Maotherium sinensis: a basal primate!

Adding
the symmetrodont mammal, Maotherium sinensis (NGMC 97415, Rougier et al. 2013, Early Cretaceous 125 mya; Fig. 1) to the large reptile tree (Fig. 2; LRT) nests it at the base of the primates. This nesting has not been recovered before.

Not sure yet
about M. asiaticus (Ji et al. 2009). It has not yet been added to the LRT.

Figure 1. Maotherium sinensis in situ and with DGS tracings and reconstructions. Inset shows skull of M. asiaticus.

Figure 1. Maotherium sinensis in situ and with DGS tracings and reconstructions. Inset shows skull of M. asiaticus. Even at this early stage the manus and pes have a primate-like appearance, more like that of Proconsul and Homo than Notharctus. The postorbital ring is present. The tail is relatively short. The ilium is long and the sacrum is robust with at least 4 sacrals, able to handle great stress, as in leaping. Note both humeri are broken.

Wikipedia reports: “Maotherium is a genus extinct symmetrodont mammal. Though little is known about this group, the symmetrodonts have several similarities – specifically their teeth. They have tall pointed, but simple molars in a triangular arrangement.”

As you know,
the large reptile tree has no characters based on variation in molar shape. Given that, Maotherium is known from a complete and articulated fossil. It has a complete postorbital ring, The tail is relatively short and without chevrons. The ilium is long and at least four sacrals were present, indicating both a strong hind limb and a reinforced sacrum, both possible leaping structures. What look like epipubes are likely displaced pubes, which are otherwise buried. Both humeri are broken at mid shaft in the fossil. No retro process is present on the lower posterior dentary. The hand and foot of Maotherium is quite primate-like, even at this early stage, 125 million years ago, and not as lemur-like as in Notharctus. 

Figure 2. Maotherium cladogram. Here it nests as a basal primate.

Figure 2. Maotherium cladogram. Here it nests as a basal primate.

I didn’t expect this nesting
but once I scored about twenty traits, the trend became apparent and finally overwhelming. This puts primate origins back about twice as far a previously figured, from 65 mya to 125 mya. This is a trend we looked at earlier here.

Other symmetrodonts
not necessarily basal primates, include Zhangheotherium and Akidolestes. At this point, symmetrodonts might just be a primitive grade, rather than a clade of mammals. Only testing will tell.

And once again,
mammal phylogeny is proving to be much more simple than conventional wisdom and paradigm seem to indicate.

Figure 3. Maotherium illustrated in situ and cleaned up from Kielan-Jaworowska  2013. The skull is missing some overlooked traits in this illustration.

Figure 3. Maotherium illustrated in situ and uncrushed from Kielan-Jaworowska 2013. The skull is missing some overlooked traits in this illustration.

References
Rougier GW, Qiang J, Novacek MJ 2003. A New Symmetrodont Mammal with Fur Impressions from the Mesozoic of China. Acta Geologica Sinica 77 (1): 7–14. doi:10.1111/j.1755-6724.2003.tb00104.x.
Ji Q, Luo Z-X, Zhang X-L, Yuan C-X and Xu L 2009. Evolutionary development of the middle ear in Mesozoic therian mammals. Science 326 (5950): 278–281. doi:10.1126/science.1178501. PMID 19815774.
Kielan-Jaworowska Z 2013. In pursuit of early mammals. Indiana University Press 272 pp.

further information online

A few more mammals added to the LRT

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.

Figure 1. Subset of the large reptile tree focusing on mammals and their immediate ancestors. Here a few more taxa have been added, many from the Early and Late Cretaceous. Vincelestes, Repenomamus, Ernanodon, Asioryctes, Liaoconodon and Jeholodens are among them.

Figure 1. Subset of the large reptile tree focusing on mammals and their immediate ancestors. Here a few more taxa have been added, many from the Early and Late Cretaceous. Vincelestes, Repenomamus, Ernanodon, Asioryctes, Liaoconodon, Proconsul and Jeholodens are among them.

Some new basal taxa have been added
and none of them have upset the basic tree topology that just keeps growing.

