Chordate Evolution -- May 14, 2019

Some random notes after several days of blogging about dinosaurs and reptile evolution.

1. Connecting all the dots, it certainly appears that ur-dinosaur first appeared in what is now northeastern Montana or northwestern North Dakota.

2. At the end of the day, among the chordates, the birds, bony fish, and mammals did well. The cartilaginous fish are basically sharks and rays. The amphibians were incredibly important and had their 15 minutes of fame, but only the frogs hung on (and they were incredibly successful and diversified, but huge question whether they will survive "man"). Reptiles get a lot of press but it's hard to come up with many successful examples outside of lizards, snakes, and turtles, and none of the three is particularly noteworthy any more, at least compared to fish, mammals, and birds.

3. At least one school of thought is that ur-archosaur (a reptile) split into four branches: the ur-dinosaur; the flying lizard (the pterosaur, but not a dinosaur); the water lizards (again, not dinosaurs); and, crocodiles.

4. Based on likely dates of various splits, at least one school of thought suggests that birds are more closely related to crocodiles than dinosaurs, but I'm not sure that really matters.

5. The accepted school of thought that ur-dinosaur quickly split into two branches, saurischians and ornithischians, is now being questioned. One finds occasional comments regarding this on the internet but I have not found much about this yet. If the accepted school of thought is turned upside down, a lot of museums are going to have to change their displays.

6. Without question, one of the best books to read is the 1995 book by Louis Jacobs, Lone Star Dinosaurs.

7. Classical taxonomy:

• Kingdom: animal
• Phylum: chordates 
• Classes of chordates include: bony fish, cartilaginous fish, amphibians, reptiles, mammals, birds, others (see wiki). Interestingly this site lists five classes which does not include birds.

• Class: Reptilia
• Subclass: Archosauria
• Orders:
• Order: Saurischia (never completely died out; lived on as sparrows)
• Suborders:
• Theropoda
• Saurpodomorpha
• Order: Ornithischia (completely died out)
• Suborders:
• Ornithopoda
• Stegosauria
• Ankylosauria
• Certopsia