American-born Malachi Davis has been chosen to represent Britain in the 400m and 4x400m relay at the Olympics.
Davis, who gained a British passport less than two weeks ago, was handed his place in Tuesday's final round of track and field selections for Athens.
Chris Tomlinson has been preferred to Nathan Morgan for the long jump.
Dean Macey's place in the decathlon was confirmed, Ricky Soos will compete in the 800m, Emeka Udechuku in the discus and Jo Pavey has a place in the 1500m.
Sarah Claxton has been called up for the 100m hurdles and Shelley Newman for the women's discus.
The relay line-ups were also finalised, with Matt Elias joining Davis in the 4x400m team and Dwayne Grant and Nick Smith added to the 4x100m squad.
Catherine Murphy joins the women's 4x400m squad after recovering from injury.
The biggest talking point is the inclusion of Davis, who had not even been to Britain until his arrival for the Norwich Union trials in Manchester.
The 26-year-old from Sacramento, whose mother was born in London, made an immediate impression when he beat several top rivals in his heat.
But he trailed in fifth in the final as Tim Benjamin and Daniel Caines sealed 400m places.
The selectors accepted Davis was jet-lagged and gave him another chance to prove himself at the Loughborough meeting on Saturday.
But Davis, who had achieved the "A" qualifying standard by 0.03 seconds in Tucson, was edged out by Welsh Commonwealth 400m hurdles silver medallist Elias.
Elias' consolation for missing out on an individual place is a call-up for the 4x400m relay, joining Benjamin, Caines, 400m hurdles medal prospect Chris Rawlinson, Sean Baldock and Robert Tobin.
Former European champions Du'aine Ladejo and Iwan Thomas both missed out.
British long jump record holder Tomlinson failed to reach the 'A' qualifying standard of 8.19 metres in Madrid on Saturday.
But he jumped the 'B' mark of 8.05m and was preferred to Morgan even though his rival achieved the 'A' standard last year.
Tomlinson's record of reaching the Commonwealth, European and world finals in the past three years counted in his favour.
Macey's inclusion was a formality after he easily achieved the 'B' qualifying standard of 7,700 points in Hexham at the weekend - his first competition for three years.
Udechuku clinched his discus place by winning with an 'A' qualifying throw in Loughborough.
And Soos bettered the 800m 'B' mark with a time of one minute 46.09 seconds in Finland.
Pavey, a finalist over 5,000m at the last Olympics, now has the option of choosing between that distance and the 1500m.
UK performance director Max Jones said: "A number of good quality performances took place in the week following the Olympic trials and as a result we have picked additional athletes.
"The squad of 58 is now equivalent to the athletics squad for Sydney when taking into consideration the high IOC and IAAF qualifying standards for the 2004 Games.
"It is good to see Dean Macey back in the team, which will be positive for all of them."