Thomas R. Holtz, Jr.

@arctomet.bsky.social

4315 Followers 648 Following

Tyrannosaur Expert; Dinosaur Paleontologist; University of Maryland Geology Faculty; Director of the College Park Scholars-Science & Global Change Program; Science Author; Cat Dad; 🦖🦕

Skeleton (above) and model of appearance in life (below) of the boomerang-headed amphibian Diplocaulus

Dozens of stacked cones of rudists (reef-making clams from the Cretaceous Period)

Skeleton of the small early primate relative Plesiadapis climbing a tree

Fossil skeleton of the large quadrupedal predator reptile Prestosuchus from the Triassic of South America

The skeleton of the skull and torso of the giant sabre-toothed gorgonopsian protomammal Inostrancevia

Skeleton of the Cretaceous coelacanth Mawsonia

Skeleton of giant duckbill dinosaur Saurolophus osborni surrounded by smaller iguanodontian skeletons

Galapagos tortoise on a beach

Numerous skulls, partial skeletons, and isolated bones of mammoths still in the sediment at the Mammoth Site, South Dakota

Skeleton of the Permian sail-backed protomammal Edaphosaurus

Skeleton of the Miocene baleen whale Eobalaenoptera, suspended from the ceiling

Oxygen curve over time. Fig. 1 from https://www.nature.com/articles/s41586-026-10291-3

Mounted skeleton of the duckbilled dinosaur Maiasaura, with a nest of eggs and skeletons of hatchling Maiasaura in front of it. Background is a mural of the same scene.

Skeleton (missing hands and feet) of the long-snouted early whale relative Kutchicetus, looking like a crocodile head stuck on an otter skeleton

The skeleton of the small bipedal frilled dinosaur Prenoceratops

Reconstructed skeleton in front view of Hadrosaurus, with its head turned towards its left.

View of current position of ArtemisII capsule on approach to the Moon

Doctor Fun cartoon of the Easter Eurypterid (sea scorpion with a rabbit face) approaching trilopeeps (soft yellow marshmallow trilobites)

Slab of greyish mudstone in plaster jacket, with 7 or 8 large spheroidal fossil eggs embedded in it.

Skull and articulated vertebrae of the dinosaur Coelophysis in reddish sandstone, with articulated bones of other specimens below it

The fossil of the enigmatic Cambrian animal Nectocaris. A brownish stain on light brown rock: two forward-protruding tentacles; a head with a pair of large eyes; and an ovoid body with denser material down the midline.

Fossils of sea lilies (crinoids) on a block of pale limestone

Composite skeleton of the Early Cretaceous sauropod dinosaur Astrodon

Skeleton in right lateral view of the early Late Jurassic metriacanthosaurid dinosaur Sinraptor dongi

Skeleton of the ground sloth Lestodon, rearing up on its stumpy hindlegs

Skeleton of the slender reptile Eudibamus in a reddish siltstone

Photograph and interpretative drawing of the partial thighbone of the dinosaur Bradycneme

Wentworth scale showing the demarcation between different grain sizes and the names for the type of sediment at that size

Fossil skull of the ichthyosaur Temnodontosaurus platyodono

Skeleton of the Miocene long-snouted toothed whale Xiphiacetus

Skeleton of the flightless bird Megalapteryx didinus

Mounted skeleton of the legged sea cow Pezosiren