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.

Advertisements

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

A peek beneath the ribs of Pterodactylus scolopaciceps

A not so recent PLOSOne paper (Vidovic and Martill 2014, Late Jurassic) on Pterodactylus scolopaciceps (Meyer 1860, BSP 1937 I 18 (Broili 1938, P. kochi No. 21 of Wellnhofer 1970, 1991) provided the images seen here (Figs. 3, 4). It is one of the best preserved pterosaurs of all. Earlier we critically examined Vidovic and Martill 2014 here. A few short notes and images (Figs. 1,2) below will summarize those criticisms. Otherwise, the photos bring today’s news: tracings of the overlooked coracoids, sternal complex and an early embryo (Figs. 4, 5).

Vidovic and Martill reported,
“The majority of pterosaur species from the Solnhofen Limestone, including P. scolopaciceps are represented by juveniles.” This is utter rubbish.  Several hummingbird- to sparrow-sized adults, yes! …and some with long rostra! …but no verifiable juveniles, EXCEPT the juvenile of the giant Rhamphorhynchus recovered and described here. Remember, pterosaur embryos and juveniles are close matches to their parents as they develop isometrically, able to fly upon hatching, not allometrically. The large pterosaur tree demonstrates the phylogenetic miniaturization is what saved certain pterosaur lineages from extinction following a great radiation in the Late Jurassic. This is evidence Vidovic and Martill refuse to accept.

Vidovic and Martill continue:
“Consequently, specimens can appear remarkably similar due to juvenile characteristics detracting from taxonomic differences that are exaggerated in later ontogeny.” More rubbish based on adherence to Bennett (1996, 1996. 3006) who synonimized dozens of Solnhofen specimens without so much as an attempt at phylogenetic analysis, which lumps and separates the lot into individual taxa here. The Vidovic and Martill cladogram includes only 33 taxa (10 from Solnhofen) and lumps several pterosaurs successfully together (tapejarids, ctenochasmatids, pteranodontids), but fails to put these clades correctly into large clades, nesting sharp beak toothless taxa with broad beak toothy taxa, etc. etc.

Vidovic and Martill dig themselves deeper
“A hypodigm for P. scolopaciceps, comprising of the holotype (BSP AS V 29 a/b) and material Broili referred to the taxon is described. P. scolopaciceps is found to be a valid taxon, but placement within Pterodactylus is inappropriate. Consequently, the new genus Aerodactylus is erected to accommodate it.” As you can see (Figs. 1, 2) and as has been tested, placement within Pterodactylus (Fig. 2)  is MORE appropriate than nesting with purported sisters promoted by Vidovic and Martill (Fig. 1).

Figure 4. Sister taxa of "Aerodactylus" according to Vidovic and Martill 2014 include Gladocephaloides and Cycnnorhamphus. More rubbish.

Figure 1. Sister taxa of “Aerodactylus” according to Vidovic and Martill 2014 include Gladocephaloideus and Cycnnorhamphus. More rubbish. Neither are even related to one another as the former is a ctenochasmatid and the latter, of course, is a cycnohrmphid. Click to enlarge.

Evolution works in minute steps
and the more traits shared between specimens, both overall and in minute detail, the more closely they are related. Vidovic and Martill may also be working under the false assumption that pterosaurs are archosaurs and follow archosaur fusion patterns. No. Pterosaurs are lepidosaurs and follow lepidosaur fusion patterns, which are largely phylogenetic, not ontogenetic, as reported earlier.

Figure 3. Click to enlarge. The large pterosaur tree nests these three taxa together. So this Pterodactylus really is a Pterodactylus.

Figure 2. Click to enlarge. The large pterosaur tree nests these three taxa together. So this Pterodactylus (BSP AS V 28a/b) really is a Pterodactylus (contra Vidovic and Martill)

 

Enough about that paper.
I was drawn to this specimen (Fig. 3) because I did not have data for the coracoids and took another look for them with this excellent photo.

Figure 1. Pterodactylus scolpaciceps from Vidovic and Martill 2014 with elements below the ribs traced in color.

Figure 3. Pterodactylus scolpaciceps from Vidovic and Martill 2014 with elements below the ribs traced in color. Soft tissue is persevered in this specimen, and so is an embryo.

Lo and behold
the coracoids and sternal complex were visible as impressions (Figs. 3, 4) and there was something else further back… an embryo. Not full term. Not fully ossified. The wings are invisible or lost among the ribs and gastralia. Unlike 3D eggs, crushed fossils lay out all the elements into a single bedding plane.

Figure 2. Closeup of the torso of Pterodactylus scolopaciceps showing the coracoids, sternal complex and a passenger.

Figure 4 Closeup of the torso of Pterodactylus scolopaciceps showing the coracoids, sternal complex and a passenger. I was drawn to revisit this specimen because I lacked data for the length of the coracoids. This excellent image provided that data and possibly more. The bones of the embryo are not fully ossified yet. The shell is not formed. Those happen closer to the time just before egg-laying.

The embryo 
is the right size, shape and morphology to someday pass through the pelvis. The bones are soft and underdeveloped. No trace of an eggshell is apparent, but that’s not supposed to happen until the last stages of gestation.

Figure 4. Pterodactylus scolopaciceps reconstructed with the passenger shown here expelled. It is the right size, shape and morphology to be an embryo within an egg.

