A juvenile Eusthenopteron enters the LRT

Fish expert, John Long 1995 (p. 209) wrote:
The juvenile skull of a crossopterygian fish, Eusthenopteron (Figs. 1,3) has more features in common with that of an early amphibian Crassigyrinus (Fig. 4), that it’s adult skull would have had.”

Long goes on to explain about paedomorphosis and heterochrony during the transition from fish to tetrapod.

Euthenopteron was a good transitional taxon several years ago. Recently it was replaced in the LRT by a flatter taxon, Cabonnichthys.

Figure 1. Eusthenopteron juvenile in situ from Schultze 1984. Large plate ventral to the mandible overlaps a convex ventral margin. The quadratojugal is not labeled here. Several bones are re-labeled here.

Figure 1. Eusthenopteron juvenile in situ from Schultze 1984. Large plate ventral to the mandible overlaps a convex ventral margin. The quadratojugal is not labeled here. Several bones are re-labeled here.

Let’s put Long’s 1995 statement to the test
by adding Eusthenopteron ‘junior’ (Schultze 1984) to the large reptile tree (LRT, 1698+ taxa; subset Fig. 5).

Results: The juvenile nested with the adult Eusthenopteron in the LRT, falsifying Long’s statement.
Note: Several bones are relabeled here vs. Schultze’s original designations.

Worthy of note:
The juvenile Eusthenopteron shares several traits with another, often overlooked, small taxon with similar large eyes, Koilops, which nests at the base of a nearby derived node in the LRT (Fig. 5). Based on phylogenetic bracketing, Koilops is also a juvenile. All sister taxa are larger and without juvenile proportions.

Figure 2. Koilops is a flat-headed sister to Spathicephalus, but with teeth, larger orbits and a shorter snout

Figure 2. Koilops is a flat-headed smaller sister to Elpistostege, but with larger teeth, larger orbits and a shorter snout. These traits indicate Koilops is a juvenile.

So Long’s point about paedomorphosis and heterochrony
was  not correct in this case. His ‘matching tetrapod’, Crassigyrinus (Fig. 4), nests several nodes apart from pre-tetrapods in the LRT (off the subset chart in Fig. 5).

Koilops post-crania remains unknown,
but it nests at the base of Elpistostege, Tiktaalik and Spathicepahlus on one branch, Panderichthys + Tetrapoda on the other. So Koilops likely had lobe fins and a straight tail. Perhaps Koilops was a juvenile elpistostegid ready to mature into something larger, with smaller eyes, more like Elpistostege.

Figure 2. Juvenile and adult Eusthenopteron compared from Schultze 1984. The cranium of the juvenile appears convex here, but was likely flatter.

Figure 3. Juvenile and adult Eusthenopteron compared from Schultze 1984. The cranium of the juvenile appears convex here, but was likely flatter based on figure 1.

From the Schultze 1984 abstract:
A size series of thirty-five specimens of Eusthenopteron foordi Whiteaves, 1881 , shows isometric and allometric changes. As in Recent fishes, the main difference between small (juvenile) and large (adult) specimens is the relative size of the orbit and of the head. With the exception of the caudal prolongation, all fin positions remain isometric to standard length.”

Figure 5. Crassigyrinus has little to no neck.

Figure 4. Crassigyrinus has little to no neck.

Contra Long 1995 and all prior basal tetrapod workers, the LRT indicates the transition from fish to tetrapod occurred among flat-head taxa, like Trypanognathus.  Crassigyrinus Fig. 4) is a distinctly different stegocephalid with a taller skull, more like those of the more famous traditional transitional taxa, Ichthyostega and Acanthostega. The new fish-to-tetrapod transitional taxa were recovered by simply adding taxa overlooked by prior workers. Taxon exclusion continues to be the number one problem with vertebrate paleontology today, according to results recovered by the LRT. This free, online resource minimizes taxon exclusion.

Figure x. Subset of the LRT, focusing on fish for July 2020.

Figure x. Subset of the LRT, focusing on fish for July 2020.

Not sure if fish expert John Long
would make the same statement today. Let’s hope things have changed in the last 25 years of vertebrate paleontology.