  1. Vincelestes – a basal carnivore with a short face and giant canines, Early Cretaceous, 125 mya.
  2. 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.
  3. Ernanodon – close to lemurs (primates), but basal to pangolins, but again on its own branch yet to be filled, Paleocene, 61 mya.
  4. Asioryctes – a tiny basal insectivore with a full arcade teeth, Middle Late Cretaceous, 85 mya.
  5. Liaoconodon – a sister to Asioryctes, Early Cretaceous, 120 mya.
  6. Jeholodens – a basal multituberculate, close to rodents, Early Cretaceous 125 mya.
  7. Proconsul – a primate nesting between lemurs and humans,

Remember 
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.

Epipubic bones
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).

 

Two Cretaceous mammals join the LRT: Asioryctes and Repenomamus

As in traditional reptiles
I’m seeking basal relationships of basal taxa in mammals. For those you have to go to the Middle and Early Cretaceous, not the Paleocene.

Asioryctes (mid-Cretaceous, 85 mya, Kielen-Jaworowska 1975, 1984, Fig. 1) was a basal eutherian mammal, not far from Eomaia (Ji et al. 2002), the basalmost eutherian. In the large reptile tree (LRT, subset Fig. 5) Asioryctes nested at the base of Tupaia + Glires (including Multituberculates). It retained most of the original arcade of teeth, but with smaller canines. The overbite is a trait of this clade.

Fig. 1. Asiorryctes skull on the tip of someone's finger. Overlays include a traditional tracing that does not have the same proportions, a stretched out version of the same and a DGS tracing from which data was scored.

Fig. 1. Asiorryctes skull on the tip of someone’s finger. Overlays include a traditional tracing that does not have the same proportions, a stretched out version of the same and a DGS tracing from which data was scored. Note the reduction in the canines (yellow), which are lost in this herbivorous clade.

Figure 2. Asioryctes in life. Post crania is imagined.

Figure 2. Asioryctes in life. Post crania is imagined. Image out of “From the Beginning – the Story of Human Evolution”.

The second Cretaceous mammal
is the predator, Repenomamus (Li et al. 2000, Hu et al. 2005; Early Cretaceous, Figs. 3, 4). One specimen of R. robustus was the size of the opossum, Didelphis, and included digested baby dinosaur bones, R. giganticus was half again as large, one of the largest known mammals of the dinosaur era. Despite its predatory nature, note the reduction in the canine teeth, a clade trait that is reversed in most primates.

Figure 3. Repenomamus in situ with bones colorized digitally (DGS) and used in the reconstruction in figure 4. This eutherian retained epipubes (prepubes) that living metatherians retain.

Figure 3. Repenomamus giganticus in situ with bones colorized digitally (DGS) and used in the reconstruction in figure 4. This eutherian retained epipubes (prepubes) that living metatherians retain. The manus and pes were reported missing here, but parts may be present. The orange parallel bones in the rib cage could be metatarsals.

Repenomamus
is traditionally considered a non-therian gobiconodontid mammal, but it nests between the bat clade and the dermopteran + primate clade in the large reptile tree (Fig. 5) where several eutherians retain epipubic bones. The clavicle is robust here, as in sister taxa.

Figure 4. Repenomamus reconstructed using DGS methods. The manus and feet are loose figments at present. Despite its predatory nature, note the reduction in canines, a clade trait.

Figure 4. Repenomamus reconstructed using DGS methods. The manus and feet are loose figments at present. Despite its predatory nature, note the reduction in canines, a clade trait.

Figure 5. Latest mammal subset of the large reptile tree with Asioryctes and Repenomamus added.

Figure 5. Latest mammal subset of the large reptile tree with Asioryctes and Repenomamus added.

You have to go with
phylogeny first, and then identify your clade traits, rather than the other way around. And be prepared for change, which has always been the nature of Science.

Chronology and Phylogeny
The nesting of Repenomamus indicates that certain mammal clades had already diverged prior to its appearance.

