PALAEONTOLOGY and EVOLUTION

Newly studied embryos of a long-necked, plant-eating dinosaur are the earliest known for any terrestrial vertebrate, or backboned animal, researchers say.

The scientists claim the discovery yields new clues to how primitive dinosaurs evolved into the largest animals ever to walk on Earth. It also provides a rare glimpse into the life of the Massospondylus, an early dinosaur that grew to five metres (more than five yards) and was fairly common in South Africa, they said.

The 190 million year-old embryos are from the beginning of the Jurassic Period, the middle of an epoch known as the age of dinosaurs. While the delicate bones of most dinosaur embryos have disintegrated over time, these embryos have well-preserved skeletons, the researchers said. One is nicely curled up in an egg.

The findings, by scientists from the University of Toronto at Mississauga and colleagues, are published in the July 29 issue of the research journal Science.

“The work on the embryo, its identification, and the fact we can see the detailed anatomy of the earliest known dinosaur embryo is extremely exciting,” said the university’s Robert Reisz. “Most dinosaur embryos are from the Cretaceous period.” [a later era lasting from 146 to 65 millions years ago.]

Reisz said the finding is interesting because it enables scientists to put the embryos into a growth series and work out for the first time how these animals grew from a tiny, 15-centimetre (6-inch) embryo into a five-metre adult. “This has never been done for a dinosaur. Only Massospondylus is represented by embryos as well as by numerous articulated [jointed] skeletons of juveniles and adults. The results have major implications for our understanding of how these animals grew and evolved.”

The hatchling was born four-legged, with a short tail, horizontally held neck, long forelimbs and huge head, the researchers said. As the beast matured, the neck grew faster than the rest of the body but the forelimb and head grew more slowly. The end result was a two-legged animal that looked very different from the four-legged embryo.

“The embryos provide insight into the origins of the later four-legged giant sauropods, a group that includes the passenger-jet sized Seismosaurus,” Reisz said. [Sauropods, a group of dinosaurs that include the largest land animals of all time, were small-headed, long-necked plant-eaters.] “The Massospondylus embryo looks like a tiny sauropod with massive limbs and a four-legged gait, he said.

For that reason, Reisz and colleagues propose that the later sauropods’ gait probably evolved through a phenomenon called paedomorphosis, the retention of embryonic and juvenile features in the adult. Another point of interest was the absence of teeth, Reisz said.

“These embryos, which were clearly ready to hatch, had overall awkward body proportions and no mechanism for feeding themselves, which suggest they required parental care. If this interpretation is correct, we have here the oldest known indication of parental care in the fossil record.”

While the embryos were discovered in 1978 in South Africa, researchers only now managed to clear surrounding rock and eggshell from the embryo.

A strange 525 million-year-old fossil creature is baffling scientists because it does not fit neatly into any existing animal groups.

The animal, from the early Cambrian Period, might have belonged to a now extinct mollusc-like phylum, academics from America and China say. Other researchers have suggested the creature could represent an early annelid or arthropod. Details are published in Proceedings of the Royal Society.

The 5-10cm-long (2-4 inch) fossil, from Anning in China, had a flattened body and horizontal fins which, researchers think, could have been used to support it as it moved along the sea floor. It also had well developed senses, including a pair of eyes on stalks.

The trouble is that the animal, named Vetustodermis planus, did not possess a set of features, or characters, which placed it clearly within any known group. When it was first described in 1979, Vetustodermis was included in the annelid category. Later researchers argued against this classification, saying it was, in fact, either an arthropod or a mollusc.

According to the latest study, the weird creature seems closest to molluscs, primarily because it had a snail or slug-like flat foot. However, the researchers say, it does not sit happily in this group.

"Phyla are defined by an organism having a set of features called characters, and currently there are no animals that we know of which contain the set of characters that Vetustodermis has," co-author David Bottjer, of the University of Southern California, US, told the BBC.

Vetustodermis planus does not fit comfortably within any known phylum "The phylum with which it shares the most characters is the Mollusca, but squeezing Vetustodermis into the mollusca is a somewhat messy job."

Since Vetustodermis requires some "pushing and pulling" to force it into any known phylum, Professor Bottjer and his colleagues are tempted to speculate it belonged to a different group entirely; one which flourished and faded within the Cambrian. "We have always been intrigued by the many molluscan features of these fossils, but in the great menagerie of organisms that have inhabited Earth through life's long history, we may come to conclude that Vetustodermis indeed represents a new phylum," he said. Jonathan Todd, a palaeontologist from the Natural History Museum, London, UK, is also mystified by the baffling animal. "It is an intriguing beast," he told BBC News."It is another strange thing from the Cambrian. It doesn't look much like an arthropod and I don't find its molluscan affinities particularly convincing."

However, Dr Todd is reluctant to create a whole new phylum to accommodate Vetustodermis; that, he thinks, would be premature. "Some scientists have thought that there were so many distinct phyla in the Cambrian," he said. "They came to that conclusion because they were not thinking in the phylogenetic sense, they were thinking 'hey, that is a unique set of features - it must be a distinct phylum'."

So rather than creating new phyla every time something doesn't fit an existing one, the really interesting exercise, Dr Todd thinks, is to establish just how Vetustodermis slotted into the greater evolutionary tree. If, indeed, it did belong to a different phylum, how did that group connect to the molluscs, annelids and arthropods?