References
Long JA 1995. The Rise of Fishes. The Johns Hopkins University Press, Baltimore and London 223 pp.
Schultze H-P 1984. Juvenile specimens of Eusthenopteron foordi Whiteaves, 1881 (Osteolepiform Rhipidistian, Pisces) from the Late Devonian of Miguasha, Quebec, Canada. Journal of Vertebrate Paleontology 4(1):1–16.

wiki/Eusthenopteron

Ontogenetic crest development in Tupuxuara

Let’s set the stage
Earlier we looked at the isometric growth of the azhdarchid pterosaur, Zhejiangopterus and the juvenile Pteranodon. Earlier we falsified unsupported claims that tiny Solnhofen pterosaurs were allometric juveniles of larger forms. Earlier we reported on four pterosaur embryos that demonstrated isometric growth. None had the larger eyes and shorter rostrum that typify hatchling and newborn mammals, birds and crocs (contra Bennett 2006). Even so, Witton 2013 continues to promote the false hypothesis of allometric growth during ontogeny in pterosaurs (Fig. 1).

But we haven’t yet touched on the crest size question
Today we’ll show evidence that yes, crest size does increase during ontogeny. And, really, how else would you ever expect to get such big crests inside an eggshell? However, rostrum length and eye size does not change during ontogeny, no matter how much Bennett and Witton want that to happen. Witton unwittingly demonstrates this himself with a juvenile Tupuxuara (Fig. 1).

Figure 2. Witton 2013 promotes the myth that small Rhamphorhynchus specimens were juveniles of larger specimens. Actually the small ones were ancestral to the larger ones as recovered in phylogenetic analysis.  Below: An actual juvenile Tupuxuara, matched to another species of Tupuxuara with a longer rostrum. Note the juvenile eyes are not large. Crest size does increase with ontogenetic age.

Figure 1. Witton 2013 promotes the myth that small Rhamphorhynchus specimens were juveniles of larger specimens. Actually the small ones were ancestral to the larger ones as recovered in phylogenetic analysis.
Below: An actual juvenile Tupuxuara, matched to another species of Tupuxuara with a longer rostrum. See figure 3 for a better match to an adult. Note the juvenile eyes are not large. Crest size does increase with ontogenetic age.

Today
we have three size of Tupuxuara (Fig. 2) based on the Goshura specimen including two likely juveniles morphologically close to it. Each has a distinct skull showing some variation, but together they shed some light on crest development with maturation in these large Cretaceous pterosaurs. Note that none have the traditional short rostrum and large eyes Bennett (2006) predicted. Neither the juveniles nor the adult have the long rostrum of the Tupuxuara longicristatus specimen that Witton (2013) substituted (Fig. 1) for an adult version of this species. Note that the middle colorized specimen has a relatively longer rostrum than the Goshura specimen. This may represent individual variation grading into speciation.

Figure 1. Ontogenetic skull and crest development in Tupuxuara. Note the eyes are small and the rostrum is long in juveniles. Only the crest expands and only posteriorly.

Figure 2. Ontogenetic skull and crest development in Tupuxuara. Note the eyes are small and the rostrum is long in juveniles and adults, even longer in the middle juvenile. Only the crest expands  posteriorly.

TMM 42489-2, the tall crested Latest Cretaceous large rostrum and mandible. It's a close match to that of Tupuxuara, otherwise known only from Early Cretaceous South American strata.

Figure 3. TMM 42489-2, the tall crested Latest Cretaceous large rostrum and mandible. It’s a close match to that of Tupuxuara longicristatus, otherwise known only from Early Cretaceous South American strata. Note the big difference in rostral length is a phylogenetic difference, not an ontogenetic one. If you were hell bent on proving allometric growth, this is the skull I would use, like the one Witton did. 

We also have a juvenile Tapejara with a crest
And the crest not much smaller than an adult crest. Skull proportions are virtually the same between adult and juvenile. And yet, look, there’s another long rostrum adult, just another variation on a theme.

Figure 4. Juvenile Tapejara with two adults of distinct species. Note the rather large crests on the juvenile, but otherwise the skull had adult proportions.

Figure 4. Juvenile Tapejara with two adults of distinct species. Note the rather large crests on the juvenile, but otherwise the skull had adult proportions.

Along the same lines:
Witton 2013 also attempted to promote the Bennett (1995) idea that small Rhamphorhynchus specimens were actually juveniles (Fig. 1). Neither worker used phylogenetic analysis which demonstrates that known small Rhamphorhychus specimens were actually primitive, closer to the outgroup taxon, Campylognathoides.

