Long one today.
Summary, for those in a hurry:
Hone et al. 2020 bring us their views
on Rhamphorhynchus ontogeny (= growth from hatchling to adult). Unfortunately, this study is based on several invalid assumptions. Lacking a phylogenetic context, Hone et al. made the mistake of comparing small adults to large adults. No juveniles were tested. Subsequent ontogeny comparisons to birds and bats were thus rendered moot.
Before we get started, you might remember:
- A competing paper has been online for 2 years: ‘First Rhamphorhynchus juvenile recovered by phylogenetic analysis’ in which only one juvenile/adult pairing was found among all 31 specimens shown in figure 1. Among the rest, no two are alike. The small ones in the top row are not juveniles, but phylogenetically miniaturized adult basal Rhamphorhynchus species. (Perhaps someday, someone will re-name them all appropriately.)
- All pterosaurs (so far tested) develop isometrically (with the exception of tapejarid crests) because that’s what lepidosaurs do.
- Hatchling pterosaurs are typically 1/8 as tall as adults.
- Only hatchlings of a certain minimum size can fly. Hatchlings below this hypothetical size risk desiccation due to a high surface-to-volume ratio. That’s when quadrupedal locomotion enters pterosaur clades. Extradermal soft tissue that limits desiccation first appears on tiny, flapping pre-pterosaurs like Cosesaurus.
- New pterosaur clades often begin with a series of phylogenetically miniaturized transitional taxa (as in Fig. 1). This only appears in phylogenetic analyses when small and large taxa are analyzed together. That has not happened yet in published analyses because other workers make the same mistake as they consider small adult taxa to be mismatched juveniles (thereby destroying the Hone et al. isometry hypothesis).
The Hone et al. 2020 paper was announced today on
Dr. Hone’s email list. After a short comparison to Pteranodon, Hone continues:
“However, if we turn to Rhamphorhynchus we have only a fraction of the number of specimens but pretty much all the other issues are absent. They also cover a near order of magnitude in size with everything for animals of c 30 cm wingspan up to nearly 2 metres and include everything from putative hatchling-sized animals to a couple of genuine outliers that are much bigger than other known individuals.”
A good sample of Rhamphorhynchus taxa are shown above (Fig. 1) in phylogenetic order. Note this genus has its genesis as a phylogenetically miniaturized series following Campylognatoides in the large pterosaur tree (LPT, 250 taxa). The sole juvenile shown above is the Vienna specimen, nesting with one of the ‘genuine outliers that are much bigger.’ This adult and juvenile pairing nest together with virtually identical scores, despite the great difference in size.The LPT was able to lump and split all tested Rhamphorhynchus taxa. So it can be done. Hone et al. omitted this all important step and ruined their paper.
“The numbers of course are not tiny, well over 100 good specimens, and that alone would make them an exceptional sample of most terrestrial Mesozoic archosaurs.”
Our first red flag! Hone et al. do not realize that when taxa are added, pterosaurs move over to lepidosaurs. On another note: relative to ‘100 good specimens’, 31 are shown above (Fig. 1).
that Wellnhofer (1975) featured 108 specimens. Hone’s group looked at 129, but, as Hone confesses, “The ‘real’ total is actually a little lower.” Oddly, in the text of the paper, Hone et al. report testing 135 specimens of R. muensteri.
“This post inevitably marks the publication of an analysis of growth in Rhamphorhyunchus. In a lot of ways, this mirrors Chris Bennett’s fantastic 1995 paper on this genus where he convincingly demonstrated that all specimens belonged to a single species and not multiple ones as previously thought, and part of his arguments for doing this looked at the relationships between various elements based on Wellhofer’s dataset.”
Our second red flag! Bennett’s 1995 paper likewise did not include a phylogenetic analysis. When several specimens of Pteranodon were added to the LPT, no two nested together as conspecific taxa (Fig. 2). Small specimens were closer to the genesis of Pteranodon following Germanodactylus. Large specimens split into several clades.
