Lisa has studied natural history for over 15 years and is a fossil collector as well. She loves sharing her knowledge with others.
A New Wave of Aquatic Predators
The Carboniferous Period began with the extinction of all armored fish and many sea scorpions, giving rise to a new wave of strange predators. This period lasted from 359 to 299 million years ago and is sometimes referred to as the "Golden Age of Sharks." The disappearance of armored super predators like Dunkleosteus allowed shark-like fish to expand and dominate most aquatic ecosystems. They took on many diverse forms, becoming the largest aquatic carnivores of the time.
Amphibians flourished during the Carboniferous Period as well. The climate was relatively warm and humid throughout the year, and shallow, warm waters frequently flooded the continents. These conditions made it possible for them to evolve into a wide variety of successful species. They colonized swamps and other freshwater ecosystems while developing their own strange physical traits.
Amphibians and shark-like fish were not the only animals that developed bizarre features. Some soft-bodied creatures also experienced unusual evolutions during the Carboniferous Period. In addition, a few species of lobe-finned, bony fish and sea scorpions had their share of quirky characteristics. Animals of the Carboniferous Period ranged from amphibians with enormous, boomerang-shaped heads to fish that looked like winged dragons.
This article covers the following Carboniferous beasts:
- Dracopristis Hoffmanorum
Tullimonstrum, also known as the Tully Monster, was a soft-bodied animal from the clade Bilateria. It lived around 307 million years ago in shallow tropical waters off the coasts of estuaries. Its fossils have been found in the Mazon Creek fossil beds located in Illinois, United States.
Tullimonstrum probably grew to around 35 centimeters (1.1 feet) in length. It had a pair of stalked eyes similar to a snail, an elongated, squid-like body, and likely a pair of vertical ventral fins at the rear end of its body. It also had a long proboscis containing around 16 small, sharp teeth (8 teeth on each "jaw"). Scientists believe that the animal used this strange appendage to probe the mud for food, possibly feeding on both living creatures and dead matter.
It has not yet been determined whether Tullimonstrum was a mollusk, a vertebrate, or some type of unclassified worm. Some researchers believe they have identified a primitive backbone in a few fossil specimens, which would classify this animal as a vertebrate. They also stated that the fossils contained internal organ structures like gill sacs, and that their teeth were similar to those of modern lampreys. Furthermore, a study of fossilized tissues (using a nondestructive laser) indicated that all of the tissues were made up of proteins rather than chitin. This is strong evidence that Tullimonstrum was a vertebrate.
Some scientists who believe Tullimonstrum was an invertebrate argue that it is difficult to prove the animal possessed a backbone. This is because its fossils come from marine rocks, where mostly just soft tissues are preserved and not much remains of the internal structure. In addition, it is possible that the results of the laser study on the fossilized tissues are inaccurate. The tissues may not have all been composed of proteins. Researchers have also noted that not a single fossil of Tullimonstrum appeared to possess otic capsules (ear components that allow an animal to balance) or a lateral line (a system of sensory organs that enables the animal to detect movement, pressure, and vibrations in its surroundings). These two features are believed to be characteristic of all aquatic vertebrates.
Edestus was a large, shark-like fish that lived between 313 and 307 million years ago in what is now the United States, Russia, and the United Kingdom. The largest species, Edestus heinrichi, was estimated to reach more than 6.7 meters (22 feet) in length. This is based on estimates of the animal's skull length and fossil remains of its tooth whorls. The upper whorl was known to reach 32 centimeters (1 foot) in length while the lower whorl reached 43 centimeters (1.4 feet) in length.
The tooth whorls were both positioned in the center of Edestus' mouth, giving this animal the nickname "Scissor tooth shark." Each whorl consisted of up to 12 serrated teeth that grew at the back of the whorl and gradually moved forward before being ejected from the front end. The lower whorl had more curvature than the upper one. Many scientists believe Edestus used its strange jaws like scissors to cut through smaller fish and soft-bodied creatures. Studies have also found that its jaws were operated by a two-gear system in which its lower jaw was capable of moving forward and backward in a sawing motion.
No fossilized imprints of Edestus' body have been discovered yet. However, based on some fossils of its close relatives, researchers can deduce that its body shape was fairly similar to that of a great white shark. It likely had triangular pectoral fins and a tall, forked tail fin as well. This design would have allowed Edestus to be a fast, open-water predator.
