Haldanodon
Haldanodon is an extinct docodont mammaliaform which lived in the Upper Jurassic. Its fossil remains have been found in Portugal, in the well-known fossil locality of Guimarota, which is in the Alcobaça Formation. It may have been a semi-aquatic burrowing insectivore, similar in habits to desmans and the platypus. Several specimens are known, include a partial skeleton and well-preserved skulls.
Description
Haldanodon was about as long as a desman, and may have had a similar ecology. The skull was low and triangular when seen from above. For many years it had the best-known skull material of any docodont, making it vital for understanding the taxonomic position of that mammaliaform group. It was the first Mesozoic mammaliaform discovered to possess turbinal plates, a complex feature of mammalian nasal cavities. However, it also retained some curiously primitive traits in common with non-mammaliaform cynodonts.The body was compact and the legs were short and robust. The articulation of the distal humerus was particularly expanded, indicating strong muscles for either digging or swimming. The front paws were relatively short, and the bones of the forelimb were curved and laterally compressed.
Classification
Haldanodon was a docodont, part of a group of Jurassic to Cretaceous early mammaliaforms with specialized teeth The docodonts were widespread in Laurasia, and show an interesting diversity of ecological lifestyles unknown in other Mesozoic mammaliaforms. Haldanodon is specifically considered a docodontid, and has been found as the sister taxon to Docodon in many analyses.;Phylogeny