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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 01/07/2026

And you can also watch an in-depth description of the paper on the @SkeleCrewPaleo Youtube channel here: youtu.be/gem3IH7P7PY

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 01/07/2026

We hope this paper, in tandem with TEX (& more future work to come soon), emphasize the necessity of classical anatomical description & direct comparison to holotypes - no matter how scrappy they may appear, we cannot ignore them.

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 01/07/2026

Speaking of Cope: this paper is the 2nd chapter of my dissertation, written while a phd student at the AMNH...which has his desk in the paleo library. So, I did make sure to write part of the paper from that desk, lol. 📷: AMNH digital coll.

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 01/07/2026

...so, we restrict our conception of the type to exclusively material that Cope describes & that either physically articulates with or matches (in color/preservation) Cope's described material.

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 01/07/2026

We also redescribe & reassess another important holotype, T nepaeolicus AMNH FARB 1565. Turns out, not all the material in the box came from one individual - I found a duplicate splenial. This of course casts doubt on the whole specimen...

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 01/07/2026

MCZ 4374 is not the most complete Tylosaurus, but it does preserve a region of anatomy that's usually destroyed in Seaway tylos: the anterior palate. We find morphology unique to Tylosaurus & lots of potential for phylogenetic characters here.

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 01/07/2026

In this paper, we give MCZ 4374 the descriptive spotlight it deserves. We also provide a detailed account of its discovery and transfer to Harvard (including its receipt! Courtesy of the Ernst Mayr Library, Harvard)

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 01/07/2026

Holotypes are critically important to studies of taxonomy & skeletal variation in extinct animals. Despite many *recent* studies addressing those topics in Tylosaurus, ED Cope was the last person to figure the holotype, MCZ VPRA 4374, in the scientific literature... in 1870.

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 01/07/2026

It's been far too long since Tylosaurus news...so here's another NEW TYLOSAURUS PAPER! 🦎 From me & Mike² (Everhart & Polcyn) For the first time in over 150 years, the holotype of Tylosaurus proriger is fully described & figured in detail. Incredible artwork by Andrey Atuchin

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 22/05/2026

I'll end this thread here for now - please check out the paper here, & check out the new Tylosaurus rex model in Path of Titans! hdl.handle.net/2246/7549

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 22/05/2026

1. Potentially monophyletic Hainosaurus 2. Derived Taniwhasaurus 3. Paraphyletic Tylosaurus Do we think Tylosaurus should be split at this time? NO-these are basically PRELIMINARY results. I expect the genus to resolve in future analyses with broader sampling & new characters.

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 22/05/2026

WE COULD TEST THAT HYPOTHESIS, & we found that TEX are apomorphically distinct from T proriger REGARDLESS of body size - importantly, this includes in the size range where they overlap. AND, even better, we *do* see onto change in TEX - & it matches onto changes in extant lizards

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 22/05/2026

wHaT aBoUt OnToGeNy?? Now that is a fair question to ask - and we of course considered that. TEX are larger, & their apomorphies could, theoretically, be ontogenetic. But here's the cool thing about an animal with a [relatively] large sample size & close living relatives...

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 22/05/2026

TEX is distinguished from T. proriger by a suite of characters associated with the attachment sites for jaw & neck musculature, as well as consistently 'serrated' teeth...now I *know* what you're thinking:

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 22/05/2026

...lo and behold, it is also NOT actually contemporaneous with T. proriger!!! Most TEX are from the Ozan Fm. - about 80-79 mil. yrs old, *younger* than the Niobrara T. proriger (~84 mya). Bunker is from the Pierre Shale - ~80 mya.

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 22/05/2026

IT'S BUNKER! 'Bunker' is on display at Kansas University...& was found in Kansas...so what gives?? A common pitfall in paleo taxonomy is to refer specimens to a species based on their locality, and NOT apomorphic comparison to the holotypes. BUNKER POSSESSES TEX APOMORPHIES...

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 22/05/2026

To give you a sense of scale: the SMALLEST specimen that we refer to TEX is on par with our largest T. proriger, & the biggest is a few feet longer than the False Lizard King itself. Our biggest individual also introduces a little twist...

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 22/05/2026

Many TEX specimens were collected decades ago & referred to an existing sp of Tylosaurus, T. proriger. These referrals were primarily based on being larger & later in time than other T. spp...& boy they sure ARE larger (graph: Tylo quadrate size across 70 specimens)

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 22/05/2026

...but wait, there's more! We are confident in referring a DOZEN specimens to T. rex. These referrals, & the taxon itself, are supported by MULTIPLE LINES OF EVIDENCE: apomorphic, stratigraphic, & geographic.

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 22/05/2026

You can visit the holotype, PMNS 8029-"Heath"-on display at the Perot Museum! "Heath" preserves a nearly complete skull & partial skeleton. Shout out & thank you to my friend & colleague Kiersten for letting us use her skeletal for highlighting how much of the beast is preserved!

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 22/05/2026

TEX is the culmination of my PhD research. Not only do we describe & figure our new species in exhaustive detail, but we include a revised phylogenetic dataset for analysis of Mosasauridae, & my measurement dataset for HUNDREDS OF MOSASAURS & EXTANT LIZARDS-& it's ALL OPEN ACCESS

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 22/05/2026

Everything IS bigger in Texas... Introducing TYLOSAURUS REX–“TEX”. A monster animal, a monster paper, & a monster project that I am *so* excited to finally share with everyone after ~5 yrs. Huge thanks to my coauthors, Mike & Ron, & to Alderon Games for bringing our lad to life!! #FossilFriday

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 18/05/2026

It's been much too long since my last #MosasaurMonday, so enjoy some southwestern seaway vibes from my trip to Dallas in 2023! 🌊🦎 Fossils are bits & bobs of Tylosaurus, [Lizard] King of the once-flooded Lone Star State. RIP Tylosaurus, you would have loved brisket sandwich 🤘😞

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 20/03/2026

Happy #FossilFriday! Our new exhibit at the Castle, PREHISTORIC WISCONSIN, opens NEXT WEEK on 3/26! If you're in the area, be sure to swing by - Chase & I will be hanging out in the exhibit from 1-3pm on April 1, 3, & 6 with answers to questions & bonus specimens from collections.

