The origin and evolution of bats part 4: distance vs. accuracy

Earlier
we looked at bat origins here, here and here from several perspectives. Some of these are now invalid given the following scenario.

Today we’ll take a fresh look at
the behavior and traits of the closest bat relatives in the large reptile tree (LRT, 1233 taxa, subset Fig. 1) and see what they can tell us about bat origins. This is called ‘phylogenetic bracketing‘. In such a thought experiment we can put forth an educated guess regarding an unknown behavior or trait for a unknown taxa (e.g. pre-bats) if all related specimens share similar behaviors and traits inherited from a known or unknown last common ancestor.

We start off with a cladogram
focusing on bat relationships (Fig. 1) and take things one logical step at a time.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

One. Living sister taxa.
The closest tested sister taxa to bats here (Fig. 1) are pangolins and colugos (flying lemurs) in order of increasing distance. The origin of bats and pangolins has remained a traditional enigma. Like the origin of pterosaurs and Longisquama, the surprise is, they are most closely related to each other, despite their current differences.

Two. Ancestral taxa
Th bat/colugo/pangolin clade had its genesis near the original dichotomy of placental mammals, when Carnivora split off from all others. At the next dichotomy the bat/colugo/pangolin clade split off from all others. So this clade is not far from an ancestral clades with living genera. Monodelphis, the short-tailed opossum today restricted to South America, nests just outside of all mammals with a placenta. Nandinia, the African palm civet, is a basal member of the Carnivora, somewhat larger than its Mesozoic forebearers.

Three. Timing for clade origins
The bat/colugo/pangolin clade had its origin in the Early Jurassic based on the more primitive egg-layers, Megazostrodon, Brasilitherium and Kuehneotherium in the Late Triassic and the much more derived arboreal multituberculate/rodent, Megaconus, in the Middle Jurassic. As you can see, Jurassic mammals remain extremely rare, currently represented only by the likes of Megaconus. Others will, no doubt, be discovered in time.

Four. Arboreality (tree niche)
Some bats, colugos and pangolins live in trees, and so do their last common ancestors, short-tailed opossums and African palm civets.

Five. Climbing trees
Bats no longer have to climb trees because they can fly. Colugos and pangolins both climb trees in a series of symmetrical short hops/extended reaches (colugo video, pangolin video), distinct from palm civets and short-tailed opossums, which put forth one hand at a time, like primates do.

Six. Descending trees.
Bats fly between trees. Colugos glide between trees. Pangolins use their prehensile tail to ease themselves down. The African palm civet drops out of trees in play. It also descends tree trunks like a squirrel, head first.

Seven. Nocturnal
Most bats, colugos, pangolins, palm civets and short-tailed opossums prefer to be active at night.

Eight. Omnivorous diet
Some bats eat insects, others prefer nectar or hanging fruit. Colugos prefer leaves, shoots, flowers, sap, and fruit. Pangolins eat ants. Palm civets and short-tailed opossums are omnivorous. African palm civets feed by holding their prey in their hand-like front paws, biting it repeatedly and then once dead, swallowing it whole.

Nine. Extradermal membranes
Colugos and bats both have extradermal membranes to their unguals that extend their glides in the former and enable flapping flying in the latter. Such membranes are lost in living pangolins, but the Early Cretaceous pangolin, Zhangheotherium appears to have scale-lined membranes between the elbows and knees. These were overlooked in the original description. The gliding membrane in colugos is fur-covered and camouflaged dorsally, naked underneath. In bats the flying membrane is naked, translucent and never camouflaged.

Ten. Mobile clavicle, interclavicle and scapula
The basal pangolin, Zhangheotherium, has a mobile clavicle-interclavicle and the large scapula rises above the  dorsal vertebrae, as in bats, but not colugos.

11. Sprawling femora
Zhangeotherium and bats share sprawling hind limbs, distinct from the more erect hind limbs of most limbed mammals.

12. Silent vs. noisy
African palm civets are noisy. Colugos and pangolins are largely silent. Bats are constantly chirping to one another and (micro-bats only) as part of their sonar attack system.

13. Enemies
All current enemies of bats (e.g. birds, snakes) evolved during or after the Late Cretaceous. Jurassic trees might have been a refuge for small early climbing mammals, like colugo, bat and pangolin ancestors. However…the minimally feathered, small theropod dinosaur, Sinosauropteryx, contained the jaws of Zhangheotherium, perhaps caught after descending from the trees or plucked out of lower branches. Certain pterosaurs (e.g. giant anurognathids) might have preyed on arboreal  mammals in the Jurassic, but no evidence of this is yet known.

FIgure x. Calcaneal spur in Zhangheotherium. Not venomous, but perhaps to anchor a uropatagium.

FIgure 2. Calcaneal spur in Zhangheotherium. Not venomous, but perhaps to anchor a uropatagium as in bats.

14. Calcaneal spurs
Hurum et al. 2006 originally considered the small spurs found on the calcaneum of Zhangheotherium (Fig. 2) similar to venom spurs found on the platypus, Ornithorhynchus. Phylogenetic bracketing indicates the closer homolog is with the basal bat, Onychonycteris, which has longer calcaneal spurs framing a trailing uropatagium.

Figure x. Monodelphis babies in an open pouch. This is how placentals began, slowly evolving from the less open pouch.

Figure 3 Monodelphis babies in an open pouch. This is how placentals began, slowly evolving from the less open pouch.

15. Newborns and mothers
All basal placental mammals give birth to helpless newborns that ride with the mother until mature enough to go out on its own. Monodelphis demonstrates a primitive version of this, protecting its ten young with lateral flaps of skin (Fig. 3). Carnivore mothers make nests for newborns (2-4 for African palm civets), but colugo, bat and pangolin mothers take their one or two babies everywhere they go, like marsupial mothers do. Zhangheotherium might have been fossilized with several newborns. (Fig. 4) and extradermal membranes between elbows and knees, as in bats and colugos. As we know from colugos, these extradermal membranes in basal pangolins (and Chriacus?) likely formed a playpen or nursery for developing young riding beneath their mother during the earliest stages of development.

Figure x. Zhangheotherium showing possible extradermal membranes (green) with keratinous scales (red) and several newborns scattered in the abdominal area, similar to Monodelphis in figure x.

Figure 4. Zhangheotherium showing possible extradermal membranes (light blue and green) with keratinous scales (red) and several newborns scattered in the abdominal area, similar to Monodelphis in figure x. These amorphous blobs with tiny tail bones need further inspection. Some may just be stains and shapes.

