Determining whether a particular fossil animal would have been kosher depends on the group we are examining. For mammals, fish, and insects, it is an issue of whether we can determine the presence or absence of the simanim. In evolutionary biology, this is equivalent to determining the presence or absence of particular characters. In some cases the characters can be directly observed; in others, we have to use the tools of phylogenetic reconstruction to reliably determine their presence. Birds (and dinosaurs) are trickier; in this case, we will have to mainly argue from reconstructions of ecology and behavior. Of necessity, we will have to largely ignore the concept of mesorah; these ancient animals long predate anyone who would have had a tradition of eating them.

Fish

As a first approach, we will assume that if a type of fish is kosher today its ancestral relatives would have also been kosher. We can thus ask: what is the fossil record of kosher fish groups? A list of those fish today that are kosher and non-kosher and what taxonomic groups they belong to was prepared decades ago by James W. Atz, a curator of ichthyology of the American Museum of Natural History and is widely distributed online (e.g., http://www.kosherquest.org/bookhtml/FISH.htm). This list includes either the taxonomic family that the fish belong to (for example, Family Clupeida, the herrings) or a genus (Coryphaena, dolphin fishes) or even a species name (Dissostichus eleginoides—Chilean sea bass). We compared the Atz list to that in the current Fishbase database (Froese and Pauly 2014) to determine if the family names listed by Atz were still in use and updated them where appropriate. For his genera and species, we used Fishbase to determine what family they belonged to. The families were then placed into the most recent classification of fishes based on molecular phylogenetic methods (Betancur et al. 2013). Finally, we used the Paleobiology Database (paleodb.org) to determine if these families had a fossil record. The Paleobiology Database is a community effort to produce a database of the occurrences of fossil organisms through time, space and environment.

Nearly all kosher fish belong to the Subclass Neopterygii of the Class Actinopterygii (ray finned bony fishes) and most (but not all) are members of the Infraclass Teleostei (teleost fishes) within Neopterygii, the most common modern group of fish. The main exceptions are the bowfins which are assigned to the Infraclass Holostei and the controversial sturgeons, which are members of the actinopterygiian Subclass Chondrostei. Being a teleost does not make a fish kosher, since catfish (Order Siluriformes) and eels (Order Anguilliformes) are non-kosher. Even a single order can contain both kosher and non-kosher fish. For example the Order Perciformes contains both perch (kosher) and sculpins (not kosher). Classification alone is thus an unreliable guide to kosher status.

Figure 1 shows the known time range of the families whose members today are considered kosher and that occur in the fossil record. The range goes from today back to the oldest fossil occurrence of that family. Of the forty-four families that are found as fossils, only 14 go back as far as the Cretaceous, four to the Jurassic, and only one, the bowfins (Family Amiidae) as far back as the Triassic.

Fig. 1 Fossil record of fish groups with living members considered to be kosher Full size image

This list, of course, only includes families of fish that are found in the water today. For fossil members of these living families and for extinct groups of fish, an observant Jew would demand that we physically demonstrate that it had fins and the correct types of scales. Like most other organisms, fish have a low probability of leaving a fossil record. The numerous biological, chemical and physical processes that occur after death, collectively known as taphonomic processes, rapidly decay the soft tissues, scatter the scales and bones, and eventually destroy even the hard tissues. Fortunately, there are sites that allow exceptional preservation, including complete fish. Paleontologists term these fossil deposits lagerstätten.

One of the most famous lagerstätte is the Green River Formation of Colorado, Wyoming, and Utah (Grande 2013). These fossils are found in fine grained and thinly layered sediments that were deposited in large lakes during the Eocene, about 55 million years ago. The fish preserved in these sediments are often preserved complete, including the fins and scales (Fig. 2a), and would qualify as kosher. It should be noted that isolated scales are also preserved in many fossil sites (Fig. 2b).

