Kayentatherium with 38 tiny hatchlings

Hoffman and Rowe 2018
bring us a large field jacket dotted with 38 tiny hatchlings of Kayentatherium, a tritylodontid synapsid the size of a cat (Figs. 1,2). In this wonderful and unique discovery the authors report, Here we present what is, to our knowledge, the first fossil record of pre- or near-hatching young of any non-mammalian synapsid. The single clutch comprises at least 38 individuals, well outside the range of litter sizes documented in extant mammals. This discoverconfirms that production of high numbers of offspring represents the ancestral condition for amniotes, and also constrains the timing of a reduction in clutch size along the mammalian stem.”

Figure 1. Kayentatherium adult.

Figure 1. Kayentatherium adult. Note the extremely narrow braincase on this herbivore. Note the pelvic opening here moved from the original drawing to provide an opening.

That last statement needs to be taken as conjecture
because we don’t have data for a long list of predecessor taxa going back to Devonian tetrapods. The authors’ statement could be true. On the other hand, the tritylodontids, being derived herbivores, might have created lots of babies, while their omnivore and carnivore ancestors, more in the line of mammal ancestry, laid smaller numbers of larger eggs. We just don’t know. The authors provided one puzzle piece. That’s not enough to make a conclusive statement.

Figure 2. Kayentatherium to scale with hatchling and in matching skull lengths for direct comparison. The orbit is larger, the rostrum and temple are smaller.

Figure 2. Kayentatherium to scale with hatchling and in matching skull lengths for direct comparison. The orbit is larger, the rostrum and temple are smaller.

Then Hoffman and Rowe double down:
The discovery of a large clutch in a stem mammal provides material evidence that producing high numbers of offspring is the ancestral condition for amniotes, and that small litters represent a derived mammalian trait.” Wait a minute… lobe-fin coelacanths embryos hatch within the female and only a few are produced at a time. What happened between coelacanths and tritylodontids? We just don’t have the data for a long list of taxa between these two. Best not to guess and make it sound like scientific canon.

Note the narrow braincase in Kayentatherium,
slightly narrower than in ancestors, like Sinoconodon (Fig. 3) and basal mammals, like Sinodelphys. A U of Texas article (ref. below) reports, “The 3D visualizations Hoffman produced allowed her to conduct an in-depth analysis of the fossil that verified that the tiny bones belonged to babies and were the same species as the adult. Her analysis also revealed that the skulls of the babies were like scaled-down replicas of the adult, with skulls a tenth the size but otherwise proportional. This finding is in contrast to mammals, which have babies that are born with shortened faces and bulbous heads to account for big brains.”

Figure 2. Sinoconodon skull(s) showing some variation in the way they were drawn originally.

Figure 3 Sinoconodon skull(s) showing some variation in the way they were drawn originally. Note the relatively large brains on this more primitive taxon.

“The discovery that Kayentatherium had a tiny brain and many babies, despite otherwise having much in common with mammals, suggests that a critical step in the evolution of mammals was trading big litters for big brains, and that this step happened later in mammalian evolution. ‘Just a few million years later, in mammals, they unquestionably had big brains, and they unquestionably had a small litter size,’ Rowe said.”

Actually brains stayed relatively small
until we get to more recent prototheres, more recent metatheres (by convergence) and more recent placentals (again, by convergence). Check out the following basal mammal taxa for cranium ‘narrowness’

  1. Sinodelphys
  2. Brasilitherium
  3. even Didelphis

Extant echidnas and platypuses, have bulbous skulls filled with brains, but not so their Cretaceous ancestors, Cifelliodon and Akidolestes.

To show that cranium width can narrow
or become relatively smaller in highly derived placental mammals check out the following taxa:

  1. Andrewsarchus
  2. Equus
  3. Lophiodon

So the skull can balloon, or narrow, depending on the situation over millions of years.