16. Curling (flexing the spine)
Mother opossums, palm civets, colugos, bats and pangolins are able to curl their spines so much that the mother’s mouth is able to assist wiggling newborns climb to the abdominal nipples. This curling ability is co-opted by pangolins as they defend themselves by rolling into a tight ball and by bats that catch prey in their tail before curling up to bite the victim as it is brought close to the jaws. Higher mammals lose the ability to curl ventrally in this manner. Humans and other primates have a limited ability to do this. Instead they use their hands. More derived mammals with stiffer backs have more developed newborns.

17. Upside-down vs. right-side up nursery for the young
Colugos may rest right-side up (preferring to hang from below a slightly leaning tree trunk) or upside down hanging by all fours beneath a horizontal branch. When doing so the mother’s extradermal membranes form walls making a protective nursery for the young ones.

By contrast, bats rest up-side down, sometimes hanging by only one locked foot. To fly bats simply release this foot lock, then plummet and start flapping. Bat membranes also provide a protective nursery for their young as they cling to their mothers’ chest and her wings fold over them.

Nowadays pangolins roll into a ball while nursing their young. Later in life, babies ride on the mother’s back and tail when able to do so. Zhangheotherium (Fig. 4) appears to have provided a colugo-like, but scale-lined membrane nursery for several growing babies. The late-surviving pre-bat, Chriacus (Fig. 5), likely did the same, based on phylogenetic bracketing.

18. Claws
Short-tailed opossums and African palm civets use their claws to climb trees and grab prey and fruit, bringing it to the mouth. So do basal primates. Colugos, bats and pangolins use their larger, curved claws principally to hang from trees, though living pangolins have co-opted their large claws to dig out ant and termite nests from trees and underground.

19. Distance vs. accuracy
Colugos leap and turn away from their tree trunk base in order to launch themselves into a glide. Can they do this while hanging beneath a branch? I don’t know. With their long limbs, colugos can just leap (without gliding) across gaps of 5m or more. With limbs extended, they can glide for 136m at 10m/second. Gliding is good for a quick escape from predators, and access to patches of food that are otherwise inaccessible. It does not save them energy to glide, let along climb back to a gliding height.

Bats drop from trees, then fly wherever they please, typically landing upside down on another high branch or cavern roof. The origin of bat flight enabled by flapping hyper-elongated webbed fingers is the key question here, and it is answered by combining all of the above numbered traits.

Before bats could fly Jurassic pre-bats had to climb trees, probably like colugos and pangolins do (see #5 above), before standing bipedally, but upside-down, on a horizontal branch. Why would they do that? To prepare to dive bomb insects on and in the leaf litter below. Here is where sonar became valuable, detecting insects in the leaf litter at night. Here is where the leaf litter became valuable, cushioning the early awkward landings of small dive-bombing pre-bats. Here is where flapping, even with small hands around colugo-like dermal membranes became valuable, at first in panic, then in gradually learning how to better direct the fall to cover the prey below.  (By analogy birds flap their wings vigorously while dropping to slow their descent.)

Upon landing the extended pre-bat nursery membranes ‘put a lid’ on the prey. Then, curling the tooth-line jaws toward the tail and the tail toward the jaws (see #16 above) spelled doom for the captured food item. Over time, larger fingers made better flapping parachutes. Ultimately flapping bats  learned how to hover before diving bombing their prey, like owls do. Later, after further development, bats gained the power and morphology to enable flight, slowly at first, then better and better to escape ground-dwelling predators and avoid having to climb a tree for the next attack. Only later did bats learn to use their sonar and flying skills on flying insects.

So what began as a small pouch, then a larger nursery membrane for bat and colugo infants became a killing zone for bat prey on the ground, another example of co-opting an old trait for a new behavior in derived taxa. Distinct from birds and pterosaurs, which used their nascent flapping behavior to ascend tree trunks to escape predators, create threat displays and slow their descents from branches, bats used their nascent flapping ability only to slow and direct their descent from branches. Distinct from colugos, which glided for distance, bats dropped for accuracy. Distance came later, after flight developed.

Remember the fall need not be far at first. Conifers can have very low branches and leaf litter can be a soft cushion for a mouse-sized mammal. Graduating slowly to higher branches provides bats a wider ‘field-of-view’ for their slowly developing sonar, and more time to develop flapping. Bat hind limbs are not long or heavily muscled. They are not good at leaping, like colugos.

Fruit eating bats could not have developed until flowering and fruit-bearing trees developed, later in the Cretaceous. The LRT and the fossil record indicates that fruit-eating bats are derived relative to smaller insect-eating bats. So sonar-emitting apparently was lost in fruit-eating bats, rather than never a part of their lineage. The great variation now seen in sonar-emitting bat morphology was likely developed during and after the Cretaceous, based on the current fossil record. I think we’ll find fully volant fossil bats in the Cretaceous someday.

I happened upon this idea while watching a pigeon descend from a roofline to a balcony beneath it and wondered if accuracy was more important for bats, while distance was more important for colugos. That distinction seems to be the key driver in both clades. In any case, it is important that any proposed scenario be viable at every point during the gradual evolution of new traits and behaviors. In this case, developing flapping forelimbs had to originate with a bipedal configuration, even it inverted. Developing sonar had to originate from simply listening to nocturnal insects and other small prey rustling in the leaf litter, not far below, gradually getting better in those families that randomly had slightly better skills once dive-bombing and trapping became the method for predation.

20. Bat ontogeny
Recapitulates this phylogenetic scenario. The fingers elongate last. 

21. Solitary vs. communal
Colugos and pangolins are solitary. So are African palm civets except when food is plentiful. Bats are communal, whether nesting in trees or caves. According to Kerth 2008, “Variable dispersal patterns, complex olfactory and acoustic communication, flexible context-related interactions, striking cooperative behaviors, and cryptic colony structures in the form of fission-fusion systems have been documented. tropical bats often form groups year-round, whereas sociality in temperate-zone species is sometimes restricted to certain times of the year. In most species, females form so-called maternity colonies to rear their young communally, whereas males are solitary, form groups of their own, or join female groups. In only a few species are both sexes solitary, meeting only to mate.”

Kerth concludes, “None of the three factors that I identify as important for the evolution of sociality in bats (ecological constraints, physiological demands, and demographic traits) can fully explain the frequency and diversity of group living in bats.”

Figure 1. Basal placentals at two scales, all arising from a Middle Jurassic sister to Monodelphis, based on the Earliest Cretaceous appearance of Zhangheotherium, in the lineage of pangolins.

Figure 5. Basal placentals at two scales, all arising from a Middle Jurassic sister to Monodelphis, based on the Earliest Cretaceous appearance of Zhangheotherium, in the lineage of pangolins..

22. Soles of the feet oriented opposite to those of most mammals
Distinct from most mammals, the knees of bats are splayed laterally, which should extend the toes laterally. However, the ankle is rotated another 90º producing a foot in which the soles are ventral during flight and while hanging. In the case of long-legged fish-eating bats, the feet help bring captured fish back to the mouth.