You’ll recall
Bennett (1991, 2000) said that short-crested, smaller specimens of Pteranodon represented juveniles and females. That was falsified using phylogenetic analysis that recovered short-crested Pteranodon specimens closer to short-crested outgroup taxa, such as Germanodactylus. We do know of Ptweety, the juvenile Pteranodon, but it had a long rostrum and, unfortunately, the crest was broken off

Nevertheless, it’s obvious that long and tall-crested pterosaur specimens could not have fit such long and tall crests into an eggshell. So there must have been some sort of crest growth during ontogeny in large crested specimens. And this, so far, is the evidence for it.

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 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 review of the genus. Journal of Vertebrate Paleontology 26:872–878.SMNS
Witton M. 2013. Pterosaurs. Princeton University Press. 291 pages.

Sometimes the larger sister has the more juvenile traits.

A few posts ago we noted the interesting fact that the larger Garjainia  (Otchev 1958, Early Triassic ~240 mya, 2 m. long) had the relatively larger skull compared to its sister, Euparkeria  (Broom 1913 Early Triassic, ~240 mya, 60 cm). Generally a larger head is considered a juvenile trait. Garjainia also had a shorter tail and a shorter torso.

In the background is Garjainia, a basal erythrosuchid. Euparkeria is at its ankles, both to scale. Euparkeria is the more derived taxon. Below the tail of Euparkeria is a greatly reduced Garjainia. No fossils exist that show Garjainia to this size.

Figure 1. In the background is Garjainia, a basal erythrosuchid. Euparkeria is at its ankles, both to scale. Euparkeria is the more derived taxon. Below the tail of Euparkeria is a greatly reduced Garjainia as if a juvenile of Euparkeria. No fossils exist of Garjainia at this size.

On the other hand
Euparkeria did have the slightly larger orbit, a trait generally considered juvenile. The skull of Euparkeria also had smoother contours (no pmx/mx notch, less of a jugal descent).

Evolution Uses Premature Maturation
The greatly reduced size of Euparkeria is yet another example of a new clade arising from shrimps arising from old clades. Others have complained that size is not pertinent to phylogenetic matrices, but this example shows otherwise. Deciding where to draw “the line” will continue to be argued, no doubt.

Figure 3. Here Euparkeria nests between Garjainia, a basal erythrosuchid, and Ornithosuchus following the nestings recovered by the large reptile tree. All three share a suite of traits that do not include a long narrow rostrum and a dorsal naris, among other traits.

Figure 2. Here Euparkeria nests between Garjainia, a basal erythrosuchid, and Ornithosuchus, an ornithosuchid, following the nestings recovered by the large reptile tree. Note the relative size of the skull in Garjainia, much larger than the much smaller Euparkeria.

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
Broom R 1913. On the South-African Pseudosuchian Euparkeria and Allied Genera. Proceedings of the Zoological Society of London 83: 619–633.
Ewer RF 1965. The Anatomy of the Thecodont Reptile Euparkeria capensis Broom Philosophical Transactions of the Royal Society London B 248 379-435.
Otchev VG 1958. Novye dannye po pseudozukhiyam SSSR: Doklady Akademii Nauk SSR, 123(4):749-751.
Parrish JM 1992. Phylogeny of the Erythrosuchidae. Journal of Vertebrate Paleontology 12:93–102.

wiki/Euparkeria
wiki/Garjainia

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.

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.

Ontogeny: Pteranodon vs. Diomedea

The Albatross (Diomedea exulans) and Pteranodon ingens (Fig. 1) were two large soaring reptiles, the former a bird, the latter a pterosaur. Insight into the ontogeny, maturity and lifespan of the extant Diomedea may shed some light on the extinct Pteranodon.

Pteranodon and the albatross

Figure 1. Left: Pteranodon. Right: Diomedea (albatross).

Widest Wingspan Among Birds
The albatross has a wingspan that reaches an extreme of 12 feet and averages 9 feet. The pterosaur Pteranodon had a similar wing plan with an enlarged wingspan up to 20 feet. Thus, and for little other reason, the albatross is the closest living analog to Pteranodon.

Albatross: Latest Maturation Among Birds
Most birds reach maturity in less than a year and many (crow, ostrich) do so in two years. By contrast, albatross males begin breeding at age 7, females at age 10. Some wait until 13. The life expectancy of an albatross is 30 years. According to Couzens (2008) it takes years for the albatross to become proficient at finding enough food for itself and more to take on the extra task of feeding a chick. The albatross also takes a long time to establish a pair bond.