According to the authors, the skull length of a hatchling
was 1/20 that of an adult with an isometric rostrum and a smaller, allometric, temporal fenestra. Is that correct? See for yourself (Fig. 2). It looks like the orbit was larger, while the rostrum and temple were both smaller. Hate to nit-pick, but there you are…

Again, this was a wonderful find and a great presentation.
We just don’t want to get ahead of ourselves after one discovery, when other hypotheses are currently possible and now on the table.

References
Hoffman EA and Rowe TB 2018. Jurassic stem-mammal perinates and the origin of mammalian reproduction and growth.

utexas.edu/mammal-forerunner-sheds-light-on-brain-evolution

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Hesperocyon: more cat than dog. Prohesperocyon: more mongoose than dog.

This post
and the next one (coming tomorrow) were prompted by a YouTube video on Bear-dogs (Fig. 1, click to play) that promoted both Prohesperocyon (Fig. 2, Wang 1994; “before Western dog”) and Hesperocyon (Scott 1890, “Western dog”) as basal dogs (clade: Canidae).

Cats and dogs are close relatives
in the large reptile tree (LRT, 1277 taxa). Aardwolves (genus: Proteles) nest with dogs and hyaenas (genus: Crocuta) nest with cats.

Prohesperocyon (Fig. 2) nests between raccoons and mongooses + moles, not with dogs (Fig. 4).

Hesperocyon (Figs. 3, 5) nests with Panthera, the lion (Fig. 6), rather than Canisthe wolf (Fig. 7).

Unfortunately,
the PBS Eons video (Fig. 1) was working from old data (Wang 1994) suffering from taxon exclusion.

Figure 1. Prohesperocyon was considered a basal dog in the video, but here nests between raccoons and mongooses + moles.

Figure 2. Prohesperocyon was considered a basal dog in the video, but here nests between raccoons and mongooses + moles.

Wang 1994 reported, “The subfamily Hesperocyoninae includes the oldest and most primitive members of the Canidae.” The LRT could not validate that statement (see Fig. 4) because either Hesperocyoninae is polyphyletic or it is a junior synonym for Carnivora.  Wang reported, “A phylogenetic analysis is performed using cladistic methodology, with Miacis as an outgroup.” In the LRT Miacis is basal to sea lions and Prohesperocyon nests as an outgroup to Miacis.

Figure 1. Hesperocyon skeletons. Note the upraised claws.

Figure 3. Hesperocyon skeletons. Note the upraised claws. That long pink bone between the legs in the photo is a baculum or penis bone.

For Hesperocyon,
the short, steep facial profile, high postorbital processes of the jugal, the extremely large upper molar 1, the longer braincase, the elevated cat-like way that Hesperocyon carried its claws, and a long suite of other traits all nest Hesperocyon with cats, not dogs (Fig. 4).

Figure 3. Subset of the LRT focusing on Carnivora, a basal placental mammal clade. Note cats and dogs in derived nodes.

Figure 4. Subset of the LRT focusing on Carnivora, a basal placental mammal clade. Note cats and dogs in derived nodes.

Some specimens wrongly attributed to Hesperocyon
that have a longer muzzle may be related to dogs, but not the specimen data presented here (Figs. 3, 5).

Figure 2. Two Hesperocyon skulls in lateral view. Note the short, high muzzle, the raised postorbital process of the jugal, the giant, cat-like upper molar.

Figure 5. Two Hesperocyon skulls in lateral view. Note the short, high muzzle, the raised postorbital process of the jugal, the giant, cat-like upper molar.

Don’t let the names fool you.
Even the raccoon (genus: Procyon) has a dog-oriented name (= “before dog”). Worse yet cats and hyaenas are more closely related to dogs than is the “before dog” or the “Western dog.”

Figure 1. Panthera leo skull and skeleton. This taxon nests basal to hyenas + wolves.

Figure 6. Panthera leo skull and skeleton. This taxon nests with hesperocyon in the LRT.

That’s why the LRT is here.
To clarify traditional relationships with more inclusive testing of a wider gamut of taxa.

