''Haldanodon'' is an extinct

docodont Docodonta is an order of extinct mammaliaforms that lived during the Mesozoic, from the Middle Jurassic to Early Cretaceous. They are distinguished from other early mammaliaforms by their relatively complex molar teeth, from which the order ge ...

mammaliaform which lived in the

Upper Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

(

Kimmeridgian In the geologic timescale, the Kimmeridgian is an age in the Late Jurassic Epoch and a stage in the Upper Jurassic Series. It spans the time between 157.3 ± 1.0 Ma and 152.1 ± 0.9 Ma (million years ago). The Kimmeridgian follows the Oxford ...

, about 145 million years ago). Its

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

remains have been found in

Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of th ...

, in the well-known fossil locality of Guimarota, which is in the

Alcobaça Formation The Alcobaça Formation, previously known as the Guimarota Formation and also known as the Consolação Unit, is a geological formation in Portugal. It dates back to the Kimmeridgian stage of the Late Jurassic. It is an important source of inform ...

. It may have been a semi-aquatic burrowing insectivore, similar in habits to desmans and the

platypus The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or mono ...

. 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 In anatomy, a nasal concha (), plural conchae (), also called a nasal turbinate or turbinal, is a long, narrow, curled shelf of bone that protrudes into the breathing passage of the nose in humans and various animals. The conchae are shaped lik ...

plates, a complex feature of mammalian

nasal cavities The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal c ...

. 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 Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a r ...

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

, part of a group of

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

early mammaliaforms with specialized teethLuo Z-X and Martin T. 2007. Analysis of molar structure and phylogeny in docodont genera. Bulletin of Carnegie Museum of Natural History. The docodonts were widespread in

Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...

, 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 In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to '' Docodon'' in many analyses. ;Phylogeny

Paleobiology

''Haldanodon'' may have been a fossorial (burrowing) and/or semi-aquatic

insectivore A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores were ...

, similar in lifestyle to the modern

desmans The desman, a snouted and naked-tailed diving insectivore of the tribe Desmanini (also considered a subfamily, Desmaninae), belongs to one of two Eurasian species of the mole family, Talpidae. This tribe consists of two monotypic genera of semi ...

and ''Ornithorhynchus'' (the duck-billed

). This is indicated by some skeletal features, such as a wide

scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eith ...

and stout limb bones with specialized joints. It likely had a sprawling gait based on the configuration of its limb joints, but this is probably a result of its specialized lifestyle instead of a primitive trait. The fingers and claws of the forelimb seem to correspond closely to scratch-digging modern mammals like

armadillo Armadillos (meaning "little armored ones" in Spanish) are New World placental mammals in the order Cingulata. The Chlamyphoridae and Dasypodidae are the only surviving families in the order, which is part of the superorder Xenarthra, alo ...

s and

pangolin Pangolins, sometimes known as scaly anteaters, are mammals of the order Pholidota (, from Ancient Greek ϕολιδωτός – "clad in scales"). The one extant family, the Manidae, has three genera: '' Manis'', ''Phataginus'', and '' Smuts ...

s, rather than shovel-diggers like

moles Moles can refer to: * Moles de Xert, a mountain range in the Baix Maestrat comarca, Valencian Community, Spain *The Moles (Australian band) *The Moles, alter ego of Scottish band Simon Dupree and the Big Sound People * Abraham Moles, French engin ...

Description

Classification

Paleobiology

References

Further reading