Sauropod feeding

[crpntr@ix.netcom.com (Kenneth Carpenter )]

original topic on sauropod feeding. I have discussed the issue of tree 
size with Kirk Johnson and he states that the two foot (60 cm) diameter 
logs in the Morrison does indicate conifers 100 ft (30 m) tall. The 
tall size of trees has nothing to do with predation pressures by 
sauropods as suggested by one person (sorry, I forgot who). Instead, 
height is related to competition for light.
     The issue of neck length still seems to bother some (e.g., Friesen 
and Paul; no Greg I was not confusing you with Bakker, I would never 
insult you in that manner : ) ). Friesen writes (22 Mar) that long 
necks of ostriches is to compensate for long legs, apparently a point 
made to him by Holtz. But geese, swans and other long necked birds have 
short legs. In addition, geese with their broad bills graze from the 
ground; maybe they are a better model for diplodocids. Although Friesen 
acknowledges that the broad muzzle of diplodocids is adapted for non 
selective grazing, he would have them "graze" from trees - isn't that 
selective browsing? After all, the tree only puts out one type of 
vegetation product.
        Greg Paul (27 Mar) argues that the only logical explanation for 
long necks is for feeding upwards. I guess then geese and other 
short-legged, long-necked birds are illogical (sounds anti-evolutionary 
doesn't it? Morris would love it)
     The latest issue of J. Vert. Paleo. has a paper (I forget who by) 
about feeding in extinct camels. The author also notes that the broad, 
squared muzzle species were grazers and the pointed muzzle species were 
browsers. This is the same point I was making with sauropods - i.e., 
niche partitioning.  
        The issue of apparent low tooth wear (a point raised by Paul 27 
Mar) to counter low feeding does not work because it assumes diplodocid 
tooth growth rate was slow. Why would it be? The teeth are long, 
slender rods which could easily and quickly be replaced. In addition, 
the roots are open indicating that growth continued even after 
eruption, hence approach the condition of the rodent incisor. However, 
this growth apparently slowed and stopped once the new replacement 
tooth was formed and began to push upwards. 
        Greg (27 Mar) still argues that the elongated chevrons were for 
rearing up, noting elongated chevrons in the tail of the ground sloth. 
Greg assumes that sloths stood on their hind legs, but has never 
demonstrated that really happened. Perhaps he was overly influenced by 
Charles Knight's paint of La Brea. Also, Greg has failed to explain why 
diplodocids had long tails whereas ground sloths had short stubby tail 
if both reared up. He also questions the functional interpretation of 
the chevrons as possibly supporting the tail. I would argue that the 
elongated chevrons stiffen the tail thus as seen from underneath: 
<>=<>, where <> are the chevrons, and = are the ligaments connecting 
the chevrons in series. Thus, they would assist the interspinous 
ligaments dorsally to hold the tail. This functional adaptation can 
also be seen in the distal caudals of theropod tails.
    Nick Longrich (27 Mar) points out that the moon rat also has 
elongated chevrons, so clearly other animals have this feature. A 
census is clearly need to determine if there is a correlation between 
elongated chevrons and the tripodal stance (my recollection is that 
Kangaroos do not have this feature, not even the giants of the 
Pleistocene). Also, why didn't stegosaurs have this feature if they 
were tripodal feeders (which I do not believe 
either).
        By the way, at the WAVP meeting, it was demonstrated that the 
holotype vertebra of Ultrasaurus (brachiosaurid) is a posterior dorsal 
of Supersaurus (a diplodocid), a pointed conceded by Jensen who at the 
meeting.

Kenneth Carpenter
Dept. of Earth Sciences
Denver Museum of Natural History
2001 Colorado Blvd.
Denver, CO 80205
crpntr@ix.netcom.com