New lineage of prehistoric, plankton-eating sharks discovered
- September 21, 2015
- DePaul University
- A new lineage of extinct plankton-feeding sharks, Pseudomegachasma, has been discovered by an international team of scientists. The sharks lived in warm oceans during the age of the dinosaurs nearly 100 million years ago. The fossil sharks had tiny teeth very similar to a modern-day, plankton-eating megamouth shark.
An international team of scientists has discovered a new lineage of extinct plankton-feeding sharks, Pseudomegachasma, that lived in warm oceans during the age of the dinosaurs nearly 100 million years ago. The fossil sharks had tiny teeth very similar to a modern-day, plankton-eating megamouth shark.
The study, "A new clade of putative plankton-feeding sharks from the Upper Cretaceous of Russia and the United States," is published in the September issue of the Journal of Vertebrate Paleontology.
Lead author, Kenshu Shimada, professor of paleobiology at DePaul University, said the findings are based on newly collected tiny fossil teeth, as well as a reinterpretation of previously reported specimens from Cretaceous rocks in the U.S. and Russia.
"The study is significant because Pseudomegachasma would represent the oldest known plankton-feeding shark in the fossil record," said Shimada. He added that these sharks would have evolved independent of the four known lineages of modern-day planktivorous cartilaginous fishes: the megamouth sharks, basking sharks, whale sharks, and manta rays.
Pseudomegachasma means "false megamouth shark" due to its dental features superficially nearly identical to the modern-day plankton-eating megamouth shark or Megachasma that evolved much later in time. The new genus is represented by two extinct species, Pseudomegachasma casei from Russia and Pseudomegachasma comanchensis from the U.S. that evolved from a group of extinct sandtiger sharks that likely had a fish-eating diet.
- Kenshu Shimada, Evgeny V. Popov, Mikael Siversson, Bruce J. Welton, Douglas J. Long. A new clade of putative plankton-feeding sharks from the Upper Cretaceous of Russia and the United States. Journal of Vertebrate Paleontology, 2015; 35 (5): e981335 DOI: 10.1080/02724634.2015.981335
Africa's earliest known coelacanth found in Eastern Cape
More than 30 complete specimens of the new fossil species, Serenichthys kowiensis, were collected
- September 21, 2015
- University of the Witwatersrand
- Various specimens of Africa's earliest coelacanth have been found in a 360-million-year-old fossil estuary near Grahamstown, in South Africa's Eastern Cape. More than 30 complete specimens of the new fossil species, Serenichthys kowiensis, were collected from the famous Late Devonian aged Waterloo Farm locality.
Various specimens of Africa's earliest coelacanth have been found in a 360 million year-old fossil estuary near Grahamstown, in South Africa's Eastern Cape.
More than 30 complete specimens of the new fossil species, Serenichthys kowiensis, were collected from the famous Late Devonian aged Waterloo Farm locality, by palaeontologist Dr Robert Gess and described by him in collaboration with Professor Michael Coates of the University of Chicago.
Gess did the research whilst he was completing his PhD at the Evolutionary Studies Institute at the University of the Witwatersrand. An article describing the new species will be published in the in the Zoological Journal of the Linnean Society of London in August.
"Remarkably, all of the delicate whole fish impressions represent juveniles. This suggests that Serenichthys was using a shallow, waterweed-filled embayment of the estuary as a nursery, as many fish do today," says Gess.
The fossils come from black shales originally disturbed by road works at Waterloo Farm. These shales are the petrified compacted remains of mud, which was deposited in the quiet reaches of an estuary not unlike some of those along the Eastern Cape coast today.
"This earliest known record of a coelacanth nursery foreshadows a much younger counterpart, known from the 300 million year old Mazon Creek beds of Illinois in the United States," says Gess.
"This glimpse into the early life history of ancient coelacanths raises further questions about the life history of the modern coelacanth, Latimeria, which is known to bear live young, but whether they, too, are clustered in nurseries remains unknown," explains Coates.
360 million years ago, Africa was part of the southern supercontinent Gondwana, made up of Africa, India, Australia, Antarctica and South America. At that time, the rocks of Waterloo Farm were forming along the shores of the semi-enclosed Agulhas Sea, not far from the South Pole.
Gess originally identified coelacanth remains from the locality whilst carrying out excavations at Waterloo Farm in the mid-1990s under the supervision of Dr Norton Hiller, of the Rhodes University Geology Department. These fossils were not, however, well enough preserved to be reconstructed and described. His painstaking excavation of tons of shale salvaged during subsequent roadworks has now shed light on dozens more specimens, a few of which are preserved in exquisite detail.
These were prepared under a microscope and have allowed the species to be reconstructed in minute detail. They prove to be a new genus and species.
