New Species of Pacific Eel shows Primitive Features

A new species of eel, discovered inside an underwater cave of the Pacific island of Palau has astonished scientists as it displays ancient characteristics of the eel family as seen in 100-million-year-old fossil material.

Primitive Eel Species

The island of Palau is certainly a remote location, being approximately 500 miles to the east of the Philippines, but here, in an undersea cave more than thirty metres down, researchers have made the amazing discovery.  A number of specimens of this new species have been collected including a juvenile fish measuring less than five centimetres in length and then a larger eel, believed to be an adult female measuring nearly twenty centimetres long.

This new species is so distinct from other known, extant eels that scientists have had to create a new taxonomic family to describe its relationship to other members of the eel family.  The international research team, the including scientists from the USA, Japan as well as Palau state that the eel’s anatomical features suggest that it has had a long and independent evolutionary history stretching back to at least the beginning of the Jurassic Period.

Lengthy Evolutionary History

A paper on the team’s research findings can be found in the latest edition of the scientific “Proceedings of the Royal Society B (Biology)”.

The research team were not sure of this creature’s affinity with the eel family (Anguilliformes), but genetic analysis confirmed that this fish was a “true-eel”, and a very primitive one at that.  It has been described as a “living fossil”, but this phrase can be misleading.

The scientists have stated:

“In some features it is more primitive than recent eels, and in others, even more primitive than the oldest known fossil eels, suggesting that it represents a ‘living fossil’ without a known fossil record.”

Protoanguilla palau

Many of the physical features of this new genus and species of eel, Protoanguilla palau, reflect its relationship to the 19 families of Anguilliformes (true eels) currently living.  Other, more primitive physical traits, such as a second upper jaw bone (premaxilla) and fewer than 90 vertebrae, have only been found in fossil forms from the Cretaceous Period (144 million to 65 million years ago).  Still other traits, such as a full set of bony toothed “rakers,” in the gill arches are a common feature in most bony fishes, but lacking in both fossil and living eels.

The team’s analyses of total mitochondrial DNA indicate that P. palau represents an ancient, independent lineage with an evolutionary history comparable to that of the entire order of living and fossil eel species.

In order to classify the new animal, the researchers had to create a new family, genus and species, bestowing on the animal the Latin name Protoanguilla palau the name means “first eel from the island of Palau”.

Photographs show one of the ten specimens of this newly discovered eel that the scientists used to determine that this was a new fish species.

A Family Tree of Eels

The team – including Masaki Miya from Chiba’s Natural History Museum in Japan, Jiro Sakaue from the Southern Marine Laboratory in Palau and G David Johnson from the Smithsonian Institute in Washington DC – drew up a family tree of different eels, showing the relationships between them, they then postulated as to the time when the ancestors of P. palau split away from other types of ancient eel.

Their results suggest this new family has been evolving independently for the last 200 million years, placing their origins in the Mesozoic era, a time when the dinosaurs were diversifying and becoming the dominant terrestrial mega fauna.

To read about the remarkable discovery of a fossil fish inside a bore hole drill: Remarkable Fossil Fish Discovery.

The researchers say the Protoanguilla lineage must have once been more widely distributed, because the undersea ridge where its cave home is located is between 60 and 70 million years old and the cave in which they were found is believed to less than two hundred thousand years old.

For models of ancient prehistoric fish and other marine monsters: Models of Prehistoric Marine Animals (PNSO).

Sea Monster in the Family Way

A paper detailing the research carried out on a superbly well preserved plesiosaur fossil has just been published in the scientific journal “Science”.  The fossil, a long-necked marine reptile (plesiosaur) nick-named “Poly” could provide proof that such aquatic reptiles gave birth to live young – that they were viviparous.

Plesiosaur Fossil

The fossil, discovered on a ranch in Kansas in 1987 when fully excavated revealed something very unusual – amongst the large bones of the long-necked plesiosaur, there were the jumbled up remains of much smaller animal.  Now, researchers have identified the mystery creature and published a paper into their research.  “Poly” the plesiosaur may have been pregnant.

The Plesiosauria were a group of marine reptiles, ranging in size from about 3 metres in length to more than 15 metres long that lived in the Jurassic and Cretaceous.  Many were long-necked, specialised fish eaters like the Late Cretaceous giant Elasmosaurus, but there were other types of plesiosaur.  One group for example, were short-necked and became predators of other marine reptiles (pliosaurs).

