Lecture 65 Cynodonts: Between Reptile and Mammal

welcome to Utah State University's vertebrate paleontology course my name is Spencer and burger in this video will list the major innovations in these cynodonts leading toward the origin of modern mammals what exactly is a mammal and how do we recognize the first mammal in the fossil record there are two characteristics that define living mammals first they all have fur or hair and second all living mammals exhibit mammillary glands and produce milk so it was this second trait that led Carl Linnaeus to name mammals in the early 1600s both of these characteristics are well they're not well preserved in the fossil record so we need to formulate a new list of characters in which to recognize mammals in the fossil record when's that hopefully can be preserved as fossils the first trait that's shared by all mammals are teeth that occlude and feature a series of characteristic teeth incisors in front canines for piercing premolars and molars for chewing in the back the second trait is a secondary palette which caps the roof of the mouth and separates the passageway for a respiration through the nose and eating through the mouth the secondary palate allows mammals to both drink and eat at the same time as they breathe in suckling infants this is really important as it allows mammals to suck at the nipple gland while also being able to breathe so for other traits are also characteristic of mammals their erect gait their larger brains and one trait that we'll look at in detail is a development of three middle ear bones from a series of jaw bones near the joint between the skull and lower jaw cynodonts as a group are a very diverse group of synapses reptile-like mammals that survived the end Permian mass extinction along with the dinosaurs the group became successful in the Triassic period one of the early survivors of the Permian Triassic extinction was Thyer accident which arose from the late permian Pro sign asuka day family fire accident is well known from some fantastic fossil skeletons from the karoon basin of South Africa and it's worth taking a closer look at fire accident had a number of characteristics that imply its close relationship to mammals it was about the size of a small house cat and exhibited a rather sprawling gait the skull features a large sagittal crest with differentiated teeth into canines and post canine teeth the lured jaw features a carotid process an attachment site for the larger temporalis or adductor muscles of the jaw the opening of the skull is expanded out into a zygomatic arch or cheek bone the brain remains small but the articulation between the neck vertebrae in the skull is achieved with a double occipital condyle which is sing a singular condyle in all other reptiles and this double occipital condyle is a unique trait found in all later mammals and it helps to make a more stable neck joint Cyrax idan is rather unusual in having robust ribs and a thick vertebral column it's thought that the robust axial skeleton may have aided in respiration during a period of time when there was very low levels of oxygen in the atmosphere in the early triassic and it helped it to survive the mass extinction at the end of the Permian another advanced mammal like feature can be seen in the roof of the mouth with the expansion of the Palatine bone which forms a longer nasal passage for respiration and forms a shelf of bone separating the two openings this is a secondary palate and wood have raised the possibility of suckling in thir oxidant and later mammals will see the further expansion of the Palatine bone to push the opening between the nasal cavity and the mouth cavity further into the back of the throat Cyrax Adhan also features many small foraminifera along the maxilla which have been interpreted as representing nerve and blood flow for whiskers and has been used to justify the reconstruction of thyroxine as a furry proto mammal although direct fossil evidence for fur is not found until the Jurassic cynodonts were successful during the Triassic and into the early Jurassic were several groups splitting off some became herbivores such as the Goffe Adhan today which includes two groups the Diadema dances and the Travis Sidhant today which lived during the Triassic in South America and in Africa another group of Triassic cynodonts are the Jin Acquia dawn today which are often grouped with the probe anthea Natha day a group more closely related to modern mammals these animals were carnivorous and feature a much more expanded secondary palate teeth with curved cuffs and very deep zygomatic arch and a tiny brain case the probe being Natha de are another group of small carnivorous proto mammals that live during the Triassic they had by far the most well-developed secondary palate and were even more mammal like the ribs were reduced to those in the thoracic region and within this group there might have been the first signs of a diaphragm a sheet of muscle tissue that helps expand the lung cavity during breathing and would have helped mammals that achieved a higher metabolic rate and endothermic thermal regulation these more advanced forms featured a more erect skeleton than those found in her accident to more advanced groups of cynodonts appear near the end of the triassic and extend into the early Jurassic they try HeLa dawn today and the trite Iliad on today the try HeLa Don today are known from South America and Africa they feature three cuffs on the post canine teeth and feature wide zygomatic arches and a robust lower jaw the try Tila dawn today are a better known group with a number of skeletons from around the world they try teyla daunted a feature really bizarre teeth which have three lobes that interlock between the upper and lower teeth to produce a grinding surface for chewing the skulls are rather large in proportion to the skeleton they have very narrow brain cases enlarged zygomatic arches for large queuing muscles some of the more well-known farms are Kayenta theorem from the early jurassic of north america an oligo clip feeis from the early jurassic of europe as well as tiny forms like brazil Adhan from south america during the Triassic these early proto mammals diversified after the mass extinction at the end of the Permian during the Jurassic they would go on to evolve into true mammals but already they were successful during the Triassic just as the dinosaurs were beginning their diversification in the next video we'll look at the key mammalian trait the origin of the three middle ear bones that shifted function from the jaw joint to noise conduits for the middle ear thank you for watching if you'd like to learn more about Utah State University's geology program check out the website geology usua edu or my own website at Benjamin slash Berger org links are found in the description below

Channel: Benjamin Burger

Views: 7,237

Rating: 4.9812207 out of 5

Keywords: paleontology, Vertebrate Paleontology, science, Education, Fossils, Evolution, Fossil Mammals, Cynodonts

Id: EMS8pSHDb_4

Length: 8min 40sec (520 seconds)

Published: Tue Nov 08 2016