Aquatic enoplid nematodes: ancestral to hagfish AND common slugs

Earlier we looked at the many homologies that unite
primitive round worms (= aquatic enoplid nematodes, Fig. 1), with primitive chordates (=  hagfish. Fig. 1).

Now let’s look at overlooked evidence
that unites nematodes and hagfish with… primitive molluscs (= slugs, Figs. 1, 2).

Largely (but not completely) overlooked until now,
nematodes (= amphistomes) could have given rise to both hagfish (chordates, deuterostomes) and slugs (molluscs, protostomes). These three taxa are all long, worm-like, bilaterals with sensory tentacles, rasping retreating mouth parts, and for one reason or another depend on producing slime from their skin.

I say ‘not completely overlooked’
because Clark and Uyeno 2019 portrayed cutaway diagrams of a slug and hagfish to show their ‘convergent’ mouth parts.

Figure 1. Nematodes, hagfish and slugs have so many traits in common, one wonders why they are not related to one another.

Figure 1. Nematodes, hagfish and slugs have so many traits in common, one wonders why they are not related to one another.

With that short list, I could be accused
of “Pulling a Larry Martin” by listing only a few traits. The fact is, these simple, soft-bodied taxa only have a few traits, and they still share these few traits 600 million years after their last common ancestor in the Ediacaran.

Figure 2. A selection of slugs (basal molluscs) to scale.

Figure 2. A selection of slugs (basal molluscs) to scale. Compare to hagfish in figure 1.

Tiny nematodes wriggle through and eat whatever falls on the sea floor.
Slugs slide over and eat whatever falls on the sea floor. Hagfish swim above and eat whatever falls on the sea floor. In the Ediacaran the only food source was the planktonic seafloor and its tiny burrowing and crawling inhabitants.

Side note: Chaetognaths (arrow worms)
(Fig. 3) document yet another clade of swimming nematode descendants with hard mouth parts and fins that evolved by convergence with those of chordates. Notably, on vertically undulating chaetognaths swimming fins appear on the lateral surfaces, distinct from horizontally undulating chordates with vertical fins. Yes, it’s that simple.

Figure 3. Chaetognath (arrow worm) diagram. Note the lateral fins and lateral caudal fin together with the grasping mouth parts.

Figure 3. Chaetognath (arrow worm) diagram. Note the lateral fins and lateral caudal fin together with the grasping mouth parts.

One reference
(Barnes 1980) considered arrow worms deuterostomes. Wikipedia labeled them protostomes, but reported, “Chaetognaths are traditionally classed as deuterostomes by embryologists. Molecular phylogenists, however, consider them to be protostomes. Thomas Cavalier-Smith places them in the protostomes in his Six Kingdom classification. The similarities between chaetognaths and nematodes mentioned above may support the protostome thesis.”

We’ve already seen that nematodes are amphistomes and that gene studies too often recover false positives. So let’s consider those gene studies unreliable. As noted above, visual examination shows chaetognaths to be deuterostomes, whether by convergence or homology.

Try Googling ‘hagfish + slugs’
and you won’t find any prior discussions of this interrelationship in the online academic literature. Any mention of worm-like ancestors for hagfish or any mention of nematode ancestors for molluscs are also rare to absent in the online literature.

Distinct from annelids, arthropods and any other segmented animals,
chordates and molluscs have no body segments.

Traditionally the most primitive mollusc
is the chiton (with eight separate plates of armor) or the heliconelid (with a slightly spiral-shaped shell).

However,
if you start with a flatworm (Platyhelminthes), as you must… then a ribbon worm (Nemertea), as you must… then a round worm (Nematoida), as you must… you’re looking for only minor adjustments to the basic worm shape in both descendants: hagfish and slugs. In this scenario hard mollusc shells are derived traits that evolve after the slug morphology was established. Thus, contra academic tradition naked slugs represent the basal condition in molluscs. They didn’t lose their shells. Slugs never had shells. Those evolved later.

Figure 5. From Peters 1991 a diagram splitting deuterostomates from protostomates.

Figure 4. From Peters 1991 a diagram splitting deuterostomates from protostomates. Now this has to be updated by putting molluscs closer to chordates and nematodes.

Traditional invertebrate clades:

  1. Bilateria (Flatworms, single digestive opening)
  2. Amphistomia (aquatic nematodes, anus and mouth at the same time)
    1. Protostomia (anus first, mouth second)
      1. Ecdysozoa (segmented invertebrates, tardigrades, arthropods)
      2. Lophotrochozoa (molluscs, annelid worms)
    2. Deuterostomia (mouth first, anus second)
      1. Chordata (hagfish, lancelets, craniates)
      2. Xenambulacraria (hemichordates, echinoderms)

Comment: Annelids should nest with arthropods. Both are elongate and segmented. Velvet worms (Onychophora) are transitional taxa.

Comment: Molluscs are  not segmented. Basal forms (slugs) have sensory tentacles and rasping eversible radula, as in nematodes and hagfish.

