Tamjacks
Tamjacks are a subgroup of furred shrews (specifically Tams) of the order Lignatores characterized by their long mustelid-like bodies, axe-like tails, and advanced nest construction. They are all descended from the Tamjack.
Tamjacks form a notable portion of the paraphyletic grouping sometimes called "seafaring shrews", consisting of all shrews which construct floating nests to live out at sea.
Anatomy
Compared to most other shrews, Tamjacks tend to have rather long, flexible bodies and relatively short legs. They have scales on their backs, which form armor in some species. Their tail bears a keratinous paddle shaped like a double-headed axe, which has a bone core in some species. This structure, sometimes called a "tail axe" or a "tail saw", is typically used to cut through wood, and the keratinous parts contain calcified "grit" which gives it a sandpaper-like texture.
Unlike other shrews, which give birth to fetal larvae like marsupials, Tamjacks have a long gestation period and give birth to far more developed young. However, they retain the pouch for carrying their offspring. Also unlike other shrews, tamjacks have internal testes, making them more streamlined for swimming and avoiding risk of castration by mating accident in basal species which had spikes on their underbellies.
Behavior
Most species of tamjack live in mated pairs with young offspring. Some, such as the Tamustel, are social and can live in groups.
Tamjacks notably have higher intelligence than most shrews, which is primarily demonstrated in their advanced nest construction. One species, the Seashrog, developed especially high intelligence and tool use.
Nest Construction
Tamjacks stand out from other shrews, and indeed most other species on Sagan IV, in the construction of their nests. Though other shrews such as the Marine Tamow build externally similar nests, the interior of Tamjack nests is completely different.
A typical nest for this lineage is radial, consisting of tree trunks bent to form rib-like supports before being covered in other materials such as leaves and sealed using saliva and waterproof berries. The trunks used for nest construction are generally chopped or sawed down using the tail axe. Though originally meant for life out at sea, these nests can take on a variety of modified forms, such as the tree houses of the arboreal Tamhook and the huts which Tamkors construct for their offspring. The Seashrog also takes nest construction a step further, including a flat deck on top which can be walked on and additional logs added to serve as support beams for weak spots. Nest maintenance is generally performed by all inhabitants of a given nest.
Evolution
The original Tamjack first evolved in Generation 151. It spawned a small radiation of descendants to populate various islands, including the large armored herbivore tamkor, the arboreal tamhook, and the social otter-like tamustel. However, rising sea levels would result in the extinction of the tamustel and reduce the range of the other species to just a single island, leaving the original Tamjack as the only one left with significant options for radiating to new biomes.
Starting in Generation 160, the original Tamjack gave rise to a second radiation of immediate descendants. Thanks to the supercontinent leaving the entirety of tropical and temperate waters open with no boundaries, one descendant, the Seashrog, successfully spread to every landmass on Sagan IV. With the original tamjack being outcompeted by the more successful shrog forms, most tamjack diversity outside of Hydro Island is limited to the more derived group. However, more basal tamjacks descended from the burrowing tamjack also continued to take on new forms, including a large herbivore which was able to make its way to Barlowe and a small hedgehog-like generalist which remained on Hydro.
Size
Tamjacks tend to be fairly large creatures, though there are exceptions. Thus far, they have ranged in size from 15 centimeters to 6.5 meters in length.