(Fig 4) both the horseshoe crab and trilobite have a stomach filling or entering the anterior of their cephalon. So the reduction and loss of antennae between trilobites and horseshoe crabs has not been documented due to taphonomic (= preservation) issues. Very few trilobites preserve antennae, legs + gills. In horse shoe crabs this oral cavity is even more central to the leg bases. They cover their food items and use their proximal legs to draw it forward into the posteriorly-oriented ventral oral cavity.

The loss of limbs or gill plates is really the only difference between Pseudosaukianda and Limulus. Trilobite limbs are rarely preserved, so Triarthrus limbs are modified here to fit the shorter morphology of Pseudosaukianda. That you can show to your trilobite-loving friends… after first rousing yourself from your own paradigm slumber to digest and accept this tiny step away from tradition and consensus.įigure 3. Here online photos and graphics are collected Sadly, all that ‘new insight’ arrived over a hundred years after Archaeopteryx was known to early adopters as a transitional dinosaur-to-bird. And China began producing feathered dinosaurs and toothy birds by the hundreds. Then teachers had to correct themselves in the 1990s when monophyletic clades based on software-assisted phylogenetic analysies suddenly became ‘a thing’.

When teachers used to tell their students dinosaurs are extinct. Though horseshoe crabs are often cited as their closest living relatives, they are no closer evolutionarily than other chelicerates.” Wikipedia repeats that adage when they report, “Trilobites have no known direct descendants. U of Houston represents the consensus: that trilobites died out. Trilobites lasted over 300-million years and finally died out not long before dinosaurs arose.” That telson-sporting clade is represented here by Pseudosaukianda (Figs 1, 3).ĭescribes how most universities think about horseshoe crabs and trilobites: “The nearest thing to a trilobite today is the horseshoe crab with a very similar exoskeleton. This is especially so for that clade of Early Cambrian trilobites sporting a long, sharp telson (= axial spine) rather than a more traditional wide pygidium. Everyone already senses this at some basic level. Horseshoe crabs (Figs 1–4) are living trilobites (Figs 1–4). Here is where I go ahead and state the unaccepted obvious:

Horseshoe crabs and velvet worms