Penguin ancestry: Genomics vs phenomics

Another New Zealand Paleocene penguin,
Kupoupou, has been published by Blokland et al. 2019 who relied on genes to determine penguin ancestry. They reported, “Sphenisciformes (penguins), Procellariiformes (tubenoses), Gaviiformes (loons) and Phaethontiformes (tropicbirds) are diverse and early diverging clades in the radiation of waterbirds. The former three form part of the well-supported core waterbird assemblage, Aequornithes, sensu Mayr (2010), among Neoaves (e.g., Hackett et al., 2008; Mayr, 2017). Tropicbirds have also been shown to have a close relationship to this core waterbird clade Late Cretaceous and early Paleogene fossils are well known for the Sphenisciformes.”

Figure 1. The extant murre, Uria, and the extant penguin, Aptenodytes to scale.

Figure 1. The extant murre, Uria, and the extant penguin, Aptenodytes to scale. Murres can fly and dive.

By contrast, using traits, not genes,
the large reptile tree (LRT 1619+ taxa) nests penguins, like Aptenodytes, with murres like Uria (Fig 1), which Wikipedia considers one of the Alcidea (auks and kin) within the Charadriiformes (tropical shorebirds, gulls and auks). We looked at the close phenomic relationship of murres and penguins back in 2017 here.

Figure 2. Uria and Aptenodytes to scale. Not sure how a cladogram cannot put these two together, unless they are based on genomics.

Figure 2. Uria and Aptenodytes to scale. Not sure how a cladogram cannot put these two together, unless they are based on genomics.

When genomic studies fail
to replicate phenomic (trait-based) studies, distrust genomic studies. Time and again gene studies fail in deep time studies for reasons that appear to be rooted in geography (e.g. Afrotheria, Laurasiatheria, etc.)

Figure 1. Several birds with zygodactyl feet (light red) and one member of the clade Zygodactylidae (red).

Figure 3. An old, but still valid subset of the LRT focusing on birds. The penguin clade appears fifth from the bottom here.

And if you’re interested
in what came before murres in the LRT: look to terns (Thalasseus, subset Fig. 3), which today routinely migrate from pole to pole. So, that takes care of distribution.

Figure 3. Skeleton of Thalasseus, the crested tern.

Figure 4. Skeleton of Thalasseus, the crested tern. Compare to similar skeletons of murres and penguins in figure 1.

Figure 1. Thalasseus the created tern nests with Rhynchetos, the kagu.

Figure 5 Thalasseus, the created tern, nests basal to murres and penguins in the LRT.

References
Blokland JC, Reid CM, Worthy TH, Tennyson AJD, Clarke JA and Scofield RP 2019. Chatham Island Paleocene fossils provide insight into the palaeobiology, evolution and diversity of early penguins (Aves, Sphenisciformes) Palaentologia Electrontica 22.3.78 1-92. https://doi.org/10.26879/1009
Deguine, J-C 1974. Emperor Penguin: Bird of the Antarctic. The Stephen Greene Press, Vermont.
Hackett S et al. 2008. A phylogenetic study of birds reveals their evolutionary history. Science 320:1763–1768.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

wiki/Aptenodytes
/wiki/Uria

 

Polydactylus: a living palaeonisciform

By adding fish
to the large reptile tree (LRT, 1618+ taxa) I wondered if I might find some sort of overlooked phylogenetic link to a traditionally long extinct clade as the LRT did with turtles and small horned pareiasaurs, with mysticete whales and desmostylians, or with lepidosaurs and pterosaurs. Among fish, lizard fish (Lepidogalaxias) and related deep sea fish (e.g. Malacosteus, Fig. 3) likewise nest apart from traditional teleosts, close to long extinct clades.

Figure 1. Subset of the LRT focusing on the clades surrounding Polydactylus.

Figure 1. Subset of the LRT focusing on the clades surrounding Polydactylus.

Earlier
Polydactylus (Girard 1858; Fig. 2) entered the LRT between the tuna, Thunnus, and flatfish (flounders, soles and halibuts, like Psettodus) following Harrington et al. 2016, who considered Polydactylus an outgroup taxon for flatfish. Unfortunately, it was never a good fit in the LRT. Polydactylus didn’t look like Thunnus or Pstettodus or anything in-between. That nesting was a mistake.

