The oldest ancestors lived here, not there
Ninety-five million years ago, in shallow seas that once covered what is now southern Mexico, a spiny fish swam through waters shared with dinosaurs — and its fossilized remains, unearthed in 2018 from a limestone quarry in Chiapas, have quietly overturned a long-held assumption about where life's great diversifications begin. Named Choichix alvaradoi in honor of a scientist who dedicated his life to Mexico's prehistoric oceans, this newly identified species has been placed at the very root of the acanthomorph family tree — the lineage that gave rise to snapper, sea bass, and grouper. What the discovery asks us to reconsider is not merely the origin of a fish, but the direction of life's dispersal: not from the Old World outward, but from the Americas into the ancient Tethys Sea.
- A fossil pulled from rock in 2018 sat quietly until researchers realized it belonged to a species entirely unknown to science — older and more primitive than anything previously catalogued in its lineage.
- The find destabilizes a foundational assumption in fish evolutionary biology: that acanthomorphs — one of the ocean's most dominant and diverse groups — originated in Europe and spread westward.
- Researchers at Mexico's National Autonomous University are now arguing that the Americas, not the Old World, were the cradle of this vast fish lineage, with dispersal flowing eastward across the Tethys Sea.
- The quarry at El Chango, already one of Mexico's richest Mesozoic fossil sites, is yielding a coherent pattern — multiple species pointing to the same rewritten origin story, not just one anomalous specimen.
- The discovery lands as both a scientific correction and a cultural affirmation, honoring indigenous language and a Mexican paleontologist's legacy while repositioning the Americas at the center of a global evolutionary narrative.
In 2018, paleontologists working a limestone quarry near Tuxtla Gutiérrez in Chiapas extracted a fossil that would quietly rewrite part of fish evolutionary history. The specimen, 95 million years old and dating to the age of dinosaurs, belonged to a species never before documented. Researchers at Mexico's National Autonomous University announced the discovery this week, naming it Choichix alvaradoi — a name honoring both the indigenous language of nearby communities and Jesús Alvarado Ortega, a paleontologist who has spent his career studying Mexico's fossilized fish.
The fish was recovered from El Chango quarry in the municipality of Ocozocoautla de Espinosa, roughly 30 kilometers from the state capital. Its defining features — rows of sharp spines along its dorsal and anal fins — place it within the acanthomorphs, a group whose modern descendants include snapper, sea bass, and grouper. The quarry itself has been productive since 2006, yielding nine fish species alongside plants, mollusks, crustaceans, and ammonites, making it one of Mexico's most important windows into the Mesozoic.
What elevates Choichix alvaradoi beyond a remarkable find is its position in the evolutionary tree. Paleoecologist Kleyton Magno Cantalice determined it to be the most primitive acanthomorph yet discovered — a placement with sweeping implications. Scientists had long assumed this fish group originated in Europe and dispersed westward. The new evidence reverses that picture entirely: acanthomorphs appear to have originated in Mexico and the broader Americas, then spread eastward across the ancient Tethys Sea.
Cantalice noted that other fossils from the same quarry reinforce this pattern, suggesting the region was home to the oldest and most primitive members of this lineage. What was once understood as a migration from the Old World now appears to have flowed in the opposite direction — rooting one of the ocean's most successful evolutionary stories not in Europe, but in the New World.
In 2018, paleontologists working in a limestone quarry near the city of Tuxtla Gutiérrez in the Mexican state of Chiapas pulled from the rock a fossil that would rewrite part of the story of how fish evolved. The specimen belonged to a species that swam through ancient seas 95 million years ago, when dinosaurs still walked the earth. Researchers at Mexico's National Autonomous University announced the discovery this week, naming the fish Choichix alvaradoi in honor of Jesús Alvarado Ortega, a paleontologist who has devoted his career to studying fossilized fish in Mexico and training the next generation of scientists in the field.
The fossil came from El Chango, a quarry in the municipality of Ocozocoautla de Espinosa, about 30 kilometers from the state capital. The name Choichix also pays tribute to the indigenous language spoken in communities near the dig site. What made this fish distinctive was its anatomy: numerous sharp spines running along both its dorsal and anal fins, characteristics that place it within a large group of fish called acanthomorphs—a name derived from the Greek words for spine and form. Modern fish like snapper, sea bass, and grouper belong to this same group.
The quarry itself has proven to be a paleontological treasure. Since 2006, researchers have recovered fossils from this single location representing not just fish but also plants, mollusks, crustaceans, and ammonites. Nine fish species have been identified there so far, making it one of Mexico's most productive windows into the Mesozoic era. Yet Choichix alvaradoi stands apart. According to Kleyton Magno Cantalice, a paleoecologist at the university, this is a genus and species entirely new to science—never before documented or named.
What makes the discovery particularly significant is what it suggests about evolutionary history. When researchers analyzed Choichix alvaradoi's place in the family tree of acanthomorph fish, they found it to be the most primitive form yet discovered. This positioning carries weight. It suggests that this entire group of fish—one of the most successful and diverse groups in the ocean today—did not originate in Europe, as scientists had long believed. Instead, the evidence now points to Mexico and the broader Americas as the birthplace of acanthomorphs. From there, these fish dispersed and diversified across the Tethys Sea, a vast ocean that existed during the Mesozoic period before the Indian Ocean took its place.
The implications extend beyond a single species. Cantalice emphasized that other fossils recovered from the same quarry tell a similar story, suggesting a broader pattern: the oldest and most primitive members of this fish group lived in this region of Mexico. What was once understood as a one-way migration—fish originating in Europe and traveling westward to the Americas—now appears to have been reversed. The university's researchers concluded that this discovery, along with evidence from other organisms found at the site, points to a fundamentally different history for this group, one rooted not in the Old World but in the New.
Citas Notables
This is a genus and a species entirely new to science— Kleyton Magno Cantalice, paleoecologist at UNAM
The oldest and most primitive fish were in this region, not in Europe as we once believed— UNAM paleontologists
La Conversación del Hearth Otra perspectiva de la historia
Why does it matter where a fish species originated 95 million years ago? Doesn't the fish itself just tell us about that moment in time?
It does tell us about that moment, but it also tells us about how we've been wrong about the whole trajectory of life. We thought fish groups like this evolved in Europe and spread outward. This fossil suggests the opposite—that diversity started here, in Mexico, and moved the other direction.
So this one fish is evidence of a larger pattern?
Exactly. The quarry has nine fish species now. They're all pointing the same way. It's not one anomaly; it's a chorus.
What does "most primitive" mean in this context? Is the fish less advanced?
It's earlier in the evolutionary line. Think of it like finding the oldest ancestor in a family tree. It's not less advanced—it's closer to the root. That position in the tree is what tells us where the whole group came from.
And the name—Choichix alvaradoi—that's honoring someone specific?
Yes, Jesús Alvarado Ortega, who's spent his life studying these fossils and training other paleontologists. But the name also honors the indigenous language of the region where it was found. It's layered.
Does this change how we understand the dinosaur era in Mexico?
It changes how we understand fish evolution globally. But yes, it also tells us that this corner of Mexico was a center of life and diversity when most of the world was still figuring things out.