FIgure 1. Wondering if Chriacus had an inverted stance and dermopteran membranes? Comparisons to Onychonycteris and Pteropus.

FIgure 6. Wondering if Chriacus had an inverted stance and dermopteran membranes? Comparisons to Onychonycteris and Pteropus are shown. Yes, the knees are straight in derived fruit bats, bent in Onychonycteris and micro bats. The uropatagia are spread while inverted and while flying. Chriacus appears to be a much larger and much later-surviving version of much smaller Jurassic pre-bats. The membranes are conjectural and may have been lost in this large specimen, but it illustrates the possibility of a dive bombing taxon that covered prey like a casserole lid.

Why do bats hang upside down?
Without a phylogenetic or deep-time perspective, the following video is the best answer current bat workers can provide:

Bats are not using their wings to cool off.
A recent heat wave killed many fruit bats. They fell dead out of the trees (see below). None were creating a cooling breeze with their wings or extending their wings in a cooling fashion, like elephants sometimes do. Microbats that live in caves never have this problem.

Bat wings notes:

  1. Finger flexibility during flight varies greatly in bats.
  2. The flight stroke is otherwise bird-like with elbows raised above the back, nearly meeting at the midline, for maximum power at low airspeed, or less so for cruising at higher airspeeds.
  3. The large fingers do nothing else but push air for thrust and lift. They are not extended to cool the bat, nor do they extend or flash during courtship.
  4. Bat fingers hyper flex at the wrist to tuck away the flight membrane and reduce its surface area when not in use, as in pterosaurs and birds. When flexed they do little but envelope the bat and its clinging young.

Miscellaneous notes:

  1. Zhangheotherium was originally considered a symmetrodont mammal, but its teeth seems to converge with archaeocete whales in this regard. The reappearance of a more primitive symmetrodont molar shape is here considered an atavism in the evolution of toothlessness in both certain odontocetes and pangolins by convergence.
  2. The uncoiled cochlea of highly derived Zhangheotherium and multituberculates, has been traditionally considered a trait that nests these taxa in more basal branches of the mammal family tree. Here, in the LRT, these traits appear to be neotonous or atavistic developments that, taken alone, tend to confuse systematics. No traits should ever be taken alone to determine systematics. That would be ‘pulling a Larry Martin.’
  3. The initial splitting up of Pangaea in the Early Jurassic gave the previously dry climate a more lush, subtropical parade of cycads, conifers, ginkgoes and tree ferns. So there were plenty of standing and fallen trees for early mammals to gambol upon, learning how to climb and leap. The forest floor was likely cushioned with a carpet of leaves and fronds to absorb accidental falls and hunger-driven dive bombs mediated by fluttering pre-wings and large membranes co-opted for eventual flight.

Addendum
Video showing a bat descending on a mouse in leaf litter appears here.

References
Byrnes, Libby, Lim & Spence. 2011. Gliding saves time but not energy in Malayan colugos. Journal of Experimental Biology http://dx.doi.org/10.1242/jeb.052993
Hurum JH, Luo Z-X and Kielan-Jaworowska Z 2006. Were mammals originally venomous? Acta Palaeontologica Polonica 51(1): 1–11.
Kerth G 2008. Causes and Consequences of Sociality in Bats. BioScience, Volume 58, Issue 8, 1 September 2008, Pages 737–746, https://doi.org/10.1641/B580810
Online here.

Massospondylus embryo joins the LRT

…and guess where it nests?

Figure 1. Massospondylus embryo from Reisz et al. 2010.

Figure 1. Massospondylus embryo from Reisz et al. 2010.

This should be easy:
The embryo nests with the adult Massospondylus in the large reptile tree (LRT, 1212 taxa), despite the many proportional and a few osteological changes that attend ontogeny in this basal sauropodomorpth from the Early Jurassic.

Figure 2. Massospondylus adult and several sub adult and juvenile skulls to scale.

Figure 2. Massospondylus adult and several sub adult and juvenile skulls to scale. Note the bipedal pose based on hind and fore limb disparity… distinct from the quadrupedal embryo.

These embryos are the oldest known
dinosaur embryos and apparently they were just days from hatching.

Massospondylus kaalae was a short-snouted basal sauropodomorph from the Early Jurassic closely related to Efraasia and SaturnaliaMassospondylus had a short round snout and long blunt fangs. Another species, Massospondylus carinatus, had a relatively longer skull as an adult.

The embryo Massospondylus
includes a taller antorbital fenestra, a premaxilla lacking a posterior narial process, a naris closer to the jaw line, a straight (not descending) jaw joint, a smaller coronoid process, a lack of teeth, relatively shorter neck, larger fore limbs, a shorter ventral pelvis, distally broader chevrons and smaller feet.

Figure 3. Embryo Massospondylus compared to hatchling Scipionyx.

Figure 3. Embryo Massospondylus compared to hatchling Scipionyx. The predator babies were larger than the bite-sized and more numerous prey babies. 

References
Barrett PM 2009. A new basal sauropodomorph dinosaur from the upper Elliot formation (Lower Jurassic) of South Africa. Journal of Vertebrate Paleontology 29(4):1032-1045.
Morris J 1843. A Catalogue of British Fossils. British Museum, London, 222 pp
Reisz RR, Scott D; Sues H-D, Evans DC and Raath MA 2005. Embryos of an Early Jurassic prosauropod dinosaur and their evolutionary significance. Science. 309(5735): 761–764.
Reisz RR, Evans DC, Roberts EM, Sues H-D and Yates AM 2012. “Oldest known dinosaurian nesting site and reproductive biology of the Early Jurassic sauropodomorph Massospondylus. Proceedings of the National Academy of Sciences of the United States of America. 109(7): 2428–2433.
Riley H and Stutchbury S 1836. A description of various fossil remains of three distinct saurian animals discovered in the autumn of 1834, in the Magnesian Conglomerate on Durdham Down, near Bristol. Proceedings of the Geological Society of London 2:397-399.

wiki/Massospondylus

Proconsul, Pan and Homo: face changes

Just some musings today
over chimps and humans (Fig. 1) and some other higher primate skulls (Figs. 2, 3). Chimps have not yet made it into the large reptile tree (LRT, 1068 taxa), but they will someday.

The tradition is
to consider chimps (genus: Pan) the starting point in human (genus: Homo) evolution and to make comparisons between the two. Once again, taxon exclusion becomes a problem.

The actual starting point
is closer to an extinct ancestor of both, Proconsul (aka: Dryopithecus; Hopwood 1933; 18–14mya; Figs. 2, 3) a genus that resembled a chimp, but did not knuckle-walk (Fig. 3) and lacked brow ridges, both traits retained by Homo.