Revised invertebrate clades:

  1. Bilateria (Flatworms, single digestive opening)
  2. Amphistomia (aquatic nematodes, anus and mouth at the same time)
    1. Protostomia (anus first, mouth second)
      1. Segmented invertebrates (tardigrades, annelid worms, arthropods)
    2. Deuterostomia (mouth first, anus second)
      1. Chordata (hagfish, lancelets, craniates)
      2. Xenambulacraria (hemichordates, echinoderms)
      3. Chaetognatha (arrow worms) or direct from Amphistomia
    3. Lophotrochozoa (molluscs, with protostome embryos convergent with segmented invertebrates)

Chitin vs. keratin
Chordates have keratin teeth. Molluscs have chitin teeth. Wikipedia reports, “The structure of chitin is comparable to another polysaccharide, cellulose, forming crystalline nanofibrils or whiskers. It is functionally comparable to the protein keratin. The only other biological matter known to approximate the toughness of keratinized tissue is chitin.”

Chordates and molluscs had a last common ancestor 600 million years ago. Numerous references discuss nematode ‘teeth’, but do not describe them as either chitinous or keratinous. So I don’t know which is the more primitive substance.

This is not the first time that professional systematists
have left ‘low hanging fruit‘ for amateurs to pluck from a long list of traditionally overlooked, ignored and enigma interrelationships. Putting taxa together that have never been put together before is what we should all do to understand our world better. Every so-called enigma taxon is the result of Darwinian evolution and thus did not and can not stand alone. Relatives are out there for all the oddballs. It’s our job to find them.

The hagfish-nematode-slug relationship seems to be a novel hypothesis
of interrelationships. If not, please send a valid citation so I can promote it.

PostScript:
I found this YouTube video of velvet worms, arthropods, Hallucigenia (shown on the screen shot) and other segmented worm-like members of Protostomia. Seems velvet worms also have sensory tentacles and eversible teeth made of chitin (close to keratiin) and spray mucous slime from glands on the side of their head. There’s a deep connection with nematodes here as well.


References
Barnes RD 1980. Invertebrate Zoology 4th ed. Saunders College, Philadelphia 1–1089.
Clark AJ and Uyeno TA 2019. Feeding in jawless fishes. In: Bels V., Whishaw I. (eds) Feeding in Vertebrates. Fascinating Life Sciences. Springer, Cham.
https://doi.org/10.1007/978-3-030-13739-7_7
Peters D 1991. From the Beginning – The story of human evolution. Wm Morrow.

For more informationm:
wiki/Nematode
wiki/Mollusca
wiki/Evolution_of_molluscs
wiki/Chordate
wiki/Hagfish
wiki/Bilateria
wiki/Annelid
wiki/Chiton
wiki/Helcionellid
wiki/Onychophora
wiki/Chaetognatha
wiki/Lophotrochozoa

Inside an odd Triassic ichthyosaur: an odd embryo, not a meal

Summary for those in a hurry:
A new 5m adult ichthyosaur displays reversals (limb-like fins, a deep pelvis and a long neck) that went unnoticed, until it came to the embryo, which was misidentified as an incomplete thalattosaur meal.

Jiang et al. 2020 brought us news
of a “4m Triassic thallatosaur” swallowed by a 5m ‘megapredator’ ichthyosaur (Fig. 1; (XNGM-WS-53-R4). “The prey is identified as the thalattosaur Xinpusaurus xingyiensis based on close similarities of appendicular skeletal elements in both shape and size. The similarity is most characteristically seen in humeral morphology—it is a robust bone with a limited shaft constriction, and with an expanded proximal extremity.”

“The skull, mandible, and tail of the prey are unlikely to be present in the bromalite (= fossil of digested or digestible remains, i.e. coprolite), given that no isolated elements from these body regions are mixed in with what is preserved.”

Figure 1. Guizhouichthyosaurus ate a Xinpusaurus

Figure 1. Images from Jiang et al. proposing their hypothesis of a thalattosaur, Xinpusaurus, as stomach contents within the much larger Guizhouichthyosaurus. This hypothesis is based on several errors.

From the Jiang et al. abstract:
“Here we report a fossil that likely represents the oldest evidence for predation on megafauna, i.e., animals equal to or larger than humans, by marine tetrapods—a thalattosaur (∼4 m in total length) in the stomach of a Middle Triassic ichthyosaur (∼5 m). The predator has grasping teeth yet swallowed the body trunk of the prey in one to several pieces.”

After tracing published photos:

  1. The larger specimen is distinct from the holotype Guizhouichthyosaurus tangae (Fig. 4; Cao & Luo, 2000; IVPP V 11853) and reconstructions (Figs. 2, 3) are distinct from the Jiang et al. reconstruction. The limb-like fins of the adult were not reported. Several bones were misidentified in the embryo.
  2. Phylogenetic analysis (Fig. 9) nests the XNGM-WS-53-R4 specimen with Shonisaurus popularis (Fig. 5), two nodes away from Guizhouichthyosaurus.
  3. The embryo is folded in thirds and surrounded by an oval membrane. The unfolded morphology of the embryo matches the adult (Fig. 3).
  4. The size of the 1m embryo is much smaller than the estimated 4m prey item.
  5. The location of the embryo is in the posterior half of the abdomen near the uterus, distinct from the location of the more anterior stomach.
Figure 8. The skull of the new specimen wrongly assigned to Guizhouichthyosaurus by Jiang et al. 2020.

Figure 2. The skull of the new specimen wrongly mistakenly assigned to Guizhouichthyosaurus by Jiang et al. 2020.

Figure 1. The XNGM-WS-53-R4 specimen does not nest with Guizhouichthys but with Shonisaurus and has a distinct morphology.

