Organism · Lizards and snakes
Pachyrhachis problematicus
Source time context (not species duration) · ≈ 143–66 Ma
Inferred life reconstruction
Pachyrhachis problematicus
Overview
Pachyrhachis problematicus is a fossil animal known for an elongated, snake-like body and one pair of small hind limbs. The connection of the pelvis and legs to the long spine attracts particular interest. It invites us to see the familiar snake body in a new way.[1]
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Key facts
One specimen preserves the skull and a long spine; another preserves vertebrae, the pelvis, and hind limbs. The two fossils reveal different body regions. Even when no single specimen preserves everything, comparisons of several sources can reveal the body.[1]
Time and place
A 2005 study records the two specimens as coming from limestone quarries near Ein Yabrud, north of Jerusalem in the West Bank. They date to the Cenomanian, the first stage of the Late Cretaceous. The Cretaceous as a whole spans approximately 140–66 million years ago.[1][2][3]
The time range describes source context, not the complete duration of this species.
Size, form and skeleton
An elongated, snake-like trunk and small hind limbs connected to the pelvis are described. The skull and vertebrae of another specimen also provide material for comparing the body.[1][2]
Gregory Paul’s 2022 reconstruction gives a total body length of about 1.93 m based on specimens HUJ-PAL 3659/3775. This is the size of a reconstruction using particular fossils, not the maximum length this species could attain.[4]
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Habitat and reproduction
The combination of an elongated trunk and small hind limbs is central to research. Whether legs were present and what behaviors they served are separate questions. Examining where the pelvis and legs connect to the body invites consideration of the diversity of snake-like bodies.[1]
Fossil discovery
A 2003 species account examined the two specimens and their hind limb evidence. A 2005 study reexamined the compressed, distorted skull using CT and shape models. This process seeks to understand the structure before compression from the fossil visible today.[1][2]
References
- Rage·Escuillié (2003) — Study of the hind-limbed snake Pachyrhachis
- Polcyn·Jacobs·Haber(2005). A morphological model and CT assessment of the skull of Pachyrhachis problematicus.
- International Commission on Stratigraphy (2024) — Geological time chart
- Paul (2022) — Body-size reconstructions of Mesozoic marine reptiles
- Rage·Escuillié (2003) — Study of the hind-limbed snake Pachyrhachis
- Rage·Escuillié (2003) — Snakes with small hind limbs
Research questions
What must be compared to restore a flattened skull to its original form? Researchers examine bone positions using CT data and reconstruction models. Reading deformation preserved in fossils is an important step toward understanding the living body.[2]
Observation
Follow the long spine to find the connections to the pelvis and small hind limbs. Returning your gaze to the head allows you to consider research on the outer body outline and internal skeleton together.[1][2]
Related organisms
Eupodophis descouensiLizards and snakesSource time context (not species duration) · ≈ 143–66 MaDifferent bodies among snakes
Compare the bodies and backgrounds of Pachyrhachis problematicus and Eupodophis descouensi. Pachyrhachis problematicus: a fossil animal with an elongated, snake-like body and one pair of small hind limbs; the connection of the pelvis and legs to the long spine is particularly interesting. Eupodophis descouensi: a fossil animal known for an elongated, snake-like body, small hind limbs, and a very short tail. The small legs on the rear part of its body attract particular interest.