Smithsonian paleontologist Hans Sues unpacks the complicated evolution of how this creature grew a home upon its back

For many years, the oldest known members of the turtle lineage were Proterochersis and Proganochelys, which are best known from Germany and Poland. They are about 210 million years old. Although less advanced in many ways than present-day turtles, these two stem-turtles already had fully formed shells, providing little insight into the origin of the turtle shell.

The origin of a biological structure as complex as the turtle shell confronted zoologists with a dilemma. Unless a complete shell suddenly evolved, its development would have taken place in a number of steps. This puzzled researchers because it was not clear what survival advantage each intermediate step would confer. Until just a few years ago, the major problem in searching for fossils of turtle precursors was that paleontologists could not easily imagine what something on the way to becoming a turtle might look like.

More:

https://www.smithsonianmag.com/smithsonian-institution/how-turtle-got-its-shell-apologies-aesop-180972929/

PermeateFree said:

Smithsonian paleontologist Hans Sues unpacks the complicated evolution of how this creature grew a home upon its back

For many years, the oldest known members of the turtle lineage were Proterochersis and Proganochelys, which are best known from Germany and Poland. They are about 210 million years old. Although less advanced in many ways than present-day turtles, these two stem-turtles already had fully formed shells, providing little insight into the origin of the turtle shell.

The origin of a biological structure as complex as the turtle shell confronted zoologists with a dilemma. Unless a complete shell suddenly evolved, its development would have taken place in a number of steps. This puzzled researchers because it was not clear what survival advantage each intermediate step would confer. Until just a few years ago, the major problem in searching for fossils of turtle precursors was that paleontologists could not easily imagine what something on the way to becoming a turtle might look like.

More:

https://www.smithsonianmag.com/smithsonian-institution/how-turtle-got-its-shell-apologies-aesop-180972929/

> Proterochersis and Proganochelys, which are about 210 million years
> 260-million-year-old Eunotosaurus, differed from turtles in many ways
> 220 million years old Odontochelys has a plastron but no carapace
> 240-million-year-old Pappochelys has belly ribs that might have later evolved into a plastron

Got it.

How does this relate to the anapsid turtle skull? As in the evolution of diapsid (two holed skulls) into anapsids (no-holed skulls). Did this occur in the same time span, earlier, or later?

mollwollfumble said:

PermeateFree said:

Smithsonian paleontologist Hans Sues unpacks the complicated evolution of how this creature grew a home upon its back

For many years, the oldest known members of the turtle lineage were Proterochersis and Proganochelys, which are best known from Germany and Poland. They are about 210 million years old. Although less advanced in many ways than present-day turtles, these two stem-turtles already had fully formed shells, providing little insight into the origin of the turtle shell.

The origin of a biological structure as complex as the turtle shell confronted zoologists with a dilemma. Unless a complete shell suddenly evolved, its development would have taken place in a number of steps. This puzzled researchers because it was not clear what survival advantage each intermediate step would confer. Until just a few years ago, the major problem in searching for fossils of turtle precursors was that paleontologists could not easily imagine what something on the way to becoming a turtle might look like.

More:

https://www.smithsonianmag.com/smithsonian-institution/how-turtle-got-its-shell-apologies-aesop-180972929/

> Proterochersis and Proganochelys, which are about 210 million years
> 260-million-year-old Eunotosaurus, differed from turtles in many ways
> 220 million years old Odontochelys has a plastron but no carapace
> 240-million-year-old Pappochelys has belly ribs that might have later evolved into a plastron

Got it.

How does this relate to the anapsid turtle skull? As in the evolution of diapsid (two holed skulls) into anapsids (no-holed skulls). Did this occur in the same time span, earlier, or later?

I don’t think they know, it would seem that diapsids is favored by some as being the most primitive, but this skull type was around before the turtles. Wiki states; Reanalysis of prior phylogenies suggests that they classified turtles as anapsids both because they assumed this classification (most of them were studying what sort of anapsid turtles are) and because they did not sample fossil and extant taxa broadly enough for constructing the cladogram. Testudines is suggested to have diverged from other diapsids between 200 and 279 million years ago, though the debate is far from settled.