I hope you’ll agree that it is indeed odd,
that even the strongest of clues, like the well-documented retractable claws of Hesperocyon (also mentioned in the PBS Eons video (Fig. 1), were not cause enough for mammal workers to take another look at their cladograms and paradigms. BTW, retractable claws are not a trait scored by the LRT.

Figure 3. Canis lupus, the wolf, nests as a sister to Crocuta in the LRT.

Figure 7. Canis lupus, the wolf, nests as a sister to Crocuta in the LRT.

We’ll take a look at the big bear-dogs tomorrow,
but you can get a sneak peek here (Fig. 4).

References
Scott 1890 WB. Hesperocyon. The dogs of the American Miocene. Princeton Coll. Bull., 2(2):37–39.
Wang X 1994. 
Phylogenetic systematics of the Hesperocyoninae (Carnivora, Canidae). Bulletin of the American Museum of Natural History. 221: 1–207.

wiki/Hesperocyon
wiki/Prohesperocyon

Caluromys vs Vulpavus vs Ptilocercus

At the base of the Eutheria (placental mammals)
nests the small, extant, didelphid marsupial Caluromys. So it’s worthwhile to put the skulls of a few basal placentals next to Caluromys to see what the similarities and differences are.

Vulpavus comparison
In the large reptile tree (LRT, 1272 taxa) Caluromys nests with Vulpavus (Fig. 1, Eocene; Marsh 1871), a basalmost member of the placental clade, Carnivora. Two molars characterize this clade. Juvenile Caluromys (Fig. 2; Flores, Abdala  and Giannini 2010) also have two molars.

Figure 1. Vulpavus compared to Caluromys skulls in lateral view.

Figure 1. Vulpavus compared to adult Caluromys skull in lateral view. These two taxa nest together in the LRT.

Ptilocercus comparison
(pen-tailed tree shrew, extant, Le Gros-Clark 1926) is best compared, both in size and morphology to the juvenile Caluromys (Fig. 2). Though not a permanent member of the LRT, a test nested the juvenile Caluromys with Ptilocercus.

Figure 2. Ptilocercus (pen-tailed tree shrew) compared to Caluromys (wooly-opossum) young juvenile.

Figure 2. Ptilocercus (pen-tailed tree shrew) compared to Caluromys (wooly-opossum) young juvenile from Flores, Abdala and Giannini 2010.

Caluromys derbianus (Allen 1904; Flores, Abdala and Giannini N 2010, Fonseca and Astúa 2018. ) is the living ‘wooly opossum’, native to Central America. This taxon nests just inside of the first placental clade, Carnivora, despite retaining a marsupium (pouch). It is an omnivore, as in related basal Carnivora, like Nandinia.

Juvenile skulls have only two molars, the same as those found in Vulpavus (below) and other Carnivora, so this trait is neotonous in Carnivora.

That Caluromys is closely related to basal placental taxa is strong… and heretical.
Earlier we looked at skull similarities between Caluromys and the fruit bat, Pteropus.

References
Allen JA 1904. Mammals from southern Mexico and Central and South America. Bulletin American Museum of Natural History 20(4): 29-80.
Flores DA, Abdala F and Giannini N 2010. Cranial ontogeny of Caluromys philander (Didelphidae: Caluromyinae): a qualitative and quantitative approach. Journal of Mammalogy 91(3):539–550.
Fonseca R and Astúa D 2018. Geographic variation in Caluromys derbianus and Caluromys lanatus (Didelphimorphia: Didelphdiae) Zoologica 32(2):109–122.
Heinrich RE and Rose KD 1997. Postcranial morphology and locomotor behavior of two early Eocene miacoid carnivorans, Vulpavus and Didymictis. Palaeontology 40:279-305
Le Gros-Clark WE 1926. On the Anatomy of the Pen-tailed Tree-Shrew (Ptilocercus lowii.) Proceedings of the Zoological Society of London 96: 1179-1309.
DOI – 10.1111/j.1096-3642.1926.tb02241.x
Marsh 0C 1871. Notice of some new fossil mammals and birds from the Tertiary formations of the West. American Journal of Science, Series 3, 2: 120-127

wiki/Vulpavus
wiki/Water_opossum_Caluromys
wiki/Ptilocercus

 

