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

Kiwi ancestors

Worthy et al. 2013 reported:
“Until now, kiwi (Apteryx owenii, Apterygidae, Shaw 1813; Fig. 1) have had no pre-Quaternary fossil record to inform on the timing of their arrival in New Zealand or on their inter-ratite relationships.” They described two fossils (femur and quadrate) from the Early Miocene (Fig. 1; 19–16mya) which they named Proapteryx. “The new fossils indicate a markedly smaller and possibly volant bird, supporting a possible overwater dispersal origin to New Zealand of kiwi independent of moa. If the common ancestor of this early Miocene apterygid species and extant kiwi was similarly small and volant, then the phyletic dwarfing hypothesis to explain relatively small body size of kiwi compared with other ratites is incorrect.

Figure 2. Jurapteryx, Pseudocrypturus, Apteryx and Proapteryx to scale.

Figure 2. Jurapteryx, Pseudocrypturus, Apteryx and Proapteryx to scale. In lateral view it is difficult to see the width of the ventral pelvic elements. They are not as wide as the egg diameter. Note the lack of a pygostyle in all three taxa.

By contrast
the large reptile tree (LRT, 1213 taxa) nest the kiwi with Pseudocrypturus (Houde 1988; Early Eocene) apart from other ratites, as the basalmost birds with living representatives.

Apteryx owenii (Shaw 1813) The extant flightless kiwi has an elongate naris that extends to the tip of its beak. Maybe two teeth are there. Here it nests with Pseudocrypturus, but flightless traits push it toward Struthio, by convergence. in the pre-cladistic era, Calder (1978, 1984) considered the kiwi a phylogenetic dwarf derived from the larger moa, but that was invalidated by Worthy et al. 2013 and the large reptile tree.

Proapteryx micromeros (Worthy et. al. 2013) was a slender, tiny Miocene (18 mya) ancestor likely capable of flight.

Pseudocrypturus cercanaxius (Houde 1988; Early Eocene) was originally considered a northern hemisphere ancestor to ratites (like the ostrich, Struthio). Today these primitive flightless birds are chiefly restricted to the southern hemisphere. It could be that early birds did start in the South and had migrated to the North during the Paleocene (66-56 mya).

Since ratites are basal to extant birds, and Pseudocrypturus is basal to ratites (paleognaths), Pseudocrypturus is also quite similar to the ancestor of all extant birds despite its late appearance in the early Eocene. Perhaps something very much like it was one of the few survivors of the K-T extinction event.

It’s notable that Pseudocrypturus has long legs. Early ducks, like Presbyornis, and basal raptors, like Sagittarius, also had long legs. Evidence is building that this is the primitive condition for the clade of living birds arising from the K-T extinction event.

Worthy et al. nest Apteryx
within the order Casuariiformes, which includes cassowaries, emirs, and kiwi, but only in the absence of Pseudocrypturus.

The kiwi egg vs ventral pelvis issue
In most tetrapods, including humans, the egg/baby passes through the cloaca/vagina which passes through the two ischia. That was also likely the case with Archaeopteryx, because this is also the case with Gallus the chicken. In extant birds the ischia posterior tips no longer touch, but are widely separated. Going several steps further, in the kiwi the enormous egg is held in front of the pubis (Fig. 1), which is also in front of the ischia.

The following video of a kiwi laying an egg
shows the cloaca a substantial distance below the swirl that marks its tail. kiwi egg video click to play pretty much located at the tip of the long axis of the egg in figure 1 (maybe a little higher/closer to the tail).

Figure 2. Kiwi laying an egg. Click to play.

Figure 2. Kiwi laying an egg. Click to play.

In the LRT
Pseudocrypturus and Apteryx (Fig. 1) nest together and apart from the ratites. Pseudocrypturus is basal to all living birds. It probably first appeared in the Early Cretaceous. It was found in the Paleocene.