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 05/12/2025

Happy #FossilFriday! I am absolutely thrilled to share the first new exhibit for the History Museum at the Castle to feature specimens from the Weis collection: bird evolution, flourite, & quartz. Many thanks to B Danz, T Green, & J Taylor for their photos & art!

A life model of Sinosauropteryx posed behind a real piece of fossilized Edmontosaurus skin.

The entire exhibit cabinet featuring specimens from the Weis museum. The top halves display specimens and photographs that teach visitors about bird evolution. The lower halves of the cabinet feature flourite and quartz mineral specimens.

The upper left section of the cabinet, which focuses on the common ancestry that birds share with dinosaurs.

The upper right section of the cabinet, which calls attention to features and behaviors that visitors can observe in modern birds that they share with their reptile relatives.

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 25/08/2025

Task completed (easy): freeing Stan from his old Podium Next Objective (difficult): getting him Off the Surprise Table that we found under the Podium #MuseumMonday

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 22/08/2025

Happy #FossilFriday! While you may have seen this cast of Tylosaurus elsewhere, this specific one is special: it is the *first* cast of the fossil that was made. Currently on display in the lobby of the History Museum at the Castle. Exciting things coming to the Castle soon - stay tuned!

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 18/07/2025

Thrilled to share that starting in late August, I'll be Natural History Museum Specialist for the History Museum at the Castle in Appleton, WI! I'll be overseeing the exhibition and programming of the nat. his. collection, which is being moved from the old Weis Earth Science Museum.

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 27/06/2025

Happy #FossilFriday from an undisclosed Kwik Trip as I embark on my trek to Kansas for my first @sternbergcamps.bsky.social !

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 01/04/2025

Happy #TylosurusTuesday! Did you know? There are seven species of Tylosurus alive today!!! They are readily distinguishable from other marine life by their toothy elongate snouts. They are of course very dangerous, & have severely injured multiple people (& killed at least one).

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 28/03/2025

Happy #FossilFriday - here's the very first mosasaur skull that I ever studied, Tylosaurus FMNH P15144, almost exactly six years ago. I've since seen over 300 of these things, & written tens of thousands of words about them in a dissertation submitted yesterday 🦎🎉

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 07/03/2025

For #FossilFriday today, Homer the Triceratops, at the Burpee Museum's Paleofest last weekend

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 28/02/2025

Happy #FossilFriday & #PaleoFest eve! Attending tomorrow's PaleoFestivities? Prepare to meet TEX; genuinely one of the coolest critters I've had the pleasure of working with! Here's a pterygoid from "the Black Knight," a specimen that exemplifies our beast's capacity for violence

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 27/02/2025

Paper submitted - my second dissertation chapter & the first of several major Tylosaurus projects I've got on deck. Just a little something that, in my opinion, was long overdue...

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 19/02/2025

When folks say that everything is bigger in Texas, does that include the mosasaurs? (spoiler: oh yeah) Thrilled to be presenting our *new beast* for the first time at PaleoFest!!!

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 03/02/2025

Happy #MosasaurMonday from the Pit of Despair (end stage PhD work), here's an appropriate lizard: Tylosaurus "Heath" on display at the Perot Museum in Dallas. Does "everything's bigger in Texas" apply to its mosasaurs? I've got a few upcoming public talks addressing just that...& more. Stay tuned!

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 31/01/2025

Today's #FossilFriday falls on the 179th 'birthday' of the city of Milwaukee! 🍻🎉 so, here's our Torosaurus, on display in the MPM

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 24/01/2025

#FossilFriday As is often the case I'm thinking a lot about mosasaur quadrates today. I can't yet share the specimens that I'm actively working on so instead, here's one from Mosasaurus on display in Maastricht. The holes in the bottom are not post-death damage, but an abscess that held ~0.5L of pus

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 31/12/2024

#MosAdvent #31: Tylosaurus "Bunker" is the largest mosasaur known (from *reliable* estimates), ~14m long with a skull as long as I am tall. Very excited to share new work involving this guy in 2025 - long live the Lizard King! 🌊🦎👑

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 30/12/2024

#MosAdvent #30: a complete mosasaur skeleton, osseous and cartilaginous - Tylosaurus AMNH 221, arguably the best preserved tylosaur (& one of the best mosasaurs) known to science. This photo was taken in 2022, when we removed the glass to scan, photograph, & study it up close.

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 29/12/2024

#MosAdvent #29: Grand Animal of Maastricht, the holotype of Mosasaurus hoffmannii, housed in Paris. It's nearly impossible to photograph, as it's in a glass box under a glass ceiling, so check out the rotisserie 3D model on my other socials to see it without obstruction

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Dr. Amelia R. Zietlow 🦎 @tyrantlzrdqueen.bsky.social · 28/12/2024

#MosAdvent #28: Mosasaurus on display in the Royal Belgian Institute of Natural Sciences. I've been in the Palate Zone lately, as it's criminally under-figured in existing mosasaur literature, & R303 has the best intact palate of any mosasaur I know (that's visible from the outside, anyway).

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