Z. Jack Tseng

@tsengzj

Paleontologist at the University of California, Berkeley. Interested in Functional Anatomy and Vertebrate Evolution. Self-proclaimed paleomammalogist.

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Z. Jack Tseng@tsengzj· 12d

This July my two major research tracks both have matured enough to be recognized by my peers via @science.org. Gratitude to my lab people & collaborators. I hope you enjoy reading the papers as much as we enjoyed working on them:(5/5) www.science.org/doi/10.1126/... www.science.org/doi/10.1126/...

Two paleontologists sit around an exposed fossil on a hill of red and green sediments, tools scattered around them, as they excavate a tan-colored fossil specimen.

A researcher wearing safety goggles and face mask looks closely at a 3D printed model of a sea snail shell placed in between compression plates on a mechanical testing frame. Wires connect sensors from the frame to electronic readouts of force and displacement values.

Z. Jack Tseng@tsengzj· 12d

Before I gave up completely on a research career, I got a job (lucky!). Four years later I got my current gig, where I felt free to "Be All You Can Be". The freedom to pursue interesting questions was FULL of false starts & dead ends, but a few projects flourished. My team endured & got funded (4/5)

A group of lab members in front of a mounted T. rex skeleton. Each person has a dinosaur hat on and is making dinosaur arm gestures with their hands.

Z. Jack Tseng@tsengzj· 12d

Later, on the job market I often felt out of place during interviews: many open positions targeted specialists. I was doing multiple lines of research that have not yet led to major results or publications. I almost chose just one aspect to drill down on. But for better or worse, I never did. (3/5)

Clipart depicting a person coming to a fork in the road. The person stands at the intersection.

Z. Jack Tseng@tsengzj· 12d

As an undergraduate just getting started in research, I could not decide which topic I loved more: functional morphology and biomechanics, or vertebrate paleontology. My mentors in two labs (S. Patek, S. Hopkins) let me work on two senior projects so I didn’t have to pick one. (📷Getty Images)(2/5)

A kangaroo rat standing on hindfeet, against white background. This image represents the first paleontology project I worked on: fossil pocket mice (Heteromyidae) from Middle Miocene rocks in Wyoming.

A colorful peacock mantis shrimp facing the camera, with mottled sediments as background. This image represents the first biomechanics project I worked on, looking at the aggressive behavior and striking force in mantis shrimp in response to color stimuli.

Z. Jack Tseng@tsengzj· 12d

#FossilFriday flashback: My lab published two major papers this month on 1) dental functional morphology and 2) vertebrate paleontology & paleobiogeography. It made me so proud of the research teams I've been a part of over the past decade, but it also prompted reflection on my academic path (🧵1/5)

Two Science Magazine cover images side by side. On the left, a vertical array of carnivore jaws with the title "A key tooth". On the right, a rendering of Central America from space with the title "Biotic Bridge".

Z. Jack Tseng@tsengzj· 13d

In sum: our new data & analyses provide a refined view of pre-GABI mammal movements, and underscore the untold stories in the latitudinal dimension of the GABI. Collection of primary field data is unreplaceable. Central America and the Panamanian land bridge region need more fieldwork! 🔨🪨🦴(11/11)

Photo of two paleontologists in broad brimmed hats excavating a plaster-jacketed specimen from a depression in the ground. Desert landscape is visible behind them.

Image of Panama viewed from space. Taken on the International Space Station by NASA astronauts. Astronaut photograph ISS054-E-44629

Z. Jack Tseng@tsengzj· 13d

What’s more: we also noticed a tendency for larger-bodied and dryer-environment adapted mammal clades to participate in the holding pen. This matches our stable isotope data from Mexico, suggesting that vegetational shifts played a role in which mammals made the journey in and across Mexico (9/11)

A graph from Tseng et al. (2026) showing density distributions of mammal body masses across five major biogeographic events leading up to the Great American Biotic Interchange.

Z. Jack Tseng@tsengzj· 13d

We then detected a different phase between the holding pen and GABI pulses, when faunal connectivity increased between Mexico and the rest of the Americas. This connectivity increased asymmetrically, with more North American taxa in Mexico earlier than increases in South American taxa there. (8/11)

Graph from Tseng et al. (2026) showing shared genera between Mexico and rest of North America and Mexico and South America, respectively. The Mexico-South America curve lags behind the North America curve during a pre-GABI phase.