3. Dracopristis Hoffmanorum
Dracopristis hoffmanorum was a shark that lived about 300 million years ago in present-day New Mexico, United States. It grew to a length of over 2 meters (6.7 feet) and was given the nickname "Godzilla shark" due to its dragon-like jawline and 76-centimeter (2.5 foot) long fin spines.
Dracopristis hoffmanorum likely lived in shallow waters along the coastline, feeding on fish, crustaceans, and smaller sharks. Its teeth were shorter and wider than many other sharks of the period, measuring only 2 centimeters (less than 1 inch) in length. These teeth would have been perfect for grasping and crushing prey rather than piercing them. Researchers have suggested this shark was a slow-moving ambush predator which spent much of its time near the bottom of the estuary that once existed in the area. It may have used its large fin spines for defense against larger sharks or fish.
Orthacanthus was a large, eel-like shark that lived during the Carboniferous and Permian periods (around 305 to 260 million years ago). Its fossils have been discovered in North America and Europe.
This shark was capable of reaching almost 3 meters (9.8 feet) in length. It lived in various freshwater ecosystems, including swamps, rivers, and lakes. Researchers believe that Orthacanthus thrived in the brackish waters of lagoons and estuaries as well. It had a long dorsal spine that may have been used for protection against equally large amphibians. It also possessed a strange set of double-fanged teeth.
Fossil remains of Orthacanthus' gut indicate that it preyed on fish, amphibians, and other sharks. It even ate juveniles of its own kind. Suggestions of these cannibalistic tendencies have been supported by the discovery of juvenile Orthacanthus teeth inside the fossilized feces of adults. The reason for this cannibalism is unknown, but some scientists believe it ate its own kind during times of hardship, when its normal food supply was depleted.
Iniopera was a small cartilaginous fish that thrived in open water environments. It lived between 320 and 299 million years ago in what is now North America. This strange fish possessed a large, blunt head, sharp teeth, a pair of huge, wing-like pectoral fins, and a rounded tail fin.
Iniopera's pectoral fins were connected high up on its body, near its neck. Scientists believe it flapped these fins up and down in a manner similar to that of a sea turtle. Males had a series of small, forward-facing hooks on their pectoral fins, but the purpose of the hooks is not yet known. It has been suggested that Iniopera was capable of taking to the air to evade aquatic predators. This animal possibly used its tail to propel itself out of the water, and its large pectoral fins may have allowed it to glide above the water's surface for very short bursts of time.
Stethacanthus was a cartilaginous fish that resembled a shark in appearance. It lived from the late Devonian Period to the late Carboniferous Period (383 to 299 million years ago). Fossils of this animal have been found in Asia, Russia, North America, and Europe.
Stethacanthus typically grew around 70 centimeters (2.3 feet) in length and is best known for its bizarre anvil-shaped dorsal fin, which has only been identified in males. Small dermal spikes covered the top of the dorsal fin and animal's head. The purpose of this large dorsal fin is still unknown. It may have played a role in attracting females or possibly was used during the mating process. It also may have been used to deter potential predators.
Researchers believe Stethacanthus was a slow swimmer, as its oversized dorsal fin likely prevented it from being able to reach high speeds in the water. Its teeth were fairly small in comparison to other predatory fish of the period, meaning that it may have been a bottom-dweller that fed on crustaceans and smaller bottom-feeding fish.
Rhizodus was a massive lobe-finned fish that resided in freshwater lakes, swamps, and rivers during the entire Carboniferous Period (359 to 299 million years ago). It lived in present-day Scotland and Ireland.
This animal was capable of reaching over 6 meters (20 feet) in length and possessed a pair of 22 centimeter (8.7 inch) long fangs. It is the largest known freshwater fish that has ever lived on Earth. Fossil imprints of Rhizodus' skin indicate that it had large, plate-like scales. It was the apex predator of its freshwater environment, likely feeding on medium-sized amphibians and fish. Some scientists believe Rhizodus was capable of traveling onto land for brief moments to snatch up shorebound prey. This is based on the fact that it possessed robust, flexible fins and was a member of the tetrapod stem group (the group that gave rise to four-legged vertebrates).
Ornithoprion was a cartilaginous fish that lived between 315 and 307 million years ago. Its fossils have been found at the Mecca and Logan Quarry Shales of Indiana, United States. Scientists are uncertain of this animal's size. However, it can be assumed that Ornithoprion was a medium-sized fish, probably reaching a length of 1.1 to 1.4 meters (3.6 to 4.6 feet). This is based on fossil remains of its close relative Caseodus, which grew to these lengths.