Asioryctes: Re-restoring a pes, re-nesting a taxon

I should have noticed this pairing earlier.
Evidently it escaped everyone else’s notice, too. Asioryctes nemegetensis (Kielan-Jaworowska 1975, 1984; Figs. 1,2; middle Late Cretaceous, Djadokhta Formation, ~85 mya) is a good match for the living bandicoot, Perameles. Maga and Beck 2017 nested Asioryctes with the coeval Ukhaatherium, and the extant Perameles with another bandicoot, Echymipera.

FIgure 1. Skulls of Asioryctes, Perameles and Macrotis compared.

FIgure 1. Skulls of Asioryctes, Perameles and Macrotis compared. The overall shapes are similar, and so are the teeth, and other details. Historically the feet have been different, and that’s our starting point. 

Figure 2. Left: original restoration of Asioryctes pes. Colors added. Right: New restoration based on phylogenetic proximity to Perameles and other marsupial taxa with vestigial digit 1 and gracile digits 2 and 3 (grooming claws).

Figure 2. Left: original restoration of Asioryctes pes. Colors added. Right: New restoration based on phylogenetic proximity to Perameles and other marsupial taxa with vestigial digit 1 and gracile digits 2 and 3 (grooming claws). 

The first three taxa
are members of the large reptile tree (LRT, 1272 taxa), but the first two don’t nest together. The LRT now nests Asioryctes with Perameles and Macrotis, two extant bandicoots. Ukhaatherium nests with the basalmost members of Theria several nodes earlier.

One of the problems with this
is the original restoration of the Asioryctes pes, based on disarticulated parts (Kielan-Jaworowska 1975; Fig. 2). The REAL problem is no other mammal has gracile lateral metatarsals. Sans the pes, the skull nests with Perameles and Macrotis (Fig. 1), taxa with only a vestige pedal digit 1 and reduced digits 2 and 3.

Hmmm.
That opens up a possibility not foreseen by Kielan-Jaworowska.

A new restoration
of the illustrated elements (Fig. 2) identifies the slender metatarsals as 2 and 3. The tarsal elements are all present (contra Kielan-Jaworowska 1975) just reidentified here in accord with a standard bandicoot foot.

And… so… for the first time
we can see a predecessor taxon demonstrating a transitional morphology to the reduced pedal digits 1–3 seen in bandicoots and kangaroos.

References
Geoffrey Saint-Hilaire E 1803. Note sur les genres Phascolomis et Perameles, nouveaux genres d’animaux à bourse. Bulletin des Sciences par la Société Philomathique de Paris 80, 49–150.
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
Maga AM and Beck RMD 2017. Skeleton of an unusual, cat-sized marsupial relative (Metatheria: Marsupialiformes) from the middle Eocene (Lutetian: 44-43 million years ago) of Turkey. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0181712

wiki/Asioryctes
wiki/Perameles
wiki/Macrotis

“An example of why we need heretics”

The following Joe Rogan video (#872, 3.5 hours)
discusses the extinction of North American megafauna about 12,000 years ago, comet research and other issues of interest. The headline (above) is a quote from the video.

There are scientists working today
and over the last century, that were dismissed by critics, accused of pseudoscience, then later lauded for their discoveries and efforts. That doesn’t happen to everybody. The guests also talk about the Spokane megaflood that hit North America and several other topics, often involving comet impacts.

References
pbs.org/wgbh/nova/earth/megafloods-of-the-ice-age.html
wiki/J_Harlen_Bretz

 

 

Not that closely related to bats…

…even so, the resemblance
clearly shows what pre-bats were like (Fig. 1), and not by convergence. Caluromys (right) is the last of the marsupials, transitional to basal placentals. Bats, like Pteropus (left), are not too far from basal placentals.