Z. Jack Tseng@tsengzj· 13d

We also observed an accumulation of higher latitude mammals in Mexico from 10-7 Ma. The pattern represents a ‘holding pen’ previously proposed by Flynn, Woodburne, and colleagues. However, this holding pen is more than twice as old as what they saw with earlier, less complete fossil records. (7/11)

A graph from Tseng et al. (2026) showing net diversification rages for three geographic regions in the Americas, displaying a peak in Mexico during the holding pen phase, and subsequent South American faunal turnover events.

Z. Jack Tseng@tsengzj· 13d

We estimated diversification rates and faunal connectivity patterns across the Americas, vetting taxonomic occurrences and accounting for uncertainties in fossil age ranges. We discovered a latitudinal signal of fossil mammal movements in the 7 million years leading up to GABI pulses (6/11)

Graphic from Tseng et al. (2026) showing pulses of rate shifts in origination and extinction patterns across the past 10 million years in northern North America, Mexico, and South America.

Z. Jack Tseng@tsengzj· 13d

We collectively conducted more than 30 years of fieldwork in Mexico in 12-3 Ma deposits. We analyzed this and other published data by treating Mexico as an intermediate biogeographic unit between higher latitude North America and South America, testing for latitudinal gradients in dispersal (5/11)

Photo of six field paleontologists in two rows of three, surrounded by trees and grass. The scientists in the photo are wearing hiking boots and outdoor work clothes; two of them hold broad brimmed hats in their hands.

Z. Jack Tseng@tsengzj· 13d

Some analyses of molecular data have also suggested that a Panamanian land corridor may be as old as 15 million years or older. Such an ‘old isthmus’ hypothesis has not been rigorously tested using the mammalian fossil record, and especially not with low-latitude data. (📷: O'Dea et al. 2016)(4/11)

Screenshot for the title page of an article titled "Formation of the Isthmus of Panama"

Chart showing number of first appearance of immigrant mammal genera through the past 13 million years in North America (top) and South America (bottom). From O'Dea et al. 2016

Z. Jack Tseng@tsengzj· 13d

Although the main GABI pulses started around the same time as the appearance of a persistent Panamanian land bridge, there has been conflicting findings as to the tempo and mode of pre-GABI land corridors. Some studies propose a Middle Miocene closure of the Central American Seaway (3/11)

Screenshot of an article titled "Middle Miocene closure of the Central American Seaway" by Montes et al. 2015.

Graphic from Montes et al. (2015) showing the arrangement of land masses near the Panamanian land bridge during Middle Miocene.

Z. Jack Tseng@tsengzj· 13d

GABI is a series of organismal dispersal events between the Americas that helped establish their current day biodiversity patterns. It has been most intensively studied in mammals, with the fossil record showing major pulses of dispersals starting around 3 Ma (image: Woodburne 2010, X. Wang) (2/11)

Part of a scientific figure from Woodburne (2010) showing the timing of the main pulses of the Great American Biotic Interchange.

Map of the Americas with immigrant mammal species labeled on each continent. The Panamanian land bridge region is labeled GABI (Great American Biotic Interchange) with bidirectional arrows. Credit: X. Wang/NHMLA

Z. Jack Tseng@tsengzj· 13d

Exhilarated to share a 2nd @science.org cover article this month from our lab @ucberkeleyofficial.bsky.social! A collaboration with US & Mexico colleagues on the role of a Mexican biogeographic holding pen in shaping the Great American Biotic Interchange (GABI)(1/11) www.science.org/doi/10.1126/...

Cover of Science magazine for July 30, 2026. Caption from Science reads: A three-dimensional rendering shows the land bridge connection between North and South America. Research on the fossil record of mammals in Mexico suggests that the geographic region acted as a biodiversity “holding pen” for 10 million years, buffering the pace of both northward and southward movements of mammal species leading up to the Great American Biotic Interchange.

Z. Jack Tseng@tsengzj· 27d

Our newest paper on mammalian dental evolution, out today as the cover article in @science.org, lead by @narimanechatar.bsky.social with a team of fantastic early career scientists!!! 🎉🥳 “Performance trade-offs define a fundamental dental dichotomy in mammals” www.science.org/doi/10.1126/...

Cover image of Science Magazine, with images of carnivore jaws and teeth on black background.