Ornithoprion is best known for its long, sword-like lower jaw, which was likely used for defense or hunting. It had a narrow head and a pointed snout. Ornithoprion also possessed a whorl of flat teeth in the center of its bottom jaw. These teeth were designed for crushing prey. Many scientists believe this fish was a bottom-dweller that used its lower jaw to unearth shellfish and other hard-bodied animals. Its sharp jaw possibly served as a tool to pry open these creatures as well.
Diplocaulus was a fairly large amphibian that lived 306 to 255 million years ago in what is now North America and Africa. It grew up to 1 meter (3.3 feet) in length and had a salamander-like body. Its diet probably consisted of insects and small fish.
Diplocaulus' most unique trait was its huge, boomerang-shaped head. Researchers have developed multiple hypotheses regarding the purpose of its bizarre head shape. Some have suggested that this amphibian's head served as a burrowing tool to survive droughts or evade predators. Others believe the extreme width of Diplocaulus' head may have discouraged predators from selecting it as prey, as they likely would have had a difficult time trying to swallow it. Another suggestion is that the two tabular horns at the base of its skull helped protect a set of external or internal gills.
One study actually found that the animal's horns generated significant lift and would have allowed it to rise to the surface of a river very quickly. Diplocaulus also could open its mouth while rising through the water without it having much impact on speed. This means that it probably could attack prey while rising without putting itself at a serious disadvantage.
Hibbertopterus was a large eurypterid (sea scorpion) that lived during the Devonian and Carboniferous periods (around 388 to 323 million years ago). It was slightly similar in appearance to modern horseshoe crabs. Fossils of this animal have been discovered in Europe, North America, and South Africa.
Hibbertopterus was capable of reaching 2 meters (6.6 feet) in length and over 65 centimeters (2.2 feet) in width. It was likely one of the heaviest eurypterids due to its broad, compact body. Fossilized tracks of this animal indicate that the South African species, Hibbertopterus wittebergensis, may have grown up to 2.4 meters (8 feet) in length.
Unlike most other eurypterids, Hibbertopterus possessed small, weak pincers that were not designed for latching onto prey. This means that it did not prey on larger animals. Instead, it was a sweep-feeder that used modified spines on its forward-facing appendages to rake through the soft sediment for food. The spines would have been quite useful at trapping small crustaceans and other invertebrates, which Hibbertopterus would then sweep into its mouth.
This animal spent the majority of its life at the bottoms of swamps and rivers. However, fossilized tracks attributed to Hibbertopterus have shown that it did occasionally leave the water. Some scientists believe it was able to survive on land as long as its gills remained wet. Hibbertopterus also may have had a dual respiratory system which would have allowed it to remain on land for brief periods of time. The fossilized tracks of this eurypterid indicate that it travelled very slowly on land, dragging and jerking its body across the ground.
The Carboniferous Extinction
During the second half of the Carboniferous Period (around 323 million years ago), average global temperatures dropped to roughly 12 °C (54 °F). Increased glaciation caused sea levels to drop by about 100 meters (328 feet). At the same time, the continents were coming together to form the supercontinent Pangaea, which decreased the sea coast area.
The drop in sea level and decreased sea coast area resulted in a marine extinction event that wiped out many shallow marine invertebrates, crinoids, corals, and ammonites. Some species of trilobites and sea scorpions likely were affected as well, but these two arthropod groups managed to survive the extinction event and make it to the Permian Period (299 to 252 million years ago).
Swamps gradually declined as a result of the drop in sea level as well. An increase in terrestrial habitat and cooler, drier climate negatively impacted amphibians. These animals began to decrease in numbers and diversity, and reptiles later occupied the new ecological niches that amphibians were not able to fill.
Although many species of amphibians perished towards the end of the Carboniferous Period, some were able to survive throughout the entire Permian Period. In addition, fossil evidence suggests that the Carboniferous extinction event did not have a significant impact on most sharks and fish. In fact, researchers have found that the number of shark and fish species actually increased in some areas during the late Carboniferous Period. This means that numerous aquatic oddities were probably able to survive into the next period, further contributing to the gene pool and establishing new lineages.
© 2021 Lisa Pizzoferrato
Rawan Osama from Egypt on June 13, 2021:
John Hansen from Australia (Gondwana Land) on June 13, 2021:
Very interesting and educational article, Lisa. I had only heard of a couple of these previously.