Figure 1. Chimp baby and human baby compared to chimp adult and human adult. See text for details.

Figure 1. Chimp baby and human baby compared to chimp adult and human adult. Pupils are aligned. Everything else morphs. See text for details.

 

Question #1 today is…
What changes can we see in the face of a human compared to a chimpanzee?

  1. Forehead present (housing more cerebral frontal matter)
  2. Longer and protruding nose with ventral nostrils (better for underwater)
  3. Shorter nose-to-lip distance with philtrum (medial furrow)
  4. Chin boss (deeper in adults)
  5. Internal lip tissue externalized
  6. Shorter muzzle
  7. Thicker, less patchy and eternally growing cranial hair (+ beard on males)
  8. The rest of the face (and most of the body) hairless
  9. Smaller iris vs. sclera (whites of the eyes)
  10. Smaller ears
  11. Fewer wrinkles on breeding adults and babies
  12. Brow ridges absent, replaced by decorative eyebrows
  13. Maturity does not include a change of face color
  14. Not visible: smaller canines
  15. Lower cheekbones (jugal, zygomatic arch) relative to tooth row

It looks like the ears are lower in humans, but relative to the eyes and nose, they are not.

Figure 2. The skulls of Pan (the chimp), Proconsul and Homo (the human) for comparison.

Figure 2. The skulls of Pan (the chimp), Proconsul and Homo (the human) for comparison.

Question #2 today is…
What changes can we see in the face of a chimp (Pan) compared to Proconsul?

  1. Loss of forehead in Pan compared to Proconsul
  2. Nose unknown in Pronsul, but bones are shorter and flatter in Pan
  3. Longer nose-to-lip distance in Pan
  4. Chin, absent, as in Proconsul
  5. Internal lip tissue unknown in Proconsul
  6. Muzzle the same in Pan, less above, but more below the nose
  7. Hair unknown in Pan
  8. Skin unknown in Pan
  9. Eyes unknown in Proconsul, but note their relatively higher placement in Pan
  10. Ears unknown in Proconsul
  11. Wrinkles unknown in Proconsul
  12. Brow ridges present in Pan, absent in Pronsul
  13. Skin color unknown in Proconsul
  14. Canines slightly larger in Pan
  15. Higher jugal relative relative to tooth row (= taller premaxilla and maxilla) and coronoid process of mandible
Figure 3. Proconsul displays primitive traits for chimps and humans. It did not walk on its knuckles.

Figure 3. Proconsul displays primitive traits for chimps and humans. It did not walk on its knuckles

And then there’s one more transitional taxon
Ardipithecus (Fig. 4) nesting somewhere between Proconsul and Homo

Figure 4. Ardipithecus is a transitional taxon between Pronconsul and Homo.

Figure 4. Ardipithecus is a transitional taxon between Pronconsul and Homo.

In Ardipithecus,
compared to Proconsul, we find larger eyes, a larger, lower nose, smaller canines, and an overall shorter/wider face… and a pelvis more appropriate for an upright stance, freeing the long arms to do something else, like carrying everything from infants to water to weapons to belongings. This is where we lost our hair, became long distance runners, developed sweat glands, and became wanderers.

Figure 5. Ardipithecus in lateral view compared to Australopithecus and Homo (ghosted out).

Figure 5. Ardipithecus in lateral view compared to Australopithecus and Homo (ghosted out).

 

 

References
Hopwood AT 1933a. Miocene primates from British East Africa. Annals and Magazine of Natural History (Series 10), 11, 96-98.
Hopwood AT 1933b. Miocene primates from Kenya. Journal of the Linnean Society of London. Zoology 38:437–464.

https://en.wikipedia.org/wiki/Proconsul

 

Helpless and able newborn mammals

I’m going to crowd source this one,
but I think I covered all the bases here. In this subset of the large reptile tree (LRT, 1165 taxa) I’ve divided placental mammals born helpless (blue) from mammals born able to walk, swim and see (pink). I’ll need your help if there are any exceptions, like pangolins, that I missed one way or the other. Fossils are colorized based on phylogenetic bracketing.

Figure 1. Newborn mammals are born either helpless, like humans, or able to keep up with their mother, like horses. I think I located the split correctly here. Let me know I missed a few.

Figure 1. Newborn mammals are born either helpless, like humans, or able to keep up with their mother, like horses. I think I located the split correctly here. Let me know I missed a few. Fossil taxa are colored based on phylogenetic bracketing. 

Marine taxa need to be ready to go from the first minute.
Apparently so do the large plant-eaters ( including ant and copepod eaters), beginning with long-legged former tree shrew, Onychodectes.

Dens and nests
are associated with basal mammals, like us. Not so much with the derived herbivores (and anteaters) of the plains and forests. All of them get milk from their mothers before they start to dine on meat, plants, ants and copepods. Some of them have to keep up with here. Some of them have to keep up with her underwater.

BTW
there also seems to be a behavioral node at Maelestes in which succeeding taxa are all leaving the trees for good. Of course, that also happens exceptionally with the various mole and aquatic clades in more basal mammals.

Ontogeny and gender dimorphism in pterosaurs – SVP abstract 2016

Unfortunately,
and apparently, this is yet another study (Anderson and O’Keefe 2016) with a priori species assignations prior to a robust phylogenetic analysis and the creation of precise reconstructions. I hope I’m wrong, but no mention of phylogenetic analysis appears in the abstract. Nor do they mention creating reconstructions. Bennett (1993ab, 1995, 1996a, 2001ab, 2006, 2007) failed several times in similar fashion (with statistical analyses) to shed light on the twin issues of pterosaur ontogeny and dimorphism, coming to the wrong conclusions every time, based on results recovered by creating reconstructions and analyses. Further thoughts follow the abstract.

From the Anderson and O’Keefe abstract:
“The relationships of pterosaurs have been previously inferred from observed traits, depositional environments, and phylogenetic associations. A great deal of research has begun to analyze pterosaur ontogeny, mass estimates, wing dynamics, and sexual dimorphism in the last two decades. The latter has received the least attention because of the large data set required for statistical analyses. Analyzing pterosaurs using osteological measurements will reveal different aspects of size and shape variation in Pterosauria (in place of character states) and sexual dimorphism when present. Some of these variations, not easily recognized visually, will be observed using multivariate allometry methods including Principle Component Analysis (PCA) and bivariate regression analysis. Using PCA to variance analysis has better visualized ontogeny and sexual dimorphism among Pterodactylus antiquus, and Aurorazhdarcho micronyx. Each of the 24 (P. antiquus) and 15 (A. micronyx) specimens had 14 length measurements used to assess isometric and allometric growth. Results for P. antiquus analyses show modular isometric growth in the 4th metacarpal, phalanges I–II, and the femur. Bivariate plots of the ln-geometric mean vs ln-lengths correlate with the PCA showing graphically the relationship between P. antiquus and A. micronyx which are argued here to be sexually dimorphic and conspecific. Wing schematic reconstructions of all 39 specimens were done to calculate individual surface areas and scaled to show relative intraspecific wing shape and size. Finally, Pteranodon, previously identified having with sexually dimorphic groups, was compared with ln-4th metacarpal vs ln-femur data, bivariately, revealing similarities between the two groups (P. antiquus and A. micronyx = group 1; Pteranodon = group 2) in terms of a sexual dimorphic presence within the data sets.”

