Pterodaustro isometric growth series

Tradtional paleontologists think pterosaur babies had a cute short rostrum that became longer with maturity and a large orbit that became smaller with maturity (Fig. 1). This is a growth pattern seen in the more familiar birds, crocs and mammals.

Pterodaustro embryo as falsely imagined in Witton 2013. The actual embryo had a small cranium, small eyes and a very long rostrum.

Figure 1. Pterodaustro embryo as falsely imagined in Witton 2013. The actual embryo had a small cranium, small eyes and a very long rostrum.

Unfortunately
these paleontologists ignore the fossil evidence (Figs 2, 3). These are the data deniers. They see things their own way, no matter what the evidence is. The data from several pterosaur growth series indicates that hatchlings had adult proportions in the skull and post-crania. We’ve seen that earlier with Zhejiangopterus (Fig. 2), Tapejara, Pteranodon, Rhamphorhynchus and others. Still traditional paleontologists ignore this evidence as they continue to insist that small short rostrum pterosaurs are babies of larger long rostrum pterosaurs.

Figure 1. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Figure 2 Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

As readers know,
several pterosaur clades went through a phase of phylogenetic miniaturization, then these small pterosaurs became ancestors for larger clades. Pterosaurs are lepidosaurs and they grow like lepidosaurs do, not like archosaurs do.

Today we’ll look at
the growth series of Pterodaustro (Fig. 1), previously known to yours truly only from adults and embryos. Today we can fill the gaps with some juveniles.

This blog post is meant to help traditional paleontologists get out of their funk.

A recent paper
on the braincase of odd South American Early Cretaceous pterosaur Pterodaustro (Codorniú et al. 2015) pictured three relatively complete skulls from a nesting site (Fig. 1). I scaled the images according to the scale bars then added other available specimens.

Figure 1. Pterodaustro skulls demonstrating an isometric growth series. One juvenile is scaled to the adult length. One adult is scaled to the embryo skull length. There is no short rostrum and large orbit in the younger specimens.

Figure 1. Pterodaustro skulls demonstrating an isometric growth series. One juvenile is scaled to the adult length. One adult is scaled to the embryo skull length. There is no short rostrum and large orbit in the younger specimens. If you can see differences in juvenile skulls vs. adult skulls, please let me know. All these specimens come from the same bone bed.

You can’t tell which skulls are adults or juveniles
without scale bars and/or comparable specimens. As we established earlier, embryos are generally one-eighth (12.5%) the size of the adult. Pterodaustro follows this pattern precisely.  We have adults and 1/8 size embryos and several juveniles of intermediate size.

No DGS was employed in this study.

If you know any traditional paleontologists, 
remind them that the data indicates that pterosaurs matured isometrically, like other  lepidosaurs. Those small, short rostrum specimens, principally from the Late Jurassic Solnhofen Formation, are small adults, transitional from larger ancestors to larger descendants. Tiny pterosaurs experiencing phylogenetic miniaturization(as in birds, mammals, crocs, turtles, basal reptiles, and many other clades) that helped their lineage survive while larger forms perished, Sadly, no tiny pterosaurs are known from the Late Cretaceous when they all became extinct.

References
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.
Codorniú L, Paulina-Carabajal A and Gianechini FA 2015.
 Braincase anatomy of Pterodaustro guinazui, pterodactyloid pterosaur from the Lower Cretaceous of Argentina. Journal of Vertebrate Paleontology, DOI:10.1080/02724634.2015.1031340

More tiny birds and tiny pterosaurs

Earlier we took a peek at a few tiny birds and pterosaurs. Here (Fig. 1) are several more.

Traditional paleontologists
insist that these tiny pterosaurs were babies of larger forms that looked different, (Bennett 1991, 1992, 1994, 1995, 1996, 2001, 2006, 2007, 2012, 2014) ignoring or not aware of the fact that we know pterosaur embryos and juveniles were virtually identical to their adult counterparts (Fig. 2). Bennett (2006) matched two tiny short-snouted pterosaurs (JME SoS 4593 and SoS 4006 (formerly  PTHE No. 1957 52) to Germanodactylus, but they don’t nest together in the large pterosaur tree.

