Sunday, July 12, 2015

Harley's Head and His Leaf-Munching Neighbors

Image of bad Iphone camera quality, but with dinosaurs.
Here's that head of Harley (LACM 23844) I promised. The biggest tyrannosaur in LANHM's collection, Harley's a monster with a five foot head and some terrifying teeth, the longest of which is nearly twelve inches. When he was first put up on display, Harley was the largest T. rex (and indeed, theropod skull period) on display anywhere in the world, and it still quite a sight to behold.

During my time working at the Los Angeles Natural History Museum, I've gotten a ton of questions relating to this skull and our other Tyrannosaurus from people glancing at it through it's display case. One of the most-asked questions I've got actually has to do with what isn't present in this mount. If you notice at the bottom of the picture, Harley's jaws are separate and not touching. This has lead to a lot of questions and suggestions from visitors that Tyrannosaurus was able to separate it's jaws out like a snake in order to swallow huge prey items.

Alas, that's not the case. Harley's jaw tip was simply not recovered during the expeditions to free him in the 1960s. Other Tyrannosaurus with complete lower jaws show such fusion between the two lower mandibles (take this image of Stan, for example). I don't see why T. rex would need to swallow massive prey items anyways. When you've got a bone-crushing bite and the power to rip chunks of bite-sized meat off prey, flexible snake-like jaws become a hindrance that I'd expect would actually weaken the overall crushing ability.

Oh yeah, and next to Harley is his neighbor, LACM 154919, a Lambeosaurus lambei. At just a little bit over two feet long, this skull has hardly any of the massive overpowering presence that Harley's skull does, and doesn't get nearly as many family pictures in front of it. It's a shame really, especially given the size of the actual animal it probably came from. We do have some other ornithischian dinosaurs with a more overpowering presence, however...

More bad Iphone camera quality, with a dinosaur.
And this is our big Triceratops prorsus (LACM 59049) skull, again. Like Harley, we decapitated this dinosaur for safety reasons, and it's head is safe in a glass case alongside two other ceratopsid skulls (which will be shown in the future). The head on the mount is a lightweight cast built to be lightweight and replaceable, which is good considering this induvidual had a skull over eight feet long (if not longer). LACM 59049 was also one of the more complete specimens of its kind during it's initial discovery. 60% of this Trike's bones were discovered over the course of a couple of field seasons, and most of those bones are on display throughout the institution; abet scattered.

You can tell that this specimen is a T. prorsus, and not a T. horridus, by the enlarged nasal horn. T. horridus has a little stub of a nasal horn on its head, but longer (proportionality speaking) brow horns than T. prorsus. Work done by
Scannella and Fowler (2009) suggests that these two species were separated stratigraphically in the Hell Creek and other similar formations, with horridus specimens appearing in older rocks and prorsus occurring closer to the K-T boundary. Some specimens of Triceratops found in the middle of the Hell Creek even show evidence of being intermediate between horridus and prorsus, suggesting that horridus directly evolved into prorsus, which would be incredibly cool if shown true.

Expect more ceratopsians soon...

- Scannella, J.B. and Fowler, D.W. (2009). "Anagenesis in Triceratops: evidence from a newly resolved stratigraphic framework for the Hell Creek Formation." Pp. 148–149 in 9th North American Paleontological Convention Abstracts. Cincinnati Museum Center Scientific Contributions 3.

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