Hone is delighted to announce
“Chris’ point [in Bennett 1993, 1995] was that while there were some discreet clusters of specimens (which he attributed to year classes) most of the alleged differences between the putative species vanished when you put them on a graph and the rest were classic ontogenetic traits like the fusion of the pelvis in large individuals of big eyes in small ones. So while he didn’t really deal with growth as such, he was already showing similar patterns to what I and my coauthors confirm now – Rhamphorhynchus was weirdly isometric in growth.”
Our third red flag! Dr. Hone does not appear to realize that ALL pterosaurs develop isometrically during ontogeny. They do this because pterosaurs are lepidosaurs. By contrast, archosaurs develop allometrically. I’m also going to throw in the objection that a graph or two (as in Bennett 1993, 1995, Hone et al. 2020] is no substitute for a thorough phylogenetic analysis.
“In other words, in the case of the vast majority of their anatomy, young animals are basically just scaled down adults.”
This is an odd statement to make considering the fact that Hone et al. are looking at phylogenetically miniaturized adults (Fig. 1) and regarding them as juveniles. That Hone considers the little specimens, “basically carbon copies of the adults” makes one question the precision of their observations. They did cherry-pick two similar taxa (Figs. 3, 4), avoiding the wider variation of other specimens. A competing online analysis (subset Fig. 5) was able to split and lump all Rhamphorhynchus specimens.
For comparison, Hone et al. also looked at ontogeny in bats,
noting hand/wing development accelerated close to sexual maturity (= shortly after weaning). He notes, “This is the pattern we would expect.”
Our fourth red flag! Since Hone et al. have blinded themselves to the possibility that pterosaurs are lepidosaurs (Peters 2007) they don’t look at lepidosaurs for comparison. Here’s why they should: pterosaurs hatch with adult proportions from leathery eggs held within the mother’s body longer than in any archosaur.
“Birds are functionally poor analogues of pterosaurs but are much closer phylogenetically and are the only other powered flying tetrapod so we also looked at some existing datasets for them too.”
More traditional myth perpetuating here. I find this all so disheartening. Colleagues, just add taxa. If I can do it as an outsider, you can do it as a PhD. Do not be afraid to do the work of constructing a cladogram.
“If you grow isometrically you wings will get longer and wider but your weight will increase much faster since you as a whole will get longer and wider and deeper. Birds increase penumaticity as they grow and there’s evidence this is the case in other pneumatic clades too and if so for pterosaurs, then the mass increase in adults would also be offset somewhat by a proportionally lower mass in adults for a given volume than juveniles.”
Very good point. But I’m ot sure of any pneumaticity studies comparing hatchling and adult pterosaurs.
“Precociousness has been suggested in pterosaurs before based on the evidence for them flying while young, but it has also been challenged. It suggested that to be flying at that size would require a huge amount of effort and this would leave little energy for growth.”
Wait a minute! Didn’t he just say the weight would increase by the cube in adults? That means juveniles were that much lighter.
“That’s largely true, but overlooks that there could be post hatching parental parental care. That is normal for archosaurs (including dinosaurs) and we would expect it for pterosaurs.”
If only pterosaurs were archosaurs, but at this point they still nest with lepidosaurs. Most lepidosaurs fend for themselves after hatching, and if pterosaur hatchlings could fly, then they would be able to fly off on their own shortly after hatching. Best not to ‘expect’ anything without a valid phylogenetic context, evidently lacking in Hone et al. 2020.
“So in short, Rhamphorhynchus is perhaps the best pterosaur for large studies about populations and growth and this genius at least grew isometrically, and this may or may not be the same for other pterosaurs.”
But for the present, every pterosaur known from embryo, juvenile and adult shows strict isometric growth (except for tapejarid crests).
“But it does imply that young pterosaur could fly, and fly well.”
Sadly, Hone et al. seem to be looking at small adults (Fig. 1) and calling them ‘young’. Of course these adult pterosaurs can fly well!
Apparently Hone et al. are comparing linear measurements and graphing them. That method produced false positives for Bennett 1995. There is no substitute for phylogenetic analysis.
