It certainly was a volatile month for the S&P/ASX 200 Index (ASX: XJO).

There were plenty of ups and downs during the 30 days but ultimately the benchmark index recorded a gain of 3.6% to finish at 8,126.2 points.

Among the best performers on the index last month were the ASX 200 shares listed below. Here's why they charged higher:

Lynas Rare Earths Ltd (ASX: LYC)

The Lynas Rare Earths share price was the best performer on the ASX 200 index last month with a 24.2% gain. This appears to have been driven by news that China is placing export restrictions on seven rare earth elements that are essential to the production of advanced technologies. Investors may believe that Lynas could be a big winner from the move. In addition, the rare earths producer released its quarterly update late in the month. For the three months ended 31 March, Lynas reported sales revenue of $123 million and sales receipts of $124.6 million. This was an increase of 21.5% and 15.7%, respectively, over the prior corresponding period.

Eagers Automotive Ltd (ASX: APE)

The Eagers Automotive share price wasn't far behind with a gain of 23.2%. This was despite there being no news out of the auto retailer last month. Though, it is worth noting that its shares have been on fire since the start of the year. This has been driven by the release of its full year results in late February. Eagers Automotive reported a 13.6% increase in revenue to $11.2 billion and record underlying EBITDAI of $550.4 million. This allowed the company to maintain its fully franked dividend at a record of 50 cents per share.

Megaport Ltd (ASX: MP1)

The Megaport share price was on form in April and charged 18.6% higher. Once again, this was despite there being no news out of the network as a service provider during the month. But much like Eagers Automotive, Megaport's shares have been on an upward trajectory since earnings season in February. So much so, its shares are now up over 50% since the start of the year. This is despite the tech selloff in March and April.

Challenger Ltd (ASX: CGF)

The Challenger share price was a strong performer and recorded a gain of 17.6% during the month. Investors were bidding the annuities company's shares higher following news that TAL Dai-ichi Life Australia agreed to acquire a 15.1% minority interest from MS&AD Insurance Group Holdings. TAL paid 763 yen per Challenger share, which was the equivalent of A$8.46 per share. That was a sizeable 52.7% premium to its last close price. Challenger's CEO, Nick Hamilton, said: "Dai-ichi Life is a global leader in life insurance and we look forward to building a relationship that will benefit both our customers and shareholders. We welcome their significant investment in our business and will explore future opportunities that support our strategic objectives."