This post is a shout-out to Fonseca et al. (2024), whose abstract states-
"Resolving the evolutionary relationships of early diverging (‘basal’) ornithischian dinosaurs is a challenging topic in palaeontology, with multiple competing hypotheses on the phylogenetic relationships of heterodontosaurids, ‘hypsilophodontids’, and other early-diverging forms. These hypotheses cannot be directly compared because they are derived from differently constructed datasets (i.e. distinct samples of taxa and characters). This study aims to address these issues by revising and combining the distinct datasets into a single analysis in order to create the most comprehensive dataset for the investigation of the phylogenetic relationships of early-diverging ornithischians."
This is the ideal for a phylogenetic analysis and exactly what I attempted for Lori, providing some useful data. They write "constrained analysis forcing a close affinity between Heterodontosauridae and Marginocephalia require at least 26 extra steps, while joining them and Pachycephalosauria require at a minimum 44 steps", so those are implausible. The weird little bipedal armored Jakapil comes out sister to Eurypoda, and "enforcing it as a marginocephalian requires 16 additional steps" so is unlikely. Making it parankylosaurian requires only 4 steps though, so is quite likely and matches geographically. For as much crap as I gave Norman's phylogenetic nomenclature, his Hypsilophodontia including Tenontosaurus (and other rhabdodontomorphs) only takes 6 more steps, so is less likely but not bad. While Fonseca et al.'s main results are interesting, I found the supplementary information where they commented on all the taxa they excluded equally informative.
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| Teeth of Ferganocephale adenticulatum- A-B paratype ZIN PH 31/42; C-F holotype ZIN PH 34/32; G-J paratype ZIN PH 36/42; K-N paratype ZIN PH 33/42. Apical- A, C, G, N; Mesial or distal- B, E, I, L; Labial or lingual- D, F, H, J, K, M. After Averianov et al., 2005. |
"Ferganocephale adenticulatum Averianov et al. (2005) displays no ankylothecodonty (ch388:0), low crowns (ch411:0), round crown apices (ch413:1), no apicobasal ridges (ch421:0), an asymmetric labiolingual expansion (ch422:1), a cingulum (ch423:1), and no denticles. While these features show the most similarity to Chaoyangsauridae, the lack of denticles and strength of the cingulum are very different from the clade, so a classification as intermediate Saphornithischia is most likely. The position of Ferganocephale adenticulatum requires further work done to assess the dental morphologies within Pan-Aves as a whole, especially due to its un-archosauriform lack of denticulation (see Ezcurra, 2016)."
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| Holotype right maxilla of Lusitanosaurus liassicus in lateral view (University of Lisbon coll.; destroyed). After Lapparent and Zbyszewski, 1957. |
"Lusitanosaurus liassicus Lapparent and Zbyszewski (1957) displays ankylothecodont teeth (ch388:1), low crowns (ch411:0), no recurvature (ch414:2), no apicobasal ridges (ch421:0), and no cingulum (ch423:0). The type specimen was lost in a fire (Mateus et al., 2022), so the only information available about the taxon is from the original description and plate of Lapparent and Zbyszewski (1957). The crowns are tricuspid, which is shared with members of Pterosauria (Dalla Vecchia, 2013), Squamata (Conrad, 2008), Tanystropheidae (Renesto & Dalla Vecchia, 2000; Spiekman et al., 2020), and basal Cynodontia (Hahn et al., 1984) but not Ornithischia. The lack of a cingulum also suggests Lusitanosaurus liassicus is not an ornithischian, as that was the only feature identified by Irmis et al. (2007) to distinguish early ornithischian teeth from similar but non-ornithischian phyllodont teeth. While it has been previously excluded from studies as a dubious basal thyreophoran (Antunes & Mateus, 2003; Norman et al., 2004a; Norman, 2020c), the distribution of anatomy instead suggests that Lusitanosaurus liassicus cannot be considered an ornithischian and should instead be considered Archosauromorpha indeterminate on the basis of ankylothecodont tooth implantation."