Fig. 2 The perciform fish Cockerellites liops, from the Fossil Butte Member of the Green River Formation (Eocene). a A specimen with well-preserved scales. b Close-up of some isolated scales from the same species. From Grande (2013); used with permission Full size image

Going much further back, animals that we would call “fish” first appear in the Cambrian, some 520 million years ago (Long 2011; Erwin and Valentine 2013). These early vertebrates not only lacked fins and scales, but had no jaws. Later examples of these fish were covered with bone, often forming an elaborate armor. The oldest ray-finned bony fishes (Actinopterygii) occur in the Late Silurian, about 420 million years ago, but are incomplete (Long 2011). Spectacular examples of complete preservation are known from the Devonian, which show these fish had fins and ganoid scales. Fish that we can definitively recognize as teleosts first appear in the Early Jurassic, but also have ganoid scales (Long 2011; Friedman 2015). The earliest teleost fish with cycloid scales and thus possibly kosher are found worldwide later in the Jurassic; these belong to extinct groups (Arratia et al. 2004; Barthel et al. 1990; Chellouche et al. 2012).

Mammals

The laws of kashrut prohibit any mammal that does not have both cloven hooves and chew the cud. Cloven hooves, in anatomical terms, refers to animals that show even-toed foot symmetry, where the digits of the foot are arranged symmetrically across an axis between the third and fourth toes, and walk on hooves on the last phalanx of the toes (on tip-toes), a posture known as unguligrade (Figs. 3, 4). Camels, in contrast, although they are cloven footed, are not considered to have “true hooves;” they walk on a broad elastic pad under the middle digits, with two fingernail-like toenails splayed out in front (Klingel 1990; Figs. 3c, 4c). Their foot posture is digitigrade.

Fig. 3 Cloven hooves. a Cloven hooves of the wild Barbary Sheep. Photo by REP, specimen on display at Field Museum. b Hindfeet of the extinct stem ruminant Hypertragulus calcaratus showing unguligrade foot posture, where the weight is borne on the last phalanx of the toes. This is from the White River Badlands, South Dakota, Eocene–Oligocene in age. Original image public domain, http://commons.wikimedia.org/wiki/File:Hypertragulus_calcaratus.JPG. c Foot of a modern camel. Photo by REP, specimen on display at Field Museum Full size image

Fig. 4 Artiodactyl forefeet. a Pig, b deer, c camel, showing paraxonic symmetry characteristic of even-toed ungulates, where the digits are symmetrical across a plane between digits 3 and 4. Pigs and deer show “true cloven hoofs”, while camels walk on their digits and do not show true cloven hoofs. Original image public domain, from Flower, 1885, An Introduction to the Osteology of the Mammalia Full size image

Cud-chewing, or rumination, is a system of fermentation of plant foods in the front portion of the stomach, which is divided into several chambers. Food is chewed, swallowed, fermented, then regurgitated and chewed into finer particles, passing into the next chamber. The fermentation takes advantage of bacteria that live in the chamber to break down cellulose, which mammals cannot ordinarily digest. Modern camels and llamas do chew the cud, although their digestive system differs from the ruminants (ruminants have four digestive chambers as part of the stomach complex, camels have three).

Applying these strictures to modern animals is fairly straightforward, since these two characteristics are restricted only to members of the clade Ruminantia, which is the subgroup of even-toed hoofed mammals that includes the cattle, goats, sheep, antelopes, deer, pronghorn, mouse deer, giraffe (Zivotofsky 2000) and okapi (a clade is a taxonomic group whose members share a common ancestry; in this case it does not have a formal associated Linnaean level, such as family or order). Camels and their relatives belong to a different clade, the Tylopoda.

The determination of whether an ancient mammal had cloven hooves can be done directly using fossils of the limbs, by inspecting the foot symmetry, to make sure it passes between toes 3 and 4, and the shape of the last phalanx of the toes, which should be wide and flat, not pointed or curved (Figs. 3, 4).

