.4 | 16.0 | 42.9 | |
| Zombie | thoracic tergite # | 11 | 2.9 | 11 |
| thoracic width | 22.5 | 12.9 | 20.4 | |
| thoracic length | 20.1 | 12.8 | 16.6 | |
| cephalothoracic joint width | 20.8 | 13.4 | 15.4 | |
| anterior cranidial width | 11.1 | 4.7 | 9.9 | |
| cranidial length | 13.2 | 7.4 | 10.3 | |
| pygidial width | 17.9 | 11.4 | 16.4 | |
| pygidial length | 10.9 | 8.3 | 8.6 | |
| total body length | 40.5 | 25.2 | 33.7 |