A rescoring of Polydactylus
and additional taxa nested it with traditionally extinct palaeonisciformes, like Moythomasia (Fig. 3), and deep sea viper fish, like Malacosteus (Fig. 4). Now Polydactylus looks like its sisters and the scores confirm it.

Figure 1. Polydactylus colored with revised skull bone identities. Of particular interest is the squamosal (hot pink), which otherwise looks like a preopercular, a bone that no sister taxa have.

Figure 2. Polydactylus colored with revised skull bone identities. Of particular interest is the squamosal (hot pink), which otherwise looks like a preopercular, a bone that no sister taxa have.

The squamosal / preopercular issue.
Taken out of a phylogenetic context, it appears that Polydactylus lacks a squamosal and has a ‘preopercular’ that articulates to the same bones as the squamosal in sister taxa.  Now take a look at its sisters. They have a squamosal and lack a preopercular. In cases like this, when a bone is missing that is supposed to be there, while a bone is present that should not be there, the most parsimonious conclusion is those two are homologous bones. The preopecular already has several other origins in the LRT. This makes one more.

Figure 1. Moythomasia, a traditional palaenisciforme, is basal to the thread fin, Polydactylus and shares many of the same skull bones. Note the placement of the squamosal, close to the maxilla and postorbital, distinct from Polydactylus, in which the squamosal is more posterior.

Figure 3. Moythomasia, a traditional palaenisciforme, is basal to the thread fin, Polydactylus and shares many of the same skull bones. Note the placement of the squamosal, close to the maxilla and postorbital, distinct from Polydactylus, in which the squamosal is more posterior, like a preopercular.

According to Wikipedia,
“The Palaeonisciformes are an extinct order of early ray-finned fishes which began in the Late Silurian and ended in the Late Cretaceous.” So the nesting of Polydactylus with other palaeonisciformes means this clade is not extinct. This is a new hypothesis of interrelationships that required confirmation from an independent analysis or several. Let me know if this has been hypothesized before and I will give proper credit to the originator. I have seen none of the above taxa firsthand. This may be the first time these taxa have been tested together… and that’s the value the LRT brings to the table.

Figure 3. Malacosteus niger in lateral view.

Figure 4. Malacosteus niger in lateral view.

Polydactylus oxtonemus (Girard 1858; up to 23cm, some species up to 2m) is the extant Atlantic threadfin. Traditionally considered a Perciforme (perch family) or an outgroup to the flatfish, here Polydactylus is shallows-dwelling survivor of a traditionally extinct clade, the Palaeonisciformes. Note the five thread-liker rays / feelers anterior to the pectoral fin arising from the gular bone. These drag along the sea floor sensing prey. Note the large eyes and angular rostrum, as in Moythomasia. An elongated premaxilla, a toothless maxilla, a second dorsal fin, an anteriorly shifted set of pelvic fins and a diphycercal tail distinguish this taxon from its sisters, convergent with the phylogenetic pattern seen in other derived teleost and non-teleost fishes.


References
Girard CF 1858. Notes upon various new genera and new species of fishes, in the museum of the Smithsonian Institution, and collected in connection with the United States and Mexican boundary survey: Major William Emory, Commissioner. Proceedings of the Academy of Natural Sciences of Philadelphia. 10: 167-171.
Harrington RC, et al. (6 co-authors) 2016.Phylogenomic analysis of carangimorph fishes reveals flatfish asymmetry arose in a blink of the evolutionary eye. BMC Evolutionary Biology 16 (224).
White EI 1933. 
New Triassic Palaeoniscids from Madagascar. The Annals and Magazine of Natural History, Tenth Series 10:118-128.

wiki/Palaeonisciformes
wiki/Moythomasia
wiki/Mimipiscis
wiki/Pteronisculus
wiki/Atlantic_threadfin (Polydactylus)

The deep sea, bisexual tripod fish enters the LRT without a skull

Fish that live on the seafloor
of the deepest oceans adapt in many strange ways to their lonely, dark, high pressure niche.

The tripod fish,
Bathypterois grallator (Fig. 1), stands on fin tips in the seafloor ooze, facing the current, waiting for tiny planktonic crustacean prey and conspecific mates to come by. If no mates come by, each individual is capable of producing both sperm and eggs.