In this topsy-turvy world of pterosaurs,
myths are popularized by PhDs while comprehensive phylogenetic analyses compiled by amateurs are ignored and suppressed. Not sure why this problem is not more widely recognized. For other missteps made by Dr. Hone with regard to pterosaurs, click here or use the keyword ‘Hone’ for that long list.
Moments ago the paper itself arrived.
In my morning email was a message from Dr. Hone: “Attached” along with a PDF of their Rhamphorhynchus paper. Two sets of graphs are present, but only a single figure combining bat allometry and Rhamphorhynchus isometry (isolated in Fig. 3).
From the paper:
“We test whether pterosaurs show a similar pattern of rapid forelimb growth during post‐hatching/ontogeny to that of bats and birds, and thus infer when in ontogeny R. muensteri would have become volant.”
Sounds laudable. Let’s see how they do it.
From the paper:
“All Rhamphorhynchus specimens from Bavaria are now considered a single species (Bennett 1995).”
No. That’s why figure 1 was created and a phylogenetic analysis of pterosaurs was run (subset Fig. 5), to see how specimens could be lumped and separated. Like Hone et al., Bennett likewise eschewed the use of phylogenetic analysis. Sadly, Hone et al. adopted without further consideration Bennett’s invalid assumption, rather than testing Rhamphorhynchus with a phylogenetic analysis.
From the paper:
“Four lines of evidence suggest that the smallest R. muensteri specimens were very young animals and potentially hatchlings.
- Histology reveals incomplete ossification of long bones in the smallest specimens tested (Prondvai et al. 2012),
- A disproportionate number of known specimens are small, consistent with high juvenile mortality (Bennett 1995; Hone & Henderson 2014)
- Late‐stage embryos of pterosaurs had well‐developed, ossified wings (Wang & Zhou 2004; Codorniú et al. 2018)
- and finally while few fossilized pterosaur embryos are known, the ratio by which adults are larger than embryos (Lü et al. 2011; Wang et al. 2017) is similar to the size ratio between the largest R. muensteri specimens and the smallest.”
Incomplete ossification: the smallest specimen studied by Prondvai et al. (2012) was BSPG 1960 I 470a = n9 (Figs. 1, 5) is also the second most primitive tested specimen (next to n28) in a phylogenetic miniaturization series that began with Campylognathoides. Among the neotonous / juvenile traits retained was incomplete ossification of the long bones. Lacking a phylogenetic context, neither Prondvai et al. nor Hone et al. were aware of the miniaturized adult status of n9.
Disproportionate number of specimens are small: lacking a phylogenetic context, Hone et al. were not aware of the phylogenetic miniaturization that preceded the evolution of larger Rhamphorhynchus specimens. In the LPT only one Rhamphorhynchus specimen is a valid juvenile nesting with larger adults.
Late‐stage embryos of other pterosaurs had well‐developed, ossified wings: So did miniaturized adults.
Size ratio of largest R. muensteri specimens to smallest similar to embryo vs adult sizes in other pterosaurs: lacking a phylogenetic context, Hone et al. were not aware of the phylogenetic miniaturization that preceded the evolution of larger Rhamphorhynchus specimens. Hone et al. made the mistake of labeling small adults as juveniles. Notably, Hone et al. did not try to match their purported juveniles with adults phylogenetically. Other tiny Rhamphorhynchus specimens have juvenilized proportions (smaller rostrum, larger orbit), but these were ignored by Hone et al., who cherry-picked two comparative taxa out of 135.
From the paper:
“We tested for isometric versus allometric growth across 135 specimens of R. muensteri using bone length and composite measures (e.g. total wing length and total leg length) relative to: (1) total body length, from rostrum tip to the end of the tail; (2) skull length; and (3) humerus length.”
Lacking a phylogenetic context (available online for several years), Hone et al. made the mistake of comparing adults to adults. No juveniles were tested. Subsequent comparisons to birds and bats were thus rendered moot.
