Ever since the bizarre anatomy of Opabinia was first recognized in the 1970s, it’s been a persistently unique “weird wonder” of the Cambrian period. Over the decades we’ve figured out that it was an early type of arthropod in an evolutionary position between lobopodians and radiodonts, but this whole time it’s still been sitting there alone as the only known representative of a weird stem-lineage with no other known close relatives.
A fossil from the Wheeler Shale in Utah, USA (~507 million years ago) that was originally thought to be a tiny radiodont has been re-studied, and now we finally have another member of the opabiniid family: Utaurora comosa.
Only about 3cm long (1.2″), Utaurora had 15 pairs of swimming flaps along the sides of its body, and a tail region with a 7-part fan and a pair of serrated spines. Hair-like gill blades covered both its back and the bases of its swimming flaps, and although its head region was poorly preserved it probably had an arrangement of 5 eyes and a long flexible claw-tipped proboscis similar to that of Opabinia.
Its discovery extends both the geographical and temporal known range of opabiniids, and suggests that their continued scarcity in other Cambrian fossil sites compared to other soft-bodied arthropods may simply be because they were just incredibly rare animals in those habitats at the time.
Kogiopsis floridana was a physeteroid whale that lived near the coast of the southeastern United States from the mid-Miocene to the early Pliocene, about 14-4 million years ago.
Known just from fossilized lower jaws and teeth, with some teeth up to nearly 13cm long (~5″), its full life appearance and size are uncertain – but it may have been slightly larger than a modern bottlenose dolphin at around 4.5m long (~14’9″). It’s traditionally been considered to be part of the kogiid family, closely related to modern pygmy and dwarf sperm whales, but some studies disagree with that classification and instead place it in the true sperm whale lineage.
It was probably a predator in a similar ecological role to modern orcas, adapted for hunting prey like squid, fish, and smaller marine mammals. But unlike orcas it wouldn’t have been the apex predator of its ecosystem, subject to predation pressure by even larger carnivores like macroraptorial sperm whales and everyone’s favorite ridiculously huge shark – and as a result it probably had a “live fast and die young” lifestyle similar to modern kogiids and other small-to-medium-sized Miocene physeteroids, rapidly maturing and only living to around 20 years old.
I’ve reconstructed Kogiopsis here as a kogiid-like animal, with a similar sort of shark-like head shape and “false gill” markings. In the background a second individual is depicted displaying “inking” behavior, releasing a defensive cloud of reddish-brown fluid from a specialized sac in its colon.
Allokotosaurs were a group of mostly-herbivorous archosauromorph reptiles, distantly related to the ancestors of crocodiles, pterosaurs, and dinosaurs. They lived across Eurasia, Africa, and North America during the mid-to-late Triassic period, and their lineage included some weird and diverse forms – such as the bull-horned Shringasaurus, the long-beaked Teraterpeton, and possibly also the gliding kuehneosaurids.
Spinosuchus caseanus here was yet another one of these Triassic allokotosaurian weirdos, part of the trilophosaurid family and closely related to Trilophosaurus and Teraterpeton.
Living about 221-212 million years ago in what is now northwest Texas, USA, Spinosuchus was around 2.2m long (~7’2″) and had distinctive elongated neural spines along the vertebrae of its back and the base of its tail, forming a “high back” or short “sail”. Since it’s only known from a partial spinal column the rest of its anatomy isn’t known for certain, but it probably had body proportions similar to its close relative Trilophosaurus, with sprawling limbs and a short-snouted beaked head adapted for herbivory.
Like many other fossil “sailbacked” animals the exact function of Spinosuchus’ elongated vertebrae is unclear, but the structure may have been used for visual display. I’ve depicted it here with a speculative frill of colorful elongated scales, along with a flashy dewlap.
Elasmotherium sibiricum was a giant rhinoceros that lived during the mid-to-late Pleistocene epoch, between about 800,000 and 39,000 years ago. Found across much of the Eurasian steppe dry grassland environments, it stood around 2.5m tall (8’2″) at the top of its humped shoulders and weighed about 4 tonnes (4.4 US tons), making it close in size and mass to a modern elephant.
It was the last known representative of a particularly ancient lineage of rhinos, last sharing a common ancestor with modern forms over 40 million years ago.
A large bony dome on its forehead is traditionally thought to have supported an enormous keratinous horn like the distantly-related woolly rhino, but a 2021 study has recently challenged that interpretation. The dome structure was actually rather thin-walled and wouldn’t have been able to support the weight of a giant horn, instead probably being covered by a much stumpier backwards-pointing nub – while an enlarged nasal cavity inside the dome also suggests it may have actually functioned as a resonating chamber, similar to the crests of hadrosaurs or the extinct wildebeest Rusingoryx.
It also had a smaller toughened “pad” on its nose that may have been used along with a prehensile upper lip to dig around in the soil for plant roots and tubers.