A part of the Jehol Biota with lots of turtles and fish

[Halichoeres]

Sure, the Jehol Biota contains feathered dinosaurs, pterosaurs, and boring stuff like that, but this paper briefly describes a section that is mostly turtles and fish, which are objectively more interesting. I'm looking forward to seeing the descriptions that come out of this locality.


From the paper. a: Lycoptera, a relative of arowanas and mooneyes
b: Sinamia, a relative of bowfins
c: a piece of boring old dinosaur
d: the turtle Ordosemys

Paper (open access): http://www.geojournals.cn/dzxben/ch/reader/create_pdf.aspx?file_no=2018endzxb05024&flag=1&journal_id=dzxben&year_id=2018

[DinoToyForum]

No plesiosaurs or ichthyosaurs, though. Not salty enough?

[Halichoeres]

No plesiosaurs or ichthyosaurs, though. Not salty enough?

Yes, I think that's the reason. They say it's a fluvio-lacustrine deposit. I know you know this, but for anyone else reading who doesn't, fluvial means pertaining to rivers and streams, and lacustrine means pertaining to lakes.

[DinoToyForum]

I wonder why basal sauropterygians never adapted to cope with fresh water environments. Turtles, fish, mammals, crocodiles, and many more did just that.

ETA, there are some plesiosaurs from brackish water deposits, just not in completely fresh water deposits.

[SBell]

Sure, the Jehol Biota contains feathered dinosaurs, pterosaurs, and boring stuff like that, but this paper briefly describes a section that is mostly turtles and fish, which are objectively more interesting. I'm looking forward to seeing the descriptions that come out of this locality.

[Halichoeres]

I wonder why basal sauropterygians never adapted to cope with fresh water environments. Turtles, fish, mammals, crocodiles, and many more did just that.

ETA, there are some plesiosaurs from brackish water deposits, just not in completely fresh water deposits.

Good question! The Wikipedia article for Yuzhoupliosaurus claims it is from a freshwater deposit. I chased down the paper (http://www.ivpp.cas.cn/cbw/gjzdwxb/xbwzxz/200903/W020090813373946642829.pdf) and translated part of it with my phone, and it says Yuzhoupliosaurus is from the Xintiangou formation, which supposedly is a lakeshore/floodplain deposit (http://en.cnki.com.cn/Article_en/CJFDTOTAL-SCDB199702004.htm). That was news to me, and I'm still not sure how well-supported that is. Even if it is true, that's quite a derived sauropterygian and doesn't really answer why basal forms didn't manage it. Maybe they were just SO GOOD at shedding salt (salt glands, concentrated urine) that they couldn't tolerate freshwater and would take on water until all their cells burst. There are lots of freshwater fish, obviously, but it's regarded as a pretty big deal when any particular lineage manages to move into freshwater from the sea.