Casiogrammus Wilson, 2005

Álvarez-Rodríguez, Michelle, Riquelme, Francisco, Hernández-Patricio, Miguel & Magaña, Fabio Cupul-, 2024, Diplopoda in the world fossil record, Zoological Systematics 49 (3), pp. 185-245 : 201-202

†Genus Casiogrammus Wilson, 2005

(25) † Casiogrammus ichthyeros Wilson, 2005

Casiogrammus icthyeros Wilson, 2005b: 1104 , pl. 1, figs 1–2.

Referred material: Holotype: NMS G.1970.2. Preservation: Impression. Repository: NMS. Locality: UK, South Lanarkshire, Smithy Burn , Hagshaw Hills Inlier. Horizon: Fish Bed Formation , Middle Silurian.

Comments: Preliminarily, Rofle (1980: 550) states that the oldest terrestrial arthropod was a probable myriapod named Archidesmus loganensis from the Middle Silurian Fish Bed Formation. According to Rofle (1980: 550, fig. 4A), A. loganensis resembles a possible juliform with 20 ornate segments. However, as this fossil is fragmented and poorly preserved, its taxonomic identity must be clarified. Almond (1985: 229–230, fig. 1) placed A. loganensis in the Middle Silurian (ca. 438 Ma) before K. obanensis from the Upper Silurian (ca. 408 Ma). But, he claimed that A. loganensis is not a myriapod. It is more like a form of alga. Wilson & Anderson (2004) also concluded that A. loganensis is more of a plant or alga. Wilson (2005b) later described another fragmentary fossil specimen from the Fish Bed Formation: Casiogrammus ichthyeros . According to Wilson (2006), C. ichthyeros belongs to the order Zosterogrammida . In a stratocladogram, Shear & Edgecombe (2010) placed C. ichthyeros in the oldest fossil record of Myriapoda, including other Diplopoda genera: Albadesmus , Cowiedesmus , and Pneumodesmus (Wilson & Anderson, 2004) . Edgecombe (2015) included C. ichthyeros in a summary taxonomic list of Diplopoda. Selden (2019) stated that C. ichthyeros is the oldest known millipede. It is recognized as having a regular series of similar short and broad tergites resembling a Polyzonida. However, Brookfield et al. (2020) raised doubts about the identity and provenance of C. ichthyeros . According to Brookfield et al. (2020), the geologic setting of the Middle Silurian Fish Bed Formation (ca. 430 Ma) is associated with a freshwater environment where fossil fish and aquatic arthropods are typically found. These later authors then concluded that if C. ichthyeros is considered a millipede, it could have come from other strata (associated with terrestrial environment) that must have been about the same age as the Upper Silurian Kerrera Sandstone Formation. Thus, C. ichthyeros must be as old as K. obanensis ( Brookfield et al., 2020) .