Figure 1. Bathypterois, the deep sea tripod fish, shown with diagram of jaws and palate from Sulak 2006, then colored and matched to in vivo specimen.

Figure 1. Bathypterois, the deep sea tripod fish, shown with diagram of jaws and palate from Sulak 2006, then colored and matched to the in vivo specimen.

The only skull reference
for Bathypterois I was able to find (Sulak 1975) documented jaws and palate bones, but not skull roofing or cranial bones (Fig. 1) for several species. Evidently skull bones are not necessary at such depths.

Figure 2. Prionotus, the sea robin, has more of a barracuda-like face. Uniquely, medial spines from the pectoral fin evolve to act like fingers for walking on the sea floor.

Figure 2. Prionotus, the sea robin, has more of a barracuda-like face. Uniquely, medial spines from the pectoral fin evolve to act like fingers for walking on the sea floor.

Even so,
Bathypterois nested between the piranha, Serrasalmus, and the scabbard fish, Aphanopus, basal to the sea robin (Prionotus) clade. Sea robins modify their pectoral fins into pseudo fingers and likewise dwell upon the seafloor, though not at such depths.


References
Sulak KJ 1975. The systematics and biology of Bathypterois (Pisces, Chlorophthalmidae) with a revised classification of benthic mystophiform fishes. University of Miami Press, 398 pp. also:  Galathea Report. 1977; 14:49pp.

wiki/Bathypterois_grallator

Sturgeons are living osteostracans. So are we.

According to Wikipedia,h
“The class Osteostraci (“bony shields”) is an extinct taxon of bony-armored jawless fish, termed “ostracoderms“, that lived in what is now North America, Europe and Russia from the Middle Silurian to Late Devonian.

“Anatomically speaking, the osteostracans, especially the Devonian species, were among the most advanced of all known agnathans. This is due to the development of paired fins, and their complicated cranial anatomy. The osteostracans were more similar to lampreys than to jawed vertebrates in possessing two pairs of semicircular canals in the inner ear, as opposed to the three pairs found in the inner ears of jawed vertebrates.”

Lampreys have no fins, nor do they have disc-shaped skulls and armor, like sturgeons do.

Figure 1. The heterostracan Cephalaspis (above) compared to the sturgeon Pseudoscaphorhynchus (below). These are similar morphologies that have been overlooked previously. In both cases the jawless or tubular mouth is below the skull.

Figure 1. The osteostracan Cephalaspis (above) compared to the sturgeon Pseudoscaphorhynchus (below). The similarities of these armored morphologies have been overlooked previously. In both cases the jawless or tubular mouth is below the skull, the former towards the front, the latter below the eyes.

The similarities of these armored morphologies
have been overlooked previously. In both cases the jawless or tubular mouth is below the disc-like skull. In sturgeons the lacrimal forms the top of the tube.

A premaxilla and maxilla arrive
with the genesis of teeth.

Here’s what Wikipedia has to say,
“These jawless vertebrates are the sister-group of gnathostomes. Several synapomorphies support this hypothesis, such as the presence of: sclerotic ossicles, paired pectoral fins, a dermal skeleton with three layers (a basal layer of isopedin, a middle layer of spongy bone, and a superficial layer of dentin), and perichondral bone.

“Most osteostracans had a massive cephalothorac shield, but all Middle and Late Devonian species appear to have had a reduced, thinner, and often micromeric dermal skeleton. This reduction may have occurred at least three times independently because the pattern of reduction is different in each taxon.”

Sturgeons retained that osteostracan cephalic shield
for the last 400 million years. And a bit of the armor,  too. The primitive nature of sturgeons has been understood since the beginning of paleoichthyology, but just how primitive has eluded workers until now. If there is an earlier citation that links sturgeons to osteostracans, let me know, so I can give proper credit.

Based on the node
on which the osteostracan Hemicyclaspis, all later taxa, including Tetrapoda and Homo, can also be considered part of the clade Osteostraci.

Figure 4. Subset of the LRT with the addition of several jawless taxa.

Figure 4. Subset of the LRT with the addition of several jawless taxa.

Pseudoscaphirhychus kaufmanni (Nikolskii 1900) is the extant amu darya sturgeon. Distinct from traditional cladograms, the LRT nests this sturgeon between the osteostracan, Hemicyclaspis and the last common ancestor of sharks and bony fish, Chondrosteus. All have weak ventral jaws, no teeth and a shark-like heterocercal tail.

