This study investigates the influence of environmental factors, specifically incubation temperature, on the development and growth of limbs in embryonic crocodiles and chickens. The research hypothesis is that changes in prenatal movement, influenced by environmental factors, can alter limb proportions during embryonic development. Key findings include: 1. **Temperature and Motility in Crocodiles**: Incubation temperature affects embryo motility and limb bone growth in West African Dwarf crocodiles. Lower temperatures (28°C) reduce embryo motility and limb length, particularly affecting hindlimb proportions. 2. **Pharmacological Immobilisation in Chickens**: In chickens, pharmacological immobilisation of embryos, while maintaining a constant incubation temperature, significantly reduces limb length, particularly in the femur and tarsometatarsus, between E13 and E18. 3. **Growth Plate Dynamics**: Altered embryo movement influences the dynamics of specific growth plates in the femur and tarsometatarsus, leading to targeted changes in chondrocyte proliferation and progression. 4. **Molecular Mechanisms**: Transcriptional profiling reveals that the mTOR pathway plays a crucial role in regulating limb growth. The mTOR pathway is more active in the femur compared to the tarsometatarsus, suggesting that reduced mTOR activity in the femur allows for greater responsiveness to mechanical cues. 5. **Developmental Plasticity**: The study demonstrates that environmental factors can influence cellular activity in growing bones, leading to phenotypic variation in limb morphology during prenatal development. This plasticity may have evolutionary implications for adapting to different environments. Overall, the research provides new insights into how environmental factors can integrate with intrinsic developmental processes to influence limb development, highlighting the potential for environmental input to shape limb proportions and performance.This study investigates the influence of environmental factors, specifically incubation temperature, on the development and growth of limbs in embryonic crocodiles and chickens. The research hypothesis is that changes in prenatal movement, influenced by environmental factors, can alter limb proportions during embryonic development. Key findings include: 1. **Temperature and Motility in Crocodiles**: Incubation temperature affects embryo motility and limb bone growth in West African Dwarf crocodiles. Lower temperatures (28°C) reduce embryo motility and limb length, particularly affecting hindlimb proportions. 2. **Pharmacological Immobilisation in Chickens**: In chickens, pharmacological immobilisation of embryos, while maintaining a constant incubation temperature, significantly reduces limb length, particularly in the femur and tarsometatarsus, between E13 and E18. 3. **Growth Plate Dynamics**: Altered embryo movement influences the dynamics of specific growth plates in the femur and tarsometatarsus, leading to targeted changes in chondrocyte proliferation and progression. 4. **Molecular Mechanisms**: Transcriptional profiling reveals that the mTOR pathway plays a crucial role in regulating limb growth. The mTOR pathway is more active in the femur compared to the tarsometatarsus, suggesting that reduced mTOR activity in the femur allows for greater responsiveness to mechanical cues. 5. **Developmental Plasticity**: The study demonstrates that environmental factors can influence cellular activity in growing bones, leading to phenotypic variation in limb morphology during prenatal development. This plasticity may have evolutionary implications for adapting to different environments. Overall, the research provides new insights into how environmental factors can integrate with intrinsic developmental processes to influence limb development, highlighting the potential for environmental input to shape limb proportions and performance.