Figure 3. The XNGM-WS-53-R4 specimen does not nest with Guizhouichthys (Fig.4). but with Shonisaurus (Fig. 5) and has a distinct morphology. Note the long neck and limb-like flippers/

Figure 2. Two closely related ichthyosaurs, Guizhouichthyosaurus tangae and "Cymbospondylus" buchseri, one with large flippers, one with small.

Figure 4. Two closely related ichthyosaurs, Guizhouichthyosaurus tangae and “Cymbospondylus” buchseri, one with large flippers, one with small.

The original diagram of the far from complete ‘stomach contents’
(Fig. 6) overlooked the skull, mandible, tail and many other bones here (Figs. 3, 4) here reconstructed (Fig. 7) as a complete skeleton of an embryo folded into a soft and pliable egg-like shape. Even the kink of the ichthyosaur tail is preserved. Both ends of the embryo were overlooked by those with firsthand access to the specimen (Fig. 1).

Figure 5. Shonisaurus popularis is a larger relative of the XNGM WS 53 R4, but retains the long slender flippers of Guizhouichthyosaurus.

Figure 5. Shonisaurus popularis is a larger relative of the XNGM WS 53 R4, but retains the long slender flippers of Guizhouichthyosaurus.

According to Laura Geggel, writing for LiveScience.com
“About 240 million years ago, one giant sea monster ate another, and then died with chunks of the beast in its belly. Researchers in China have now discovered and analyzed the fossilized corpses of these beasts, which they are calling the oldest evidence of megapredation — when one large animal eats another — on record.”

“The ichthyosaur may have attacked and killed the thalattosaur before eating it, but it’s also feasible that the ichthyosaur was simply scavenging the thalattosaur’s remains, the researchers said.”

Figure 8. Photo from Jiang et al. 2020. The XNGM-WS-53-R4 embryo in situ. Colors added.

Figure 6. Photo from Jiang et al. 2020. The XNGM-WS-53-R4 embryo in situ. Colors added. Note the posterior mandible was misidentified as a humerus. The distal humerus was tentatively misidentified as an interclavicle. One ilium is another jaw element .The other ilium is an ulna.

Figure 7. The XNGM embryo traced, unfolded and reconstructed from the tracing using DGS methods, as in the adult.

Figure 7. The XNGM embryo traced, unfolded and reconstructed from the tracing using DGS methods, as in the adult.

The IVPP holotype of Guizhouichthyosaurus
has much longer fins with more phalanges than the Jiang et al. adult and embryo specimens.

In the large reptile tree
(LRT, 1737+ taxa) thalattosaurs and mesosaurs are sister clades to ichthyosaurs. Why is this important? This XNGM specimens have long proximal limb element proportions and short digits. They also have more cervical vertebrae creating a longer neck. This odd morphology is more similar to those of thalattosaurs, mesosaurs and basal ichthyopteryigians like Wumengosaurus and Thaisaurus (Fig. 7) than to the XNGM specimen’s closer ichthyosaur relatives (Fig. 9), like Shonisaurus.

Phylogenetic reversals like this are rare.
Now we have one more example to add to that list.

Figure 2. Basal Ichthyosauria, including Wumengosaurus, Eohupehsuchus, Hupehsuchus and Thaisaurus

Figure 7. Basal Ichthyosauropterygia. The limb-like flipper and additional cervicals in the XNGM-WS-53-specimen are reversals to these more primitive taxa.

Figure 2. Guizhouichthyosaurus tangae skull preserved in three dimensions.

Figure 8. Guizhouichthyosaurus tangae skull preserved in three dimensions.

Figure 9. Subset of the LRT focusing on ichthyosaurs.

Figure 9. Subset of the LRT focusing on ichthyosaurs.

Displaying an unexpected limb/fin reversal,
a deep pelvis and a long neck, the XNGM adult and embryo were not typical of closely related ichthyosaurs. This odd morphology was originally overlooked in the adult and only partly observed in the embryo. This resulted in an incorrect assessment of the embryo as a thalattosaur meal. Tracing, reconstruction and phylogenetic analysis of both adult and embryo corrected the relationship and revealed the overlooked reversals in this unusual ichthyosaur. The XNGM specimen needs a new generic name because it is not congeneric with the holotype of Guizhouichthyosaurus.


References
Cao and Luo 2000. Published in: in Yin, Zhou, Cao, Yu & Luo, 2000. Geol Geochem 28 (3), Aug 8, 2000.
Jiang D-Y et al. (7 co-authors) 2020. Evidence supporting predation of 4-m marine reptile by Triassic megapredator. online
Maisch M et al. 2015. Cranial osteology of Guizhouichthyosaurus tangae (Reptilia: Ichthyosauria) from the Upper Triassic of China. Journal of Vertebrate Paleontology 26(3): 588-597.

Publicity
https://www.livescience.com/triassic-sea-monster-ate-huge-reptile.html
https://www.livescience.com/24031-ancient-sea-monsters-predator-x.html

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

Giant flying arboreal mammal-killer in the Jehol (Early Cretaceous, China)

So… this one has been under the radar since 2004
And you’ll see why.

Like a prehistoric eagle,
this was the largest flying predator in the Jehol biota (Early Cretaceous, China). It had no feathers. And it has gone unrecognized as a giant flying predator since Wang and Zhou 2004 announced it in Nature for other reasons.

