LOWER K SAUROPODS

[darren.naish@port.ac.uk]

I have seen some recent emails where people have asserted that 
"Large diplodocoids and brachiosaurids pretty much vanish across the 
J-K boundary, replaced by much smaller sauropods." Sorry, am not sure 
who to attribute this actual quote to. 

I am well aware that many of the Lower Cretaceous North American 
brachiosaurid-type sauropods, the astrodons, or _Pleurocoelus_-group, 
or whatever you want to call them (I note Bakker (1998) uses the term 
brachiosauroid for 'astrodons' + Jurassic brachiosaurs), often appear 
small compared to _Brachiosaurus_, but by means is it true that 
Cretaceous sauropods are diminutive compared to Jurassic ones. In 
fact, Cretaceous titanosaurians (and maybe the American 
_Sauroposeidon_) are among the *biggest* of known sauropods. Also, 
brachiosaurids appear to have hung around for some time into the 
Cretaceous: I am unable to get to the reference right now, but a mid 
Cretaceous brachiosaur femur from northern Africa was described 
recently.

To put the Wealden spin on this, we have probable brachiosaurs here 
that were >>enormous<<. Last week, I examined a proximal humerus in 
Steve Hutt's collection at Sandown (Isle of Wight) that was about a 
metre across at its longest axis. It looks identical (but is not the 
same specimen of course) to a humerus referred to _Pleurocoelus_ by 
Mantell (possibly 1852, I'm not sure). Also, Dave Martill and I 
recently photographed a partial cervical vert that was 30 cm long: we 
both know of others from the island that are twice as big! The 
not-insubstantial new brachiosaur, which is estimated to have been 
about 10 m long, is, don't forget, a juvenile. 

Had these giant sauropods _recovered_ from an end-J extinction, or 
was the J-K transition not really that severe?

"Lottery: a tax for people who who do not understand statistics"

DARREN NAISH 
PALAEOBIOLOGY RESEARCH GROUP
School of Earth, Environmental & Physical Sciences
UNIVERSITY OF PORTSMOUTH
Burnaby Building
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