Haldanodon

Haldanodon Temporal range: 145 Ma PreЄ Є O S D C P T J K Pg N ↓
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
(unranked):	Amniota
(unranked):	Therapsida
(unranked):	Cynodontia
(unranked):	Mammaliaformes
Order:	Docodonta
Genus:	Haldanodon Kühne & Krusat, 1972
Binomial name
Haldanodon exspectatus

Haldanodon exspectatus is an extinct mammaliaform, specifically a docodont. It lived in the Upper Jurassic (Kimmeridgian, about 145 million years ago). Its fossil remains have been found in Portugal, in the famous field Guimarota.

Description

The appearance of this animal, a little more than 38 cm (15 in) in length, must have been quite similar to that of the current desman (genera Desmana and Galemys), small insectivores related to the moles. The body was compact, while the legs were short and robust; the articulation of the distal humerus was particularly expanded, indicating strong muscles. The first forepaw phalanges were short, while those terminals were curved and laterally compressed. The skull was equipped with roughness on the nasal bones, which suggest the presence of a shield of keratin. The 7.6 cm (3 in) jaws were robust; in particular, the mandible was equipped with a highly developed coronoid process, which indicated the presence of very powerful jaw muscles.

Classification

The shape and arrangement of its indicate that this animal was a representative of docodonts, a group of primitive mammaliforms, but specialized with regard to the teeth, who lived in the first part of the Mesozoic Era. The skeleton of Haldanodon is well known and has allowed a comparative study with that of other primitive mammaliaforms, such as the monotremes, Morganucodon and Hadrocodium. According to the results of these analyses, Haldanodon would be in a position evolutionary intermediate between Morganucodon and Hadrocodium.

Lifestyle

Haldanodon was probably an aquatic insectivore akin to the modern platypus and desmans. This is indicated by numerous skeletal features, such as the strong forelimbs and specialized ends, the skull and the cephalic shield with eyes small and tight, all adaptations for fossoriality and swimming. It occurred in a wetland environment, so aquatic foraging was very likely.

The wide disparity in size in the long bones of the feet (such as the humerus and femur) may indicate that Haldanodon never ceased to grow in size throughout the life span, such as reptiles today.

References

• Kühne & Krusat (1972), Legalisierung des taxon Haldonodon (Mammalia, Docodonta)
• Neues Jahrbuch für Geologie, Paläontologie and Mineralogie, Monatshefte 5, P.300-302
• Martin T (2005), postcranial anatomy of Haldanodon exspectatus (Mammalia, Docodonta) from the Late Jurassic (Kimmeridgian) of Portugal and Its bearing for mammalian evolution, Zoological Journal of the Linnean Society, 145, p. 219-248
• Martin T & M Nowotny (2000), The docodont Haldanodon Guimarota from the mines, p. 91-96
• Martin T & Krebs B (eds), Guimarota - A Jurassic Ecosystem, Verlag Dr. Friedrich Pfeil, München