At this time the only evidence
for this taxon comes in the form of a giant embryo anurognathid pterosaur, IVPP V13758 (Fig. 1) the size of other adult anurognathids. As an adult it would have been 8x larger (if similar to other pterosaur and based on the pelvic opening). The skull retains traits of the related, but more basal Dimorphodon from the Early Jurassic of England, but the giant anurognathid was coeval and similar in size to another Jehol predator, the pre-tyrannosauroid, Tianyuraptor, and larger than a coeval four-winged, flight-feathered ornitholestid, Microraptor (Fig. 1). It was also larger than the modern bald eagle (Haliaeetus leucocephalus). All the early Cretaceous toothed birds, like Yanornis, and Hongshanornis, were smaller.

Figure 1. Adult scaled version of the IVPP anurognathid pterosaur, with a skull similar in size to those attributed to Dimorphdodon. Bergamodactylus and Preondactylus are ancestral to Dimorphodon. Other Jehol predators are shown in white.

Figure 1. Adult scaled version of the IVPP anurognathid pterosaur, with a skull similar in size to those attributed to Dimorphdodon. Bergamodactylus and Preondactylus are ancestral to Dimorphodon. Other Jehol predators are shown in white.

If early Cretaceous mammals thought they were safe up in the trees,
think again. This giant anurognathid kept their numbers in check by going after them in the trees. That’s a big guess, but if you’re looking for a predator capable of snatching mammals out of the trees, there are no other candidates in the Early Cretaceous of China. Just look at those teeth!

Most anurognathids were small
because they ate small insect prey. Ask yourself if something as large as the IVPP embryo as an adult would have been satisfied eating insects. No, it was going after larger prey.

Figure 1. Large anurognathids and their typical-sized sisters. Here the IVPP embryo enlarged to adult size is larger than D. weintraubi and both are much larger than more typical basal anurognathids, Mesadactylus and MCSNB 8950.

Figure 2. Large anurognathids and their typical-sized sisters. Here the IVPP embryo enlarged to adult size is larger than D. weintraubi and both are much larger than more typical basal anurognathids, Mesadactylus and MCSNB 8950.

Unfortunately
Wang and Zhou 2004 (Fig. 3) didn’t know what sort of pterosaur their first embryo/egg was. Back then they thought pterosaur babies had a shorter rostrum that adults. Wrong. Back then they thought anurognathids were all small taxa. Wrong. Back then they didn’t spend much time tracing traits (Fig. 3) and reconstructions were largely guesswork. We fix all those problems here and at ReptileEvolution.com

The IVPP embryo pterosaur

Figure 3. Click to enlarge DGS tracing. The IVPP embryo pterosaur (far left) as originally traced, (near left) as originally reconstructed as a baby ornithocheirid, (near right) traced using the DGS method, (far right) adult reconstructed at 8x the embryo size.

We first looked at the IVPP embryo
here, several years ago and several times since.

Figure 4. The IVPP embryo anurognathid compared to other basal pterosaurs.

Figure 4. The IVPP embryo anurognathid enlarged to adult size and compared to other basal pterosaurs.

References
Wang X-L and Zhou Z 2004. Palaeontology: pterosaur embryo from the Early Cretaceous. Nature 429: 623.

http://reptileevolution.com/dimorphodon.htm
http://reptileevolution.com/ivpp-embryo.htm

https://pterosaurheresies.wordpress.com/2011/07/26/what-do-those-pterosaur-embryos-really-look-like/

Another long-necked embryo tritosaur: Li et al. in press

This appears to be
yet another Tanystropheus-like and Dinocephalosaurus-like taxon, yet not closely related to either. Earlier we looked at another similar embryo, still within its mother.

Li, Rieppel and Fraser in press (2017)
bring us a new curled up (as if in an egg, but without a shell) embryo from the Guanling Formation (Anisian), Yunnan province, China (Figs. 1, 2). The specimen is unnamed and not numbered. It appears to combine the large head and eyes of langobardisaurs with the short limbs and many cervical vertebrae of Dinocephalosaurus. Please remember, in this clade, juveniles do not have a short rostrum and large eyes unless their parents also had these traits.

Figure 1. The unnamed and not numbered Triassic embryo Li et al. assign to a new species close to Dinocephalosaurus.

Figure 1. The unnamed and not numbered Triassic embryo Li et al. assign to a new species close to Dinocephalosaurus. At 72 dpi monitor resolution, this image is 2.5x life size. Here bones are colorized, something Li et al. could have done, but avoided. I’m happy to report that the line drawing was traced by Li et al. on their own photo. The two are a perfect match.

Unfortunately
Li et al. have no idea what they’re dealing with phylogenetically. They relied on old invalidated hypotheses of relationships. They report the specimen:

  1.  is a marine protorosaur and an archosauromorph – actually it is a marine tritosaur lepidosaur. Taxon exclusion and traditional bias hampered the opinion of Li et al. They did not perform a phylogenetic analysis.
  2. is closely related to Dinocephalosaurus – actually it is more closely related to the much smaller, but longer-legged Pectodens (Figs. 4, 5). In the large reptile tree (LRT, 1036 taxa) 8 steps are added when the embryo is force-nested with Dinocephalosaurus. The embryo is distinct enough that the new specimen deserves a new genus.
  3. confirms viviparity – probably not (but see below). The specimen is confined within an elliptical shape (Fig. 1), as if bound by an eggshell or membrane, which was not preserved. Perhaps, as in pterosaurs and many other lepidosaurs, the embryo was held within the mother’s body until just before hatching, within the thinnest of egg shells and/or membranes.
  4. is too immature to describe it as a new taxon – not so. Tritosaur lepidosaurs (from Huehuecuetzpalli to Pterodaustro) develop isometrically. Thus, full-term embryos and hatchlings have adult proportions.
Figure 2. The specimen from figure 1 unrolled for clarity. This specimen most closely resembles the basal langobardisaur, Pectodens, not Dinocephalosaurus. Remember, tritosaurs develop isometrically. Embryos closely resemble adults. That's why three scale bars are included.