Yixian Formation, Early Cretaceous, 125 mya yields Eomaia and Repenomamus from this list. Other Early Cretaceous mammals include:

  1. Astroconodon – 2mm triconodont molars, likely a predator
  2. Jugulator – 5mm triconodont molars, likely a predator
  3. Pinheirodontidae – clade of multituberculates
  4. Spinolestes – 24 cm long triconodont teeth, skeleton and fur along with xenarthrous vertebrae.
  5. Vincelestes – a 4 cm  skull with large canines described as a stem-therian, I’ll test it next to see how it nests.

The presence of
Early Cretaceous multituberculates implies the presence of more primitive coeval stem rodents and rabbits and perhaps stem tenrecs.

References
Hu Y, Meng J, Wang Y-Q and Li C-K 2005. Large Mesozoic mammals fed on young dinosaurs. Nature 433:149-152.
Li J-L., Wang Y.Wang Y-Q and Li C.-K. 2000. A new family of primitive mammal from the Mesozoic of western Liaoning, China [in Chinese]. Chin. Sci. Bull. 45, 2545–2549).
Ji et al 2002. The earliest known eutherian mammal, Nature 416:816-822.
Kielan-Jaworowska Z 1975. Preliminary description of two new eutherian genera from the Late Cretaceous of Mongolia. Palaeontologia Polonica 33:5-15.
Kielan-Jaworowska, Z 1984. Evolution of the therian mammals in the Late Cretaceous of Asia. Part VII. Synopsis. Palaeontologia Polonica 4: 173-183. online pdf

wiki/Asioryctes
wiki/Eomaia

Tenrecs and Echolocation

Just a short note before the weekend…
Earller here, here and here we looked at the traditionally overlooked morphological traits that link little tenrecs to larger whales.

Well, here’s one more
that I just became reacquainted with. Tenrecs, like whales, hunt by echolocation. I think we all heard that somewhere in our past. I did, but forgot it in the last fifty years. Here’s the reference:

References
Gould E 1965. Evidence for Echolocation in the Tenrecidae of Madagascar
Proceedings of the American Philosophical Society 109 (6): 352-360. online here.

Let’s talk about mammal interrelationships

Now that a wide gamut of mammals
has been added to the large reptile tree (LRT, subset Fig. 1), the tree topology has become distinct from prior studies, many of which depend on DNA, which does well in many cases, but makes untenable sisters of several genera.

Figure 1. Mammal subset of the large reptile tree with clades named.

Figure 1. Mammal subset of the large reptile tree with clades named.

Case in point: Macroscelidea
(elephant shrews, Fig. 2). Stanhope et al. (1998) proposed the clade Afrotheria based on molecular evidence. Their clade members included elephants and elephant shrews. That’s difficult to accept on the face of it, and the large reptile tree does not recover that relationship.

Figure 2. Macroscelides proboscideus, the elephant shrew or sengis is NOT more closely related to elephants with the purported 'Afrotheria.' but instead is related to Tupaia, the tree shrew.

Figure 2. Macroscelides proboscideus, the elephant shrew or sengis is NOT more closely related to elephants with the purported ‘Afrotheria.’ but instead is related to Tupaia, the tree shrew.

Rather
the large reptile tree recovers:

  1. Monotremata (Ornthorhynchus) as the most basal mammal clade.
  2. Didelphis (opossum) is basal to both Metatheria (so far only three genera) and Eutheria.
  3. The first eutherian split occurs between small carnivores and smaller insectivores
  4. Carnivora also splits into small insectivores: Chiroptera + (Dermoptera + Primates, including Manis)
  5. The two tree shrews, Tupaia and Ptilocercus, are not sister taxa.
  6. The former clade Insectivora is resurrected. It includes Tupaia + elephant shrews, Trogosus + Apatemys and Glires.
  7. Glires includes the traditional rabbits and rodents, but also shrews, moles and multituberculates
  8. Condylartha is resurrected and is the sister to Insectivora.
  9. Condylartha splits between the taeniodont, Onychodectes and the pantodonts, Pantolambda + Ectoconus.
  10. Onychodectes gives rise to tenrecs, which give rise to giant tenrecs and whales
  11. Pantolambda + Ectoconus give rise to Xenarthra (sloths, anteaters), Paenungulata (elephants and kin) and Ungulata (hoover mammals).