Determining whether an animal chewed the cud is much more challenging. Because teeth are what are used to chew and they are by far the most common mammalian remains, they would be the logical place to determine from fossils whether or not an animal chewed the cud. Unfortunately, there are no discernable differences between the teeth of cud-chewers and non-cud chewing artiodactyls. First, one might think that regurgitating so much material back into the mouth might bring excess stomach acid into the mouth and cause recognizable damage to the teeth; however, part of the evolution of rumination (cud-chewing and multi-chambered stomachs) included a system of acid reducing mechanisms. The chewed and digested plant matter is regurgitated into the mouth, where the saliva has a high concentration of bicarbonate, which acts as a buffer to the stomach acid coming into the mouth with the cud (McDougall 1948). This reduces the incidence of acid wear on the teeth.

Another option is to test fossil teeth for the ratio of stable isotopes present for a given element, such as the ratio of carbon C12 to C13. These ratios are changed by passing through the cells of living organisms, a process called fractionation. Different types of plants have different ratios of C12 to C13, and these ratios can be seen in the teeth of the animals that eat them. This means that by looking at the ratios of C12 to C13 in fossil teeth, we can tell what kinds of plants a herbivore was eating (Cerling and Harris, 1999). This type of analysis is widely used in paleontology to better understand mammals and what they ate at different times. There are clear differences in the digestion of ruminants from other mammals, since they not only digest the plant matter but also the bacteria that live in the gut and digest the cellulose. It is not yet technically possible to determine whether an extinct animal chewed the cud from stable isotope analysis, although this approach may someday prove to be useful in determining whether a particular fossil indicates a ruminant digestion.

The best available approach to identifying extinct kosher animals is called the ‘extant phylogenetic bracket’ (Witmer 1995). This method relies on our ability to use the evolutionary history of a group to predict the characteristics of an extinct member, given what we know of its living relatives. The relationships of artiodactyls to each other are summarized in the phylogeny in Fig. 5 (a summary of our knowledge of the interrelationships of groups of organisms. We know that all living ruminants chew the cud, and of all the other artiodactyls, only camels also do this. The fossil animal at position A can be confidently assigned within the ruminants based on other diagnostic characteristics, such as having two fused bones in the ankle (the navicular and cuboid). Based on this, we can infer that fossil A should share all the other traits that all ruminants share that cannot be directly observed in the fossil, such as cud-chewing. In contrast, the fossil animal at position B is outside the portion of tree containing modern ruminants and is therefore not surrounded by living members whose characteristics we know; as a result we cannot use this method to predict its characteristics. The terrestrial artiodactyls, the larger clade containing the ruminants, are known in the fossil record only back to the earliest Eocene, and the Ruminantia themselves first appear in the late Eocene (Fig. 3b). Ruminantia are native to Eurasia, Africa and North America, and have been introduced to the remaining continents. South America had its own native ungulate (hoofed) mammals, all of whom are now extinct and none of which had even-toed foot symmetry (Buckley 2015). The beginning of the migration of North American species, the Great American Biotic Interchange (Marshall et al. 1982), brought deer into South America, which would have been the first kosher mammalian species on that continent.

Fig. 5 Simplified phylogeny of even-toed ungulates, showing the positions of two fossils, a and b. a Falls within the extant phylogenetic bracket for Ruminantia, and can be expected to share the features shared by all living ruminants, such as chewing the cud. b Falls outside this group and we cannot infer that they shared all of the characteristics of living ruminants. Phylogeny follows Price et al. (2005) Full size image

Interestingly, although modern camels are expressly forbidden in the Torah, the oldest camelids in the fossil record are actually unguligrade. The problem for ancient camels is exactly the situation as the fossil in position B in Fig. 5—we have relatively few living camels and most fossil camels are not in the group that contains modern camels. Although modern camels chew the cud, we cannot safely assume that ancient camels would have had the same ability. So, although it is possible that some of the earliest camels in the fossil record might have been considered kosher if they already chewed the cud, this is uncertain.

Birds, Other Dinosaurs, Pterosaurs

Birds pose an unusual set of difficulties. Unlike fish and mammals, there are no explicit simanim to look for. In a maximally permissive scenario, we could take the position that the 24 kinds of birds specifically forbidden are the only birds prohibited, and thus all extinct birds (especially before any of the extant birds arose) would be kosher. A variation of this would be to also exclude the extinct members of the forbidden extant groups. For this purpose we can examine the relationships of the nearly all 10,000 living bird species that have been worked out in detail (Jetz et al. 2012; Jarvis et al. 2014). Many birds of the Cenozoic Era are identifiable to the particular branch of this tree where they belong, including the early representatives of the fowl and waterfowl.

