dv said:
Bubblecar said:
Who knows, mammals might even predate dinosaurs.
reasonable
“The oldest known dinosaurs – from roughly 230 million years ago … southern Brazil”
> southern-most section of Brazil
Hang on. Same location as earliest known dinosaurs.
What used to be called “mammal-like-reptiles” then synapsids, is still sometimes separated from mammals. Synapsids are now more correctly referred to as stem mammals, and sometimes as proto-mammals, or paramammals. They roamed around 299 to 251 million years ago in the Permian. https://en.wikipedia.org/wiki/Synapsid
“After the Permian extinction, the synapsids did not count more than three surviving clades. The first comprised the therocephalians, which only lasted the first 20 million years of the Triassic period. The second were specialised, beaked herbivores known as dicynodonts (such as the Kannemeyeriidae), which contained some members that reached large size (up to a tonne or more). And finally there were the increasingly mammal-like carnivorous, herbivorous, and insectivorous cynodonts, including the eucynodonts from the Olenekian age, an early representative of which was Cynognathus. Cynognathus was the largest predatory cynodont of the Triassic.”
“Unlike the dicynodonts, which were large, the cynodonts became progressively smaller and more mammal-like as the Triassic progressed, though some forms like Trucidocynodon remained large. The first mammaliaforms evolved from the cynodonts during the early Norian age of the Late Triassic, about 225 mya.”
dv said:
London (CNN)The world’s oldest mammal has been identified using fossil dental records — predating the previously confirmed earliest mammal by about 20 million years — in a new discovery hailed as “very significant” by researchers.
Brasilodon quadrangularis was a small shrew-like creature, around 20 centimeters (8 inches) long, that walked the earth 225 million years ago at the same time as some of the oldest dinosaurs and sheds light on the evolution of modern mammals, according to a team of Brazilian and British scientists.
https://edition.cnn.com/2022/09/06/world/earliest-mammal-teeth-scn-scli-intl/index.html
> If you think about reptiles, they have many, many different replacement teeth throughout their lives but we mammals only have two. Firstly, the milk teeth and then the second dentition which replaces the original set. This is what defines mammals. Brasilodon is the oldest extinct vertebrate with two successive sets of teeth — baby teeth and one permanent set — also known as a diphyodonty, the news release said.
Interesting. I hadn’t heard that definition of “mammal” before.