References
Calder WA 1978. The kiwi. Scientific American 239(1):132–142.
Calder WA 1984. Size, function and life history. 448 pp. Cambridge (Harvard U Press).
Houde PW 1986. Ostrich ancestors found in the northern hemisphere suggest new hypothesis of ratite origins. Nature 324:563–565.
Houde PW 1988. Paleognathus birds from the early Tertiary of the northern hemisphere. Publications of the Nuttall Ornithological Club 22. 147 pp.
Shaw 1813. Naturalist’s Miscellany 19:
Worthy, TH. et al. (5 coauthors) 2013. Miocene fossils show that kiwi (Apteryx, Apterygidae) are probably not phyletic dwarves. Paleornithological Research 2013, Proceedings of the 8th International Meeting of the Society of Avian Paleontology and Evolution. Retrieved 16 September 2017.

wiki/Pseudocrypturus
wiki/Apteryx, Kiwi
wiki/Proapteryx

Tachyglossus, the other egg-laying mammal

Figure 1. The echidna (genus: Tachyglossus) in life. This slow-moving spine-covered anteater has digging claws.

Figure 1. The echidna (genus: Tachyglossus) in life. This slow-moving spine-covered anteater has digging claws.

Tachyglossus aculeatus (Shaw 1792) is the echidna and the only other genus of egg-laying mammal. It protects itself with sharp spines and has a long, ant-catching tongue. The hands and feet are adapted to digging with short, almost immobile proximal elements (Fig. 3) and long claws. Prepubic bones precede the pubis. A proximal process sits atop the fibula. The leathery snout without whiskers is sensitive to vibrations.

Figure 2. The skull of Tachyglossus is largely fused together, lacks teeth and has no lateral temporal fenestra (because the jaws don't move much in this anteater.

Figure 2. The skull of Tachyglossus is largely fused together, lacks teeth and has no lateral temporal fenestra (because the jaws don’t move much in this anteater. Hard to find sutures here. Let me know if you have better data to make corrections.

Distinct for its sister,
Ornithorhynchus, and many other mammals, the acetabulum is perforated. The lateral temporal fenestra is absent. So are the teeth. Like the hedgehog, the echidna can roll itself into a ball for protection.

Figure 3. Tachyglossus skeleton, manus and x-rays. Note the perforated pelvis.

Figure 3. Tachyglossus skeleton, manus and x-rays. Note the perforated pelvis.

There are those
who say characters define a taxon. We have to get away from that hypothesis. Here a perforated acetabulum would make Tachyglossus a dinosaur, to the late Larry Martin’s delight. Tachyglossus has no temporal fenestra. So, does that make it an anapsid? No. The only thing that tells us what a taxon is… is its placement on a wide gamut cladogram that tests hundreds of candidate sister taxa and hundreds of traits. Testing a suite of several hundred traits in a wide gamut study is the only way to confidently determine taxonomy and avoid the pitfalls of convergence and taxon exclusion that plague smaller studies that too often fail to minimize false positives and ‘by default’ nestings. And some DNA studies cannot be validated, except by morphological studies.

References
Shaw G 1792. Musei Leveriani explicatio, anglica et latina.

wiki/Tachyglossus

Meiolania eggs confirm basal turtle status

Earlier the horned turtles, Meiolania and Niolamia, were nested in the large reptile tree (LRT) as basalmost hardshell turtles, closely related to the toothed horned stem turtle/pareiasaur, Elginia. This was heresy when introduced.

Now
newly discovered turtle eggs (Lawver and Jackson 2016) add evidence to the basal status of Meiolania.

From the Lawver and Jackson 2016 abstract:
“A fossil egg clutch from the Pleistocene of Lord Howe Island, Australia that we assign to Testudoolithus lordhowensis, oosp. nov. belongs to the stem turtle Meiolania platyceps.  Thin sections and scanning electron microscopy demonstrate that these eggs are composed of radiating acicular aragonite crystals. This mineral composition first evolved either before the split between Meiolaniformes and crown Testudines or prior to Proterochersis robusta, the earliest known stem turtle. Meiolania platyceps deposited its eggs inside an excavated hole nest. This nesting strategy likely evolved no later than the Early to Middle Jurassic.”

All known meiolanids
are from later, higher Late Cretaceous and Tertiary strata.

Figure 5. Meiolania, the most primitive of known turtles, has lateral forelimbs, like non turtles.

Figure 1. Meiolania, one of the most primitive of known hard-shell turtles, has lateral forelimbs, like non turtles. All extant turtles have anteriorly-directed humeri. It also had cranial horns, like the toothed pareiasaur/turtle? Elginia.

