Late Jurassic Hybodus seems to have extant relatives in the LRT
Today’s experiment had its genesis
when the odd hole in the snout of Hybodus basanus (Figs 1, 2) made me wonder if a fragile, overhanging rostrum had been lost or knocked off prior to study and publication. With a new, restored (= imagined) rostrum this taxon was re-scored in the LRT.
Figure 1. Hybodus basanus. DGS colors and a ?missing rostrum added here.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/04/hybodus_basanus1983-skull588.jpg?w=198″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/04/hybodus_basanus1983-skull588.jpg?w=584″ class=”size-full wp-image-85153″ src=”https://pterosaurheresies.files.wordpress.com/2024/04/hybodus_basanus1983-skull588.jpg?w=584&h=885″ alt=”Figure 1. Hybodus basanus. DGS colors and a ?missing rostrum added here. ” width=”584″ height=”885″ srcset=”https://pterosaurheresies.files.wordpress.com/2024/04/hybodus_basanus1983-skull588.jpg?w=584&h=885 584w, https://pterosaurheresies.files.wordpress.com/2024/04/hybodus_basanus1983-skull588.jpg?w=99&h=150 99w, https://pterosaurheresies.files.wordpress.com/2024/04/hybodus_basanus1983-skull588.jpg?w=198&h=300 198w, https://pterosaurheresies.files.wordpress.com/2024/04/hybodus_basanus1983-skull588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Hybodus basanus. DGS colors and a possible ?missing rostrum” added here.
Perhaps not surprisingly, given its new appearance,
Jurassic Hybodus basanus (skull data only) nested with extant Carcharodon (dorsal skull view not yet scored while awaiting data). In other words, with the present character list, the two resemble one another more than competing taxa.
FIgure 1. Carcharodon, Isurus and Hylobates basanus compared.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/04/carcharodon_carcharias_588.jpg?w=256″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/04/carcharodon_carcharias_588.jpg?w=584″ class=”size-full wp-image-85151″ src=”https://pterosaurheresies.files.wordpress.com/2024/04/carcharodon_carcharias_588.jpg?w=584&h=685″ alt=”FIgure 1. Carcharodon, Isurus and Hylobates basanus compared. ” width=”584″ height=”685″ srcset=”https://pterosaurheresies.files.wordpress.com/2024/04/carcharodon_carcharias_588.jpg?w=584&h=685 584w, https://pterosaurheresies.files.wordpress.com/2024/04/carcharodon_carcharias_588.jpg?w=128&h=150 128w, https://pterosaurheresies.files.wordpress.com/2024/04/carcharodon_carcharias_588.jpg?w=256&h=300 256w, https://pterosaurheresies.files.wordpress.com/2024/04/carcharodon_carcharias_588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. Carcharodon, Isurus and Hylobates basanus compared.
For the next experiment, a related taxon,
Hybodus fraasi (= Egertonodus fraasi, Fig 3), was also updated based on an extant Bauplan.
Figure 1. Alopias, the extant thresher shark, is much larger than it s
Perhaps not surprisingly,
Hybodus fraasi nested with extant Alopias, the extant thresher shark (Figs 2, 3). The two resemble one another more than competing tested taxa. Turns out those large dorsal spines on Hybodus (Fig 3) are not that important in the LRT. A hyperelongate caudal fin is not a character that is scored in the LRT. So that resemblance is a bonus that doesn’t count.
Figure 3. The skull of the thresher shark, Alopias, in two views. DGS colors added here.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/04/alopias-vulpinus-skull588.jpg?w=206″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/04/alopias-vulpinus-skull588.jpg?w=584″ class=”size-full wp-image-85162″ src=”https://pterosaurheresies.files.wordpress.com/2024/04/alopias-vulpinus-skull588.jpg?w=584&h=850″ alt=”Figure 3. The skull of the thresher shark, Alopias, in two views. DGS colors added here.” width=”584″ height=”850″ srcset=”https://pterosaurheresies.files.wordpress.com/2024/04/alopias-vulpinus-skull588.jpg?w=584&h=850 584w, https://pterosaurheresies.files.wordpress.com/2024/04/alopias-vulpinus-skull588.jpg?w=103&h=150 103w, https://pterosaurheresies.files.wordpress.com/2024/04/alopias-vulpinus-skull588.jpg?w=206&h=300 206w, https://pterosaurheresies.files.wordpress.com/2024/04/alopias-vulpinus-skull588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 3. The skull of the thresher shark, Alopias, in two views. DGS colors added here.
From Maisey 1986,
“The skeletal anatomy of Hybodus fraasi, an Upper Jurassic hybodontid shark from Solnhofen, has been reinvestigated. Its cranial anatomy is very similar to that of H. basanus, a Lower Cretaceous species, and both taxa share certain features not so far identified in Lower Jurassic hybodontids. Previous interpretation of the pectoral fin morphology is shown to be incorrect, and instead the pectorals of H. fraasi conform to a pattern that is apparently conservative for hybodontids. Dermal denticles from various regions of the body, together with special lateral line scales and teeth, are subjected to SEM investigation. The shagreen consists only of nongrowing denticles.”
At this stage
it appears that these two Hybodus species (Figs 1–3) were basal to two large extant sharks. The headline above says, ‘seems to have’. All hypotheses introduced here should be considered as hypotheses, awaiting confirmation, refutation or modification. Changes, to date, number around a million. So mistakes can happen. They just have to be recognized.
Phylogeny is interesting
because your cladogram can teach you to see taxa in new ways, if you let it. Some of those ways can take you down the wrong path (based on personal experience), so keep testing until all the square pegs fit tightly into all the square holes of your current hypothesis.
And don’t be afraid to restore parts that appear to be missing.
References
Brown C 1900. Ueber das Genus Hybodus und seine systematische Stellung. Palaeontographica, 46, 149–174.
Maisey JG 1986. Anatomical revision of the fossil shark Hybodus fraasi (Chondrichthyes: Elasmobranchii). Novitates 2857:1–16.
Source: https://pterosaurheresies.wordpress.com/2024/04/04/late-jurassic-hybodus-seems-to-have-extant-relatives-in-the-lrt/
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