Z. Jack Tseng@tsengzj· 28d

Excited for a major paper drop tomorrow with @narimanechatar.bsky.social! Watch this space if you like mammals and teeth!

A meme containing an image from the movie “A few good men” of a man in military uniform yelling emphatically. The caption of the meme says “You can’t handle the tooth”.

Z. Jack Tseng@tsengzj· Jun 24

Granitic intrusions forming sheer cliffs in the Hua Shan (华山) UNESCO World Heritage Site. Our cable car gliding over 2000-m high peaks that formed over the past 70 million years.

Z. Jack Tseng@tsengzj· Jun 18

The Badaling Great Wall in the Yan mountains (燕山) and dinosaur-age granites and limestones originating from the Jurassic/Cretaceous Yanshanian tectonic events.

A grayscale photo of the Great Wall of China, showing stone walls meandering over steep hills covered with trees.

Z. Jack Tseng@tsengzj· Jun 5

The final perspective of Smilodon populator a prey sees. Museo Argentino de Ciencias Naturales. #FossilFriday

A mounted skeleton of a sabertooth cat in pouncing posture, leaping from a rocky perch extending from an orange colored wall in a museum exhibit. Viewed from below.

Z. Jack Tseng@tsengzj· May 18

Humanity is experiencing technical difficulties at the moment with humanity-ing, please check back later…😓 (seen in San Francisco).

Advertisement at a bus stop shelter showing an artificial human-like face with the phrase “stop hiring humans” above it.

Z. Jack Tseng@tsengzj· May 15

The gigantic ground sloth Megatherium at MACN in Buenos Aires, Argentina. The size of this herbivore is difficult to appreciate from the photo. A human would only stand near hip height (on the platform) next to this Ice Age megamammal! #FossilFriday

A beige colored fossil skeleton mounted in the middle of a cavernous hall, with ornamental arches all around the room.

Z. Jack Tseng@tsengzj· May 12

So excited to see dueling Smilodon populator in front of the Museo Argentino de Ciencias Naturales! Spending this week in Buenos Aires looking at South American fossil mammals.

A display of two fossil sabertooth skeletons mounted on a rocky foundation with a red and white brick building in the backdrop and lush tree canopy overhead.

Z. Jack Tseng@tsengzj· Mar 31

Mesquite Flat Sand Dunes in Timbisha (“Death Valley National Park”), home of the Timbisha Shoshone.

Wind-carved wavy texture of a sand dune with oblique sunlight casting shadows diagonally across a tanned desert landscape.

Z. Jack Tseng@tsengzj· Feb 25

Our BioSci library did this Valentine’s themed mystery book feature at the front desk, where you can unwrap a secret valentine book to check out if the keywords catch your eye. I couldn’t resist this one, which seems to be edited by none other than @arctomet.bsky.social!

A book wrapped in heart-shape patterned wrapping paper, with the words “fossil hunter”, “autobiography “, and “paleontology” on the front.

The inside cover of a book called “From Siberian Prisoner to Dinosaur Egg Detective”, edited by Thomas Holtz

Z. Jack Tseng@tsengzj· Dec 20

It’s a wrap for my vertebrate morphology class. Students surveyed the vertebrate fossil record, functional anatomy, phylogenetic comparative methods, geometric morphometrics, scientific writing, + more! A doubly meaningful experience for me because I took this class as an undergrad 24 years ago! 💙💛🐻

A classroom with orange chairs clustered somewhat out of order.

Z. Jack Tseng@tsengzj· Nov 11

Safe travels all #2025SVP folks! En route to Birmingham via London…and who am I to argue with the NHM’s kids pack swag? 😁

Z. Jack Tseng@tsengzj· Oct 15

Celebrating #NationalFossilDay with a new paper describing specimens of the most whimsical of weasel relatives, leptarctine ("slender bear") mustelids, from the collections of @ucmpberkeley.bsky.social. Their teeth are so much fun to look at! 🦷 doi.org/10.5070/P9.4... (Cover image by P. Holroyd)

Image of three brown and black fossil jaw fragments of extinct weasel relatives, Leptarctus, with short but sharp cusps. Open access paper at https://doi.org/10.5070/P9.48360

Z. Jack Tseng@tsengzj· Sep 19

Studying wrist and ankle bones for fossil id and found it amusing how carpals have wired names like magnum and unciform but tarsals have tired names like cuneiform 1, 2, 3. Like they ran out of cool names for bones by the time they got to feet 😆