This does leave open the question, however, as how broadly we encompass the term “bird.” Do we restrict the concept only to the crown group, which is the group comprised of all living and extinct descendants of the most recent common ancestor of all living birds? Do we want to exclude some or all members of the stem group: that is, species of lines collateral to the extant bird group, but closer to birds than to their closest living relatives (the crocodilians)? If we include stem members, how far down the family tree do we go (Fig. 6)? While there are some branches of the stem that would unquestionably be considered “birds” had they survived, this becomes more problematic further down the tree. And all this is further complicated by the fact that the dietary laws include bats (as prohibited) among the birds despite the fact that bats are biologically mammals. The dietary category of “bird”, therefore, is complicated: it is neither simply based on the ability to fly or not (ostriches are included among “birds”), but neither does it strictly map along modern biological nomenclature.

Fig. 6 Simplified phylogeny of birds and their extinct relatives (extinct forms indicated with a dagger). Aves represents the group of extant birds, their most recent common ancestor, and all of that ancestor’s descendants: the crown group. All groups sharing a more recent common ancestor with Aves than with their closest living relatives (Crocodylia) are part of the stem. Some stem-members share most but not all of the traits of modern birds: Ichthyornis retains teeth, but otherwise has a relatively modern anatomy. But more distant groups have proportionately fewer traits of modern birds. Silhouettes from PhyloPic.org, from the contributors Andrew Farke, FunkMonk, Scot Hartman, Lukasiniho, Matt Martyniuk, Steve Traver, and Emily Willoughby. Silhouettes not to scale Full size image

An alternative approach is to assess the ecology and anatomy of extinct taxa (either within the crown or within the stem), and regard those that share the traits of forbidden birds today as being considered forbidden. As we can with mammals, we can identify the evolutionary position of fossil birds with their extant relatives and determine their life habits and soft tissue anatomy based on preserved anatomical features.

Rabbinic discussions in the Mishnah, the part of the Talmud that focuses on the details of Jewish law and observance, provide some guidelines. In particular, the tractate (sub-section of the Mishnah) that deals with eating of meat is Hullin (or Chullin). Zivotovksy (2014) recently summarized the discussions in Chullin and related rabbinical literature concerning the kashrut of birds. Following his summary, a bird is not kosher if it is dores (a predator), but the demarcation of what makes a predator itself has been debated. Among the alternative definitions of dores are a bird that either (1) seizes its food with its claws and lifts it off the ground to its mouth; (2) holds its prey down with its claws and breaks it into smaller pieces to eat; (3) strikes its prey and feeds on it while it is still alive (with the caveat that the “prey” in this context excludes worms and insects; otherwise chickens would be treif); or (4) claws its prey to death or envenomates its prey (the latter is a moot point, as no known bird engages in this behavior).

These specific sets of behaviors are not directly observable in fossil forms, so we will utilize a more generalized concept of dores: a bird that feeds on the flesh of other vertebrates. As such, fossil birds such as the Teratornithidae (recently extinct scavenging or predaceous, superficially vulture-like birds of sometimes immense size), Pelagornithidae (fish-feeding birds of the Cenozoic Era, the largest of whom rivalled the largest teratornithids as the biggest flying birds in Earth history), and the Phorusrhacidae (predatory “terror birds”, some of them fliers but the largest of these up to 3 m tall and flightless) would all be forbidden.

Once considered predatory, the Gastornithidae (Paleocene Gastornis of Europe and Eocene Diatryma of North America) are now interpreted as likely herbivores (Mustoe et al. 2012). However, these large (2 m tall) flightless birds would likely be forbidden, given that other flightless birds (ostrich) and large long-legged volant birds which nevertheless spend a considerable amount of time walking rather than flying (bustards, storks, herons) are specifically excluded.