The Pterodactylus lineage and mislabeled specimens formerly attributed to this "wastebasket" genus

Figure 3. Click to enlarge. The Pterodactylus lineage and mislabeled specimens formerly attributed to this “wastebasket” genus

If these two workers actually had 24 P. antiquus specimens to work with,
then it was only because the labels told them so. Or they came across a cache on a slab of matrix I’m not aware of. Pterodactylus has been a wastebasket taxon for a long time (Fig.1) that, apparently the authors didn’t bother to segregate with analysis. Anderson and O’Keefe do not indicate they arrived at a large clade of P. antiquus specimens after phylogenetic analysis. Having done so, I can tell you that no other tested Pterodactylus is  identical to the holotype and no two adult pterosaurs I’ve tested are alike, even among RhamphorhynchusGermanodactylus and Pteranodon. The differences I’ve scored are individual to phylogenetic and they create cladograms that illuminate interrelationships, not sexual dimorphism or ontogeny. There are sequences of smaller species and larger ones. These can appear to be two genders, but that is a false result.

Embryo to juvenile pterosaurs
are isometrically miniaturized versions of their parents as the evidence shows time and again across the pterosaur clade. These facts have been known for over five years and it’s unfortunate that old traditions continue like this unfettered and untested under phylogenetic analysis… or so it seems… I could be wrong having not seen the presentation.

References
Anderson EC and O’Keefe FR 2016. Analyzing pterosaur ontogeny and sexual dimorphism with multivariate allometery. Abstracts from the 2016 meeting of the Society of Vertebrate Paleontology.
Bennett SC 1993a. The ontogeny of Pteranodon and other pterosaurs. Paleobiology 19, 92–106.
Bennett SC 1993b. Year classes of pterosaurs from the Solnhofen limestone of southern Germany. Journal of Vertebrate Paleontology. 13, 26A.
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 1996a. Year-classes of pterosaurs from the Solnhofen limestones of Germany: taxonomic and systematic implications. Journal of Vertebrate Paleontology 16:432–444.
Bennett SC 2001a, b. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. Palaeontographica, Abteilung A, 260:1–112. Part II. Functional morphology. Palaeontographica, Abteilung A, 260:113–153.
Bennett SC 2006. Juvenile specimens of the pterosaur Germanodactylus cristatus, with a review of the genus. Journal of Vertebrate Paleontology 26:872–878.
Bennett SC 2007. A review of the pterosaur Ctenochasma: taxonomy and ontogeny. Neues Jahrbuch fur Geologie und Paläontologie, Abhandlungen 245:23–31.

One more look at Rhamphorhynchus growth

Usually I avoid histological (bone microstructure) studies.
But here’s one that merits one more extended report based on its many incorrect assumptions and overlooked comparisons.

Summary of key facts in this long blog:

  1. both phylogenetically miniaturized adult pteros and mammals had juvenile-like “woven” bone texture
  2. Pterosaur embryos develop in utero and had adult proportions, so they could fly upon hatching
  3. Pterosaurs develop isometrically, thus immature pteros can only be identified in phylogenetic analysis (= when larger identical adults are known).

Prondvai et al. 2012 tested growth strategies in Rhamphorhynchus. As noted earlier, Prondvai et al. confused small adults with juveniles and hatchlings, not following the clear data that pterosaurs grow isometrically, not allometrically. Thus the morphological difference shown here (Fig. 1) are phylogenetic, not ontogenetic. Phylogenetic analysis supports this hypothesis.

Figure 1. Bennett 1975 determined that all these Rhamphorhynchus specimens were conspecific and that all differences could be attributed to ontogeny, That is clearly false as shown here and by phylogenetic analysis. Only the juvenile between the two largest specimens is a non-adult. Click to enlarge.

Figure 1. Bennett 1975 determined that all these Rhamphorhynchus specimens were conspecific and that all differences could be attributed to ontogeny, That is clearly false as shown here and by phylogenetic analysis. Only the juvenile between the two largest specimens is a non-adult. Click to enlarge.

 

Age of first flight
Prondvai et al. 2012 report,
The initial rapid growth phase early in Rhamphorhynchus ontogeny supports the non-volant nature of its hatchlings, and refutes the widely accepted ‘superprecocial hatchling’ hypothesis. We suggest the onset of powered flight, and not of reproduction as the cause of the transition from the fast growth phase to a prolonged slower growth phase. Rapidly growing early juveniles may have been attended by their parents, or could have been independent precocial, but non-volant arboreal creatures until attaining a certain somatic maturity to get airborne.” Prondvai et all did not realize they were examining small adult pterosaur specimens, not juveniles. So rapid growth was part of their growth strategy. More refutations relevant to the above statements follow.

Powered flight is one of the most energy-consuming locomotion types in tetrapods, therefore high growth rates and a superprecocial onset of the flying lifestyle in a highly developed hatchling are mutually exclusive developmental parameters. The validity of this simple trade-off model is supported by the fact that the only extant superprecocial fliers, the megapod birds have very low if not the lowest growth rates among extant birds.” Prondvai et al. ignore the fact that megapodes have their rapid growth phase inside the egg shell. Hatchling megapodes are relatively “very large with a wingspan up to half that of the adult).”  By contrast, pterosaurs hatch at 1/8 the height of the adult and 1/8 the wingspan.

In support of supreprecocial flight…
pterosaur hatchlings had adult proportions. Tiny adults, the size of sparrows and hummingbirds, had larger pterosaur proportions. The smallest pterosaur that Prondvai et al. tested had wing tips that extended way over their heads when folded and quadrupedal (Figs. 1, 2). We’ve seen the short wings of flightless pterosaurs. Hatchlings of volant taxa don’t have short wings. Tiny adult pterosaurs may have ‘rapidly growing” bone microstructure because they matured quickly, reproduced as often as possible then died early, like tiny mammals do. More on this below:

Sexual maturity vs. size:
Prondvai et al. report, “According to the hypothesis presented here, the onset of powered-flight in Pterodaustro occurred after attaining 53% of adult size. Here we prefer the hypothesis that bone growth is slowed down by the initiation of a new, and much more energy consuming locomotory activity, namely powered flight.” Not by coincidence, this is the size that Chinsamy et al. (2008) determined that sexual maturity was attained. After observing the morphology of the embryo Pterodaustro, which matches the morphology of the adult, there is no supporting evidence for the Prondvai et al. hypothesis.

