The last few days
have been spent out of town on family business and updating the LRT (large reptile tree, now 761 taxa) with a few more mammals (Fig. 1). Sorry to be gone. Now I’m back.
Some new basal taxa have been added
and none of them have upset the basic tree topology that just keeps growing.
- Vincelestes – a basal carnivore with a short face and giant canines, Early Cretaceous, 125 mya.
- Repenomamus – large enough to eat baby dinosaurs, this carnivore sister with smaller canines nested basal to bats, flying lemurs, pangolins and primates, but definitely on its own branch yet to be filled, Early Cretaceous, 125 mya.
- Ernanodon – close to lemurs (primates), but basal to pangolins, but again on its own branch yet to be filled, Paleocene, 61 mya.
- Asioryctes – a tiny basal insectivore with a full arcade teeth, Middle Late Cretaceous, 85 mya.
- Liaoconodon – a sister to Asioryctes, Early Cretaceous, 120 mya.
- Jeholodens – a basal multituberculate, close to rodents, Early Cretaceous 125 mya.
- Proconsul – a primate nesting between lemurs and humans,
each fossil is likely not found at the origin of each genus, but probably later, at its fullest and most populous time.
These nestings indicate
that the radiation of basal carnivorous and insectivorous mammals occurred much earlier than 65 million years ago, prior to 125 mya. The large herbivores listed above (Fig. 1) likely appeared later.
The multituberculate/triconodont issue.
Traditional paleontologists consider (eu)triconodonts and multituberculates basal mammals (= Mammaliaformes) that radiated prior to the origin of the Monotremes, Metatherians and Eutherians. By contrast, and using far fewer dental characters, the large reptile tree found these two clades were sisters to rodents (multituberculates) or nested at various places elsewhere within the Mammalia. Basal mammals from the Early Cretaceous listed above (Fig. 1) typically (but see Sinocondon) have a full arcade of teeth and other traits, not found in multituberculates and triconodonts. On the other hand, multituberculates share a long list of traits with rodents and kin, from their skulls to their toes. That should not happen if they were indeed non-mammals mammaliaformes.
Why don’t we see rodents, rabbits and other taxa earlier than we do?
Perhaps those taxa did not inhabit substrates that encourage fossilization. This tree does indeed upset current thinking regarding the emergence of certain clades and interrelationships. I don’t want it to. It simply does this on its own, as it has done identifying pterosaurs within a new clade of lizards, the Tritosauria, etc. etc.
In the large reptile tree epipubic bones continue in several Cretaceous clades and disappeared several times by convergence.
All sister taxa here
look similar to one another and share long lists of traits that lump them together. Short lists split sisters apart. I’ll start listing traits and showing reconstructions over the next few weeks and you’ll see where the data have produced the above cladogram (Fig. 1).