The Mishnah further states that a bird is kosher if it has a gizzard with a lining that can be peeled, a crop, and an “extra” toe (Zivotovksy 2014). The gizzard (ventriculus) is a trait shared by all extant birds, and indeed by their closest living relatives the crocodilians. Based on their phylogenetic position, it is thus inferred that the two groups inherited this trait from their common ancestor and passed it down in both lineages. This inference is independently supported by direct fossil evidence of gastroliths (gizzard stones) in various extinct members of the lineage leading to birds: extinct groups of birds and other dinosaurs. Thus, our default assumption would be that any extinct bird or other archosaur (birds, dinosaurs, crocodilians, and pterosaurs) possessed a ventriculus without positive evidence that it had been lost. Whether it could be peeled would depend on direct observation.

The crop (ingluvies) is a more problematic structure. It is an expansion of the esophagus used to store food prior to digestion. It is quite large and muscular in seed-eating birds, smaller in birds of other diets (such as geese and swans), and nearly absent in the owls. The presence of the ingluvies is very difficult to detect in typical fossils. It is inferred in the extinct Cretaceous seed-eating birds Sapeornis and Hongshanornis (Zheng et al. 2011) and the fish-eating Confuciusornis (Dalsätt et al. 2006) and Yanornis (Zheng et al. 2014) due to a mass of seeds and/or fish bones and scales (respectively) present in the appropriate region of fossil specimens of these. The lack of such masses in other fossil specimens does not indicate that the crop was missing; it may simply indicate that the animal had not recently fed at time of death or that the mass was not preserved.

The “extra toe” is not in fact extra: it is simply pedal digit I, the hallux, more familiar to us as the big toe of humans or the dewclaw of the hind foot of some dogs. The typical interpretation of what is meant by an “extra” toe is that the bird exhibits the anisodactyl condition: the hallux points posteriorly, while digits II–IV point anteriorly (Fig. 7a). The anisodactyl condition gives the birds with this trait an opposable hallux useful for perching (Francisco Botelho et al. 2015). The oldest birds (such as Jurassic Archaeopteryx) lack a fully opposable hallux (Middleton 2001; Mayr et al. 2007), while many Cretaceous birds show a condition where the hallux is partially opposable rather than pointing fully backwards. Given that in such birds the hallux would not be oriented with the remaining toes, this could qualify as “extra,” even though it represents a condition not expressed in any living bird species. Other Cretaceous birds have a fully opposable hallux (Fig. 7b).

Fig. 7 Modern and fossil bird feet. A. Ceylon junglefowl (Gallus lafayetti) showing the rear facing “extra toe” or hallux (digit 1; arrow). Photography by REP, specimen on display at Field Museum. B. Anisodactyl foot of the Cretaceous stem-bird Confuciusornis. Photograph by TRH. Note the rear-facing hallux for perching (arrow) Full size image

Therefore, using an approach based on the characteristics outlined above, we might accept as kosher a number of bird species from the Cretaceous Period, but exclude fish-eaters such as Ichthyornis, the hesperornithines, the longipterygids, confuciusornithids, and Jeholornis. Other primitive Cretaceous birds (the above-mentioned Sapeornis and Hongshanornis) might conceivably be kosher, if we overlook the fact that they have teeth!

But where does birdy-ness begin? Birds are simply one branch of the more inclusive group Dinosauria (Brett-Surman et al. 2012) and there is no single point along the gradations from clearly non-bird theropod dinosaurs (aka “non-avian dinosaurs”) to definite birds (Fig. 6). Indeed, this is one of the most completely known transitions in the history of vertebrates (Brusatte et al. 2014), such that primitive birds (or proto-birds) such as Archaeopteryx and primitive members of closely related groups like the dromaeosaurids (Microraptor) and the troodontids (Anchiornis) are nearly identical (Fig. 8). These bipedal feathered dinosaurs (Rauhut et al. 2012) would almost certainly fall under the category “bird” in the Levitical division of the living world into quadrupedal animals, birds, creeping things, and sea life. The majority of these can be easily determined as non-kosher because they were predators; even those that evolved a herbivorous diet (Zanno and Makovicky 2011; Novas et al. 2015) lack the opposable hallux; and would further have fallen under the same aspect as ostriches and bustards as either incapable of flight or rarely using flight.