Lizards vs Birds: Traditional Views
Most workers follow the paradigm that cold-blooded lizards mature more slowly than warm-blooded birds and mammals. Often, but not always, this is the case. However, more than mere physiology, size is typically an overriding factor. As everyone knows, mice mature faster than dogs, which mature faster than elephants and humans. The blue whale, which matures at 5 (females) or 8+ (males), does not follow this pattern. Among cold-blooded reptiles, iguanas are sexually mature at 50% of maximum size before the end of the second year (Kaplan 2007). Varanus hatchlings triple in size to sexual maturity and reach maximum size by the end of the first year (Pianka 1971). However some may continue growing thereafter, reaching up to 50% longer.

Pterodaustro Ontogeny
The only pterosaur for which a complete record of growth is known is the filter-feeder Pterodaustro. Chinsamy et al. (2008) reported: “…upon hatching, Pterodaustro juveniles grew rapidly for approximately 2 years until they reached approximately 53% of their mature body size, whereupon they attained sexual maturity. Thereafter, growth continued for at least another 3–4 years at comparatively slower rates until larger adult body sizes were attained.” So, this pterosaur’s growth rate, despite an apparent warm-blooded metabolism and active lifestyle, was not dissimilar to that of other lizards, reaching sexual maturity at 50% of the ultimate size. However, Pterodaustro took twice as long as Varanus, a cold-blooded lizard. Apparently, growth was not so rapid in pterosaurs — more along the lines of Iguana.

Pteranodon
If we add in the factor of increased size to what we know of Pterodaustro, we can imagine that Pteranodon might have had a maturation rate similar to that of the albatross (sexually mature at 7 to 10) along with a similar lifespan (30 years). However, if Pteranodon was more like Pterodaustro we get 2 years until half-grown, 5 to 6 years until fully grown.

Where Are the Juvenile Pterosaurs?
A long maturation brings up a problem. Where are the juveniles and immature forms (ages 0 to 6)? The Pterodaustro bone beds (nesting sites) provide the only evidence. There we find all sizes of Pterodaustro.

Ptweety the Only Juvenile Pteranodon
We know of only one juvenile Pteranodon. All others are adults that fit neatly into a phylogenetic framework of increasing size and crest size originating with a specimen of Germanodactylus (SMNK-PAL 6592) as an outgroup. This falsifies the current paradigm presented by Bennett (1991, 2001) and followed by others (Hone et al. 2011) of gender and maturation variation in most known specimens of Pteranodon. Here there is evidence of speciation leading to the largest crested forms (that in one clade only preceded a continuing clade of smaller crested, smaller forms.)

Bone Histology
The age of sexual maturity in Pteranodon has not yet been determined. Neither has the lifespan. Bone histology in Pteranodon has not provided the data needed due to crushing and resorption of the inner walls of the extremely thin long bones. At present we can only guess using extant analogs, like the albatross, and extinct analogs, like Pterodaustro.

Then There’s the Tiny Pterosaur Hypothesis
Tiny pterosaurs giving birth to fly-sized hatchlings were likely terrestrial until reaching adult-size due to desiccation problems, as discussed earlier. Larger pterosaur hatchlings, like Pteranodon (and all known, apparently flight ready pterosaur embryos), did not have a problem with desiccation — but they may have retained some sort of non-flying lifestyle living in environments not conducive to fossilization. This may explain the lack of immature pterosaurs in the fossil record (contra all traditional studies that considered tiny adults to be juveniles and embryos to be flight ready).

Not ready to jump on the flightless hatchling hypotheses quite yet, but it’s something to consider when faced with current and future evidence.

Just a Reminder
Maisano (2002) provides guidance on lizard ontogeny that can be applied to pterosaurs. That is: fusion can precede maturation and ultimate size or fusion may never take place in the oldest individuals, depending on their phylogeny. Recent work by Lü et al. (2012) show that the archosaur model continues to be wrongly applied to pterosaur studies.

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.
Couzens D 2008. Extreme Birds: The world’s most extreme and bizarre birds. Firefly Books.
Hone DWE Naish D and Cuthill IC 2011. Does mutual sexual selection explain the evolution of head crests in pterosaurs and dinosaurs? Lethaia, DOI: 10.1111/j.1502-3931.2011.00300.x
Kaplan M 2007. Iguana Age and Expected Size. iguana/agesize online
Lü J, Unwin DM, Zhao B, Gao C and Shen C 2012. A new rhamphorhynchid (Pterosauria: Rhamphorhynchidae) from the Middle/Upper Jurassic of Qinglong, Hebei Province, China. Zootaxa 3158:1-19. online first page
Maisano JA 2002. Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.
Pianka E 1971.
 
Notes on the Biology of Varanus tristis. West. Aust, Natur, 11(8):80-183.