Archosaur vs. lepidosaur
Prondvai et al. do not consider the growth strategies and histology of lepidosaurs, only archosaurs. So they are making comparisons to the wrong clade. Pterosaurs nest within the Lepidosauria. Growth patterns in lepidosaurs are distinct and do not follow archosaur growth patterns (Masisano 2002). But this may not be the key factor in observed differences.

Chinsamy and Hurum 2006
looked at the basal lepidosaur, Gephyrosaurus. “The [bone] compacta consists of essentially parallel−fibred bone tissue interrupted by several lines of arrested growth (LAGs). The first LAG visible from the medullary cavity appears to be a hatchling line with its more haphazardly oriented, globular-shaped, osteocyte lacunae.”  This was not a phylogenetically miniaturized taxon even though it was a basal lepidosaur.

More to the point
Chinsamy and Hurum 2006 also looked at the basal and phylogenetically miniaturized mammal, Morganucodon. They report on, “distinct woven bone tissue with large, irregularly oriented osteocyte lacunae and several primary osteons. No secondary osteons were visible, though several enlarged erosion cavities are evident in the compacta. In the same section, it appears that substantial endosteal resorption had occurred, and parallel−fibred bone tissue is evident only in a localized area peripherally. This area includes several rest lines, which indicate pauses in the rate of bone formation, and hence, pauses in growth.” Perhaps these pauses indicate a lifespan of “several” years. Note the “woven bone” texture description.

Figure 1. Several tiny Rhmphorhynchus adults, among them is the n7 specimen tested by Prondvai et al. and considered a juvenile by them.

Figure 2. Several tiny Rhmphorhynchus adult sister taxa, among them is the n7 specimen tested by Prondvai et al. and considered a juvenile by them shown here about 7/10 of in vivo size. As you can see, these pterosaurs do not appear to have any impediments to flapping and flying. However their tiny hatchlings would probably not have flown based on their high surface/volume ratio. The adults had juvenile traits due to phylogenetic miniaturization.

The smallest sampled Rhamph bone microstructure
Prondvai et al. report about the tiny Rhamph, BSPG 1960 I 470a, (n7 in the Wellnhofer 1970 catalog, Fig. 2): “A thin layer of lamellar bone of endosteal origin rims the medullar [central] cavity. There seem to be only a few longitudinally oriented vascular canals, but these have rather large diameter in relation to the overall thickness of the cortex. The bone matrix is typically woven with some poorly defined, immature primary osteons, hence the majority of the cortex does not show the mature fibrolamellar pattern yet. The osteocyte lacunae are large and plump throughout the cortex, and possess an extremely well-developed system of dense, radially oriented canaliculi implying extensive communication and nutrient-exchange between the osteocytes. No LAGs or any other growth marks can be observed.”  Maybe LAGs were never present in this taxon if it lived for just a short time. Remember, we’re talking about phylogenetic miniaturization here.  If the small precocial Rhamphorhynchus specimens were maturing quickly and laying eggs early, they likely followed the life patterns of other tiny tetrapods, like Morganucodon (above) and died early, perhaps living only one or two years, not five or more as in mid-sized pterosaurs.

Note: Like Morganucodon (above) the phylogenetically miniaturized mammal, 
the bone structure in the smallest tested Rhamphorhynchus is described as “woven”.

Age vs size:
Prondvai et al. report, “The ontogenetic validity of the smallest size category of Bennett is clearly supported by the overall microstructure found in the bones of the three small specimens.” Unfortunately, without a phylogenetic analysis, Prondvai et al. did not realize that the smallest specimens were small due to phylogenetic miniaturization. Their ancestors were larger. Thus small Rhamphs retained juvenile and embryonic traits into adulthood, including the typical short rostrum and smaller wings. These traits also included juvenile “woven” bone tissue. Essentially these tiny pterosaurs were precocious sexually active adults in the former juvenile phase of development.

Precocial hatchling?
Prondvai et al. report, “Superprecocial embryos require substantial amount of nutrients stored in their eggs to reach an advanced level of somatic maturity state by the time the embryo hatches. If the egg volume of Darwinopterus was relatively as low as that of squamates, then how could it have contained so much yolk as to cover the energy requirements of an extremely well-developed, volant hatchling?” Prondvai are assuming that pterosaur eggs developed outside the uterus. As lepidosaurs, pterosaur embryos developed inside the uterus and the super thin eggshell was deposited last. Thus they could “cover the energy requirements.”

Apparently Prondvai et al. are not looking
at verified pterosaur hatchlings (in eggs), which are identical in morphology to adults. In some cases large embryos can be larger than small adult sister taxa! The Prondvai team know that the tiny Rhamps don’t have the same morphology as the medium or big rhamphs. Unfortunately, and this is a continuing problem… they don’t realize those changes are phylogenetic, not ontogneric.

With similar proportions of bone and muscle,
but at 1/8 as tall and therefore (8 cube rooted or) 1/512 as massive, juvenile pterosaur bone tissue would have been strong enough for sustained flight in such lightweight specimens. But that overlooks reality, where the specimens Prondvai are looking at are in fact tiny adults with juvenile bone structure, as in Morganucodon. We don’t know where small, medium and large Rhamphorhynchus laid its eggs, which were likely ready to hatch shortly after deposition. We don’t have any hatchling Rhamphorhynchus fossils. Hatchlings of the small and tiny adults would have been in danger of desiccation (high surface area/volume ratio), so we can presume they grew up in moist environs. Unfortunately Prondvai et al. did not test the one verified juvenile among in the Rhamphorhynchus clade, NHMW 1998z0077/0001 (Fig. 3), the Vienna specimen. No one thinks this juvenile could not fly based on its age/relative size.

Figure 1. Two specimens attributed to Rhamphorhynchus longiceps along with a third specimen that nested with the larger of the two with identical scores, thus identifying it as a juvenile R. longiceps.

Figure 3. Two specimens attributed to Rhamphorhynchus longiceps along with a third specimen, NHMW 1998z0077/0001, that nested with the larger of the two with identical scores, thus identifying it as a juvenile R. longiceps. No one thinks this Rhamph could not fly, despite its young age.

To their credit, Pronvai et al. suggest (following a hypothesis first presented here): “Alternatively, Rhamphorhynchus hatchlings could have been precocial to the effect that they could have left their nests immediately after hatching, but they must have been exclusively terrestrial or rather arboreal. They could have clambered around quadrupedally on the branches of trees feeding themselves with smaller invertebrates or vertebrates without any parental contribution.”

