For some strange reason, small and microscopic fossils fascinate me much more than huge dinosaur fossils. I realized this in my social service at the INAH (National Institute of Anthropology and History) when I started working on the Paleontology collection of my state. I was impressed when I saw the immense amount of fossils that were kept in the museum, complete plates of glyptodonts, giant bones and enormous defenses of mammoths, which filled most of the shelves, however, when working with the fossils of invertebrates and wood fossils, I felt amazed! It was as if I were reading a letter from a childhood friend, seeing a photograph of my great-grandparents or learning to cook a secret family recipe, do you know what I mean? It was a magical moment, it was as if I could travel being a plant or a gastropod, feel the wind full of oxygen and the humidity of the Carboniferous, swim in the oceans of the Cretaceous and die of fear of becoming the food of some mosasaur or ichthyosaur.

Today I will tell you a little about the invertebrate fossils that exist in my country (Mexico) and in the state where I live (Puebla).

What are fossils to you?

The short and concrete definition that I like the most is that fossils are evidence of life in the past, regardless of the age of that evidence, as long as the species is completely extinct. Fossils can be bones, molds, impressions of leaves, eggs, shells or other organic remains, but also footprints and coprolites: the feces of organisms that lived in the past!, which are indirect evidence of life, that is, ichnofossils.

If tomorrow, “for some strange reason”, we became extinct and there were no human beings, our organic remains would become fossils and our phones, houses, cars, clothes, etc., would be ichnofossils.

What must have happened for the fossils we know to be fossilized and preserved?

For fossilization to occur, a complex series of events occurs that is studied by a branch of paleontology called Taphonomy, which is responsible for analyzing the processes that happened to the organism after its death, as well as studying the substrates and paleoenvironments where it was found, its role in the ecosystem and its evolutionary history.

Another important point is to know the age of the rocks and for that analysis such as radiometric dating is carried out, but the organic matter that is deposited in these foundations is also used, such as the shells of some protists (radiolarians and foraminifera) and fossils also of some invertebrates, mainly for marine substrates. For terrestrial substrates, the fossilized outer walls of pollen are used. Yeah, the pollen fossilizes! That's why I love microfossils and invertebrate fossils.

But anyway, I'll tell you a little about the invertebrate fossils of my country.

Mexican fossil invertebrates

At the beginning of the 20th century, in Mexico there were no paleontologists who explored the areas of the country, so researchers began to arrive from different parts of the world. One of the states that caught their attention the most was Tamaulipas, where they found corals, bivalves, decapods and echinoids. Years later, Mexican researchers began carrying out paleontological expeditions and found countless fossils of gastropods, bivalves, echinoids, cephalopods, crinoids, brachiopods, and ammonites (Becerra et al., 2020). Today there are still finds of these incredible organisms!

In Sonora there are fossils that belong to the Cambrian period, the most predominant are archaeocyatids, of the genera Ethmophyllum and Ajacicyathus (Cuen et al., 2016). Fossils of cephalopods, crustaceans, rudists, bivalves, gastropods, corals, bryozoans, brachiopods, ammonites, trilobites and crinoids have been found in the states of Hidalgo and Oaxaca (Esquivel, 2009).

Among the states with the greatest abundance and diversity of invertebrate fossil records is Puebla (my state of residence).

My favorite fossils

The history of the fossils of Puebla begins when Nyst and Galeotti, two researchers from Belgium, traveled to Tehuacán to carry out a paleontological exploration and were excited to find fossils of sea urchins, this finding indicated that a large number of marine fossil organisms could exist (Buitrón, 2019).

110 million years ago Puebla was part of the ocean, for this reason, there was a great diversity of marine organisms, both invertebrates and vertebrates. The most incredible thing is that their fossil remains have been preserved so well that we now know more about them and their history.

One of the most important aspects of the paleontology of Puebla and that differentiates it from other states is that there is a great variety of fossiliferous strata from different periods (Herrera, 2019), mainly from the Mesozoic era.

In my state there are many paleontological sites with great diversity of invertebrate fossils, I will tell you about my three favorite sites: San Juan Raya, La Cantera de Tlayúa in Tepexi de Rodriguez and the town of Petlalcingo Santa Cruz in the municipality of Acatlán.

San Juan Raya

San Juan Raya has an immense amount of fossil invertebrates from the Cretaceous period, fossils from 120 million years ago. Those that dominate are oysters and clams (pelecypods), and gastropods (snails), especially the genera Nerinea, and Cassiope (Buitrón and Barceló, 1980). Corals, echinoderms, sponges and brachiopods are also found. And the best of all is that we can visit this site, since the town has a paleontological ecotourism program and a museum where activities are carried out and content is generated to disseminate paleontology. You can watch this YouTube video so you can learn a little about the place.

Figure 1. Marine fossils. The place is full of shells, mainly turitelas.

La Cantera de Tlayúa

My second favorite fossil site is La Cantera de Tlayúa, where fossils are found in an almost perfect state of preservation, from 100 million years ago, also from the Cretaceous period, a magical and unique place in the world. In addition to the large number of fish fossils there are, there are also starfish, sponges, cephalopods, annelids, sea cucumbers and all the others that remain to be discovered. Whatch this video.

Figure 2. Fossils of Tlayúa: 1) seashells and 2) starfish.

Santa Cruz

Finally, the town of Petlalcingo Santa Cruz, which is located in the municipality of Acatlán, has an abundant number of fossils, and unlike the previous places, the fossils at this site belong to the Jurassic period, they are fossils from 150 million years ago! To date, speaking of invertebrate organisms, corals, oysters, clams, snails, ammonites, brachiopods and sea urchins have been found (Buitrón, 2019).

That's why I love living here, there is a great variety of fossils and the most impressive is that they have been preserved so well that observing one is like traveling to the past as an organism from that time.

Fossils are impressive, from them we can narrate our evolutionary history, know where we and our environment come from, and, in addition, project what may happen in the future.

Tell me, what paleontological sites do you know in your community or country?


Becerra, A. G., Correa, A. y Torres, M. Á. (2020). Revisión histórica del registro fósil de Protozoos e invertebrados marinos del estado de Tamaulipas, México. Paleontología Mexicana, 9(2), 135-143.

Buitrón, B. E. (2019). Los invertebrados fósiles del estado de Puebla. Paleontología en Puebla, Saberes y ciencias, monthly Supplement, december, p. 4.

Buitrón, B. E. y Barceló, J. (1980). Nerineidos (Mollusca-Gastropoda) del Cretácico inferior de la región de San Juan Raya, Puebla. Revista mexicana de ciencias geológicas, 4(1), 46-55.

Cuen, F. J., Valdez, J. E., Montijo, A. y Monreal, R. (2016). Invertebrados Fósiles del Paleozoico de Sonora, México. EPISTEMUS, 10(21), 75-83.

Esquivel, C. (2009). Panorama de los invertebrados fósiles. En González, K. A,, Cuevas, C. y Castillo, J. M. (Eds.), Los fósiles del estado de Hidalgo (pp. 39-58). Hidalgo, México: Universidad Autónoma de Hidalgo.

Herrera, J. A. (2019). El registro paleontológico del estado de Puebla. Paleontología en Puebla, Saberes y ciencias, monthly Supplement, december p. 6.