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| Teeth of Taveirosaurus costai- A paratype TV 16; B paratype TV 11; C paratype 14; D-E, J-K holotype TV 10; F paratype TV 8; G paratype TV 7; H paratype TV 13; I paratype TV 9. Lingual- A-D, F-J; Labial- E, K. After Antunes and Sigogneau-Russell, 1991. |
"Taveirosaurus costai Antunes and Sigogneau-Russell (1991) displays cheek tooth crowns without mesial and distal ‘kinks’ (ch412:0), low crown height (ch411:0), coarse denticles (ch416:2), and no cingulum (ch423:0), which would support a position just within or outside Ornithischia. However, the morphology of the crowns is very divergent from ornithischians, and the only features linking the taxon with Ornithischia are also found in non-ornithischian archosauromorphs (Irmis et al., 2007), mammaliforms (Luo et al., 2002) and even hybodontiformes (Stumpf et al., 2022). Taveirosaurus costai is considered to belong to Eutriconodonta here on the basis of linear molar cusps and a distinct, straight cingulum (Luo et al., 2002) as well as its Late Cretaceous age, until further work is done to establish possible shared dental morphology with Ornithischia."
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| Holotype tooth of Trimucrodon cuneatus (Lehrstuhl für Paläontologie coll.). Lingual- a; Labial- b. After Thulborn, 1973. |
"Trimucrodon cuneatus Thulborn (1973) displays sporadic wear facets (ch407:0), low crowns (ch411:0), kinked mesial and distal crown edges (ch412:1), triangular crown apices (ch413:0), no recurvature (ch414:2), mesiodistal expansion above the root (ch415:1), no apicobasal ridges (ch421:0), symmetric labiolingual expansion (ch422:0), and no cingulum (ch423:0). These features show significant conflict, especially the lack of a cingulum and asymmetrical labiolingual swelling which are exclusive synapomorphies of Parapredentata except for clades that are excluded for other characters (eg. lack of apicobasal ridges). Until further work is done to assess the dental morphologies within Pan-Aves as a whole, Trimucrodon cuneatus should be retained as a possibly valid taxon that cannot be classified beyond Ornithischia outside Parapredentata."
Several taxa like Alocodon, Phyllodon and Xiaosaurus are considered valid despite generally being ignored due to being fragmentary. They even include a large supplement illustrating their characters, and justifying which characters were not included. And you can tell they went up to the submission limit by commenting on recent taxa like Vectidromeus and Chakisaurus.
Things I wish Fonseca et al. would have done are list the possible positions of the taxa excluded WISELY a posteriori- "Daemonosaurus chauliodus; Diodorus scytobrachion; Gamatavus antiquus; Sacisaurus agudoensis; Mymoorapelta maysi; Nevadadromeus schmitti; Hualianceratops wucaiwaneisis; Beg tse; Ceratops montanus; the ‘Vegagete ornithopod’; Weewarrasaurus pobeni; Atlascopcosaurus loadsi; Galleonosaurus dorisae; Leaellynasaura amicagraphica; Qantassaurus intrepidus; Trinisaura santamartaensis; Isasicursor santacrucensis; Sektensaurus sanjuanboscoi; Callovosaurus leedsi; and Draconyx loureiroi", and scorings for the excluded taxa like Vectidromeus and "Hypsilophodon" wielandi. Also more constraint analyses for things like the position of Lesothosaurus and Albalophosaurus (here the earliest pachycephalosaur).
Now we need someone to do this for the 30+ incertae sedis sauropodomorph taxa everyone's ignored for over three decades since they were kicked out of Plateosaurus/Massospondylus/Euskelosaurus using Yates' matrix or something better.
References-
Lapparent and Zbyszewski, 1957. Les dinosauriens du Portugal. Mémoires des Services Géologiques du Portugal, nouvelle
série. 2, 1-63.
Thulborn, 1973. Teeth of ornithischian dinosaurs from the Upper
Jurassic of Portugal. Memórias dos Serviços Geológicos de
Portugal. 22, 89-134.
Antunes and Sigogneau-Russell, 1991. Nouvelles données sur les Dinosaures du Crétacé supérieur du Portugal. Comptes rendus de l'Académie des sciences. Série 2, Mécanique, Physique, Chimie, Sciences de l'univers, Sciences de la Terre. 313(1), 113-119.
Averianov, Martin and Bakirov, 2005. Pterosaur and dinosaur remains from the Middle Jurassic Balabansai Svita in the northern Fergana depression, Kyrgyzstan (central Asia). Palaeontology. 48(1), 135-155.