No universal growth strategy in pterosaurs
Prondvai et al. report, “In the light of the histological results it becomes evident that there is no universal pattern in the growth strategy of pterosaurs.” I am concerned that this conclusion was made without the the benefit of a phylogenetic analysis and without knowledge of phylogenetic miniaturization in the clade.

To their credit
Prondvai et al. report, “In contrast to Bennett’s  suggestion, the second size category of Rhamphorhynchus does not only include subadult but also adult specimens, hence it cannot be used as an indicator of real ontogenetic stage.”

References
Chinsamy A, Codorniu ́ L, Chiappe L 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biol Lett 4: 282–285.
Chinsamy A and Hurum JH 2006. Bone microstructure and growth patterns of early mammals. Acta Palaeontologica Polonica 51 (2): 325–338.
Maisano JA 2002. Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.
Prondvai E, Stein K, O0 si A, Sander MP 2012. Life History of Rhamphorhynchus Inferred from Bone Histology and the Diversity of Pterosaurian Growth Strategies. PLoS ONE 7(2): e31392. doi:10.1371/journal.pone.0031392
Sekercioglu C 1999. Megapodes: A fascinating incubation strategy. Online article. 

Allometry during ontogeny in the basal tritosaur, Huehuecuetzpalli

Huehuecuetzpalli (Reynoso 1998) is a basal tritosaur according to the large reptile tree, a lepidosaur nesting outside of the Squamata, and ancestral to Tanystropheus, Macrocnemus, drepanosaurids, fenestrasaurs and ultimately, pterosaurs. The lineage of pterosaurs is shown here.

Huehuecuetzpalli specimens are only known from the Early Cretaceous, with ghost lineage origins going back to the Late Permian. Long species survival is not uncommon among lepidosaurs, as in the extant Sphenodon with relatives in the Triassic.

Figure 1. Two specimens of Huehuecuetzpalli were found, one adult and one juvenile. Here they are shown together to scale along with manus and pes comparisons scale to a common length for metacarpal 4 and metatarsal 4.

Figure 1. Two specimens of Huehuecuetzpalli were found, one adult and one juvenile. Here they are shown together to scale along with manus and pes comparisons scale to a common length for metacarpal 4 and metatarsal 4.

Reynoso 1998 reported,
“The relative length of the snout, and the proportions of the skull and limbs relative to the presacral vertebral column, do not show signifcant differences between the juvenile and adult specimens, although these features usually change in ontogeny. This suggests that adult proportions were already acquired at the ontogenetic stage of the younger specimen in spite of its relatively smaller size.”

I have been repeating this observation
with regard to pterosaurs, which likewise do not show any significant differences (apart from the enlargement of any skull crests) in their morphological proportions. For examples click here, here and here and other references therein.

But is it true for Huehuecuetzpalli?
That’s why side-by-side comparisons are so useful. Sadly, I have not done so until just yesterday (Figs. 1, 2).

Figure 2. Huehuecuetzpalli, adult and juvenile skulls to scale. note the relatively shorter rostrum in the juvenile, which also had smaller teeth and a shorter set of parietals (with a smaller braincase and smaller jaw adductor chamber). In the juvenile the ascending process of the premaxilla was more robust.

Figure 2. Huehuecuetzpalli, adult and juvenile skulls to scale. note the relatively shorter rostrum in the juvenile, which also had smaller teeth and a shorter set of parietals (with a smaller braincase and smaller jaw adductor chamber). In the juvenile the ascending process of the premaxilla was more robust and the tooth-bearing portion was shorter with fewer teeth.

Reynoso 1998 reported,
“The complete fusion of the cranial elements suggests that the larger specimen is of post-juvenile age, and probably an adult condition was already acquired. The olecranon process of the ulna, however, is not completely ossified and attached to the ulna, and only a ball of hard tissue (calcified cartilage or bone) is preserved. It was impossible to find information in the literature about the time when the precursor of the olecranon process become fused to the ulna.

“The age of the smaller specimen is more difficult to establish. The complete ossification of the fourth distal tarsal and the still separated astragalus and calcaneum undoubtedly suggest a post-hatchling stage. The complete fusion of the frontal, however, shows that it is older than Rieppel’s specimen number 18 and the hatchling of Cyrtodactylus pubisulcus (Gekkonidae) illustrated by Rieppel (1992a: ¢g. 1). The high degree of ossification indicates that it is close to the latest stages of development preceding complete ossification. Juvenile skull characters are the presence of a broader parietal table with short lateral processes. Compared with the adult skull, the juvenile parietal table is more than 15% broader on the narrower section excluding the ventrolateral flanges for the dorsal attachment of the jaw adductor musculature.”

We looked at olecranon ossification in tritosaurs earlier here.

As a rule, lepidosaurs don’t change much during ontogeny
as we’ve seen earlier here with Shinisaurus. But they do change… a little.

References
Reynoso V-H 1998. Huehuecuetzpalli mixtecus gen. et sp. nov: a basal squamate (Reptilia) from the Early Cretaceous of Tepexi de Rodríguez, Central México. Philosophical Transactions of the Royal Society, London B 353:477-500.

 

Allometry and Isometry in Shinisaurus Ontogeny

There are those who insist that pterosaur juveniles and hatchlings had a short rostrum and large orbit (Bennett 1995, 1996), citing similar allometric changes during ontogeny in mammals and archosaurs. The fact that pterosaurs are not mammals or archosaurs does not appear to matter. The large reptile tree nests pterosaurs firmly within the Fenestrasauria, within the Tritosauria, within the Lepidosauria (outside the Squamates) and within the Lepidosauriformes.

Earlier we looked at isometry (relative lack of change) during ontogeny (maturation) in several pterosaurs for which we have juveniles associated with adults. These observations don’t seem to matter much to pterosaur experts who want to believe that hatchling pterosaurs had cute features. Isometry during ontogeny is generally found trait among lepidosaurs and especially so among tritosaur lepidosaurs, as evidenced by Reynoso (1989) who noticed little to no change between a juvenile and an adult Huehuecuetzpalli.

Today we’ll take a look at allometry AND isometry during ontogeny in a rare living lizard (Squamata, Autarchoglossa, Anguimorpha), Shinisaurus crocodilurus (Figs. 1, 2, the Chinese crocodile lizard).

Figure 1. Lateral views of Shinisaurus adult and juvenile, to scale and to the same skull length. While the skull proportions are roughly the same (isometry) changes that can be noted are noted (allometry).

Figure 1. Lateral views of Shinisaurus adult and juvenile, to scale and to the same skull length. While the skull proportions are roughly the same (isometry) changes that can be noted are noted (allometry). Note there is no rostral elongation during maturation in this taxon. Images from Digimorph.org

The skulls of the juvenile and adult
show very little rostral elongation during maturity. The orbit is only slightly reduced in the adult. Larger changes are noted on the figures. Surprisingly, the teeth are relatively smaller in the adult. The expanded braincase in the juvenile is reduced in the adult, but an expanded (inflated) occiput is retained and further expanded in several burrowing lizards, retained in a process called neotony.

