Pleistocene Bats from San Josecito Cave, Nuevo Leon, Mexico

In Short

This brief paleontological study classifies eighty-nine fossilized bat skull and jaw specimens recovered from San Josecito Cave in Nuevo León, Mexico. Paleontologist J. Knox Jones, Jr. examines these late Pleistocene remains, categorizing them into three distinct families and five separate genera. The text details anatomical measurements, compares ancient specimens with modern living species, and formalizes the discovery of a newly identified extinct species of vampire bat. The paper remains a classic reference because it documents crucial historical shifts in Central American chiropteran distribution and ancestral mammalian evolution.

The Story

The narrative of the study traces the scientific examination of a long-neglected fossil hoard gathered during previous field expeditions. Field parties from the California Institute of Technology, led by Chester Stock, originally excavated the rich deposits of San Josecito Cave near Aramberri, Mexico. In 1950, a subset of eighty-nine cranial elements and rami was loaned to the University of Kansas for definitive identification and morphological description.

Jones begins his investigation by establishing the geographic and biological scope of the collection. The fossils represent three major families: Phyllostomidae, Desmodontidae, and Vespertilionidae. Systematically evaluating the remains species by species, he first addresses Leptonycteris nivalis, the long-nosed bat. By carefully cross-referencing skull measurements, he establishes that these cave specimens average slightly larger than living modern counterparts, yet fall squarely within the natural range of variation seen in the region today.

The core of the study shifts to the primary discovery within the cave collection: a distinct, large vampire bat. Jones compares these substantial crania to the modern Desmodus rotundus and the South American Diaemus youngi. Noting a broader rostrum, a more rounded braincase, and heavier dentition with unique incisor shapes, he formally designates this newly recognized extinct species Desmodus stocki. He posits that this robust ice-age bat may serve as an immediate direct ancestor to the living vampire bat species known today.

Moving through the remaining specimens, Jones examines fragmentary rostra and partial crania of insect-eating bats. He provisionally assigns a large jaw fragment to Eptesicus cf. grandis, noting its heavier tooth row and pronounced dorsal ridges compared to modern big brown bats. He then evaluates a single skull of Lasiurus cinereus, the hoary bat, observing that its un-worn teeth and discovery in surface talus suggest it might be of recent origin rather than ancient Pleistocene stock. Finally, he summarizes the status of Corynorhinus tetralophodon, a distinct fossil big-eared bat previously described from the very same cave material.

The work concludes by cataloging precise skull metrics, diagnostic characters, and literature citations. Through this systematic accounting, the author constructs a clear picture of the late Pleistocene cave fauna, illustrating how environmental conditions and evolutionary lineages transformed ancient mammalian populations into the modern species inhabiting the region today.

How It Unfolds

The loan of the cave material The author receives eighty-nine cranial specimens collected by Chester Stock's team from San Josecito Cave for official identification at the University of Kansas.

Measuring the long-nosed bats Analysis of seventy Leptonycteris nivalis crania shows they are slightly larger on average than modern local populations, though still within expected anatomical variation.

Establishing a new vampire bat Detailed diagnostic work on twelve fossil crania reveals a massive, broad-skulled bat, which the author officially names Desmodus stocki in honor of Chester Stock.

Assessing the brown and hoary bats A single robust rostrum is referred to the ancestral Eptesicus cf. grandis, while a preserved Lasiurus cinereus skull found in surface talus is noted as possibly modern.

Synthesizing the cavern collection The survey closes with a review of the plecotine bat Corynorhinus tetralophodon, completing the breakdown of the five bat species recovered from the cave deposits.

The People

• J. Knox Jones, Jr.: The primary researcher and author who seeks to categorize the unidentified fossil bats. He meticulously measures crania, detects structural differences, and establishes the formal taxonomy of the ancient cave species.
• Chester Stock: The late professor and expedition leader who originally directed the California Institute of Technology excavations at San Josecito Cave. He collected the mammal fauna and stands as the dedicated namesake for the newly discovered fossil vampire bat.
• E. Raymond Hall: The museum editor and supervisor who grants permission for the fossil bat material to be studied and published at the University of Kansas.
• Robert W. Wilson: A research colleague who critically reviews the manuscript drafts to ensure accurate paleontological reporting.
• Charles O. Handley, Jr.: A fellow scientist who previously borrowed a distinct plecotine cranium from the collection to describe the new species Corynorhinus tetralophodon.

In Its Own Voice

"Included therein were 89 crania and rami of bats, representing three families (Phyllostomidae, Desmodontidae and Vespertilionidae) and five genera, each represented by a single species."

This opening summary establishes the exact physical contents and taxonomic variety found within the borrowed San Josecito Cave fossil collection.

"I do not doubt that the two species are closely related; possibly stocki is ancestral to rotundus."

Here, Jones proposes an evolutionary connection between his newly named extinct vampire bat and the living modern species.

"A label with the skull bears the notation 'talus' in parentheses, which, in so far as I am able to determine, indicates surface talus inside the cave."

The author explains why a particular hoary bat skull might be a recent intrusion into the cave rather than an ancient Pleistocene fossil.

What It's Really About

The paper centers on the process of using comparative osteology to reconstruct past biodiversity. By placing ancient fossilized skull measurements alongside modern biological data, the text explores how species change in size, shape, and distribution over geological time. It addresses the broader question of how late Pleistocene mammal communities in Mexico survived or adapted as the ice age drew to a close. On a methodological level, it highlights the collaborative nature of mid-century paleontology, where shared museum specimens, precise anatomical measurements, and formal taxonomies allow scientists to reconstruct evolutionary lines and recognize previously unknown extinct species.

Why Read It Today

This text appeals directly to paleontology enthusiasts, mammalogists, and readers interested in late Pleistocene natural history. Reading it feels like looking over the shoulder of a meticulous specialist at his workbench, examining clean bone fragments under strong light. The writing carries a quiet, orderly rhythm, built on precise physical descriptions and numerical tables rather than dramatic flourishes.

The primary difficulty for a general reader lies in the heavy density of technical anatomical jargon, such as interorbital constrictions, mesopterygoid fossae, and detailed cranial measurements. However, what stays with you is the satisfying clarity of scientific deduction. Out of a handful of cracked, discolored skulls retrieved from a cave in Nuevo León, the author successfully reconstructs the presence of ancient tree-dwelling fliers, ancestral big brown bats, and a formidable extinct vampire bat that once haunted the prehistoric Mexican night.