Order: PROETIDA Fortey and Owens, 1975
Superfamily: AULACOPLEUROIDEA Angelin, 1854
Family: AULACOPLEURIDAE Angelin, 1854
Subfamily: CYPHASPIDINAE Pribyl, 1947
Genus: CYPHASPIDES Novak, 1890
Diagnosis
Cyphaspides has small, widely spaced eyes on short stalks. The glabella is inflated and it is covered with numerous small and fewer large tubercles. It also has one or more rows of outward-directed slightly spinose tubercles around the front and sides of the cephalon. The genal spines are sharp and curve sideways, a bit backwards.
The thorax has between 11 and 13 segments. At this moment we advice not to use this feature to determin the name of this trilobite. It is possible that all Cyphaspides species actually have 13 segments, but that some are hidden under the cephalon. The pleural spines on the first segments of the thorax are short and point to the sides. The ones on the segments on the back are longer and these point more to the back. There are small pleural spines.
The pygidium is relatively long (for family), and has distinct marginal spines at tips of four or more pleural ribs. The pygidium is not half round, it turns back a bit in the middle. There are small pygidial spines that continue on the same line as the pleural spines.
Occurence
There are many species of Cyphaspides. We will discuss only discuss the 3 species that occur in Morocco: Cyphaspides ammari, Cyphaspides nikoleae and Cyphaspides pankowskiorum. Cyphaspides occurs in the Pragian to Givetian.
Recognizing Cyphaspides species
Cyphaspides ammari
Chatterton, Gibb and McKellar, 2019
Cephalon
Cyphaspides ammari has particularly small eyes. The eyes are also placed wider than in the other species. Genal spines are shorter than the other Cyphaspides species. The cephalon is semicircular in form. The spines on the margin are placed in at least two rows. Some are quite long when fully preserved.
Thorax
There are 13 segments in the thorax. The spines on the pleurae of the thorax are moderate in length. The tips of the thoracic segments grow longer towards the tail of the trilobite. In the beginning of the thorax they are oriented to the sides but they turn more to the back on the lower thorax segments. The axial rings are strongly arched. The axis is narrow, making up only 13% of the maximum width of the torax. There is not much sculture on the thorax, only fine tubercles or granules.
Pygidium
The pygidium is about twice as width as long. The sculpture consists of granules and single row of fine tubercles, one on each posterior pleural rib. The Pygidial axis has 12 rings plus the terminal piece. The axial rings are short and curve forward in the middle to create a V-like pattern. The first 4 or 5 segments end in a distinct marginal spine. Smaller spines are also present elsewhere on the margin of the pygidium. On the pleurae there is a tubercle on each of the first 4 or 5 segments.
Cyphaspides nicoleae
Chatterton, Gibb and McKellar, 2019
Cyphaspides nicoleae differs from Cyphaspides ammari because it has only 11 thoracic segments (versus 13 with C. ammari), but as we discussed this should not be considered as a good feature to name your Cyphasides trilobite (see above).
The genal spines and the thoracic pleural spines are distinctly longer.
The difference in size between larger and smaller tubercles in sculpture is greater (on cephalon and thoracic axis)
The eyes are closer together and slightly larger
There are fewer rows of marginal spinose tubercles on cephalon
pygidial axial furrows converge more strongly posteriorly.
Cyphaspides pankowskiorum
Chatterton, Gibb and McKellar, 2019
Cyphaspides pankowskiorum has 13 segments in the thorax.
It differs from C. nicoleae because the tubercles are not so obviously bimodal (large and small). The large tubercles are not so obviously organised in pairs. The frontal lobe of the glabella is wider and is les protruding forward. It does not overhang the anterior border. The genal spines are shorter. The spines on the margin of the cephalon are larger, shorter and blunter. The spines on the pleurae of the thorax (especially towards the pygidium) are shorter. The spines on the margin of the pygidium are larger.
It differs from C. ammari because the genal spines are longer. The tubercles of the sculpture are coarser and not organized radially. The tubercles are also less bimodal (large and small). The eyes are less stalked and not as far apart and not placed as far to the back. The spines on the margin of the cephalon are shorter and blunter. The pleural spine on the 13th thoracic segment extends beyond the pygidium. There are fewer marginal spines on the pygidium.
References
- Chatterton, B., Gibb, S., McKellar, R., 2019. Species of the Devonian aulacopleurid trilobite Cyphaspides from southeastern Morocco. Journal of Paleontology