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Which Appeared First: Sharks or Crocodiles?

Category: Living Things

The oldest known fossils of crocodile relatives date back to about 231 million years ago. At that time, shark relatives had already been leaving body fossils for about 200 million years. This article compares the oldest fossils of sharks and crocodiles to see which came first. It also explains how the numbers change depending on where you draw the line for what counts as a "shark" or a "crocodile".

1. Fossils Show Shark Relatives Appeared First

Shark relatives appeared first. When comparing body fossils, the oldest shark relative (a cartilaginous fish) dates to about 436 million years ago (Early Silurian period) [1]. The oldest known crocodile relative fossils are from about 231 million years ago (Late Triassic period) [5]. The difference is about 200 million years. This gap is nearly 90% of the time span from the oldest crocodile fossils to today. Note that fossil preservation varies. The shark fossils are nearly complete bodies, while the crocodile fossils were found as scattered bones. Sharks also have older fragment records, such as scales and fin spines, reaching back about 439 million years [2]. There are even "possible" scale records from about 455 million years ago [3]. However, the authors of those studies are cautious about whether scales alone prove they were shark relatives [4]. The following sections look at shark fossils, then crocodile fossils, and finally how definitions affect the dates.

2. How Shark Fossils Are Found: Scales, Fragments, and Bodies

Sharks and rays are called "cartilaginous fish" because their skeletons are made of cartilage, not hard bone. Their fossils are categorized by how they are preserved. The oldest records are scales. There are possible records of scales and skin teeth from the Late Ordovician period, about 455 million years ago [3]. Scales of Tantalepis found in Middle Ordovician rocks in central Australia looked similar to cartilaginous fish scales. However, the study states this "may" push back the origin of the group [4]. Next are fragments like scales, fin spines, and shoulder plates from Fanjingshania, found in Early Silurian rocks in southern China. It is reported as a cartilaginous fish, but the whole body shape is unknown [2]. Its date is about 439 million years ago [10]. The oldest nearly complete body fossil is Shenacanthus vermiformis, reported in 2022 from Chongqing, China, dating to about 436 million years ago [1]. Before this, the oldest body fossil was from the Late Silurian, about 425 million years ago [1]. Shenacanthus had armor-like plates around its chest and features common in other fish groups.

3. The Oldest Crocodile Relative, Carnufex, Lived on Land

One of the oldest known crocodile relatives is Carnufex carolinensis, found in North Carolina, USA. It was collected in 2003 and reported as a new species in 2015 [5][7]. The rock layer dates to about 231 million years ago, the beginning of the Late Triassic (Carnian stage). The paper describes it as one of the earliest diverging crocodylomorphs [5]. It was about 9 feet (2.7 m) long, lived on land, and walked on two legs, according to university news [6]. It was one of the top predators before dinosaurs spread in North America. Do not imagine modern crocodiles. One researcher explains that during the time dinosaurs grew large, many crocodile relatives had bodies like foxes or jackals: small, slim, and long-legged [6]. Carnufex was unexpectedly large for its group.

4. How Defining "Crocodile" Changes the Dates

There are two ways to count "crocodiles." One includes extinct close relatives like Carnufex ("crocodylomorphs"). The other is the "crown group" (Crocodylia), which includes the last common ancestor of all living crocodiles and all its descendants. A 2026 study shows the origin of living crocodiles changes greatly depending on the dating method. Using "tip calibration" (placing fossils at branch tips), the origin is the Early Cretaceous (about 125–102 million years ago). Using "node calibration" (assigning fossil dates to branching points), it is the Late Cretaceous (about 95–78 million years ago). Researchers say the first method does not match the rock record, and the second is more plausible [8]. Either way, living crocodiles appeared more than 100 million years after the oldest crocodylomorphs (about 231 million years ago). For sharks, the oldest fossil record also changes depending on how far you extend the definition of "shark relatives." Cartilaginous fish include rays and chimaeras [3]. If you narrow the definition to "only modern shark lineages," the oldest fossil date would change. The source material does not provide that specific number.