Figure 1. Pteropus and Caluromys compared in vivo and three views of their skulls. Caluromys is in the ancestry of bats and shows where they inherited their inverted posture.

Figure 1. Pteropus and Caluromys compared in vivo and three views of their skulls. Note the hourglass-shaped nasals, similar frontals, similar overall silhouettes and similar palates. Juvenile Caluromys has only two molars, the same number found in all members of the Carnivora and by convergence Pteropus. Other basal placentals retain 4 or 4 molars.

Caluromys is in the ancestry of bats
in the large reptile tree (LRT, 1272 taxa). Caluromys shows where bats inherited their signature inverted posture, even though that genus is several nodes away from Pteropus.

Since Caluromys is basal to all other placentals,
maybe bats aren’t the odd ones after all, for hanging inverted. It’s the primitive way to go.  All the other placentals that stopped hanging inverted are the derived ones.

We looked at the origin of bats
here and in earlier posts linked therein.

Teeth in the shrew/rodent/rabbit/multituberculate clade

The problem:
Always ready for a review, I noticed in the rat/rabbit clade of the large reptile tree (LRT, 1272 taxa) canine teeth (and sometimes nearby others) were lost creating a diastema in seven subclades (Fig. 1). The biggest worry was the apparent reappearance of a full arcade of teeth in highly derived taxa, like Paulchaffotia and Carpolestes, after a several clades without a full arcade (including rodents and the aye-aye). Generally, that’s not supposed to happen. So I reviewed all the data and made a helpful image (Fig. 2).

Figure 1. Subset of the LRT focusing on the clade of rodents, shrews, rabbits and multituberculates. White taxa have a small or large tooth gap between the incisors and premolars.

Figure 1. Subset of the LRT focusing on the clade of rodents, shrews, rabbits and multituberculates. White taxa have a small or large tooth gap between the incisors and premolars.

The solution:
After trying and failing to force all taxa with a diastema together, the LRT recovered a cladogram in which canine teeth disappeared creating a diastema seven times by convergence in the rabbit/rodent clade (Fig. 1). Apparently unknown taxa with small canines linked the last taxa with canines (hedgehogs) with the first taxa with canines beyond rodents (multituberculates).

You might remember
that marsupials and large placental ungulates also produced taxa with a similar diastema. So it is a common convergent trait.

When charts don’t help, sometimes pictures  do.
Here (Fig. 2) are several taxa from the the subset cladogram above (Fig. 1) so you can see for yourself how evolution works in tiny steps that slowly add up to large changes. Particularly interesting here is the central place of hedgehogs (with a full arcade of teeth) basal to higher clades with a full arcade of teeth alongside yet another clade or two with lost canines (diastema).

Figure 2. A selection of taxa from figure 1 more or less to scale and in phylogenetic order (pink arrows). Hope this helps with the concept of a gradual accumulation of traits. The hedgehogs Erinaceus and Echinops are transitional to the higher taxa with teeth and without.

Figure 2. A selection of taxa from figure 1 more or less to scale and in phylogenetic order (pink arrows). Hope this helps with the concept of a gradual accumulation of traits. The hedgehogs Erinaceus and Echinops are transitional to the higher taxa with teeth and without.

Note:
The rodent-like ‘primates’ Ignacius, Plesiadapis and Daubentonia (Figs. 1, 2) are more closely related to rodents in the LRT (contra Gunnell et al. 2018.) That’s heresy, still waiting to be confirmed or refuted by testing by other workers. Note how similar Ignacius is to the hedgehog, Erinaceus (Fig. 3).

Figure 3. The hedgehog, Erinanceus, compared to Ignacius from the Paleocene.

Figure 3. The hedgehog, Erinanceus, compared to Ignacius from the Paleocene. Note the reduction to loss of the canine in the latter.

References
Gunnell GF et al. (9 co-authors) 2018. Fossil lemurs from Egypt and Kenya suggest an African origin for Madagacar’s  aye-aye. Nature Communications 9(3193).