Life Through Geologic Time

Marella splendens

Marella splendens was an arthropod that occupied the Mid-Cambrian and is found in the Burgess Shale formation, and is the most common animal found in said formation. It was once thought to be a trilobite of sorts, but this has since been corrected. It has, since being described as a trilobite, been found to be another type of arthropod all together, and has gained it’s own distinction among them.

M. splendens grew to about two centimeters, had 24 to 26 segments, each with a pair of branched legs; the branches being gills located on the upper portion of each leg, with the lower portion being used for walking. It had two pairs of antennae, one pair being long and sweeping and the other pair being short and stout. It’s head also had two pairs of rearward facing, for lack of a better term, spikes. It had too few segments per leg to be a trilobite, not to mention too many antennae. It also couldn’t be a crustacean as it lacked the three pairs of legs located behind the mouth. Studies show that it had an iridescent sheen and would have appeared colorful.

Fossil:

By Wilson44691 (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Living Fossils - Opossum

Let’s talk about these little garbage diggers. I, personally, think they are quite cute, when they aren’t all hostile or splattered on the road. 

Opossums, commonly and wrongfully referred to as possums, are omnivorous marsupials of the western hemisphere. The Virginia Opossum (pictured above) was the first to be named an opossum, it’s name comes from the Virginia Algonquian word aposoum, meaning “white dog,” or “white beast/ animal.”  They belong to the Family Didelphidae, in the order Didelphimorphia, which are marsupials that are about the size of a house cat at the largest, and at the smallest, about the size of a mouse. They tend to be partially arboreal and, again, omnivorous, though there are always exceptions. Most have long snouts and a narrow braincase, along with a prominent sagittal crest. They are plantigrade, and have an opposable digit on their hind feet with no claw. They have prehensile tails, quite like lemurs. Like all marsupials, the females have a pouch, and all of their fur is made up of awn hair. 

Pictured Above: Virginia Opossum (Didelphis virginiana)

By Cody Pope (Wikipedia:User:Cody.pope) [CC-BY-SA-2.5 (http://creativecommons.org/licenses/by-sa/2.5)], via Wikimedia Commons

Things that Weren’t - Pterodactyl

Okay, so I know somebody’s going to get mad that I’m nit picking, but so what? This is an issue that I need to get off my chest. There is no such thing as a pterodactyl. Usually when somebody says pterodactyl, they are thinking of a pteranodon, any other pterosaur, or, maybe, pterodactylus, which is really close, but it’s not really the same, is it? Anyway, let’s talk about pterosaurs. Pterosaurs were flying reptiles, as you may guess by their name, as it means winged lizard, though ptero has been used in place of fins in some cases. They lived in the late Triassic through the end of the Cretaceous. They were the earliest known vertebrates to evolve powered flight. Their wing was formed by a membrane of skin, muscle, and tissues, stretched between an extremely exaggerated fourth finger and somewhere on the torso of the pterosaur. They are often referred to as flying dinosaurs in popular media and by the general public, but are not dinosaurs, as they do not fit into the clade dinosauria. I may have been a bit misleading before that Pterodactyls don’t exist. They do, but it’s an improper name for the genus pterodactylus, and, occasionally, pterodactyloidea, however, it’s like calling an apatosaurus a brontosaurus, it is not correct, and you are a detriment to the scientific literacy if you do it. 

Photo:

By Kenn Chaplin from Toronto, Canada (ROM Dinosaurs 019  Uploaded by FunkMonk) [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

Living Fossils - Metasequoia

Metasequoia, or, more commonly, the dawn red wood, and more specifically M. glyptostroboides is one of three species of that we call redwoods, the other two being Sequoia sempervirens (Coast Redwood) and Sequoiadendron giganteum (Giant Sequoia). They are all members of Sequoioideae, which is a subfamily within Cupressacae, which are, more or less, the Cyprus family. Metasequoia are deciduous trees, but are still, coniferous. There is one extant species of Metasequioa, and three recognized fossil species, all found in the northern hemisphere, and the living species being native to China. The fossils in question are all found around the 80N latitude line, which would have been tropical or sub-tropical at the time (Paleocene and Eocene), and it is thought that it was already deciduous at this time, and therefore that being deciduous developed not because of seasonal variance in temperature, but instead because of light variance. It was thought to be extinct, before the discovery of an extant specimen in a shrine in China. It has recently become a popular ornamental plant.

Photo:

By User:Substatique (English Wikipedia) [CC-BY-SA-3.0 (www.creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

Things That Weren’t - The “Dinosauroid”

So I was thinking of doing something on Troodon (Which I will, its probably one of my favorite dinosaurs) and I found this. Sure I knew about it beforehand, but I just want to share it with you guys now, and also start a new series, because I’m running out of living fossils that I find particularly interesting. Any-who, welcome to things that never existed! Here we will discuss misconceptions, misnomers, and weird things scientists think of sometimes. Today, we’ll be talking about the “Dinosauroid.” This creature, as it were, was a hypothesized path for the evolution of Troodon, had it not died out in the K/T extinction event. It was proposed by the curator of the National Museum of Canada in Ottawa, Dale Russel, in 1982. It was largely rejected because of its anthropomorphism. Russel based his speculation on the EQ values of Troodontids, though they were low, they were 6 times those of other dinosaurs at the time, and, given time, they could have developed brain cases rivaling our own in size (roughly 1100 cubic centimeters.) Russel proposed that Dinosauroids would have large eyes, with binocular vision (a trait troodontids have,) 3 slightly opposed fingers (another.) He proposed it would have a toothless beak, and, like most modern reptiles and birds, internal genitalia. He speculated that they would be placental, as the placenta is seen in correlation with larger brain cases, but would lack mammary glands, and would feed its young much like a bird does. It was also speculated that it would communicate in a fashion of birdsong. 

Image:

By Jim from London [CC-BY-2.0 (www.creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

Living Fossil - Coelacanth

Coelacanth is a lobe-finned fish that dates all the way back to the Devonian, and were believed to have gone extinct around the end of the Cretaceous. Before its rediscovery in 1938 it was thought to be the “missing link” between fish and tetrapods, though it is apparently no longer the case that it is the link, coelacanth is still closer related to tetrapods than to ray-finned fish. It has remained roughly unchanged for ~400 million years. There are two living species, Latimeria chalumnae (West Indian Ocean Coelacanth (pictured above,)) and L. menadoensis (the Indonesian Coelacanth.) Its rediscovery in 1938 after virtually falling off the fossil record qualifies it as probably the best example of the Lazarus Taxon. 

Photo is from the Wikimedia Commons, its information can be found at this link.