Before the major planet lostT. rexand other carnivorous giant , mammal - like reptiles began to grow whiskers . The findings , release inScientific Reportslast month , propose that many mammal - defining features were already present in our distant ancestor 240 million years ago . And these may have contributed to the subsequent evolutionary succeeder of mammals .
Therapsid reptiles are the distant ancestors of mammal , and they walked the Earth long before dinosaur dominated . One group of Canis familiaris - like therapsid called probainognathians eventually evolve into mammal as we love them today . But since mild tissue paper do n’t promptly fossilize , evidence of hair in the fossil record has been confine to just mammal .
Rather than look for fogey traces of hair with therapsid corpse , a University of the Witwatersrand squad led by Julien Benoit searched instead for the neural structure that innervate the hairs . By using disco biscuit - ray micro - CT skim to image 29 therapsid skull unearthed in Karoo , South Africa , the researchers reveal that protomammal had likely evolved haircloth and whiskers . " Whiskers are an amazing sensory tool to have when you are nocturnal and the evolution of hairsbreadth possibly help in the natural selection of the therapsids – and more specifically the probainognathians , " Benoit said in astatement .
The team bump that the maxillary epithelial duct – a bony tube in the snout – is shorter in therapsid than in reptiles . house within the maxillary canal is a spunk that provide sensitivity to the animal ’s schnozzle , called the trigeminal nerve . A cut maxillary canal permit for nerve movement as it branch into backtalk and olfactory organ soft tissue . This is how whiskers are innervated . " This lead the trigeminal nerve free to follow the movements of a flexible snoot , " Benoit explained . " In reptiles , this duct is long and the nerve is confine in the maxilla all along its length , which prevent any movement of the nose and backtalk . "
Previous mouse studies revealed that a gene predict MSX2 is imply in the ontogenesis of mammalian traits including a large cerebellum , mammary secretor , and body hairs . Based on this newfangled study , the expression of the MSX2 gene undergo a monolithic change some 246 to 240 million years ago . This trip the evolution of many feature that define mammal – including a mobile snout . And it coincide with the appearance of prozonstrodontians – a member of the probainognathians and the direct antecedent of mammal we have today . That means trait we associate with mammals were already present in advanced therapsids , before mammals even showed up .
Evolution of the maxillary canal for the trigeminal nerve ( light-green ) in Therapsida . humour University
