Life Through Geologic Time

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

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.

Living Fossils - Goblin Shark

The Goblin Shark is a deep sea shark and the sole living species in the family Mitsukurinidae, which consists of four extinct genera, and one extant species (Mitsukurina owstoni). Their most notable feature is the trowel-shaped snout, which contains a high concentration of electrosensory organs, which the shark uses to find prey. It has long, protrusible jaws, and when said jaws are retracted, the shark may appear similar to a pink (as goblin sharks are, in fact, a pink-ish colour) Sand Tiger Shark with a long rostrum (Remember! Rostrum means snout (in this context)) (Grey Nurse Shark (<— This is a relatively new synonym to me, how long has this been around?)).

The goblin shark is a deep sea shark, found at depths greater than 200 meters deep, which is well below where light dissipates. They are found throughout the world, in places like the Gulf of Mexico in the Atlantic Ocean and off the coast of Australia, in the Pacific, but are most notably found near Japan, where the species was originally discovered. 

Image is in the Public Domain

Living Fossils - Paddlefish

The Paddlefish is a primitive ray-finned fish, belonging to the order Acipenserifrmes, which includes sturgeons, Paddlefish, and some extinct families, they are considered to be relatively primitive fish (Read more here.) They can be distinguished by their long, spatula-shaped snouts, called rostrum, and their large, gaping mouths. While not closely related to sharks, they have similarities, such as a cartilaginous skeleton, and highly forked heteroceral tail fins.

There are two extant (possibly) species of Paddlefish, including the American Paddlefish (Spoonbill, Mississippi Paddlefish, Spoonie, Spoonbill Catfish) (pictured above,) and the Chinese Paddlefish (Chinese Swordfish,) which may be extinct, but is believed to be critically endangered. That said, there are four, maybe five extinct genera. 

They feed on zooplankton by filtering water through their gaping mouths as they swim, catching said plankton in filaments in their gill arches called gill rakers, much like basking sharks. It has electroreceptors in its rostrum, which allow it to detect weak electrical fields, and a potential meal. 

Picture comes from the Wikimedia Commons, it is in the public domain, as it is the work of the Fish and Wildlife Service, but can be credited to Timothy Knepp,  information here: http://en.wikipedia.org/wiki/File:Paddlefish_Polyodon_spathula.jpg

Living Fossils - Queensland Lungfish

The Queensland Lungfish is the only surviving member of its Family, Ceratodonitidae, and the Order Ceratodontiformes. That doesn’t mean that there aren’t other lungfish, though! There are six extant species, including the Queensland Lungfish. 

The Queensland Lungfish is a lobe-finned fish, sometimes called fleshy-finned fish, which is interesting enough because Tetrapoda descended from Sarcopterygii (Lobe-finned fish.) (Remember, evolution isn’t progress, it’s diversification through change through decent.) (See Tiktaalik song) It is one of the six extant species of Dipnoi (lungfishes) which flourished during the Devonian, and is the most primitive surviving member of Dipnoi. It can survive out of water for several days, but, unlike its four African cousins, it cannot survive total water depletion and must be kept moist. Fossils almost identical to the Queensland Lungfish have been found, indicating that it has remained nigh unchanged since 100 mya , and, therefor, is a viable living fossil.

Living Fossils - Red Panda

Red pandas are small arboreal mammals of the genus Ailurus, and are the only extant species (Ailurus fulgens) in said genus. The red panda is slightly larger than a domestic cat, looks a bit like a red raccoon, and waddles because it’s front legs are shorter than the back legs. It feeds mostly on bamboo, but is omnivorous, eating birds, eggs, insects, and small mammals. It is mainly nocturnal, and, much like tumblr users, leads a very sedentary lifestyle in the day. It used to be classified with raccoons, and then bears, but is now seperated into it’s own family, Ailuridae. 

Photo from the Wikimedia Commons, for more information visit: http://en.wikipedia.org/wiki/File:Ailurus_fulgens_RoterPanda_LesserPanda.jpg

Living Fossils - Neolecta

This is the reason I’ve been saying organisms rather than animals, we have ourselves a fungus!

Neolecta is a genus of ascomycetous fungus that have fruiting bodies in the shape of unbranched to lobed bright yellowish, orangish to pale yellow-green colored, club-shaped, smooth, fleshy columns up to about 7 cm tall. They may be refered to as Earth Tongues, along with morphologically similar species, but are distantly related. It grows in close relation to trees, but it is unknown as to whether it is parasitic, saprotrophic, or mutualistic. It is said to be edible. It provides important evidence for the evolution of Ascomycota, and, as such, is referred to as a living fossil. 

(This picture is from the Wikimedia Commons, for more information visit: http://en.wikipedia.org/wiki/File:Neolecta_irregularis_76559.jpg )

Living Fossils - Triops

I could have sworn I already wrote this, alas, it would appear as though I did not. 

Triops are small crustaceans belonging to Notostraca (tadpole shrimp) with a fossil record reaching back to the Carboniferous. As you may know, Triops eggs enter a state of diapause when dry, and can survive in temperatures up to 98 °C (208 °F). This diapause prevents the eggs from hatching too soon after it rains, the area they inhabit must fill with enough water first for diapause to be broken. Most Triops reproduce sexually, but there are some populations that are hermaphroditic. One species of triops has barely changed since the Jurassic, and all can be traced back to the Carboniferous 300 mya.

(Picture is from the Wikimedia Commons for more information, visit: http://en.wikipedia.org/wiki/File:Triops_longicaudatus2.jpg)

Living Fossils - Elephant Shrew or Hopping Shrew

We’re going to jump right into this with elephant shrews. Elephant shrews (named as such because of the length of their snouts and resemblance to shrews) are small, insectivorous, belong to the family Macroscelididae and only ressemble shrews superficially (the alternate name “sengi” has been proposed). Although they aren’t a particularly common animal, they can be found throughout the Southern part of Africa, in almost any environment. They get their secondary name (hopping shrew) from their movement, which arises as they have relatively long hind legs, so they move about like rabbits. They aren’t a terribly social animal, but do usually live in monogamous pairs which share a territory. They may live in burrows much like bandicoots (not to be confused with Crash Bandicoot), but generally make leaf nests or live in natural crevices. The two will have separate nests, and will generally only interact to reproduce, each living a relatively solitary life. Now, onto why they’re living fossils. Elephant shrews have remained relatively unchanged from their fossil relatives, which were, at first, misidentified as hyraxes, because of morphological similarities in certain groups. Other fossil forms were relatively similar to rodents. These forms have died out, leaving us with what we have today, the several genus of elephant shrew that resemble shrews, rather than rodents or hyraxes.

(Picture from the Wikimedia Commons, for more information visit: http://en.wikipedia.org/wiki/File:Rhynchocyon_petersi_from_side.jpg )