Episode 366 is all about Saltopus, a Triassic dinosauriform from Scotland which was originally thought to be a theropod.

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In this episode, we discuss:

News:

• We discuss the Biomechanics, Taphonomy, & Quantitative Methods sessions from the Society of Vertebrate Paleontology annual meeting source
• A new juvenile hadrosauroid, Parrosaurus/Hypsibema missouriensis, was found in Missouri source
• A puzzle of 4 Stegosaurus pictures was misprinted so there was no difference to find between the pictures source

The dinosaur of the day: Saltopus

• Dinosauriform that lived in the Late Triassic in what is now Scotland (Lossiemouth Sandstone Formation )
• First thought to be a theropod
• Looks like other early dinosaurs, small, slender, and bipedal
• Described as cat-sized
• Estimated to be 31 to 39 in (80 to 100 cm) long and weigh about 2.2 lb (1 kg)
• Later estimates of about 20 in (50 cm) long and about 0.2 lb (110 g)
• Had some very slender elements, like neural spines less than 1 mm wide
• Had a long tail, about half its body length was the tail
• Had five fingers on its hands (the fourth and fifth fingers were reduced/short)
• Had relatively long legs
• Had relatively short arms
• Possible that Saltopus hunted insects and small vertebrates, but no skull or teeth have been found
• Type species is Saltopus elginensis
• Found around Elgin, Scotland
• Found by William Taylor, who showed it to Friedrich von Huene in 1909. Taylor was a well known fossil collector in the area from 1890 to 1920
• Named by Friedrich von Huene in 1910
• Genus name means “hopping foot”
• Huene thought Saltopus was a frog-like hopper and said that the “thin and flexible tail could be no hindrance to hopping despite its length”
• Most scientists think Saltopus was a bipedal runner that used its long tail to help balance
• Species name refers to Elgin (the Permian and Triassic fossils found in the sandstone deposits in and around the town of Elgin, in Moray, Scotland are referred to as the Elgin Reptiles)
• Holotype includes parts of the vertebral column, forelimbs, pelvis, and hindlimbs (no skull)
• In 2010, according to Michael Benton, who with a team in 2010 re-analyzed the type specimen of Saltopus, “The preservation of the Saltopus specimen is modest to poor.”
• Preserved as part and counterpart slabs that show the middle part of the skeleton, lying belly-down
• “The fossil is represented, as is typical of specimens from the Lossiemouth Sandstone Formation, by hollows in the medium-grained yellow sandstone; essentially all bone material has vanished.”
• Huene wrote: “Most of the bones are changed into brown iron sand”
• In other words, the specimen is known from the spaces left in the rock where the bones had dissolved
• Skeleton includes vertebral column, left forelimb, pelvic region, hindlimbs (sprawled to the sides) and part of the tail that attaches to the body (24 caudal vertebrae)
• Some scaly skin also preserved
• Benton and others used casts, X-rays, and CT scans to reexamine the fossil
• Many casts and molds have been made
• Debates about whether it was a dinosaur or dinosauromorph, based on the specimen being incomplete and poorly preserved
• Had two sacral vertebrae (used to be dinosaurs had more than two sacral vertebrae, but later dinosaurs such as Herrerasaurus were found to have two sacral vertebrae)
• Based on cladistic analysis, Benton and others found Saltopus to be a dinosauromorph because of the reduced fourth and fifth digits on its hands, as well as other features of the bones
• Also found it to still be a valid taxon based on unique characters
• May be the closest relative of true dinosaurs (a common dinosaur ancestor)
• In 2017, Matthew Baron and others proposed that dinosaurs be divided into the clades Ornithoscelida and Saurischia (instead of Ornithischia and Saurischia)
• Saurischia had lizard-like hip bones and included theropods and sauropods, Ornithischia had bird-like hop bones and included ceratopsians and thyreophorans
• Interviewed Matt Baron in episode 145
• Found there were carnivores in both the clades Ornithoscelida and Saurischia, and the sister taxon to Dinosauria, Silesauridae, mostly includes herbivores. This may mean the common ancestors of both were omnivores, and omnivorous ancestors lived in both the northern and southern hemispheres
• Baron said it may not be possible to know for sure the origin of dinosaurs but they may have originated in the northern hemisphere, not the southern hemisphere as previously thought (one possibility is Saltopus)
• Not everyone agreed that Saltopus was a good candidate for a dinosaur common ancestor (lived about the right time but not the best fossils to work with)
• Also, another genus, Agnosphitys cromhallensis, found in England, was found to be a basal member of Silesauridae. Together with Saltopus, also helps show dinosaurs and silesaurids may have originated in Laurasia
• In 2018, Matthew Baron and Megan Williams redescribed the holotype of the Late Triassic dinosauriform Caseosaurus crosbyensis, and found that Caseosaurus, along with Saltopus, were herrerasaurs and that herrerasaurs were a sister taxon of dinosaurs (not dinosaurs themselves)
• Makes all the herrerasaurs non-dinosaurian dinosauriforms
• Wrote that their phylogenetic analysis, “along with other recent analyses of early dinosaurs, pulls apart what remains of the “traditional” group of dinosaurs collectively termed saurischians into a polyphyletic assemblage and implies that Dinosauria should be regarded as composed exclusively of Ornithoscelida (Ornithischia + Theropoda) and Sauropodomorpha.”
• Suggested reviving the name Herrerasauria for the clade (any and all taxa in the herrerasaur lineage).
• Also found Silesauridae to be the sister taxon to the clade that contained dinosaurs and herrerasaurs
• If Saltopus elginensis is a herrerasaur, it helps show herrerasaurs were in Europe in the Late Triassic and Saltopus would be the first named herrerasaur from outside the Americas
• Because they found herrerasaurs to not be dinosaurs (in 2017 in the new model Herrerasauridae and Sauropodomorpha formed Saurischia, the sister group to Ornithoscelida), they said that Saurischia became a paraphyletic group and proposed that “Saurischia should now be abandoned as a clade name” and to only include Ornithoscelida (Ornithischia and Theropoda) and Sauropodomorpha as dinosaurs
• Other animals that lived around the same time and place as Saltopus include Scleromochlus, a small archosauriform with long legs; Brachyrhinodon, a lizard-like reptile; Stagonolepis, an armored reptile; Hyperodapedon , a beaked, lizard-like reptile; and Ornithosuchus and Erpetosuchus, pseudosuchians (crocodilian-line archosaurs)

Fun Fact: T. rex had large powerful teeth, but several modern animals have much bigger teeth.

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