The S&P/ASX 200 Index (ASX: XJO) is out of form again on Thursday and sliding into the red. At the time of writing, the benchmark index is down 0.45% to 8,105.4 points.

Four ASX shares that are falling more than most today are listed below. Here's why they are dropping:

Appen Ltd (ASX: APX)

The Appen share price is down 4% to $1.38. This artificial intelligence data services company's shares have been under significant pressure since the release of its full year results last month. Appen reported a 14% decline in revenue to $234.3 million and a net loss of $20 million. No guidance was given for FY 2025, but management stated its ambition to "deliver profitable growth." Investors may have doubts that this will be achieved or at a level that justified its market capitalisation.

Mesoblast Ltd (ASX: MSB)

The Mesoblast share price is down 4.5% to $2.29. This is despite the biotechnology company's shares being added to the benchmark ASX 200 index on Thursday. They join the index as a replacement for Arcadium Lithium, which has just been acquired by Rio Tinto. Today's decline could be due to profit taking from some investors. After all, even after today's weakness they remain up over 600% since this time last year. This incredible return has been driven by the company finally having one of its stem cell therapies approved by US regulators.

Rio Tinto Ltd (ASX: RIO)

The Rio Tinto share price is down 1.5% to $115.88. This has been driven by the mining giant's shares going ex-dividend this morning for its final dividend of FY 2024. Last month, Rio Tinto released its full year results and revealed a 1% decline in sales revenue to US$53.7 billion and 15% increase in profit after tax to US$11.6 billion. However, this didn't stop the Rio Tinto board from cutting its fully franked final dividend to 225 US cents per share (from 258 US cents per share). Eligible shareholders can look forward to receiving this dividend next month on 17 April.

Woodside Energy Group Ltd (ASX: WDS)

The Woodside share price is down 4% to $23.06. This has also been caused by the energy giant's shares going ex-dividend today. Last month, Woodside released its full year results and declared a fully franked final dividend of 53 US cents per share. This was down 12% on the prior corresponding period. At current exchange rates, this equates to an 84 Australian cents per share fully franked dividend, which represents an attractive 3.5% dividend yield based on yesterday's close price.