Crotalocephalina gibbus

Crotalocephalina is an extinct genus of trilobites (fossil marine arthropods) belonging to the order Phacopida and the family Cheiruridae . This taxon—formally described by Přibyl and Vaněk in 1964—lived during the Early Devonian (≈419–383 million years ago) in marine environments of what is now North Africa, especially Morocco , where its fossils are relatively common in strata of the Ihandar/Lhandar Formation of the Northern Atlas Mountains.

From a systematic perspective , Crotalocephalina has historically been confused with, or treated as a synonym or subgenus of , Crotalocephalus , and material labeled in collections sometimes appears as Crotalocephalina (Crotalocephalus) gibbus. In taxonomic revisions based on paleontological databases such as the Paleobiology Database, Crotalocephalina is maintained as a valid genus within Cheiruridae , although with a need for revision regarding the delimitation of species and subspecies, reflecting the phylogenetic complexity of these phacopid trilobites.

From an anatomical and morphological perspective, the trilobites of this group are characterized by a calcareous dorsal exoskeleton divided into three well-defined regions —cephalon (head), segmented thorax, and pygidium (tail)—with joints that allowed for partial rolling as a defense mechanism against predators. The head (cephalon) features a prominent central glabella accompanied by well-defined axial and pleural grooves, and relatively well-developed compound eyes , indicating visual capacity adapted to life in shallow seas. The thoracic pleurae had spines or lateral projections that increased the body surface area and may have played a role in hydrodynamic stability.

The morphometrics of Crotalocephalina are poorly described in modern scientific publications, but fossils recovered from Morocco show specimens with total body lengths reaching approximately 4–7 cm or more when complete, with the cephalon occupying a significant proportion of the total length and with ornate segmental features that are useful in taxonomic identification. Cephalic ornamentation , glabella shape , and the configuration and length of the pleural spines are metric and qualitative traits used to distinguish species or groupings within the genus, although a formal modern revision that quantifies intra- and interspecific variation using statistical methods is still under development or is the subject of ongoing taxonomic work.

Paleoecology and habitat: Crotalocephalina inhabited shallow marine environments , typical of shallow continental shelves during the Devonian, when extensive warm seas covered large areas of the supercontinent Gondwana. Fossil preservation in calcareous and mudstone sediments indicates deposition on soft benthic substrates , where these trilobites could move along the seafloor, likely feeding on microbenthic organisms or organic detritus. As part of the fauna associated with phacopid trilobites and other marine invertebrates, their presence contributes to paleoenvironmental reconstructions that point to biodiverse and dynamic marine ecosystems during the Early Devonian , a critical period for the diversification of benthic arthropods and other marine groups.

Approximate measurements of the Crotalocephalina:

• Full 1:1 Scale
• Length 52 mm
• Height 32 mm
• Width 28 mm
• Snout-tail length 70 mm