At present,
soft-shell and hard-shell turtles have a dual origin from separate small Late Permian and Middle Triassic pareiasaur ancestors, Elginia and Sclerosaurus. Both were also horned. The traditional earliest known turtles, Proganochelys and Odontochelys are both known from later, Late Triassic, strata.

Not on topic, but worth watching on YouTube:
Here’s a video about the origin of oil in the Jurassic. It runs for 90 minutes and is fascinating throughout. The video reminds us what a recent Golden Age we currently live in based on a limited supply of petroleum products. The video concludes we have long passed the tipping point for climate change based on the flood of cheap energy. And the end of the oil age is something our children will see. Ironically, climate change in the ice-free Jurassic was one factor in the Earth producing the oil we now use.

References
Lawver DR and Jackson FD 2016. A fossil egg clutch from the stem turtle Meiolania platyceps: implications for the evolution of turtle reproductive biology. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1223685.

DGS Embryo Lizards at PLOS

I’m happy to show you
examples of professional paleontologists using digital equipment to render bones, segregate bones and reconstruct fossil taxa. This one is from Fernandez et al. 2015.

Figure 1. Fossil lizard eggs rendered after CT scanning. Colors represent various parts of the body. Their digital segmentation is the same as my digital segregation, only hi-tech . THIS is the way to render bones in roadkill fossils. Let's make this standard practice.

Figure 1. Fossil lizard eggs rendered after CT scanning. Colors represent various parts of the body. Their digital segmentation is the same as my digital segregation, only hi-tech . THIS is the way to render bones in roadkill fossils. Let’s make this standard practice.

The above eggs are totally scrambled.
Lucky for us Fernandez et al. put in the effort to segregate, identify and reconstruct every bone in the egg. They did an excellent job!

From the Discussion:
“The digital segmentation of the two least crushed eggs (SK1-1 and SK1-2) shows that both embryonic skeletons are mostly disarticulated, but assembled into clusters reflecting the original position.” (Fig. 1). These workers used a CT scanner to reassemble this scrambled egg.

Along the same lines
and lacking a CT scanner, I use Photoshop, but the idea is the same: to extract as much data as possible from difficult specimens.

And after the bones are digitized
they can be moved about and reconstructed (Fig. 2). I want to encourage all workers to adopt the practice of coloring each bone in situ. Much better than simply drawing a line to the center of each bone and leaving the shape of the bone to the reader’s imagination.

Figure 2. Reconstructed embryo lizard skull from digitized data.

Figure 2. Reconstructed embryo lizard skull from digitized data.

Which lizard is it?
Just eyeballing it here, but Liushusaurus (Fig. 3) and Bahndwivici are close matches and the former is a contemporary. Not a perfect match, but close enough for now.

Figure 3. The basal scleroglossan, Liushusaurus, is a close match to the lizard embryo.

Figure 3. The basal scleroglossan, Liushusaurus, is a close match to the lizard embryo. The post cranial bones are likewise quite similar. Note the rostrum does not elongate here, another example of isometric growth.

Both are basal scleroglossans.
Based on sister taxon first appearances, both had been around since the Late Permian.

Figure 5. Bahndwivici, a basal anguimorph, scleroglossan squamate similar to the embryo in the egg.

Figure 4. Bahndwivici, a basal anguimorph, scleroglossan squamate similar to the embryo in the egg.

Npw, about those eggs
The authors noted these eggs had gekko-like hard eggshells, but attributed them to anguimorph lizards (monitors, mosasaurs, etc.). In the large reptile tree Liushusaurus nests just basal to geckos AND anguimorphs. So, the diversity described in the paper’s headline is maybe… not so much. Bahndwivici nests basal to anguimorphs like monitors and mosasaurs.

And please note
the embryo is an isometric match to its adult counterpart. So isometry can and does occur in the growth of certain lepidosaurs, like pterosaurs.

And on that note
Wills someone please fix the Wikipedia entry for Aurorazhdarcho. It includes a wide variety of pterosaurs of all shapes and sizes, some with small rostra and some with elongate rostra, all attributed to one genus based on the false paradigm of allometry during isometry in pterosaurs.

References
Fernandez V, Buffetaut E, Suteethorn V,  Rage J-C, Tafforeau P and Kundrát M 2015. Evidence of Egg Diversity in Squamate Evolution from Cretaceous Anguimorph Embryos. PLoS ONE 10(7):e0128610. doi:10.1371/journal.pone.0128610