The lacrimal and mandible support a bottom-feeding extendable tube disconnected from the quadrate. Breathing is hampered whenever the mouth is in the mud, so water enters the top of the operculum, then exits laterally.


References
Nikolskii AM 1900. Pseudoscaphirhynchus rossikowi, n. gen, et spec. Ann. Mus. Imp. Sci. St. Petersburg 4, 257–260 (text in Russian).

wiki/Pseudoscaphirhychus
wiki/Sturgeon 
wiki/Chondrosteus
wiki/Osteostraci

Embryos inside placoderms: Austroptyctodus and Materpiscis

According to Wikipedia,
Materpiscis (Latin for mother fish) is a genus of ptyctodontid placoderm from the Late Devonian located at the Gogo Formation of Western Australia. Known from only one specimen, it is unique in having an unborn embryo present inside the mother, with remarkable preservation of a mineralised placental feeding structure (umbilical cord). This makes Materpiscis the oldest known vertebrate to show viviparity, or giving birth to live young. The juvenile Materpiscis was about 25 percent of its adult size. Materpiscis would have been about 11 inches (28 cm) long and had powerful crushing tooth plates to grind up its prey, possibly hard shelled invertebrates like clams or corals.”

Figure 1. Austroptytodus is a better documented (Long 1997) sister to Materpiscis here colorized with tetrapod bone homologs.

Figure 1. Austroptytodus is a better documented (Long 1997) sister to Materpiscis here colorized with tetrapod bone homologs. The jugal (unlabeled) is the blue bone between the green maxilla (mx) and the yellow premaxilla (pms). The quadrate homolog is unlabeled in red.

When added to
the large reptile tree (LRT, 1615+ taxa) Austroptyctodus (Long, Trinajstic, Young and Senden 2008; Devonian 380 mya, 11cm estimated length) nests with another mild-mannered placoderm with a tall head, Bothriolepis (Fig. 2). Note the use of tetrapod homologs in the renaming of several skull bones. This facilitates the comparison of all vertebrates with other vertebrates.

Figure 2. A sample of taxa related to Autroptyctodus with homologous skull bones color identified

Figure 2. A sample of taxa related to Autroptyctodus with homologous skull bones color identified. Note the anterior migration of the post parietal. Some bone identities are changed hear from earlier interpretations consistent with new knowledge gleaned from the ptyctodontids.

Wikipedia reports,
“The ptyctodontid fishes are the only group of placoderms to display sexual dimorphism, where males have clasping organs and females have smooth pelvic fin bases. It had long been suspected that they reproduced using internal fertilisation, but finding fossilised embryos inside both Materpiscis and in a similar form also from Gogo, Austroptyctodus, proved the deduction was true.”

Some videos about Materpiscis attenboroughi

Austroptyctodus gardineri (originally Ctenurella (Miles and Young 1977; Long 1997; Late Devonian) appears to be toothless in the illustration above, but had tooth plates. Bones are relabeled here with tetrapod homologs. Distinct from relatives, Austroptyctodus had a conjoined upper and lateral temporal fenestra, an antorbital fenestra, and fused temporal bones. One specimen is pregnant with three embryos inside, indicating another example of internal fertilization.

Materpiscis attenboroughi (Long, Trinjstic, Young and Senden 2008; Late Devonian; 28cm long est.) is similar to Austroptyctodus and includes a single embryo one-fourth the size of the adult, likely indicating viviparity. Note the ratfish (Chimaera)-like appearance of this placoderm, by convergence.


References
Long JA 1997. Ptyctodontid fishes from the Late Devonian Gogo Formation, Western Australia, with a revision of the German genus Ctenurella Orvig 1960. Geodiversitas 19: 515-555.
Long JA, Trinajstic K, Young GC and Senden T 2008. Live birth in the Devonian period. Nature. 453 (7195): 650–652. doi:10.1038/nature06966

wiki/Materpiscis
wiki/Austroptyctodus

Tetrapod ancestors updated back to Cambrian finless fish

Pictures tell the story, for the most part today.
The large reptile tree
(LRT, 1615+ taxa) presents an occasionally novel and growing list of taxa between Cambrian pre-fish and the first listed tetrapod, Laidleria (Fig. 1 bottom). This list is updated from the previous time this list was first presented without so many basal chordates. Note, it still does not include traditional members, Acanthostega and Ichthyostega. which nest at more derived nodes as they venture back into a more fish-like niche.