Figure 1. Tiny pterosaurs and tiny birds to scale showing that tiny pterosaurs were generally about the size of the tiny Early Cretaceous bird.

Figure 1. Tiny pterosaurs and tiny birds to scale showing that tiny pterosaurs were generally about the size of the tiny Early Cretaceous bird. I have, for over a decade, promoted the fact that these tiny pterosaurs were adults, the size of modern hummingbirds and wrens.

One of the most disappointing aspects of modern paleontology
is the refusal of modern pterosaur workers to include in their analyses the small and tiny pterosaurs. They were all the size of living hummingbirds and wrens. Many were similar in size to extinct Early Cretaceous birds (Fig. 1). Those workers don’t want to add these taxa to their lists on the false supposition that the tiny pterosaurs are babies of, so far unknown adults. Note Bennett’s long body of work (see below) indicated otherwise, but never with phylogenetic analysis.

Phylogenetic analysis (Peters 2007) reveals these tiny pterosaurs are adults or can be scored as adults. They are surrounded by adults and they often form transitional taxa in the evolutionary process of phylogenetic miniaturization between larger long-tailed pterosaurs and larger short-tailed pterosaurs.

Figure 1. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Figure 2. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen. This is evidence that juveniles were virtually identical to adults, except in size.

More importantly,
earlier we discussed several examples of juvenile pterosaurs morphologically matching adults here, here and here. So young pterosaurs have been shown to match their adult counterparts. They don’t transform like young mammals and dinosaurs do. They were ready to fly upon hatching IF they were the minimum size to avoid desiccation, as discussed earlier here.

The most interesting aspect
to the whole tiny pterosaur story is how small their smallest hatchlings would be. We looked at that earlier here.

References
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 1992. 
Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Bennett SC 1994. 
Taxonomy and systematics of the Late Cretaceous pterosaur Pteranodon (Pterosauria, Pterodactyloidea). Occassional Papers of the Natural History Museum University of Kansas 169: 1–70.
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.
Bennett SC 2001.
 
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 revision of the genus. Journal of Vertebrate Paleontology 26(4): 872–878.
Bennett SC 2007. A second specimen of the pterosaur Anurognathus ammoni. Paläontologische Zeitschrift 81(4):376-398.
Bennett  SC (2012) [2013] 
New information on body size and cranial display structures of Pterodactylus antiquus, with a revision of the genus. Paläontologische Zeitschrift (advance online publication) doi: 10.1007/s12542-012-0159-8
http://link.springer.com/article/10.1007/s12542-012-0159-8
Bennett SC 2014. A new specimen of the pterosaur Scaphognathus crassirostris, with comments on constraint of cervical vertebrae number in pterosaurs. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 271(3): 327-348.
Peters D 2007. The origin and radiation of the Pterosauria. Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27

 

Getting Big and Getting Small, a NEXT Page from Nat Geo

The most recent issue of Nat Geo included a one page note called, “Sizing Up.”

Nat Geo reporter Gretchen Parker sourced Allistair Evans, of Monash U, Australia, who noted “It takes a minimum of 3 million generations for a dolphin-sized aquatic mammal to increase to the size of a blue whale.” 1000x change in size, graphics impressive.

“It takes 1.6 million generations for a sheep-size land mammal to increase to the size of an elephant.” 100x change in size

“But it takes only a minimum of 0.1 million generations for an elephant-sized land mammals to decrease to the size of a sheep. 100x change in size.

“5 million generations” to go from rabbit-sized to elephant-size. 1000x

“24 million generations” to go from mouse-size to elephant-size. 100,000x

All this is interesting, but more interesting to PterosaurHeresies readers might be some similar hypotheses regarding prehistoric reptiles, particularly pterosaurs.

Pterodaustro embryo

Figure 1. Pterodaustro embryo. At one-eighth the size of a large adult, this embryo retains most of the proportions of the adult, including a long rostrum and tiny eye.