An Illustration of a Typical Late Cretaceous Plesiosaur

Picture credit: Everything Dinosaur

If this fossil has been interpreted correctly and the small creature does resemble an unborn plesiosaur, then this sheds light on the mystery of how these large creatures bred.  Some marine reptiles such as the extant turtles (Chelonia) are able to return to land and lay eggs.  The females then return to the water abandoning the eggs to their fate.  For plesiosaurs, returning to land may not have been an option, as certainly many later forms would have found locomotion on land with their flippers very awkward, and indeed out of the water their bodies would have been crushed by their own weight.

Commenting on the research, Xiao-Chun Wu, a palaeontologist at the Canadian Museum of Nature in Ottawa, stated that pregnant marine reptiles, although rare in the fossil record, were not that unusual.  Dinosaurs living on land may have preferred laying eggs, but their aquatic kin, more closely related to modern lizards than to dinosaurs such as Triceratops and Diplodocus, had given up the terrestrial life.  The flipper-ed plesiosaurs, in fact, seemed incapable of hauling themselves out of the water to find a spot on land, where it’s much safer for an egg.  Researchers had discovered a number of other pregnant marine reptiles, including “fish lizards” – ichthyosaurs with several young inside their bodies. But they had yet to find a single fossil of a pregnant plesiosaur and could only speculate on how these predators that dominated the oceans of the Mesozoic reproduced.

A Plesiosaur Fossil on Display (Anterior View)

The teeth of the plesiosaur were well adapted for catching fish.  Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Fossils from Germany show a young ichthyosaur emerging from an adult.  A number of fossilised bones of other babies can be seen in the body cavity.  More than twenty years after the fossil was removed from the Kansas ranch, preparators have put together the bones and discovered the evidence for a viviparous plesiosaur.

The species Polycotylus latippinus a typical plesiosaur of the Western Interior Seaway is quite well known but no fossil like this has been found before.  This specimen part of a new exhibition opened last month at the Natural History Museum of Los Angeles County, to celebrate the opening of the new dinosaur halls, measures five metres long and according to the research team, the more than a metre long youngster is not a meal but a baby inside its mum.

Polycotylus latippinus

Writing in the journal Science, the researchers state that the small creature has all the indications of being a baby, with its stubby limbs and big head.  The embryos vertebrae, which in a more mature animal would be much more solid were still separated into smaller pieces.  The little reptile had also been inside its mother when they met their end from an unknown fate, a thin layer of rock had fused the baby’s pelvis to the inside of its mother’s shoulder blade, something that wouldn’t be possible if the two had died side by side. O’Keefe estimates that the young marine predator was only about two-thirds developed.

Scientists have speculated that when the baby plesiosaur came to term, it could easily have exceeded 1.5 metres in length, or about a third of the mother’s body length.   Having one big offspring that had a long gestation period is more akin to whale behaviour than to breeding behaviour associated with reptiles.

Most known lizards, snakes, and even ichthyosaurs produced many, even dozens of babies all at once.  Marine mammals such as Orcas (killer whales) in contrast, have fewer young but also tend to be more diligent parents, suggesting that the fierce plesiosaur may have been a nurturer.

One of the researchers stated that plesiosaurs were not Orcas, but a few living reptiles also partake in mammalian-style baby making and rearing.  For example, some species of Australian skinks, for instance, live in warrens with as many as seventeen relatives.  Their stable family home makes child care convenient. Poly’s briny lagoon, which extended along what’s now the Mississippi River into Kansas, may have been equally calm, a researcher commented:

“It is plausible that plesiosaurs lived in some fairly stable environments in which they didn’t move around too much.”

Alternatively, plesiosaurs may have migrated to a quiet, shallow lagoon type of environment specifically so that they could give birth and spend the first few weeks in relative safety with their offspring.  Although, given the state of the fossilised bones of the embryo, it is likely that the gestation period had sometime to go before this  mother would give birth.

However, other palaeontologists have challenged the viviparous view, claiming that the plesiosaur baby is in fact the remains of a meal.  This would explain why only one small plesiosaur was found inside the body cavity.

Kenneth Carpenter, a palaeontologist at Utah State University believes that “Poly” should not be considered as an example of live birth in plesiosaurs.  The young reptile in her abdomen is missing a few bones, and he suspects that “mum” lopped them off when she fed on the unfortunate youngster.  Many modern-day reptiles similarly feast on juveniles, even those from the same species:

He stated:

“This is a stronger case for cannibalism than it is for live birth.”

For models and replicas of plesiosaurs and other marine reptiles: Plesiosaurs and Prehistoric Animal Figures from CollectA.