5. Why "Oldest" Changes With New Discoveries

"Oldest fossil" means "oldest found so far." Numbers change when new specimens are found or dating methods are revised. Before a 2003 paper, the oldest articulated body fossil was about 394 million years old. The 2003 paper reported Doliodus problematicus from New Brunswick, Canada, dating to about 409 million years ago, pushing the record back by about 15 million years [3]. Before this, Doliodus was known only from specimens with teeth and was classified as either a cartilaginous fish or an acanthodian. The name "problematicus" reflects uncertainty. The new specimen showed tooth rows, brain-case bones, and paired fin spines, a feature unique among cartilaginous fish [3]. This record was updated in 2022 when Shenacanthus (about 436 million years ago) was found, pushing the oldest body fossil back by about 11 million years from the previous 425 million-year-old record [1]. Carnufex’s date also shifted. The Pekin Formation was initially thought to be Early Carnian, but revised time scales place it in the Late Carnian (about 231 million years ago) [7]. The numbers in this article may change. However, the shifts seen here (about 15 million or 11 million years) are small compared to the 200-million-year gap between sharks and crocodiles.

6. How to Check an "Oldest" Claim

If you see "oldest" in a book or museum, check three things: What was found (scales, fragments, or whole body)? What is the range of the rock layer's age? What is included in the group definition? For shark fossil dates in Japanese, the abstract of Miller et al. (2003) is available on the Nature Asia Pacific Japanese page [3]. For crocodiles, the North Carolina State University news release is easy to read and uses researcher quotes [6].

Sources

  1. Zhu, Y., et al. (2022) "The oldest complete jawed vertebrates from the early Silurian of China", Nature 609(7929): 954-958. https://doi.org/10.1038/s41586-022-05136-8 (Reports Shenacanthus from about 436 million years ago; previous oldest complete fossil was about 425 million years ago.)
  2. Andreev, P. S., et al. (2022) "Spiny chondrichthyan from the lower Silurian of South China", Nature 609(7929): 969-974. https://doi.org/10.1038/s41586-022-05233-8 (Fanjingshania consists of scales, fin spines, and shoulder plates; predates oldest articulated jawed vertebrate fossils.)
  3. Miller, R. F., et al. (2003) "The oldest chondrichthyan fossil assemblage from the Early Devonian of New Brunswick", Nature 425: 501-504. https://www.natureasia.com/ja-jp/nature/425/6957/nature02001/ (Includes scales from about 455 million years ago, previous record of 394 million years ago, and Doliodus specimen from about 409 million years ago.)
  4. Sansom, I. J., et al. (2012) "Chondrichthyan-like scales from the Middle Ordovician of Australia", Palaeontology 55(2): 243-247. https://doi.org/10.1111/j.1475-4983.2012.01127.x (Tantalepis scales from Middle Ordovician; described as "may" extend the chondrichthyan lineage.)
  5. Zanno, L. E., et al. (2015) "Early crocodylomorph increases top tier predator diversity during rise of dinosaurs", Scientific Reports 5: 9276. https://www.nature.com/articles/srep09276 (Reports Carnufex; about 231 million years ago, one of the earliest crocodylomorphs.)
  6. https://news.ncsu.edu/2015/03/zanno-carnufex/ ()
  7. Drymala, S. M., Zanno, L. E. (2016) "Osteology of Carnufex carolinensis...", PLoS ONE 11(6): e0157528. https://doi.org/10.1371/journal.pone.0157528 (Notes specimen collection year, disarticulated bones, and revision of Pekin Formation dating.)
  8. Davies, S., et al. (2026) "Competing methods of divergence time estimation recover diverse evolutionary timescales", Proceedings of the Royal Society B 293(2080): 20260635. https://doi.org/10.1098/rspb.2026.0635 (Shows range of origin dates for living crocodiles (crown group).)
  9. Wikipedia "Crocodylomorpha". https://en.wikipedia.org/wiki/Crocodylomorpha (Mentions Trialestes as oldest; reference only as it is a summary article.)
  10. "The shoulder girdle of early chondrichthyans grew by skeletal remodelling" (PubMed Central). https://pmc.ncbi.nlm.nih.gov/articles/PMC12459293/ (States Fanjingshania date is about 439 million years ago, Aeronian stage.)