Age of Arthropods

In part one, we discussed the phylogenetic placement of Chasmataspididae and concluded that Chasmataspididae is closer to Xiphosura than to Eurypterida. However, Chasmataspidida consists of two clades: Chasmataspididae and Diploaspididae. Surprisingly enough, the case of Diploaspididae is entirely different than that of Chasmataspididae. Even though they are relatively unknown by the public, their fossil record is quite extensive. Unlike Chasmataspididae, which only contains one genus, Diploaspididae consists of as much as 10 genera, all well-spread across the globe (ranging from the USA to Russia). Recent discoveries have revealed that Diploaspidids filled in more ecological niches as previously thought. A reconstruction of Hoplitaspis , a suprisingly well-developed predator. It even has forward-placed eyes, providing improved binocular vision. Figure obtained from Lamsdell et al. (2019). When looking at Diploaspidids, the resemblance to Eurypterids quickly becomes obv...

Megarachne servinei is quite a strange critter, even for an Eurypterid. It possesses unusual structures, such as an enlarged and round second tergite, a shovel shaped cephalothorax and blades on its appendages. The function of many of these structures remains unknown up until this day, but I have several hypotheses that might possibly explain what purpose they served and how they might have looked like in life. The enlarged and round second tergite is perhaps the most peculiar structure of Mycteroptids. The shape and texture caused Hu ̈nicken 1980 to believe that Megarachne was a giant mygalomorph spider. Selden et al. 2005 wasn’t able to figure out what function it could have, stating that “the function of the large, circular second opisthosomal tergite remains a mystery.” The holotype of Megarachne servinei . The second tergite was mistaken for the opisthosoma of a spider. However, one thing I noticed at looking at the holotype of Woodwardopterus scabrosus , a close re...

Chasmataspidida is an order of peculiar arthropods, which seem to resemble both xiphosurans and eurypterids. Their phylogenetic placement is still very uncertain because of this. Therefore, I decided to learn more about these creatures in order to see if I would be able to come up with my own hypothesis regarding their phylogenetic placement. Chasmataspidida consists of two clades: Chasmataspididae (one genus) and Diploaspididae (10 genera). I decided to focus on Chasmataspididae first. The only genus in Chasmataspididae is Chasmataspis . It was first described by Caster and Brooks, and later redescribed by Dunlop et al. Reconstruction of Chasmataspis according to Caster and Brooks. Something that sets Chasmataspidids apart from Eurypterids is the clear separation of the carapace, abdomen and postabdomen, making them resemble Xiphosurans a lot more. Reconstruction of Chasmataspis by Dunlop et al. Dunlop et al. noted that Chasmataspis would have likely h...