Doppler ultrasound is a type of ultrasound that depends on the Doppler Effect, a change in the wave's frequency, which can occur from the motion of a reflector, such a red blood cell. We experience the Doppler Effect when, for example, an ambulance approaches us, passes and then drives away.
Definition of PLACODERM. : any of a class (Placodermi) of extinct chiefly Devonian fishes with an armor of bony plates and primitive jaw structures.ADVERTISEMENT. New Latin Placodermi, ultimately from GK plak-, plax + derma skin â more at derm-. any of a class (Placodermi) of extinct chiefly Devonian fishes with an armor of bony plates and primitive jaw structures. ADVERTISEMENT.
At about the same time as this happened, paired fins, (eventually to become our arms and legs) evolved also. Fins give the fish lift as it moves forward, an important aspect of the physics of swimming. The earliest jawed fish were called Placoderms and Acanthodii and they first appear in the fossil record about 435 MYA.