Figure 1. These taxa are those closest to main line of tetrapod ancestors. That makes these taxa human ancestors, too.

Figure 1. These taxa are those closest to main line of tetrapod ancestors. That makes these taxa human ancestors, too.

Qiao et al. 2016 report,
“Our findings consistently corroborate the paraphyly of placoderms, all ‘acanthodians’ as a paraphyletic stem group of chondrichthyans, Entelognathus as a stem gnathostome, and the Guiyu-lineage as stem sarcopterygians.”

Figure 3. Traditional cladogram from Lingham-Soliar 2014.

Figure 2. Traditional cladogram from Lingham-Soliar 2014. This has been invalidated by the LRT.

Figure 4. Subset of the LRT with the addition of several jawless taxa.

Figure 3. Subset of the LRT with the addition of several jawless taxa.

References
Brazeau MD and Friedman M 2015. The origin and early phylogenetic history of jawed vertebrates. Nature. 2015;520(7548):490–7. pmid:25903631.
Davis SP, Finarelli JA and Coates MI 2012. Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes. Nature. 2012;486(7402):247–250. pmid:22699617
Dupret V, Sanchez S, Goujet D, Tafforeau P and Ahlberg PE 2014. A primitive placoderm sheds light on the origin of the jawed vertebrate face. Nature. 2014;507:500–503. pmid:24522530
Lingham-Soliar T 2014. The vertebrate integument volume 1. origin and evolution. Springer.com  PDF
Qiao T, King B, Long JA, Ahlberg PE and Zhu M 2016. Early gnathostome phylogeny revisited: multiple method consensus. PLoS ONE 11(9): e0163157. https://doi.org/10.1371/journal.pone.0163157
Zhu M, Zhao W-J, Jia L-T, Lu J, Qiao T and Qu Q-M. 2009. The oldest articulated osteichthyan reveals mosaic gnathostome characters. Nature. 2009;458:469–474. pmid:19325627
Zhu M, Yu X-B, Ahlberg PE, Choo B, Lu J, Qiao T, et al. 2013. A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature. 2013;502(7470):188–193. pmid:24067611
Zhu M, Yu X-B and Janvier P 1999. A primitive fossil fish sheds light on the origin of bony fishes. Nature. 1999;397:607–610.

https://pterosaurheresies.wordpress.com/2019/10/24/tetrapod-evolution-without-ichthyostega-and-acanthostega/

Can an Early Cretaceous ‘stem mammal’ be considered ‘transitional’?

The transition from pre-mammals to early mammals
occurred during the Triassic era, despite the fact that many extremely rare pre-mammals, are known from post-Triassic strata (Fig. 1), but, so far, not post-Cretaceous strata.

Figure 1. Pre-mammal synapsids in the LRT colorized chronologically.

Figure 1. Pre-mammal synapsids in the LRT colorized chronologically. The extreme rarity of these often late-surviving fossils is indicated by the scattershot chronology of sister taxa.

The new tiny Origolestes (Mao et al. 2019; Fig. 2) is an Early Cretaceaous late survivor of a Triassic radiation of pre-mammals. Therefore it is NOT in the lineage of the Mammalia, but retains traits from that clade.

Figure 1. Origolestes in situ with colors added using DGS methods.

Figure 1. Origolestes in situ with colors added using DGS methods. Note the tiny canines and odd coronoid process. These are indicators of a parallel evolution.

From the Mao et al. abstract:
“Based on multiple 3D skeletal specimens we report a new Cretaceous stem therian mammal that displays decoupling of hearing and chewing apparatuses and functions.

Just three days ago we looked at a similar situation in Jeholbaatar, only in that case the loose ear bones represented a reversal. Similar morphologies MUST be seen in a phylogenetic context.

“The auditory bones, including the surangular, have no bone contact with the ossified Meckel’s cartilage; the latter is loosely lodged on the medial rear of the dentary.”

“This configuration probably represents the initial morphological stage of the definitive mammalian middle ear.

Except that it arrives way too late in the fossil record.

