It occurs to me I need a single place to collate all my various “infographic” art pieces discussing a variety of topics, so here we go. Brief summaries of their content when not obvious will follow.

A reconstruction of the cranial crests in some dinosaurs requires distinguishing between a keratin-bearing display structure, a “casque,” and skin-covered, possibly pneumatic-supporting structures, some which resemble casques superficially. Crests in Dilophosaurus wetherilli and “Citipati” (GIN 100/42) lack indicators for keratin coverings, even when the latter is pneumatically inflated; in the former, there is no clear border between the antorbital fossa and the edges of the crest, suggesting the antorbital sinus might extend onto the crest itself. Verdict: Dilophosaurus bore skin/scaly or pneumatic structures on its crests; Oviraptorids probably bore skin or vascular structures, but probably not pneumatic.

A recent paper (Cerda, Novas, Carballido & Salgado, 2022) regarding the cervical neural spines of the dicraeosaurine Amargasaurus cazaui indicated that there is no evidence for support for a “sail-like” structure between the spine; specifically, that the spines could not support tension between adjacent spines in the matter we might expect. Instead, normal neck tissues would have been present as in typical sauropods. Problematically, that study also indicated that the spines themselves could bear almost no strain in nearly any direction except distobasally, suggesting the spines aren’t really supporting much of anything. Muscle attachment to the spines appears located exclusively on the lateral edges and are aligned anteriorly (cranially) and posteriorly (caudally), rather than between the spines, or attaching left and right, indicating a lack of strong connective tissues. The neck here is reconstructed with the typical tissues of the sauropod neck in a diplodocine sauropod, then expanded vertically in a progressively taller, dicraeosaurine form.

Including Amargasaurus cazaui and Bajadasaurus prnuspinax, the spines are covered with epaxial muscles from head to shoulder and there’s no real reason to support a gap between left and right spines. Nor would the spines have spikes or be distally distinct from one another. Thus, both of these Diplodocidae groups would instead simply have a progressively taller neck hump.

This one’s a lot more speculative. The bony nostril of several saurolophine hadrosaurs are surrounded by extremely large, long fossae resembling those of typical dinosaurs, and which may be connected to vascular tissue around the fleshy nostril. However, rather than limited to a small area around and mostly in front of the bony nostril, in these hadrosaurs it extends to the edge of the beak, and may have formed a bulbous mass of vascularized, even pneumatic tissue. This feature may be present in edmontosaurine hadrosaurs to a more limited degree, but in saurolophine hadrosaurs, like Saurolophus angustirostris (above), the fossa extends to the posterior limit of the premaxilla crest, which forms a spike bearing a distinct lip for the fossa.

Here, we see the extrapolation of the hadrosaur model shown for a saurolophine extended to lambeosaurines, but for different reasons. The lateral crest is not confluent with the bony nostril or the fossa that surrounds it, instead the lateral crest bears what appears to be pneumatic fossae connected to a small lateral opening. This is highly speculative.

There is an additional speculative note here: In almost every single skull of Saurolophus angustirostis, the beak portion of the premaxilla forms an upturned lip and not a ventral pointed tomia/blade. Unlike other hadrosaurs, this implies the rhamphotheca was attached in a different manner, has a different form, or may not have been present at all. This latter idea is likened to the condition in artiodactyles in which the upper jaw lacks anterior teeth, forming a cornified, rough pad on the front of the snout against which the insicors of the mandible may grip food. I thus speculate rather than a “beak” these hadrosaurs would have a similar cornified pad.

Wherein I lay out the evidence for fleshy extraoral tissues (or “lips”) and why we estimate these structures in dinosaurs, compared to crocs (which bear teeth) or birds (in which case absence of all markers for lips is not controversial). These are markers for inference for lips, and not absolute indicators, and the issue is complicated in some taxa. Chiefly, this infographic regards one of the main problems with regard to the inference for lips: the Extant Phylogenetic Bracket (EPB). This being a subject of inference, it is needful to contextualize the EPB: Archosauria does not exist in a vacuum; not only does convergence occurs, it is implied to be the case between birds and turtles, neither of which develop beaks the same way (turtles from coalesced scales, birds from hardening [“cornification”] of the skin), and the baseline case for all tetrapods, and indeed all Osteichthyes, is extensive fleshy extraoral tissues comprised of different tissue types, covered in various things. The EPD is an inference only, it is not evidence, and the majority of tetrapods, barring some few turtles, birds, crocs (it’s even congercent within the crocodilian stem lineage), and theropsids like dicynodonts (also convergently). That weight is so strong that comparison to ancestral state reconstruction in crocs and birds shows that the ancestor of all archosaurs was lipped.

Absence of an upper beak on some ornithischians like many baseline “hypsilophodont-grade” animals, pachycephalosaurs, and possibly even stegosaurs is indicated by the apparent lack of a large, strong tomia ridge on the premaxilla and the presence of teeth. A study on the therizinosaur Erlikosaurus andrewsi (Lautenschlager, Witmer, Perle & Rayfield, 2013) suggested that beaks and teeth form a similar function in reducing strain along the jaw edge: teeth by creating critical points of failure, in which strain is redistributed into the tooth, causing it to break and dissipate the force; and beaks, by distributeing straight across bone sutures and through the beak itself, allowing no single point a critical failure condition. Thus, they hypothesized, a beak and teeth serve similar functions (although beaks are overall apparently costlier tissues). We can apply this model to every animal in which a beak is hypothesized, where those animals with premaxillary teeth and predentary beaks coexist. In almost none of these animals does a primary inference for a beak exist: That is, a sharpened tomia, many small tiny foramina, closed or fused sutures reducing cross-bone strain. Instead, even when the premaxilla has a sharpened tip but also beak, the beak portion is very small and the premaxilla is almost never fused to adjacent bones or each other.

In ceratopsians, in which a rostral bone is present, inference for a beak increases as this structure adds vasculature-related groove structures to the inference model. Even when teeth are absent, an inference for a beak would require more additional evidence than “teeth absent,” as indicated via several lizards such as Uromastyx.

For no real purpose, a comparison between the two terrestrial paradigms for Spinosaurus aegyptiacus, conveniently completed mere weeks before publication of the very novel tail model. The novel terrestrial model has been widely panned and several claims made in papers regarding the “neotype” material remain controversial and will not be further covered.

A history of reconstruction for Spinosaurus aegyptiacus was unlucky enough to precede the description of a bizarre tail. However, many claims made in the infographic have not changed.

Wherein I show that there was no evidence for the theropod “half” lip that seemed to arise as a compromise from the croc-faces and the full-lipped model in the waning years of Jurassic Park‘s influence on paleontological art. Bizarrely, it’s only Tyrannosaurus rex in that film that shows this model, yet it influenced almost every reconstruction of any theropod dinosaur thereafter.