Chinsamy et al. (2008) noted that in Pterodaustro, the only pterosaur for which we have a complete growth series, half grown specimens appear to be sexually mature. At half size, the pelvis is also half size, able to pass eggs of half size producing hatchlings of half size, more or less. In three generations such a progression could lead to a one-eighth size adult, which would be the size of a hatchling of the original Pterodaustro. Now I’m not saying this is exactly how size reduction happened in pterosaurs. The three generations is just the ‘speed limit’ for getting small, something pterosaurs did over and over again, producing new clades following these many size decreases as size thereafter increased.

Some pterosaurs, like Quetzalcoatlus, became very large and very famous. Other pterosaurs became very small. They’re not famous. They don’t even rate a distinct genus, having been relegated to the trash heap with the label, “juvenile.” They are excluded from phylogenetic analysis  and unjustly so. They are important.

Of course getting big again simply depends on creating eggs later in life when the mother is slightly surpassing the 8x growth pattern having a larger pelvis to pass a larger egg. Like elephants, getting bigger probably took more time than getting smaller.

Overall size does affect morphology and evolution. Early and late maturation affects the next generation. Hormones count! Hormones also drive secondary sexual characteristics, like frills and crests. These things add up, or subtract out, over many generations.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.

Birds have paedomorphic dinosaur skulls

A new paper by Bhullar et al. (2012) proposes that birds had paedomorphic dinosaur skulls.  They retained juvenile traits as adults. This seems quite reasonable. They also had paedomorphic bodies, the smallest of all dinosaurs. Not sure if that’s mentioned in the paper or not. I haven’t read it.

Pairs of archosaur skulls demonstrating ontogenetic changes.

Figure 1. Pairs of archosaur skulls demonstrating ontogenetic changes. Young ones on the left. Adults on the right. The greatest disparity appears to be in crocs, but the youngest Coelophysis and Archaeopteryx are unknown and not shown. Compare the juvenile Coelophysis to the adult Archaeopteryx for rostral length and eye size. This is allometric growth. From. Bhullar et al. 2012.

Allometric vs Isometric Growth
Crocs and dinos experience(d) allometric growth. The proportions of the skull change(d) during ontogeny (growth, maturity). Mammals, with their cute features as juveniles experienced the same sort of growth. All three are new archosauromorphs.

Move over to the other side of the reptile tree and you have pterosaurs. The embryos and juveniles are virtual copies of adults, only smaller. This is termed isometric growth. However, among living new lepidosauromorphs, turtles and lizards, allometric growth still rules. What spurred the development of isometric growth? It’s hard to say. It has nothing to do with maternal care, because cute baby turtles are on their own.

Juvenile fossils are rare.
Immature specimens are rarities, but close to pterosaurs we have Huehuecuetzpalli, a tritosaur lizard, known from a single adult and juvenile, both proportionally identical according to Reynoso (1989). Other smaller vs. larger tritosaurs, including freaky, long-necked Tanystropheus purports to have distinct juveniles with a shorter rostrum and multi-cusped teeth, but these traits distinguish species and genera, not adult and juvenile. The closest sisters of the smaller Tanystropheus are smaller still and have a shorter rostrum. One of these is tiny Cosesaurus. Others include a variety of Langobardisaurus and Tanytrachelos, all considered adults.

Tiny Pterosaurs
Many, but not all, of the tiniest pterosaurs have a short rostrum and large eyes. Traditionally these traits have labeled them juveniles, but no attempts have been made to match juveniles to adults phylogenetically — except here. And here is where tiny pterosaurs with a short rostrum have been linked to larger pterosaurs also with a short rostrum. Note: not all tiny pterosaurs had a short rostrum!

No doubt the tiny scaphognathid descendants of larger scaphognathids had a shorter rostrum and traditional juvenile features. Since hatchling and embryo pteros were identical to adults, these paedomorphic traits must be retentions of embryonic, not juvenile traits. Just a genetic time shift is all that is necessary to make this happen.