Evidence shows that hearing and chewing apparatuses have evolved in a modular fashion. Starting as an integrated complex in non-mammaliaform cynodonts, the two modules, regulated by similar developmental and genetic mechanisms, eventually decoupled during the evolution of mammals, allowing further improvement for more efficient hearing and mastication.”

This represents a parallel evolution of the decoupling of the middle ear bones. Let’s see how the popular press represented this finding, led by the authors.

From an online ScienceNews.org article by Carolyn Gramling:
“Exceptionally preserved skulls of a mammal that lived alongside the dinosaurs may be offering scientists a glimpse into the evolution of the middle ear.”

We don’t need another ‘glimpse’. We know exactly how this happened in the pre-Late Triassic ancestors of mammals.

“The separation of the three tiny middle ear bones — known popularly as the hammer, anvil and stirrup — from the jaw is a defining characteristic of mammals. The evolutionary shift of those tiny bones, which started out as joints in ancient reptilian jaws and ultimately split from the jaw completely, gave mammals greater sensitivity to sound, particularly at higher frequencies. But finding well-preserved skulls from ancient mammals that can help reveal the timing of this separation is a challenge.”

All true and good background for a popular article.

“Now, scientists have six specimens — four nearly complete skeletons and two fragmented specimens — of a newly described, shrew-sized critter dubbed Origolestes lii that lived about 123 million years ago. O. lii was part of the Jehol Biota, an ecosystem of ancient wetlands-dwellers that thrived between 133 million and 120 million years ago in what’s now northeastern China.”

“The skulls on the nearly complete skeletons were so well-preserved that they were able to be examined in 3-D, say paleontologist Fangyuan Mao of the Chinese Academy of Sciences in Beijing and colleagues. That analysis suggests that O. lii’s middle ear bones were fully separated from its jaw, the team reports online December 5 in Science.”

So they’re setting up a narrative without the proper background that mammals with this configuration first appeared in the Late Triassic, tens of millions of years earlier. Then they talk to another expert.

“This paper describes a spectacular fossil,” says vertebrate paleontologist Zhe-Xi Luo of the University of Chicago, who was not involved in the new study. But he’s not convinced that O. lii represents an evolutionary leap forward in mammalian ear evolution.

“Luo notes that O. lii is closely related to the mammal genus Maotherium, which lived around the same time and in roughly the same location. In Science in July, Luo and colleagues reported that a new analysis of Maotherium revealed that its middle ear bones were still connected to its jawbones by a strip of cartilage (SN: 7/18/19).

That finding, Luo says, was expected. Maotherium is well-known as a transitional organism, in which the middle ear bones had begun to rotate away from the jaw but were still loosely connected by that cartilage. There are numerous branches and twigs on the mammal family tree, Luo says, and evolution occurred at a different pace on them. But, he says, it’s unlikely that O. lii would have had separated ear bones when Maotherium didn’t, given the pair’s close positioning on the tree.”

Still no mention of the Late Triassic origin for mammals and the parallel development in this late survivor.

“Luo says he also doesn’t find the study’s evidence that the separation was complete in O. lii convincing. Three of the four skulls in the study were missing all or part of the middle ear, and the gap between the middle ear bones and jaw in the fourth skull may have been a break that occurred during fossilization, he adds.”

See how paleontologists try to put the brakes on the work of their colleagues?

“However, the new study’s researchers reject this idea. “It’s common that different interpretations may exist for a discovery in paleontology,” says vertebrate paleontologist Jin Meng of the American Museum of Natural History in New York, a coauthor of the study. But, Meng says, none of the ear bones or the cartilage in any of the skulls show fractured or broken edges. That, he says, suggests that these features were already separated in the animals before their demise.”

See how paleontologists try to bounce back from criticism? Meng is correct. Such ‘different interpretations’ are common. I have them. Others have them. You have them. In any case, the indisputable late appearances of Origolestes and Maotherium attest to their removal from the origin of the Mammalia. What they can offer us is a parallel look at this chapter in synapsid evolution. In other words, they are not the main attraction. They are a side show.


References
Mao F, Hu Y-M, Li C-K, Wang YQ, Chase MH, Smith AK and Meng J 2019. Integrated hearing and chewing modules decoupled in a Cretaceous stem therian mammal. Science eaay9220 (advance online publication). online here

An ancient critter may shed light on when mammals’ middle ear evolved

wiki/Zhangheotheriidae