This area chart displays the average body mass of three penguin species—Adelie, Chinstrap, and Gentoo—using animated hover interactions that enlarge data points and reveal exact values. Built with D3 v7, it uses `d3.rollups` to aggregate the CSV data, `d3.scalePoint` and `d3.scaleLinear` for positioning, and `d3.area` with a monotone curve to render the filled SVG path. Circles respond to mouseover/mouseout via D3 transitions, while axes and labels are generated with `d3.axisBottom` and `d3.axisLeft`.