Figure 2. The specimen from figure 1 unrolled for clarity. This specimen most closely resembles the basal langobardisaur, Pectodens, not Dinocephalosaurus. Remember, tritosaurs develop isometrically. Embryos closely resemble adults. That’s why three scale bars are included. This specimen has feeble limbs but a strong swimming tail, distinct from that of Dinocephalosaurus.

Li et al. report
“In the fossil record only oviparity and viviparity can be distinguished, Ovoviviparity of different intermediate stages, which is often observed in modern squamates would then be referred to the category of viviparity, whatever the stages of maturity and nutritional patterns are.” Yes, they correctly report ovoviviparity in squamates, which are the closet living relatives of tritosaur lepidosaurs. That’s exactly what we have here.

Figure 1. The new Dinocephalosaurus has traits the holotype does not, like a longer neck with more vertebrae, a robust tail with deep chevrons and a distinct foot morphology with an elongate pedal digit 4.

Figure 3. The new Dinocephalosaurus has traits the holotype does not, like a longer neck with more vertebrae, a robust tail with deep chevrons and a distinct foot morphology with an elongate pedal digit 4.

Li et al. report,
“[The] skeleton is preserved tightly curled so as to produce an almost perfect circular outline, which is strongly indicative of an embryonic position constrained by an uncalcified egg membrane.”

Figure 2. Pectodens skull traced using DGS techniques and reassembled below.

Figure 4. Pectodens skull traced using DGS techniques and reassembled below. No sclerotic ring here. 

Distinct from Pectodens the new genus embryo has:

  1. 24 cervicals
  2. 29 dorsals
  3. 2 sacrals
  4. and about 64 caudals
Figure 1. Pectodens reconstructed using the original tracings of the in situ fossil in Li et al. 2017.

Figure 5. Pectodens reconstructed using the original tracings of the in situ fossil in Li et al. 2017. The skull shown here is the original reconstruction. Compare it to figure 4.

Li et al overlooked:

  1. strap-like coracoids, strip-like clavicle and T-shaped interclavicle
  2. scattered manual elements
  3. pelvic girdle
  4. ectopterygoid, jugal, articular, angular, surangular

Li et al. report:
“The fewer cervical vertebrae (24 as opposed to 33 (based on an undescribed specimen kept in the IVPP)), and the presence of sclerotic plates are features inconsistent with Dinocephalosaurus.This embryo therefore documents the presence of at least one additional dinocephalosaur-like species swimming in the Middle Triassic of the Eastern Tethys Sea.

“Scleral ossicles have previously not been described in any protorosaur.”
– but they are common in tritosaur lepidosaurs, like pterosaurs.

Figure 6. Pectodens adult compared to today's embryo and its 8x larger adult counterpart after isometric scaling.

Figure 6. Pectodens adult compared to today’s embryo and its 8x larger adult counterpart after isometric scaling. Looks more like Pectodens than Dinocephalosaurus, doesn’t it? See taxon inclusion WORKS! Sclerotic rings were omitted here to show skull bones. The ring would have had a smaller diameter if if were surrounding a sphere, rather than crushed flat. 

A word to traditional paleontologists:
Don’t keep digging yourself deeper into invalidated hypotheses and paradigms. Use the LRT, at least for options.

Don’t give up on naming embryos
and adding them to phylogenetic analysis, especially if they are tritosaur lepidosaurs. Hatchlings nest with adults so you can used hatchlings in analysis.

Don’t avoid creating reconstructions.
That’s a great way to discover little splinters of bone, like clavicles and coracoids, that would have been otherwise overlooked.

The LRT is here for you.
BETTER to check this catalog prior to submission rather than have your work criticized for being unaware of the latest discoveries or overlooking pertinent taxa AFTER publication.

References
Li C, Rieppel O, Fraser N C, in press. Viviparity in a Triassic marine archosauromorph reptile. Vertebrata PalAsiatica, online here.

Ornithischian incubation longer and relatively longer than bird incubation

A new paper by Erickson et al. 2017 reports:
“Birds stand out from other egg-laying amniotes by producing relatively small numbers of large eggs with very short incubation periods (average 11–85 d). Here, nonavian dinosaurian incubation periods in both small and large ornithischian taxa (Protoceratops and Hypacrosaurus) are empirically determined through growth-line counts in embryonic teeth. Our results show unexpectedly slow incubation (2.8 and 5.8 mo) like those of outgroup reptiles.”