Fig. 8 Dromaeosaurid dinosaur Microraptor from the Cretaceous of China. Photograph by TRH Full size image

The other two major branches of Dinosauria are the herbivorous Sauropodomorpha and Ornithischia (Fig. 6). Modern reconstructions show that they had upright limbs: they could not in any way be said to have “creeped (or swarmed) along the ground.” Hence they cannot fall under the category of creeping things with modern reptiles. The ancestral members of all dinosaur groups were bipedal. At least some small bipedal ornithischians are known to have had a fluffy body covering (Zheng et al. 2009; Godefroit et al. 2014). Even if we counted them as birds, they still lacked the opposable hallux. Therefore, we cannot see any non-avian dinosaur being considered kosher. So much for Fred Flintstone’s “Bronto-burgers” (if Fred kept kosher)!

What of the Pterosauria? These were flying relatives of the dinosaurs (Witton 2013). While neither birds nor any other dinosaur in the biological sense, they would assuredly fall in the “bird” dietary category just as bats do. And, like bats, their possession of membranous rather than feathered wings, a furry pelage, and (for many species at least) a fish- or flesh-diet, would seem sufficient to place them among the forbidden foods.

Other Fossil Vertebrates

There is a vast diversity of additional groups of fossil vertebrates, including: (1) crocodilians and their extinct pseudosuchian kin; (2) marine reptiles such as plesiosaurs, ichthyosaurs, placodonts, and the like; (3) lepidosaurs (snakes, lizards, mosasaurs, tuataras, and their extinct relatives); (4) other fossil reptiles; (5) the extinct synapsid ancestors and relatives of mammals; and (6) amphibian-grade animals such as lepospondyls, temnospondyls, and seymouriamorphs (Benton 2014). None of these would be kosher, following Lev. 11:29:30.

Insects

Although all other insects are forbidden, the Torah specifically permits all grasshoppers, locusts and possibly crickets (some translations disagree; Regenstein pers. com). It also gives a definite simanim: the presence of the jumping hind legs that define the insect Class Orthoptera (Song et al. 2015). Despite common opinion, insects, including orthopterans, have an excellent fossil record (Grimaldi and Engel 2005). Beautiful examples of fossil crickets are known from the same Green River Shale that yields the well-preserved fossil fish (Fig. 2). The Santana Formation of the Cretaceous of Brazil has excellently preserved fossil grasshopper relatives (Fig. 9). Overall, the oldest known definitive orthopteran is 300 million years old (Late Carboniferous) (Song et al. 2015).

Fig. 9 Fossil Orthoptera. Left cricket from the Eocene Green River Formation, Colorado. Right Elcanid from the Lower Cretaceous Crato Formation of Brazil Full size image

The oldest known fossils, however, are almost certainly younger than the actual first appearance of a group. Because of the vagaries of fossilization, millions of years may separate the origin of a group and its first preservation in the fossil record. Until recently, that was all that could be said about the time of origin based on fossils. The last decade, however, has seen a tremendous advance in our ability to estimate these divergence times; that is, the time of splitting of a group from its closest relatives. This advance results from a combination of new rapid methods to determine sequences in nuclear, mitochondrial, and ribosomal DNA; the development of highly sophisticated and computer intensive methods to construct phylogenies based on those data; and the ability to calibrate the branching patterns in those phylogenies with the fossil record to produce increasingly reliable estimates of divergence times (Wilke et al. 2009).

This approach to estimating divergence times was recently applied by Song et al. (2015) to the evolution of the Orthoptera. Using a combination of mitochondrial and nuclear genes, they produced a detailed phylogenetic tree for nearly the entire group. They then calibrated this tree with nine well-dated fossil occurrences. The results indicate an origin for the Orthoptera in the Carboniferous, at about 316 million years ago, about 15 million years older than the oldest fossil. Of the groups that can be considered kosher, therefore, the orthopterans go the furthest back in time.