Figure 5. Pterodactylus scolopaciceps reconstructed with the passenger shown here expelled. It is the right size, shape and morphology to be an embryo within an egg.

Unlike archosaurs
lepidosaurs carry their young for longer terms, sometimes to the point of live birth (viviparity). Earlier I proposed that pterosaurs, like some of their sister lepidosaurs, carried their embryos until just prior to hatching. Other workers, all of whom consider pterosaurs archosaurs, thought egg burial was their method of reproduction. Not sure how they imagine a fragile pterosaur with tearable wing membranes would manage to dig through whatever dirt, sand or debris they were buried in. The aborted egg of Darwinopterus similarly contains an immature and unossified embryo. We also have an aborted fetus in Anurognathus and an aborted egg in the tiny pterosaur, Ornithocephalus added to the Pterodaustro embryo, the ornithocheirid embryo (revised recently) and the (relatively) giant, proto-anurognathid embryo.

How many pterosaur fossils are pregnant?
If they are doing their job, half of the adults should be pregnant, unless females greatly outnumber males, then that percentage goes up. Very few, however, will be preserved with late stage embryos that preserve even impressions of bones. As everyone knows the thinnest bone walls in the animal kingdom are pterosaur bones, thinner yet in embryos and  softer yet in younger embryos.

It’s time people
It’s time to let go of those old paradigms about pterosaur origins, wing shape and interrelationships. Those old hypotheses are not working. They cannot be verified. They are the stuff of myth. I would hate to think that these workers are refereeing manuscripts.

Carl Sagan said this about letting go of old paradigms,
“The essence of the Scientific method is the willingness to admit your’re wrong, to abandon ideas that don’t work, and the essence of religion is not to change anything, that supposed truths are handed down by some revered figure and no one is to make any progress beyond that because all the truth is thought to be in hand.”

References
Bennett SC 1995. A statistical study of Rhamphorhynchus from the Solnhofen Limestone of Germany: Year-classes of a single large species. Journal of Paleontology 69:569-580.
Bennett SC 1996. Year-classes of pterosaurs from the Solnhofen limestone of Germany: Taxonomic and systematic implications. Journal of Vertebrate Paleontology 16: 432–444.
Bennett SC 2006. Juvenile specimens of the pterosaur Germanodactylus cristatus, with a review of the genus. Journal of Vertebrate Paleontology 26:872–878.
Vidovic SU, Martill DM 2014. Pterodactylus scolopaciceps Meyer, 1860 (Pterosauria, Pterodactyloidea) from the Upper Jurassic of Bavaria, Germany: The Problem of Cryptic Pterosaur Taxa in Early Ontogeny. PLoS ONE 9(10): e110646. doi:10.1371/journal.pone.0110646

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

Viviparity in lizards

A new paper by Pyron and Burbrink (2013) combines lizard viviparity and lizard phylogeny and finds multiple origins for viviparity…and, multiple reversals to oviparity. The paper also suggests that the basal condition in lizards was oviparity. Only living taxa were tested.

Figure 1. From Wang and Evans 2011, a gravid Cretaceous lizard with 2 embryos. Odd that they are located as high as the forelimb.

Figure 1. From Wang and Evans 2011, a gravid Cretaceous lizard with 2 embryos. Odd that they are located as high as the forelimb, but when you have 15, allowances have to be made.

Earlier, Wang and Evans (2011) produced fossils of a Cretaceous lizard and her embryos (Fig. 1), all 15 of them!

From the Wang and Evans abstract:
“Although viviparity is most often associated with mammals, roughly one fifth of extant squamate reptiles give birth to live young. Phylogenetic analyses indicate that the trait evolved more than 100 times within Squamata, a frequency greater than that of all other vertebrate clades combined. However, there is debate as to the antiquity of the trait and, until now, the only direct fossil evidence of squamate viviparity was in Late Cretaceous mosasauroids, specialised marine lizards without modern equivalents. Here, we document viviparity in a specimen of a more generalised lizard, Yabeinosaurus, from the Early Cretaceous of China. The gravid female contains more than 15 young at a level of skeletal development corresponding to that of late embryos of living viviparous lizards. This specimen documents the first occurrence of viviparity in a fossil reptile that was largely terrestrial in life, and extends the temporal distribution of the trait in squamates by at least 30 Ma. As Yabeinosaurus occupies a relatively basal position within crown-group squamates, it suggests that the anatomical and physiological preconditions for viviparity arose early within Squamata.”

I would hasten add: perhaps not early in pylogeny, but often. Note these yabeinosaurs (Fig. 1) are beneath the rib cage close to the humerus. Moreover, the orientation is not head first toward the cloaca. Evidently it all works out.

We’ve seen fossils of reptiles huddling together in Decuriasuchus, Heleosaurus and others.

We’ve also looked a possible viviparity in mesosaurs. Ichthyosaurs and plesiosaurs are also notable live-bearers. Pterosaurs maintained embryos within the mother until shortly before hatching took place, based on the extreme thinness of the leathery eggshells and the degree of development of known embryos.

References
Pyron RA and Burbrink FT 2013. Early origin of viviparity and multiple reversions to oviparity in squamate reptiles. Ecology letters. doi: 10.1111/ele.12168.
Wang Y and Evans SE 2011. A gravid lizard from the Cretaceous of China and the early history of squamate viviparity. Naturwissenschaften Sept 98(9):739-43.