Coelacanths are believed to have arisen during the Devonian Period (about 419.2 ± 3.2 million years ago), however only five species of reconstructable Devonian coelacanths have previously been described, in addition to a number of very fragmentary remains. None of these came from Africa, but rather from North America, Europe, China and Australia. The new species gives important additional information on the early evolution of coelacanths.
"According to our evolutionary analysis (conducted by Gess and Coates), it is the Devonian species that most closely resembles the line leading to modern coelacanths," says Gess.
The new species was discovered a mere 100km from the mouth of the Chalumna River, off which the type specimen of Latimeria chalumnae (the first discovered modern coelacanth) was caught in 1938.
Furthermore, the Geology Department at Rhodes, where Gess was based when he found his first fossil coelacanth, is on the site of the former Chemistry Department where Latimeria was first described. In keeping with the naming of its living relative (after an Eastern Cape river), the species name of the new fossil form, kowiensis, is after the Kowie River which rises among the hills where it was found, and the genus name, Serenichthys, honours Serena Gess, who provided land for the storage of more than 70 tons of black shale rescued from roadworks for ongoing research -- in which all the new material was found.
All specimens have been deposited in the palaeontological collection of the Albany Natural History Museum, in Grahamstown, Eastern Cape Province, South Africa.
How Do Fossils Form?
| Skeleton of the bird-like specimen (Aurornis xui) found in Yizhou Fossil & Geology Park, China. |
Credit: Thierry Hubin/IRSNB
When animals, plants and other organisms die, they typically decay completely. But sometimes, when the conditions are just right, they're preserved as fossils.
Several different physical and chemical processes create fossils, according to the New York State Geological Survey.
Freezing, drying and encasement, such as in tar or resin, can create whole-body fossils that preserve bodily tissues. These fossils represent the organisms as they were when living, but these types of fossils are very rare.
Most organisms become fossils when they're changed through various other means.
The heat and pressure from being buried in sediment can sometimes cause the tissues of organisms — including plant leaves and the soft body parts of fish, reptiles and marine invertebrates — to release hydrogen and oxygen, leaving behind a residue of carbon.
This process — which is called carbonization, or distillation — yields a detailed carbon impression of the dead organism in sedimentary rock.
The most common method of fossilization is called permineralization, or petrification. After an organism's soft tissues decay in sediment, the hard parts — particularly the bones — are left behind.
Water seeps into the remains, and minerals dissolved in the water seep into the spaces within the remains, where they form crystals. These crystallized minerals cause the remains to harden along with the encasing sedimentary rock.
In another fossilization process, called replacement, the minerals in groundwater replace the minerals that make up the bodily remains after the water completely dissolves the original hard parts of the organism.
Fossils also form from molds and casts. If an organism completely dissolves in sedimentary rock, it can leave an impression of its exterior in the rock, called an external mold. If that mold gets filled with other minerals, it becomes a cast.
An internal mold forms when sediments or minerals fill the internal cavity, such as a shell or skull, of an organism, and the remains dissolve.
In recent years, researchers have discovered that some fossils aren't just made of minerals. Fossil analyses have shown, for instance, that some retain organic material dated to the Cretaceous, a period that lasted from 65.5 million to 145.5 million years ago, and the Jurassic period, which lasted from 145.5 million to 199.6 million years ago
Tests suggest that these organic materials belong to dinosaurs because they match certain proteins from birds, which evolved from dinosaurs.
"It used to be that no one thought it was possible for any endogenous material — material that comes from the animal — could be left behind after the fossilization process," said Ken Lacovara, the dean of the School of Earth and Environment at Rowan University in New Jersey. "[But] that's not really the case."
It's unclear how the organic material is preserved, but iron might help the proteins become cross-linked and unrecognizable, or unavailable to the bacteria that would otherwise consume them, Lacovara said. (Formaldehyde works in a similar way, cross-linking the amino acids that make up proteins, making them more resistant to decay, Mary Schweitzer, a molecular paleontologist at North Carolina State University, told Live Science.)
Another idea is "microbial masonry," Lacovara said. "It's possible that the bacteria that initially chomped through the tissue are secreting minerals as a waste product that then hermetically [airtight] seal a little bit of what remains behind," almost like a stone mason sealing off a structure, he told Live Science.
Moreover, sandstone — rock made of sand-size grains of minerals, sediments or inorganic material — seems to be the best type of environment for preserving organic material in fossils.
"Sandstone is like a bunch of volleyballs sitting on top of each other with big interstitial [spaced] areas between them," Lacovara said. "So it seems like rapid decay might promote the preservation process. Maybe we need the bacteria to get through fast and to chomp through the sediment so that they can sequester some of [the surviving organic material] in the process."
Additional reporting by Staff Writer Laura Geggel.