The Spaniard's last defeat in this event was against Guillermo Coria 10 years ago.
Gumy has worked with Argentines Guillermo Canas and Guillermo Coria, as well as Brazilian Kuerten.
Fellow Argentine Guillermo Coria fared better, the eighth seed seeing off experienced Spaniard Felix Mantilla 7-6 6-1 6-3.
Argentina's Guillermo Coria came through a topsy-turvy encounter against Davide Sanguinetti of Italy, eventually winning 6-0 2-6 6-0.
Second seed Guillermo Coria stormed into the third round with a 7-6 6-3 win over France's Paul-Henri Mathieu.
Nalbandian could make it three Argentines in the semi-finals, after Guillermo Coria's win over Carlos Moya on Tuesday.
Dr Coria said the evidence suggested the animals were together before they died.
Calleri saved two set points in the opening set, before Coria's accuracy from the baseline saw him move into the lead.
Co-author Rodolfo Coria of the Carmen Funes Museum in Plaza Huincul, Argentina, said the dig showed evidence of social behaviour in Mapusaurus.
"(Kuerten's) beaten me twice, in Monte Carlo and Roland Garros, and it would be good to play him in his home, " said Coria.
Nalbandian, ranked ninth in the world, will also have to recover quickly if Coria wins, taking on Beck in the final singles match.
Monte Carlo finalist Guillermo Coria , the 13th seed, kept his recent good form going with a comfortable 6-2 6-2 win over Fernando Verdasco.
Kuerten will now play Guillermo Coria in the final on Sunday after the unseeded Argentine beat Cecil Mamiit of the United States 7-5 6-2.
In the final set, Coria twice broke serve to move into a 3-0 lead before Calleri broke back for the first time in the match.
But Federer regained his composure in the the third and broke serve in the sixth game before closing out the match on a Coria double-fault.
The second-seeded Spaniard, who is bidding for a sixth straight Monaco title, has not suffered defeat in Monaco since losing in the third round to Argentine Guillermo Coria in 2003.
Coria, who lost only one set in the whole tournament, broke serve for a 5-4 lead in the second and Calleri sent a backhand wide to drop the second set.
Guillermo Coria, ranked eighth in the world, will have to bounce back in his reverse singles on Sunday after an opening loss to Beck when he faces Slovak number one Dominik Hrbaty.
Nadal's only defeat at the tournament was against Guillermo Coria as a 16-year-old in 2003, and world No. 12 Verdasco never looked like registering his first win over his compatriot in 10 encounters.
His last defeat at the Monte Carlo Country Club came as a 16-year-old against Guillermo Coria in 2003, and he has lost only six career matches out of 164 on his favored clay surface.
But Calleri - who made 48 unforced errors - could not sustain the momentum and another wide backhand that sailed wide gave Coria his first match point which he converted with a big service winner.
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