Figure 2. Dorsal views of Shinisaurus juvenile and adult with notes on isometric and allometric changes.

Figure 2. Dorsal views of Shinisaurus juvenile and adult with notes on isometric and allometric changes. Left image from Digimorph.org.

Wikipedia reports: Shinisaurus, the Chinese crocodile lizard, was once also regarded as a member of Xenosauridae, but most recent studies of the evolutionary relationships of anguimorphs consider Shinisaurus to be more closely related to monitor lizardsand helodermatids than to Xenosaurus. It is now placed in its own family Shinisauridae. The large reptile tree agrees with this nesting.

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 limestones of Germany: taxonomic and systematic implications. Journal of Vertebrate Paleontology 16:432–444.

http://digimorph.org/specimens/Shinisaurus_crocodilurus/juvenile/
wiki/Chinese_crocodile_lizard

Anshunsaurus (thalattosaur) juvenile notes

Anshunsaurus (Liu 1999) was a late middle Triassic (Landinian) thalattosaur close to Askeptosaurus. It is known from an adult and a juvenile.

From the abstract: “A marine reptile from the Ladinian deposits near Xingyi is described and identified as a juvenile of Anshunsaurus wushaensis on the basis of similar skull proportions and many postcranial characters. Based on this specimen and observations of the holotype of A. wushaensis, there is no distinct ontogenetic differentiation in the length of the jugal. The absence of an astragalus in the holotype, and the greater length of metacarpal V relative to metacarpal IV, could be due to intraspecific variation. Ossification is not synchronous for corresponding elements on both sides of the body.”

This asymmetry is the key point to this post, and something to consider when thinking about adult/juvenile matching.

Figure 1. The two Anshunsaurus skull, adult and juvenile.

Figure 1. The two Anshunsaurus skull, adult (from Liu and Rieppel 2005) and a  juvenile (from Liu 2007). Scale bar is 10cm. So on a 72dpi screen the skulls are shown at 0.8 scale or 20 percent smaller.

What are thalattosaurs?
Liu and Rieppel 2004 wrote, “The phylogenetic position of thalattosaurs within amniotes is controversial: They have been suggested to be diapsids with possible affinities to the Lepidosauromorpha (Romer, 1956; Rieppel, 1998), Archosauromorpha (Evans, 1988), to be Neodiapsida inc. sed. (Benton, 1985), or else to be the sister taxon of Sauria (Mu¨ller, 2004) or of Ichthyopterygia (Müller, 2003).”

According to the large reptile tree, Müller is correct.

The Triassic marine reptile Anshunsaurus huangguoshuensis was originally described by Liu (1999) as a sauropterygian (likely a plesiosaur or nothosaur) on the basis of a dorsal view of a skull. The specimen was recognized as thalattosaurian by Rieppel et al. (2000). So errors happen.

Figure 2. The manus and pes of the large and small Anshunsaurus specimens.

Figure 2. The manus and pes of the large and small Anshunsaurus specimens. In the manus note the difference in metacarpal/digit proportions along with carpal ossification. In the pes note similar differences, and also a lengthening of mt4 and a narrowing of its proximal articulation. Individual variation or speciation?

Genus differences
Anshunsaurus differed from the previously known but similar Askeptosaurus by the maxilla forming part of the  anteroventral orbital margin; fusion of the postorbital and postfrontal; the posterolateral process of the frontal extending posteriorly far beyond the anterior margin of lower temporal fossa, narrowly approaching but not contacting the supratemporal; the long and slender ventral process of the squamosal extending to the lower margin of the cheek; jugal with an elongate posterior process; lateral exposure of the angular equal to that of the surangular; deltopectoral crest on the humerus developed; fibula expanded.

Species differences
A. wushaensis
 was slightly smaller and differed from the holotype A. huangguoshuensis in the following characters (Rieppel et al., 2006):

  1. relatively smaller skull relative to the glenoid-acetabulum length;
  2. short posterior process of the jugal that does not extend backward beyond the midpoint of the lower temporal fossa;
  3. neural spines in the posterior dorsal region that are not taller than their anteroposterior width and with a distinct ornamentation of vertical grooves and ridges near their dorsal margin;
  4. cruciform interclavicle with a broad-based anterior process;
  5. ectepicodylar groove and notch on humerus distinct;
  6. entepicondyle well developed, with ridge on ventral side of medial margin but no foramen;
  7. metacarpal V slightly longer than metacarpal IV;
  8. loss of one phalanx in fourth digit;
  9. iliac blade posterodorsally expanded; 
  10. seven ossified tarsals.

In the skull, the major difference between A. huangguoshuensis and A. wushaensis is the degree of extension of the posterior process of the jugal.

Rieppel et al. (2006) report on the new species, “The specimen here described is remarkable with respect to the asymmetry of the maxillae, scapulae, and ilia. The scapular and iliac asymmetry is due to different degrees of ossification. It indicates that the corresponding elements on two sides are not synchronous in the process of ossification.”

Worth remembering.

References
Liu J 1999. New discovery of sauropterygian from Triassic of Guizhou, China. Chinese Science Bulletin 44: 1312–1315.
Liu J 2007. A Juvenile Specimen of Anshunsaurus (Reptilia: Thalattosauria). American Museum Novitates 3582, 9 pp.
Liu J and Rieppel O 2005. Restudy of Anshunsaurus huangguoshuensis (Reptilia: Thalattosauria) from the Middle Triassic of Guizhou, China. American Museum Novitates 3488, 34 pp.
Rieppel O, Liu J and Li C 2006. A new species of the thalattosaur genus Anshunsaurus (Reptilia: Thalattosauria) from the Middle Triassic of Guizhou Province, southwestern China. Vertebrata PalAsiatica 44: 285–296.

Something about Turkeys on Thanksgiving

Happy Thanksgiving (America).
I encourage my readers, if they have not already done so, to check out My Life as a Turkey online at PBS (Fig. 1, click here). They’re curious, affectionate, loyal and when they hit puberty all hell can break loose. They’re beset by enemies and they learn to control their enemies. They are hit with disease and they mourn their losses. Some are independent. Others, from the same brood, seek touch. Watch them learn to fly, loose their cuteness, play with the mammals and, in the end, go out on their own.

Click to go to online video at PBS/Nature. My Life as a Turkey explores the ontogeny of these little dinosaurs as thoroughly as I've ever seen.

Click to go to online video at PBS/Nature. My Life as a Turkey explores the ontogeny of these little dinosaurs as thoroughly as I’ve ever seen.