From the paper:
“Our results suggest that even the smallest Rhamphorhynchus had adult skeletal proportions and thus wings sufficient for flight.” This confirms the conclusions of Peters (2018) using a phylogenetically validated juvenile Rhamphorhynchus, rather than a dataset full of large and small adults.
From the paper:
“Wang et al. (2017) noted that in embryos of the pterodactyloid Hamipterus, although there was greater ossification of the limbs and vertebrae than the head, including of the shafts of longbones, there was limited ossification of some other parts of the skeleton that may have related to flight. They hypothesize in this case that hatchlings may have been able to walk before they could fly, though still imply relatively early flight for these animals.”
These were not hatchlings, but embryos still developing within the egg, within the mother in the tradition of lepidosaurs. Eruptive gases killed flocks en masse. Details here.
From the paper:
“Pterosaurs, like almost all other archosaurs, probably provided parental care (Witton 2013), and precocial flight need not preclude this possibility.”
This is myth. We’ve known since Peters 2007 that adding taxa moves pterosaurs to nest within Lepidosauria.
From the paper:
“Thus, while Rhamphorhynchus apparently flew at a young age, such volant offspring may have plausibly received parental care, including provisioned food, as they became independent foragers.”
There is no evidence for this bit of speculation. But it cannot be ruled out. According to Gans 1996, “Many aspects of reptilian reproductive patterns prove to be vagile among the vertebrates. Reversals complicate, and may even invalidate, the characterization of broad trends. Furthermore, the 7000 species of reptiles show dozens of modes that seem to enhance the fitness of their offspring, thereby providing a vast opportunity of testing the reality of these adaptations.” (‘vagile’ = able or tending to move from place to place or disperse)
Hone et al. assumed that phylogenetically miniaturized adults at the genesis of Rhamphorhynchus were juveniles. While testing small adults against large adults (Figs. 1–5) the authors determined that Rhamphorhynchus ontogeny proceeded isometrically.
Ironically this confirms earlier findings by Peters (2018 and elsewhere in this blog) using the only known phylogenetically validated juvenile and a matching adult Rhamphorhynchus. As longtime readers know, all other pterosaurs develop isometrically because they are lepidosaurs arising from taxa close to late-surviving Huehuecuetzpalli, known from matching juvenile and adult specimens.
Dr. Hone needs to show more leadership. He needs to create reconstructions of the specimens under study so visual comparisons can be made by his team and readers. Roadkill specimens are too difficult to compare otherwise. He also needs to run a phylogenetic analysis to determine interrelationships between pterosaur taxa and within all amniotes to see where pterosaurs nest. At present he’s perpetuating old myths and traditions that were invalidated twenty years. He’s that far behind the times.
I’ll never forget the day several decades ago
when Dr. Kevin Padian and Dr. Chris Bennett told me, “nothing can be known about a taxon until it is put into a phylogenetic context.” I took that advice to heart. That is why the LRT and LPT now include more than 2000 taxa.
Bennett SC 1993. The ontogeny of Pteranodon and other pterosaurs. Paleobiolgy 19(1):92-106.
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.
Gans C 1996. An overview of parental care among the Reptilia. Advances in the Study of Behaviour 25:145–157.
Hone DWE, Ratcliffe JM, Riskin DK, Hemanson JW and Reisz RR 2020. Unique near isometric ontogeny in the pterosaur Rhamphorhynchus suggests hatchlings could fly. Lethaia. Paywall access here.
Hone 2020. Email post. How to grow your dragon – pterosaur onotgeny [sp]
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Peters D 2018. First juvenile Rhamphorhynchus recovered by phylogenetic analysis. PDF here.
Prondvai E, Stein K, Ösi A, Sander MP 2012. Life History of Rhamphorhynchus Inferred from Bone Histology and the Diversity of Pterosaurian Growth Strategies. PlosOne. online pdf
Wellnhofer P 1975a-c. Teil I. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Allgemeine Skelettmorphologie. Paleontographica A 148: 1-33. Teil II. Systematische Beschreibung. Paleontographica A 148: 132-186. Teil III. Paläokolgie und Stammesgeschichte. Palaeontographica 149:1-30.