Laboratory # 4: Dinosauria - Brad Bartelme and Michele Nelson

Blog Entry 4: Lab Notes (February 10th 2012)

Location: Cleveland Museum of Natural History

Time: 1:30pm

Objective: To observe the diversity of Dinosauria.

(Above) Sue - one of the largest Tyrannosaurus rex specimens (on display at CMNH in 2007)

Background:

With over 1000 species of dinosaurs and over 500 genera, Dinosauria comprised a large part of Reptilian diversity. Rooted within Archosauromorpha, they had a very distinct morphology, having 4 basic characteristics: 1.) supracetabular crest; 2.) antorbital fenestrae; 3.) enlarged fourth trochanter; 4.) digitigrade stance (tip-toe stance). In general, within Dinosauria, there are two distinct clades: Saurischia and Ornithischia. There are many features that distinct the Saurischian dinosaurs (Lizard-like dinosaurs) from the Ornithischian dinosaurs (Bird-like dinosaurs).

Main characteristic that distinguishes Saurischian dinosaurs:

• Presence of 3 pronged pelvic girdle with pubis projecting anteriorly and ventrally

Main characteristics that distinguish Ornithischian dinosaurs:

• Reduced antorbital fenestra
• Ventral margin of the antorbital fenestra that parallels the maxillary tooth row
• Pubis typically directed posteriorly

Lab:

Step 1: We began the lab by first observing a Baby Tyrannosaurus rex skeleton (or what some may consider Nanotyranus). This was obviously a Saurischian dinosaur, due to the apparent 3-pronged pelvic girdle and anteriorly/ventrally projecting pubis.

Step 2: Next we entered the Hall of Prehistoric Life, where most of the dinosaurs were on display. The main display (seen below) was a beautiful scene with classic examples of Saurischian (Tyrannosaurus rex) and Ornithischian (Triceratops horridis) dinosaurs. While there are a number of synapomorphies for both the Saurischian and Ornitithischian dinosaurs, by looking at the main characterstics (listed above in the blog) we were able to identify which species represented the appropriate clade.

Step 3: Although this was mainly a Dinosaur lab, there were many interesting extinct mammals on display as well. Notice the prominent synapsid condition of the Saber-toothed cat, as well a the Mammoth. These large fenestrae, (especially for the Saber-tooth) support optimal means of muscle innervation and insertion, providing a lot of bite force and strength in the jaw for chewing.

Step 4: Below is a picture of a very large predatory bird Diatryma. Notice the typical bird pelvis condition (somewhat fused ilium, ischium, and pubis).

Step 5: Next we observed skulls of Corythosaurus (bottom left), Parasaurolophus (right), and Edmontosaurus (top left). All have clear diapsid fenestration, but no antorbital fenestrae.

Step 6: Below is a picture of the limbs and girdles of a very large herbivore known as Haplocanthus delfsi.

Step 7: The limbs and girdles of Tyrannosaurus rex are very prominent Saurischian type (picture below)

Step 8: In comparing the pelvic girdles and skeletons of both Haplocanthus delfsi (below right) and Allosaurus fragilis (bottom left), there is a relatively large difference in terms of skeletal arrangement. The pelvic girdles however are very similar, both showing the Saurischian condition.

Step 9: Coelophysis (as pictured below) was a very interesting specimen, showing characteristics of both Saurischian and Ornithischian dinosaurs. While it is mostly Saurishcian, the pelvic girdle does appear to be more fused, with the pubis directed in an odd manner, relative to the other dinosaurs on display. Prominent antorbital fenestrae and classic diapsid fenestration of the skull.

Step 10: Next we observed Phytosaurus, Ichthyosaurus, and Stenopterygius fossil material. Phytosaurus was a large crocodilian-like reptile that had a clear diapsid skull condition. Both Ichthyosaurus and Stenopterygius were more cetacean-like, both displaying the euryapsid condition, whereby there is a single supratemporal fenestra.

<--Stenopterygius

Ichthyosaurus

<--Phytosaurus

Step 11: Below is a photo of an early synapsid reptile-like animal, Dimetrodon limbatus. Observe the single sub-temporal fenestra.

Step 12: The last specimen we observed was of an extant group of organism in the clade Sphenodontida, (photo below of Sphenodon punctatus). This nearly extinct lineage is localized to islands off the coast of New Zealand and regions nearby that locale. This clade is known for its classic diapsid temporal fenestration (both supra and sub-temporal fenestrae present)