Now let’s do the math:
2.8 mo @ 30 days/month = 84 d. Hey! That’s one less than the upper limit in brds! 5.8 mo = 178 days (a few 31 day months added). Actual figures are 83 d for Protoceratops. 172 d for the much larger Hypacrosaurus. At this point, let’s remind ourselves that larger mammals have larger gestation/incubation times, too. And it’s also important to note that no theropod eggs were tested. Oviraptor embryos have no teeth.

Now let’s see some details
Comparison of Protoceratops incubation period relative to that typical for birds with same-sized eggs shows greater than twofold slower values (83.16 vs. 39.72 d). Relative to that typical for reptiles Protoceratops was modestly faster values (∼17%, 83.16 vs. 100.40 d) than predicted for typical reptiles.

Comparison of Hypacrosaurus incubation period relative to that typical for birds with same-sized eggs shows greater than twofold slower values (171.47 vs. 81.54 d). Relative to that typical for reptiles Hypacrosaurus was modestly faster values (∼12%, 171.47 vs. 153.72 d) than predicted for typical reptiles.

Phylogenetically 
all phytodinosaurs, including Ornithischia, are about as distant from birds as are the crocs, which are also proximal outgroups to the Theropoda in the LRT, contra many other studies that nest crocs much more distantly.

Figure 1 Full chart from Erickson et al. 2017. See figure 2 for details.

Figure 1 Full chart from Erickson et al. 2017. See figure 2 for details.

If you’re curious
The ostrich (Struthio) egg is not listed in the Erickson chart. Ostrich eggs are the largest of all birds, but the smallest bird eggs in relation to the adult bird’s size. Their incubation range is well within the Ercikson bird cloud.

Figure 2. Closeup of figure 1. In both cases Struthio was added.

Figure 2. Closeup of figure 1. In both cases Struthio was added. Two ornithischian dinos are shown. No theropods are shown. Cd – crocs.

The slowest incubation period among birds,
is among the Procellariformes, a clade of seabirds including the albatrosses and petrels. Not the chart above it’s blue and labeled Pr. See how closely it comes to the Protoceratops icon?

Oddly, turtles
have a relatively faster incubation time than do lizards and crocs.

Apparently no data yet on theropod dinosaur embryo teeth.
I’m sure that’s where it gets even more interesting (i.e. closer to birds).

References
Erickson GM, Zelenitsky DK, Kay DI, and Norell MA 2017. Dinosaur incubation periods directly determined from growth-line counts in embryonic teeth show reptilian-grade development. Proceedings of the National Academy of Sciences (advance online publication).doi: 10.1073/pnas.1613716114  PDF

Liaoning bird embryo IS a Chinese Archaeopteryx

Updated 11/22/2015 with high rez data sent by Dr. Zhou. A new analysis nests the embryo with the holotype Archaeopteryx lithographica, the London specimen, a basal enantiornithine bird. 

Zhou and Zhang (2004)
described a small, precocial, final stage bird embryo from the Liaoning Province (Early Cretaceous, 121mya, IVPP V14238). Strangely, no eggshell was preserved (Fig. 1), but the tucked shape of the embryo indicated that it had not yet hatched. Northern China was a forested landscape dominated by active volcanoes and sprinkled with lakes and streams at the time. No adults were closely associated, but enantiornithine birds are common in that formation.

Figure 1. Click to enlarge. Liaoning bird embryo IVPP V14238 reconstructed Egg tracing in DGS compared to original tracing (in olive). Note the universally observed long tail and the continuation of the tail vertebrae past the back of the skull. Note the broken clavicles. When rotated they form more of a U shape. The dorsal coracoid is a convex and the ventral scapula is concave, an enanthiornithine key trait.

Figure 1. Click to enlarge. Liaoning bird embryo IVPP V14238 reconstructed Egg tracing in DGS compared to original tracing (in olive). Note the universally observed long tail and the continuation of the tail vertebrae past the back of the skull. Note the broken clavicles. When rotated they form more of a U shape with appropriate spacing of the coracoids. The dorsal coracoid is a convex and the ventral scapula is concave, an enanthiornithine key trait.

The Zhou and Zhang Abstract
“An embryo of an enantiornithine bird has been recovered from the Lower Cretaceous rocks of Liaoning, in northeast China. The bird has a nearly complete articulated skeleton with feather sheet impressions and is enclosed in egg-shaped confines. The tucking posture of the skeleton suggests that the embryo had attained the final stage of development. The presence of well-developed wing and tail feather sheets indicates a precocial developmental mode, supporting the hypothesis that precocial birds appeared before altricial birds.”

Figure 2. The Liaoning bird egg IVPP V14238 in situ with DGS tracing in color. This hirez version updates a prior lo rez version. Length of shell is 3.5 cm.

Figure 2. The Liaoning bird egg IVPP V14238 in situ with DGS tracing in color. This hirez version updates a prior lo rez version. Length of shell is 3.5 cm.

Zhou and Zhang 
did not create a reconstruction (Fig.1) nor attempt to untuck the embryo. Bird embryos shift into a tuck position before hatching as they begin to occupy most of the egg. No egg tooth is present on this specimen.

