Plesiosaur Rib Bone From Late Triassic Of South Wales

[-Andy-]

Hi all, I've just acquired what is supposedly a Plesiosaur rib from the Late Triassic of the South Wales coast, dating to the Penarth Group.

I am not aware of late Triassic Plesiosaur material from South Wales however. I know that any plesiosaur material (Jurassic and onwards) from that area is somewhat fragmentary, and it would be hard to pinpoint it to any species or genus. But I would still like to narrow down the possibilities.

1) Let's say it is not a plesiosaur rib, what large marine reptile rib could it be?

2) What plesiosaur genus existed in the late Triassic of South Wales?

Thank you!

EDIT: This rib is 135mm in length and 33mm in width (widest point)

Edited May 3, 2014 by -Andy-

[Tennessees Pride]

The question seems to be out of my league.....but, nice bone!

Edited May 3, 2014 by Tennessees Pride

[4circle]

Hello,

- There are bona fide Triassic Plesiosaurs including from the south west of England and Wales. Most texts will tell you about the sudden radiation of plesiosaurs in the early Jurassic, but obviously this is just an artefact of the fossil record. Late Triassic marine deposits are rare (due to perturbations in sea level at the time), and so there isn't a particularly good wealth of knowledge or literature about them. This doesn't mean there wasn't anything in the oceans at this time!

- There's a rich diversity of plesiosaurs in the lowermost Jurassic, and it can be assumed that many of these had Triassic origins. Indeed, one plesiosaur - Thalassiodracon hawkinsii, which is locally abundant in southwest England - now has a Triassic fossil record as well.

- Plesiosaur ribs are notoriously difficult to classify precisely, even when you have the whole bone! Indeed most sauropterygian (Plesiosaur, ichthyosaur) ribs are pretty featureless, and it's not wise to try to assign them to meaningful taxa. I used to describe plesiosaur type specimens (the name-bearing specimens) and I've never had any luck with ribs. The rib head (where it joins the spine) is the most diagnostic feature, but this is highly variable, so sadly it's not possible to tell from your photos exactly what they are. The only way to be completely certain is to cut a thin section and look at the bone histology under the microscope.

- I can't see a scale in your photos but from experience, these ribs from the Penarth are usually about an inch in diameter, which is why theu're roughly classified as plesiosaurs. The other main marine reptiles at this time were the nothosaurs and pistosaurs which were generally pretty small (too small for these), and a group called Thalattosaurs which were large (up to 4m length) aquatic reptiles. The only way to definitively tell who your rib belonged to is to cut an end and look inside.

Hope I've managed to answer your questions there!

[-Andy-]

Hello,

- There are bona fide Triassic Plesiosaurs including from the south west of England and Wales. Most texts will tell you about the sudden radiation of plesiosaurs in the early Jurassic, but obviously this is just an artefact of the fossil record. Late Triassic marine deposits are rare (due to perturbations in sea level at the time), and so there isn't a particularly good wealth of knowledge or literature about them. This doesn't mean there wasn't anything in the oceans at this time!

- There's a rich diversity of plesiosaurs in the lowermost Jurassic, and it can be assumed that many of these had Triassic origins. Indeed, one plesiosaur - Thalassiodracon hawkinsii, which is locally abundant in southwest England - now has a Triassic fossil record as well.

- Plesiosaur ribs are notoriously difficult to classify precisely, even when you have the whole bone! Indeed most sauropterygian (Plesiosaur, ichthyosaur) ribs are pretty featureless, and it's not wise to try to assign them to meaningful taxa. I used to describe plesiosaur type specimens (the name-bearing specimens) and I've never had any luck with ribs. The rib head (where it joins the spine) is the most diagnostic feature, but this is highly variable, so sadly it's not possible to tell from your photos exactly what they are. The only way to be completely certain is to cut a thin section and look at the bone histology under the microscope.

- I can't see a scale in your photos but from experience, these ribs from the Penarth are usually about an inch in diameter, which is why theu're roughly classified as plesiosaurs. The other main marine reptiles at this time were the nothosaurs and pistosaurs which were generally pretty small (too small for these), and a group called Thalattosaurs which were large (up to 4m length) aquatic reptiles. The only way to definitively tell who your rib belonged to is to cut an end and look inside.

Hope I've managed to answer your questions there!

Thank you! Your post was very helpful and informative!

This rib is slightly over 1 1/4 inch in diameter.

[Welsh Wizard]

Hi

Along the South Wales coast between Sully and Cardiff are a number of thin Rhaetian bone beds from the end of the Triassic. These beds contain the remains of ichthyosaurs, plesiosaurs, fish, sharks, other reptiles and sometimes what could be dinosaurs. The remains are fragmentary and tend to be isolated bones, although you do get the odd articulated pieces but they tend to be just a couple of bones together........no skeletons that I'm aware of.

The bone beds are varied, with some containing a lot of quartz and rolled pebbles and others being monolithic and really hard to break. They were formed at the same time as the more famous and more productive bone beds at Aust cliff near Bristol.

Here are a couple of plesiosaur verts from the South Wales beds.

As Andy says, the fauna was very rich and varied and you can get teeth and ribs and other bones from all sorts of beasts, but it can be difficult sometimes to identify these isolated bones.

I hope this helps

Nick