Assessing ontogenetic maturity in extinct saurian reptiles

Griffin et al 2021 assessed
the ontogenetic maturity in extinct saurian reptiles. The authors started off well when they reported, “Morphology forms the most fundamental level of data in vertebrate palaeontology.” Then the authors followed traditional academic thinking in repeating “Saurian reptiles (the least-inclusive clade containing Lepidosauria and Archosauria).”

In the LRT, that clade definition = Reptilia
because the first reptile = amniote dichotomy in the LRT split Archosauromorpha (= chroniosuchids, synapsids and diapids including archosauriformes, ichthyosaurs, mesosaurs and sauropterygians) from Lepidosaurormorpha (= captorhinids, caseasaurs, diadectids, turtles and lepidosaurs including pterosaurs).

Griffin et al reported,
“We compiled a novel database of literature, assembling >900 individual instances
of saurian maturity assessment, to examine critically how saurian maturity has been diagnosed.

Part 2:
“We describe the various methods that have been used to assess maturity in every
major saurian group, integrating data from both extant and extinct taxa to give a full account of the current state of the field and providing method-specific pitfalls, best practices, and fruitful directions for future research.”

Part 3:
“We recommend that a new standard subsection, ‘Ontogenetic Assessment’, be added to the Systematic Palaeontology portions of descriptive studies to provide explicit ontogenetic diagnoses with clear criteria.”

Griffin et al reported,
“Because different growth stages of a single species may be mistaken for distinct
species, or conversely, individuals within a hypothesized growth series may actually pertain to multiple taxa, assessing maturity has clear implications for determining species synonymy, species abundances, and ecosystem/community structure.”

So true.

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. ” data-image-caption=”

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.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2015/12/pterodaustro-size-comparison1000.jpg?w=196″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2015/12/pterodaustro-size-comparison1000.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-21311″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2015/12/pterodaustro-size-comparison1000.jpg” alt=”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.” width=”584″ height=”892″ />

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.

This is where invalid clades screw things up for Griffin et al.
“Saurian reptiles have almost no consistent skeletal indicator of ontogenetic stage and possess extremely disparate life histories. For example, separate epiphyseal ossifications
that fuse to the diaphysis during ontogeny are present in lepidosaurs (Maisano, 2001, 2002c; Frýdlová et al., 2017) but do not occur at all among archosaurs (Chinsamy-Turan, 2005) except for disputed cases in some birds.”

See what I mean?
That’s why it is so important to base all studies on a valid phylogeny.

Griffin et al made the mistake of lumping pterosaurs 
with archosaurs, citing Frey et al 2006 (Muzquizopteryx paper), Hone et al 2012 (Bellubrunnus paper), Kellner 2013 (Caupedactylus paper).

Muzquizopteryx was a basal nyctosaurid, an adult.
Bellubrunnus was a basal Rhamphorhynchus, an adult, not a juvenile.
Caupedactylus was a derived sinopterid, an adult.

Griffin et al wrote,
“The most common single co-ossification, or at least the most phylogenetically
widespread, may be the fusion of the scapula and coracoid into a single element.”

In pterosaurs this is phylogenetic, not ontogenetic.

“Pterosaurs fuse their carpals together.”

In pterosaurs this is phylogenetic, not ontogenetic.

“pterosaurs co-ossify the olecranon-like extensor tendon process to the first wing phalanx.”

In pterosaurs this is phylogenetic, not ontogenetic.

“Ossification of sternal (Hone et al., 2012b; Kellner, 2015) and podial elements (Hone et al., 2012b) has also been used to assess maturity in pterosaurs, although distal tarsals are
thought to remain unossified through ontogeny in many pterosaurs.”

In pterosaurs this is phylogenetic, not ontogenetic.

Apparently there was no discussion of ‘phylogenetic miniaturization’
in Griffin et all 2021. That’s how new clades often, but not always start in the LRT. ‘Neoteny’ and ‘juvenilization’ are not mentioned in the text. ‘Paedomorphism’ is mentioned as a potential pitfall. One discovers phylogenetic miniaturization in wide gamut analyses like the large reptile tree (LRT), large pterosaur tree (LPT), and therapsid skull tree (TST).

References
Griffin CT et al (8 co-authors) 2021. Assessing ontogenetic maturity in extinct saurian reptiles. Biol. Rev. (2021), 96, pp. 470–525. doi: 10.1111/brv.12666
Maisano JA 2002a. The potential utility of postnatal skeletal developmental patterns in squamate phylogenetics. Journal of Vertebrate Paleontology 22:82A.
Maisano JA 2002b.Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.

Phylogenetic fusion patterns in pterosaurs