Dugong and Trichechus (the extant manatee) enter the LRT

Earlier
the large reptile tree (LRT, 2340 taxa) nested the basal sirenian Dusisiren with extinct, aquatic, short-legged Moeritherium and the beavers, Castor and Castoroides.

Today
the extant sirenians, Dugong, the East Asian marine dugong, and Trichechus, the East American marine manatee, enter alongside the North Pacific extinct sirenian Dusisiren. No surprises there. The three sirenians differ quite a bit in skull shape and tooth number yet still nest together based on other traits.

Click the links above to see the data.

Yesterday
I discovered online an old rendering of the palate of Moeritherium, a manatee and dugong ancestor in the LRT. Aquatic Moeritherium had more cheek teeth than the related beavers, Castoroides and Castor. Moeritherium had the same number and type of teeth as their mutual precursor, Plesiadapis, an arboreal basalmost rodent in the LRT – traditionally mistaken for a primate ancestor despite the hyper-robust incisors and lost canine creating a diastema = toothless space in the jaws.

Plesiadapis takes us on a tangent that needs to be explored.

Ever wonder why
‘plesidapiformes’ were and are traditionally nested with primates, rather than rodents?
Here are some answers (from a 2014 online Nature citation listed below).

1. Molar cusps: Plesiadapiforms look quite similar to definitive primates, with broad talonid basins and a similar pattern of cusps and crests.
2. Long fingers well designed for grasping, and other features of the skeleton related to arboreality
3. Carpolestes simpsoni had a divergent big toe with a nail
4. Molecular analyses of mammalian relationships have fairly consistently placed primates in a group called Euarchonta with two other living orders: Scandentia (tree shrews) and Dermoptera (colugos = ‘flying’ lemurs).

In the LRT primate ancestors include
taxa overall similar in size and shape to Notharctus. These include (in order of increasing distance) Paroodectes, Magnadapis + Adapis, Kopidodon, Alcidedorbignya, Dissacus, Amphicyon major and Vulpavus ovatus. These are all arboreal taxa with a primate-like full dental arcade, including canines and lacking a rodent-like diastema and hyperrobust incisors.

By testing traditionally omitted taxa,
the LRT recovers novel hypotheses of interrelationships that were waiting to be discovered. These hypotheses now need to be tested with a similar list of taxa by independent workers. Based on personal experience, this may take 15 years of 12-hour days, so don’t hold your breath waiting for this competing test requiring more motivation and time than most PhD theses.

If not tested, then the sin of taxon exclusion, the number one problem in paleontology, will continue to stain traditional myths like the LRT invalidated plesiadapiform + primate interrelationship.

References
Slicox MT 2014. Primate Origins and the Plesiadapiforms. Nature Education Knowledge 5(3):1

nature.com/scitable/knowledge/library/primate-origins-and-the-plesiadapiforms-106236783/