Adaptation of morphology in response to varying environments is a crucial feature seen in biological organisms. While some robots emulate adaptability through the use of adaptive body parts, practical implementation of morphological transformations in robotics remains limited. This limitation arises due to the complexity of such transformations, demanding the fusion of advanced materials, control systems, and design approaches. In our paper, we introduce a bioinspired quadruped robot equipped with a laterally undulating spine, designed to adapt its posture specifically for navigating complex terradynamic environments. Leveraging a symmetrical parallelogram mechanism, this robot can alter both height and width, enabling traversal across varied surfaces, collision avoidance, passage through narrow channels, and obstacle negotiation. Additionally, our robot's innovative design strategically positions its center of gravity within its support triangle throughout the gait cycle using lateral undulation, eliminating the need for posture-stabilizing sensors or learning algorithms.