Figure 3. The Liaoning embryo compared to its closest sister, the London specimen of Archaeopteryx (holotype). The egg is the correct size to pass through the ischia if they were separated distally. like modern birds,

Figure 3. The Liaoning embryo compared to its closest sister, the London specimen of Archaeopteryx (holotype). The egg is the correct size to pass through the ischia if they were separated distally. like modern birds,

Zhou and Zhang report [with my observations in brackets]:
“The embryo has several enantiornithine apomorphies such as a strutlike coracoid with a convex lateral margin [yes], a V-shaped furcula [maybe], metacarpal III extending well past metacarpal II distally  [no], and metatarsal IV being more slender than metatarsals II or III [no]. My observations were improved with a high resolution image (Fig. 2). The Liaoning embryo nests with the holotype Archaeopteryx (London specimen), which nests at the base of the Enantiornithes.

This is the first
Cretaceous avian embryo preserved with feathers, sheathed, not open vanes. These indicate the embryo was precocial, able to move and feed independently shortly after hatching. This specimen demonstrates that the genus Archaeopteryx survived into the Early Cretaceous.

Figure 4. The Liaoning embryo bird nests with several Archaeopteryx specimens in the large reptile tree, AND with enanthiornithes. The large reptile tree does not specifically test for the classic enantiornithine traits, but correctly nested the embryo with adult enantiornithines.

Figure 4. The Liaoning embryo bird nests with several Archaeopteryx specimens in the large reptile tree, AND with enanthiornithes. The large reptile tree does not specifically test for the classic enantiornithine traits, but correctly nested the embryo with adult enantiornithines.

Compare this bird embryo to a precocial pterosaur embryo or three
like Pterodaustro, the IVPP embryo or the JZMP embryo. Embryo pterosaurs have the proportions of an adult. They grow isometrically. Hatchling birds, like the Liaoning embryo, had juvenile proportions with a large head, short tibia and short metatarsus. They grew allometrically, but not as allometric as living altricial (helpless) bird hatchlings.

“Several previously known theropod embryos and the late Cretaceous avian embryos all seem to be preocial animals, judged purely from skeletal evidence,” Zhou said.

Nat Geo
reported, “Zhou said several other enantiornithine species are known from the deposit where the latest fossil was found, but that it was difficult to link the embryo to a specific genus or species.” Unfortunately Zhou and Zhang eyeballed the embyro. They did not attempt a phylogenetic analysis (Fig. 4).

Kevin Padian
quoted in NatGeoOnline noted that half of the fossil’s characteristics are not exclusive to enantiornithines. He added that characteristics that would identify the fossil an enantiornithine are “either dubious or not well preserved on the specimen. But then, what else could it be?” Padian asked. I agree, but then neither of us has seen the fossil first hand.

Figure 4. Enanthiornithine birds to scale. Click to enlarge.

Figure 4.  A selection of Enanthiornithine birds to scale. None of these nest closer to the Liaoning embryo. These taxa all have a shorter tail and a more gracile clavicle and other traits listed in the large reptile tree.

Others have warned me
that juveniles and embryo reptiles, like pterosaurs and tritosaurs, cannot be added to phylogenetic analyses because they tend to nest with other adults*. Actually I’d like to see that happen. At present I’m a skeptic. This was a test of that hypothesis, but it was done with a precocial embryo with a relatively larger head, shorter neck and shorter limbs. I don’t see the problem with adding this embryo (Fig. 1) or precocial pterosaur embryos to analyses. But I’m willing to listen to good arguments with valid data.

*Bennett (2006) considered small adult pterosaurs as juveniles of larger germanodactylids based on long bone lengths rather than phylogenetic analysis. Eyeballing, charts and clouds of data points are no replacements for reconstructions and phylogenetic analysis. Hope you agree…

If this is an enantiornithine
which one is it most like? Archaeopteryx lithographica.

If this is an archaeopterygid
we now have some more ontogenetic clues and patterns to work with. You can see (Fig. 1) which body parts get larger and which get smaller during maturation.

Actually it’s both!

References
Bennett SC 2006. Juvenile specimens of the pterosaur Germanodactylus cristatus, with a review of the genus. Journal of Vertebrate Paleontology 26:872–878.
Zhou Z and Zhang F-C 2004. A Precocial Avian Embryo from the Lower Cretaceous of China. BREVIA Science 22 October 2004: 306 no. 5696 p. 653. DOI: 10.1126/science.1100000. online abstract here

NatGeoOnline

Two really big anurognathids

Yesterday we looked at the adult sisters to the JZMP embryo. Today we’ll do the same with the IVPP embryo.

Figure 1. Large anurognathids and their typical-sized sisters. Here the IVPP embryo enlarged to adult size is larger than  D. weintraubi and both are much larger than more typical basal anurognathids, Mesadactylus and MCSNB 8950.

Figure 1. Large anurognathids and their typical-sized sisters. Here the IVPP embryo enlarged to adult size is larger than D. weintraubi and both are much larger than more typical basal anurognathids, Mesadactylus and MCSNB 8950.

The IVPP embryo pterosaur (Wang et al. 2004), the first ever described, was wrongly considered a juvenile ornithocheirid based on its small tail and short rostrum. At the time pterosaur juveniles were purported to have a short rostrum, but this has been proven wrong at every turn. First on that list: the JZMP embryo is an ornithocheirid and it has a long rostrum.

Phylogenetic analysis nests the IVPP embryo pterosaur together with Mesadactylus, a poorly known anurognathid. Both are sister to another large anurognathid, the misnamed “Dimorphodon” weintraubi. And all three were derived from a sister to MCSNB 8950, wrongly considered a juvenile “Eudimorphodon.