Not only do these relationships make more sense
on their face, they provide a gradual accumulation of derived characters down to the toes. You can’t do that with ‘Afrotheria’ and other odd-bedfellow sisters that have become widely accepted within paleontology, despite the fact that they make no sense at several nodes. At other nodes, some DNA clades do match morph studies.

Once again,
we need to look at the results, put our thinking caps on, and toss out DNA results that do not make sense and cannot be supported with morphological studies.

Don’t take my word for it.
I’m reporting results, like Galieo looking through a telescope for the first time or dropping balls off the leaning tower of Pisa. Because this is Science, you can repeat the experiment and discover the mammal family tree for yourself. If you do, let us all know what you recover.

References
Stanhope MJ, Waddell VG, Madsen O, de Jong W, Hedges SB. Cleven GC, Kao D and Springer MS 1998. Molecular evidence for multiple origins of Insectivora and for a new order of endemic African insectivore mammals. Proceedings of the National Academy of Sciences 95 (17): 9967–9972. Bibcode:1998PNAS…95.9967S. doi:10.1073/pnas.95.17.9967. PMC 21445. PMID 9707584.

The human occiput and palate

We looked at the facial portion
of the human skull earlier. Today we’ll look at the occiput and palate (Fig. 1).

Figure 1. Human occiput and palate. On most tetrapods these two are usually set at right angles to each other, but an upright stance has rotated the occiput to a ventral orientation.

Figure 1. Human occiput and palate. On most tetrapods these two are usually set at right angles to each other, but an upright stance has rotated the occiput to a ventral orientation.

There’s nothing new here. 
This is just an opportunity to educate myself on the human palate and occiput. Only the endotympanic (En) is a novel ossification. The occiput is a single bone here, the product of the fusion of several occipital bones. Can you find the suborbital fenestra? It’s pretty small here.

The asymmetry is interesting here.
Sure, this is an old adult, missing some teeth, but you’ll see other examples elsewhere.

Let me know
if you see any errors and they will be corrected. As you already know, everything I present here was learned only 48 hours earlier — or less.

The vague persistence of ‘absent’ bones in the human skull

Humans
(genus: Homo) are, of course mammals, and basal mammals lose the postorbital bar found in cynodonts like Chiniquodon. But even that postorbital bar does not include two bones found in more basal therapsids, the postfrontal and postorbital. In Chiniquodon the postorbital bar is created by a process of the frontal meeting a process of the jugal.

So I was surprised to find
what appear to be vague apparitions that look like those lost bones in the frontal of the human skull. There are 17 frames in this animation (Fig. 1). The last one holds for five seconds and reveals where I think I see vague outlines of the the prefrontal, postfrontal and postorbital bones all fused to the frontals, which are themselves fused medially.

Figure 1. Labeled skull bones in Homo sapiens. The last frame appears to identify the lost prefrontal, postfrontal and postorbital bones last seen in our ancestors from the Permian.

Figure 1. Labeled skull bones in Homo sapiens. The last frame appears to identify the lost prefrontal, postfrontal and postorbital bones last seen in our ancestors from the Permian. Note the dislocated jaw articulation.

The last part of the postorbitals

to ‘disappear’ are the posterior processes, which seem to laminate to the cranial bones in several therapsids, including dinocephalians. But there is also a vague portion that appears on the duckbill platypus, Ornithorhynchus.

The prefrontals
were the last to fuse and so appear to be the easiest to see now. Like gills and a tail, humans retain the genes for these, but they get resorbed or fused during embryonic ontogeny.

There is a difference between losing a bone
and fusing a bone. Phylogenetically losing a bone is usually marked by a reduction to disappearance. Fusion is, well, fusion. And that can be more readily reversed.

The pterygoid and lateral sphenoid
are both bones typically seen in palatal view, but in mammals and humans they rise, tent-like, to appear in the nasal and orbital cavities.

In mammals the bones sometimes get new names
but they’re still the same bones. The jugal becomes the zygomatic arch, for instance. The bones that make up the occiput fuse to form the occipital.

We’ll look at the palate and occiput soon. 
And a fetus.