Reptiles of Anza-Borrego Desert State Park
Ancient Reptiles of Southern California

​Reptiles have inhabited the Anza-Borrego region for millions of years, and their fossil remains provide valuable evidence of ancient climates and environments. Although reptile fossils are generally less abundant than those of large mammals, Anza-Borrego Desert State Park preserves one of the most diverse Pliocene and early Pleistocene reptile assemblages known from North America.
The fossil deposits of Anza-Borrego preserve a remarkable diversity of lizards, snakes, crocodilians, and other reptiles that document the transition from subtropical woodlands and river systems to the arid desert landscape of today. Fossil turtles and tortoises are discussed separately because of their abundance and scientific importance.

Reptiles in Ancient Anza-Borrego
During the Pliocene and Pleistocene, Anza-Borrego supported a rich reptile fauna living among rivers, wetlands, woodlands, and expanding grasslands. Lizards occupied a variety of habitats, while snakes ranged from riparian environments to increasingly arid uplands.

Many of these reptiles belong to the same genera that inhabit the deserts of the American Southwest today, suggesting that much of the modern desert reptile fauna evolved locally as climates gradually became drier.
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Other reptiles no longer occur in southern California, providing evidence that ancient environments differed significantly from those of the present.

Lizards and Snakes
Anza-Borrego preserves one of the richest fossil lizard assemblages known from the North American late Cenozoic. Fossils include whiptail lizards, horned lizards, desert iguanas, alligator lizards, skinks, night lizards, kingsnakes, coachwhips, garter snakes, rattlesnakes, and several extinct species.

One of the most significant discoveries is the presence of the Gila monster (Heloderma), a venomous lizard that no longer inhabits southern California. Fossils of tropical and subtropical reptiles such as this indicate that the region once experienced warmer and wetter conditions than those found in today's Colorado Desert.

The extinct iguana Pumilia novaceki, known only from the fossil record, further demonstrates that ancient Anza-Borrego supported reptile communities unlike those living in the region today.

Crocodilians
Among the oldest reptile fossils preserved in Anza-Borrego are crocodilians recovered from marine and estuarine deposits. Fossils of Crocodylus and the extinct gavial Gavialosuchus indicate that warm coastal environments extended into the Salton Trough during the late Miocene and early Pliocene.

These reptiles occupied waterways connected to the ancestral Gulf of California and provide evidence for subtropical climates that contrast sharply with the modern desert.

What Reptile Fossils Tell Us
Reptile fossils help scientists reconstruct:
  • Ancient climates and environmental change
  • The transition from subtropical woodlands to desert habitats
  • The development of modern southwestern reptile communities
  • The history of rivers and wetlands in the Salton Trough
  • Evolutionary relationships among North American reptiles

Because reptiles are highly sensitive to temperature and moisture, they are excellent indicators of past environmental conditions. The changing composition of the reptile fauna records the gradual shift toward the arid desert ecosystem that characterizes Anza-Borrego today.

Explore a Fossil in 3D
Rotate, zoom, and examine this specimen from the Anza-Borrego Desert State Park collections.
Interactive 3D Model: Teiidae Cnemidophorus
Specimen Information
  • Catalog Number: LACM6831 V20929
  • Element: Skull
  • Formation: Olla
  • Epoch: Pliocene
  • Age: Blancan and/or Irvingtonian
  • Locality: Fish Creek / Vallecito Creek
  • Scanned using Agisoft Metashape
  • Specimen © California State Parks. 3D model produced by the Anza-Borrego Desert State Park Paleontology Society.

​Why Anza-Borrego Matters
Anza-Borrego Desert State Park preserves one of North America's most complete records of late Cenozoic environmental change. Its fossil reptiles document millions of years of climatic evolution, recording the transition from subtropical landscapes to the deserts of modern southern California.

Together with fossil fish, amphibians, birds, mammals, and the abundant fossil turtles and tortoises described elsewhere on this website, the reptiles of Anza-Borrego help reconstruct the remarkable ecosystems that once flourished across southern California.

The Fossil Record
Order Crocodilia
  • Crocodile (Crocodylus)
  • Gavial (Gavialosuchus)
Order Squamata
  • Desert iguana (Dipsosaurus dorsalis)
  • Crowned leopard lizard (Gambelia corona)
  • Horned lizard (Phrynosoma)
  • Anza horned lizard (Phrynosoma anzaense)
  • Novacek's small iguana (Pumilia novaceki)
  • Spiny lizards (Sceloporus)
  • Side-blotched lizard (​Uta)
  • Ground lizard or whiptail (Ameiva or Cnemidophorus)
  • Skinks (Eumeces)
  • Night lizard (Xantusia downsi)
  • Alligator lizard (Gerrhonotus)
  • Gila monster (Heloderma)
  • Night snake (Hypsiglena)
  • Common kingsnake (Lampropeltis getulus)
  • Coachwhip (Masticophis flagellum)
  • Garter snake (Thamnophis)
  • Rattlesnake (Crotalus)

Quick Facts
​Class: Reptilia
Includes: Crocodilians, lizards, and snakes
Famous species: Gila monster (Heloderma) and Novacek's small iguana (Pumilia novaceki)
Age: Late Miocene through Pleistocene
Role: Predators, insectivores, and small vertebrate hunters
Significance: Evidence for changing climates and the development of the modern desert reptile fauna
Location: Anza-Borrego Desert State Park, California

Learn More
Read Chapter 8, "The Fossil Lower Vertebrates: Fish, Amphibians, and Reptiles," in Fossil Treasures of the Anza-Borrego Desert for a detailed discussion of the reptiles of ancient Anza-Borrego. A separate page on this website explores the Park's remarkable fossil Turtles and Tortoises in greater detail.
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