Tiny Birds
The Smithsonian blog reports, “the skulls of young birds are anatomically almost identical to those of adults.” Hmmm. How interesting with regard to arboreal vertebrates finding convergent ways to go — if true. But let’s picture a baby chick, eaglet or ostrich compared to an adult and immediately this fantasy of isometric growth vanishes. The Archaeopteryx teenager (Fig. 1) is far from being a hatchling. The blog reports, “As a new Nature study by Bhart-Anjan Bhullar and collaborators suggests, this feature of bird life can be traced back to ancient transformations that effectively locked bird skulls into a permanent juvenile anatomy.” 

Let’s test this:
As a test Google: “hatchling stork,” “hatchling hummingbird,” and “hatchling pelican.” They ALL have a short rostrum — unlike the embryo Pterodaustro and the JZMP embryo ornithocheirid. So, not all birds experience isometric growth. These were very much like the alligator (Fig. 1) in their allometric growth.

Speaking of Dinosaurs…
There are some adult dinos with a short rostrum and big eyes. I direct your attention to MassospondylusDaemonosaurus and their plant-eating descendants. All adults and I’ll wager their rostrum was not appreciably shorter as a hatchling.

Nature carves out its own rules. We have to find them.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Bhullar B, Marugán-Lobón J, Racimo F, Bever G, Rowe T, Norell M and Abzhanov A 2012. Birds have paedomorphic dinosaur skulls Nature DOI: 10.1038/nature11146
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.

Another “Wingless, Juvenile” Rhamphorhynchus

Rhamphorhynchus sp. (BSPG 1960 I 470a) was considered a juvenile without a head or wings. The specimen appears to be largely unprepared. Earlier we looked at another purportedly wingless Rhamphorhynchus (BML-37012, No. 85 in the Wellnhofer 1975 catalog), also from the Solnhofen formation, in which the wings were buried.

juvenile Rhamphorhynchus BSPG 1960 I 470a in situ

Figure 1. Click to enlarge. The purported juvenile Rhamphorhynchus BSPG 1960 I 470a in situ (above) and traced in black. Buried elements (skull, wings) traced in gray. This specimen demonstrates the value of using Digital Segregation to trace buried elements. Digging into the matrix using this map should reveal more bones.

As Before…
When a fossil specimen is discovered by splitting Solnhofen limestones, typically many bones remain invisible, hidden beneath a thin blanket of limestone at the separation layer. Preparators can usually create a precise outline of the specimen, even when the bones are rather deep, because preparators can see the general direction of the fossil (head on one end, tail on the other) and the exact location of other elements are often betrayed by a slight rise in the matrix. Like a blanket over a child in bed, the limestone tells you exactly where to dig.

Above, Rhamphorhynchus intermedius (n28 in the Wellnhofer 1975 catalog) was recovered as a sister to BSPG 1960 I 470, below.

Figure 2. Above, Rhamphorhynchus intermedius (n28 in the Wellnhofer 1975 catalog) was recovered as a sister to BSPG 1960 I 470, below. If your computer screen is set to 72 dpi these two specimens will be shown at full scale. Both are among the most primitive known species of Rhamphorhynchus. Unlike the BML specimen reconstructed earlier, the BSPG specimen had a relatively small skull, based on the size of the mandible.

Reconstruction and Phylogenetic Analysis
We can’t just trace ephemeral elements without testing them in a reconstruction and phylogenetic analysis. The reconstruction is shown in Figure 2 alongside its phylogenetic sister, Rhamphorhynchus intermedius. The relatively short neck and robust torso mark these as primitive for the genus. The pedal phalangeal patterns are also primitive. The very wide jaws of the BSPG specimen are similar to those found in a more derived sister, also tiny, the BMM specimen.

A better test would be for a preparator to dig into the matrix where I have mapped the buried elements.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Wellnhofer P 1975a. Teil I. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Allgemeine Skelettmorphologie. – Paleontographica A 148: 1-33.
1975b. Teil II. Systematische Beschreibung. – Paleontographica A 148: 132-186.
1975c. Teil III. Paläokolgie und Stammesgeschichte. – Palaeontographica 149: 1-30.
Wellnhofer P 1991. The Illustrated Encyclopedia of Pterosaurs. London, Salamander Books, Limited: 1-192.