It’s a wonder to see a giant anurognathoid with an embryo the size of other anurognathoids. Only D. weintraubi approaches the embryo enlarged to adult size. Can’t wait for someone in China to come out with the big news of the discovery of the adult.

References
Wang X-L and Zhou Z 2004. Palaeontology: pterosaur embryo from the Early Cretaceous. Nature 429: 623.

Head-first birth in an ichthyosaur – mesosaurs were first with viviparity

Fantastic new fossils
of a head-first live birth in a very basal ichthyosaur, Chaohusaurus (Figs. 1, 2) inspired Motani et al. (2014) to conclude that viviparity in ichthyosaurs (and tetrapods in general, since ichthyosaurs were the last hold out) evolved first on land. They concluded in their abstract, “Therefore, obligate marine amniotes appear to have evolved almost exclusively from viviparous land ancestors. Viviparous land reptiles most likely appeared much earlier than currently thought, at least as early as the recovery phase from the end-Permian mass extinction.” Tail first viviparity is a derived condition in marine reptiles and mammals.

Figure 1. Chaohusaurus embryo at the moment of birth. Nice use of digital coloring here for clarity, even in a perfect fossil like this.

Figure 1. Chaohusaurus embryo at the head-first moment of birth from Motani et al. 2014. Nice use of digital coloring by them for clarity, even in a perfect fossil like this.

Embryo vertebral curling is an issue
Motani et al. report, “The embryos of the sauropterygian Keichousaurus are preserved with their skulls pointing caudally without a clear sign of vertebral curling [7], as in Chaohusaurus. This condition strongly indicates a terrestrial origin of viviparity in Sauropterygia.” and “The presence of curled-up embryos in other Triassic sauropterygians, such as Neusticosaurus and Lariosarus, suggests that the reproductive strategy of these amphibious  marine reptiles may have been variable.” and  “Embryos of the mosasauroid Carsosaurus are preserved curled-up, with their heads inclined cranially. Their tails are positioned more cranially than their respective skulls, making tail-first birth unlikely. They may have been born curled-up, as in some extant lizards that give birth on land.” and  “Hyphalosaurus from the Cretaceous of China is another example of viviparous aquatic reptile, although it lived in freshwater. A case is known where two terminal embryos within the maternal body cavity were straightened while the others still remained curled, most likely in their egg sacs.”

Figure 2. Ichythosaur mothers and embryos from Motani et al. 2014. Red tint added to Chaohusaurus embryo to show connection. Lower derived ichthyosaur is Stenopterygius .

Figure 2. Ichythosaur mothers and embryos from Motani et al. 2014. Red tint added to Chaohusaurus embryo to show connection. Lower derived ichthyosaur is Stenopterygius.

Earlier
Piñeiro et al. (2012)  found curled mesosaur embryos in and out of the body. The large reptile tree found mesosaurs and ichthyosaurs to be closely related and also related to the sauropterygians listed above. So this is about as far back as viviparity originated in that lineage. So Montani et al. (2014) were right. They just needed to know about mesosaurs to  put the cherry on top. Look for viviparity in Wumengosaurus some day. 

References
Piñeiro G, Ferigolo J, Meneghel M and Laurin M 2012. The oldest known amniotic embryos suggest viviparity in mesosaurs, Historical Biology: An International Journal of Paleobiology, DOI:10.1080/08912963.2012.662230
Motani R, Jiang D-Y, Tintori A, Rieppel O and Chen G-B 2014. Terrestrial Origin of Viviparity in Mesozoic Marine Reptiles Indicated by Early Triassic Embryonic Fossils. Plos one. DOI: 10.1371/journal.pone.0088640

Second egg in Momma Darwinopterus?

Figure 1. Darwinopterus pelvic area in situ.

Figure 1. Darwinopterus pelvic area in situ.

Mrs. T, the AMNH specimen of Darwinopterus (Lü et al. 2011a, Figs. 1-3), preserves a well-defined egg just past her  fossilized cloaca, oddly on top of the tail in ventral view. This is the fourth pterosaur egg recognized by paleontologists. The other three, the IVPP specimen, the JZMP specimen and the MHIN specimen (embryo Pterodaustro), preceded it and preserve embryos with well-defined bones and a bit more leathery eggshell.

Figure 2. Pelvic elements colorized. Red-prepubes. Magenta-femora. Green-ilia. Blues-ventral pelvis. Yellow-vertebrae.

Figure 2. Pelvic elements colorized. Red-prepubes. Magenta-femora. Green-ilia. Blues-ventral pelvis. Yellow-vertebrae.

While trying to colorize the pelvic elements (Fig. 2), I came across a smaller oval that did not leave the body (Fig. 3).

Figure 3. Darwinopterus egg (lower left), and possible egg (upper right). What is it really?

Figure 3. Darwinopterus egg (lower left), and possible egg (upper right). What is it really?

I wondered if it was a younger egg? There’s little reason for this. The eggshell, never substantial even in full term embryos, would not have formed at the early stage this size would represent. And the contents of the egg are mostly goo. Nevertheless, the larger more mature and verified egg, has little more substance than the small one.

So, if anyone out there can help with this  I.D., let me know.

References
Lü J, Unwin DM, Deeming DC, Jin X, Liu Y and Ji Q 2011a. An egg-adult association, gender, and reproduction in pterosaurs. Science, 331(6015): 321-324. doi:10.1126/science.1197323