Mako Shark Tooth- Which Species?

[Paleoworld-101]

This shark tooth was found on the foreshore at Beaumaris in Victoria, Australia. It is 5-6 million years old. I am confident it is a mako shark tooth but i am trying to decide which species to label it. The following shark taxa are listed in the fauna found at this location:

 

Heterodontus cainozoicus, Carcharias taurus, Carcharodon megalodon, Parotodus benedeni, Isurus desori, Isurus oxyrinchus, Isurus hastalis, Isurus retroflexus, Lamna?, Megascyliorhinus sp., Carcharhinus cf. brachyurus, Carcharhinus sp., Galeocerdo aduncus

 

The majority of teeth at the site are from Carcharodon hastalis (or Isurus hastalis depending on who you believe). However i feel like my tooth is too narrow to be a C. hastalis tooth. Even the first lower anteriors of C. hastalis that i have seen are somewhat proportionally wider than my example, hence why i am leaning towards one of the other species of mako but i want to know what the shark tooth experts on this forum think. I had a look in the book 'Vertebrate Palaeontology of Australasia' (which has a nice section on fossil chondrichthyans) and the closest match i could see was a first lower anterior tooth from Isurus paucus (tooth A on page 552 if anyone has the book) but this species isn't listed in the fauna for Beaumaris. Might it instead be an Isurus oxyrinchus or desori tooth? Additionally my tooth is fairly straight, and most of the other mako specimens i am seeing are more curved. 

 

It measures 24 mm long and 11 mm wide. 

 

 

 

 

 

 

 

[Trilobiting]

I'm guessing Isurus desori, but I may be wrong. 

[britishcanuk]

I would say desori/oxyrinchus as well.

[jhw]

If I found one like that here in California, that's what I would consider it to be too. Narrow toothed Mako.