In this format, rows represent specimens, and columns represent variables.

We begin with our 3D array of landmarks: 
lmks
## , , Specimen1
## 
##         [,1]     [,2]
## [1,] 8.89372 53.77644
## [2,] 9.26840 52.77072
## [3,] 5.56104 54.21028
## [4,] 1.87340 52.75100
## [5,] 1.28180 53.18484
## 
## , , Specimen2
## 
##          [,1]     [,2]
## [1,] 8.679762 54.57819
## [2,] 8.935628 53.83027
## [3,] 5.451914 54.65691
## [4,] 1.987882 52.68871
## [5,] 1.515514 53.02331
## 
## , , Specimen3
## 
##           [,1]     [,2]
## [1,]  9.805328 56.06903
## [2,] 10.137712 55.27961
## [3,]  6.647680 55.73664
## [4,]  3.448484 53.86698
## [5,]  3.012230 54.34478



And convert it to a 2D matrix: 
lmks <- two.d.array(lmks)
lmks
##               [,1]     [,2]      [,3]     [,4]     [,5]     [,6]     [,7]     [,8]     [,9]    [,10]
## Specimen1 8.893720 53.77644  9.268400 52.77072 5.561040 54.21028 1.873400 52.75100 1.281800 53.18484
## Specimen2 8.679762 54.57819  8.935628 53.83027 5.451914 54.65691 1.987882 52.68871 1.515514 53.02331
## Specimen3 9.805328 56.06903 10.137712 55.27961 6.647680 55.73664 3.448484 53.86698 3.012230 54.34478